release: 2.94.0 "Açaí na tigela"

Release produced with releng/create_release.xsh

Change-Id: If2ac30e569759c9035a6fc999c631ec545d190fa

.clang-tidy

@@ -20,6 +20,8 @@ Checks:
   - -bugprone-multi-level-implicit-pointer-conversion
     # we don't compile out our asserts
   - -bugprone-assert-side-effect
+    # FIXME(jade): figure out if this warning is any good
+  - -bugprone-exception-escape
     # all thrown exceptions must derive from std::exception
   - hicpp-exception-baseclass
     # capturing async lambdas are dangerous

Cargo.lock

@@ -1,6 +1,6 @@
 # This file is automatically @generated by Cargo.
 # It is not intended for manual editing.
-version = 3
+version = 4
 
 [[package]]
 name = "countme"
@@ -47,9 +47,9 @@ checksum = "3fdb12b2476b595f9358c5161aa467c2438859caa136dec86c26fdd2efe17b92"
 
 [[package]]
 name = "rnix"
-version = "0.11.0"
+version = "0.12.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "bb35cedbeb70e0ccabef2a31bcff0aebd114f19566086300b8f42c725fc2cb5f"
+checksum = "6f15e00b0ab43abd70d50b6f8cd021290028f9b7fdd7cdfa6c35997173bc1ba9"
 dependencies = [
  "rowan",
 ]

OWNERS

@@ -0,0 +1,26 @@
+# Docs
+per-file README.md=*
+per-file CONTRIBUTING.md=*
+
+# DevX
+per-file justfile=*
+per-file .envrc=*
+per-file .gitignore=*
+per-file .github=*
+per-file .mailmap=*
+
+# Build
+per-file meson.build=*
+per-file meson.options=*
+per-file flake.nix=*
+per-file flake.lock=*
+per-file *.nix=*
+per-file Cargo.lock=*
+per-file Cargo.toml=*
+per-file version.json=*
+
+# Code style
+per-file .clang-tidy=*
+per-file .clang-format=*
+per-file .editorconfig=*
+per-file treefmt.toml=*

bench/OWNERS

@@ -0,0 +1 @@
+*

bench/bench.py

@@ -7,15 +7,44 @@ import os
 import json
 import tempfile
 import platform
+import shlex
+import textwrap
+import dataclasses
 
-flake_args = ["--extra-experimental-features","'nix-command flakes'"]
-# hyperfine has its own variable substitution, so we use that and pass build="{BUILD}" here.
-# perf doesn't have variable substitution, so we call these with build being the actual build directory.
+flake_args = ["--extra-experimental-features", "nix-command flakes"]
 cases = {
-    "search": lambda build: [f"{build}/bin/nix", *flake_args, "search", "--no-eval-cache", "github:nixos/nixpkgs/e1fa12d4f6c6fe19ccb59cac54b5b3f25e160870", "hello"],
-    "rebuild": lambda build: [f"{build}/bin/nix", *flake_args, "eval", "--raw", "--impure", "--expr", "'with import <nixpkgs/nixos> {}; system'"],
-    "rebuild_lh": lambda build: ["GC_INITIAL_HEAP_SIZE=10g", f"{build}/bin/nix", *flake_args, "eval", "--raw", "--impure", "--expr", "'with import <nixpkgs/nixos> {}; system'"],
-    "parse": lambda build: [f"{build}/bin/nix", *flake_args, "eval", "-f", "bench/nixpkgs/pkgs/development/haskell-modules/hackage-packages.nix"],
+    "search": lambda build: [
+        f"{build}/bin/nix",
+        *flake_args,
+        "search",
+        "--no-eval-cache",
+        "github:nixos/nixpkgs/e1fa12d4f6c6fe19ccb59cac54b5b3f25e160870",
+        "hello",
+    ],
+    "rebuild": lambda build: [
+        f"{build}/bin/nix",
+        *flake_args,
+        "eval",
+        "--raw",
+        "--impure",
+        "--expr",
+        textwrap.dedent("""
+            (import <nixpkgs/nixos> {
+                configuration = ./bench/nixpkgs/nixos/modules/installer/cd-dvd/installation-cd-graphical-calamares-plasma6.nix;
+            }).config.system.build.toplevel
+        """).replace("\n", " "),
+    ],
+    "rebuild_lh": lambda build: [
+        "GC_INITIAL_HEAP_SIZE=10g",
+        *cases['rebuild'](build),
+    ],
+    "parse": lambda build: [
+        f"{build}/bin/nix",
+        *flake_args,
+        "eval",
+        "-f",
+        "bench/nixpkgs/pkgs/development/haskell-modules/hackage-packages.nix",
+    ],
 }
 
 arg_parser = argparse.ArgumentParser()
@@ -24,46 +53,81 @@ arg_parser = argparse.ArgumentParser()
 # mode, we would have to combine the JSON ourselves to support that, which
 # would probably be better done by writing a benchmarking script in
 # not-bash.
-arg_parser.add_argument('builds', nargs='+', help="At least two build directories to compare, containing bin/nix")
-arg_parser.add_argument('--cases', type=str, help="A comma-separated list of cases you want to run. Defaults to running all")
-available_modes = [ "walltime" ] + [ "icount" ] if platform.system() == 'Linux' else [] # perf doesn't run on Darwin
-arg_parser.add_argument('--mode', choices=available_modes, default="walltime")
+arg_parser.add_argument(
+    'builds',
+    nargs='+',
+    help="At least two build directories to compare, containing bin/nix",
+)
+arg_parser.add_argument(
+    '--cases',
+    type=str,
+    help="A comma-separated list of cases you want to run. Defaults to running all",
+)
+arg_parser.add_argument(
+    '--mode',
+    nargs='+',
+    choices=[ "walltime", "memory" ] + [ "icount" ] if platform.system() == 'Linux' else [], # perf doesn't run on Darwin
+    default=[ "walltime" ],
+)
+arg_parser.add_argument(
+    '--daemon',
+    action='store_true',
+    help='Run a temporary daemon for the benchmark instead of using a local store directly',
+)
 args = arg_parser.parse_args()
-if len(args.builds) < 2:
-    raise ValueError("need at least two build directories to compare")
+if len(args.builds) < 1:
+    raise ValueError("need at least one build directory to benchmark")
 
 benchmarks: list[str] = []
 if args.cases is None:
     benchmarks = list(cases.keys())
 else:
     for case in args.cases.split(","):
-        if case not in cases: raise ValueError(f"no such case: {case}")
+        if case not in cases:
+            raise ValueError(f"no such case: {case}")
         benchmarks.append(case)
 
+def make_full_command(build, case):
+    cmd = " ".join(map(shlex.quote, cases[case](build)))
+    if args.daemon:
+        return " ".join([
+            f"{build}/bin/nix --extra-experimental-features nix-command daemon &",
+            "trap 'kill %1' EXIT;",
+            f"NIX_REMOTE=daemon {cmd}",
+        ])
+    else:
+        return cmd
+
 def bench_walltime(env):
-    hyperfine_args = ["--parameter-list", "BUILD", ','.join(args.builds), "--warmup", "2", "--runs", "10"]
     for case in benchmarks:
-        case_command = cases[case]("{BUILD}") # see the comment on cases
-        subprocess.run([
-            "taskset", "-c", "2,3",
-            "chrt", "-f","50",
-            "hyperfine", *hyperfine_args, "--export-json", f"bench/bench-{case}.json", "--export-markdown", f"bench/bench-{case}.md", "--", " ".join(case_command)
-        ], env=env, check=True)
+        for build in args.builds:
+            subprocess.run([
+                "taskset", "-c", "2,3",
+                "chrt", "-f","50",
+                *[
+                    "hyperfine", "--warmup", "2", "--runs", "10",
+                    "--export-json", f"bench/bench-{case}-{build}.json",
+                    "--export-markdown", f"bench/bench-{case}-{build}.md",
+                    "--", make_full_command(build, case),
+                ],
+            ], env=env, check=True)
 
     print("Benchmarks summary\n---\n")
     for case in benchmarks:
-        fd = open(f"bench/bench-{case}.json")
-        result_json = json.load(fd)
-        fd.close()
-        for result in result_json["results"]:
+        results = []
+        for build in args.builds:
+            with open(f"bench/bench-{case}-{build}.json") as fd:
+                results.append(json.load(fd)["results"][0])
+        for result in results:
             print(result["command"])
             print("-" * min(80,len(result["command"])))
-            attr_rounded = lambda attr: f"{result[attr]:.3f}"
+            def attr_rounded(attr):
+                return f"{result[attr]:.3f}"
             print("  mean:    ", attr_rounded("mean"), "±", attr_rounded("stddev"))
             print("            user:",  attr_rounded("user"), "| system", attr_rounded("system"))
             print("  median:  ", attr_rounded("median"))
             print("  range:   ", attr_rounded("min") + "s.." + attr_rounded("max")+"s")
-            print("  relative:", f"{result["mean"]/result_json["results"][0]["mean"]:.3f}")
+            print("  relative:", f"{result["mean"]/results[0]["mean"]:.3f}")
             print("\n")
 
 
@@ -71,12 +135,14 @@ def bench_icount(env):
     perf_results_for: dict[str, list[tuple[str, float]]] = {}
     for case in benchmarks:
         for build in args.builds:
-            case_command = cases[case](build)
             # the perf stat -j output (incorrectly) localizes numbers, which will trip up the json parser.
             env["LC_ALL"]="C"
+            case_command = make_full_command(build, case)
             commandline = [
-                "perf", "stat", "-o", f"bench/perf-{case}.json", "-j", "sh", "-c", " ".join(case_command)
+                "perf", "stat", "-o", f"bench/perf-{case}.json", "-j",
+                "sh", "-c", case_command,
             ]
+            print("running", case_command)
             subprocess.run(commandline, env=env, check=True, stdout=subprocess.DEVNULL) # warmup run
             subprocess.run(commandline, env=env, check=True, stdout=subprocess.DEVNULL)
             perf_fd = open(f"bench/perf-{case}.json")
@@ -84,8 +150,9 @@ def bench_icount(env):
             perf_fd.close()
 
             instr = next(x for x in perf_data if x["event"] in ["instructions", "instructions:u"]) # an implementation of a find_first iterator
-            if case not in perf_results_for: perf_results_for[case] = []
-            perf_results_for[case].append((" ".join(case_command), float(instr["counter-value"])))
+            if case not in perf_results_for:
+                perf_results_for[case] = []
+            perf_results_for[case].append((case_command, float(instr["counter-value"])))
 
     print("Benchmarks summary\n---\n")
     for (case, entries) in perf_results_for.items():
@@ -97,6 +164,54 @@ def bench_icount(env):
             print("  relative instructions:", int(instr)/perf_results_for[case][0][1])
             print("\n")
 
+@dataclasses.dataclass
+class MemoryStatistics:
+    envBytes: int
+    listBytes: int
+    setBytes: int
+    valueBytes: int
+    heapBytes: int
+    heapSize: int
+
+def bench_memory(env):
+    path = "bench/bench-memory.json"
+    env = env | {
+        'NIX_SHOW_STATS': '1',
+        'NIX_SHOW_STATS_PATH': path,
+    }
+    results: dict[str, list[tuple[str, MemoryStatistics]]] = {}
+    for case in benchmarks:
+        for build in args.builds:
+            case_command = make_full_command(build, case)
+            commandline = [ "sh", "-c", case_command ]
+            print("running", case_command)
+            subprocess.run(commandline, env=env, check=True, stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)
+            with open(path) as fd:
+                stats = json.load(fd)
+            results.setdefault(case, []).append((case_command, MemoryStatistics(
+                envBytes=stats['envs']['bytes'],
+                listBytes=stats['list']['bytes'],
+                setBytes=stats['sets']['bytes'],
+                valueBytes=stats['values']['bytes'],
+                heapSize=stats['gc']['heapSize'],
+                heapBytes=stats['gc']['totalBytes'],
+            )))
+
+    print("Benchmarks summary\n---\n")
+    for (case, entries) in results.items():
+        for cmd, stats in entries:
+            print(cmd)
+            print("-" * min(80, len(cmd)))
+            print(f"  env bytes:    {stats.envBytes  :15d}   |  {(stats.envBytes / entries[0][1].envBytes)    :.3f}x")
+            print(f"  list bytes:   {stats.listBytes :15d}   |  {(stats.listBytes / entries[0][1].listBytes)  :.3f}x")
+            print(f"  set bytes:    {stats.setBytes  :15d}   |  {(stats.setBytes / entries[0][1].setBytes)    :.3f}x")
+            if not entries[0][1].valueBytes:
+                print(f"  value bytes:  {0:15d}")
+            else:
+                print(f"  value bytes:  {stats.valueBytes:15d}   |  {(stats.valueBytes / entries[0][1].valueBytes):.3f}x")
+            print(f"  heap alloc'd: {stats.heapBytes :15d}   |  {(stats.heapBytes / entries[0][1].heapBytes)  :.3f}x")
+            print(f"  heap size:    {stats.heapSize  :15d}   |  {(stats.heapSize / entries[0][1].heapSize)    :.3f}x")
+            print("\n")
 
 with tempfile.TemporaryDirectory() as tmp_dir:
     subprocess.run([
@@ -108,9 +223,15 @@ with tempfile.TemporaryDirectory() as tmp_dir:
     subenv = os.environ.copy()
     subenv["NIX_CONF_DIR"] = "/var/empty"
     subenv["NIX_REMOTE"] = tmp_dir
-    subenv["NIX_PATH"] = "nixpkgs=bench/nixpkgs:nixos-config=bench/configuration.nix"
+    subenv["NIX_PATH"] = ":".join([
+        "nixpkgs=bench/nixpkgs",
+    ])
+    subenv["NIX_DAEMON_SOCKET_PATH"] = f"{tmp_dir}/daemon"
 
-    if args.mode == "walltime":
-        bench_walltime(subenv)
-    else:
-        bench_icount(subenv)
+    for mode in args.mode:
+        if mode == "walltime":
+            bench_walltime(subenv)
+        elif mode == "memory":
+            bench_memory(subenv)
+        else:
+            bench_icount(subenv)

bench/configuration.nix

@@ -1,314 +0,0 @@
-{
-  config,
-  pkgs,
-  lib,
-  ...
-}:
-
-{
-  boot = {
-    initrd = {
-      availableKernelModules = [
-        "xhci_pci"
-        "ahci"
-      ];
-      kernelModules = [ "dm-snapshot" ];
-      luks.devices = {
-        croot = {
-          device = "/dev/sdb";
-          allowDiscards = true;
-        };
-      };
-    };
-    kernelModules = [ "kvm-intel" ];
-    kernelPackages = pkgs.linuxPackages_latest;
-
-    loader = {
-      systemd-boot.enable = true;
-      efi.canTouchEfiVariables = true;
-    };
-  };
-
-  hardware = {
-    enableRedistributableFirmware = true;
-    cpu.intel.updateMicrocode = true;
-    graphics.enable32Bit = true;
-    graphics.extraPackages = with pkgs; [
-      vaapiIntel
-      intel-media-driver
-      intel-compute-runtime
-    ];
-  };
-
-  fileSystems = {
-    "/" = {
-      device = "/dev/sda2";
-      fsType = "xfs";
-      options = [ "noatime" ];
-    };
-
-    "/boot" = {
-      device = "/dev/sda1";
-      fsType = "vfat";
-    };
-
-    "/nas" = {
-      device = "nas:/";
-      fsType = "nfs4";
-      options = [
-        "ro"
-        "x-systemd.automount"
-      ];
-    };
-  };
-  swapDevices = [ { device = "/dev/swap"; } ];
-
-  networking = {
-    useDHCP = false;
-    hostName = "host";
-    wireless = {
-      enable = true;
-      interfaces = [ "eth1" ];
-    };
-    interfaces = {
-      eth0.useDHCP = true;
-      eth1.useDHCP = true;
-    };
-    wg-quick.interfaces = {
-      wg0 = {
-        address = [ "2001:db8::1" ];
-        privateKeyFile = "/etc/secrets/wg0.key";
-        peers = [
-          {
-            publicKey = "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=";
-            endpoint = "[2001:db8::2]:61021";
-            allowedIPs = [ "2001::db8:1::/64" ];
-          }
-        ];
-      };
-    };
-
-    firewall.allowedUDPPorts = [ 4567 ];
-  };
-
-  i18n = {
-    defaultLocale = "en_US.UTF-8";
-    inputMethod.enable = true;
-    inputMethod.type = "ibus";
-  };
-
-  services = {
-    libinput.enable = true;
-    xserver = {
-      enable = true;
-      xkb.layout = "us";
-      xkb.variant = "altgr-intl";
-      xkb.options = "ctrl:nocaps";
-      wacom.enable = true;
-      videoDrivers = [ "modesetting" ];
-      modules = [ pkgs.xf86_input_wacom ];
-
-      displayManager.sx.enable = true;
-      windowManager.i3.enable = true;
-    };
-
-    udev.extraHwdb = ''
-      # not like this mattered at all
-      # we're not running udev from here
-    '';
-
-    udev.extraRules = ''
-      # ACTION=="add", SUBSYSTEM=="input", ...
-    '';
-  };
-
-  programs = {
-    light.enable = true;
-    wireshark = {
-      enable = true;
-      package = pkgs.wireshark-qt;
-    };
-    gnupg.agent = {
-      enable = true;
-    };
-  };
-
-  fonts.packages = with pkgs; [
-    font-awesome
-    noto-fonts
-    noto-fonts-cjk-sans
-    noto-fonts-emoji
-    noto-fonts-extra
-    dejavu_fonts
-    powerline-fonts
-    source-code-pro
-    cantarell-fonts
-  ];
-
-  users = {
-    mutableUsers = false;
-
-    users = {
-      user = {
-        isNormalUser = true;
-        group = "user";
-        extraGroups = [
-          "wheel"
-          "video"
-          "audio"
-          "dialout"
-          "users"
-          "kvm"
-          "wireshark"
-        ];
-        password = "unimportant";
-      };
-    };
-
-    groups = {
-      user = { };
-    };
-  };
-
-  security = {
-    pam.loginLimits = [
-      {
-        domain = "@audio";
-        item = "memlock";
-        type = "-";
-        value = "unlimited";
-      }
-      {
-        domain = "@audio";
-        item = "rtprio";
-        type = "-";
-        value = "99";
-      }
-      {
-        domain = "@audio";
-        item = "nofile";
-        type = "soft";
-        value = "99999";
-      }
-      {
-        domain = "@audio";
-        item = "nofile";
-        type = "hard";
-        value = "99999";
-      }
-    ];
-
-    sudo.extraRules = [
-      {
-        users = [ "user" ];
-        commands = [
-          {
-            command = "${pkgs.linuxPackages.cpupower}/bin/cpupower";
-            options = [ "NOPASSWD" ];
-          }
-        ];
-      }
-    ];
-  };
-
-  environment.systemPackages = with pkgs; [
-    a2jmidid
-    age
-    ardour
-    bemenu
-    blender
-    breeze-icons
-    breeze-qt5
-    bubblewrap
-    calf
-    claws-mail
-    darktable
-    duperemove
-    emacs
-    feh
-    file
-    firefox
-    fluidsynth
-    adwaita-icon-theme
-    gnuplot
-    graphviz
-    helm
-    i3status-rust
-    inkscape
-    jack2
-    jq
-    krita
-    ldns
-    libqalculate
-    libreoffice
-    man-pages
-    nix-diff
-    nix-index
-    nix-output-monitor
-    open-music-kontrollers.patchmatrix
-    pamixer
-    pavucontrol
-    pciutils
-    picom
-    pwgen
-    redshift
-    ripgrep
-    rlwrap
-    silver-searcher
-    soundfont-fluid
-    whois
-    wol
-    xclip
-    xdot
-    xdotool
-    xorg.xkbcomp
-    yt-dlp
-    zathura
-    borgbackup
-    linuxPackages.cpupower
-    mtr
-    kitty
-    xf86_input_wacom
-  ];
-
-  environment.pathsToLink = [ "/share/soundfonts" ];
-
-  systemd.user.services.run-python = {
-    after = [ "network-online.target" ];
-    script = ''
-      exec ${pkgs.python3}/bin/python
-    '';
-    serviceConfig = {
-      CapabilityBoundingSet = [ "" ];
-      KeyringMode = "private";
-      LockPersonality = true;
-      MemoryDenyWriteExecute = true;
-      NoNewPrivileges = true;
-      PrivateDevices = true;
-      PrivateTmp = true;
-      PrivateUsers = true;
-      ProcSubset = "pid";
-      ProtectClock = true;
-      ProtectControlGroups = true;
-      ProtectHome = true;
-      ProtectHostname = true;
-      ProtectKernelLogs = true;
-      ProtectKernelModules = true;
-      ProtectKernelTunables = true;
-      ProtectProc = "invisible";
-      ProtectSystem = "strict";
-      RestrictAddressFamilies = "AF_INET AF_INET6";
-      RestrictNamespaces = true;
-      RestrictRealtime = true;
-      RestrictSUIDSGID = true;
-      SystemCallArchitectures = "native";
-      SystemCallFilter = [
-        "@system-service"
-        "~ @resources @privileged"
-      ];
-      UMask = "077";
-    };
-  };
-
-  system.stateVersion = "23.11";
-}

contrib/OWNERS

@@ -0,0 +1 @@
+*

doc/OWNERS

@@ -0,0 +1 @@
+*

doc/manual/change-authors.yml

@@ -77,10 +77,20 @@ edolstra:
   display_name: Eelco Dolstra
   github: edolstra
 
+emilazy:
+  display_name: Emily
+  forgejo: emilazy
+  github: emilazy
+
 ericson:
   display_name: John Ericson
   github: ericson2314
 
+getchoo:
+  display_name: Seth Flynn
+  forgejo: getchoo
+  github: getchoo
+
 gilice:
   forgejo: gilice
 
@@ -115,6 +125,11 @@ jade:
 just1602:
   forgejo: just1602
 
+kasimeka:
+  display_name: ورد
+  forgejo: janw4ld
+  github: kasimeka
+
 kfears:
   display_name: KFears
   forgejo: kfearsoff
@@ -153,6 +168,9 @@ ma27:
 matthewbauer:
   github: matthewbauer
 
+mic92:
+  github: mic92
+
 midnightveil:
   display_name: julia
   forgejo: midnightveil
@@ -252,6 +270,9 @@ winter:
 xanderio:
   github: xanderio
 
+xokdvium:
+  github: xokdvium
+
 yorickvp:
   github: yorickvp
 

doc/manual/generate-manpage.nix

@@ -225,7 +225,7 @@ let
           showCategory = cat: ''
             ${optionalString (cat != "") "**${cat}:**"}
 
-            ${listOptions (filterAttrs (n: v: v.category == cat) allOptions)}
+            ${listOptions (filterAttrs (n: v: v.category == cat && !v.hidden) allOptions)}
           '';
           listOptions = opts: concatStringsSep "\n" (attrValues (mapAttrs showOption opts));
           showOption =

doc/manual/rl-next/arg-identifier.md

@@ -1,16 +0,0 @@
----
-synopsis: First argument to `--arg`/`--argstr` must be a valid Nix identifier
-issues: [fj#496]
-category: "Breaking Changes"
-credits: [ma27]
----
-
-The first argument to `--arg`/`--argstr` must be a valid Nix identifier, i.e.
-`nix-build --arg config.allowUnfree true` is now rejected.
-
-This is because that invocation is a false friend since it doesn't set
-`{ config = { allowUnfree = true; }; }`, but `{ "config.allowUnfree" = true; }`.
-
-The idea is to change the behavior to the latter in the long-term. For that,
-non-identifiers started giving a warning since 2.92 and are now rejected to give people
-who depend on that a chance to notice and potentially weigh in on the discussion.

doc/manual/rl-next/async-query.md

@@ -1,20 +0,0 @@
----
-synopsis: "Improved susbtituter query speed"
-issues: []
-cls: []
-category: Improvements
-credits: [horrors]
----
-
-The code used to query substituters for derivations has been rewritten slightly
-to take advantage of our asynchronous runtime. Such queries run for every build
-that could download from substituters and processes every derivation that isn't
-yet present on the local system. Previously Lix would use `http-connections` to
-limit query concurrency, even for modern caches that support HTTP/2 and have no
-limit on how many queries can be run concurrently on one single connection. Lix
-no longer does this, resulting in approximately 60% reduction in query time for
-medium-sized closures (e.g. NixOS system closures) during testing, although the
-exact number depends greatly on local network latency and generally improves as
-latency increases. Unlike previously setting `http-connections` to `1` or other
-low values no longer brings a massive penalty in query performance if the cache
-in use by the querying system supports HTTP/2 (as e.g. `cache.nixos.org` does).

doc/manual/rl-next/build-dir-mandatory.md

@@ -1,12 +0,0 @@
----
-synopsis: "`build-dir` no longer defaults to `temp-dir`"
-cls: [3453]
-category: "Fixes"
-credits: [horrors]
----
-
-The directory in which temporary build directories are created no longer defaults
-to the value of the `temp-dir` setting to avoid builders making their directories
-world-accessible. This behavior has been used to escape the build sandbox and can
-cause build impurities even when not used maliciously. We now default to `builds`
-in `NIX_STATE_DIR` (which is `/nix/var/nix/builds` in the default configuration).

doc/manual/rl-next/cgroups-delegation.md

@@ -1,69 +0,0 @@
----
-synopsis: New cgroup delegation model
-issues: [fj#537, fj#77]
-cls: [3230]
-category: "Breaking Changes"
-credits: [raito, horrors, lheckemann]
----
-
-Builds using cgroups (i.e. `use-cgroups = true` and the experimental feature
-`cgroups`) now always delegate a cgroup tree to the sandbox.
-
-Compared to the original C++ Nix project, our delegation includes the
-`subtree_control` file as well, which means that the sandbox can disable
-certain controllers in its own cgroup tree.
-
-This is a breaking change because this requires the Nix daemon to run with an
-already delegated cgroup tree by the service manager.
-
-## How to setup the cgroup tree with systemd?
-
-systemd offers knobs to perform the required setup using:
-
-```
-[Service]
-Delegate=yes
-DelegateSubtree=supervisor
-```
-
-These directives are now included in our systemd packaging.
-
-## What about using Nix as root without connecting to the daemon?
-
-Builds run as `root` without connecting to the daemon relying on the cgroup
-feature are now broken, i.e.
-
-```console
-# nix-build --use-cgroups --sandbox ... # will not work
-```
-
-Consider doing instead:
-
-```console
-# systemd-run --same-dir --wait -p Delegate=yes -p DelegateSubgroup=supervisor nix-build --use-cgroups ...
-```
-
-If you need to disable cgroups temporarily, remember that you can do
-`NIX_CONF='include /etc/nix/nix.conf\nuse-cgroups = false' nix-build ...` or
-`nix-build --no-use-cgroups ...`.
-
-## What about other service managers than systemd?
-
-systemd has a [documentation](https://systemd.io/CGROUP_DELEGATION/) on how to
-handle cgroup delegation from service management perspective.
-
-If your service manager adheres to systemd semantics, e.g. writing an extended
-attribute `user.delegate=1` on the delegated cgroup tree directory and moving
-the `nix-daemon` process inside a cgroup tree to respect the inner process
-rule, then, the feature will work as well.
-
-## Why is the cgroup feature still experimental?
-
-While the cgroup feature unlocks many use cases, its behavior and integration (e.g. user experience), especially at scale on build farms or in multi-tenant environments, are not yet fully matured. There’s also potential for deeper systemd integration (e.g. using slices and scopes) that has not been fully explored.
-
-To avoid locking in an unstable interface, we’re keeping the experimental flag until we have validated the feature across a broader range of scenarios, including but not limited to:
-
-* Nix as root
-* Hydra-style build farms
-* Forgejo CI runners
-* Shared remote builders

doc/manual/rl-next/deprecated-derivation-types.md

@@ -1,16 +0,0 @@
----
-synopsis: Deprecation of CA derivations, dynamic derivations, and impure derivations
-issues: [fj#815]
-cls: []
-significance: significant
-category: Miscellany
-credits: []
----
-
-Content-addressed derivations are now deprecated and slated for removal in Lix 2.94.
-We're doing this because the CA derivation system has been a known cause of problems
-and inconsistencies, is unmaintained, habitually makes improving the store code very
-difficult (or blocks such improvements outright), and is beset by a number of design
-flaws that in our opinion cannot be fixed without a full reimplementation from zero.
-Dynamic derivations and impure derivations are built on the CA derivation framework,
-and owing to this they too are deprecated and slated for removal in another release.

doc/manual/rl-next/fix-gc-links.md

@@ -1,13 +0,0 @@
----
-synopsis: "nix-store --delete: always remove obsolete hardlinks"
-issues: []
-cls: [3188]
-category: Fixes
-credits: [lheckemann]
----
-
-Deleting specific paths using `nix-store --delete` or `nix store
-delete` previously did not delete hard links created by `nix-store
---optimise` even if they became obsolete, unless _all_ of the given
-paths were deleted successfully. Now, hard links are always cleaned
-up, even if some of the given paths could not be deleted.

doc/manual/rl-next/fix-gc-stats.md

@@ -1,24 +0,0 @@
----
-synopsis: "Report GC statistics correctly"
-issues: []
-cls: [3188]
-category: Fixes
-credits: [lheckemann]
----
-
-Deleting specific paths using `nix-store --delete` or `nix store delete` previously did
-not report statistics correctly when some of the paths could not be deleted, even if
-others were deleted:
-
-```
-$ nix store delete /nix/store/9bwryidal9q3g91cjm6xschfn4ikd82q-hello-2.12.1 --delete-closure -v
-finding garbage collector roots...
-deleting '/nix/store/9bwryidal9q3g91cjm6xschfn4ikd82q-hello-2.12.1'
-0 store paths deleted, 0.00 MiB freed
-error: Cannot delete some of the given paths because they are still alive. Paths not deleted:
-         k9bxzr1l92r5y6mihrkbpbr3fmc8qszx-libidn2-2.3.8
-         mbx9ii53lzjlrsnlrfmzpwm33ynljwdn-libunistring-1.3
-         rf8hcy6bldxdqc0g6q1dcka1vh47x69s-xgcc-14.2.1.20250322-libgcc
-         vbrdc5wgzn0w1zdp10xd2favkjn5fk7y-glibc-2.40-66
-       To find out why, use nix-store --query --roots and nix-store --query --referrers.
-```

doc/manual/rl-next/ignore-try-default.md

@@ -1,24 +0,0 @@
----
-synopsis: Repl debugger uses `--ignore-try` by default
-issues: [lix#666]
-cls: [3488]
-category: Breaking Changes
-credits: [jade]
----
-Previously, using the debugger meant that exceptions thrown in `builtins.tryEval` would trigger the debugger.
-
-However, this caught nixpkgs initialization code, which is unhelpful in the majority of cases, so we changed the default.
-
-To get the old behaviour, use `--no-ignore-try`.
-
-```
-$ nix repl --debugger --expr 'with import <nixpkgs> {}; pkgs.hello'
-Lix 2.94.0-dev-pre20250625-9a59106
-Type :? for help.
-error: file 'nixpkgs-overlays' was not found in the Nix search path (add it using $NIX_PATH or -I)
-
-This exception occurred in a 'tryEval' call. Use --ignore-try to skip these.
-
-Added 13 variables.
-nix-repl>
-```

doc/manual/rl-next/infallible-build-dirs.md

@@ -1,25 +0,0 @@
----
-synopsis: "Fallback to safe temp dir when build-dir is unwritable"
-issues: [fj#876]
-cls: [3501]
-category: "Fixes"
-credits: ["raito", "horrors"]
----
-
-Non-daemon builds started failing with a permission error after introducing the `build-dir` option:
-
-```
-$ nix build --store ~/scratch nixpkgs#hello --rebuild
-error: creating directory '/nix/var/nix/builds/nix-build-hello-2.12.2.drv-0': Permission denied
-```
-
-This happens because:
-
-1. These builds are not run via the daemon, which owns `/nix/var/nix/builds`.
-2. The user lacks permissions for that path.
-
-We considered making `build-dir` a store-level option and defaulting it to `<chroot-root>/nix/var/nix/builds` for chroot stores, but opted instead for a fallback: if the default fails, Nix now creates a safe build directory under `/tmp`.
-
-To avoid CVE-2025-52991, the fallback uses an extra path component between `/tmp` and the build dir.
-
-**Note**: this fallback clutters `/tmp` with build directories that are not cleaned up. To prevent this, explicitly set `build-dir` to a path managed by Lix, even for local workloads.

doc/manual/rl-next/integer-coercion.md

@@ -1,47 +0,0 @@
----
-synopsis: Experimental integer coercion in interpolated strings
-issues: []
-cls: [3198]
-category: "Features"
-credits: [raito, delroth, horrors, winter]
----
-
-Ever tried interpolating a port number in Lix and ended up with something like this?
-
-```nix
-"http://${config.network.host}:${builtins.toString config.network.port}/"
-```
-
-You're not alone. Thousands of Lix users suffer every day from excessive `builtins.toString` syndrome. It’s 2025, and we still have to cast integers to use them in strings.
-
-To address this, Lix introduces the **`coerce-integers`** experimental feature. When enabled, interpolated integers within `"${...}"` are automatically coerced to strings. This allows writing:
-
-```nix
-"http://${config.network.host}:${config.network.port}/"
-```
-
-without additional conversion.
-
-To enable the feature, you need to add `coerce-integers` to your set of experimental features.
-
-### Stabilization criteria
-
-The `coerce-integers` feature is experimental and limited strictly to string interpolation (`"${...}"`). Before stabilization, the following must hold:
-
-1. **Interpolation-only**
-   Coercion must not occur outside interpolation. Expressions like `"" + 42` must continue to fail.
-
-2. **Expectation that no explicit cast are being observed**
-   Cases observing explicit coercion (e.g., via `tryEval` gadget or similar) are expected not to be load-bearing in actual production code.
-
-### Timeline for stabilization
-
-If the feature proves safe and is widely adopted across typical usage (e.g., actual configurations in the wild turning on the flag, non-trivial out-of-tree projects using it), the experimental flag will be removed **after six months of active use or two Lix releases**, whichever is longer.
-
-This avoids locking the feature in experimental status indefinitely, as happened with Flakes, while allowing time for validation and ecosystem integration.
-
-### What about coercing floats or more?
-
-Coercion beyond integers -- such as for floats or other types -- is **not planned**, even under an experimental flag. Questions like "what is the canonical string representation of a float?" involve subtle and context-dependent trade-offs. Without a robust and principled mechanism to define and audit such behavior, introducing broader coercion risks setting unintended and hard-to-reverse precedents. The scope of `coerce-integers` is intentionally narrow and will remain so.
-
-In terms of outlook, a proposal like https://git.lix.systems/lix-project/lix/issues/835 could pave the way for a better solution.

doc/manual/rl-next/log-output-terminal-codes.md

@@ -1,11 +0,0 @@
----
-synopsis: Fix handling of OSC codes in terminal output
-issues: [fj#160]
-cls: [3143]
-category: Fixes
-credits: [lilyball]
----
-
-OSC codes in terminal output are now handled correctly, where OSC 8 (hyperlink) is preserved any
-time color codes are allowed and all other OSC codes are stripped out. This applies not only to
-output from build commands but also to rendered documentation in the REPL.

doc/manual/rl-next/mismatch-check-path.md

@@ -1,14 +0,0 @@
----
-synopsis: Better debuggability on fixed-output hash mismatches
-issues: []
-cls: []
-category: Improvements
-credits: [lheckemann]
----
-
-Fixed-output derivation hash mismatch error messages will now include the path that was
-produced unexpectedly, and this path will be registered as valid even if `--check`
-(`nix-store`, `nix-build`) or `--rebuild` (`nix build`) was passed. This makes comparing
-the expected path with the obtained path easier, and is useful for debugging when
-upstreams modify previously-published releases or when changes in fixed-output
-derivations' dependencies affect their output unexpectedly.

doc/manual/rl-next/nix-instantiate-raw.md

@@ -1,12 +0,0 @@
----
-synopsis: "Add --raw flag to `nix-instantiate --eval` for unescaped output"
-issues: []
-prs: [gh#12119]
-cls: [2886]
-category: Improvements
-credits: [not-my-profile, infinisil, raito]
----
-
-The `nix-instantiate --eval` command now supports a `--raw` flag. When used,
-the result must be coercible to a string (as with `${...}`) and is printed
-verbatim, without quotes or escaping.

doc/manual/rl-next/nix-store-ls-read-nar-listings.md

@@ -1,12 +0,0 @@
----
-synopsis: Allow `nix store ls` to read nar listings from binary cache stores.
-issues: []
-cls: [3225]
-category: Improvements
-credits: [vlinkz]
----
-
-The `nix store ls` command now supports reading `.ls` nar listings from binary cache stores.
-If a listing is detected for the store path being queried, the nar is no longer downloaded.
-These nar listings are available in binary cache stores where the `write-nar-listing` option is
-enabled, such as cache.nixos.org.

doc/manual/rl-next/pasta.md

@@ -1,20 +0,0 @@
----
-synopsis: "Fixed output derivations can be run using `pasta` network isolation"
-cls: [3452]
-issues: [fj#285]
-category: "Breaking Changes"
-credits: [horrors, puck]
----
-
-Fixed output derivations traditionally run in the host network namespace.
-On Linux this allows such derivations to communicate with other sandboxes
-or the host using the abstract Unix domains socket namespace; this hasn't
-been unproblematic in the past and has been used in two distinct exploits
-to break out of the sandbox. For this reason fixed output derivations can
-now run in a network namespace (provided by [`pasta`]), restricted to TCP
-and UDP communication with the rest of the world. When enabled this could
-be a breaking change and we classify it as such, even though we don't yet
-enable or require such isolation by default. We may enforce this in later
-releases of Lix once we have sufficient confidence that breakage is rare.
-
-[`pasta`]: https://passt.top/

doc/manual/rl-next/reliance-on-bash-for-ssh.md

@@ -1,21 +0,0 @@
----
-synopsis: Remove reliance on Bash for remote stores via SSH
-issues: [fj#830, fj#805, fj#304]
-cls: [3159]
-category: "Fixes"
-credits: [raito]
----
-
-The pre-flight `echo started` handshake -- added years ago to catch race conditions -- has been removed.
-
-After removal of connection sharing in Lix 2.93, it required a Bash-compatible shell and a standard `echo`, so it failed on:
-
-  * builders protected by `ForceCommand` wrappers (e.g. `nix-remote-build`),
-  * BusyBox / initrd images with no Bash,
-  * hosts using non-POSIX shells such as Nushell.
-
-The race the probe once addressed was tied to SSH connection-sharing -- since connection-sharing code has already been removed, the probe is now pointless.
-
-Real connection or protocol errors are now left to SSH/Nix to report directly.
-
-This is technically a breaking change if you had scripts that relied on the literal "started" which needs to be updated to rely on other signals, e.g., exit codes.

doc/manual/rl-next/remove-old-wires.md

@@ -1,20 +0,0 @@
----
-synopsis: Remove support for daemon protocols before 2.18
-issues: []
-cls: [3249]
-significance: significant
-category: "Breaking Changes"
-credits: [horrors]
----
-
-Support for daemon wire protocols belonging to Nix 2.18 or older have been
-removed. This impacts clients connecting to the local daemon socket or any
-remote builder configured using the `ssh-ng` protocol. Builders configured
-with the `ssh` protocol are still accessible from clients such as Nix 2.3.
-Additionally Lix will not be able to connect to an old daemon locally, and
-remote build connections to old daemons is likewise limited to `ssh` urls.
-
-We have decided to take this step because the old protocols are very badly
-tested (if at all), maintenance overhead is high, and a number of problems
-with their design makes it infeasible to remain backwards compatible while
-we move Lix to a more modern RPC mechanism with better versioning support.

doc/manual/rl-next/remove-xp-derivations.md

@@ -1,17 +0,0 @@
----
-synopsis: Remove impure derivations and dynamic derivations
-issues: [fj#815]
-cls: [3210]
-significance: significant
-category: "Breaking Changes"
-credits: [horrors]
----
-
-The `impure-derivations` and `dynamic-derivations` experimental feature have
-been removed.
-
-New impure or dynamic derivations cannot be created from this point forward, and
-any such pre-existing store derivations canot be read or built any more.
-Derivation outputs created by building such a derivation are still valid
-until garbage collected; existing store derivations can only be garbage
-collected.

doc/manual/rl-next/repl-overlays-pure.md

@@ -1,20 +0,0 @@
----
-synopsis: "repl-overlays now work in the debugger for flakes"
-issues: [fj#777]
-cls: [3398]
-category: Fixes
-credits: [jade]
----
-Due to a bug, it was previously not possible to use the debugger on flakes with repl-overlays, or with pure evaluation in general:
-
-```
-$ nix repl --pure-eval
-Lix 2.94.0-dev-pre20250617-87d99da
-Type :? for help.
-Loading 'repl-overlays'...
-error: access to absolute path '/Users/jade/.config/nix/repl.nix' is forbidden in pure eval mode (use '--impure' to override)
-```
-
-This is now fixed.
-The contents of the repl-overlays file itself (i.e. most typically the top level lambda in it) will be evaluated in impure mode.
-It may be necessary to use `builtins.seq` to force the impure operations to happen first if one wants to do impure operations inside a repl-overlays file in pure evaluation mode.

doc/manual/rl-next/symbol-value-reuse.md

@@ -1,32 +0,0 @@
----
-synopsis: Symbols reuses once-allocated Value to reduce garbage collected allocations
-issues: []
-cls: [3308, 3300, 3314, 3310, 3312, 3313]
-category: Improvements
-credits: [raito, horrors, thubrecht, nan-git]
----
-
-In the Lix evaluator, **symbols** represent immutable strings, like those used
-for attribute names.
-
-In evaluator design, such strings are typically [**interned**](https://en.wikipedia.org/wiki/String_interning), stored uniquely
-to save memory, and Lix inherits this approach from the original C++ codebase.
-
-However, some builtins, like `builtins.attrNames`, must return a `Value` type
-that can represent any Nix value (strings, integers, lists, etc.).
-
-Before this change, these builtins would create lists of `Value` objects by
-allocating them through the garbage collector, copying the symbol’s string
-content each time.
-
-This allocation is unnecessary if the interned symbols themselves also hold a
-`Value` representation allocated outside the garbage collector, since these
-live for the full duration of evaluation.
-
-As a result, this reduces the number of allocations, leading to:
-
-* A significant drop in maximum [resident set memory](https://en.wikipedia.org/wiki/Resident_set_size) (RSS), with some large-scale
-  tests showing up to 11% (about 500 MiB) savings in large colmena deployments.
-* A slight decrease in CPU usage during Nix evaluations.
-
-This change is inspired by https://github.com/NixOS/nix/pull/13258 but the approach is different.

doc/manual/rl-next/uid-range-requires-cgroups.md

@@ -1,15 +0,0 @@
----
-synopsis: uid-range depends on cgroups
-issues: []
-cls: [3230]
-category: "Breaking Changes"
-credits: [raito, horrors]
----
-
-`uid-range` builds now depends on `cgroups`, an experimental feature.
-
-`uid-range` builds already depended upon `auto-allocate-uids`, another experimental feature.
-
-The rationale for doing so is that `uid-range` provides a sandbox with many
-UIDs, this is useful for re-mapping them into a nested namespace, e.g. a
-container.

doc/manual/src/SUMMARY.md

@@ -39,6 +39,9 @@
   - [Tuning Cores and Jobs](advanced-topics/cores-vs-jobs.md)
   - [Verifying Build Reproducibility](advanced-topics/diff-hook.md)
   - [Using the `post-build-hook`](advanced-topics/post-build-hook.md)
+  - [Pasta](advanced-topics/pasta.md)
+- [Known Issues](known-issues/known-issues.md)
+  - [Limitations around non-isolated builds](known-issues/non-isolated-build-limits.md)
 - [Command Reference](command-ref/command-ref.md)
   - [Common Options](command-ref/opt-common.md)
   - [Common Environment Variables](command-ref/env-common.md)
@@ -197,6 +200,7 @@
 - [Release Notes](release-notes/release-notes.md)
   - [Upcoming release](release-notes/rl-next.md)
     <!-- RELENG-AUTO-INSERTION-MARKER (see releng/release_notes.py) -->
+  - [Lix 2.94 (2025-11-17)](release-notes/rl-2.94.md)
   - [Lix 2.93 (2025-05-09)](release-notes/rl-2.93.md)
   - [Lix 2.92 (2025-01-18)](release-notes/rl-2.92.md)
   - [Lix 2.91 (2024-08-12)](release-notes/rl-2.91.md)

doc/manual/src/advanced-topics/pasta.md

@@ -0,0 +1,19 @@
+# [Pasta](https://passt.top/passt/about/): a network sandbox for fixed-output derivations
+
+## Introduction
+
+This section only applies to **Linux systems** as Pasta is a Linux-only measure.
+
+Since [CVE-2025-46416](https://lix.systems/blog/2025-06-24-lix-cves/), the Lix project decided to adopt [Pasta](https://passt.top/passt/about/) for all fixed-output derivations, protecting against various attack vectors such as UNIX abstract domain sockets or more manipulation at the network layer from a malicious fixed-output derivation code.
+
+Pasta acts as a translation layer between a layer-2 network interface and layer-4 sockets (TCP, UDP, ICMP/ICMPv6 echo) on the host. It requires no special privileges and can serve as a alternative to [SLiRP](https://en.wikipedia.org/wiki/Slirp) which was used [by Guix to mitigate the same problem](https://codeberg.org/guix/guix/commit/fb42611b8f27960304db5a1c0d33b8371dcde2a8).
+
+## How to disable Pasta?
+
+It's sufficient to pass `pasta-path = ""` in your `/etc/nix/nix.conf` or on the command line `--pasta-path ""` of a Lix invocation.
+
+## Known issues surrounding Pasta
+
+- Only the first DNS server in `/etc/resolv.conf` is considered: failover is not possible.
+- [Reduced feature set compared to the Linux kernel](https://passt.top/passt/about/#features)
+- [Performance overhead in multi-gigabits contexts and IMIX MTUs](https://passt.top/passt/about/#performance_1)

doc/manual/src/command-ref/nix-build.md

@@ -58,7 +58,7 @@ $ nix-build flake:nixpkgs -A firefox
 $ nix-build flake:github:NixOS/nixpkgs/release-23.11 -A firefox
 ```
 
-Finally, for legacy reasons, if a path starts with `channel:`, the rest of the argument is interpreted as the name of a *nixpkgs* channel tarball to fetch from `https://nixos.org/channels/$CHANNEL_NAME/nixexprs.tar.xz`.
+Finally, for legacy reasons, if a path starts with `channel:`, the rest of the argument is interpreted as the name of a *nixpkgs* channel tarball to fetch from `https://channels.nixos.org/$CHANNEL_NAME/nixexprs.tar.xz`.
 This is a **hard coded URL** pattern and is *not* related to the subscribed channels managed by the [nix-channel](./nix-channel.md) command.
 
 > **Note**: any of the special syntaxes may always be disambiguated by prefixing the path.

doc/manual/src/command-ref/nix-channel.md

@@ -11,7 +11,7 @@
 Channels are a mechanism for referencing remote Nix expressions and conveniently retrieving their latest version.
 
 The moving parts of channels are:
-- The official channels listed at <https://nixos.org/channels>
+- The official channels listed at <https://channels.nixos.org>
 - The user-specific list of [subscribed channels](#subscribed-channels)
 - The [downloaded channel contents](#channels)
 - The [Nix expression search path](@docroot@/command-ref/conf-file.md#conf-nix-path), set with the [`-I` option](#opt-I) or the [`NIX_PATH` environment variable](#env-NIX_PATH)
@@ -77,9 +77,9 @@ This command has the following operations:
 Subscribe to the Nixpkgs channel and run `hello` from the GNU Hello package:
 
 ```console
-$ nix-channel --add https://nixos.org/channels/nixpkgs-unstable
+$ nix-channel --add https://channels.nixos.org/nixpkgs-unstable
 $ nix-channel --list
-nixpkgs https://nixos.org/channels/nixpkgs
+nixpkgs https://channels.nixos.org/nixpkgs
 $ nix-channel --update
 $ nix-shell -p hello --run hello
 hello

doc/manual/src/command-ref/nix-instantiate.md

@@ -107,20 +107,27 @@ See that section for complete details (`nix-build --help`), but in summary, a pa
     > This option can cause non-termination, because lazy data
     > structures can be infinitely large.
 
-  - `--raw`
+  - `--raw`\
     When used with `--eval`, the result must be coercible to a string, i.e.,
-    something that can be converted using `${...}`. The output is
-    printed exactly as-is, with no quotes, escaping, or trailing newline.
+    something that can be converted using `${...}`.
+
+    Integers will always generate an error when output via `--raw`, regardless of
+    [`coerce-integers`](../contributing/experimental-features.md#xp-feature-coerce-integers) being enabled, to avoid ambiguity.
+
+    The output is printed exactly as-is, with no quotes, escaping, or trailing
+    newline.
 
   - `--json`\
     When used with `--eval`, print the resulting value as an JSON
-    representation of the abstract syntax tree rather than as a Nix expression.
+    representation of the resulting value rather than as a Nix expression.
+
+    The conversion behaviour, if `--strict` is passed, is the same as
+    [`builtins.toJSON`](../language/builtins.md#builtins-toJSON).
 
   - `--xml`\
     When used with `--eval`, print the resulting value as an XML
-    representation of the abstract syntax tree rather than as a Nix expression.
-    The schema is the same as that used by the [`toXML`
-    built-in](../language/builtins.md).
+    representation of the resulting value rather than as a Nix expression.
+    The schema is the same as that used by [`builtins.toXML`](../language/builtins.md#builtins-toXML).
 
   - `--read-write-mode`\
     When used with `--eval`, perform evaluation in read/write mode so

doc/manual/src/contributing/cli-guideline.md

@@ -661,8 +661,8 @@ Verbosity levels are:
 
 The default level that the command starts is `ERROR`. The simplest way to
 increase the verbosity by stacking `-v` option (eg: `-vvv == level 3 == INFO`).
-There are also two shortcuts, `--debug` to run in `DEBUG` verbosity level and
-`--quiet` to run in `ERROR` verbosity level.
+Use `--quiet` to decrease verbosity by one level.
+There is one shortcut, `--debug` to run in `DEBUG` verbosity level.
 
 ----------
 

doc/manual/src/contributing/hacking.md

@@ -11,7 +11,19 @@ The following instructions assume you already have some version of Nix or Lix in
 
 [installation instructions]: ../installation/installation.md
 
-## Building Lix in a development shell
+A typical development flow for simple changes in Lix looks like:
+- [Set up and build Lix](#building)
+- For large changes, check in regarding design and possibly create an RFD issue on Forgejo
+- Make the changes in your editor
+- [Send the changes to Gerrit](#sending-to-gerrit)
+- Once you have the number for the CL from Gerrit to put in the changelog, [write a changelog entry](#release-notes) and amend it into the commit
+- Update the Gerrit change by submitting it with the same command as the first time
+- Request and receive a code review
+- Address feedback from the review
+- Amend commits, send to Gerrit again
+- Submit the approved change
+
+## Building Lix in a development shell {#building}
 
 ### Setting up the development shell
 
@@ -48,7 +60,7 @@ $ just setup build test-unit
 $ just install test-integration
 ```
 
-Many targets have a `-custom` variant which pass extra arguments to `meson`.
+Many justfile aliases have a `-custom` variant which pass extra arguments to `meson`.
 For example, to work on both Lix and nix-eval-jobs you can run:
 
 ```
@@ -129,7 +141,44 @@ To inspect the canonical source of truth on what the state of the buildsystem co
 $ meson introspect
 ```
 
-## Building Lix outside of development shells
+## Sending changes to Gerrit for review {#sending-to-gerrit}
+
+We use Gerrit for all our code review in Lix.
+Our instance is at <https://gerrit.lix.systems>.
+
+There's much more information about how to use Gerrit in the [wiki section on Gerrit][wiki-gerrit] including how to use Jujutsu, how to use the UI and more.
+The Snix project also has some Gerrit information [in their contributing docs][snix-gerrit].
+
+[wiki-gerrit]: https://wiki.lix.systems/books/lix-contributors/chapter/gerrit
+[snix-gerrit]: https://snix.dev/docs/guides/contributing/
+
+The gist is that once you have your SSH key and git remote set up, you can send commits for review with:
+
+```
+$ git remote set-url origin ssh://YOURUSERNAME@gerrit.lix.systems:2022/lix
+$ git push origin HEAD:refs/for/main
+```
+
+Then, you can request a review via the "Reply" button on the web UI.
+If you click "Suggest Owners", it will try to suggest the maintainers of the area of the code change to send review requests to.
+Requesting reviews from multiple people is normal.
+
+We do our best to respond to directly sent reviews in a few days, so feel free to request another reviewer or ask on Matrix if you've not got a response for a while.
+Keep in mind that Lix is a volunteer project and we have limited bandwidth, so some changes aren't feasible to shepherd through; please check in on Matrix at design time when doing large changes.
+
+Once you get a `Code-Review+2` vote on your change, it's rebased on `main` and CI marks it `Verified+1`, you're able (and usually expected, so you can have a second chance to check it over) to hit the Submit button to merge it.
+If the change appears as "Rebase Required", you need to rebase it on `main` locally or via the Gerrit UI and wait for `Verified+1` before the Submit button is made active
+The `Code-Review+2` from before will stick around through trivial rebases so no need to re-request review for a mere rebase.
+
+## Interacting with the CI, Buildkite
+
+We use Buildkite for our CI, usually you will not have to interact directly with it other than reviewing any errors it produces, which are linked from Gerrit.
+
+However in certain cases a CI run will fail due to transient issues not related to your code and you will need to rerun it by hand.
+You can log in to the CI via [SSO](https://buildkite.com/sso/lix-project). On your job you can then hit the "Retry failed" button to rerun it, normally you will not have a repeat of the transient issue.
+If the build still fails on CI issues or all builds are failing this should be reported via [Zulip on #T-infra](https://zulip.lix.systems/#narrow/channel/7-T-infra) or [Matrix on #dev](https://matrix.to/#/%23dev%3Alix.systems?via=lix.systems).
+
+## Building Lix with `nix`
 
 To build a release version of Lix for the current operating system and CPU architecture:
 
@@ -286,10 +335,10 @@ Configure your editor to use the `clangd` from the shell, either by running it i
 > Some other editors (e.g. Emacs, Vim) need a plugin to support LSP servers in general (e.g. [lsp-mode](https://github.com/emacs-lsp/lsp-mode) for Emacs and [vim-lsp](https://github.com/prabirshrestha/vim-lsp) for vim).
 > Editor-specific setup is typically opinionated, so we will not cover it here in more detail.
 
-### Checking links in the manual
+# Manual and documentation
+
+## Building the manual
 
-The build checks for broken internal links.
-This happens late in the process, so `nix build` is not suitable for iterating.
 To build the manual incrementally, run:
 
 ```console
@@ -301,15 +350,20 @@ meson compile -C build manual
 [`mdbook-linkcheck`]: https://github.com/Michael-F-Bryan/mdbook-linkcheck
 [URI fragments]: https://en.wikipedia.org/wiki/URI_fragment
 
-#### `@docroot@` variable
+The built manual is in `build/doc/manual/manual/index.html`.
 
-`@docroot@` provides a base path for links that occur in reusable snippets or other documentation that doesn't have a base path of its own.
+The build checks for broken internal links.
+This happens late in the process, so `nix build` is not suitable for iterating and it's recommended to use the `meson` command above instead.
 
-If a broken link occurs in a snippet that was inserted into multiple generated files in different directories, use `@docroot@` to reference the `doc/manual/src` directory.
+### `@\docroot\@` variable
 
-If the `@docroot@` literal appears in an error message from the `mdbook-linkcheck` tool, the `@docroot@` replacement needs to be applied to the generated source file that mentions it.
-See existing `@docroot@` logic in the [Makefile].
-Regular markdown files used for the manual have a base path of their own and they can use relative paths instead of `@docroot@`.
+`@\docroot\@` provides a base path for links that occur in reusable snippets or other documentation that doesn't have a base path of its own.
+
+If a broken link occurs in a snippet that was inserted into multiple generated files in different directories, use `@\docroot\@` to reference the `doc/manual/src` directory.
+
+If the `@\docroot\@` literal appears in an error message from the `mdbook-linkcheck` tool, the `@\docroot\@` replacement needs to be applied to the generated source file that mentions it.
+See existing `@\docroot\@` logic in `doc/manual/substitute.py`.
+Regular markdown files used for the manual have a base path of their own and they can use relative paths instead of `@\docroot\@`.
 
 ## API documentation
 
@@ -341,7 +395,7 @@ You can build it yourself:
 
 Metrics about the change in line/function coverage over time will be available in the future (FIXME(lix-hydra)).
 
-## Add a release note
+## Add a release note {#release-notes}
 
 `doc/manual/rl-next` contains release notes entries for all unreleased changes.
 
@@ -410,15 +464,15 @@ The following properties are supported:
 ### Build process
 
 Releases have a precomputed `rl-MAJOR.MINOR.md`, and no `rl-next.md`.
-Set `buildUnreleasedNotes = true;` in `flake.nix` to build the release notes on the fly.
+Development releases have a generated `rl-next.md`.
 
-## Adding experimental or deprecated features, global settings, or builtins
+# Adding experimental or deprecated features, global settings, or builtins
 
 Experimental and deprecated features, global settings, and builtins are generally referenced both in the code and in the documentation.
 To prevent duplication or divergence, they are defined in data files, and a script generates the necessary glue.
 The data file format is similar to the release notes: it consists of a YAML metadata header, followed by the documentation in Markdown format.
 
-### Experimental or deprecated features
+## Experimental or deprecated features
 
 Experimental and deprecated features support the following metadata properties:
 * `name` (required): user-facing name of the feature, to be used in `nix.conf` options and on the command line.
@@ -428,7 +482,7 @@ Experimental and deprecated features support the following metadata properties:
 Experimental feature data files should live in `lix/libutil/experimental-features`, and deprecated features in `lix/libutil/deprecated-features`.
 They must be listed in the `experimental_feature_definitions` or `deprecated_feature_definitions` lists in `lix/libutil/meson.build` respectively to be considered by the build system.
 
-### Global settings
+## Global settings
 
 Global settings support the following metadata properties:
 * `name` (required): user-facing name of the setting, to be used as key in `nix.conf` and in the `--option` command line argument.
@@ -456,7 +510,7 @@ Settings are not collected in a single place in the source tree, so an appropria
 Look for related setting definition files under second-level subdirectories of `lix` whose name includes `settings`.
 Then add the new file there, and don't forget to register it in the appropriate `meson.build` file.
 
-### Builtin functions
+## Builtin functions
 
 The following metadata properties are supported for builtin functions:
 * `name` (required): the language-facing name (as a member of the `builtins` attribute set) of the function.
@@ -472,7 +526,7 @@ The following metadata properties are supported for builtin functions:
 
 New builtin function definition files must be added to `lix/libexpr/builtins` and registered in the `builtin_definitions` list in `lix/libexpr/meson.build`.
 
-### Builtin constants
+## Builtin constants
 The following metadata properties are supported for builtin constants:
 * `name` (required): the language-facing name (as a member of the `builtins` attribute set) of the constant.
 * `type` (required): the Nix language type of the constant; the C++ type is automatically derived.

doc/manual/src/contributing/testing.md

@@ -62,6 +62,12 @@ For `installcheck` specifically, first run `just install` before running the tes
 
 Finer-grained filtering within a test suite is also possible using the [--gtest_filter](https://google.github.io/googletest/advanced.html#running-a-subset-of-the-tests) command-line option to a test suite executable, or the `GTEST_FILTER` environment variable.
 
+### Inspecting failures
+
+The test suite emits logs in `build/meson-logs/`; the full textual failure logs are in `build/meson-logs/testlog.txt`.
+
+If you want a much nicer experience of viewing the logs in a structured manner, use `xunit-viewer --results build/meson-logs/testlog.junit.xml --server` to view them in a web browser.
+
 ### Unit test support libraries
 
 There are headers and code which are not just used to test the library in question, but also downstream libraries.

doc/manual/src/installation/installing-docker.md

@@ -60,3 +60,10 @@ Then:
 ```console
 $ docker run -ti lix
 ```
+
+# Known issues
+
+Lix in Docker is very sensitive to **functional** DNS resolution if you are running with [Pasta protections](../advanced-topics/pasta.md) which are enabled by default since Lix 2.93.0 on most distributions.
+If you notice failure to download things, double check whether your **first** DNS entry in `/etc/resolv.conf` is functional.
+
+Lix with [Pasta protections](../advanced-topics/pasta.md) does not support failing over the next entries.

doc/manual/src/installation/prerequisites-source.md

@@ -54,11 +54,6 @@ The most current alternative to this section is to read `package.nix` and see wh
     obtained from the its repository
     <https://github.com/troglobit/editline>.
 
-  - The `libsodium` library for verifying cryptographic signatures
-    of contents fetched from binary caches.
-    It can be obtained from the official web site
-    <https://libsodium.org>.
-
   - Recent versions of Bison and Flex to build the parser. (This is
     because Nix needs GLR support in Bison and reentrancy support in
     Flex.) For Bison, you need version 2.6, which can be obtained from

doc/manual/src/known-issues/known-issues.md

@@ -0,0 +1 @@
+This section lists known issues around Lix.

doc/manual/src/known-issues/non-isolated-build-limits.md

@@ -0,0 +1,21 @@
+# Limitations of non-isolated builds
+
+## What are non-isolated builds?
+
+In Lix, only builds done on Linux with `sandbox = true` and a functioning
+`pasta-path` are isolated from the rest of the system, all other builds are
+considered non-isolated to some degree.
+
+For example, running Lix with [Pasta](@docroot@/advanced-topics/pasta.md)
+disabled makes the host network visible to fixed-output derivations, reducing
+isolation somewhat.
+
+## Clean termination of non-isolated builds
+
+Non-isolated builds may not terminate cleanly in all cases due to limitations in Lix's process management.
+
+This occurs when a build keeps the build log file descriptor open past the end of the actual build. A common cause of this are background tasks that aren't properly terminated before the main build process exits, for example: HTTP servers run as part of a test suite.
+
+See [issue #1018](https://git.lix.systems/lix-project/lix/issues/1018) for an example.
+
+The only solution is to manually terminate leftover processes in your derivation, including during failure scenarios.

doc/manual/src/language/advanced-attributes.md

@@ -302,8 +302,6 @@ Derivations can declare some infrequently used optional attributes.
 
     - `maxSize` defines the maximum size of the resulting [store object](../glossary.md#gloss-store-object).
     - `maxClosureSize` defines the maximum size of the output's closure.
-    - `ignoreSelfRefs` controls whether self-references should be considered when
-      checking for allowed references/requisites.
 
     Example:
 

doc/manual/src/package-management/basic-package-mgmt.md

@@ -41,7 +41,7 @@ install Lix. If this is not the case for some reason, you can add it
 as follows:
 
 ```console
-$ nix-channel --add https://nixos.org/channels/nixpkgs-unstable
+$ nix-channel --add https://channels.nixos.org/nixpkgs-unstable
 $ nix-channel --update
 ```
 
@@ -49,7 +49,7 @@ $ nix-channel --update
 >
 > On NixOS, you’re automatically subscribed to a NixOS channel
 > corresponding to your NixOS major release (e.g.
-> <http://nixos.org/channels/nixos-21.11>). A NixOS channel is identical
+> <https://channels.nixos.org/nixos-21.11>). A NixOS channel is identical
 > to the Nixpkgs channel, except that it contains only Linux binaries
 > and is updated only if a set of regression tests succeed.
 

doc/manual/src/release-notes/rl-2.94.md

@@ -0,0 +1,955 @@
+# Lix 2.94 "Açaí na tigela" (2025-11-17)
+
+
+# Lix 2.94.0 (2025-11-17)
+## Breaking Changes
+
+- Remove support for daemon protocols before 2.18 [fj#510](https://git.lix.systems/lix-project/lix/issues/510) [cl/3249](https://gerrit.lix.systems/c/lix/+/3249)
+
+  Support for daemon wire protocols belonging to Nix 2.17 or older have been
+  removed. This impacts clients connecting to the local daemon socket or any
+  remote builder configured using the `ssh-ng` protocol. Builders configured
+  with the `ssh` protocol are still accessible from clients such as Nix 2.3.
+  Additionally Lix will not be able to connect to an old daemon locally, and
+  remote build connections to old daemons is likewise limited to `ssh` urls.
+
+  We have decided to take this step because the old protocols are very badly
+  tested (if at all), maintenance overhead is high, and a number of problems
+  with their design makes it infeasible to remain backwards compatible while
+  we move Lix to a more modern RPC mechanism with better versioning support.
+
+  Many thanks to [eldritch horrors](https://git.lix.systems/pennae) for this.
+
+- Remove impure derivations and dynamic derivations [fj#815](https://git.lix.systems/lix-project/lix/issues/815) [cl/3210](https://gerrit.lix.systems/c/lix/+/3210)
+
+  The `impure-derivations` and `dynamic-derivations` experimental feature have
+  been removed.
+
+  New impure or dynamic derivations cannot be created from this point forward, and
+  any such pre-existing store derivations canot be read or built any more.
+  Derivation outputs created by building such a derivation are still valid
+  until garbage collected; existing store derivations can only be garbage
+  collected.
+
+  Many thanks to [eldritch horrors](https://git.lix.systems/pennae) for this.
+
+- First argument to `--arg`/`--argstr` must be a valid Nix identifier [fj#496](https://git.lix.systems/lix-project/lix/issues/496)
+
+  The first argument to `--arg`/`--argstr` must be a valid Nix identifier, i.e.
+  `nix-build --arg config.allowUnfree true` is now rejected.
+
+  This is because that invocation is a false friend since it doesn't set
+  `{ config = { allowUnfree = true; }; }`, but `{ "config.allowUnfree" = true; }`.
+
+  The idea is to change the behavior to the latter in the long-term. For that,
+  non-identifiers started giving a warning since 2.92 and are now rejected to give people
+  who depend on that a chance to notice and potentially weigh in on the discussion.
+
+  Many thanks to [ma27](https://git.lix.systems/ma27) for this.
+
+- New cgroup delegation model [fj#537](https://git.lix.systems/lix-project/lix/issues/537) [fj#77](https://git.lix.systems/lix-project/lix/issues/77) [cl/3230](https://gerrit.lix.systems/c/lix/+/3230)
+
+  Builds using cgroups (i.e. `use-cgroups = true` and the experimental feature
+  `cgroups`) now always delegate a cgroup tree to the sandbox.
+
+  Compared to the original C++ Nix project, our delegation includes the
+  `subtree_control` file as well, which means that the sandbox can disable
+  certain controllers in its own cgroup tree.
+
+  This is a breaking change because this requires the Nix daemon to run with an
+  already delegated cgroup tree by the service manager.
+
+  ## How to setup the cgroup tree with systemd?
+
+  systemd offers knobs to perform the required setup using:
+
+  ```
+  [Service]
+  Delegate=yes
+  DelegateSubtree=supervisor
+  ```
+
+  These directives are now included in our systemd packaging.
+
+  ## What about using Nix as root without connecting to the daemon?
+
+  Builds run as `root` without connecting to the daemon relying on the cgroup
+  feature are now broken, i.e.
+
+  ```console
+  # nix-build --use-cgroups --sandbox ... # will not work
+  ```
+
+  Consider doing instead:
+
+  ```console
+  # systemd-run --same-dir --wait -p Delegate=yes -p DelegateSubgroup=supervisor nix-build --use-cgroups ...
+  ```
+
+  If you need to disable cgroups temporarily, remember that you can do
+  `NIX_CONF='include /etc/nix/nix.conf\nuse-cgroups = false' nix-build ...` or
+  `nix-build --no-use-cgroups ...`.
+
+  ## What about other service managers than systemd?
+
+  systemd has a [documentation](https://systemd.io/CGROUP_DELEGATION/) on how to
+  handle cgroup delegation from service management perspective.
+
+  If your service manager adheres to systemd semantics, e.g. writing an extended
+  attribute `user.delegate=1` on the delegated cgroup tree directory and moving
+  the `nix-daemon` process inside a cgroup tree to respect the inner process
+  rule, then, the feature will work as well.
+
+  ## Why is the cgroup feature still experimental?
+
+  While the cgroup feature unlocks many use cases, its behavior and integration (e.g. user experience), especially at scale on build farms or in multi-tenant environments, are not yet fully matured. There’s also potential for deeper systemd integration (e.g. using slices and scopes) that has not been fully explored.
+
+  To avoid locking in an unstable interface, we’re keeping the experimental flag until we have validated the feature across a broader range of scenarios, including but not limited to:
+
+  * Nix as root
+  * Hydra-style build farms
+  * Forgejo CI runners
+  * Shared remote builders
+
+  Many thanks to [Raito Bezarius](https://git.lix.systems/raito), [eldritch horrors](https://git.lix.systems/pennae), and [lheckemann](https://git.lix.systems/lheckemann) for this.
+
+- Enable high compress ratio zstd compression by default for binary caches uploads [fj#945](https://git.lix.systems/lix-project/lix/issues/945) [cl/4503](https://gerrit.lix.systems/c/lix/+/4503)
+
+  The default compression method for binary cache uploads has been switched from
+  [`xz`](https://github.com/tukaani-project/xz) to
+  [`zstd`](https://github.com/facebook/zstd) to address performance and usability
+  issues related to modern hardware and high-speed connections.
+
+  ## Why?
+
+  `xz` offers compression ratios but is single-threaded in our implementation and
+  very slow (~10-20 Mbps in our test), preventing full utilization of 100Mbps+
+  connections and significantly slowing decompression for end users.
+
+  Lix is a "compress once, decompress many" application: build farms can afford
+  to spend more time compressing to achieve a faster download transfer for the
+  end user. More importantly, it matters that all end users spend the least
+  amount of time decompressing.
+
+  ## What about compression ratios?
+
+  `zstd` cannot achieve the same peaks as `xz`, nonetheless, `zstd` compression
+  level has been increased to level 12 by default to balance compression ratio
+  and performance.
+
+  ## Synthetic test case data
+
+  * **xz** (default compression level) on a 4.4GB file: ~632MB (77s)
+  * **zstd** (level 12) on the same file: ~775MB (18s), 18% larger but 50% faster
+  * **zstd** (level 14): ~773MB (37s)
+  * **zstd** (level 16): ~735MB (66s)
+
+  Many thanks to [eldritch horrors](https://git.lix.systems/pennae) and [Raito Bezarius](https://git.lix.systems/raito) for this.
+
+- Repl debugger uses `--ignore-try` by default [lix#666](https://git.lix.systems/lix-project/lix/issues/666) [cl/3488](https://gerrit.lix.systems/c/lix/+/3488)
+
+  Previously, using the debugger meant that exceptions thrown in `builtins.tryEval` would trigger the debugger.
+
+  However, this caught nixpkgs initialization code, which is unhelpful in the majority of cases, so we changed the default.
+
+  To get the old behaviour, use `--no-ignore-try`.
+
+  ```
+  $ nix repl --debugger --expr 'with import <nixpkgs> {}; pkgs.hello'
+  Lix 2.94.0-dev-pre20250625-9a59106
+  Type :? for help.
+  error: file 'nixpkgs-overlays' was not found in the Nix search path (add it using $NIX_PATH or -I)
+
+  This exception occurred in a 'tryEval' call. Use --ignore-try to skip these.
+
+  Added 13 variables.
+  nix-repl>
+  ```
+
+  Many thanks to [jade](https://git.lix.systems/jade) for this.
+
+- Strings may now contain NUL bytes [cl/3968](https://gerrit.lix.systems/c/lix/+/3968)
+
+  Lix now allows strings to contain NUL bytes instead of silently truncating the
+  string before the first such byte. Notably NUL-bearing strings were allowed as
+  attribute names—even though the corresponding strings were not representable!—
+  leading to very surprising and incorrect behavior in corner cases, for example
+
+  ```
+  nix-repl> builtins.fromJSON ''{"a": 1, "a\u0000b": 2}''
+  {
+    a = 1;
+    "ab" = 2;
+  }
+
+  nix-repl> builtins.attrNames (builtins.fromJSON ''{"a": 1, "a\u0000b": 2}'')
+  [
+    "a"
+    "a"
+  ]
+  ```
+
+  rather than the more correct but still with the terminal eating NUL on display
+
+  ```
+  nix-repl> builtins.fromJSON ''{"a": 1, "a\u0000b": 2}''
+  {
+    a = 1;
+    "ab" = 2;
+  }
+
+  nix-repl> builtins.attrNames (builtins.fromJSON ''{"a": 1, "a\u0000b": 2}'')
+  [
+    "a"
+    "ab"
+  ]
+  ```
+
+  We consider this a breaking change since eval results *will* change if strings
+  with embedded NUL bytes were used, but we also consider the old behavior to be
+  not intentional (seeing how inconsistent it was) but merely fallout from a old
+  and misguided implementation decision to be worked around, not actually fixed.
+
+  Many thanks to [eldritch horrors](https://git.lix.systems/pennae) for this.
+
+- Fixed output derivations can be run using `pasta` network isolation [fj#285](https://git.lix.systems/lix-project/lix/issues/285) [cl/3452](https://gerrit.lix.systems/c/lix/+/3452)
+
+  Fixed output derivations traditionally run in the host network namespace.
+  On Linux this allows such derivations to communicate with other sandboxes
+  or the host using the abstract Unix domains socket namespace; this hasn't
+  been unproblematic in the past and has been used in two distinct exploits
+  to break out of the sandbox. For this reason fixed output derivations can
+  now run in a network namespace (provided by [`pasta`]), restricted to TCP
+  and UDP communication with the rest of the world. When enabled this could
+  be a breaking change and we classify it as such, even though we don't yet
+  enable or require such isolation by default. We may enforce this in later
+  releases of Lix once we have sufficient confidence that breakage is rare.
+
+  [`pasta`]: https://passt.top/
+
+  Many thanks to [eldritch horrors](https://git.lix.systems/pennae) and [puck](https://git.lix.systems/puck) for this.
+
+- Function equality semantics are more consistent, but still bad [cl/4556](https://gerrit.lix.systems/c/lix/+/4556) [cl/4244](https://gerrit.lix.systems/c/lix/+/4244)
+
+  Lix has inherited a historic misfeature from CppNix in the form of pointer
+  equality checks built into the `==` operator. These checks were originally
+  meant to optimize comparison for large sets, but they have the unfortunate
+  side effect of producing unexpected results when sets containing functions
+  are compared. **Lix 2.93 and earlier** behave as shown in the repl session
+
+  ```
+  Lix 2.93.3
+  Type :? for help.
+  nix-repl> f = x: x
+  Added f.
+
+  nix-repl> f == f
+  false
+
+  nix-repl> let s.f = f; in s.f == s.f
+  false
+
+  nix-repl> # however!
+            { inherit f; } == { inherit f; }
+  true
+
+  nix-repl> [ f ] == [ f ]
+  true
+
+  nix-repl> # and, in another twist:
+            [ f ] == map f [ f ]
+  false
+  ```
+
+  Nixpkgs relies on sets containing functions being comparable, so we cannot
+  simply deprecate this behavior. Due to changes to the object model used by
+  Lix ***all* comparisons above now evaluate to `true`**. This is considered
+  a breaking change because eval results may differ, but we also consider it
+  minor because the optimization is unsound (c.f. `let l = [NaN]; in l == l`
+  evaluates to `true` even though floating point `NaN` is incomparable). Lix
+  intends to remove this optimization altogether in the future, but until we
+  can do that we instead make it slightly less broken to allow other, *real*
+  optimizations. Function equality comparison remains **undefined behavior**
+  and should not be relied upon in Nixlang code that intends to be portable.
+
+  Many thanks to [eldritch horrors](https://git.lix.systems/pennae) for this.
+
+- `nix eval --write-to` has been removed [fj#974](https://git.lix.systems/lix-project/lix/issues/974) [fj#227](https://git.lix.systems/lix-project/lix/issues/227) [cl/4045](https://gerrit.lix.systems/c/lix/+/4045)
+
+  `nix eval --write-to` has been removed since it was underspecified, not widely
+  useful, and prone to security-sensitive misbehaviors. The feature was added in
+  Nix 2.4 purely for internal use in the build system. According to our research
+  it hasn't found any use outside of some distribution packaging scripts. Please
+  use structured outputs formats (such as JSON) instead as they have better type
+  fidelity, don't conflate attributes with paths, and are useful to other tools.
+
+  Many thanks to [eldritch horrors](https://git.lix.systems/pennae) for this.
+
+- Remove the `parse-toml-timestamps` experimental feature
+
+  The `parse-toml-timestamps` experimental feature has been removed.
+
+  This feature used in‐band signalling to mark timestamps, making it
+  impossible to unambiguously parse TOML documents. It also exposed
+  implementation‐defined behaviour in the TOML specification that
+  changed in the toml11 parser library.
+
+  Any interface for parsing TOML timestamps suitable for future
+  stabilization would necessarily involve breaking changes, and there
+  is no evidence this experimental feature is being relied upon in the
+  wild, so it has been removed.
+
+  Many thanks to [Emily](https://git.lix.systems/emilazy) for this.
+
+- Reject overflowing TOML integer literals [cl/3916](https://gerrit.lix.systems/c/lix/+/3916)
+
+  The toml11 library used by Lix was updated. The new
+  version aligns with the [TOML v1.0.0 specification’s
+  requirement](https://toml.io/en/v1.0.0#integer) to reject integer
+  literals that cannot be losslessly parsed. This means that code like
+  `builtins.fromTOML "v=0x8000000000000000"` will now produce an error
+  rather than silently saturating the integer result.
+
+  Many thanks to [Emily](https://git.lix.systems/emilazy) for this.
+
+- uid-range depends on cgroups [cl/3230](https://gerrit.lix.systems/c/lix/+/3230)
+
+  `uid-range` builds now depends on `cgroups`, an experimental feature.
+
+  `uid-range` builds already depended upon `auto-allocate-uids`, another experimental feature.
+
+  The rationale for doing so is that `uid-range` provides a sandbox with many
+  UIDs, this is useful for re-mapping them into a nested namespace, e.g. a
+  container.
+
+  Many thanks to [Raito Bezarius](https://git.lix.systems/raito) and [eldritch horrors](https://git.lix.systems/pennae) for this.
+
+
+## Features
+
+- Add `inputs.self.submodules` flake attribute [fj#942](https://git.lix.systems/lix-project/lix/issues/942) [cl/3839](https://gerrit.lix.systems/c/lix/+/3839)
+
+  A port of <https://github.com/NixOS/nix/pull/12421> to Lix, which:
+
+  - adds a general `inputs.self` flake attribute that retroactively applies
+    configurations to a flake after it's been fetched, then triggers a refetch of
+    the flake with the new config.
+  - implements `inputs.self.submodules` that allows a flake to declare its need
+    for submodules, which are then fetched automatically with no need to pass
+    `?submodules=1` anywhere.
+
+  Many thanks to [Eelco Dolstra](https://github.com/edolstra) and [ورد](https://git.lix.systems/janw4ld) for this.
+
+- Lix supports HTTP/3 behind `--http3` [fj#1033](https://git.lix.systems/lix-project/lix/issues/1033)
+
+  Lix now supports HTTP/3 for file transfers when the linked curl version
+  supports it.
+
+  By default, HTTP/3 is disabled notably due to performance issues reported in
+  mid-2024. [More details
+  here](https://daniel.haxx.se/blog/2024/06/10/http-3-in-curl-mid-2024/).
+
+  As of 2025-11-14, [NixOS official cache](https://cache.nixos.org) supports
+  HTTP/3 via Fastly. [More info
+  here](https://github.com/NixOS/infra/commit/157fa70e46afbd6338a32407be461fce05c57bf8).
+
+  To enable HTTP/3:
+
+  * Use `--http3` for individual transfers.
+  * Add `http3 = true` in your Nix configuration for permanent activation.
+
+  To disable it, use `--no-http3`.
+
+  **Note**:
+
+  * `--no-http2 --http3` will still enable both HTTP/2 and HTTP/3.
+  * `--http2 --http3` will prioritize HTTP/3 and fall back to HTTP/2 (and then
+    HTTP/1.1).
+
+  These are current CLI limitations. In the future, we plan to replace `--httpX`
+  options with `--max-http-version [1,2,3]` for easier version selection in Lix
+  transfers.
+
+  Many thanks to [Raito Bezarius](https://git.lix.systems/raito) and [eldritch horrors](https://git.lix.systems/pennae) for this.
+
+- Add hyperlinks in attr set printing [cl/3790](https://gerrit.lix.systems/c/lix/+/3790)
+
+  The attribute set printer, such as is seen in `nix repl` or in type errors, now prints hyperlinks on each attribute name to its definition site if it is known.
+
+  Example: all of the attributes shown here are hyperlinks to the exact definition site of the attribute in question:
+
+  ```
+  $ nix eval -f '<nixpkgs>' lib.licenses.mit
+  { deprecated = false; free = true; fullName = "MIT License"; redistributable = true; shortName = "mit"; spdxId = "MIT"; url = "https://spdx.org/licenses/MIT.html"; }
+  ```
+
+  Many thanks to [jade](https://git.lix.systems/jade) for this.
+
+- Experimental integer coercion in interpolated strings [cl/3198](https://gerrit.lix.systems/c/lix/+/3198)
+
+  Ever tried interpolating a port number in Lix and ended up with something like this?
+
+  ```nix
+  "http://${config.network.host}:${builtins.toString config.network.port}/"
+  ```
+
+  You're not alone. Thousands of Lix users suffer every day from excessive `builtins.toString` syndrome. It’s 2025, and we still have to cast integers to use them in strings.
+
+  To address this, Lix introduces the **`coerce-integers`** experimental feature. When enabled, interpolated integers within `"${...}"` are automatically coerced to strings. This allows writing:
+
+  ```nix
+  "http://${config.network.host}:${config.network.port}/"
+  ```
+
+  without additional conversion.
+
+  To enable the feature, you need to add `coerce-integers` to your set of experimental features.
+
+  ### Stabilization criteria
+
+  The `coerce-integers` feature is experimental and limited strictly to string interpolation (`"${...}"`). Before stabilization, the following must hold:
+
+  1. **Interpolation-only**
+     Coercion must not occur outside interpolation. Expressions like `"" + 42` must continue to fail.
+
+  2. **Expectation that no explicit cast are being observed**
+     Cases observing explicit coercion (e.g., via `tryEval` gadget or similar) are expected not to be load-bearing in actual production code.
+
+  ### Timeline for stabilization
+
+  If the feature proves safe and is widely adopted across typical usage (e.g., actual configurations in the wild turning on the flag, non-trivial out-of-tree projects using it), the experimental flag will be removed **after six months of active use or two Lix releases**, whichever is longer.
+
+  This avoids locking the feature in experimental status indefinitely, as happened with Flakes, while allowing time for validation and ecosystem integration.
+
+  ### What about coercing floats or more?
+
+  Coercion beyond integers -- such as for floats or other types -- is **not planned**, even under an experimental flag. Questions like "what is the canonical string representation of a float?" involve subtle and context-dependent trade-offs. Without a robust and principled mechanism to define and audit such behavior, introducing broader coercion risks setting unintended and hard-to-reverse precedents. The scope of `coerce-integers` is intentionally narrow and will remain so.
+
+  In terms of outlook, a proposal like https://git.lix.systems/lix-project/lix/issues/835 could pave the way for a better solution.
+
+  Many thanks to [Raito Bezarius](https://git.lix.systems/raito), [delroth](https://github.com/delroth), [eldritch horrors](https://git.lix.systems/pennae), and [winter](https://git.lix.systems/winter) for this.
+
+- nix-eval-jobs: support `--no-instantiate` flag [fj#987](https://git.lix.systems/lix-project/lix/issues/987)
+
+  `nix-eval-jobs` now supports a flag called `--no-instantiate`. With this enabled,
+  no write operations on the eval store are performed. That means, only evaluation is
+  performed, but derivations (and their gcroots) aren't created.
+
+  Many thanks to [mic92](https://github.com/mic92) and [ma27](https://git.lix.systems/ma27) for this.
+
+
+## Improvements
+
+- Assess current profile generations pointers in `nix doctor` [cl/3108](https://gerrit.lix.systems/c/lix/+/3108)
+
+  Added a new check to `nix doctor` that verifies whether the current generation of
+  a Nix profile can be resolved. This helps users diagnose issues with broken or
+  misconfigured profile symlinks.
+
+  This helps determining if you have broken symlinks or misconfigured packaging.
+
+  Many thanks to [Raito Bezarius](https://git.lix.systems/raito) for this.
+
+- Improved susbtituter query speed
+
+  The code used to query substituters for derivations has been rewritten slightly
+  to take advantage of our asynchronous runtime. Such queries run for every build
+  that could download from substituters and processes every derivation that isn't
+  yet present on the local system. Previously Lix would use `http-connections` to
+  limit query concurrency, even for modern caches that support HTTP/2 and have no
+  limit on how many queries can be run concurrently on one single connection. Lix
+  no longer does this, resulting in approximately 60% reduction in query time for
+  medium-sized closures (e.g. NixOS system closures) during testing, although the
+  exact number depends greatly on local network latency and generally improves as
+  latency increases. Unlike previously setting `http-connections` to `1` or other
+  low values no longer brings a massive penalty in query performance if the cache
+  in use by the querying system supports HTTP/2 (as e.g. `cache.nixos.org` does).
+
+  Many thanks to [eldritch horrors](https://git.lix.systems/pennae) for this.
+
+- Hitting Control-C twice always terminates Lix [cl/3574](https://gerrit.lix.systems/c/lix/+/3574)
+
+  Hitting Control-C or sending `SIGINT` to Lix now prints an informational message
+  if it is still running after on second, the second Control-C/`SIGINT` terminates
+  Lix immediately without waiting for any shutdown code to finish running. Lix did
+  not treat the second such event differently from first in the past; this made it
+  impossible to easily terminate running Lix processes that got stuck in e.g. very
+  expensive Nixlang code that never interacted with the store. We now terminate as
+  soon as the user hits Control-C again without waiting any more, to much the same
+  effect as putting Lix into the background and killing it immediately afterwards.
+
+  This means you can now more conveniently break out of stuck Nixlang evaluations:
+  ```
+  ❯ nix-instantiate --eval --expr 'let f = n: if n == 0 then 0 else f (n - 1) + f (n - 1); in f 32'
+  ^CStill shutting down. Press ^C again to abort all operations immediately.
+  ^C
+
+  ❌130 ❯
+  ```
+
+  Many thanks to [eldritch horrors](https://git.lix.systems/pennae) for this.
+
+- `--keep-failed` chowns the build directory to the user that request the build
+
+  Running a build with `--keep-failed` now chowns the temporary directory from the
+  builder user and group to the user that request the build if the build came from
+  a local user connected to the daemon. This makes inspecting failed derivations a
+  lot easier. On Linux the build directory made visible to the user will not be in
+  the same path as it was in the sandbox and continuing builds will usually break.
+
+  Many thanks to [eldritch horrors](https://git.lix.systems/pennae) for this.
+
+- Better debuggability on fixed-output hash mismatches
+
+  Fixed-output derivation hash mismatch error messages will now include the path that was
+  produced unexpectedly, and this path will be registered as valid even if `--check`
+  (`nix-store`, `nix-build`) or `--rebuild` (`nix build`) was passed. This makes comparing
+  the expected path with the obtained path easier, and is useful for debugging when
+  upstreams modify previously-published releases or when changes in fixed-output
+  derivations' dependencies affect their output unexpectedly.
+
+  Many thanks to [lheckemann](https://git.lix.systems/lheckemann) for this.
+
+- Add --raw flag to `nix-instantiate --eval` for unescaped output [gh#12119](https://github.com/NixOS/nix/pull/12119) [cl/2886](https://gerrit.lix.systems/c/lix/+/2886)
+
+  The `nix-instantiate --eval` command now supports a `--raw` flag. When used,
+  the result must be coercible to a string (as with `${...}`) and is printed
+  verbatim, without quotes or escaping.
+
+  Many thanks to [Martin Fischer](https://github.com/not-my-profile), [infinisil](https://github.com/infinisil), and [Raito Bezarius](https://git.lix.systems/raito) for this.
+
+- Allow `nix store ls` to read nar listings from binary cache stores. [cl/3225](https://gerrit.lix.systems/c/lix/+/3225)
+
+  The `nix store ls` command now supports reading `.ls` nar listings from binary cache stores.
+  If a listing is detected for the store path being queried, the nar is no longer downloaded.
+  These nar listings are available in binary cache stores where the `write-nar-listing` option is
+  enabled, such as cache.nixos.org.
+
+  Many thanks to [Victor Fuentes](https://git.lix.systems/vlinkz) for this.
+
+- show tree with references that lead to an output cycle [fj#551](https://git.lix.systems/lix-project/lix/issues/551)
+
+  When Lix determines a cyclic dependency between several outputs of a derivation,
+  it now displays which files in which outputs lead to an output cycle:
+
+  ```
+  error: cycle detected in build of '/nix/store/gc5h2whz3rylpf34n99nswvqgkjkigmy-demo.drv' in the references of output 'bar' from output 'foo'.
+
+         Shown below are the files inside the outputs leading to the cycle:
+         /nix/store/3lrgm74j85nzpnkz127rkwbx3fz5320q-demo-bar
+         └───lib/libfoo: …stuffbefore /nix/store/h680k7k53rjl9p15g6h7kpym33250w0y-demo-baz andafter.…
+             → /nix/store/h680k7k53rjl9p15g6h7kpym33250w0y-demo-baz
+             └───share/snenskek: …???? /nix/store/dm24c76p9y2mrvmwgpmi64rryw6x5qmm-demo-foo ....…
+                 → /nix/store/dm24c76p9y2mrvmwgpmi64rryw6x5qmm-demo-foo
+                 └───bin/alarm: …textexttext/nix/store/3lrgm74j85nzpnkz127rkwbx3fz5320q-demo-bar abcabcabc.…
+                     → /nix/store/3lrgm74j85nzpnkz127rkwbx3fz5320q-demo-bar
+  ```
+
+  Please note that showing the files and its contents while displaying the cycles only works
+  on Linux.
+
+  Many thanks to [ma27](https://git.lix.systems/ma27) for this.
+
+- Lix now enables parallel marking in boehm-gc [fj#983](https://git.lix.systems/lix-project/lix/issues/983) [cl/3880](https://gerrit.lix.systems/c/lix/+/3880)
+
+  This brings a fairly modest performance improvement (~38% for `nixpkgs search hello`) to evaluation, especially in scenarios that necessitate larger heap sizes.
+
+  Many thanks to [Eelco Dolstra](https://github.com/edolstra) and [Seth Flynn](https://git.lix.systems/getchoo) for this.
+
+- `disallowedRequisites` now reports chains of disallowed requisites [fj#334](https://git.lix.systems/lix-project/lix/issues/334) [fj#626](https://git.lix.systems/lix-project/lix/issues/626) [gh#10877](https://github.com/NixOS/nix/issues/10877)
+
+  When a build fails because of [`disallowedRequisites`](@docroot@/language/advanced-attributes.md#adv-attr-disallowedRequisites), the error message now includes the chain of references that led to the failure. This makes it easier to see in which derivations the chain can be broken, to resolve the problem.
+
+  Example:
+
+  ```
+  $ nix-build -A hello
+  error: output '/nix/store/0b7k85gg5r28gb54px9nq7iv5986mns9-hello-2.12.2' is not allowed to refer to the following paths:
+         /nix/store/eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-glibc-2.40-66
+         Shown below are chains that lead to the forbidden path(s).
+         /nix/store/0b7k85gg5r28gb54px9nq7iv5986mns9-hello-2.12.2
+         └───/nix/store/eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-glibc-2.40-66
+  ```
+
+  Many thanks to [ma27](https://git.lix.systems/ma27) and [Robert Hensing](https://github.com/roberth) for this.
+
+- Stack traces now summarize involved derivations at the bottom [cl/4493](https://gerrit.lix.systems/c/lix/+/4493)
+
+  When evaluation errors and a stack trace is printed,
+
+  For example, if I add Nheko to a NixOS `environment.systemPackages` without adding `olm-3.2.16` `nixpkgs.config.permittedInsecurePackages`, then without `--show-trace`, I previously got this:
+
+  ```
+  error:
+         … while calling the 'head' builtin
+           at /nix/store/9v6qa656sq3xc58vkxslqy646p0ajj61-source/lib/attrsets.nix:1701:13:
+           1700|           if length values == 1 || pred here (elemAt values 1) (head values) then
+           1701|             head values
+               |             ^
+           1702|           else
+
+         … while evaluating the attribute 'value'
+           at /nix/store/9v6qa656sq3xc58vkxslqy646p0ajj61-source/lib/modules.nix:1118:7:
+           1117|     // {
+           1118|       value = addErrorContext "while evaluating the option `${showOption loc}':" value;
+               |       ^
+           1119|       inherit (res.defsFinal') highestPrio;
+
+         (stack trace truncated; use '--show-trace' to show the full trace)
+
+         error: Package ‘olm-3.2.16’ in /nix/store/9v6qa656sq3xc58vkxslqy646p0ajj61-source/pkgs/by-name/ol/olm/package.nix:37 is marked as insecure, refusing to evaluate.
+
+         < -snip the whole explanation about olm's CVEs- >
+  ```
+
+  This doesn't tell me anything about where `olm-3.2.16` came from.
+  With `--show-trace`, there's 1 155 lines to sift through, but does contain lines like "while evaluating derivation 'nheko-0.12.1'".
+
+  With this change, those lines are summarized and collected at the bottom, regardless of `--show-trace`:
+
+  ```
+  error:
+         … while calling the 'head' builtin
+           at /nix/store/9v6qa656sq3xc58vkxslqy646p0ajj61-source/lib/attrsets.nix:1701:13:
+           1700|           if length values == 1 || pred here (elemAt values 1) (head values) then
+           1701|             head values
+               |             ^
+           1702|           else
+
+         … while evaluating the attribute 'value'
+           at /nix/store/9v6qa656sq3xc58vkxslqy646p0ajj61-source/lib/modules.nix:1118:7:
+           1117|     // {
+           1118|       value = addErrorContext "while evaluating the option `${showOption loc}':" value;
+               |       ^
+           1119|       inherit (res.defsFinal') highestPrio;
+
+         (stack trace truncated; use '--show-trace' to show the full trace)
+
+         error: Package ‘olm-3.2.16’ in /nix/store/9v6qa656sq3xc58vkxslqy646p0ajj61-source/pkgs/by-name/ol/olm/package.nix:37 is marked as insecure, refusing to evaluate.
+
+
+         < -snip the whole explanation about olm's CVEs- >
+
+
+         note: trace involved the following derivations:
+         derivation 'etc'
+         derivation 'dbus-1'
+         derivation 'system-path'
+         derivation 'nheko-0.12.1'
+         derivation 'mtxclient-0.10.1'
+  ```
+
+  Now we finally know that olm was evaluated because of Nheko, without sifting through *thousands* of lines of error message.
+
+  Many thanks to [Qyriad](https://git.lix.systems/Qyriad) for this.
+
+- Symbols reuses once-allocated Value to reduce garbage collected allocations [cl/3308](https://gerrit.lix.systems/c/lix/+/3308) [cl/3300](https://gerrit.lix.systems/c/lix/+/3300) [cl/3314](https://gerrit.lix.systems/c/lix/+/3314) [cl/3310](https://gerrit.lix.systems/c/lix/+/3310) [cl/3312](https://gerrit.lix.systems/c/lix/+/3312) [cl/3313](https://gerrit.lix.systems/c/lix/+/3313)
+
+  In the Lix evaluator, **symbols** represent immutable strings, like those used
+  for attribute names.
+
+  In evaluator design, such strings are typically [**interned**](https://en.wikipedia.org/wiki/String_interning), stored uniquely
+  to save memory, and Lix inherits this approach from the original C++ codebase.
+
+  However, some builtins, like `builtins.attrNames`, must return a `Value` type
+  that can represent any Nix value (strings, integers, lists, etc.).
+
+  Before this change, these builtins would create lists of `Value` objects by
+  allocating them through the garbage collector, copying the symbol’s string
+  content each time.
+
+  This allocation is unnecessary if the interned symbols themselves also hold a
+  `Value` representation allocated outside the garbage collector, since these
+  live for the full duration of evaluation.
+
+  As a result, this reduces the number of allocations, leading to:
+
+  * A significant drop in maximum [resident set memory](https://en.wikipedia.org/wiki/Resident_set_size) (RSS), with some large-scale
+    tests showing up to 11% (about 500 MiB) savings in large colmena deployments.
+  * A slight decrease in CPU usage during Nix evaluations.
+
+  This change is inspired by https://github.com/NixOS/nix/pull/13258 but the approach is different.
+
+  **Note** : [`xokdvium`](https://github.com/xokdvium) is the rightful author of https://gerrit.lix.systems/c/lix/+/3300 and the credit was missed on our end during the development process. We are deeply sorry for this mistake.
+
+  Many thanks to [Raito Bezarius](https://git.lix.systems/raito), [eldritch horrors](https://git.lix.systems/pennae), [Tom Hubrecht](https://git.lix.systems/tom-hubrecht), [xokdvium](https://github.com/xokdvium), and [NaN-git](https://github.com/NaN-git) for this.
+
+
+## Fixes
+
+- `build-dir` no longer defaults to `temp-dir` [cl/3453](https://gerrit.lix.systems/c/lix/+/3453)
+
+  The directory in which temporary build directories are created no longer defaults
+  to the value of the `temp-dir` setting to avoid builders making their directories
+  world-accessible. This behavior has been used to escape the build sandbox and can
+  cause build impurities even when not used maliciously. We now default to `builds`
+  in `NIX_STATE_DIR` (which is `/nix/var/nix/b` in the default configuration).
+
+  Many thanks to [eldritch horrors](https://git.lix.systems/pennae) for this.
+
+- Global certificate authorities are copied inside the builder's environment [gh#12698](https://github.com/NixOS/nix/issues/12698) [fj#885](https://git.lix.systems/lix-project/lix/issues/885) [cl/3765](https://gerrit.lix.systems/c/lix/+/3765)
+
+  Previously, CA certificates were only installed at
+  `/etc/ssl/certs/ca-certificates.crt` for sandboxed builds on Linux.
+
+  This setup was insufficient in light of recent changes in `nixpkgs`, which now
+  enforce HTTPS usage for `fetchurl`, even for fixed-output derivations, to
+  mitigate confidentiality risks such as `netrc` or credentials leakage.
+  `nixpkgs` still make use of a special package called `cacerts` which contains a
+  copy of the CA certificates maintained by Nixpkgs and added as a reference for
+  TLS-enabled fetchers.
+
+  As a result, having a consistent and trusted certificate authority in all
+  builder environments is becoming more essential.
+
+  On `nix-darwin`, the `NIX_SSL_CERT_FILE` environment variable is always
+  explicitly defined, but it is ignored by the sandbox setup.
+
+  Simultaneously, Nix evaluates and propagates impure environment variables via
+  `lib.proxyImpureEnvVars`, meaning that if `NIX_SSL_CERT_FILE` is set (which
+  influences the default value for `ssl-cert-file`), it will be forwarded
+  unchanged into the builder environment.
+
+  However, on Linux, Nix also *copies* the CA file into the sandbox, creating a
+  discrepancy between the value of `NIX_SSL_CERT_FILE` and the actual trusted
+  certificate path used during the build.
+
+  This divergence caused confusion and was partially addressed by attempts to
+  whitelist the CA path in the Darwin sandbox (see cl/2906), but that approach
+  involved a non-trivial path canonicalization step and is not as general as this one.
+
+  To address this properly, we now emit a warning and override
+  `NIX_SSL_CERT_FILE` inside the builder, explicitly pointing it to the CA file
+  copied into the sandbox.
+
+  This eliminates ambiguity between `NIX_SSL_CERT_FILE`
+  and `ssl-cert-file`, ensuring consistent trust anchors across platforms.
+
+  This warning might become a hard error as we figure out what to do regarding
+  `lib.proxyImpureEnvVars` in nixpkgs.
+
+  The behavior has been verified across sandboxed and unsandboxed builds on both
+  Linux and Darwin.
+
+  As a consequence of this change, approximately 500 KB of CA certificate data is
+  now unconditionally copied into the build directory for fixed-output
+  derivations.
+
+  While this ensures consistent trust verification without having to restart the
+  daemon after system upgrades, it may introduce a slight overhead in build
+  performance. At present, no optimizations have been implemented to avoid this
+  copy, but if this overhead proves noticeable in your workflows, please open an
+  issue so we can evaluate and possibly implement different strategies to render
+  trust anchors visible.
+
+  Many thanks to [Raito Bezarius](https://git.lix.systems/raito) and [Emily](https://git.lix.systems/emilazy) for this.
+
+- libstore: exponential backoff for downloads [lix#932](https://git.lix.systems/lix-project/lix/issues/932) [cl/3856](https://gerrit.lix.systems/c/lix/+/3856)
+
+  The connection timeout when downloading from e.g. a binary cache is exponentially
+  increased per failure. The option `connect-timeout` is now an alias to `max-connect-timeout`
+  which is the maximum value for a timeout. The start value is controlled
+  by `initial-connect-timeout` which is `5` by default.
+
+  Many thanks to [ma27](https://git.lix.systems/ma27) for this.
+
+- Fix develop shells for derivations with escape codes [fj#991](https://git.lix.systems/lix-project/lix/issues/991) [cl/4154](https://gerrit.lix.systems/c/lix/+/4154) [cl/4155](https://gerrit.lix.systems/c/lix/+/4155)
+
+  ASCII control characters (including `\e`, used for ANSI escape codes) in derivation variables are now correctly escaped for `nix develop` and `nix print-dev-env`, instead of erroring.
+
+  Many thanks to [Qyriad](https://git.lix.systems/Qyriad) for this.
+
+- nix-store --delete: always remove obsolete hardlinks [cl/3188](https://gerrit.lix.systems/c/lix/+/3188)
+
+  Deleting specific paths using `nix-store --delete` or `nix store
+  delete` previously did not delete hard links created by `nix-store
+  --optimise` even if they became obsolete, unless _all_ of the given
+  paths were deleted successfully. Now, hard links are always cleaned
+  up, even if some of the given paths could not be deleted.
+
+  Many thanks to [lheckemann](https://git.lix.systems/lheckemann) for this.
+
+- Report GC statistics correctly [cl/3188](https://gerrit.lix.systems/c/lix/+/3188)
+
+  Deleting specific paths using `nix-store --delete` or `nix store delete` previously did
+  not report statistics correctly when some of the paths could not be deleted, even if
+  others were deleted:
+
+  ```
+  $ nix store delete /nix/store/9bwryidal9q3g91cjm6xschfn4ikd82q-hello-2.12.1 --delete-closure -v
+  finding garbage collector roots...
+  deleting '/nix/store/9bwryidal9q3g91cjm6xschfn4ikd82q-hello-2.12.1'
+  0 store paths deleted, 0.00 MiB freed
+  error: Cannot delete some of the given paths because they are still alive. Paths not deleted:
+           k9bxzr1l92r5y6mihrkbpbr3fmc8qszx-libidn2-2.3.8
+           mbx9ii53lzjlrsnlrfmzpwm33ynljwdn-libunistring-1.3
+           rf8hcy6bldxdqc0g6q1dcka1vh47x69s-xgcc-14.2.1.20250322-libgcc
+           vbrdc5wgzn0w1zdp10xd2favkjn5fk7y-glibc-2.40-66
+         To find out why, use nix-store --query --roots and nix-store --query --referrers.
+  ```
+
+  Many thanks to [lheckemann](https://git.lix.systems/lheckemann) for this.
+
+- Fallback to safe temp dir when build-dir is unwritable [fj#876](https://git.lix.systems/lix-project/lix/issues/876) [cl/3501](https://gerrit.lix.systems/c/lix/+/3501)
+
+  Non-daemon builds started failing with a permission error after introducing the `build-dir` option:
+
+  ```
+  $ nix build --store ~/scratch nixpkgs#hello --rebuild
+  error: creating directory '/nix/var/nix/builds/nix-build-hello-2.12.2.drv-0': Permission denied
+  ```
+
+  This happens because:
+
+  1. These builds are not run via the daemon, which owns `/nix/var/nix/builds`.
+  2. The user lacks permissions for that path.
+
+  We considered making `build-dir` a store-level option and defaulting it to `<chroot-root>/nix/var/nix/builds` for chroot stores, but opted instead for a fallback: if the default fails, Nix now creates a safe build directory under `/tmp`.
+
+  To avoid CVE-2025-52991, the fallback uses an extra path component between `/tmp` and the build dir.
+
+  **Note**: this fallback clutters `/tmp` with build directories that are not cleaned up. To prevent this, explicitly set `build-dir` to a path managed by Lix, even for local workloads.
+
+  Many thanks to [Raito Bezarius](https://git.lix.systems/raito) and [eldritch horrors](https://git.lix.systems/pennae) for this.
+
+- Parse overflowing JSON number literals as floating‐point [cl/3919](https://gerrit.lix.systems/c/lix/+/3919)
+
+  Previously, `builtins.fromJSON "-9223372036854775809"` would
+  return a floating‐point number, while `builtins.fromJSON
+  "9223372036854775808"` would cause an evaluation error. This was
+  introduced with the banning of integer overflow in Lix 2.91; previously
+  the latter would result in C++ undefined behaviour. These cases are
+  now treated consistently with JSON’s model of a single numeric type,
+  and JSON number literals that do not fit in a Nix‐language integer
+  will be parsed as floating‐point numbers.
+
+  Many thanks to [Emily](https://git.lix.systems/emilazy) for this.
+
+- Fix handling of OSC codes in terminal output [fj#160](https://git.lix.systems/lix-project/lix/issues/160) [cl/3143](https://gerrit.lix.systems/c/lix/+/3143)
+
+  OSC codes in terminal output are now handled correctly, where OSC 8 (hyperlink) is preserved any
+  time color codes are allowed and all other OSC codes are stripped out. This applies not only to
+  output from build commands but also to rendered documentation in the REPL.
+
+  Many thanks to [lilyball](https://git.lix.systems/lilyball) for this.
+
+- Fix nix develop for derivations that rejects dependencies with structured attrs [fj#997](https://git.lix.systems/lix-project/lix/issues/997) [cl/4182](https://gerrit.lix.systems/c/lix/+/4182)
+
+  For the sake of concision, we refer to `disallowedReferences` in what follows,
+  but all output checks were equally fixed:
+  `{dis,}allowed{References,Requisites}`.
+
+  Derivations can define *output checks* to reject unwanted dependencies, such as
+  interpreters like `bash` or compilers like `gcc`. This can be done in two ways:
+
+  * **Legacy style**: `disallowedReferences = [ ... ]` in the environment.
+  * **Structured attrs**: `outputChecks.<output>.disallowedReferences = [ ... ]`,
+    typically used in `__json`.
+
+  Only the structured form supports derivations with multiple outputs.
+
+  `nix develop` internally rewrites derivations to create development shells. It
+  relied on the legacy `disallowedReferences`, and failed to honor the structured
+  variant. This led to broken shells in cases where `bashInteractive` was
+  explicitly disallowed using structured output checks, e.g. `nix develop
+  nixpkgs#systemd` after the "bash-less NixOS" changes.
+
+  This fix teaches `nix develop` to respect structured output checks, restoring
+  support for such derivations.
+
+  Many thanks to [Raito Bezarius](https://git.lix.systems/raito) for this.
+
+- nix-eval-jobs: retain NIX_PATH [cl/3859](https://gerrit.lix.systems/c/lix/+/3859)
+
+  `nix-eval-jobs` doesn't clear the `NIX_PATH` from the environment anymore. This matches the behavior
+  of [upstream version `2.30`](https://github.com/nix-community/nix-eval-jobs/releases/tag/v2.30.0).
+
+  Many thanks to [ma27](https://git.lix.systems/ma27) and [mic92](https://github.com/mic92) for this.
+
+- Remove reliance on Bash for remote stores via SSH [fj#830](https://git.lix.systems/lix-project/lix/issues/830) [fj#805](https://git.lix.systems/lix-project/lix/issues/805) [fj#304](https://git.lix.systems/lix-project/lix/issues/304) [cl/3159](https://gerrit.lix.systems/c/lix/+/3159)
+
+  The pre-flight `echo started` handshake -- added years ago to catch race conditions -- has been removed.
+
+  After removal of connection sharing in Lix 2.93, it required a Bash-compatible shell and a standard `echo`, so it failed on:
+
+    * builders protected by `ForceCommand` wrappers (e.g. `nix-remote-build`),
+    * BusyBox / initrd images with no Bash,
+    * hosts using non-POSIX shells such as Nushell.
+
+  The race the probe once addressed was tied to SSH connection-sharing -- since connection-sharing code has already been removed, the probe is now pointless.
+
+  Real connection or protocol errors are now left to SSH/Nix to report directly.
+
+  This is technically a breaking change if you had scripts that relied on the literal "started" which needs to be updated to rely on other signals, e.g., exit codes.
+
+  Many thanks to [Raito Bezarius](https://git.lix.systems/raito) for this.
+
+- repl-overlays now work in the debugger for flakes [fj#777](https://git.lix.systems/lix-project/lix/issues/777) [cl/3398](https://gerrit.lix.systems/c/lix/+/3398)
+
+  Due to a bug, it was previously not possible to use the debugger on flakes with repl-overlays, or with pure evaluation in general:
+
+  ```
+  $ nix repl --pure-eval
+  Lix 2.94.0-dev-pre20250617-87d99da
+  Type :? for help.
+  Loading 'repl-overlays'...
+  error: access to absolute path '/Users/jade/.config/nix/repl.nix' is forbidden in pure eval mode (use '--impure' to override)
+  ```
+
+  This is now fixed.
+  The contents of the repl-overlays file itself (i.e. most typically the top level lambda in it) will be evaluated in impure mode.
+  It may be necessary to use `builtins.seq` to force the impure operations to happen first if one wants to do impure operations inside a repl-overlays file in pure evaluation mode.
+
+  Many thanks to [jade](https://git.lix.systems/jade) for this.
+
+- `nix-shell` default shell directory is not `/tmp` anymore for `$NIX_BUILD_TOP` [fj#940](https://git.lix.systems/lix-project/lix/issues/940)
+
+  Previously, Lix `nix-shell`s could exit non-zero status when `stdenv`'s `dumpVars` phase failed to write to `$NIX_BUILD_TOP/env-vars`, despite `dumpVars` being intended as a debugging aid.
+
+  This happens when `TMPDIR` is not set and defaults therefore to `/tmp`, resulting in a `/tmp/env-vars` global file that every `nix-shell` wants to write.
+
+  We fix this issue by reusing a pre-created, unique, and writable location, as the build top directory, avoiding shell exiting from write failures silently.
+
+  Many thanks to [Raito Bezarius](https://git.lix.systems/raito) for this.
+
+- libstore/binary-cache-store: don't cache narinfo on nix copy, remove negative entry [cl/3789](https://gerrit.lix.systems/c/lix/+/3789)
+
+  When using e.g. [Snix's nar-bridge](https://snix.dev/docs/components/overview/#nar-bridge) via
+  an `http`-store, Lix would create cache entries with a wrong URL to the NAR when uploading
+  a store-path.
+
+  This caused hard build failures for Hydra.
+
+  Lix doesn't create these entries on upload anymore. Instead, it only removes negative cache entries.
+  The cache entry for a narinfo is now created the first time, Lix queries the cache
+  for the previously uploaded store-path again.
+
+  Many thanks to [ma27](https://git.lix.systems/ma27) for this.
+
+- Lix libraries can now be linked statically [fj#789](https://git.lix.systems/lix-project/lix/issues/789) [cl/3775](https://gerrit.lix.systems/c/lix/+/3775) [cl/3778](https://gerrit.lix.systems/c/lix/+/3778)
+
+  Previously the pkg-config files distributed with Lix were only suitable for dynamic linkage, causing "undefined reference to…" linker errors when trying to link statically.
+  Private dependency information has now been added to make static linkage work as expected without user intervention.
+  In addition, relevant static libraries are now prelinked to avoid strange failures due to missing static initializers.
+
+  Many thanks to [alois31](https://git.lix.systems/alois31) for this.
+
+- add description to zsh completions [fj#910](https://git.lix.systems/lix-project/lix/issues/910) [cl/3632](https://gerrit.lix.systems/c/lix/+/3632)
+
+  Emit descriptions when completing args in zsh completions. This uses the descriptions we already
+  provided in NIX\_GET\_COMPLETIONS.
+
+  Many thanks to [matthewbauer](https://github.com/matthewbauer) for this.
+
+
+## Miscellany
+
+- Deprecation of CA derivations, dynamic derivations, and impure derivations [fj#815](https://git.lix.systems/lix-project/lix/issues/815)
+
+  Content-addressed derivations are now deprecated and slated for removal in Lix 2.94.
+  We're doing this because the CA derivation system has been a known cause of problems
+  and inconsistencies, is unmaintained, habitually makes improving the store code very
+  difficult (or blocks such improvements outright), and is beset by a number of design
+  flaws that in our opinion cannot be fixed without a full reimplementation from zero.
+  Dynamic derivations and impure derivations are built on the CA derivation framework,
+  and owing to this they too are deprecated and slated for removal in another release.

doc/manual/substitute.py

@@ -90,6 +90,11 @@ def recursive_replace(data, book_root, search_path):
                     ).replace(
                         '@docroot@',
                         ("../" * len(path_to_chapter.parent.parts) or "./")[:-1]
+                    ).replace(
+                        # this replacement is to avoid corrupting the
+                        # hacking.md manual section on docroot
+                        '@\\docroot\\@',
+                        '@docroot@',
                     ),
                     sub_items = [
                         recursive_replace(sub_item, book_root, search_path)

docker.nix

@@ -8,7 +8,7 @@
   tag ? "latest",
   bundleNixpkgs ? true,
   channelName ? "nixpkgs",
-  channelURL ? "https://nixos.org/channels/nixpkgs-unstable",
+  channelURL ? "https://channels.nixos.org/nixpkgs-unstable",
   extraPkgs ? [ ],
   maxLayers ? 100,
   nixConf ? { },
@@ -62,38 +62,37 @@ let
     ++ autoLayered
     ++ extraPkgs;
 
-  users =
-    {
+  users = {
 
-      root = {
-        uid = 0;
-        shell = "${pkgs.bashInteractive}/bin/bash";
-        home = "/root";
-        gid = 0;
-        groups = [ "root" ];
-        description = "System administrator";
-      };
+    root = {
+      uid = 0;
+      shell = "${pkgs.bashInteractive}/bin/bash";
+      home = "/root";
+      gid = 0;
+      groups = [ "root" ];
+      description = "System administrator";
+    };
 
-      nobody = {
-        uid = 65534;
-        shell = "${pkgs.shadow}/bin/nologin";
-        home = "/var/empty";
-        gid = 65534;
-        groups = [ "nobody" ];
-        description = "Unprivileged account (don't use!)";
+    nobody = {
+      uid = 65534;
+      shell = "${pkgs.shadow}/bin/nologin";
+      home = "/var/empty";
+      gid = 65534;
+      groups = [ "nobody" ];
+      description = "Unprivileged account (don't use!)";
+    };
+  }
+  // lib.listToAttrs (
+    map (n: {
+      name = "nixbld${toString n}";
+      value = {
+        uid = 30000 + n;
+        gid = 30000;
+        groups = [ "nixbld" ];
+        description = "Nix build user ${toString n}";
       };
-    }
-    // lib.listToAttrs (
-      map (n: {
-        name = "nixbld${toString n}";
-        value = {
-          uid = 30000 + n;
-          gid = 30000;
-          groups = [ "nixbld" ];
-          description = "Nix build user ${toString n}";
-        };
-      }) (lib.lists.range 1 32)
-    );
+    }) (lib.lists.range 1 32)
+  );
 
   groups = {
     root.gid = 0;
@@ -361,7 +360,8 @@ let
         "org.opencontainers.image.version" = pkgs.nix.version;
         "org.opencontainers.image.description" =
           "Minimal Lix container image, with some batteries included.";
-      } // lib.optionalAttrs (lixRevision != null) { "org.opencontainers.image.revision" = lixRevision; };
+      }
+      // lib.optionalAttrs (lixRevision != null) { "org.opencontainers.image.revision" = lixRevision; };
     };
 
     meta = {

flake.lock

@@ -108,11 +108,11 @@
     },
     "nixpkgs_2": {
       "locked": {
-        "lastModified": 1749522908,
-        "narHash": "sha256-eWANkhWXFL1MmaxzsZ9bhLCNT8OVs7CC+OXaSDGlA8A=",
+        "lastModified": 1757198069,
+        "narHash": "sha256-m3VUcOD4rTs8J7S+3dOjWMrAjw6RcITC3XYQ98zhEFs=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "e5cb99555c45a13dcc5f1317462238530b0066b7",
+        "rev": "0747026fc57ecb9c28901c7f7a2b5dc40e8af43c",
         "type": "github"
       },
       "original": {

flake.nix

@@ -88,7 +88,7 @@
         else
           "pre${
             builtins.substring 0 8 (self.lastModifiedDate or self.lastModified or "19700101")
-          }_${self.shortRev or "dirty"}";
+          }-dev_${self.shortRev or "dirty"}";
 
       linux32BitSystems = [ "i686-linux" ];
       linux64BitSystems = [
@@ -100,6 +100,7 @@
         "x86_64-darwin"
         "aarch64-darwin"
       ];
+      nonDarwinSystems = linuxSystems;
       systems = linuxSystems ++ darwinSystems;
 
       # If you add something here, please update the list in doc/manual/src/contributing/hacking.md.
@@ -175,8 +176,13 @@
         {
           nixStable = prev.nix;
 
-          # Nix 2.18 has been removed from Nixpkgs ≥ 25.05, so we need to reintroduce it ourselves for our tests.
           nixVersions = prev.nixVersions // {
+            nix_2_3 = prev.nixVersions.nix_2_3.overrideAttrs (old: {
+              meta = old.meta // {
+                knownVulnerabilities = [ ];
+              };
+            });
+            # Nix 2.18 has been removed from Nixpkgs ≥ 25.05, so we need to reintroduce it ourselves for our tests.
             nix_2_18 = nix_2_18.outputs.packages.${currentStdenv.hostPlatform.system}.default;
           };
 
@@ -238,6 +244,35 @@
           boehmgc-nix = final.nix.passthru.boehmgc-nix;
           # And same thing for our build-release-notes package.
           build-release-notes = final.nix.passthru.build-release-notes;
+
+          lowdown_1_3 =
+            # If the stable channel we are using ships lowdown >= 1.4, we need
+            # to swap this around, take the default lowdown from the stable
+            # channel and add an overridden one for the legacy version.
+            assert lib.versionOlder prev.lowdown.version "1.4.0";
+            prev.lowdown;
+          lowdown = prev.lowdown.overrideAttrs (prevAttrs: rec {
+            version = "2.0.2";
+            src = final.fetchurl {
+              url = "https://kristaps.bsd.lv/lowdown/snapshots/lowdown-${version}.tar.gz";
+              sha512 = "2a4d0rqh8gkw4ca3gkzddp0hjpmmw74cbks8k0inhh0vizmgbn188zdv6m1kgmr019b99g7insli8js3ci1ji7y4n5nk704bswf3z3i";
+            };
+            nativeBuildInputs = prevAttrs.nativeBuildInputs ++ [ final.buildPackages.bmake ];
+            postInstall = lib.replaceStrings [ "lowdown.so.1" ] [ "lowdown.so.2" ] prevAttrs.postInstall;
+          });
+
+          capnproto = prev.capnproto.overrideAttrs (old: {
+            patches =
+              old.patches or [ ]
+              ++ [
+                # backport of https://github.com/capnproto/capnproto/pull/1810
+                ./misc/capnproto-promise-nodiscard.patch
+              ]
+              ++ lib.optionals (lib.versionOlder old.version "1.2.0") [
+                # backport of https://github.com/capnproto/capnproto/pull/2296
+                ./misc/capnproto-monotonic-clocks-are-a-lie.patch
+              ];
+          });
         };
     in
     {
@@ -252,6 +287,30 @@
         # Binary package for various platforms.
         build = forAllSystems (system: self.packages.${system}.nix);
 
+        # Building Lix twice in CI is expensive, but we can catch a lot of static
+        # build regressions by at least making sure it evals and configures.
+        configure-static = lib.genAttrs linux64BitSystems (
+          system:
+          self.packages.${system}.nix-static.overrideAttrs {
+            dontBuild = true;
+            installPhase = ''
+              runHook preInstall
+
+              echo "configure-static complete. exiting with success"
+              mkdir -p "$out"
+              exit 0
+            '';
+          }
+        );
+
+        # Ensure support for lowdown < 1.4 doesn't regress
+        build-lowdown_1_3 = forAllSystems (
+          system:
+          self.packages.${system}.nix.override {
+            lowdown = nixpkgsFor.${system}.native.lowdown_1_3;
+          }
+        );
+
         devShell = forAllSystems (system: {
           default = self.devShells.${system}.default;
           clang = self.devShells.${system}.native-clangStdenvPackages;
@@ -326,7 +385,10 @@
               ;
           }
           // {
-            nix-eval-jobs = forAllSystems (system: self.packages.${system}.nix-eval-jobs.tests.nix-eval-jobs);
+            # the n-e-j test suite is unusably slow in darwin ci. disbled until anywho fixes this.
+            nix-eval-jobs = (lib.genAttrs nonDarwinSystems) (
+              system: self.packages.${system}.nix-eval-jobs.tests.nix-eval-jobs
+            );
 
             # This is x86_64-linux only, just because we have significantly
             # cheaper x86_64-linux compute in CI.
@@ -398,15 +460,16 @@
               in
               pkgs.symlinkJoin {
                 name = "nixpkgs-lib-tests";
-                paths =
-                  [ testWithNix ]
-                  # NOTE: nixpkgs 25.05 is being ... *creative*, and requires this dance to override
-                  # the evaluator used for the test. it will break again in the future, don't worry.
-                  ++ lib.optionals pkgs.stdenv.isLinux [
-                    ((pkgs.callPackage "${nixpkgs}/ci/eval" { nixVersions.latest = nix; }).attrpathsSuperset {
-                      evalSystem = system;
-                    })
-                  ];
+                paths = [
+                  testWithNix
+                ]
+                # NOTE: nixpkgs 25.05 is being ... *creative*, and requires this dance to override
+                # the evaluator used for the test. it will break again in the future, don't worry.
+                ++ lib.optionals pkgs.stdenv.isLinux [
+                  ((pkgs.callPackage "${nixpkgs}/ci/eval" { inherit nix; }).attrpathsSuperset {
+                    evalSystem = system;
+                  })
+                ];
               }
             );
           };
@@ -455,6 +518,7 @@
           # devShells and packages already get checked by nix flake check, so
           # this is just jobs that are special
 
+          build-lowdown_1_3 = self.hydraJobs.build-lowdown_1_3.${system};
           binaryTarball = self.hydraJobs.binaryTarball.${system};
           perlBindings = self.hydraJobs.perlBindings.${system};
           nix-eval-jobs = self.hydraJobs.nix-eval-jobs.${system};

lix/OWNERS

@@ -0,0 +1,10 @@
+# This reproduces the Lix Approvers plus Lix groups to yield the status quo
+alois1@gmx-topmail.de
+jade@lix.systems
+lunaphied@lunaphied.me
+maximilian@mbosch.me
+me@0upti.me
+pennae@lix.systems
+qyriad@qyriad.me
+raito@lix.systems
+rbt@sent.as

lix/code-generation/capnpc_wrapper.py

@@ -0,0 +1,64 @@
+#!@python@
+
+import argparse
+import capnp
+from pathlib import Path
+import os
+import subprocess
+import sys
+
+if lang := os.environ.get('lix_capnp_lang'):
+    outputs = os.environ['lix_capnp_outputs'].split()
+    old_cwd = os.environ['lix_capnp_old_cwd']
+    schema = capnp.load('@capnp_include@/capnp/schema.capnp', imports=['@capnp_include@'])
+    request = schema.CodeGeneratorRequest.read(sys.stdin)
+
+    subprocess.run([lang], input=request.as_builder().to_bytes()).check_returncode()
+
+    base_dir = os.getcwd()
+    os.chdir(old_cwd)
+
+    include = [ str(Path(p).resolve()) for p in os.environ['lix_capnp_include'].split(':') ]
+
+    if depfile := os.environ['lix_capnp_depfile']:
+        deps = ""
+        for input in request.requestedFiles:
+            deps += " ".join(f"{input.filename}.{o}" for o in outputs)
+            deps += ":"
+            for dep in input.imports:
+                if dep.name.startswith("/"):
+                    for candidate in (Path(i + dep.name) for i in include):
+                        if candidate.exists():
+                            deps += " " + str(candidate)
+                            break
+                else:
+                    raise RuntimeError("not handling relative includes")
+            deps += "\n\n"
+        Path(depfile).write_text(deps)
+else:
+    parser = argparse.ArgumentParser()
+    parser.add_argument('--language')
+    parser.add_argument('--outdir')
+    parser.add_argument('--src-prefix')
+    parser.add_argument('--depfile', default="")
+    parser.add_argument('-I', '--include', action='append', default=['@capnp_include@'])
+    parser.add_argument('inputs', nargs='+')
+    args = parser.parse_args()
+
+    for infile in args.inputs:
+        os.environ['lix_capnp_lang'] = f"capnpc-{args.language}"
+        os.environ['lix_capnp_include'] = ':'.join(args.include)
+        os.environ['lix_capnp_depfile'] = args.depfile
+        os.environ['lix_capnp_old_cwd'] = os.getcwd()
+        if args.language == "c++":
+            os.environ['lix_capnp_outputs'] = "c++ h"
+        else:
+            raise RuntimeError("unknown language " + args.language)
+        subprocess.run([
+            '@capnp@',
+            'compile',
+            f'-o{sys.argv[0]}:{args.outdir}',
+            f'--src-prefix={args.src_prefix}',
+            *(f"-I{i}" for i in args.include),
+            infile
+        ]).check_returncode()

lix/legacy/build-remote.cc

@@ -1,7 +1,22 @@
+#include "lix/libstore/path.hh"
+#include "lix/libutil/async.hh"
+#include "lix/libutil/c-calls.hh"
+#include "lix/libutil/error.hh"
+#include "lix/libutil/file-descriptor.hh"
+#include "lix/libutil/logging-rpc.hh"
+#include "lix/libutil/logging.hh"
+#include "lix/libutil/rpc.hh"
+#include "lix/libutil/types-rpc.hh" // IWYU pragma: keep
+#include "lix/libutil/types.hh"
 #include <algorithm>
-#include <chrono>
+#include <capnp/rpc-twoparty.h>
+#include <cstring>
+#include <exception>
+#include <kj/async.h>
+#include <kj/time.h>
 #include <set>
 #include <memory>
+#include <string>
 #include <tuple>
 #if __APPLE__
 #include <sys/time.h>
@@ -17,13 +32,29 @@
 #include "lix/libstore/derivations.hh"
 #include "lix/libutil/strings.hh"
 #include "lix/libstore/local-store.hh"
+#include "lix/libstore/types-rpc.hh"
 #include "lix/libcmd/legacy.hh"
 #include "lix/libutil/experimental-features.hh"
 #include "lix/libutil/hash.hh"
 #include "build-remote.hh"
 
+#include "lix/libstore/build/hook-instance.capnp.h"
+
 namespace nix {
 
+namespace {
+struct Instance final : rpc::build_remote::HookInstance::Server
+{
+    unsigned int maxBuildJobs;
+    bool initialized = false, used = false;
+
+    kj::Promise<void> init(InitContext context) override;
+
+    kj::Promise<void> buildImpl(BuildContext context);
+    kj::Promise<void> build(BuildContext context) override;
+};
+}
+
 std::string escapeUri(std::string uri)
 {
     std::replace(uri.begin(), uri.end(), '/', '_');
@@ -53,11 +84,278 @@ static bool allSupportedLocally(Store & store, const std::set<std::string>& requ
     return true;
 }
 
+static std::tuple<bool, Machine *, AutoCloseFD> selectBestMachine(
+    Machines & machines,
+    const std::string & neededSystem,
+    const std::set<std::string> & requiredFeatures
+)
+{
+    bool rightType = false;
+    Machine * bestMachine = nullptr;
+    AutoCloseFD bestSlotLock;
+    uint64_t bestLoad = 0;
+
+    for (auto & m : machines) {
+        debug("considering building on remote machine '%s'", m.storeUri);
+
+        if (m.enabled && m.systemSupported(neededSystem) && m.allSupported(requiredFeatures)
+            && m.mandatoryMet(requiredFeatures))
+        {
+            rightType = true;
+            AutoCloseFD free;
+            uint64_t load = 0;
+            for (uint64_t slot = 0; slot < m.maxJobs; ++slot) {
+                auto slotLock = openSlotLock(m, slot);
+                if (tryLockFile(slotLock.get(), ltWrite)) {
+                    if (!free) {
+                        free = std::move(slotLock);
+                    }
+                } else {
+                    ++load;
+                }
+            }
+            if (!free) {
+                continue;
+            }
+            bool best = false;
+            if (!bestSlotLock) {
+                best = true;
+            } else if (load / m.speedFactor < bestLoad / bestMachine->speedFactor) {
+                best = true;
+            } else if (load / m.speedFactor == bestLoad / bestMachine->speedFactor) {
+                if (m.speedFactor > bestMachine->speedFactor) {
+                    best = true;
+                } else if (m.speedFactor == bestMachine->speedFactor) {
+                    if (load < bestLoad) {
+                        best = true;
+                    }
+                }
+            }
+            if (best) {
+                bestLoad = load;
+                bestSlotLock = std::move(free);
+                bestMachine = &m;
+            }
+        }
+    }
+
+    return {rightType, bestMachine, std::move(bestSlotLock)};
+}
+
+static void printSelectionFailureMessage(
+    Verbosity level,
+    const std::string_view drvstr,
+    const Machines & machines,
+    const std::string & neededSystem,
+    const std::set<std::string> & requiredFeatures
+)
+{
+    std::string machinesFormatted;
+
+    for (auto & m : machines) {
+        machinesFormatted += HintFmt(
+                                 "\n([%s], %s, [%s], [%s])",
+                                 concatStringsSep<StringSet>(", ", m.systemTypes),
+                                 m.maxJobs,
+                                 concatStringsSep<StringSet>(", ", m.supportedFeatures),
+                                 concatStringsSep<StringSet>(", ", m.mandatoryFeatures)
+        )
+                                 .str();
+    }
+
+    printMsg(
+        level,
+        "Failed to find a machine for remote build!\n"
+        "derivation: %s\n"
+        "required (system, features): (%s, [%s])\n"
+        "%s available machines:\n"
+        "(systems, maxjobs, supportedFeatures, mandatoryFeatures)%s",
+        drvstr,
+        neededSystem,
+        concatStringsSep<StringSet>(", ", requiredFeatures),
+        machines.size(),
+        Uncolored(machinesFormatted)
+    );
+}
+
+namespace {
+struct BuilderConnection
+{
+    AutoCloseFD slotLock;
+    std::shared_ptr<Store> sshStore;
+    std::string storeUri;
+    Pipe logPipe;
+
+    // start the thread that reads ssh stderr and turns it into log items.
+    // this future *must* outlive sshStore, otherwise it will never finish
+    kj::Promise<Result<void>> startLogThread(std::string buildDescription, std::string drvPath)
+    try {
+        if (!logPipe.readSide) {
+            co_return result::success();
+        }
+
+        logPipe.writeSide.close();
+
+        // NOTE this is very similar to handleBuilderOutput in DerivationGoal, but unlike
+        // the derivation goal we do not need to handle EIO from a pty here. we also have
+        // no timeouts or limits to keep track of, which makes deduplication less useful.
+        auto act = logger->startActivity(
+            lvlInfo, actBuild, buildDescription, Logger::Fields{drvPath, storeUri, 1, 1}
+        );
+
+        std::map<ActivityId, Activity> activities;
+
+        auto reader = AIO().lowLevelProvider.wrapInputFd(logPipe.readSide.get());
+
+        LogLineSplitter splitter;
+
+        auto flushLine = [&](const std::string & line) {
+            if (const auto state =
+                    handleJSONLogMessage(line, act, activities, "the derivation builder"))
+            {
+                return *state;
+            } else {
+                return act.result(resBuildLogLine, line);
+            }
+        };
+
+        auto buf = kj::heapArray<char>(4096);
+        while (true) {
+            const auto got = co_await reader->tryRead(buf.begin(), 1, buf.size());
+            if (got == 0) {
+                break;
+            }
+
+            std::string_view data{buf.begin(), got};
+            while (!data.empty()) {
+                if (auto line = splitter.feed(data)) {
+                    if (flushLine(*line) == Logger::BufferState::NeedsFlush) {
+                        TRY_AWAIT(act.getLogger().flush());
+                    }
+                }
+            }
+        }
+
+        if (auto line = splitter.finish(); !line.empty()) {
+            (void) flushLine(line);
+            TRY_AWAIT(act.getLogger().flush());
+        }
+
+        co_return result::success();
+    } catch (...) {
+        co_return result::current_exception();
+    }
+};
+
+struct AcceptedBuild final : rpc::build_remote::HookInstance::AcceptedBuild::Server
+{
+    ref<Store> store;
+    StorePath drvPath;
+    BuilderConnection builder;
+    bool used = false;
+
+    AcceptedBuild(ref<Store> store, StorePath drvPath, BuilderConnection builder)
+        : store(store)
+        , drvPath(drvPath)
+        , builder(std::move(builder))
+    {
+    }
+
+    kj::Promise<void> runImpl(RunContext context);
+    kj::Promise<void> run(RunContext context) override;
+};
+
+enum class BuildRejected { Temporarily, Permanently };
+}
+
+static kj::Promise<Result<std::variant<BuildRejected, BuilderConnection>>> connectToBuilder(
+    const ref<Store> & store,
+    const StorePath & drvPath,
+    Machines & machines,
+    const unsigned int maxBuildJobs,
+    const bool amWilling,
+    const std::string & neededSystem,
+    const std::set<std::string> & requiredFeatures
+)
+try {
+    AutoCloseFD bestSlotLock;
+
+    /* It would be possible to build locally after some builds clear out,
+       so don't show the warning now: */
+    bool couldBuildLocally = maxBuildJobs > 0
+        && (neededSystem == settings.thisSystem
+            || settings.extraPlatforms.get().count(neededSystem) > 0)
+        && allSupportedLocally(*store, requiredFeatures);
+    /* It's possible to build this locally right now: */
+    bool canBuildLocally = amWilling && couldBuildLocally;
+
+    /* Error ignored here, will be caught later */
+    (void) sys::mkdir(currentLoad, 0777);
+
+    while (true) {
+        bestSlotLock.reset();
+        AutoCloseFD lock = openLockFile(currentLoad + "/main-lock", true);
+        TRY_AWAIT(lockFileAsync(lock.get(), ltWrite));
+
+        auto [rightType, bestMachine, slotLock] =
+            selectBestMachine(machines, neededSystem, requiredFeatures);
+        bestSlotLock = std::move(slotLock);
+
+        if (!bestSlotLock) {
+            if (rightType && !canBuildLocally) {
+                co_return BuildRejected::Temporarily;
+            } else {
+                printSelectionFailureMessage(
+                    couldBuildLocally ? lvlChatty : lvlWarn,
+                    drvPath.to_string(),
+                    machines,
+                    neededSystem,
+                    requiredFeatures
+                );
+
+                co_return BuildRejected::Permanently;
+            }
+        }
+
+#if __APPLE__
+        futimes(bestSlotLock.get(), nullptr);
+#else
+        futimens(bestSlotLock.get(), nullptr);
+#endif
+
+        lock.reset();
+
+        std::shared_ptr<Store> sshStore;
+        Pipe logPipe;
+
+        try {
+            auto act = logger->startActivity(
+                lvlTalkative, actUnknown, fmt("connecting to '%s'", bestMachine->storeUri)
+            );
+
+            std::tie(sshStore, logPipe) = TRY_AWAIT(bestMachine->openStore());
+            TRY_AWAIT(sshStore->connect());
+            co_return BuilderConnection{
+                std::move(bestSlotLock), sshStore, bestMachine->storeUri, std::move(logPipe)
+            };
+        } catch (std::exception & e) { // NOLINT(lix-foreign-exceptions)
+            std::string msg = logPipe.readSide ? chomp(drainFD(logPipe.readSide.get(), false)) : "";
+            printError(
+                "cannot build on '%s': %s%s",
+                bestMachine->storeUri,
+                e.what(),
+                msg.empty() ? "" : ": " + msg
+            );
+            bestMachine->enabled = false;
+        }
+    }
+} catch (...) {
+    co_return result::current_exception();
+}
+
 static int main_build_remote(AsyncIoRoot & aio, std::string programName, Strings argv)
 {
     {
-        logger = makeJSONLogger(*logger);
-
         /* Ensure we don't get any SSH passphrase or host key popups. */
         unsetenv("DISPLAY");
         unsetenv("SSH_ASKPASS");
@@ -70,240 +368,181 @@ static int main_build_remote(AsyncIoRoot & aio, std::string programName, Strings
 
         verbosity = (Verbosity) std::stoll(argv.front());
 
-        FdSource source(STDIN_FILENO);
+        auto conn = aio.kj.lowLevelProvider->wrapUnixSocketFd(1);
+        capnp::TwoPartyServer srv(kj::heap<Instance>());
+        srv.accept(*conn, 1).wait(aio.kj.waitScope);
+        return 0;
+    }
+}
+
+kj::Promise<void> Instance::init(InitContext context)
+{
+    try {
+        if (initialized) {
+            throw Error("build hook can only be initialized once");
+        }
+
+        logger = rpc::log::makeRpcLoggerClient(context.getParams().getLogger());
 
         /* Read the parent's settings. */
-        while (readInt(source)) {
-            auto name = readString(source);
-            auto value = readString(source);
+        for (const auto & [name, value] : rpc::to<StringMap>(context.getParams().getSettings())) {
             settings.set(name, value);
         }
 
-        auto maxBuildJobs = settings.maxBuildJobs;
+        maxBuildJobs = settings.maxBuildJobs;
         settings.maxBuildJobs.set("1"); // hack to make tests with local?root= work
 
         initPlugins();
 
-        // FIXME this does not open a daemon connection for historical reasons.
-        // we may create a lot of build hook instances, and having each of them
-        // also create a daemon instance is inefficient and wasteful. in future
-        // versions of the build hook (where we don't need one hook process per
-        // build) we should change this to using a daemon connection, ideally a
-        // daemon connection provided by the parent via file descriptor passing
-        auto store = aio.blockOn(openStore(settings.storeUri, {}, AllowDaemon::Disallow));
+        initialized = true;
 
-        /* It would be more appropriate to use $XDG_RUNTIME_DIR, since
-           that gets cleared on reboot, but it wouldn't work on macOS. */
-        auto currentLoadName = "/current-load";
-        if (auto localStore = store.try_cast_shared<LocalFSStore>())
-            currentLoad = std::string { localStore->config().stateDir } + currentLoadName;
-        else
-            currentLoad = settings.nixStateDir + currentLoadName;
+        context.getResults().initResult().setGood();
+    } catch (...) {
+        RPC_FILL(context.getResults(), initResult, std::current_exception());
+    }
 
-        std::shared_ptr<Store> sshStore;
-        AutoCloseFD bestSlotLock;
+    return kj::READY_NOW;
+}
 
-        auto machines = getMachines();
-        debug("got %d remote builders", machines.size());
+kj::Promise<void> Instance::buildImpl(BuildContext context)
+{
+    if (!initialized) {
+        throw Error("build hook not fully initialized");
+    }
 
-        if (machines.empty()) {
-            std::cerr << "# decline-permanently\n";
-            return 0;
+    // FIXME this does not open a daemon connection for historical reasons.
+    // we may create a lot of build hook instances, and having each of them
+    // also create a daemon instance is inefficient and wasteful. in future
+    // versions of the build hook (where we don't need one hook process per
+    // build) we should change this to using a daemon connection, ideally a
+    // daemon connection provided by the parent via file descriptor passing
+    auto store = TRY_AWAIT(openStore(settings.storeUri, {}, AllowDaemon::Disallow));
+
+    /* It would be more appropriate to use $XDG_RUNTIME_DIR, since
+       that gets cleared on reboot, but it wouldn't work on macOS. */
+    auto currentLoadName = "/current-load";
+    if (auto localStore = store.try_cast_shared<LocalFSStore>()) {
+        currentLoad = std::string{localStore->config().stateDir} + currentLoadName;
+    } else {
+        currentLoad = settings.nixStateDir + currentLoadName;
+    }
+
+    auto machines = getMachines();
+    debug("got %d remote builders", machines.size());
+
+    if (machines.empty()) {
+        context.getResults().initResult().initGood().setDeclinePermanently();
+        co_return;
+    }
+
+    auto amWilling = context.getParams().getAmWilling();
+    auto neededSystem = rpc::to<std::string>(context.getParams().getNeededSystem());
+    auto drvPath = from(context.getParams().getDrvPath(), *store);
+    auto requiredFeatures =
+        rpc::to<std::set<std::string>>(context.getParams().getRequiredFeatures());
+
+    auto result = TRY_AWAIT(connectToBuilder(
+        store, drvPath, machines, maxBuildJobs, amWilling, neededSystem, requiredFeatures
+    ));
+
+    if (auto immediateResponse = std::get_if<BuildRejected>(&result)) {
+        switch (*immediateResponse) {
+        case BuildRejected::Temporarily:
+            context.getResults().initResult().initGood().setPostpone();
+            co_return;
+        case BuildRejected::Permanently:
+            context.getResults().initResult().initGood().setDecline();
+            co_return;
         }
+    }
 
-        std::optional<StorePath> drvPath;
-        std::string storeUri;
+    auto builder = std::get_if<BuilderConnection>(&result);
+    assert(builder);
 
-        while (true) {
+    auto ac = context.getResults().initResult().initGood().initAccept();
+    ac.setMachine(kj::heap<AcceptedBuild>(store, drvPath, std::move(*builder)));
+}
 
-            try {
-                auto s = readString(source);
-                if (s != "try") return 0;
-            } catch (EndOfFile &) { return 0; }
+kj::Promise<void> Instance::build(BuildContext context)
+try {
+    if (used) {
+        throw Error("build hooks can only accept a single job");
+    }
+    used = true; // lock out other rpc calls during processing
+    co_await buildImpl(context);
+    TRY_AWAIT(logger->flush());
+    used = context.getResults().getResult().getGood().isAccept();
+} catch (...) {
+    RPC_FILL(context.getResults(), getResult, std::current_exception());
+}
 
-            auto amWilling = readInt(source);
-            auto neededSystem = readString(source);
-            drvPath = store->parseStorePath(readString(source));
-            auto requiredFeatures = readStrings<std::set<std::string>>(source);
+kj::Promise<void> AcceptedBuild::run(RunContext context)
+{
+    try {
+        auto oldLogger = logger;
+        logger = rpc::log::makeRpcLoggerClient(context.getParams().getLogger());
+        TRY_AWAIT(oldLogger->flush());
+        KJ_DEFER({
+            delete logger;
+            logger = oldLogger;
+        });
 
-            /* It would be possible to build locally after some builds clear out,
-               so don't show the warning now: */
-            bool couldBuildLocally = maxBuildJobs > 0
-                 &&  (  neededSystem == settings.thisSystem
-                     || settings.extraPlatforms.get().count(neededSystem) > 0)
-                 &&  allSupportedLocally(*store, requiredFeatures);
-            /* It's possible to build this locally right now: */
-            bool canBuildLocally = amWilling && couldBuildLocally;
-
-            /* Error ignored here, will be caught later */
-            mkdir(currentLoad.c_str(), 0777);
-
-            while (true) {
-                bestSlotLock.reset();
-                AutoCloseFD lock = openLockFile(currentLoad + "/main-lock", true);
-                lockFile(lock.get(), ltWrite);
-
-                bool rightType = false;
-
-                Machine * bestMachine = nullptr;
-                uint64_t bestLoad = 0;
-                for (auto & m : machines) {
-                    debug("considering building on remote machine '%s'", m.storeUri);
-
-                    if (m.enabled &&
-                        m.systemSupported(neededSystem) &&
-                        m.allSupported(requiredFeatures) &&
-                        m.mandatoryMet(requiredFeatures))
-                    {
-                        rightType = true;
-                        AutoCloseFD free;
-                        uint64_t load = 0;
-                        for (uint64_t slot = 0; slot < m.maxJobs; ++slot) {
-                            auto slotLock = openSlotLock(m, slot);
-                            if (tryLockFile(slotLock.get(), ltWrite)) {
-                                if (!free) {
-                                    free = std::move(slotLock);
-                                }
-                            } else {
-                                ++load;
-                            }
-                        }
-                        if (!free) {
-                            continue;
-                        }
-                        bool best = false;
-                        if (!bestSlotLock) {
-                            best = true;
-                        } else if (load / m.speedFactor < bestLoad / bestMachine->speedFactor) {
-                            best = true;
-                        } else if (load / m.speedFactor == bestLoad / bestMachine->speedFactor) {
-                            if (m.speedFactor > bestMachine->speedFactor) {
-                                best = true;
-                            } else if (m.speedFactor == bestMachine->speedFactor) {
-                                if (load < bestLoad) {
-                                    best = true;
-                                }
-                            }
-                        }
-                        if (best) {
-                            bestLoad = load;
-                            bestSlotLock = std::move(free);
-                            bestMachine = &m;
-                        }
-                    }
-                }
-
-                if (!bestSlotLock) {
-                    if (rightType && !canBuildLocally)
-                        std::cerr << "# postpone\n";
-                    else
-                    {
-                        // add the template values.
-                        std::string drvstr;
-                        if (drvPath.has_value())
-                            drvstr = drvPath->to_string();
-                        else
-                            drvstr = "<unknown>";
-
-                        std::string machinesFormatted;
-
-                        for (auto & m : machines) {
-                            machinesFormatted += HintFmt(
-                                "\n([%s], %s, [%s], [%s])",
-                                concatStringsSep<StringSet>(", ", m.systemTypes),
-                                m.maxJobs,
-                                concatStringsSep<StringSet>(", ", m.supportedFeatures),
-                                concatStringsSep<StringSet>(", ", m.mandatoryFeatures)
-                            ).str();
-                        }
-
-                        auto error = HintFmt(
-                            "Failed to find a machine for remote build!\n"
-                            "derivation: %s\n"
-                            "required (system, features): (%s, [%s])\n"
-                            "%s available machines:\n"
-                            "(systems, maxjobs, supportedFeatures, mandatoryFeatures)%s",
-                            drvstr,
-                            neededSystem,
-                            concatStringsSep<StringSet>(", ", requiredFeatures),
-                            machines.size(),
-                            Uncolored(machinesFormatted)
-                       );
-
-                        printMsg(couldBuildLocally ? lvlChatty : lvlWarn, error.str());
-
-                        std::cerr << "# decline\n";
-                    }
-                    break;
-                }
-
-#if __APPLE__
-                futimes(bestSlotLock.get(), nullptr);
-#else
-                futimens(bestSlotLock.get(), nullptr);
-#endif
-
-                lock.reset();
-
-                try {
-
-                    Activity act(*logger, lvlTalkative, actUnknown, fmt("connecting to '%s'", bestMachine->storeUri));
-
-                    sshStore = aio.blockOn(bestMachine->openStore());
-                    aio.blockOn(sshStore->connect());
-                    storeUri = bestMachine->storeUri;
-
-                } catch (std::exception & e) { // NOLINT(lix-foreign-exceptions)
-                    auto msg = chomp(drainFD(5, false));
-                    printError("cannot build on '%s': %s%s",
-                        bestMachine->storeUri, e.what(),
-                        msg.empty() ? "" : ": " + msg);
-                    bestMachine->enabled = false;
-                    continue;
-                }
-
-                goto connected;
-            }
+        if (used) {
+            throw Error("build hooks builds are single-use items");
         }
+        used = true;
+        co_await runImpl(context);
+        TRY_AWAIT(logger->flush());
+    } catch (...) {
+        RPC_FILL(context.getResults(), getResult, std::current_exception());
+    }
+}
 
-connected:
-        close(5);
+kj::Promise<void> AcceptedBuild::runImpl(RunContext context)
+{
+    try {
+        auto logHandler = builder.startLogThread(
+            fmt("%s on '%s'",
+                rpc::to<std::string_view>(context.getParams().getDescription()),
+                builder.storeUri),
+            store->printStorePath(drvPath)
+        );
 
-        assert(sshStore);
+        auto & sshStore = builder.sshStore;
+        auto & storeUri = builder.storeUri;
 
-        std::cerr << "# accept\n" << storeUri << "\n";
-
-        auto inputs = readStrings<PathSet>(source);
-        auto wantedOutputs = readStrings<StringSet>(source);
+        auto inputs = rpc::to<std::set<StorePath>>(context.getParams().getInputs(), *store);
+        auto wantedOutputs = rpc::to<std::set<std::string>>(context.getParams().getWantedOutputs());
 
         auto lockFileName = currentLoad + "/" + makeLockFilename(storeUri) + ".upload-lock";
 
         AutoCloseFD uploadLock = openLockFile(lockFileName, true);
 
         {
-            Activity act(*logger, lvlTalkative, actUnknown, fmt("waiting for the upload lock to '%s'", storeUri));
+            auto act = logger->startActivity(
+                lvlTalkative, actUnknown, fmt("waiting for the upload lock to '%s'", storeUri)
+            );
 
-            if (!unsafeLockFileSingleThreaded(uploadLock.get(), ltWrite, std::chrono::minutes(15)))
+            auto result = TRY_AWAIT(
+                AIO().timeoutAfter(15 * kj::MINUTES, lockFileAsync(uploadLock.get(), ltWrite))
+            );
+            if (!result) {
                 printError("somebody is hogging the upload lock for '%s', continuing...");
+            }
         }
 
         auto substitute = settings.buildersUseSubstitutes ? Substitute : NoSubstitute;
 
         {
-            Activity act(*logger, lvlTalkative, actUnknown, fmt("copying dependencies to '%s'", storeUri));
-            aio.blockOn(copyPaths(
-                *store,
-                *sshStore,
-                store->parseStorePathSet(inputs),
-                NoRepair,
-                NoCheckSigs,
-                substitute
-            ));
+            auto act = logger->startActivity(
+                lvlTalkative, actUnknown, fmt("copying dependencies to '%s'", storeUri)
+            );
+            TRY_AWAIT(copyPaths(*store, *sshStore, inputs, NoRepair, NoCheckSigs, substitute));
         }
 
         uploadLock.reset();
 
-        auto drv = aio.blockOn(store->readDerivation(*drvPath));
+        auto drv = TRY_AWAIT(store->readDerivation(drvPath));
 
         std::optional<BuildResult> optResult;
 
@@ -311,7 +550,7 @@ connected:
         // stores), we assume we are. This is necessary for backwards
         // compat.
         bool trustedOrLegacy = ({
-            std::optional trusted = aio.blockOn(sshStore->isTrustedClient());
+            std::optional trusted = TRY_AWAIT(sshStore->isTrustedClient());
             !trusted || *trusted;
         });
 
@@ -330,46 +569,61 @@ connected:
             //
             // 2. Changing the `inputSrcs` set changes the associated
             //    output ids, which break CA derivations
-            if (!drv.inputDrvs.empty())
-                drv.inputSrcs = store->parseStorePathSet(inputs);
-            optResult = aio.blockOn(sshStore->buildDerivation(*drvPath, (const BasicDerivation &) drv));
-            auto & result = *optResult;
-            if (!result.success())
-                throw Error("build of '%s' on '%s' failed: %s", store->printStorePath(*drvPath), storeUri, result.errorMsg);
+            if (!drv.inputDrvs.empty()) {
+                drv.inputSrcs = inputs;
+            }
+            optResult =
+                TRY_AWAIT(sshStore->buildDerivation(drvPath, (const BasicDerivation &) drv));
         } else {
-            aio.blockOn(copyClosure(
-                *store, *sshStore, StorePathSet{*drvPath}, NoRepair, NoCheckSigs, substitute
+            TRY_AWAIT(copyClosure(
+                *store, *sshStore, StorePathSet{drvPath}, NoRepair, NoCheckSigs, substitute
             ));
-            auto res = aio.blockOn(sshStore->buildPathsWithResults({
-                DerivedPath::Built {
-                    .drvPath = makeConstantStorePath(*drvPath),
-                    .outputs = OutputsSpec::All {},
-                }
-            }));
+            auto res = TRY_AWAIT(sshStore->buildPathsWithResults({DerivedPath::Built{
+                .drvPath = makeConstantStorePath(drvPath),
+                .outputs = OutputsSpec::All{},
+            }}));
             // One path to build should produce exactly one build result
             assert(res.size() == 1);
             optResult = std::move(res[0]);
         }
 
+        auto & result = *optResult;
+        if (!result.success()) {
+            throw Error(
+                "build of '%s' on '%s' failed: %s",
+                store->printStorePath(drvPath),
+                storeUri,
+                result.errorMsg
+            );
+        }
 
         StorePathSet missingPaths;
         auto outputPaths = drv.outputsAndPaths(*store);
         for (auto & [outputName, outputPath] : outputPaths) {
-            if (!aio.blockOn(store->isValidPath(outputPath.second)))
+            if (!TRY_AWAIT(store->isValidPath(outputPath.second))) {
                 missingPaths.insert(outputPath.second);
+            }
         }
 
         if (!missingPaths.empty()) {
-            Activity act(*logger, lvlTalkative, actUnknown, fmt("copying outputs from '%s'", storeUri));
+            auto act = logger->startActivity(
+                lvlTalkative, actUnknown, fmt("copying outputs from '%s'", storeUri)
+            );
             if (auto localStore = store.try_cast_shared<LocalStore>())
                 for (auto & path : missingPaths)
                     localStore->locksHeld.insert(store->printStorePath(path)); /* FIXME: ugly */
-            aio.blockOn(
+            TRY_AWAIT(
                 copyPaths(*sshStore, *store, missingPaths, NoRepair, NoCheckSigs, NoSubstitute)
             );
         }
 
-        return 0;
+        // drop store connection, let log handler process any remaining input
+        builder.sshStore = nullptr;
+        TRY_AWAIT(logHandler);
+
+        context.getResults().initResult().setGood();
+    } catch (...) {
+        RPC_FILL(context.getResults(), initResult, std::current_exception());
     }
 }
 

lix/legacy/nix-build.cc

@@ -9,6 +9,7 @@
 #include "lix/libstore/store-api.hh"
 #include "lix/libstore/local-fs-store.hh"
 #include "lix/libstore/globals.hh"
+#include "lix/libutil/c-calls.hh"
 #include "lix/libutil/current-process.hh"
 #include "lix/libstore/derivations.hh"
 #include "lix/libmain/shared.hh"
@@ -18,6 +19,8 @@
 #include "lix/libcmd/common-eval-args.hh"
 #include "lix/libexpr/attr-path.hh"
 #include "lix/libcmd/legacy.hh"
+#include "lix/libutil/finally.hh"
+#include "lix/libutil/processes.hh"
 #include "lix/libutil/regex.hh"
 #include "lix/libutil/shlex.hh"
 #include "nix-build.hh"
@@ -29,7 +32,7 @@ namespace nix {
 
 using namespace std::string_literals;
 
-static void main_nix_build(AsyncIoRoot & aio, std::string programName, Strings argv)
+static int main_nix_build(AsyncIoRoot & aio, std::string programName, Strings argv)
 {
     auto dryRun = false;
     auto runEnv = std::regex_search(programName, regex::parse("nix-shell$"));
@@ -187,7 +190,8 @@ static void main_nix_build(AsyncIoRoot & aio, std::string programName, Strings a
     if (packages && fromArgs)
         throw UsageError("'-p' and '-E' are mutually exclusive");
 
-    AutoDelete tmpDir(createTempDir("", myName));
+    AutoDelete tmpDir(createTempDir(myName));
+    AutoDelete buildTopTmpDir(createTempSubdir(tmpDir, "build-top"));
     if (outLink.empty())
         outLink = (Path) tmpDir + "/result";
 
@@ -224,8 +228,9 @@ static void main_nix_build(AsyncIoRoot & aio, std::string programName, Strings a
             left = {"default.nix"};
     }
 
-    if (runEnv)
-        setenv("IN_NIX_SHELL", pure ? "pure" : "impure", 1);
+    if (runEnv) {
+        (void) sys::setenv("IN_NIX_SHELL", pure ? "pure" : "impure", 1);
+    }
 
     DrvInfos drvs;
 
@@ -272,7 +277,7 @@ static void main_nix_build(AsyncIoRoot & aio, std::string programName, Strings a
             }
             bool add = false;
             if (v.type() == nFunction) {
-                if (auto pattern = dynamic_cast<AttrsPattern *>(v.lambda.fun->pattern.get())) {
+                if (auto pattern = dynamic_cast<AttrsPattern *>(v.lambda().fun->pattern.get())) {
                     for (auto & i : pattern->formals) {
                         if (evaluator->symbols[i.name] == "inNixShell") {
                             add = true;
@@ -285,12 +290,12 @@ static void main_nix_build(AsyncIoRoot & aio, std::string programName, Strings a
         };
 
         for (auto & i : attrPaths) {
-            Value & v(*findAlongAttrPath(
-                *state,
-                i,
-                takesNixShellAttr(vRoot) ? *autoArgsWithInNixShell : *autoArgs,
-                vRoot
-            ).first);
+            Value v(
+                findAlongAttrPath(
+                    *state, i, takesNixShellAttr(vRoot) ? *autoArgsWithInNixShell : *autoArgs, vRoot
+                )
+                    .first
+            );
             state->forceValue(v, noPos);
             getDerivations(
                 *state,
@@ -397,7 +402,9 @@ static void main_nix_build(AsyncIoRoot & aio, std::string programName, Strings a
 
         buildPaths(pathsToBuild);
 
-        if (dryRun) return;
+        if (dryRun) {
+            return 0;
+        }
 
         if (shellDrv) {
             auto shellDrvOutputs =
@@ -419,24 +426,24 @@ static void main_nix_build(AsyncIoRoot & aio, std::string programName, Strings a
         }
 
         // Don't use defaultTempDir() here! We want to preserve the user's TMPDIR for the shell
-        env["NIX_BUILD_TOP"] = env["TMPDIR"] = env["TEMPDIR"] = env["TMP"] = env["TEMP"] = getEnvNonEmpty("TMPDIR").value_or("/tmp");
+        env["NIX_BUILD_TOP"] = env["TMPDIR"] = env["TEMPDIR"] = env["TMP"] = env["TEMP"] =
+            getEnvNonEmpty("TMPDIR").value_or(buildTopTmpDir);
         env["NIX_STORE"] = store->config().storeDir;
         env["NIX_BUILD_CORES"] = std::to_string(settings.buildCores);
 
         auto passAsFile = tokenizeString<StringSet>(getOr(drv.env, "passAsFile", ""));
 
-        bool keepTmp = false;
         int fileNr = 0;
 
         for (auto & var : drv.env)
             if (passAsFile.count(var.first)) {
-                keepTmp = true;
                 auto fn = ".attr-" + std::to_string(fileNr++);
                 Path p = (Path) tmpDir + "/" + fn;
                 writeFile(p, var.second);
                 env[var.first + "Path"] = p;
-            } else
+            } else {
                 env[var.first] = var.second;
+            }
 
         std::string structuredAttrsRC;
 
@@ -469,7 +476,6 @@ static void main_nix_build(AsyncIoRoot & aio, std::string programName, Strings a
 
                 env["NIX_ATTRS_SH_FILE"] = attrsSH;
                 env["NIX_ATTRS_JSON_FILE"] = attrsJSON;
-                keepTmp = true;
             }
         }
 
@@ -479,24 +485,13 @@ static void main_nix_build(AsyncIoRoot & aio, std::string programName, Strings a
            lose the current $PATH directories. */
         auto rcfile = (Path) tmpDir + "/rc";
         auto tz = getEnv("TZ");
-        std::string rc = fmt(
-            R"(_nix_shell_clean_tmpdir() { command rm -rf %1%; }; )"
-            "%2%"
-            "%3%"
-            // always clear PATH.
-            // when nix-shell is run impure, we rehydrate it with the `p=$PATH` above
-            "unset PATH;"
-            "dontAddDisableDepTrack=1;\n",
-            shellEscape(tmpDir),
-            (keepTmp
-                ? "trap _nix_shell_clean_tmpdir EXIT; "
-                  "exitHooks+=(_nix_shell_clean_tmpdir); "
-                  "failureHooks+=(_nix_shell_clean_tmpdir); "
-                : "_nix_shell_clean_tmpdir; "),
-            (pure
-                ? ""
-                : "[ -n \"$PS1\" ] && [ -e ~/.bashrc ] && source ~/.bashrc; p=$PATH; ")
-        );
+        std::string rc =
+            fmt("%1%"
+                // always clear PATH.
+                // when nix-shell is run impure, we rehydrate it with the `p=$PATH` above
+                "unset PATH;"
+                "dontAddDisableDepTrack=1;\n",
+                (pure ? "" : "[ -n \"$PS1\" ] && [ -e ~/.bashrc ] && source ~/.bashrc; p=$PATH; "));
         rc += structuredAttrsRC;
         rc += fmt(
             "\n[ -e $stdenv/setup ] && source $stdenv/setup; "
@@ -526,27 +521,38 @@ static void main_nix_build(AsyncIoRoot & aio, std::string programName, Strings a
         vomit("Sourcing nix-shell with file %s and contents:\n%s", rcfile, rc);
         writeFile(rcfile, rc);
 
-        Strings envStrs;
-        for (auto & i : env)
-            envStrs.push_back(i.first + "=" + i.second);
-
-        auto args = interactive
-            ? Strings{"bash", "--rcfile", rcfile}
-            : Strings{"bash", rcfile};
-
-        auto envPtrs = stringsToCharPtrs(envStrs);
-
-        environ = envPtrs.data();
-
-        auto argPtrs = stringsToCharPtrs(args);
-
-        restoreProcessContext();
+        auto args = interactive ? Strings{"--rcfile", rcfile} : Strings{rcfile};
 
+        // We are going to run an interactive command, do not let the logger send a line.
         logger->pause();
 
-        execvp(shell->c_str(), argPtrs.data());
+        printMsg(lvlChatty, "running shell: %s", concatMapStringsSep(" ", args, shellEscape));
 
-        throw SysError("executing shell '%s'", *shell);
+        RunningProgram proc = runProgram2(
+            {.program = *shell,
+             .searchPath = true,
+             .args = args,
+             .environment = env,
+             .dieWithParent = true}
+        );
+
+        // NOTE: we wait and return the status check immediately.
+        // If there's interruption, we will swallow it and wait again for termination.
+        auto toExitStatus = [](int waitRes) {
+            if (WIFEXITED(waitRes)) {
+                return WEXITSTATUS(waitRes);
+            } else if (WIFSIGNALED(waitRes)) {
+                return 128 + WTERMSIG(waitRes);
+            } else {
+                return 255;
+            }
+        };
+
+        try {
+            return toExitStatus(proc.wait());
+        } catch (Interrupted &) {
+            return toExitStatus(proc.wait());
+        }
     }
 
     else {
@@ -580,7 +586,9 @@ static void main_nix_build(AsyncIoRoot & aio, std::string programName, Strings a
 
         buildPaths(pathsToBuild);
 
-        if (dryRun) return;
+        if (dryRun) {
+            return 0;
+        }
 
         std::vector<StorePath> outPaths;
 
@@ -609,6 +617,8 @@ static void main_nix_build(AsyncIoRoot & aio, std::string programName, Strings a
         for (auto & path : outPaths)
             std::cout << store->printStorePath(path) << '\n';
     }
+
+    return 0;
 }
 
 void registerLegacyNixBuildAndNixShell() {

lix/legacy/nix-channel.cc

@@ -8,7 +8,9 @@
 #include "lix/libexpr/eval-settings.hh" // for defexpr
 #include "lix/libstore/temporary-dir.hh"
 #include "lix/libutil/async.hh"
+#include "lix/libutil/c-calls.hh"
 #include "lix/libutil/regex.hh"
+#include "lix/libutil/result.hh"
 #include "lix/libutil/users.hh"
 #include "nix-channel.hh"
 
@@ -43,7 +45,7 @@ static void readChannels()
 // Writes the list of channels.
 static void writeChannels()
 {
-    auto channelsFD = AutoCloseFD{open(channelsList.c_str(), O_WRONLY | O_CLOEXEC | O_CREAT | O_TRUNC, 0644)};
+    auto channelsFD = sys::open(channelsList, O_WRONLY | O_CLOEXEC | O_CREAT | O_TRUNC, 0644);
     if (!channelsFD)
         throw SysError("opening '%1%' for writing", channelsList);
     for (const auto & channel : channels)
@@ -65,13 +67,18 @@ static void addChannel(const std::string & url, const std::string & name)
 static Path profile;
 
 // Remove a channel.
-static void removeChannel(const std::string & name)
-{
+static kj::Promise<Result<void>> removeChannel(const std::string & name)
+try {
     readChannels();
     channels.erase(name);
     writeChannels();
 
-    runProgram(settings.nixBinDir + "/nix-env", true, { "--profile", profile, "--uninstall", name });
+    TRY_AWAIT(runProgram(
+        settings.nixBinDir + "/nix-env", true, {"--profile", profile, "--uninstall", name}
+    ));
+    co_return result::success();
+} catch (...) {
+    co_return result::current_exception();
 }
 
 static Path nixDefExpr;
@@ -127,8 +134,14 @@ static void update(AsyncIoRoot & aio, const StringSet & channelNames)
 
             bool unpacked = false;
             if (std::regex_search(filename, regex::parse("\\.tar\\.(gz|bz2|xz)$"))) {
-                runProgram(settings.nixBinDir + "/nix-build", false, { "--no-out-link", "--expr", "import " + unpackChannelPath +
-                            "{ name = \"" + cname + "\"; channelName = \"" + name + "\"; src = builtins.storePath \"" + filename + "\"; }" });
+                aio.blockOn(runProgram(
+                    settings.nixBinDir + "/nix-build",
+                    false,
+                    {"--no-out-link",
+                     "--expr",
+                     "import " + unpackChannelPath + "{ name = \"" + cname + "\"; channelName = \""
+                         + name + "\"; src = builtins.storePath \"" + filename + "\"; }"}
+                ));
                 unpacked = true;
             }
 
@@ -158,15 +171,16 @@ static void update(AsyncIoRoot & aio, const StringSet & channelNames)
     for (auto & expr : exprs)
         envArgs.push_back(std::move(expr));
     envArgs.push_back("--quiet");
-    runProgram(settings.nixBinDir + "/nix-env", false, envArgs);
+    aio.blockOn(runProgram(settings.nixBinDir + "/nix-env", false, envArgs));
 
     // Make the channels appear in nix-env.
     struct stat st;
-    if (lstat(nixDefExpr.c_str(), &st) == 0) {
+    if (sys::lstat(nixDefExpr, &st) == 0) {
         if (S_ISLNK(st.st_mode))
             // old-skool ~/.nix-defexpr
-            if (unlink(nixDefExpr.c_str()) == -1)
+            if (sys::unlink(nixDefExpr) == -1) {
                 throw SysError("unlinking %1%", nixDefExpr);
+            }
     } else if (errno != ENOENT) {
         throw SysError("getting status of %1%", nixDefExpr);
     }
@@ -244,7 +258,7 @@ static int main_nix_channel(AsyncIoRoot & aio, std::string programName, Strings
             case cRemove:
                 if (args.size() != 1)
                     throw UsageError("'--remove' requires one argument");
-                removeChannel(args[0]);
+                aio.blockOn(removeChannel(args[0]));
                 break;
             case cList:
                 if (!args.empty())
@@ -259,7 +273,11 @@ static int main_nix_channel(AsyncIoRoot & aio, std::string programName, Strings
             case cListGenerations:
                 if (!args.empty())
                     throw UsageError("'--list-generations' expects no arguments");
-                std::cout << runProgram(settings.nixBinDir + "/nix-env", false, {"--profile", profile, "--list-generations"}) << std::flush;
+                std::cout << aio.blockOn(runProgram(
+                    settings.nixBinDir + "/nix-env",
+                    false,
+                    {"--profile", profile, "--list-generations"}
+                )) << std::flush;
                 break;
             case cRollback:
                 if (args.size() > 1)
@@ -271,7 +289,7 @@ static int main_nix_channel(AsyncIoRoot & aio, std::string programName, Strings
                 } else {
                     envArgs.push_back("--rollback");
                 }
-                runProgram(settings.nixBinDir + "/nix-env", false, envArgs);
+                aio.blockOn(runProgram(settings.nixBinDir + "/nix-env", false, envArgs));
                 break;
         }
 

lix/legacy/nix-collect-garbage.cc

@@ -1,3 +1,4 @@
+#include "lix/libutil/c-calls.hh"
 #include "lix/libutil/file-system.hh"
 #include "lix/libstore/store-api.hh"
 #include "lix/libstore/store-cast.hh"
@@ -24,9 +25,11 @@ bool dryRun = false;
 
 static void removeOldGenerations(std::string dir, NeverAsync = {})
 {
-    if (access(dir.c_str(), R_OK) != 0) return;
+    if (sys::access(dir, R_OK) != 0) {
+        return;
+    }
 
-    bool canWrite = access(dir.c_str(), W_OK) == 0;
+    bool canWrite = sys::access(dir, W_OK) == 0;
 
     for (auto & i : readDirectory(dir)) {
         checkInterrupt();
@@ -103,7 +106,7 @@ static int main_nix_collect_garbage(AsyncIoRoot & aio, std::string programName,
         if (dryRun) {
             // Only print results for dry run; when !dryRun, paths will be printed as they're deleted.
             for (auto & i : results.paths) {
-                printInfo("%s", i);
+                printInfo("%s", Uncolored(i));
             }
         }
 

lix/legacy/nix-copy-closure.cc

@@ -23,7 +23,7 @@ static int main_nix_copy_closure(AsyncIoRoot & aio, std::string programName, Str
                 printVersion("nix-copy-closure");
             else if (*arg == "--gzip" || *arg == "--bzip2" || *arg == "--xz") {
                 if (*arg != "--gzip")
-                    warn("'%1%' is not implemented, falling back to gzip", *arg);
+                    printTaggedWarning("'%1%' is not implemented, falling back to gzip", *arg);
                 gzip = true;
             } else if (*arg == "--from")
                 toMode = false;

lix/legacy/nix-env.cc

@@ -1,6 +1,7 @@
 #include "lix/libcmd/cmd-profiles.hh"
 #include "lix/libexpr/attr-path.hh"
 #include "lix/libcmd/common-eval-args.hh"
+#include "lix/libexpr/value.hh"
 #include "lix/libstore/derivations.hh"
 #include "lix/libutil/terminal.hh"
 #include "lix/libexpr/eval.hh"
@@ -150,11 +151,12 @@ static void getAllExprs(Evaluator & state,
                 continue;
             }
             /* Load the expression on demand. */
-            auto vArg = state.mem.allocValue();
-            vArg->mkString(path2.canonical().abs());
+            Value vArg;
+            vArg.mkString(path2.canonical().abs());
             if (seen.size() == maxAttrs)
                 throw Error("too many Nix expressions in directory '%1%'", path);
-            attrs.alloc(attrName).mkApp(&state.builtins.get("import"), vArg);
+            attrs.alloc(attrName
+            ) = {NewValueAs::app, state.mem, state.builtins.get("import"), vArg};
         }
         else if (st.type == InputAccessor::tDirectory)
             /* `path2' is a directory (with no default.nix in it);
@@ -181,7 +183,7 @@ static void loadSourceExpr(EvalState & state, const SourcePath & path_, Value &
        directory). */
     else if (st.type == InputAccessor::tDirectory) {
         auto attrs = state.ctx.buildBindings(maxAttrs);
-        attrs.alloc("_combineChannels").mkList(0);
+        attrs.alloc("_combineChannels") = Value::EMPTY_LIST;
         StringSet seen;
         getAllExprs(state.ctx, path, seen, attrs);
         v.mkAttrs(attrs);
@@ -198,7 +200,7 @@ static void loadDerivations(EvalState & state, const SourcePath & nixExprPath,
     Value vRoot;
     loadSourceExpr(state, nixExprPath, vRoot);
 
-    Value & v(*findAlongAttrPath(state, pathPrefix, autoArgs, vRoot).first);
+    Value v(findAlongAttrPath(state, pathPrefix, autoArgs, vRoot).first);
 
     getDerivations(state, v, pathPrefix, autoArgs, elems, true);
 
@@ -317,9 +319,9 @@ std::vector<Match> pickNewestOnly(EvalState & state, std::vector<Match> matches)
     matches.clear();
     for (auto & [name, match] : newest) {
         if (multiple.find(name) != multiple.end())
-            warn(
-                "there are multiple derivations named '%1%'; using the first one",
-                name);
+            printTaggedWarning(
+                "there are multiple derivations named '%1%'; using the first one", name
+            );
         matches.push_back(match);
     }
 
@@ -425,7 +427,7 @@ static void queryInstSources(EvalState & state,
                 Expr & eFun = state.ctx.parseExprFromString(i, CanonPath::fromCwd());
                 Value vFun, vTmp;
                 state.eval(eFun, vFun);
-                vTmp.mkApp(&vFun, &vArg);
+                vTmp = {NewValueAs::app, state.ctx.mem, vFun, vArg};
                 getDerivations(state, vTmp, "", *instSource.autoArgs, elems, true);
             }
 
@@ -480,7 +482,7 @@ static void queryInstSources(EvalState & state,
             Value vRoot;
             loadSourceExpr(state, *instSource.nixExprPath, vRoot);
             for (auto & i : args) {
-                Value & v(*findAlongAttrPath(state, i, *instSource.autoArgs, vRoot).first);
+                Value v(findAlongAttrPath(state, i, *instSource.autoArgs, vRoot).first);
                 getDerivations(state, v, "", *instSource.autoArgs, elems, true);
             }
             break;
@@ -515,8 +517,8 @@ static bool keep(EvalState & state, DrvInfo & drv)
 static void setMetaFlag(EvalState & state, DrvInfo & drv,
     const std::string & name, const std::string & value)
 {
-    auto v = state.ctx.mem.allocValue();
-    v->mkString(value);
+    Value v;
+    v.mkString(value);
     drv.setMeta(state, name, v);
 }
 
@@ -686,8 +688,12 @@ static void upgradeDerivations(Globals & globals,
                 {
                     const char * action = compareVersions(drvName.version, bestVersion) <= 0
                         ? "upgrading" : "downgrading";
-                    printInfo("%1% '%2%' to '%3%'",
-                        action, i.queryName(*state), bestElem->queryName(*state));
+                    printInfo(
+                        "%1% '%2%' to '%3%'",
+                        Uncolored(action),
+                        i.queryName(*state),
+                        bestElem->queryName(*state)
+                    );
                     newElems.push_back(*bestElem);
                 } else newElems.push_back(i);
 
@@ -845,7 +851,7 @@ static void uninstallDerivations(Globals & globals, Strings & selectors,
                 );
             }
             if (split == workingElems.end())
-                warn("selector '%s' matched no installed derivations", selector);
+                printTaggedWarning("selector '%s' matched no installed derivations", selector);
             for (auto removedElem = split; removedElem != workingElems.end(); removedElem++) {
                 printInfo("uninstalling '%s'", removedElem->queryName(*state));
             }
@@ -1267,39 +1273,43 @@ static void opQuery(Globals & globals, Strings opFlags, Strings opArgs)
                         else {
                             if (v->type() == nString) {
                                 attrs2["type"] = "string";
-                                attrs2["value"] = v->string.s;
+                                attrs2["value"] = v->str();
                                 xml.writeEmptyElement("meta", attrs2);
                             } else if (v->type() == nInt) {
                                 attrs2["type"] = "int";
-                                attrs2["value"] = fmt("%1%", v->integer);
+                                attrs2["value"] = fmt("%1%", v->integer());
                                 xml.writeEmptyElement("meta", attrs2);
                             } else if (v->type() == nFloat) {
                                 attrs2["type"] = "float";
-                                attrs2["value"] = fmt("%1%", v->fpoint);
+                                attrs2["value"] = fmt("%1%", v->fpoint());
                                 xml.writeEmptyElement("meta", attrs2);
                             } else if (v->type() == nBool) {
                                 attrs2["type"] = "bool";
-                                attrs2["value"] = v->boolean ? "true" : "false";
+                                attrs2["value"] = v->boolean() ? "true" : "false";
                                 xml.writeEmptyElement("meta", attrs2);
                             } else if (v->type() == nList) {
                                 attrs2["type"] = "strings";
                                 XMLOpenElement m(xml, "meta", attrs2);
-                                for (auto elem : v->listItems()) {
-                                    if (elem->type() != nString) continue;
+                                for (auto & elem : v->listItems()) {
+                                    if (elem.type() != nString) {
+                                        continue;
+                                    }
                                     XMLAttrs attrs3;
-                                    attrs3["value"] = elem->string.s;
+                                    attrs3["value"] = elem.str();
                                     xml.writeEmptyElement("string", attrs3);
                                 }
                             } else if (v->type() == nAttrs) {
                                 attrs2["type"] = "strings";
                                 XMLOpenElement m(xml, "meta", attrs2);
-                                Bindings & attrs = *v->attrs;
+                                Bindings & attrs = *v->attrs();
                                 for (auto &i : attrs) {
-                                    Attr & a(*attrs.find(i.name));
-                                    if(a.value->type() != nString) continue;
+                                    const Attr & a(*attrs.get(i.name));
+                                    if (a.value.type() != nString) {
+                                        continue;
+                                    }
                                     XMLAttrs attrs3;
                                     attrs3["type"] = globals.state->symbols[i.name];
-                                    attrs3["value"] = a.value->string.s;
+                                    attrs3["value"] = a.value.str();
                                     xml.writeEmptyElement("string", attrs3);
                             }
                             }

lix/legacy/nix-instantiate.cc

@@ -38,7 +38,7 @@ void processExpr(EvalState & state, const Strings & attrPaths,
     state.eval(e, vRoot);
 
     for (auto & i : attrPaths) {
-        Value & v(*findAlongAttrPath(state, i, autoArgs, vRoot).first);
+        Value v(findAlongAttrPath(state, i, autoArgs, vRoot).first);
         state.forceValue(v, noPos);
 
         NixStringContext context;

lix/legacy/nix-store.cc

@@ -17,11 +17,15 @@
 #include "graphml.hh"
 #include "lix/libcmd/legacy.hh"
 #include "lix/libstore/path-with-outputs.hh"
+#include "lix/libutil/serialise.hh"
 #include "nix-store.hh"
 
+#include <cstdint>
+#include <ctime>
 #include <iostream>
 #include <algorithm>
 
+#include <ranges>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>
@@ -85,6 +89,16 @@ try {
             if (i == drv.outputs.end())
                 throw Error("derivation '%s' does not have an output named '%s'",
                     store2->printStorePath(path.path), j);
+            if (!outputPaths.contains(i->first)) {
+                throw Error(
+                    "Possible SQLite database corruption: derivation '%s' output map contains only "
+                    "outputs '{%s}', not '%s'\n"
+                    "Note: derivation output maps are stored in the SQLite database.",
+                    store2->printStorePath(path.path),
+                    concatStringsSep(", ", std::views::keys(outputPaths)),
+                    i->first
+                );
+            }
             auto outPath = outputPaths.at(i->first);
             auto retPath = store->printStorePath(outPath);
             if (store2) {
@@ -823,7 +837,7 @@ opVerify(std::shared_ptr<Store> store, AsyncIoRoot & aio, Strings opFlags, Strin
         else throw UsageError("unknown flag '%1%'", i);
 
     if (aio.blockOn(store->verifyStore(checkContents, repair))) {
-        warn("not all store errors were fixed");
+        printTaggedWarning("not all store errors were fixed");
         throw Exit(1);
     }
 }
@@ -896,11 +910,11 @@ opServe(std::shared_ptr<Store> store, AsyncIoRoot & aio, Strings opFlags, String
     FdSink out(STDOUT_FILENO);
 
     /* Exchange the greeting. */
-    unsigned int magic = readInt(in);
+    unsigned int magic = readNum<unsigned>(in);
     if (magic != SERVE_MAGIC_1) throw Error("protocol mismatch");
     out << SERVE_MAGIC_2 << SERVE_PROTOCOL_VERSION;
     out.flush();
-    ServeProto::Version clientVersion = readInt(in);
+    ServeProto::Version clientVersion = readNum<unsigned>(in);
 
     ServeProto::ReadConn rconn {
         .from = in,
@@ -918,12 +932,12 @@ opServe(std::shared_ptr<Store> store, AsyncIoRoot & aio, Strings opFlags, String
         verbosity = lvlError;
         settings.keepLog.override(false);
         settings.useSubstitutes.override(false);
-        settings.maxSilentTime.override(readInt(in));
-        settings.buildTimeout.override(readInt(in));
+        settings.maxSilentTime.override(readNum<unsigned>(in));
+        settings.buildTimeout.override(readNum<unsigned>(in));
         if (GET_PROTOCOL_MINOR(clientVersion) >= 2)
             settings.maxLogSize.override(readNum<unsigned long>(in));
         if (GET_PROTOCOL_MINOR(clientVersion) >= 3) {
-            auto nrRepeats = readInt(in);
+            auto nrRepeats = readNum<unsigned>(in);
             if (nrRepeats != 0) {
                 throw Error("client requested repeating builds, but this is not currently implemented");
             }
@@ -933,19 +947,19 @@ opServe(std::shared_ptr<Store> store, AsyncIoRoot & aio, Strings opFlags, String
             // `nrRepeats` in fact is 0, so we can safely ignore this
             // without doing something other than what the client
             // asked for.
-            readInt(in);
+            readNum<unsigned>(in);
 
             settings.runDiffHook.override(true);
         }
         if (GET_PROTOCOL_MINOR(clientVersion) >= 7) {
-            settings.keepFailed.override((bool) readInt(in));
+            settings.keepFailed.override((bool) readNum<unsigned>(in));
         }
     };
 
     while (true) {
         ServeProto::Command cmd;
         try {
-            cmd = (ServeProto::Command) readInt(in);
+            cmd = (ServeProto::Command) readNum<unsigned>(in);
         } catch (EndOfFile & e) {
             break;
         }
@@ -953,8 +967,8 @@ opServe(std::shared_ptr<Store> store, AsyncIoRoot & aio, Strings opFlags, String
         switch (cmd) {
 
             case ServeProto::Command::QueryValidPaths: {
-                bool lock = readInt(in);
-                bool substitute = readInt(in);
+                bool lock = readNum<unsigned>(in);
+                bool substitute = readNum<unsigned>(in);
                 auto paths = ServeProto::Serialise<StorePathSet>::read(rconn);
                 if (lock && writeAllowed)
                     for (auto & path : paths)
@@ -997,7 +1011,7 @@ opServe(std::shared_ptr<Store> store, AsyncIoRoot & aio, Strings opFlags, String
             }
 
             case ServeProto::Command::ExportPaths: {
-                readInt(in); // obsolete
+                readNum<unsigned>(in); // obsolete
                 aio.blockOn(store->exportPaths(
                     ServeProto::Serialise<StorePathSet>::read(rconn), out
                 ));
@@ -1043,7 +1057,7 @@ opServe(std::shared_ptr<Store> store, AsyncIoRoot & aio, Strings opFlags, String
             }
 
             case ServeProto::Command::QueryClosure: {
-                bool includeOutputs = readInt(in);
+                bool includeOutputs = readNum<unsigned>(in);
                 StorePathSet closure;
                 aio.blockOn(store->computeFSClosure(
                     ServeProto::Serialise<StorePathSet>::read(rconn),
@@ -1067,13 +1081,43 @@ opServe(std::shared_ptr<Store> store, AsyncIoRoot & aio, Strings opFlags, String
                 if (deriver != "")
                     info.deriver = store->parseStorePath(deriver);
                 info.references = ServeProto::Serialise<StorePathSet>::read(rconn);
-                in >> info.registrationTime >> info.narSize >> info.ultimate;
+                info.registrationTime = readNum<time_t>(in);
+                info.narSize = readNum<uint64_t>(in);
+                info.ultimate = readBool(in);
                 info.sigs = readStrings<StringSet>(in);
                 info.ca = ContentAddress::parseOpt(readString(in));
 
                 if (info.narSize == 0)
                     throw Error("narInfo is too old and missing the narSize field");
 
+                struct SizedSource : Source
+                {
+                    Source & orig;
+                    size_t remain;
+                    SizedSource(Source & orig, size_t size) : orig(orig), remain(size) {}
+                    size_t read(char * data, size_t len) override
+                    {
+                        if (this->remain <= 0) {
+                            throw EndOfFile("sized: unexpected end-of-file");
+                        }
+                        len = std::min(len, this->remain);
+                        size_t n = this->orig.read(data, len);
+                        this->remain -= n;
+                        return n;
+                    }
+
+                    size_t drainAll()
+                    {
+                        std::vector<char> buf(8192);
+                        size_t sum = 0;
+                        while (this->remain > 0) {
+                            size_t n = read(buf.data(), buf.size());
+                            sum += n;
+                        }
+                        return sum;
+                    }
+                };
+
                 SizedSource sizedSource(in, info.narSize);
                 AsyncSourceInputStream stream{sizedSource};
 

lix/legacy/user-env.cc

@@ -1,4 +1,5 @@
 #include "user-env.hh"
+#include "lix/libexpr/value.hh"
 #include "lix/libstore/derivations.hh"
 #include "lix/libstore/store-api.hh"
 #include "lix/libstore/path-with-outputs.hh"
@@ -32,7 +33,8 @@ bool createUserEnv(EvalState & state, DrvInfos & elems,
 
     /* Construct the whole top level derivation. */
     StorePathSet references;
-    Value manifest = state.ctx.mem.newList(elems.size());
+    auto manifest = state.ctx.mem.newList(elems.size());
+    Value vManifest{NewValueAs::list, manifest};
     size_t n = 0;
     for (auto & i : elems) {
         /* Create a pseudo-derivation containing the name, system,
@@ -55,9 +57,10 @@ bool createUserEnv(EvalState & state, DrvInfos & elems,
 
         // Copy each output meant for installation.
         auto & vOutputs = attrs.alloc(state.ctx.s.outputs);
-        vOutputs = state.ctx.mem.newList(outputs.size());
+        auto outputsList = state.ctx.mem.newList(outputs.size());
+        vOutputs = {NewValueAs::list, outputsList};
         for (const auto & [m, j] : enumerate(outputs)) {
-            (vOutputs.listElems()[m] = state.ctx.mem.allocValue())->mkString(j.first);
+            outputsList->elems[m].mkString(j.first);
             auto outputAttrs = state.ctx.buildBindings(2);
             outputAttrs.alloc(state.ctx.s.outPath).mkString(state.ctx.store->printStorePath(*j.second));
             attrs.alloc(j.first).mkAttrs(outputAttrs);
@@ -75,12 +78,12 @@ bool createUserEnv(EvalState & state, DrvInfos & elems,
         for (auto & j : metaNames) {
             Value * v = i.queryMeta(state, j);
             if (!v) continue;
-            meta.insert(state.ctx.symbols.create(j), v);
+            meta.insert(state.ctx.symbols.create(j), *v);
         }
 
         attrs.alloc(state.ctx.s.meta).mkAttrs(meta);
 
-        (manifest.listElems()[n++] = state.ctx.mem.allocValue())->mkAttrs(attrs);
+        manifest->elems[n++].mkAttrs(attrs);
 
         if (drvPath) references.insert(*drvPath);
     }
@@ -89,7 +92,7 @@ bool createUserEnv(EvalState & state, DrvInfos & elems,
        the store; we need it for future modifications of the
        environment. */
     std::ostringstream str;
-    printAmbiguous(manifest, state.ctx.symbols, str, nullptr, std::numeric_limits<int>::max());
+    printAmbiguous(vManifest, state.ctx.symbols, str, nullptr, std::numeric_limits<int>::max());
     auto manifestFile = state.aio.blockOn(state.ctx.store->addTextToStore("env-manifest.nix",
         str.str(), references));
 
@@ -103,21 +106,20 @@ bool createUserEnv(EvalState & state, DrvInfos & elems,
        builder with the manifest as argument. */
     auto attrs = state.ctx.buildBindings(3);
     state.ctx.paths.mkStorePathString(manifestFile, attrs.alloc("manifest"));
-    attrs.insert(state.ctx.symbols.create("derivations"), &manifest);
+    attrs.insert(state.ctx.symbols.create("derivations"), vManifest);
     Value args;
     args.mkAttrs(attrs);
 
-    Value topLevel;
-    topLevel.mkApp(&envBuilder, &args);
+    Value topLevel{NewValueAs::app, state.ctx.mem, envBuilder, args};
 
     /* Evaluate it. */
     debug("evaluating user environment builder");
     state.forceValue(topLevel, noPos);
     NixStringContext context;
-    Attr & aDrvPath(*topLevel.attrs->find(state.ctx.s.drvPath));
-    auto topLevelDrv = state.coerceToStorePath(aDrvPath.pos, *aDrvPath.value, context, "");
-    Attr & aOutPath(*topLevel.attrs->find(state.ctx.s.outPath));
-    auto topLevelOut = state.coerceToStorePath(aOutPath.pos, *aOutPath.value, context, "");
+    const Attr & aDrvPath(*topLevel.attrs()->get(state.ctx.s.drvPath));
+    auto topLevelDrv = state.coerceToStorePath(aDrvPath.pos, aDrvPath.value, context, "");
+    const Attr & aOutPath(*topLevel.attrs()->get(state.ctx.s.outPath));
+    auto topLevelOut = state.coerceToStorePath(aOutPath.pos, aOutPath.value, context, "");
 
     /* Realise the resulting store expression. */
     debug("building user environment");

lix/libcmd/command.cc

@@ -4,6 +4,9 @@
 #include "lix/libstore/derivations.hh"
 #include "lix/libstore/profiles.hh"
 #include "lix/libcmd/repl.hh"
+#include "lix/libutil/async.hh"
+#include "lix/libutil/c-calls.hh"
+#include "lix/libutil/error.hh"
 
 extern char * * environ __attribute__((weak));
 
@@ -39,14 +42,15 @@ StoreCommand::StoreCommand()
 
 ref<Store> StoreCommand::getStore()
 {
-    if (!_store)
-        _store = createStore();
+    if (!_store) {
+        _store = createStore(aio());
+    }
     return *_store;
 }
 
-ref<Store> StoreCommand::createStore()
+ref<Store> StoreCommand::createStore(AsyncIoRoot & in)
 {
-    return aio().blockOn(openStore());
+    return in.blockOn(openStore());
 }
 
 void StoreCommand::run()
@@ -71,9 +75,9 @@ CopyCommand::CopyCommand()
     });
 }
 
-ref<Store> CopyCommand::createStore()
+ref<Store> CopyCommand::createStore(AsyncIoRoot & in)
 {
-    return srcUri.empty() ? StoreCommand::createStore() : aio().blockOn(openStore(srcUri));
+    return srcUri.empty() ? StoreCommand::createStore(in) : in.blockOn(openStore(srcUri));
 }
 
 ref<Store> CopyCommand::getDstStore()
@@ -301,8 +305,10 @@ void MixEnvironment::setEnviron() {
             throw UsageError("--unset does not make sense with --ignore-environment");
 
         for (const auto & var : keep) {
-            auto val = getenv(var.c_str());
-            if (val) stringsEnv.emplace_back(fmt("%s=%s", var.c_str(), val));
+            auto val = sys::getenv(var);
+            if (val) {
+                stringsEnv.emplace_back(fmt("%s=%s", var, val));
+            }
         }
 
         vectorEnv = stringsToCharPtrs(stringsEnv);
@@ -312,7 +318,7 @@ void MixEnvironment::setEnviron() {
             throw UsageError("--keep does not make sense without --ignore-environment");
 
         for (const auto & var : unset)
-            unsetenv(var.c_str());
+            (void) sys::unsetenv(var);
     }
 }
 

lix/libcmd/command.hh

@@ -39,7 +39,7 @@ struct StoreCommand : virtual Command
     StoreCommand();
     void run() override;
     ref<Store> getStore();
-    virtual ref<Store> createStore();
+    virtual ref<Store> createStore(AsyncIoRoot & in);
     /**
      * Main entry point, with a `Store` provided
      */
@@ -59,7 +59,7 @@ struct CopyCommand : virtual StoreCommand
 
     CopyCommand();
 
-    ref<Store> createStore() override;
+    ref<Store> createStore(AsyncIoRoot & in) override;
 
     ref<Store> getDstStore();
 };

lix/libcmd/common-eval-args.cc

@@ -113,7 +113,7 @@ MixEvalArgs::MixEvalArgs()
 
   ```
   -I nixpkgs=channel:nixos-21.05
-  -I nixpkgs=https://nixos.org/channels/nixos-21.05/nixexprs.tar.xz
+  -I nixpkgs=https://channels.nixos.org/nixos-21.05/nixexprs.tar.xz
   ```
 
   You can also fetch source trees using [flake URLs](./nix3-flake.md#url-like-syntax) and add them to the
@@ -183,13 +183,13 @@ Bindings * MixEvalArgs::getAutoArgs(Evaluator & state)
 {
     auto res = state.buildBindings(autoArgs.size());
     for (auto & i : autoArgs) {
-        auto v = state.mem.allocValue();
+        Value v;
         if (i.second[0] == 'E')
             state.evalLazily(
-                state.parseExprFromString(i.second.substr(1), CanonPath::fromCwd()), *v
+                state.parseExprFromString(i.second.substr(1), CanonPath::fromCwd()), v
             );
         else
-            v->mkString(((std::string_view) i.second).substr(1));
+            v.mkString(((std::string_view) i.second).substr(1));
         res.insert(state.symbols.create(i.first), v);
     }
     return res.finish();

lix/libcmd/installable-attr-path.cc

@@ -12,9 +12,10 @@ namespace nix {
 InstallableAttrPath::InstallableAttrPath(
     ref<eval_cache::CachingEvaluator> state,
     SourceExprCommand & cmd,
-    Value * v,
+    Value & v,
     const std::string & attrPath,
-    ExtendedOutputsSpec extendedOutputsSpec)
+    ExtendedOutputsSpec extendedOutputsSpec
+)
     : InstallableValue(state)
     , cmd(cmd)
     , v(allocRootValue(v))
@@ -22,10 +23,10 @@ InstallableAttrPath::InstallableAttrPath(
     , extendedOutputsSpec(std::move(extendedOutputsSpec))
 { }
 
-std::pair<Value *, PosIdx> InstallableAttrPath::toValue(EvalState & state)
+std::pair<Value, PosIdx> InstallableAttrPath::toValue(EvalState & state)
 {
-    auto [vRes, pos] = findAlongAttrPath(state, attrPath, *cmd.getAutoArgs(*evaluator), **v);
-    state.forceValue(*vRes, pos);
+    auto [vRes, pos] = findAlongAttrPath(state, attrPath, *cmd.getAutoArgs(*evaluator), *v);
+    state.forceValue(vRes, pos);
     return {vRes, pos};
 }
 
@@ -34,7 +35,7 @@ DerivedPathsWithInfo InstallableAttrPath::toDerivedPaths(EvalState & state)
     auto [v, pos] = toValue(state);
 
     if (std::optional derivedPathWithInfo = trySinglePathToDerivedPaths(
-            state, *v, pos, fmt("while evaluating the attribute '%s'", attrPath)
+            state, v, pos, fmt("while evaluating the attribute '%s'", attrPath)
         ))
     {
         return { *derivedPathWithInfo };
@@ -43,7 +44,7 @@ DerivedPathsWithInfo InstallableAttrPath::toDerivedPaths(EvalState & state)
     Bindings & autoArgs = *cmd.getAutoArgs(*evaluator);
 
     DrvInfos drvInfos;
-    getDerivations(state, *v, "", autoArgs, drvInfos, false);
+    getDerivations(state, v, "", autoArgs, drvInfos, false);
 
     // Backward compatibility hack: group results by drvPath. This
     // helps keep .all output together.
@@ -92,9 +93,10 @@ DerivedPathsWithInfo InstallableAttrPath::toDerivedPaths(EvalState & state)
 InstallableAttrPath InstallableAttrPath::parse(
     ref<eval_cache::CachingEvaluator> state,
     SourceExprCommand & cmd,
-    Value * v,
+    Value & v,
     std::string_view prefix,
-    ExtendedOutputsSpec extendedOutputsSpec)
+    ExtendedOutputsSpec extendedOutputsSpec
+)
 {
     return {
         state, cmd, v,

lix/libcmd/installable-attr-path.hh

@@ -20,13 +20,14 @@ class InstallableAttrPath : public InstallableValue
     InstallableAttrPath(
         ref<eval_cache::CachingEvaluator> state,
         SourceExprCommand & cmd,
-        Value * v,
+        Value & v,
         const std::string & attrPath,
-        ExtendedOutputsSpec extendedOutputsSpec);
+        ExtendedOutputsSpec extendedOutputsSpec
+    );
 
     std::string what() const override { return attrPath; };
 
-    std::pair<Value *, PosIdx> toValue(EvalState & state) override;
+    std::pair<Value, PosIdx> toValue(EvalState & state) override;
 
     DerivedPathsWithInfo toDerivedPaths(EvalState & state) override;
 
@@ -35,9 +36,10 @@ public:
     static InstallableAttrPath parse(
         ref<eval_cache::CachingEvaluator> state,
         SourceExprCommand & cmd,
-        Value * v,
+        Value & v,
         std::string_view prefix,
-        ExtendedOutputsSpec extendedOutputsSpec);
+        ExtendedOutputsSpec extendedOutputsSpec
+    );
 };
 
 }

lix/libcmd/installable-derived-path.cc

@@ -26,35 +26,27 @@ InstallableDerivedPath InstallableDerivedPath::parse(
     std::string_view prefix,
     ExtendedOutputsSpec extendedOutputsSpec)
 {
-    auto derivedPath = std::visit(overloaded {
-        // If the user did not use ^, we treat the output more
-        // liberally: we accept a symlink chain or an actual
-        // store path.
-        [&](const ExtendedOutputsSpec::Default &) -> DerivedPath {
-            auto storePath = store->followLinksToStorePath(prefix);
-            // Remove this prior to stabilizing the new CLI.
-            if (storePath.isDerivation()) {
-                auto oldDerivedPath = DerivedPath::Built {
-                    .drvPath = makeConstantStorePath(storePath),
-                    .outputs = OutputsSpec::All { },
+    auto derivedPath = std::visit(
+        overloaded{
+            // If the user did not use ^, we treat the output more
+            // liberally: we accept a symlink chain or an actual
+            // store path.
+            [&](const ExtendedOutputsSpec::Default &) -> DerivedPath {
+                return DerivedPath::Opaque{
+                    .path = store->followLinksToStorePath(prefix),
                 };
-                warn(
-                    "The interpretation of store paths arguments ending in `.drv` recently changed. If this command is now failing try again with '%s'",
-                    oldDerivedPath.to_string(*store));
-            };
-            return DerivedPath::Opaque {
-                .path = std::move(storePath),
-            };
+            },
+            // If the user did use ^, we just do exactly what is written.
+            [&](const ExtendedOutputsSpec::Explicit & outputSpec) -> DerivedPath {
+                auto drv = DerivedPathOpaque::parse(*store, prefix);
+                return DerivedPath::Built{
+                    .drvPath = std::move(drv),
+                    .outputs = outputSpec,
+                };
+            },
         },
-        // If the user did use ^, we just do exactly what is written.
-        [&](const ExtendedOutputsSpec::Explicit & outputSpec) -> DerivedPath {
-            auto drv = DerivedPathOpaque::parse(*store, prefix);
-            return DerivedPath::Built {
-                .drvPath = std::move(drv),
-                .outputs = outputSpec,
-            };
-        },
-    }, extendedOutputsSpec.raw);
+        extendedOutputsSpec.raw
+    );
     return InstallableDerivedPath {
         store,
         std::move(derivedPath),

lix/libcmd/installable-flake.cc

@@ -60,7 +60,8 @@ InstallableFlake::InstallableFlake(
 
 DerivedPathsWithInfo InstallableFlake::toDerivedPaths(EvalState & state)
 {
-    Activity act(*logger, lvlTalkative, actUnknown, fmt("evaluating derivation '%s'", what()));
+    auto act =
+        logger->startActivity(lvlTalkative, actUnknown, fmt("evaluating derivation '%s'", what()));
 
     auto attr = getCursor(state);
 
@@ -136,9 +137,9 @@ DerivedPathsWithInfo InstallableFlake::toDerivedPaths(EvalState & state)
     }};
 }
 
-std::pair<Value *, PosIdx> InstallableFlake::toValue(EvalState & state)
+std::pair<Value, PosIdx> InstallableFlake::toValue(EvalState & state)
 {
-    return {&getCursor(state)->forceValue(state), noPos};
+    return {getCursor(state)->forceValue(state), noPos};
 }
 
 std::vector<ref<eval_cache::AttrCursor>>

lix/libcmd/installable-flake.hh

@@ -55,7 +55,7 @@ struct InstallableFlake : InstallableValue
 
     DerivedPathsWithInfo toDerivedPaths(EvalState & state) override;
 
-    std::pair<Value *, PosIdx> toValue(EvalState & state) override;
+    std::pair<Value, PosIdx> toValue(EvalState & state) override;
 
     /**
      * Get a cursor to every attrpath in getActualAttrPaths() that

lix/libcmd/installable-value.cc

@@ -9,8 +9,9 @@ std::vector<ref<eval_cache::AttrCursor>>
 InstallableValue::getCursors(EvalState & state)
 {
     auto evalCache =
-        std::make_shared<nix::eval_cache::EvalCache>(std::nullopt,
-            [&](EvalState & state) { return toValue(state).first; });
+        std::make_shared<nix::eval_cache::EvalCache>(std::nullopt, [&](EvalState & state) {
+            return toValue(state).first;
+        });
     return {evalCache->getRoot()};
 }
 

lix/libcmd/installable-value.hh

@@ -77,7 +77,7 @@ struct InstallableValue : Installable
 
     virtual ~InstallableValue() { }
 
-    virtual std::pair<Value *, PosIdx> toValue(EvalState & state) = 0;
+    virtual std::pair<Value, PosIdx> toValue(EvalState & state) = 0;
 
     /**
      * Get a cursor to each value this Installable could refer to.

lix/libcmd/installables.cc

@@ -61,7 +61,7 @@ MixFlakeOptions::MixFlakeOptions()
         .category = category,
         .handler = {[&]() {
             lockFlags.useRegistries = false;
-            warn("'--no-registries' is deprecated; use '--no-use-registries'");
+            printTaggedWarning("'--no-registries' is deprecated; use '--no-use-registries'");
         }}
     });
 
@@ -235,15 +235,14 @@ void SourceExprCommand::completeInstallable(EvalState & state, AddCompletions &
                 prefix_ = "";
             }
 
-            auto [v, pos] = findAlongAttrPath(state, prefix_, *autoArgs, root);
-            Value &v1(*v);
+            auto [v1, pos] = findAlongAttrPath(state, prefix_, *autoArgs, root);
             state.forceValue(v1, pos);
             Value v2;
             state.autoCallFunction(*autoArgs, v1, v2, pos);
 
             if (v2.type() == nAttrs) {
-                for (auto & i : *v2.attrs) {
-                    std::string name = evaluator->symbols[i.name];
+                for (auto & i : *v2.attrs()) {
+                    std::string name{evaluator->symbols[i.name]};
                     if (name.find(searchWord) == 0) {
                         if (prefix_ == "")
                             completions.add(name);
@@ -344,7 +343,7 @@ void completeFlakeRefWithFragment(
             }
         }
     } catch (Error & e) {
-        warn(e.msg());
+        printTaggedWarning("%1%", Uncolored(e.msg()));
     }
 }
 
@@ -412,12 +411,12 @@ ref<eval_cache::EvalCache> openEvalCache(
             if (getEnv("NIX_ALLOW_EVAL").value_or("1") == "0")
                 throw Error("not everything is cached, but evaluation is not allowed");
 
-            auto vFlake = state.ctx.mem.allocValue();
-            flake::callFlake(state, *lockedFlake, *vFlake);
+            Value vFlake;
+            flake::callFlake(state, *lockedFlake, vFlake);
 
-            state.forceAttrs(*vFlake, noPos, "while parsing cached flake data");
+            state.forceAttrs(vFlake, noPos, "while parsing cached flake data");
 
-            auto aOutputs = vFlake->attrs->get(state.ctx.symbols.create("outputs"));
+            auto aOutputs = vFlake.attrs()->get(state.ctx.symbols.create("outputs"));
             assert(aOutputs);
 
             return aOutputs->value;
@@ -450,25 +449,24 @@ Installables SourceExprCommand::parseInstallables(
             throw UsageError("'--file' and '--expr' are exclusive");
 
         auto evaluator = getEvaluator();
-        auto vFile = evaluator->mem.allocValue();
+        Value vFile;
 
         if (file == "-") {
             auto & e = evaluator->parseStdin();
-            state.eval(e, *vFile);
+            state.eval(e, vFile);
         }
         else if (file)
-            state.evalFile(state.aio.blockOn(lookupFileArg(*evaluator, *file)).unwrap(), *vFile);
+            state.evalFile(state.aio.blockOn(lookupFileArg(*evaluator, *file)).unwrap(), vFile);
         else {
             auto & e = evaluator->parseExprFromString(*expr, CanonPath::fromCwd());
-            state.eval(e, *vFile);
+            state.eval(e, vFile);
         }
 
         for (auto & s : ss) {
             auto [prefix, extendedOutputsSpec] = ExtendedOutputsSpec::parse(s);
-            result.push_back(
-                make_ref<InstallableAttrPath>(
-                    InstallableAttrPath::parse(
-                        evaluator, *this, vFile, std::move(prefix), std::move(extendedOutputsSpec))));
+            result.push_back(make_ref<InstallableAttrPath>(InstallableAttrPath::parse(
+                evaluator, *this, vFile, std::move(prefix), std::move(extendedOutputsSpec)
+            )));
         }
 
     } else {

lix/libcmd/legacy.hh

@@ -9,7 +9,7 @@
 
 namespace nix {
 
-typedef std::function<void(AsyncIoRoot &, std::string, std::list<std::string>)> MainFunction;
+typedef std::function<int(AsyncIoRoot &, std::string, std::list<std::string>)> MainFunction;
 
 struct LegacyCommandRegistry
 {

lix/libcmd/lix-cmd.pc.in

@@ -5,5 +5,6 @@ includedir=@includedir@
 Name: Lix (libcmd)
 Description: Lix Package Manager (libcmd)
 Version: @PACKAGE_VERSION@
-Requires: lix-base lix-util
-Libs: -L${libdir} -llixcmd
+Requires: lix-base lix-util lix-store
+Requires.private: lix-fetchers lix-expr lix-main @BOEHM_IF_FOUND@ libeditline lowdown ncurses
+Libs: -L${libdir} @LIBLIX_DOC_IF_STATIC@ -llixcmd

lix/libcmd/markdown.cc

@@ -51,13 +51,28 @@ static void processLinks(struct lowdown_node * node)
 std::string renderMarkdownToTerminal(std::string_view markdown, StandardOutputStream fileno)
 {
     int windowWidth = getWindowSize().second;
+    size_t lowdown_cols = std::max(windowWidth - 5, 60);
 
-    struct lowdown_opts opts {
+    struct lowdown_opts opts{
         .type = LOWDOWN_TERM,
+#ifdef LOWDOWN_SEPARATE_TERM_OPTS
+        .term =
+            {
+                .cols = lowdown_cols,
+                .width = 0,
+                .hmargin = 0,
+                .hpadding = 4,
+                .vmargin = 0,
+                .centre = 0,
+            },
+        // maxdepth needs to be part of the ifdefs to match declaration order
         .maxdepth = 20,
-        .cols = (size_t) std::max(windowWidth - 5, 60),
+#else
+        .maxdepth = 20,
+        .cols = lowdown_cols,
         .hmargin = 0,
         .vmargin = 0,
+#endif /* LOWDOWN_SEPARATE_TERM_OPTS */
         .feat = LOWDOWN_COMMONMARK | LOWDOWN_FENCED | LOWDOWN_DEFLIST | LOWDOWN_TABLES,
         .oflags = LOWDOWN_TERM_NOLINK,
     };

lix/libcmd/meson.build

@@ -43,15 +43,16 @@ libcmd = library(
   dependencies : [
     liblixutil,
     liblixstore,
-    liblixexpr,
     liblixfetchers,
+    liblixexpr,
     liblixmain,
-    ncurses,
-    editline,
-    lowdown,
-    nlohmann_json,
     liblix_doc,
+    boehm,
+    editline,
     kj,
+    lowdown,
+    ncurses,
+    nlohmann_json,
   ],
   # '../..' for self references like "lix/libcmd/*.hh"
   include_directories : [ '../..' ],
@@ -72,6 +73,11 @@ custom_target(
 
 liblixcmd = declare_dependency(
   include_directories : include_directories('../..'),
+  dependencies : [
+    liblixutil,
+    liblixstore,
+    kj,
+  ],
   link_with : libcmd,
 )
 meson.override_dependency('lix-cmd', liblixcmd)
@@ -87,5 +93,7 @@ configure_file(
     'libdir' : libdir,
     'includedir' : includedir,
     'PACKAGE_VERSION' : meson.project_version(),
+    'BOEHM_IF_FOUND' : boehm.found() ? 'bdw-gc' : '',
+    'LIBLIX_DOC_IF_STATIC' : is_static ? '-llix_doc' : '',
   },
 )

lix/libcmd/repl-interacter.cc

@@ -1,3 +1,4 @@
+#include "lix/libutil/c-calls.hh"
 #include "lix/libutil/error.hh"
 #include "lix/libutil/file-system.hh"
 #include "lix/libutil/logging.hh"
@@ -110,7 +111,7 @@ static el_status_t doCompletion() {
     if (possible.size() == 1) {
         const auto completion = *possible.cbegin();
         if (completion.size() > s.size()) {
-            rl_insert_text(completion.c_str() + s.size());
+            rl_insert_text(requireCString(completion.substr(s.size())));
             return redisplay();
         }
 
@@ -134,7 +135,7 @@ static el_status_t doCompletion() {
     }
     if (len > 0) {
         auto commonPrefix = possible.begin()->substr(start, len);
-        rl_insert_text(commonPrefix.c_str());
+        rl_insert_text(requireCString(commonPrefix));
         el_ring_bell();
         return redisplay();
     }
@@ -154,7 +155,7 @@ ReadlineLikeInteracter::Guard ReadlineLikeInteracter::init(detail::ReplCompleter
         logWarning(e.info());
     }
     el_hist_size = 1000;
-    read_history(historyFile.c_str());
+    read_history(requireCString(historyFile));
     auto oldRepl = curRepl;
     curRepl = repl;
     Guard restoreRepl([oldRepl] { curRepl = oldRepl; });
@@ -202,7 +203,7 @@ bool ReadlineLikeInteracter::getLine(std::string & input, ReplPromptType promptT
     };
 
     setupSignals();
-    char * s = readline(promptForType(promptType));
+    char * s = readline(promptForType(promptType)); // NOLINT(lix-unsafe-c-calls)
     Finally doFree([&]() { free(s); });
     restoreSignals();
 
@@ -223,7 +224,7 @@ bool ReadlineLikeInteracter::getLine(std::string & input, ReplPromptType promptT
 
 void ReadlineLikeInteracter::writeHistory()
 {
-    int ret = write_history(historyFile.c_str());
+    int ret = write_history(requireCString(historyFile));
     int writeHistErr = errno;
 
     if (ret == 0) {
@@ -244,8 +245,7 @@ void ReadlineLikeInteracter::writeHistory()
     // them so the user isn't confused why their history is getting eaten.
 
     std::string_view const errMsg(std::strerror(writeHistErr));
-    warn("ignoring error writing repl history to %s: %s", this->historyFile, errMsg);
-
+    printTaggedWarning("ignoring error writing repl history to %s: %s", this->historyFile, errMsg);
 }
 
 ReadlineLikeInteracter::~ReadlineLikeInteracter()

lix/libcmd/repl.cc

@@ -5,6 +5,7 @@
 #include <cstring>
 #include <string_view>
 
+#include "lix/libexpr/value.hh"
 #include "lix/libutil/box_ptr.hh"
 #include "lix/libcmd/repl-interacter.hh"
 #include "lix/libcmd/repl.hh"
@@ -55,6 +56,7 @@ using NdString = std::unique_ptr<const char, decltype(&lixdoc_free_string)>;
  */
 NdString lambdaDocsForPos(SourcePath const path, nix::Pos const &pos) {
   std::string const file = path.to_string();
+  // NOLINTNEXTLINE(lix-unsafe-c-calls): paths are safe
   return NdString{lixdoc_get_function_docs(file.c_str(), pos.line, pos.column), &lixdoc_free_string};
 }
 
@@ -173,35 +175,37 @@ struct NixRepl
     /**
      * Get a list of each of the `repl-overlays` (parsed and evaluated).
      */
-    Value * replOverlays();
+    Value replOverlays();
 
     /**
      * Get the Nix function that composes the `repl-overlays` together.
      */
-    Value * getReplOverlaysEvalFunction();
+    Value getReplOverlaysEvalFunction();
 
     /**
      * Cached return value of `getReplOverlaysEvalFunction`.
      *
      * Note: This is `shared_ptr` to avoid garbage collection.
      */
-    std::shared_ptr<Value *> replOverlaysEvalFunction =
-        std::allocate_shared<Value *>(TraceableAllocator<Value *>(), nullptr);
+    std::shared_ptr<std::optional<Value>> replOverlaysEvalFunction =
+        std::allocate_shared<std::optional<Value>>(
+            TraceableAllocator<std::optional<Value>>(), std::nullopt
+        );
 
     /**
      * Get the `info` AttrSet that's passed as the first argument to each
      * of the `repl-overlays`.
      */
-    Value * replInitInfo();
+    Value replInitInfo();
 
     /**
      * Get the current top-level bindings as an AttrSet.
      */
-    Value * bindingsToAttrs();
+    Value bindingsToAttrs();
     /**
      * Parse a file, evaluate its result, and force the resulting value.
      */
-    Value * evalFile(SourcePath & path);
+    Value evalFile(SourcePath & path);
 
     void printValue(std::ostream & str,
                               Value & v,
@@ -290,7 +294,7 @@ ReplExitStatus NixRepl::mainLoop()
         if (evaluator.debug && evaluator.debug->inDebugger) {
             debuggerNotice = " debugger";
         }
-        notice("Lix %1%%2%\nType :? for help.", nixVersion, debuggerNotice);
+        notice("Lix %1%%2%\nType :? for help.", Uncolored(nixVersion), debuggerNotice);
     }
 
     isFirstRepl = false;
@@ -306,7 +310,7 @@ ReplExitStatus NixRepl::mainLoop()
     std::string input;
 
     while (true) {
-        _isInterrupted = false;
+        unsetUserInterruptRequest();
 
         // When continuing input from previous lines, don't print a prompt, just align to the same
         // number of chars as the prompt.
@@ -337,14 +341,14 @@ ReplExitStatus NixRepl::mainLoop()
                 // input without clearing the input so far.
                 continue;
             } else {
-              printMsg(lvlError, e.msg());
+                printMsg(lvlError, "%1%", Uncolored(e.msg()));
             }
         } catch (EvalError & e) {
-            printMsg(lvlError, e.msg());
+            printMsg(lvlError, "%1%", Uncolored(e.msg()));
         } catch (Error & e) {
-            printMsg(lvlError, e.msg());
+            printMsg(lvlError, "%1%", Uncolored(e.msg()));
         } catch (Interrupted & e) {
-            printMsg(lvlError, e.msg());
+            printMsg(lvlError, "%1%", Uncolored(e.msg()));
         }
 
         // We handled the current input fully, so we should clear it
@@ -450,7 +454,7 @@ StringSet NixRepl::completePrefix(const std::string &prefix)
             e.eval(state, *env, v);
             state.forceAttrs(v, noPos, "while evaluating an attrset for the purpose of completion (this error should not be displayed; file an issue?)");
 
-            for (auto & i : *v.attrs) {
+            for (auto & i : *v.attrs()) {
                 std::ostringstream output;
                 printAttributeName(output, evaluator.symbols[i.name]);
                 std::string name = output.str();
@@ -653,7 +657,7 @@ ProcessLineResult NixRepl::processLine(std::string line)
                 auto path = state.coerceToPath(noPos, v, context, "while evaluating the filename to edit");
                 return {path, 0};
             } else if (v.isLambda()) {
-                auto pos = evaluator.positions[v.lambda.fun->pos];
+                auto pos = evaluator.positions[v.lambda().fun->pos];
                 if (auto path = std::get_if<CheckedSourcePath>(&pos.origin))
                     return {*path, pos.line};
                 else
@@ -788,7 +792,7 @@ ProcessLineResult NixRepl::processLine(std::string line)
         Value v;
         evalString(arg, v);
         if (v.type() == nString) {
-            std::cout << v.string.s;
+            std::cout << v.str();
         } else {
             printValue(std::cout, v);
         }
@@ -822,7 +826,7 @@ ProcessLineResult NixRepl::processLine(std::string line)
 
             logger->cout(trim(renderMarkdownToTerminal(markdown)));
         } else if (v.isLambda()) {
-            auto pos = evaluator.positions[v.lambda.fun->pos];
+            auto pos = evaluator.positions[v.lambda().fun->pos];
             if (auto path = std::get_if<CheckedSourcePath>(&pos.origin)) {
                 // Path and position have now been obtained, feed to nix-doc library to get data.
                 auto docComment = lambdaDocsForPos(*path, pos);
@@ -862,10 +866,10 @@ ProcessLineResult NixRepl::processLine(std::string line)
         std::visit(overloaded {
             [&](ExprReplBindings & b) {
                 for (auto & [name, e] : b.symbols) {
-                    Value * v = state.ctx.mem.allocValue();
-                    e->eval(state, *env, *v);
+                    Value v;
+                    e->eval(state, *env, v);
                     (void) e.release(); // NOLINT(bugprone-unused-return-value): leak because of thunk references
-                    addVarToScope(name, *v);
+                    addVarToScope(name, v);
                 }
             },
             [&](std::unique_ptr<Expr> & e) {
@@ -948,7 +952,7 @@ void NixRepl::loadFiles()
 
     for (auto & [i, what] : getValues()) {
         notice("Loading installable '%1%'...", Magenta(what));
-        addAttrsToScope(*i);
+        addAttrsToScope(i);
     }
 
     loadReplOverlays();
@@ -960,12 +964,12 @@ void NixRepl::loadReplOverlays()
         return;
     }
 
-    notice("Loading '%1%'...", Magenta("repl-overlays"));
+    notice("Loading '%1%'...", "repl-overlays");
     auto replInitFilesFunction = getReplOverlaysEvalFunction();
 
-    Value &newAttrs(*evaluator.mem.allocValue());
-    SmallValueVector<3> args = {replInitInfo(), bindingsToAttrs(), replOverlays()};
-    state.callFunction(*replInitFilesFunction, args.size(), args.data(), newAttrs, noPos);
+    Value newAttrs;
+    Value args[] = {replInitInfo(), bindingsToAttrs(), replOverlays()};
+    state.callFunction(replInitFilesFunction, args, newAttrs, noPos);
 
     // n.b. this does in fact load the stuff into the environment twice (once
     // from the superset of the environment returned by repl-overlays and once
@@ -975,14 +979,14 @@ void NixRepl::loadReplOverlays()
     addAttrsToScope(newAttrs);
 }
 
-Value * NixRepl::getReplOverlaysEvalFunction()
+Value NixRepl::getReplOverlaysEvalFunction()
 {
     if (replOverlaysEvalFunction && *replOverlaysEvalFunction) {
-        return *replOverlaysEvalFunction;
+        return **replOverlaysEvalFunction;
     }
 
     auto evalReplInitFilesPath = CanonPath::root + "repl-overlays.nix";
-    *replOverlaysEvalFunction = evaluator.mem.allocValue();
+    *replOverlaysEvalFunction = Value{};
     auto code =
         #include "repl-overlays.nix.gen.hh"
         ;
@@ -994,14 +998,14 @@ Value * NixRepl::getReplOverlaysEvalFunction()
 
     state.eval(expr, **replOverlaysEvalFunction);
 
-    return *replOverlaysEvalFunction;
+    return **replOverlaysEvalFunction;
 }
 
-Value * NixRepl::replOverlays()
+Value NixRepl::replOverlays()
 {
-    Value * replInits(evaluator.mem.allocValue());
-    *replInits = evaluator.mem.newList(evalSettings.replOverlays.get().size());
-    Value ** replInitElems = replInits->listElems();
+    Value replInits;
+    auto replInitStorage = evaluator.mem.newList(evalSettings.replOverlays.get().size());
+    replInits = {NewValueAs::list, replInitStorage};
 
     size_t i = 0;
     for (auto path : evalSettings.replOverlays.get()) {
@@ -1017,27 +1021,32 @@ Value * NixRepl::replOverlays()
         auto replInit = evalFile(sourcePath);
         evalSettings.pureEval.setDefault(prevPureEval);
 
-        if (!replInit->isLambda()) {
-            evaluator.errors.make<TypeError>(
-                "Expected `repl-overlays` entry %s to be a lambda but found %s: %s",
-                path,
-                showType(*replInit),
-                ValuePrinter(state, *replInit, errorPrintOptions)
-            )
-            .debugThrow();
-        }
-
-        if (auto attrs = dynamic_cast<AttrsPattern *>(replInit->lambda.fun->pattern.get()); attrs && !attrs->ellipsis) {
-            evaluator.errors.make<TypeError>(
-                "Expected first argument of %1% to have %2% to allow future versions of Lix to add additional attributes to the argument",
-                "repl-overlays",
-                "..."
-            )
-                .atPos(replInit->lambda.fun->pos)
+        if (!replInit.isLambda()) {
+            evaluator.errors
+                .make<TypeError>(
+                    "Expected `repl-overlays` entry %s to be a lambda but found %s: %s",
+                    path,
+                    showType(replInit),
+                    ValuePrinter(state, replInit, errorPrintOptions)
+                )
                 .debugThrow();
         }
 
-        replInitElems[i] = replInit;
+        if (auto attrs = dynamic_cast<AttrsPattern *>(replInit.lambda().fun->pattern.get());
+            attrs && !attrs->ellipsis)
+        {
+            evaluator.errors
+                .make<TypeError>(
+                    "Expected first argument of %1% to have %2% to allow future versions of Lix to "
+                    "add additional attributes to the argument",
+                    "repl-overlays",
+                    "..."
+                )
+                .atPos(replInit.lambda().fun->pos)
+                .debugThrow();
+        }
+
+        replInitStorage->elems[i] = replInit;
         i++;
     }
 
@@ -1045,16 +1054,16 @@ Value * NixRepl::replOverlays()
     return replInits;
 }
 
-Value * NixRepl::replInitInfo()
+Value NixRepl::replInitInfo()
 {
     auto builder = evaluator.buildBindings(2);
 
-    Value * currentSystem(evaluator.mem.allocValue());
-    currentSystem->mkString(evalSettings.getCurrentSystem());
+    Value currentSystem;
+    currentSystem.mkString(evalSettings.getCurrentSystem());
     builder.insert(evaluator.symbols.create("currentSystem"), currentSystem);
 
-    Value * info(evaluator.mem.allocValue());
-    info->mkAttrs(builder.finish());
+    Value info;
+    info.mkAttrs(builder.finish());
     return info;
 }
 
@@ -1089,7 +1098,9 @@ void NixRepl::addToScope(T && things, NameFn nameFn, ValueFn valueFn)
 void NixRepl::addAttrsToScope(Value & attrs)
 {
     state.forceAttrs(attrs, noPos, "while evaluating an attribute set to be merged in the global scope");
-    addToScope(*attrs.attrs, [](Attr & a) { return a.name; }, [](Attr & a) { return a.value; });
+    addToScope(
+        *attrs.attrs(), [](const Attr & a) { return a.name; }, [](const Attr & a) { return a.value; }
+    );
 }
 
 void NixRepl::addValMapToScope(const ValMap & attrs)
@@ -1110,19 +1121,19 @@ void NixRepl::addVarToScope(const Symbol name, Value & v)
     } else {
         notice("Added %s.", evaluator.symbols[name]);
     }
-    env->values[displ++] = &v;
+    env->values[displ++] = v;
     varNames.emplace(evaluator.symbols[name]);
 }
 
-Value * NixRepl::bindingsToAttrs()
+Value NixRepl::bindingsToAttrs()
 {
     auto builder = evaluator.buildBindings(staticEnv->vars.size());
     for (auto & [symbol, displacement] : staticEnv->vars) {
         builder.insert(symbol, env->values[displacement]);
     }
 
-    Value * attrs(evaluator.mem.allocValue());
-    attrs->mkAttrs(builder.finish());
+    Value attrs;
+    attrs.mkAttrs(builder.finish());
     return attrs;
 }
 
@@ -1145,12 +1156,12 @@ void NixRepl::evalString(std::string s, Value & v)
     state.forceValue(v, noPos);
 }
 
-Value * NixRepl::evalFile(SourcePath & path)
+Value NixRepl::evalFile(SourcePath & path)
 {
     auto & expr = evaluator.parseExprFromFile(evaluator.paths.checkSourcePath(path), staticEnv);
-    Value * result(evaluator.mem.allocValue());
-    expr.eval(state, *env, *result);
-    state.forceValue(*result, noPos);
+    Value result;
+    expr.eval(state, *env, result);
+    state.forceValue(result, noPos);
     return result;
 }
 

lix/libcmd/repl.hh

@@ -8,7 +8,7 @@ namespace nix {
 
 struct AbstractNixRepl : NeverAsync
 {
-    typedef std::vector<std::pair<Value*,std::string>> AnnotatedValues;
+    typedef std::vector<std::pair<Value, std::string>> AnnotatedValues;
 
     static ReplExitStatus
     run(const SearchPath & searchPath,

lix/libexpr/attr-path.cc

@@ -69,13 +69,12 @@ std::string unparseAttrPath(std::vector<std::string> const & attrPath)
     return ret.str();
 }
 
-
-std::pair<Value *, PosIdx> findAlongAttrPath(EvalState & state, const std::string & attrPath,
-    Bindings & autoArgs, Value & vIn)
+std::pair<Value, PosIdx>
+findAlongAttrPath(EvalState & state, const std::string & attrPath, Bindings & autoArgs, Value & vIn)
 {
     auto tokens = parseAttrPath(attrPath);
 
-    Value * v = &vIn;
+    Value v = vIn;
     PosIdx pos = noPos;
 
     for (auto [attrPathIdx, attr] : enumerate(tokens)) {
@@ -84,10 +83,10 @@ std::pair<Value *, PosIdx> findAlongAttrPath(EvalState & state, const std::strin
         auto attrIndex = string2Int<unsigned int>(attr);
 
         /* Evaluate the expression. */
-        Value * vNew = state.ctx.mem.allocValue();
-        state.autoCallFunction(autoArgs, *v, *vNew, pos);
+        Value vNew;
+        state.autoCallFunction(autoArgs, v, vNew, pos);
         v = vNew;
-        state.forceValue(*v, noPos);
+        state.forceValue(v, noPos);
 
         /* It should evaluate to either a set or an expression,
            according to what is specified in the attrPath. */
@@ -96,7 +95,7 @@ std::pair<Value *, PosIdx> findAlongAttrPath(EvalState & state, const std::strin
             if (attr.empty())
                 throw Error("empty attribute name in selection path '%1%'", attrPath);
 
-            if (v->type() != nAttrs) {
+            if (v.type() != nAttrs) {
                 auto pathPart =
                     std::vector<std::string>(tokens.begin(), tokens.begin() + attrPathIdx);
                 state.ctx.errors
@@ -105,17 +104,18 @@ std::pair<Value *, PosIdx> findAlongAttrPath(EvalState & state, const std::strin
                         "set but is %3%: %4%",
                         attrPath,
                         unparseAttrPath(pathPart),
-                        showType(*v),
-                        ValuePrinter(state, *v, errorPrintOptions)
+                        showType(v),
+                        ValuePrinter(state, v, errorPrintOptions)
                     )
                     .debugThrow();
             }
 
-            Bindings::iterator a = v->attrs->find(state.ctx.symbols.create(attr));
-            if (a == v->attrs->end()) {
+            auto a = v.attrs()->get(state.ctx.symbols.create(attr));
+            if (!a) {
                 std::set<std::string> attrNames;
-                for (auto & attr : *v->attrs)
-                    attrNames.insert(state.ctx.symbols[attr.name]);
+                for (auto & attr : *v.attrs()) {
+                    attrNames.emplace(state.ctx.symbols[attr.name]);
+                }
 
                 auto suggestions = Suggestions::bestMatches(attrNames, attr);
                 auto pathPart =
@@ -127,33 +127,33 @@ std::pair<Value *, PosIdx> findAlongAttrPath(EvalState & state, const std::strin
                     attr,
                     attrPath,
                     unparseAttrPath(pathPart),
-                    ValuePrinter(state, *v, errorPrintOptions)
+                    ValuePrinter(state, v, errorPrintOptions)
                 );
             }
-            v = &*a->value;
+            v = a->value;
             pos = a->pos;
         } else {
-            if (!v->isList()) {
+            if (!v.isList()) {
                 state.ctx.errors
                     .make<TypeError>(
                         "the expression selected by the selection path '%1%' should be a list but "
                         "is %2%: %3%",
                         attrPath,
-                        showType(*v),
-                        ValuePrinter(state, *v, errorPrintOptions)
+                        showType(v),
+                        ValuePrinter(state, v, errorPrintOptions)
                     )
                     .debugThrow();
             }
-            if (*attrIndex >= v->listSize()) {
+            if (*attrIndex >= v.listSize()) {
                 throw AttrPathNotFound(
                     "list index %1% in selection path '%2%' is out of range for list %3%",
                     *attrIndex,
                     attrPath,
-                    ValuePrinter(state, *v, errorPrintOptions)
+                    ValuePrinter(state, v, errorPrintOptions)
                 );
             }
 
-            v = v->listElems()[*attrIndex];
+            v = v.listElems()[*attrIndex];
             pos = noPos;
         }
 
@@ -165,7 +165,7 @@ std::pair<Value *, PosIdx> findAlongAttrPath(EvalState & state, const std::strin
 
 std::pair<SourcePath, uint32_t> findPackageFilename(EvalState & state, Value & v, std::string what)
 {
-    Value * v2;
+    Value v2;
     try {
         auto dummyArgs = state.ctx.mem.allocBindings(0);
         v2 = findAlongAttrPath(state, "meta.position", *dummyArgs, v).first;
@@ -176,7 +176,9 @@ std::pair<SourcePath, uint32_t> findPackageFilename(EvalState & state, Value & v
     // FIXME: is it possible to extract the Pos object instead of doing this
     //        toString + parsing?
     NixStringContext context;
-    auto path = state.coerceToPath(noPos, *v2, context, "while evaluating the 'meta.position' attribute of a derivation");
+    auto path = state.coerceToPath(
+        noPos, v2, context, "while evaluating the 'meta.position' attribute of a derivation"
+    );
 
     auto fn = path.canonical().abs();
 

lix/libexpr/attr-path.hh

@@ -10,11 +10,9 @@ namespace nix {
 MakeError(AttrPathNotFound, Error);
 MakeError(NoPositionInfo, Error);
 
-std::pair<Value *, PosIdx> findAlongAttrPath(
-    EvalState & state,
-    const std::string & attrPath,
-    Bindings & autoArgs,
-    Value & vIn);
+std::pair<Value, PosIdx> findAlongAttrPath(
+    EvalState & state, const std::string & attrPath, Bindings & autoArgs, Value & vIn
+);
 
 /**
  * Heuristic to find the filename and lineno or a nix value.

lix/libexpr/attr-set.cc

@@ -7,8 +7,7 @@
 
 namespace nix {
 
-Bindings Bindings::EMPTY{0};
-
+Bindings Bindings::EMPTY{};
 
 /* Allocate a new array of attributes for an attribute set with a specific
    capacity. The space is implicitly reserved after the Bindings
@@ -21,15 +20,14 @@ Bindings * EvalMemory::allocBindings(size_t capacity)
         throw Error("attribute set of size %d is too big", capacity);
     stats.nrAttrsets++;
     stats.nrAttrsInAttrsets += capacity;
-    return new (gcAllocBytes(sizeof(Bindings) + sizeof(Attr) * capacity)) Bindings((Bindings::Size) capacity);
+    return new (allocBytes(sizeof(Bindings) + sizeof(Attr) * capacity)) Bindings();
 }
 
 
 Value & BindingsBuilder::alloc(Symbol name, PosIdx pos)
 {
-    auto value = mem.allocValue();
-    bindings->push_back(Attr(name, value, pos));
-    return *value;
+    bindings->push_back(Attr(name, {}, pos));
+    return (bindings->end() - 1)->value;
 }
 
 

lix/libexpr/attr-set.hh

@@ -23,9 +23,8 @@ struct Attr
        way we keep Attr size at two words with no wasted space. */
     Symbol name;
     PosIdx pos;
-    Value * value;
-    Attr(Symbol name, Value * value, PosIdx pos = noPos)
-        : name(name), pos(pos), value(value) { };
+    mutable Value value;
+    Attr(Symbol name, Value value, PosIdx pos = noPos) : name(name), pos(pos), value(value) {}
     Attr() { };
     bool operator < (const Attr & a) const
     {
@@ -44,7 +43,7 @@ static_assert(sizeof(Attr) == 2 * sizeof(uint32_t) + sizeof(Value *),
  * elements allocated after this structure, while the size corresponds to
  * the number of elements already inserted in this structure.
  */
-class Bindings
+class alignas(Value::TAG_ALIGN) Bindings
 {
 public:
     using Size = uint32_t;
@@ -53,10 +52,10 @@ public:
     static Bindings EMPTY;
 
 private:
-    Size size_, capacity_;
+    Size size_ = 0;
     Attr attrs[0];
 
-    Bindings(Size capacity) : size_(0), capacity_(capacity) { }
+    Bindings() = default;
     Bindings(const Bindings & bindings) = delete;
 
 public:
@@ -68,21 +67,12 @@ public:
 
     void push_back(const Attr & attr)
     {
-        assert(size_ < capacity_);
         attrs[size_++] = attr;
     }
 
-    iterator find(Symbol name)
+    const Attr * get(Symbol name)
     {
-        Attr key(name, 0);
-        iterator i = std::lower_bound(begin(), end(), key);
-        if (i != end() && i->name == name) return i;
-        return end();
-    }
-
-    Attr * get(Symbol name)
-    {
-        Attr key(name, 0);
+        Attr key(name, {});
         iterator i = std::lower_bound(begin(), end(), key);
         if (i != end() && i->name == name) return &*i;
         return nullptr;
@@ -98,8 +88,6 @@ public:
 
     void sort();
 
-    Size capacity() { return capacity_; }
-
     /**
      * Returns the attributes in lexicographically sorted order.
      */
@@ -126,21 +114,28 @@ public:
  */
 class BindingsBuilder
 {
+public:
+    using Size = Bindings::Size;
+
+private:
     Bindings * bindings;
     EvalMemory & mem;
     SymbolTable & symbols;
+    Size capacity;
 
 public:
     // needed by std::back_inserter
     using value_type = Attr;
 
-    BindingsBuilder(EvalMemory & mem, SymbolTable & symbols, Bindings * bindings)
+    BindingsBuilder(EvalMemory & mem, SymbolTable & symbols, Bindings * bindings, Size capacity)
         : bindings(bindings)
         , mem(mem)
         , symbols(symbols)
-    { }
+        , capacity(capacity)
+    {
+    }
 
-    void insert(Symbol name, Value * value, PosIdx pos = noPos)
+    void insert(Symbol name, Value value, PosIdx pos = noPos)
     {
         insert(Attr(name, value, pos));
     }
@@ -152,6 +147,7 @@ public:
 
     void push_back(const Attr & attr)
     {
+        assert(bindings->size() < capacity);
         bindings->push_back(attr);
     }
 
@@ -159,6 +155,7 @@ public:
 
     Value & alloc(std::string_view name, PosIdx pos = noPos);
 
+    [[nodiscard("must use created bindings")]]
     Bindings * finish()
     {
         bindings->sort();

lix/libexpr/eval-cache.cc

@@ -341,7 +341,7 @@ EvalCache::EvalCache(
 {
 }
 
-Value * EvalCache::getRootValue(EvalState & state)
+Value & EvalCache::getRootValue(EvalState & state)
 {
     if (!value) {
         debug("getting root value");
@@ -362,8 +362,9 @@ AttrCursor::AttrCursor(
     std::optional<std::pair<AttrId, AttrValue>> && cachedValue)
     : root(root), parent(parent), cachedValue(std::move(cachedValue))
 {
-    if (value)
-        _value = allocRootValue(value);
+    if (value) {
+        _value = allocRootValue(*value);
+    }
 }
 
 AttrKey AttrCursor::getKey()
@@ -383,14 +384,14 @@ Value & AttrCursor::getValue(EvalState & state)
         if (parent) {
             auto & vParent = parent->first->getValue(state);
             state.forceAttrs(vParent, noPos, "while searching for an attribute");
-            auto attr = vParent.attrs->get(state.ctx.symbols.create(parent->second));
+            auto attr = vParent.attrs()->get(state.ctx.symbols.create(parent->second));
             if (!attr)
                 throw Error("attribute '%s' is unexpectedly missing", getAttrPathStr(state));
             _value = allocRootValue(attr->value);
         } else
             _value = allocRootValue(root->getRootValue(state));
     }
-    return **_value;
+    return *_value;
 }
 
 std::vector<std::string> AttrCursor::getAttrPath(EvalState & state) const
@@ -437,16 +438,17 @@ Value & AttrCursor::forceValue(EvalState & state)
 
     if (root->db && (!cachedValue || std::get_if<placeholder_t>(&cachedValue->second))) {
         if (v.type() == nString)
-            cachedValue = {root->db->setString(getKey(), v.string.s, v.string.context),
-                           string_t{v.string.s, {}}};
+            cachedValue = {
+                root->db->setString(getKey(), v.str(), v.string().context), string_t{v.str(), {}}
+            };
         else if (v.type() == nPath) {
             auto path = v.path().canonical().abs();
             cachedValue = {root->db->setString(getKey(), path), string_t{path, {}}};
         }
         else if (v.type() == nBool)
-            cachedValue = {root->db->setBool(getKey(), v.boolean), v.boolean};
+            cachedValue = {root->db->setBool(getKey(), v.boolean()), v.boolean()};
         else if (v.type() == nInt)
-            cachedValue = {root->db->setInt(getKey(), v.integer.value), int_t{v.integer}};
+            cachedValue = {root->db->setInt(getKey(), v.integer().value), int_t{v.integer()}};
         else if (v.type() == nAttrs)
             ; // FIXME: do something?
         else
@@ -499,7 +501,7 @@ std::shared_ptr<AttrCursor> AttrCursor::maybeGetAttr(EvalState & state, const st
         return nullptr;
         //errors.make<TypeError>("'%s' is not an attribute set", getAttrPathStr()).debugThrow();
 
-    auto attr = v.attrs->get(state.ctx.symbols.create(name));
+    auto attr = v.attrs()->get(state.ctx.symbols.create(name));
 
     if (!attr) {
         if (root->db) {
@@ -518,7 +520,8 @@ std::shared_ptr<AttrCursor> AttrCursor::maybeGetAttr(EvalState & state, const st
     }
 
     return make_ref<AttrCursor>(
-        root, std::make_pair(shared_from_this(), name), attr->value, std::move(cachedValue2));
+        root, std::make_pair(shared_from_this(), name), &attr->value, std::move(cachedValue2)
+    );
 }
 
 ref<AttrCursor> AttrCursor::getAttr(EvalState & state, const std::string & name)
@@ -563,7 +566,7 @@ std::string AttrCursor::getString(EvalState & state)
         state.ctx.errors.make<TypeError>("'%s' is not a string but %s", getAttrPathStr(state), v.type()).debugThrow();
     }
 
-    return v.type() == nString ? v.string.s : v.path().to_string();
+    return v.type() == nString ? std::string(v.str()) : v.path().to_string();
 }
 
 string_t AttrCursor::getStringWithContext(EvalState & state)
@@ -605,7 +608,7 @@ string_t AttrCursor::getStringWithContext(EvalState & state)
     if (v.type() == nString) {
         NixStringContext context;
         copyContext(v, context);
-        return {v.string.s, std::move(context)};
+        return {std::string(v.str()), std::move(context)};
     } else if (v.type() == nPath) {
         return {v.path().to_string(), {}};
     } else {
@@ -632,7 +635,7 @@ bool AttrCursor::getBool(EvalState & state)
     if (v.type() != nBool)
         state.ctx.errors.make<TypeError>("'%s' is not a Boolean", getAttrPathStr(state)).debugThrow();
 
-    return v.boolean;
+    return v.boolean();
 }
 
 NixInt AttrCursor::getInt(EvalState & state)
@@ -654,7 +657,7 @@ NixInt AttrCursor::getInt(EvalState & state)
     if (v.type() != nInt)
         state.ctx.errors.make<TypeError>("'%s' is not an integer", getAttrPathStr(state)).debugThrow();
 
-    return v.integer;
+    return v.integer();
 }
 
 std::vector<std::string> AttrCursor::getListOfStrings(EvalState & state)
@@ -681,11 +684,15 @@ std::vector<std::string> AttrCursor::getListOfStrings(EvalState & state)
 
     std::vector<std::string> res;
 
-    for (auto & elem : v.listItems())
-        res.push_back(std::string(state.forceStringNoCtx(*elem, noPos, "while evaluating an attribute for caching")));
+    for (auto & elem : v.listItems()) {
+        res.push_back(std::string(
+            state.forceStringNoCtx(elem, noPos, "while evaluating an attribute for caching")
+        ));
+    }
 
-    if (root->db)
+    if (root->db) {
         cachedValue = {root->db->setListOfStrings(getKey(), res), res};
+    }
 
     return res;
 }
@@ -710,8 +717,8 @@ std::vector<std::string> AttrCursor::getAttrs(EvalState & state)
         state.ctx.errors.make<TypeError>("'%s' is not an attribute set", getAttrPathStr(state)).debugThrow();
 
     fullattr_t attrs;
-    for (auto & attr : *getValue(state).attrs)
-        attrs.p.push_back(state.ctx.symbols[attr.name]);
+    for (auto & attr : *getValue(state).attrs())
+        attrs.p.emplace_back(state.ctx.symbols[attr.name]);
     std::sort(attrs.p.begin(), attrs.p.end());
 
     if (root->db)

lix/libexpr/eval-cache.hh

@@ -12,7 +12,7 @@ namespace nix::eval_cache {
 struct AttrDb;
 class AttrCursor;
 
-typedef std::function<Value *(EvalState &)> RootLoader;
+typedef std::function<Value(EvalState &)> RootLoader;
 
 /**
  * EvalState with caching support. Historically this was part of EvalState,
@@ -42,7 +42,7 @@ class EvalCache : public std::enable_shared_from_this<EvalCache>
     RootLoader rootLoader;
     RootValue value;
 
-    Value * getRootValue(EvalState & state);
+    Value & getRootValue(EvalState & state);
 
 public:
 

lix/libexpr/eval-inline.hh

@@ -5,59 +5,95 @@
 #include "lix/libexpr/eval.hh"
 #include "lix/libexpr/eval-error.hh"
 #include "lix/libexpr/gc-alloc.hh"
+#include "value.hh"
+#include <cstdint>
 
 namespace nix {
 
+inline Value::Value(app_t, EvalMemory & mem, Value & lhs, Value & rhs)
+{
+    auto app = static_cast<Value::App *>(mem.allocBytes(sizeof(Value::App) + sizeof(Value *)));
+    app->_left = lhs;
+    app->_n = 1;
+    app->_args[0] = rhs;
+    raw = tag(tApp, app);
+}
+
+inline Value::Value(app_t, EvalMemory & mem, Value & lhs, std::span<Value> args)
+{
+    auto app = static_cast<Value::App *>(mem.allocBytes(sizeof(Value::App) + args.size_bytes()));
+    app->_left = lhs;
+    app->_n = args.size();
+    std::copy(args.begin(), args.end(), app->_args);
+    raw = tag(tApp, app);
+}
+
+inline Value::Value(thunk_t, EvalMemory & mem, Env & env, Expr & expr)
+{
+    auto thunk = mem.allocType<Thunk>();
+    *thunk = {._env = &env, .expr = &expr};
+    raw = tag(tThunk, thunk);
+}
+
+inline Value::Value(lambda_t, EvalMemory & mem, Env & env, ExprLambda & lambda)
+{
+    auto lp = mem.allocType<Lambda>();
+    new (lp) Lambda{env, lambda};
+    raw = tag(tAuxiliary, lp);
+}
+
 [[gnu::always_inline]]
-Value * EvalMemory::allocValue()
+void * EvalMemory::allocBytes(size_t size)
 {
 #if HAVE_BOEHMGC
     /* We use the boehm batch allocator to speed up allocations of Values (of which there are many).
        GC_malloc_many returns a linked list of objects of the given size, where the first word
        of each object is also the pointer to the next object in the list. This also means that we
        have to explicitly clear the first word of every object we take. */
-    if (!*valueAllocCache) {
-        *valueAllocCache = GC_malloc_many(sizeof(Value));
-        if (!*valueAllocCache) throw std::bad_alloc();
-    }
+    // NOTE: we purposely do not allocate 0 byte blocks on caches; we never allocate
+    // zero bytes anyway, and it makes cache index calculation a little bit simpler.
+    const auto cacheIdx = (size - 1) / CACHE_INCREMENT;
+    if (cacheIdx < CACHES) {
+        const auto roundedSize = (cacheIdx + 1) * CACHE_INCREMENT;
+        auto & cache = gcCache[cacheIdx];
+        if (!cache) {
+            cache = GC_malloc_many(roundedSize);
+            if (!cache) {
+                throw std::bad_alloc();
+            }
+        }
 
-    /* GC_NEXT is a convenience macro for accessing the first word of an object.
-       Take the first list item, advance the list to the next item, and clear the next pointer. */
-    void * p = *valueAllocCache;
-    *valueAllocCache = GC_NEXT(p);
-    GC_NEXT(p) = nullptr;
-#else
-    void * p = gcAllocBytes(sizeof(Value));
+        /* GC_NEXT is a convenience macro for accessing the first word of an object.
+           Take the first list item, advance the list to the next item, and clear the next pointer.
+         */
+        void * p = cache;
+        cache = GC_NEXT(p);
+        GC_NEXT(p) = nullptr;
+        return p;
+    }
 #endif
 
-    stats.nrValues++;
-    return static_cast<Value *>(p);
+    return gcAllocBytes(size);
 }
 
+/// `gcAllocType`, but using allocation caches to amortize allocation overhead.
+template<typename T>
+[[gnu::always_inline]]
+T * EvalMemory::allocType(size_t n)
+{
+    // NOLINTNEXTLINE(bugprone-sizeof-expression)
+    return static_cast<T *>(allocBytes(checkedArrayAllocSize(sizeof(T), n)));
+}
 
 [[gnu::always_inline]]
 Env & EvalMemory::allocEnv(size_t size)
 {
+    static_assert(CACHES * CACHE_INCREMENT >= sizeof(Env) + sizeof(Value *));
+
     stats.nrEnvs++;
     stats.nrValuesInEnvs += size;
 
-    Env * env;
-
-#if HAVE_BOEHMGC
-    if (size == 1) {
-        /* see allocValue for explanations. */
-        if (!*env1AllocCache) {
-            *env1AllocCache = GC_malloc_many(sizeof(Env) + sizeof(Value *));
-            if (!*env1AllocCache) throw std::bad_alloc();
-        }
-
-        void * p = *env1AllocCache;
-        *env1AllocCache = GC_NEXT(p);
-        GC_NEXT(p) = nullptr;
-        env = static_cast<Env *>(p);
-    } else
-#endif
-        env = static_cast<Env *>(gcAllocBytes(sizeof(Env) + size * sizeof(Value *)));
+    Env * env = static_cast<Env *>(allocBytes(sizeof(Env) + size * sizeof(Value *)));
 
     /* We assume that env->values has been cleared by the allocator; maybeThunk() and lookupVar fromWith expect this. */
 
@@ -69,22 +105,38 @@ Env & EvalMemory::allocEnv(size_t size)
 void EvalState::forceValue(Value & v, const PosIdx pos)
 {
     if (v.isThunk()) {
-        Env * env = v.thunk.env;
-        Expr & expr = *v.thunk.expr;
-        try {
-            v.mkBlackhole();
-            expr.eval(*this, *env, v);
-        } catch (...) {
-            v.mkThunk(env, expr);
-            tryFixupBlackHolePos(v, pos);
-            throw;
+        auto & thunk = v.thunk();
+        if (thunk.resolved()) {
+            v = thunk.result();
+        } else {
+            const auto backup = thunk;
+            Env * env = thunk.env();
+            Expr & expr = *thunk.expr;
+            thunk = Value::blackHole;
+            try {
+                expr.eval(*this, *env, v);
+                thunk.resolve(v);
+            } catch (...) {
+                thunk = backup;
+                tryFixupBlackHolePos(v, pos);
+                throw;
+            }
+        }
+    } else if (v.isApp()) {
+        auto & app = v.app();
+        if (app.resolved()) {
+            v = app.result();
+        } else {
+            auto target = app.target();
+            if (!target.isPrimOp() || target.primOp()->arity <= app.totalArgs()) {
+                auto tmp = v.app().left();
+                callFunction(tmp, v.app().args(), v, pos);
+                app.resolve(v);
+            }
         }
     }
-    else if (v.isApp())
-        callFunction(*v.app.left, *v.app.right, v, pos);
 }
 
-
 [[gnu::always_inline]]
 inline void EvalState::forceAttrs(Value & v, const PosIdx pos, std::string_view errorCtx)
 {

lix/libexpr/eval-settings.cc

@@ -82,7 +82,7 @@ bool EvalSettings::isPseudoUrl(std::string_view s)
 std::string EvalSettings::resolvePseudoUrl(std::string_view url)
 {
     if (url.starts_with("channel:"))
-        return "https://nixos.org/channels/" + std::string(url.substr(8)) + "/nixexprs.tar.xz";
+        return "https://channels.nixos.org/" + std::string(url.substr(8)) + "/nixexprs.tar.xz";
     else
         return std::string(url);
 }

lix/libexpr/eval.hh

@@ -36,52 +36,7 @@ namespace eval_cache {
     class EvalCache;
 }
 
-/**
- * Function that implements a primop.
- */
-using PrimOpImpl = void(EvalState & state, Value ** args, Value & v);
-
-/**
- * Info about a primitive operation, and its implementation
- */
-struct PrimOp
-{
-    /**
-     * Name of the primop. `__` prefix is treated specially.
-     */
-    std::string name;
-
-    /**
-     * Names of the parameters of a primop, for primops that take a
-     * fixed number of arguments to be substituted for these parameters.
-     */
-    std::vector<std::string> args;
-
-    /**
-     * Aritiy of the primop.
-     *
-     * If `args` is not empty, this field will be computed from that
-     * field instead, so it doesn't need to be manually set.
-     */
-    size_t arity = 0;
-
-    /**
-     * Optional free-form documentation about the primop.
-     */
-    const char * doc = nullptr;
-
-    /**
-     * Implementation of the primop.
-     */
-    std::function<PrimOpImpl> fun;
-
-    /**
-     * Optional experimental for this to be gated on.
-     */
-    std::optional<ExperimentalFeature> experimentalFeature;
-};
-
-std::ostream & operator<<(std::ostream & output, PrimOp & primOp);
+std::ostream & operator<<(std::ostream & output, const PrimOp & primOp);
 
 /**
  * Info about a constant
@@ -106,12 +61,12 @@ struct Constant
     bool impureOnly = false;
 };
 
-using ValMap = GcMap<std::string, Value *>;
+using ValMap = GcMap<std::string, Value>;
 
-struct Env
+struct alignas(Value::Acb::TAG_ALIGN) Env
 {
     Env * up;
-    Value * values[0];
+    Value values[0];
 };
 
 void printEnvBindings(const EvalState &es, const Expr & expr, const Env & env);
@@ -224,43 +179,44 @@ struct StaticSymbols
 
 class EvalMemory
 {
-    /**
-     * Allocation cache for GC'd Value objects.
-     */
-    std::shared_ptr<void *> valueAllocCache;
+    static constexpr size_t CACHES = 8;
+    static constexpr size_t CACHE_INCREMENT = sizeof(void *);
 
     /**
-     * Allocation cache for size-1 Env objects.
+     * Allocation caches for small values.
      */
-    std::shared_ptr<void *> env1AllocCache;
+    void * gcCache[CACHES] = {};
 
 public:
     struct Statistics
     {
         unsigned long nrEnvs = 0;
         unsigned long nrValuesInEnvs = 0;
-        unsigned long nrValues = 0;
         unsigned long nrAttrsets = 0;
         unsigned long nrAttrsInAttrsets = 0;
         unsigned long nrListElems = 0;
     };
 
     EvalMemory();
+    ~EvalMemory();
 
     EvalMemory(const EvalMemory &) = delete;
     EvalMemory(EvalMemory &&) = delete;
     EvalMemory & operator=(const EvalMemory &) = delete;
     EvalMemory & operator=(EvalMemory &&) = delete;
 
-    inline Value * allocValue();
+    inline void * allocBytes(size_t size);
+    template<typename T>
+    inline T * allocType(size_t n = 1);
+
     inline Env & allocEnv(size_t size);
 
     Bindings * allocBindings(size_t capacity);
-    Value newList(size_t length);
+    Value::List * newList(size_t length);
 
     BindingsBuilder buildBindings(SymbolTable & symbols, size_t capacity)
     {
-        return BindingsBuilder(*this, symbols, allocBindings(capacity));
+        return BindingsBuilder(*this, symbols, allocBindings(capacity), capacity);
     }
 
     const Statistics getStats() const { return stats; }
@@ -307,11 +263,9 @@ private:
 
     void createBaseEnv(const SearchPath & searchPath, const Path & storeDir);
 
-    Value * addConstant(const std::string & name, const Value & v, Constant info);
+    void addConstant(const std::string & name, const Value & v, Constant info);
 
-    void addConstant(const std::string & name, Value * v, Constant info);
-
-    Value * addPrimOp(PrimOp && primOp);
+    void addPrimOp(PrimOpDetails primOp);
 
     Value prepareNixPath(const SearchPath & searchPath);
 
@@ -839,13 +793,11 @@ public:
 
     bool isFunctor(Value & fun);
 
-    // FIXME: use std::span
-    void callFunction(Value & fun, size_t nrArgs, Value * * args, Value & vRes, const PosIdx pos);
+    void callFunction(Value & fun, std::span<Value> args, Value & vRes, const PosIdx pos);
 
     void callFunction(Value & fun, Value & arg, Value & vRes, const PosIdx pos)
     {
-        Value * args[] = {&arg};
-        callFunction(fun, 1, args, vRes, pos);
+        callFunction(fun, {&arg, 1}, vRes, pos);
     }
 
     /**
@@ -885,7 +837,8 @@ public:
         const SingleDerivedPath & p,
         Value & v);
 
-    void concatLists(Value & v, size_t nrLists, Value * * lists, const PosIdx pos, std::string_view errorCtx);
+    void
+    concatLists(Value & v, std::span<Value> lists, const PosIdx pos, std::string_view errorCtx);
 
 private:
 

lix/libexpr/flake/config.cc

@@ -41,14 +41,24 @@ static bool askForSetting(
     auto reply = logger->ask(fmt("Do you want to allow configuration setting '%s' to be set to '" ANSI_RED "%s" ANSI_NORMAL "'?\nThis may allow the flake to gain root, see the nix.conf manual page (" ANSI_BOLD "y" ANSI_NORMAL "es/" ANSI_BOLD "n" ANSI_NORMAL "o/" ANSI_BOLD "N" ANSI_NORMAL "o to all) ", name, valueS)).value_or('n');
 
     if (reply == 'N') {
-        warn("Rejecting all untrusted nix.conf entries");
-        warn("you can set '%s' to '%b' to automatically reject configuration options supplied by flakes", "accept-flake-config", false);
+        printTaggedWarning("Rejecting all untrusted nix.conf entries");
+        printTaggedWarning(
+            "you can set '%s' to '%b' to automatically reject configuration options supplied by "
+            "flakes",
+            "accept-flake-config",
+            false
+        );
         negativeTrustOverride = true;
     } else {
         if (std::tolower(reply) == 'y') {
             trusted = true;
         } else {
-            warn("you can set '%s' to '%b' to automatically reject configuration options supplied by flakes", "accept-flake-config", false);
+            printTaggedWarning(
+                "you can set '%s' to '%b' to automatically reject configuration options supplied "
+                "by flakes",
+                "accept-flake-config",
+                false
+            );
         }
 
         if (std::tolower(logger->ask(fmt("do you want to permanently (in %s) mark this value as %s? (y/N) ", trustedListPath(), trusted ? "trusted": "untrusted" )).value_or('n')) == 'y') {
@@ -117,7 +127,12 @@ void ConfigFile::apply()
             debug("accepting trusted flake configuration setting '%s'", name);
             globalConfig.set(name, valueS);
         } else {
-            warn("ignoring untrusted flake configuration setting '%s', pass '%s' to trust it (may allow the flake to gain root, see the nix.conf manual page)", name, "--accept-flake-config");
+            printTaggedWarning(
+                "ignoring untrusted flake configuration setting '%s', pass '%s' to trust it (may "
+                "allow the flake to gain root, see the nix.conf manual page)",
+                name,
+                "--accept-flake-config"
+            );
         }
     }
 }

lix/libexpr/flake/flake.cc

@@ -94,15 +94,67 @@ static void expectType(EvalState & state, ValueType type,
             showType(type), showType(value.type()), state.ctx.positions[pos]);
 }
 
-static std::map<FlakeId, FlakeInput> parseFlakeInputs(
-    EvalState & state, Value * value, const PosIdx pos,
-    const std::optional<Path> & baseDir, InputPath lockRootPath, unsigned depth);
+static std::pair<std::map<FlakeId, FlakeInput>, std::optional<fetchers::Attrs>> parseFlakeInputs(
+    EvalState & state,
+    Value & value,
+    const PosIdx pos,
+    const std::optional<Path> & baseDir,
+    InputPath lockRootPath,
+    unsigned depth,
+    bool allowSelf
+);
 
-static FlakeInput parseFlakeInput(EvalState & state,
-    const std::string & inputName, Value * value, const PosIdx pos,
-    const std::optional<Path> & baseDir, InputPath lockRootPath, unsigned depth)
+static void parseFlakeInputAttr(EvalState & state, const Attr & attr, fetchers::Attrs & attrs)
 {
-    expectType(state, nAttrs, *value, pos);
+// Allow selecting a subset of enum values
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wswitch-enum"
+    switch (attr.value.type()) {
+    case nString:
+        attrs.emplace(state.ctx.symbols[attr.name], std::string(attr.value.str()));
+        break;
+    case nBool:
+        attrs.emplace(state.ctx.symbols[attr.name], Explicit<bool>{attr.value.boolean()});
+        break;
+    case nInt: {
+        auto intValue = attr.value.integer().value;
+
+        if (intValue < 0) {
+            state.ctx.errors
+                .make<EvalError>(
+                    "negative value given for flake input attribute %1%: %2%",
+                    state.ctx.symbols[attr.name],
+                    intValue
+                )
+                .debugThrow();
+        }
+        uint64_t asUnsigned = intValue;
+        attrs.emplace(state.ctx.symbols[attr.name], asUnsigned);
+        break;
+    }
+    default:
+        state.ctx.errors
+            .make<TypeError>(
+                "flake input attribute '%s' is %s while a string, Boolean, or integer is expected",
+                state.ctx.symbols[attr.name],
+                showType(attr.value)
+            )
+            .debugThrow();
+    }
+#pragma GCC diagnostic pop
+}
+
+static FlakeInput parseFlakeInput(
+    EvalState & state,
+    const std::string & inputName,
+    Value & value,
+    const PosIdx pos,
+    const std::optional<Path> & baseDir,
+    InputPath lockRootPath,
+    unsigned depth
+)
+{
+    expectType(state, nAttrs, value, pos);
 
     FlakeInput input;
 
@@ -114,48 +166,28 @@ static FlakeInput parseFlakeInput(EvalState & state,
     fetchers::Attrs attrs;
     std::optional<std::string> url;
 
-    for (nix::Attr attr : *(value->attrs)) {
+    for (nix::Attr attr : *(value.attrs())) {
         try {
             if (attr.name == sUrl) {
-                expectType(state, nString, *attr.value, attr.pos);
-                url = attr.value->string.s;
+                expectType(state, nString, attr.value, attr.pos);
+                url = attr.value.str();
                 attrs.emplace("url", *url);
             } else if (attr.name == sFlake) {
-                expectType(state, nBool, *attr.value, attr.pos);
-                input.isFlake = attr.value->boolean;
+                expectType(state, nBool, attr.value, attr.pos);
+                input.isFlake = attr.value.boolean();
             } else if (attr.name == sInputs) {
-                input.overrides = parseFlakeInputs(state, attr.value, attr.pos, baseDir, lockRootPath, depth + 1);
+                input.overrides =
+                    parseFlakeInputs(
+                        state, attr.value, attr.pos, baseDir, lockRootPath, depth + 1, false
+                    )
+                        .first;
             } else if (attr.name == sFollows) {
-                expectType(state, nString, *attr.value, attr.pos);
-                auto follows(parseInputPath(attr.value->string.s));
+                expectType(state, nString, attr.value, attr.pos);
+                auto follows(parseInputPath(attr.value.str()));
                 follows.insert(follows.begin(), lockRootPath.begin(), lockRootPath.end());
                 input.follows = follows;
             } else {
-                // Allow selecting a subset of enum values
-                #pragma GCC diagnostic push
-                #pragma GCC diagnostic ignored "-Wswitch-enum"
-                switch (attr.value->type()) {
-                    case nString:
-                        attrs.emplace(state.ctx.symbols[attr.name], attr.value->string.s);
-                        break;
-                    case nBool:
-                        attrs.emplace(state.ctx.symbols[attr.name], Explicit<bool> { attr.value->boolean });
-                        break;
-                    case nInt: {
-                        auto intValue = attr.value->integer.value;
-
-                        if (intValue < 0) {
-                            state.ctx.errors.make<EvalError>("negative value given for flake input attribute %1%: %2%", state.ctx.symbols[attr.name], intValue).debugThrow();
-                        }
-                        uint64_t asUnsigned = intValue;
-                        attrs.emplace(state.ctx.symbols[attr.name], asUnsigned);
-                        break;
-                    }
-                    default:
-                        state.ctx.errors.make<TypeError>("flake input attribute '%s' is %s while a string, Boolean, or integer is expected",
-                            state.ctx.symbols[attr.name], showType(*attr.value)).debugThrow();
-                }
-                #pragma GCC diagnostic pop
+                parseFlakeInputAttr(state, attr, attrs);
             }
         } catch (Error & e) {
             e.addTrace(
@@ -190,26 +222,72 @@ static FlakeInput parseFlakeInput(EvalState & state,
     return input;
 }
 
-static std::map<FlakeId, FlakeInput> parseFlakeInputs(
-    EvalState & state, Value * value, const PosIdx pos,
-    const std::optional<Path> & baseDir, InputPath lockRootPath, unsigned depth)
+static std::pair<std::map<FlakeId, FlakeInput>, std::optional<fetchers::Attrs>> parseFlakeInputs(
+    EvalState & state,
+    Value & value,
+    const PosIdx pos,
+    const std::optional<Path> & baseDir,
+    InputPath lockRootPath,
+    unsigned depth,
+    bool allowSelf = true
+)
 {
     std::map<FlakeId, FlakeInput> inputs;
 
-    expectType(state, nAttrs, *value, pos);
+    expectType(state, nAttrs, value, pos);
 
-    for (nix::Attr & inputAttr : *(*value).attrs) {
-        inputs.emplace(state.ctx.symbols[inputAttr.name],
-            parseFlakeInput(state,
-                state.ctx.symbols[inputAttr.name],
-                inputAttr.value,
-                inputAttr.pos,
-                baseDir,
-                lockRootPath,
-                depth));
+    std::optional<fetchers::Attrs> selfAttrs = std::nullopt;
+    for (const nix::Attr & inputAttr : *value.attrs()) {
+        std::string inputName{state.ctx.symbols[inputAttr.name]};
+        if (inputName == "self") {
+            experimentalFeatureSettings.require(Xp::FlakeSelfAttrs);
+
+            if (!allowSelf) {
+                throw Error(
+                    "'self' input attributes not allowed at %s", state.ctx.positions[inputAttr.pos]
+                );
+            }
+            expectType(state, nAttrs, inputAttr.value, inputAttr.pos);
+
+            selfAttrs = selfAttrs.value_or(fetchers::Attrs{});
+            for (auto & attr : *inputAttr.value.attrs()) {
+                parseFlakeInputAttr(state, attr, *selfAttrs);
+            }
+        } else {
+            inputs.emplace(
+                inputName,
+                parseFlakeInput(
+                    state, inputName, inputAttr.value, inputAttr.pos, baseDir, lockRootPath, depth
+                )
+            );
+        }
     }
 
-    return inputs;
+    return {inputs, selfAttrs};
+}
+
+static std::optional<FlakeRef> applySelfAttrs(const FlakeRef & ref, const Flake & flake)
+{
+    // silently failing here is ok; since the parser requires the feature, we'll
+    // crash much earlier if it wasn't enabled
+    if (!flake.selfAttrs.has_value() || !experimentalFeatureSettings.isEnabled(Xp::FlakeSelfAttrs))
+    {
+        return std::nullopt;
+    }
+
+    static std::set<std::string> allowedAttrs{"submodules"};
+    auto newRef(ref);
+
+    for (auto & attr : *flake.selfAttrs) {
+        if (!allowedAttrs.contains(attr.first)) {
+            throw Error("flake 'self' attribute '%s' is not supported", attr.first);
+        }
+        newRef.input.attrs.insert_or_assign(attr.first, attr.second);
+    }
+    if (newRef != ref) {
+        return newRef;
+    }
+    return std::nullopt;
 }
 
 static Flake getFlake(
@@ -256,26 +334,55 @@ static Flake getFlake(
     Value vInfo;
     state.eval(flakeExpr, vInfo);
 
-    if (auto description = vInfo.attrs->get(state.ctx.s.description)) {
-        expectType(state, nString, *description->value, description->pos);
-        flake.description = description->value->string.s;
+    if (auto description = vInfo.attrs()->get(state.ctx.s.description)) {
+        expectType(state, nString, description->value, description->pos);
+        flake.description = description->value.str();
     }
 
     auto sInputs = state.ctx.symbols.create("inputs");
 
-    if (auto inputs = vInfo.attrs->get(sInputs))
-        flake.inputs = parseFlakeInputs(state, inputs->value, inputs->pos, flakeDir, lockRootPath, 0);
+    if (auto inputs = vInfo.attrs()->get(sInputs)) {
+        auto [flakeInputs, selfAttrs] =
+            parseFlakeInputs(state, inputs->value, inputs->pos, flakeDir, lockRootPath, 0, true);
+        flake.inputs = std::move(flakeInputs);
+        flake.selfAttrs = std::move(selfAttrs);
+    }
 
-    if (auto outputs = vInfo.attrs->get(state.ctx.s.outputs)) {
-        expectType(state, nFunction, *outputs->value, outputs->pos);
+    auto newLockedRef = applySelfAttrs(lockedRef, flake);
+    if (newLockedRef.has_value()) {
+        debug("refetching input '%s' due to self attribute", *newLockedRef);
+        // FIXME: need to remove attrs that are invalidated by the changed input
+        // attrs, such as 'narHash'.
+        newLockedRef->input.attrs.erase("narHash");
+        auto [sourceInfo2, resolvedRef2, lockedRef2] =
+            state.aio.blockOn(fetchOrSubstituteTree(state.ctx, *newLockedRef, false, flakeCache));
 
-        if (outputs->value->isLambda()) {
-            if (auto pattern = dynamic_cast<AttrsPattern *>(outputs->value->lambda.fun->pattern.get()); pattern) {
+        lockedRef = lockedRef2;
+        flake.lockedRef = lockedRef;
+
+        sourceInfo = sourceInfo2;
+        flake.sourceInfo = std::make_shared<fetchers::Tree>(std::move(sourceInfo));
+
+        resolvedRef = resolvedRef2;
+        flake.resolvedRef = resolvedRef;
+    }
+
+    if (auto outputs = vInfo.attrs()->get(state.ctx.s.outputs)) {
+        expectType(state, nFunction, outputs->value, outputs->pos);
+
+        if (outputs->value.isLambda()) {
+            if (auto pattern =
+                    dynamic_cast<AttrsPattern *>(outputs->value.lambda().fun->pattern.get());
+                pattern)
+            {
                 for (auto & formal : pattern->formals) {
                     if (formal.name != state.ctx.s.self)
-                        flake.inputs.emplace(state.ctx.symbols[formal.name], FlakeInput {
-                            .ref = parseFlakeRef(state.ctx.symbols[formal.name])
-                        });
+                        flake.inputs.emplace(
+                            state.ctx.symbols[formal.name],
+                            FlakeInput{
+                                .ref = parseFlakeRef(std::string(state.ctx.symbols[formal.name]))
+                            }
+                        );
                 }
             }
         }
@@ -285,46 +392,71 @@ static Flake getFlake(
 
     auto sNixConfig = state.ctx.symbols.create("nixConfig");
 
-    if (auto nixConfig = vInfo.attrs->get(sNixConfig)) {
-        expectType(state, nAttrs, *nixConfig->value, nixConfig->pos);
+    if (auto nixConfig = vInfo.attrs()->get(sNixConfig)) {
+        expectType(state, nAttrs, nixConfig->value, nixConfig->pos);
 
-        for (auto & setting : *nixConfig->value->attrs) {
-            forceTrivialValue(state, *setting.value, setting.pos);
-            if (setting.value->type() == nString)
+        for (auto & setting : *nixConfig->value.attrs()) {
+            forceTrivialValue(state, setting.value, setting.pos);
+            if (setting.value.type() == nString) {
                 flake.config.settings.emplace(
                     state.ctx.symbols[setting.name],
-                    std::string(state.forceStringNoCtx(*setting.value, setting.pos, "")));
-            else if (setting.value->type() == nPath) {
+                    std::string(state.forceStringNoCtx(setting.value, setting.pos, ""))
+                );
+            } else if (setting.value.type() == nPath) {
                 NixStringContext emptyContext = {};
                 flake.config.settings.emplace(
                     state.ctx.symbols[setting.name],
-                    state.coerceToString(setting.pos, *setting.value, emptyContext, "", StringCoercionMode::Strict, true, true) .toOwned());
-            }
-            else if (setting.value->type() == nInt)
+                    state
+                        .coerceToString(
+                            setting.pos,
+                            setting.value,
+                            emptyContext,
+                            "",
+                            StringCoercionMode::Strict,
+                            true,
+                            true
+                        )
+                        .toOwned()
+                );
+            } else if (setting.value.type() == nInt) {
                 flake.config.settings.emplace(
                     state.ctx.symbols[setting.name],
-                    state.forceInt(*setting.value, setting.pos, "").value);
-            else if (setting.value->type() == nBool)
+                    state.forceInt(setting.value, setting.pos, "").value
+                );
+            } else if (setting.value.type() == nBool) {
                 flake.config.settings.emplace(
                     state.ctx.symbols[setting.name],
-                    Explicit<bool> { state.forceBool(*setting.value, setting.pos, "") });
-            else if (setting.value->type() == nList) {
+                    Explicit<bool>{state.forceBool(setting.value, setting.pos, "")}
+                );
+            } else if (setting.value.type() == nList) {
                 std::vector<std::string> ss;
-                for (auto elem : setting.value->listItems()) {
-                    if (elem->type() != nString)
-                        state.ctx.errors.make<TypeError>("list element in flake configuration setting '%s' is %s while a string is expected",
-                            state.ctx.symbols[setting.name], showType(*setting.value)).debugThrow();
-                    ss.emplace_back(state.forceStringNoCtx(*elem, setting.pos, ""));
+                for (auto & elem : setting.value.listItems()) {
+                    if (elem.type() != nString) {
+                        state.ctx.errors
+                            .make<TypeError>(
+                                "list element in flake configuration setting '%s' is %s while a "
+                                "string is expected",
+                                state.ctx.symbols[setting.name],
+                                showType(setting.value)
+                            )
+                            .debugThrow();
+                    }
+                    ss.emplace_back(state.forceStringNoCtx(elem, setting.pos, ""));
                 }
                 flake.config.settings.emplace(state.ctx.symbols[setting.name], ss);
+            } else {
+                state.ctx.errors
+                    .make<TypeError>(
+                        "flake configuration setting '%s' is %s",
+                        state.ctx.symbols[setting.name],
+                        showType(setting.value)
+                    )
+                    .debugThrow();
             }
-            else
-                state.ctx.errors.make<TypeError>("flake configuration setting '%s' is %s",
-                    state.ctx.symbols[setting.name], showType(*setting.value)).debugThrow();
         }
     }
 
-    for (auto & attr : *vInfo.attrs) {
+    for (auto & attr : *vInfo.attrs()) {
         if (attr.name != state.ctx.s.description &&
             attr.name != sInputs &&
             attr.name != state.ctx.s.outputs &&
@@ -457,9 +589,11 @@ LockedFlake lockFlake(
                 auto follow = inputPath2.back();
                 inputPath2.pop_back();
                 if (inputPath2 == inputPathPrefix && !flakeInputs.count(follow))
-                    warn(
+                    printTaggedWarning(
                         "input '%s' has an override for a non-existent input '%s'",
-                        printInputPath(inputPathPrefix), follow);
+                        printInputPath(inputPathPrefix),
+                        follow
+                    );
             }
 
             /* Go over the flake inputs, resolve/fetch them if
@@ -670,12 +804,17 @@ LockedFlake lockFlake(
 
         for (auto & i : lockFlags.inputOverrides)
             if (!overridesUsed.count(i.first))
-                warn("the flag '--override-input %s %s' does not match any input",
-                    printInputPath(i.first), i.second);
+                printTaggedWarning(
+                    "the flag '--override-input %s %s' does not match any input",
+                    printInputPath(i.first),
+                    i.second
+                );
 
         for (auto & i : lockFlags.inputUpdates)
             if (!updatesUsed.count(i))
-                warn("'%s' does not match any input of this flake", printInputPath(i));
+                printTaggedWarning(
+                    "'%s' does not match any input of this flake", printInputPath(i)
+                );
 
         /* Check 'follows' inputs. */
         newLockFile.check();
@@ -693,7 +832,12 @@ LockedFlake lockFlake(
                 if (sourcePath || lockFlags.outputLockFilePath) {
                     if (auto unlockedInput = newLockFile.isUnlocked()) {
                         if (fetchSettings.warnDirty)
-                            warn("will not write lock file of flake '%s' because it has an unlocked input ('%s')", topRef, *unlockedInput);
+                            printTaggedWarning(
+                                "will not write lock file of flake '%s' because it has an unlocked "
+                                "input ('%s')",
+                                topRef,
+                                *unlockedInput
+                            );
                     } else {
                         if (!lockFlags.updateLockFile)
                             throw Error("flake '%s' requires lock file changes but they're not allowed due to '--no-update-lock-file'", topRef);
@@ -713,11 +857,19 @@ LockedFlake lockFlake(
                             auto s = chomp(diff);
                             if (lockFileExists) {
                                 if (s.empty())
-                                    warn("updating lock file '%s'", outputLockFilePath);
+                                    printTaggedWarning(
+                                        "updating lock file '%s'", outputLockFilePath
+                                    );
                                 else
-                                    warn("updating lock file '%s':\n%s", outputLockFilePath, Uncolored(s));
+                                    printTaggedWarning(
+                                        "updating lock file '%s':\n%s",
+                                        outputLockFilePath,
+                                        Uncolored(s)
+                                    );
                             } else
-                                warn("creating lock file '%s':\n%s", outputLockFilePath, Uncolored(s));
+                                printTaggedWarning(
+                                    "creating lock file '%s':\n%s", outputLockFilePath, Uncolored(s)
+                                );
 
                             std::optional<std::string> commitMessage = std::nullopt;
 
@@ -735,9 +887,13 @@ LockedFlake lockFlake(
                                 commitMessage = cm;
                             }
 
-                            topRef.input.putFile(
-                                CanonPath((topRef.subdir == "" ? "" : topRef.subdir + "/") + "flake.lock"),
-                                newLockFileS, commitMessage);
+                            state.aio.blockOn(topRef.input.putFile(
+                                CanonPath(
+                                    (topRef.subdir == "" ? "" : topRef.subdir + "/") + "flake.lock"
+                                ),
+                                newLockFileS,
+                                commitMessage
+                            ));
                         }
 
                         /* Rewriting the lockfile changed the top-level
@@ -750,7 +906,10 @@ LockedFlake lockFlake(
                         if (lockFlags.commitLockFile &&
                             flake.lockedRef.input.getRev() &&
                             prevLockedRef.input.getRev() != flake.lockedRef.input.getRev())
-                            warn("committed new revision '%s'", flake.lockedRef.input.getRev()->gitRev());
+                            printTaggedWarning(
+                                "committed new revision '%s'",
+                                flake.lockedRef.input.getRev()->gitRev()
+                            );
 
                         /* Make sure that we picked up the change,
                            i.e. the tree should usually be dirty
@@ -763,7 +922,9 @@ LockedFlake lockFlake(
                 } else
                     throw Error("cannot write modified lock file of flake '%s' (use '--no-write-lock-file' to ignore)", topRef);
             } else {
-                warn("not writing modified lock file of flake '%s':\n%s", topRef, chomp(diff));
+                printTaggedWarning(
+                    "not writing modified lock file of flake '%s':\n%s", topRef, chomp(diff)
+                );
                 flake.forceDirty = true;
             }
         }
@@ -780,34 +941,39 @@ void callFlake(EvalState & state,
     const LockedFlake & lockedFlake,
     Value & vRes)
 {
-    auto vLocks = state.ctx.mem.allocValue();
-    auto vRootSrc = state.ctx.mem.allocValue();
-    auto vRootSubdir = state.ctx.mem.allocValue();
-    auto vTmp1 = state.ctx.mem.allocValue();
-    auto vTmp2 = state.ctx.mem.allocValue();
+    Value vLocks;
+    Value vRootSrc;
+    Value vRootSubdir;
+    Value vTmp1;
+    Value vTmp2;
 
-    vLocks->mkString(lockedFlake.lockFile.to_string());
+    vLocks.mkString(lockedFlake.lockFile.to_string());
 
     emitTreeAttrs(
         state.ctx,
         *lockedFlake.flake.sourceInfo,
         lockedFlake.flake.lockedRef.input,
-        *vRootSrc,
+        vRootSrc,
         false,
-        lockedFlake.flake.forceDirty);
+        lockedFlake.flake.forceDirty
+    );
 
-    vRootSubdir->mkString(lockedFlake.flake.lockedRef.subdir);
+    vRootSubdir.mkString(lockedFlake.flake.lockedRef.subdir);
 
     if (!state.ctx.caches.vCallFlake) {
-        state.ctx.caches.vCallFlake = allocRootValue(state.ctx.mem.allocValue());
-        state.eval(state.ctx.parseExprFromString(
-            #include "call-flake.nix.gen.hh"
-            , CanonPath::root), **state.ctx.caches.vCallFlake);
+        state.ctx.caches.vCallFlake = allocRootValue({});
+        state.eval(
+            state.ctx.parseExprFromString(
+#include "call-flake.nix.gen.hh"
+                , CanonPath::root
+            ),
+            *state.ctx.caches.vCallFlake
+        );
     }
 
-    state.callFunction(**state.ctx.caches.vCallFlake, *vLocks, *vTmp1, noPos);
-    state.callFunction(*vTmp1, *vRootSrc, *vTmp2, noPos);
-    state.callFunction(*vTmp2, *vRootSubdir, vRes, noPos);
+    state.callFunction(*state.ctx.caches.vCallFlake, vLocks, vTmp1, noPos);
+    state.callFunction(vTmp1, vRootSrc, vTmp2, noPos);
+    state.callFunction(vTmp2, vRootSubdir, vRes, noPos);
 }
 
 void prim_getFlake(EvalState & state, Value * * args, Value & v)
@@ -857,10 +1023,10 @@ void prim_flakeRefToString(
     state.forceAttrs(*args[0], noPos,
         "while evaluating the argument passed to builtins.flakeRefToString");
     fetchers::Attrs attrs;
-    for (const auto & attr : *args[0]->attrs) {
-        auto t = attr.value->type();
+    for (const auto & attr : *args[0]->attrs()) {
+        auto t = attr.value.type();
         if (t == nInt) {
-            auto intValue = attr.value->integer.value;
+            auto intValue = attr.value.integer().value;
 
             if (intValue < 0) {
                 state.ctx.errors.make<EvalError>("negative value given for flake ref attr %1%: %2%", state.ctx.symbols[attr.name], intValue).debugThrow();
@@ -869,17 +1035,18 @@ void prim_flakeRefToString(
 
             attrs.emplace(state.ctx.symbols[attr.name], asUnsigned);
         } else if (t == nBool) {
-            attrs.emplace(state.ctx.symbols[attr.name],
-                          Explicit<bool> { attr.value->boolean });
+            attrs.emplace(state.ctx.symbols[attr.name], Explicit<bool>{attr.value.boolean()});
         } else if (t == nString) {
-            attrs.emplace(state.ctx.symbols[attr.name],
-                          std::string(attr.value->str()));
+            attrs.emplace(state.ctx.symbols[attr.name], std::string(attr.value.str()));
         } else {
-            state.ctx.errors.make<EvalError>(
-                "flake reference attribute sets may only contain integers, Booleans, "
-                "and strings, but attribute '%s' is %s",
-                state.ctx.symbols[attr.name],
-                showType(*attr.value)).debugThrow();
+            state.ctx.errors
+                .make<EvalError>(
+                    "flake reference attribute sets may only contain integers, Booleans, "
+                    "and strings, but attribute '%s' is %s",
+                    state.ctx.symbols[attr.name],
+                    showType(attr.value)
+                )
+                .debugThrow();
         }
     }
     auto flakeRef = FlakeRef::fromAttrs(attrs);

lix/libexpr/flake/flake.hh

@@ -72,25 +72,39 @@ struct Flake
      * The original flake specification (by the user)
      */
     FlakeRef originalRef;
+
     /**
      * registry references and caching resolved to the specific underlying flake
      */
     FlakeRef resolvedRef;
+
     /**
      * the specific local store result of invoking the fetcher
      */
     FlakeRef lockedRef;
+
     /**
      * pretend that 'lockedRef' is dirty
      */
     bool forceDirty = false;
+
     std::optional<std::string> description;
+
     std::shared_ptr<const fetchers::Tree> sourceInfo;
+
     FlakeInputs inputs;
+
+    /**
+     * Attributes to be retroactively applied to the `self` input
+     * (such as `submodules = true`).
+     */
+    std::optional<fetchers::Attrs> selfAttrs;
+
     /**
      * 'nixConfig' attribute
      */
     ConfigFile config;
+
     ~Flake();
 };
 

lix/libexpr/function-trace.cc

@@ -6,13 +6,13 @@ namespace nix {
 FunctionCallTrace::FunctionCallTrace(const Pos & pos) : pos(pos) {
     auto duration = std::chrono::high_resolution_clock::now().time_since_epoch();
     auto ns = std::chrono::duration_cast<std::chrono::nanoseconds>(duration);
-    printMsg(lvlInfo, "function-trace entered %1% at %2%", pos, ns.count());
+    printMsg(lvlInfo, "function-trace entered %1% at %2%", Uncolored(pos), Uncolored(ns.count()));
 }
 
 FunctionCallTrace::~FunctionCallTrace() {
     auto duration = std::chrono::high_resolution_clock::now().time_since_epoch();
     auto ns = std::chrono::duration_cast<std::chrono::nanoseconds>(duration);
-    printMsg(lvlInfo, "function-trace exited %1% at %2%", pos, ns.count());
+    printMsg(lvlInfo, "function-trace exited %1% at %2%", Uncolored(pos), Uncolored(ns.count()));
 }
 
 }

lix/libexpr/gc-alloc.hh

@@ -95,6 +95,24 @@ inline void * gcAllocBytes(size_t n)
     return ptr;
 }
 
+[[gnu::always_inline]]
+inline size_t checkedArrayAllocSize(size_t size, size_t howMany)
+{
+    // NOTE: size_t * size_t, which can definitely overflow.
+    // Unsigned integer overflow is definitely a bug, but isn't undefined
+    // behavior, so we can just check if we overflowed after the fact.
+    // However, people can and do request zero sized allocations, so we need
+    // to check that neither of our multiplicands were zero before complaining
+    // about it.
+    auto checkedSz = checked::Checked<size_t>(howMany) * size;
+    if (checkedSz.overflowed()) {
+        // Congrats, you done did an overflow.
+        throw std::bad_alloc();
+    }
+
+    return checkedSz.valueWrapping();
+}
+
 /// Typed, safe wrapper around calloc() (transparently GC-enabled). Allocates
 /// enough for the requested count of the specified type. Also checks for
 /// nullptr (and throws @ref std::bad_alloc), and casts the void pointer to
@@ -103,21 +121,7 @@ template<typename T>
 [[gnu::always_inline]]
 inline T * gcAllocType(size_t howMany = 1)
 {
-    // NOTE: size_t * size_t, which can definitely overflow.
-    // Unsigned integer overflow is definitely a bug, but isn't undefined
-    // behavior, so we can just check if we overflowed after the fact.
-    // However, people can and do request zero sized allocations, so we need
-    // to check that neither of our multiplicands were zero before complaining
-    // about it.
-    // NOLINTNEXTLINE(bugprone-sizeof-expression): yeah we only seem to alloc pointers with this. the calculation *is* correct though!
-    auto checkedSz = checked::Checked<size_t>(howMany) * sizeof(T);
-    size_t sz = checkedSz.valueWrapping();
-    if (checkedSz.overflowed()) {
-        // Congrats, you done did an overflow.
-        throw std::bad_alloc();
-    }
-
-    return static_cast<T *>(gcAllocBytes(sz));
+    return static_cast<T *>(gcAllocBytes(checkedArrayAllocSize(sizeof(T), howMany)));
 }
 
 /// GC-transparently allocates a buffer for a C-string of @ref size *bytes*,

lix/libexpr/gc-small-vector.hh

@@ -17,8 +17,8 @@ using SmallVector = boost::container::small_vector<T, nItems, TraceableAllocator
 /**
  * A vector of value pointers. See `SmallVector`.
  */
-template <size_t nItems>
-using SmallValueVector = SmallVector<Value *, nItems>;
+template<size_t nItems>
+using SmallValueVector = SmallVector<Value, nItems>;
 
 /**
  * A vector of values that must not be referenced after the vector is destroyed.

lix/libexpr/get-drvs.cc

@@ -64,9 +64,13 @@ try {
 std::string DrvInfo::queryName(EvalState & state)
 {
     if (name == "" && attrs) {
-        auto i = attrs->find(state.ctx.s.name);
-        if (i == attrs->end()) state.ctx.errors.make<TypeError>("derivation name missing").debugThrow();
-        name = state.forceStringNoCtx(*i->value, noPos, "while evaluating the 'name' attribute of a derivation");
+        auto i = attrs->get(state.ctx.s.name);
+        if (!i) {
+            state.ctx.errors.make<TypeError>("derivation name missing").debugThrow();
+        }
+        name = state.forceStringNoCtx(
+            i->value, noPos, "while evaluating the 'name' attribute of a derivation"
+        );
     }
     return name;
 }
@@ -75,8 +79,12 @@ std::string DrvInfo::queryName(EvalState & state)
 std::string DrvInfo::querySystem(EvalState & state)
 {
     if (system == "" && attrs) {
-        auto i = attrs->find(state.ctx.s.system);
-        system = i == attrs->end() ? "unknown" : state.forceStringNoCtx(*i->value, i->pos, "while evaluating the 'system' attribute of a derivation");
+        auto i = attrs->get(state.ctx.s.system);
+        system = !i
+            ? "unknown"
+            : state.forceStringNoCtx(
+                  i->value, i->pos, "while evaluating the 'system' attribute of a derivation"
+              );
     }
     return system;
 }
@@ -85,12 +93,18 @@ std::string DrvInfo::querySystem(EvalState & state)
 std::optional<StorePath> DrvInfo::queryDrvPath(EvalState & state)
 {
     if (!drvPath && attrs) {
-        Bindings::iterator i = attrs->find(state.ctx.s.drvPath);
+        auto i = attrs->get(state.ctx.s.drvPath);
         NixStringContext context;
-        if (i == attrs->end())
+        if (!i) {
             drvPath = {std::nullopt};
-        else
-            drvPath = {state.coerceToStorePath(i->pos, *i->value, context, "while evaluating the 'drvPath' attribute of a derivation")};
+        } else {
+            drvPath = {state.coerceToStorePath(
+                i->pos,
+                i->value,
+                context,
+                "while evaluating the 'drvPath' attribute of a derivation"
+            )};
+        }
     }
     return drvPath.value_or(std::nullopt);
 }
@@ -107,10 +121,13 @@ StorePath DrvInfo::requireDrvPath(EvalState & state)
 StorePath DrvInfo::queryOutPath(EvalState & state)
 {
     if (!outPath && attrs) {
-        Bindings::iterator i = attrs->find(state.ctx.s.outPath);
+        auto i = attrs->get(state.ctx.s.outPath);
         NixStringContext context;
-        if (i != attrs->end())
-            outPath = state.coerceToStorePath(i->pos, *i->value, context, "while evaluating the output path of a derivation");
+        if (i) {
+            outPath = state.coerceToStorePath(
+                i->pos, i->value, context, "while evaluating the output path of a derivation"
+            );
+        }
     }
     if (!outPath)
         throw UnimplementedError("CA derivations are not yet supported");
@@ -133,7 +150,7 @@ void DrvInfo::fillOutputs(EvalState & state, bool withPaths)
         return;
     }
 
-    Attr * outputs = this->attrs->get(state.ctx.s.outputs);
+    const Attr * outputs = this->attrs->get(state.ctx.s.outputs);
     if (outputs == nullptr) {
         fillDefault();
         return;
@@ -141,27 +158,21 @@ void DrvInfo::fillOutputs(EvalState & state, bool withPaths)
 
     // NOTE(Qyriad): I don't think there is any codepath that can cause this to error.
     state.forceList(
-        *outputs->value,
-        outputs->pos,
-        "while evaluating the 'outputs' attribute of a derivation"
+        outputs->value, outputs->pos, "while evaluating the 'outputs' attribute of a derivation"
     );
 
-    for (auto [idx, elem] : enumerate(outputs->value->listItems())) {
+    for (auto && [idx, elem] : enumerate(outputs->value.listItems())) {
         // NOTE(Qyriad): This error should be *extremely* rare in practice.
         // It is impossible to construct with `stdenv.mkDerivation`,
         // `builtins.derivation`, or even `derivationStrict`. As far as we can tell,
         // it is only possible by overriding a derivation attrset already created by
         // one of those with `//` to introduce the failing `outputs` entry.
         auto errMsg = fmt("while evaluating output %d of a derivation", idx);
-        std::string_view outputName = state.forceStringNoCtx(
-            *elem,
-            outputs->pos,
-            errMsg
-        );
+        std::string_view outputName = state.forceStringNoCtx(elem, outputs->pos, errMsg);
 
         if (withPaths) {
             // Find the attr with this output's name...
-            Attr * out = this->attrs->get(state.ctx.symbols.create(outputName));
+            const Attr * out = this->attrs->get(state.ctx.symbols.create(outputName));
             if (out == nullptr) {
                 // FIXME: throw error?
                 continue;
@@ -169,10 +180,10 @@ void DrvInfo::fillOutputs(EvalState & state, bool withPaths)
 
             // Meanwhile we couldn't figure out any circumstances
             // that cause this to error.
-            state.forceAttrs(*out->value, outputs->pos, errMsg);
+            state.forceAttrs(out->value, outputs->pos, errMsg);
 
             // ...and evaluate its `outPath` attribute.
-            Attr * outPath = out->value->attrs->get(state.ctx.s.outPath);
+            const Attr * outPath = out->value.attrs()->get(state.ctx.s.outPath);
             if (outPath == nullptr) {
                 continue;
                 // FIXME: throw error?
@@ -181,12 +192,7 @@ void DrvInfo::fillOutputs(EvalState & state, bool withPaths)
             NixStringContext context;
             // And idk what could possibly cause this one to error
             // that wouldn't error before here.
-            auto storePath = state.coerceToStorePath(
-                outPath->pos,
-                *outPath->value,
-                context,
-                errMsg
-            );
+            auto storePath = state.coerceToStorePath(outPath->pos, outPath->value, context, errMsg);
             this->outputs.emplace(outputName, storePath);
         } else {
             this->outputs.emplace(outputName, std::nullopt);
@@ -216,9 +222,9 @@ DrvInfo::Outputs DrvInfo::queryOutputs(EvalState & state, bool withPaths, bool o
     // output by its attribute, e.g. `pkgs.lix.dev`, which (lol?) sets the magic
     // attribute `outputSpecified = true`, and changes the `outputName` attr to the
     // explicitly selected-into output.
-    if (Attr * outSpecAttr = attrs->get(state.ctx.s.outputSpecified)) {
+    if (const Attr * outSpecAttr = attrs->get(state.ctx.s.outputSpecified)) {
         bool outputSpecified = state.forceBool(
-            *outSpecAttr->value,
+            outSpecAttr->value,
             outSpecAttr->pos,
             "while evaluating the 'outputSpecified' attribute of a derivation"
         );
@@ -238,14 +244,17 @@ DrvInfo::Outputs DrvInfo::queryOutputs(EvalState & state, bool withPaths, bool o
         /* ^ this shows during `nix-env -i` right under the bad derivation */
     if (!outTI->isList()) throw Error(errMsg + "expected a list but got %s", Uncolored(showType(outTI->type())));
     Outputs result;
-    for (auto elem : outTI->listItems()) {
-        if (elem->type() != nString)
+    for (auto & elem : outTI->listItems()) {
+        if (elem.type() != nString) {
             throw Error(
                 errMsg + "element is %s where a string was expected",
-                Uncolored(showType(elem->type()))
+                Uncolored(showType(elem.type()))
             );
-        auto out = outputs.find(elem->string.s);
-        if (out == outputs.end()) throw Error(errMsg + "output '%s' does not exist", elem->string.s);
+        }
+        auto out = outputs.find(std::string(elem.str()));
+        if (out == outputs.end()) {
+            throw Error(errMsg + "output '%s' does not exist", elem.str());
+        }
         result.insert(*out);
     }
     return result;
@@ -255,8 +264,11 @@ DrvInfo::Outputs DrvInfo::queryOutputs(EvalState & state, bool withPaths, bool o
 std::string DrvInfo::queryOutputName(EvalState & state)
 {
     if (outputName == "" && attrs) {
-        Bindings::iterator i = attrs->find(state.ctx.s.outputName);
-        outputName = i != attrs->end() ? state.forceStringNoCtx(*i->value, noPos, "while evaluating the output name of a derivation") : "";
+        auto i = attrs->get(state.ctx.s.outputName);
+        outputName = i ? state.forceStringNoCtx(
+                             i->value, noPos, "while evaluating the output name of a derivation"
+                         )
+                       : "";
     }
     return outputName;
 }
@@ -266,10 +278,12 @@ Bindings * DrvInfo::getMeta(EvalState & state)
 {
     if (meta) return meta;
     if (!attrs) return 0;
-    Bindings::iterator a = attrs->find(state.ctx.s.meta);
-    if (a == attrs->end()) return 0;
-    state.forceAttrs(*a->value, a->pos, "while evaluating the 'meta' attribute of a derivation");
-    meta = a->value->attrs;
+    auto a = attrs->get(state.ctx.s.meta);
+    if (!a) {
+        return 0;
+    }
+    state.forceAttrs(a->value, a->pos, "while evaluating the 'meta' attribute of a derivation");
+    meta = a->value.attrs();
     return meta;
 }
 
@@ -288,15 +302,23 @@ bool DrvInfo::checkMeta(EvalState & state, Value & v)
 {
     state.forceValue(v, noPos);
     if (v.type() == nList) {
-        for (auto elem : v.listItems())
-            if (!checkMeta(state, *elem)) return false;
+        for (auto & elem : v.listItems()) {
+            if (!checkMeta(state, elem)) {
+                return false;
+            }
+        }
         return true;
     }
     else if (v.type() == nAttrs) {
-        Bindings::iterator i = v.attrs->find(state.ctx.s.outPath);
-        if (i != v.attrs->end()) return false;
-        for (auto & i : *v.attrs)
-            if (!checkMeta(state, *i.value)) return false;
+        auto i = v.attrs()->get(state.ctx.s.outPath);
+        if (i) {
+            return false;
+        }
+        for (auto & i : *v.attrs()) {
+            if (!checkMeta(state, i.value)) {
+                return false;
+            }
+        }
         return true;
     }
     else return v.type() == nInt || v.type() == nBool || v.type() == nString ||
@@ -307,9 +329,11 @@ bool DrvInfo::checkMeta(EvalState & state, Value & v)
 Value * DrvInfo::queryMeta(EvalState & state, const std::string & name)
 {
     if (!getMeta(state)) return 0;
-    Bindings::iterator a = meta->find(state.ctx.symbols.create(name));
-    if (a == meta->end() || !checkMeta(state, *a->value)) return 0;
-    return a->value;
+    auto a = meta->get(state.ctx.symbols.create(name));
+    if (!a || !checkMeta(state, a->value)) {
+        return 0;
+    }
+    return &a->value;
 }
 
 
@@ -317,7 +341,7 @@ std::string DrvInfo::queryMetaString(EvalState & state, const std::string & name
 {
     Value * v = queryMeta(state, name);
     if (!v || v->type() != nString) return "";
-    return v->string.s;
+    return std::string(v->str());
 }
 
 
@@ -325,12 +349,15 @@ NixInt DrvInfo::queryMetaInt(EvalState & state, const std::string & name, NixInt
 {
     Value * v = queryMeta(state, name);
     if (!v) return def;
-    if (v->type() == nInt) return v->integer;
+    if (v->type() == nInt) {
+        return v->integer();
+    }
     if (v->type() == nString) {
         /* Backwards compatibility with before we had support for
            integer meta fields. */
-        if (auto n = string2Int<NixInt::Inner>(v->string.s))
+        if (auto n = string2Int<NixInt::Inner>(v->str())) {
             return NixInt{*n};
+        }
     }
     return def;
 }
@@ -339,18 +366,23 @@ bool DrvInfo::queryMetaBool(EvalState & state, const std::string & name, bool de
 {
     Value * v = queryMeta(state, name);
     if (!v) return def;
-    if (v->type() == nBool) return v->boolean;
+    if (v->type() == nBool) {
+        return v->boolean();
+    }
     if (v->type() == nString) {
         /* Backwards compatibility with before we had support for
            Boolean meta fields. */
-        if (strcmp(v->string.s, "true") == 0) return true;
-        if (strcmp(v->string.s, "false") == 0) return false;
+        if (v->str() == "true") {
+            return true;
+        }
+        if (v->str() == "false") {
+            return false;
+        }
     }
     return def;
 }
 
-
-void DrvInfo::setMeta(EvalState & state, const std::string & name, Value * v)
+void DrvInfo::setMeta(EvalState & state, const std::string & name, Value & v)
 {
     getMeta(state);
     auto attrs = state.ctx.buildBindings(1 + (meta ? meta->size() : 0));
@@ -359,7 +391,7 @@ void DrvInfo::setMeta(EvalState & state, const std::string & name, Value * v)
         for (auto i : *meta)
             if (i.name != sym)
                 attrs.insert(i);
-    if (v) attrs.insert(sym, v);
+    attrs.insert(sym, v);
     meta = attrs.finish();
 }
 
@@ -378,7 +410,7 @@ static bool getDerivation(EvalState & state, Value & v,
         state.forceValue(v, noPos);
         if (!state.isDerivation(v)) return true;
 
-        DrvInfo drv(attrPath, v.attrs);
+        DrvInfo drv(attrPath, v.attrs());
 
         drv.queryName(state);
 
@@ -402,10 +434,9 @@ std::optional<DrvInfo> getDerivation(EvalState & state, Value & v,
     return std::move(drvs.front());
 }
 
-
-static std::string addToPath(const std::string & s1, const std::string & s2)
+static std::string addToPath(std::string_view s1, std::string_view s2)
 {
-    return s1.empty() ? s2 : s1 + "." + s2;
+    return s1.empty() ? std::string(s2) : fmt("%s.%s", s1, s2);
 }
 
 
@@ -432,19 +463,13 @@ static void getDerivations(EvalState & state, Value & vIn, PosIdx pos,
     if (v.type() == nList) {
         // NOTE we can't really deduplicate here because small lists don't have stable addresses
         // and can cause spurious duplicate detections due to v being on the stack.
-        for (auto [n, elem] : enumerate(v.listItems())) {
+        for (auto && [n, elem] : enumerate(v.listItems())) {
             std::string joinedAttrPath = addToPath(pathPrefix, fmt("%d", n));
-            bool shouldRecurse = getDerivation(state, *elem, joinedAttrPath, drvs, ignoreAssertionFailures);
+            bool shouldRecurse =
+                getDerivation(state, elem, joinedAttrPath, drvs, ignoreAssertionFailures);
             if (shouldRecurse) {
                 getDerivations(
-                    state,
-                    *elem,
-                    pos,
-                    joinedAttrPath,
-                    autoArgs,
-                    drvs,
-                    done,
-                    ignoreAssertionFailures
+                    state, elem, pos, joinedAttrPath, autoArgs, drvs, done, ignoreAssertionFailures
                 );
             }
         }
@@ -459,7 +484,7 @@ static void getDerivations(EvalState & state, Value & vIn, PosIdx pos,
 
     /* Dont consider sets we've already seen, e.g. y in
        `rec { x.d = derivation {...}; y = x; }`. */
-    auto const &[_, didInsert] = done.insert(v.attrs);
+    auto const &[_, didInsert] = done.insert(v.attrs());
     if (!didInsert) {
         return;
     }
@@ -467,14 +492,14 @@ static void getDerivations(EvalState & state, Value & vIn, PosIdx pos,
     // FIXME: what the fuck???
     /* !!! undocumented hackery to support combining channels in
        nix-env.cc. */
-    bool combineChannels = v.attrs->find(state.ctx.symbols.create("_combineChannels")) != v.attrs->end();
+    bool combineChannels = v.attrs()->get(state.ctx.symbols.create("_combineChannels"));
 
     /* Consider the attributes in sorted order to get more
        deterministic behaviour in nix-env operations (e.g. when
        there are names clashes between derivations, the derivation
        bound to the attribute with the "lower" name should take
        precedence). */
-    for (auto & attr : v.attrs->lexicographicOrder(state.ctx.symbols)) {
+    for (auto & attr : v.attrs()->lexicographicOrder(state.ctx.symbols)) {
         debug("evaluating attribute '%1%'", state.ctx.symbols[attr->name]);
         // FIXME: only consider attrs with identifier-like names?? Why???
         if (!std::regex_match(std::string(state.ctx.symbols[attr->name]), attrRegex)) {
@@ -484,7 +509,7 @@ static void getDerivations(EvalState & state, Value & vIn, PosIdx pos,
         if (combineChannels) {
             getDerivations(
                 state,
-                *attr->value,
+                attr->value,
                 attr->pos,
                 joinedAttrPath,
                 autoArgs,
@@ -492,17 +517,19 @@ static void getDerivations(EvalState & state, Value & vIn, PosIdx pos,
                 done,
                 ignoreAssertionFailures
             );
-        } else if (getDerivation(state, *attr->value, joinedAttrPath, drvs, ignoreAssertionFailures)) {
+        } else if (getDerivation(state, attr->value, joinedAttrPath, drvs, ignoreAssertionFailures))
+        {
             /* If the value of this attribute is itself a set,
                should we recurse into it?  => Only if it has a
                `recurseForDerivations = true' attribute. */
-            if (attr->value->type() == nAttrs) {
-                Attr * recurseForDrvs = attr->value->attrs->get(state.ctx.s.recurseForDerivations);
+            if (attr->value.type() == nAttrs) {
+                const Attr * recurseForDrvs =
+                    attr->value.attrs()->get(state.ctx.s.recurseForDerivations);
                 if (recurseForDrvs == nullptr) {
                     continue;
                 }
                 bool shouldRecurse = state.forceBool(
-                    *recurseForDrvs->value,
+                    recurseForDrvs->value,
                     attr->pos,
                     fmt("while evaluating the '%s' attribute", Magenta("recurseForDerivations"))
                 );
@@ -512,7 +539,7 @@ static void getDerivations(EvalState & state, Value & vIn, PosIdx pos,
 
                 getDerivations(
                     state,
-                    *attr->value,
+                    attr->value,
                     attr->pos,
                     joinedAttrPath,
                     autoArgs,

lix/libexpr/get-drvs.hh

@@ -73,7 +73,7 @@ public:
     std::string queryMetaString(EvalState & state, const std::string & name);
     NixInt queryMetaInt(EvalState & state, const std::string & name, NixInt def);
     bool queryMetaBool(EvalState & state, const std::string & name, bool def);
-    void setMeta(EvalState & state, const std::string & name, Value * v);
+    void setMeta(EvalState & state, const std::string & name, Value & v);
 
     /*
     MetaInfo queryMetaInfo(EvalState & state) const;

lix/libexpr/json-to-value.cc

@@ -1,4 +1,5 @@
 #include "lix/libexpr/json-to-value.hh"
+#include "gc-alloc.hh"
 #include "lix/libexpr/value.hh"
 #include "lix/libexpr/eval.hh"
 #include "lix/libutil/json.hh"
@@ -7,11 +8,6 @@
 
 namespace nix {
 
-/*
- * Used for `JSONObjectState`
- */
-using ValueMap = GcMap<Symbol, Value *>;
-
 // for more information, refer to
 // https://github.com/nlohmann/json/blob/master/include/nlohmann/detail/input/json_sax.hpp
 class JSONSax : nlohmann::json_sax<JSON> {
@@ -25,13 +21,14 @@ class JSONSax : nlohmann::json_sax<JSON> {
             assert(false && "tried to close toplevel json parser state");
         }
         explicit JSONState(std::unique_ptr<JSONState> && p) : parent(std::move(p)) {}
-        explicit JSONState(Value * v) : v(allocRootValue(v)) {}
+        JSONState() = default;
         JSONState(JSONState & p) = delete;
-        Value & value(EvalState & state)
+        Value & value()
         {
-            if (!v)
-                v = allocRootValue(state.ctx.mem.allocValue());
-            return **v;
+            if (!v) {
+                v = allocRootValue({});
+            }
+            return *v;
         }
         virtual ~JSONState() {}
         virtual void add() {}
@@ -39,35 +36,41 @@ class JSONSax : nlohmann::json_sax<JSON> {
 
     class JSONObjectState : public JSONState {
         using JSONState::JSONState;
-        ValueMap attrs;
+        GcMap<Symbol, Value> attrs;
+        Symbol _key;
         std::unique_ptr<JSONState> resolve(EvalState & state) override
         {
             auto attrs2 = state.ctx.buildBindings(attrs.size());
             for (auto & i : attrs)
                 attrs2.insert(i.first, i.second);
-            parent->value(state).mkAttrs(attrs2.alreadySorted());
+            parent->value().mkAttrs(attrs2.alreadySorted());
             return std::move(parent);
         }
-        void add() override { v = nullptr; }
+        void add() override
+        {
+            attrs.insert_or_assign(_key, value());
+            v = nullptr;
+        }
     public:
         void key(string_t & name, EvalState & state)
         {
-            attrs.insert_or_assign(state.ctx.symbols.create(name), &value(state));
+            _key = state.ctx.symbols.create(name);
         }
     };
 
     class JSONListState : public JSONState {
-        ValueVector values;
+        GcVector<Value> values;
         std::unique_ptr<JSONState> resolve(EvalState & state) override
         {
-            Value & v = parent->value(state);
-            v = state.ctx.mem.newList(values.size());
+            auto list = state.ctx.mem.newList(values.size());
+            parent->value() = {NewValueAs::list, list};
             for (size_t n = 0; n < values.size(); ++n) {
-                v.listElems()[n] = values[n];
+                list->elems[n] = values[n];
             }
             return std::move(parent);
         }
-        void add() override {
+        void add() override
+        {
             values.push_back(*v);
             v = nullptr;
         }
@@ -82,25 +85,30 @@ class JSONSax : nlohmann::json_sax<JSON> {
     std::unique_ptr<JSONState> rs;
 
 public:
-    JSONSax(EvalState & state, Value & v) : state(state), rs(new JSONState(&v)) {};
+    JSONSax(EvalState & state) : state(state), rs(new JSONState()) {};
+
+    Value result()
+    {
+        return rs->value();
+    }
 
     bool null() override
     {
-        rs->value(state).mkNull();
+        rs->value().mkNull();
         rs->add();
         return true;
     }
 
     bool boolean(bool val) override
     {
-        rs->value(state).mkBool(val);
+        rs->value().mkBool(val);
         rs->add();
         return true;
     }
 
     bool number_integer(number_integer_t val) override
     {
-        rs->value(state).mkInt(val);
+        rs->value().mkInt(val);
         rs->add();
         return true;
     }
@@ -108,24 +116,26 @@ public:
     bool number_unsigned(number_unsigned_t val_) override
     {
         if (val_ > std::numeric_limits<NixInt::Inner>::max()) {
-            throw Error("unsigned json number %1% outside of Nix integer range", val_);
+            // Parse as a float for consistency with signed integers
+            // and interoperability with JSON’s single numeric type.
+            return number_float(static_cast<number_float_t>(val_), "");
         }
         NixInt::Inner val = val_;
-        rs->value(state).mkInt(val);
+        rs->value().mkInt(val);
         rs->add();
         return true;
     }
 
     bool number_float(number_float_t val, const string_t & s) override
     {
-        rs->value(state).mkFloat(val);
+        rs->value().mkFloat(val);
         rs->add();
         return true;
     }
 
     bool string(string_t & val) override
     {
-        rs->value(state).mkString(val);
+        rs->value().mkString(val);
         rs->add();
         return true;
     }
@@ -176,10 +186,11 @@ public:
 
 void parseJSON(EvalState & state, const std::string_view & s_, Value & v)
 {
-    JSONSax parser(state, v);
+    JSONSax parser(state);
     bool res = JSON::sax_parse(s_, &parser);
     if (!res)
         throw JSONParseError("Invalid JSON Value");
+    v = parser.result();
 }
 
 }

lix/libexpr/lix-expr.pc.in

@@ -5,5 +5,6 @@ includedir=@includedir@
 Name: Lix libexpr
 Description: Lix Package Manager (libexpr)
 Version: @PACKAGE_VERSION@
-Requires: lix-base lix-util lix-fetchers lix-store bdw-gc
+# dependencies on boost is omitted since it is optional (only required by some headers)
+Requires: lix-base lix-util lix-store lix-fetchers @BOEHM_IF_FOUND@
 Libs: -L${libdir} -llixexpr

lix/libexpr/meson.build

@@ -270,32 +270,59 @@ libexpr_headers = files(
   # keep-sorted end
 )
 
-libexpr = library(
-  'lixexpr',
+dependencies = [
+  liblixutil,
+  liblixstore,
+  liblixfetchers,
+  boehm,
+  boost,
+  kj,
+  nlohmann_json,
+  toml11,
+]
+
+libexpr_temp = library(
+  is_static ? 'lixexpr_temp' : 'lixexpr',
   libexpr_sources,
   libexpr_settings_header,
   libexpr_generated_headers,
   register_builtins_header,
   register_builtin_constants_header,
-  dependencies : [
-    liblixutil,
-    liblixstore,
-    liblixfetchers,
-    boehm,
-    boost,
-    toml11,
-    nlohmann_json,
-    kj,
-  ],
+  dependencies : dependencies,
   # for shared.hh
   include_directories : [
     '../libmain',
   ],
   cpp_pch : cpp_pch,
-  install : true,
+  install : not is_static,
   # FIXME(Qyriad): is this right?
   install_rpath : libdir,
 )
+# FIXME: remove when https://git.lix.systems/lix-project/lix/issues/359 is fixed.
+# FIXME: replace by prelink when https://github.com/mesonbuild/meson/pull/14846 is widely available.
+if is_static
+  libexpr_prelink = custom_target(
+    'lixexpr-prelink',
+    output : 'lixexpr-prelink.o',
+    input : libexpr_temp,
+    command : [
+      cxx.cmd_array(),
+      '-r',
+      '-o',
+      '@OUTPUT@',
+      is_darwin ? '-Wl,-force_load' : '-Wl,--whole-archive',
+      '@INPUT@',
+    ],
+  )
+  libexpr = library(
+    'lixexpr',
+    [libexpr_prelink],
+    dependencies : dependencies,
+    install : true,
+  )
+else
+  libexpr = libexpr_temp
+endif
 
 install_headers(
   libexpr_headers,
@@ -306,23 +333,16 @@ install_headers(
 liblixexpr = declare_dependency(
   include_directories : include_directories('../..'),
   sources : libexpr_settings_header,
-  # Parallels the requirement to link with boehm of the pkg-config but for internal targets.
-  dependencies : [boehm],
+  dependencies : [
+    liblixutil,
+    liblixfetchers,
+    boehm,
+    boost,
+  ],
   link_with : libexpr,
 )
 
-# FIXME: remove when https://git.lix.systems/lix-project/lix/issues/359 is fixed.
-if is_static
-  liblixexpr_mstatic = declare_dependency(
-    include_directories : include_directories('../..'),
-    sources : libexpr_settings_header,
-    dependencies : [boehm],
-    link_whole : libexpr,
-  )
-else
-  liblixexpr_mstatic = liblixexpr
-endif
-meson.override_dependency('lix-expr', liblixexpr_mstatic)
+meson.override_dependency('lix-expr', liblixexpr)
 
 # FIXME: not using the pkg-config module because it creates way too many deps
 # while meson migration is in progress, and we want to not include boost here
@@ -335,5 +355,6 @@ configure_file(
     'libdir' : libdir,
     'includedir' : includedir,
     'PACKAGE_VERSION' : meson.project_version(),
+    'BOEHM_IF_FOUND' : boehm.found() ? 'bdw-gc' : '',
   },
 )