release: 2.94.1 "Açaí na tigela"

Release produced with releng/create_release.xsh

Change-Id: Ie38032fe8dfebed83f9d24762ce48f73b23149b5

bench/bench.py

@@ -9,6 +9,7 @@ import tempfile
 import platform
 import shlex
 import textwrap
+import dataclasses
 
 flake_args = ["--extra-experimental-features", "nix-command flakes"]
 cases = {
@@ -64,8 +65,9 @@ arg_parser.add_argument(
 )
 arg_parser.add_argument(
     '--mode',
-    choices=[ "walltime" ] + [ "icount" ] if platform.system() == 'Linux' else [], # perf doesn't run on Darwin
-    default="walltime",
+    nargs='+',
+    choices=[ "walltime", "memory" ] + [ "icount" ] if platform.system() == 'Linux' else [], # perf doesn't run on Darwin
+    default=[ "walltime" ],
 )
 arg_parser.add_argument(
     '--daemon',
@@ -73,8 +75,8 @@ arg_parser.add_argument(
     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:
@@ -162,6 +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([
@@ -178,7 +228,10 @@ with tempfile.TemporaryDirectory() as tmp_dir:
     ])
     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)

doc/manual/change-authors.yml

@@ -86,6 +86,11 @@ ericson:
   display_name: John Ericson
   github: ericson2314
 
+getchoo:
+  display_name: Seth Flynn
+  forgejo: getchoo
+  github: getchoo
+
 gilice:
   forgejo: gilice
 

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/certificate-authorities.md

@@ -1,60 +0,0 @@
----
-synopsis: "Global certificate authorities are copied inside the builder's environment"
-issues: [gh#12698, fj#885]
-cls: [3765]
-category: Fixes
-credits: [raito, emilazy]
----
-
-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.

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/double-sigint.md

@@ -1,25 +0,0 @@
----
-synopsis: "Hitting Control-C twice always terminates Lix"
-cls: [3574]
-issues: []
-category: "Improvements"
-credits: [horrors]
----
-
-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 ❯
-```

doc/manual/rl-next/exponential-backoff.md

@@ -1,12 +0,0 @@
----
-synopsis: "libstore: exponential backoff for downloads"
-issues: [lix#932]
-cls: [3856]
-category: Fixes
-credits: [ma27]
----
-
-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.

doc/manual/rl-next/fix-develop-esc.md

@@ -1,9 +0,0 @@
----
-synopsis: Fix develop shells for derivations with escape codes
-issues: [fj#991]
-cls: [4154, 4155]
-category: Fixes
-credits: [Qyriad]
----
-
-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.

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/flake-self-attrs.md

@@ -1,16 +0,0 @@
----
-synopsis: Add `inputs.self.submodules` flake attribute
-issues: [fj#942]
-cls: [3839]
-category: Features
-credits: [edolstra, kasimeka]
----
-
-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.

doc/manual/rl-next/hyperlinks-in-attrsets.md

@@ -1,16 +0,0 @@
----
-synopsis: Add hyperlinks in attr set printing
-issues: []
-cls: [3790]
-category: Features
-credits: [jade]
----
-
-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"; }
-```

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/json-number-overflow.md

@@ -1,16 +0,0 @@
----
-synopsis: Parse overflowing JSON number literals as floating‐point
-issues: []
-cls: [3919]
-category: "Fixes"
-credits: [emilazy]
----
-
-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.

doc/manual/rl-next/keep-failed-chown.md

@@ -1,13 +0,0 @@
----
-synopsis: "`--keep-failed` chowns the build directory to the user that request the build"
-issues: []
-cls: []
-category: Improvements
-credits: [horrors]
----
-
-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.

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/nej-no-instantiate.md

@@ -1,10 +0,0 @@
----
-synopsis: "nix-eval-jobs: support `--no-instantiate` flag"
-issues: [fj#987]
-category: Features
-credits: [mic92,ma27]
----
-
-`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.

doc/manual/rl-next/nix-develop-output-checks.md

@@ -1,29 +0,0 @@
----
-synopsis: "Fix nix develop for derivations that rejects dependencies with structured attrs"
-issues: [fj#997]
-cls: [4182]
-category: Fixes
-credits: [raito]
----
-
-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.

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/nix_path-nix-eval-jobs.md

@@ -1,10 +0,0 @@
----
-synopsis: "nix-eval-jobs: retain NIX_PATH"
-issues: []
-cls: [3859]
-category: Fixes
-credits: [ma27,mic92]
----
-
-`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).

doc/manual/rl-next/output-cycle-refs.md

@@ -1,25 +0,0 @@
----
-synopsis: "show tree with references that lead to an output cycle"
-issues: [fj#551]
-category: Improvements
-credits: [ma27]
----
-
-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.

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: [fj#510]
-cls: [3249]
-significance: significant
-category: "Breaking Changes"
-credits: [horrors]
----
-
-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.

doc/manual/rl-next/remove-write-to.md

@@ -1,14 +0,0 @@
----
-synopsis: "`nix eval --write-to` has been removed"
-cls: [4045]
-issues: [fj#974, fj#227]
-category: "Breaking Changes"
-credits: [horrors]
----
-
-`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.

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/remove-xp-parse-toml-timestamps.md

@@ -1,17 +0,0 @@
----
-synopsis: Remove the `parse-toml-timestamps` experimental feature
-category: "Breaking Changes"
-credits: [emilazy]
----
-
-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.

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/report-forbidden-path-as-chain.md

@@ -1,19 +0,0 @@
----
-synopsis: "`disallowedRequisites` now reports chains of disallowed requisites"
-issues: [fj#334,fj#626,gh#10877]
-category: Improvements
-credits: [ma27,roberth]
----
-
-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
-```

doc/manual/rl-next/snix-http-cache-integration.md

@@ -1,17 +0,0 @@
----
-synopsis: "libstore/binary-cache-store: don't cache narinfo on nix copy, remove negative entry"
-issues: []
-cls: [3789]
-category: Fixes
-credits: [ma27]
----
-
-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.

doc/manual/rl-next/static-linking.md

@@ -1,10 +0,0 @@
----
-synopsis: "Lix libraries can now be linked statically"
-issues: [fj#789]
-cls: [3775, 3778]
-category: Fixes
-credits: [alois31]
----
-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.

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

@@ -1,34 +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, xokdvium, 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.
-
-**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.

doc/manual/rl-next/toml-number-overflow.md

@@ -1,14 +0,0 @@
----
-synopsis: Reject overflowing TOML integer literals
-issues: []
-cls: [3916]
-category: "Breaking Changes"
-credits: [emilazy]
----
-
-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.

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/rl-next/zsh-completions-desc.md

@@ -1,10 +0,0 @@
----
-synopsis: add description to zsh completions
-issues: [fj#910]
-cls: [3632]
-category: "Fixes"
-credits: [matthewbauer]
----
-
-Emit descriptions when completing args in zsh completions. This uses the descriptions we already
-provided in NIX\_GET\_COMPLETIONS.

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/contributing/hacking.md

@@ -170,6 +170,14 @@ Once you get a `Code-Review+2` vote on your change, it's rebased on `main` and C
 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:

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/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/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 +1,958 @@
+# Lix 2.94 "Açaí na tigela" (2025-11-17)
+# Lix 2.94.1 (2026-03-13)
+
+
+
+
+# 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.

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 ? { },

flake.lock

@@ -108,11 +108,11 @@
     },
     "nixpkgs_2": {
       "locked": {
-        "lastModified": 1758391731,
-        "narHash": "sha256-UuwQoPWv13DVKMveeev+F0OC/N95AOmAz6SzCuGhxjQ=",
+        "lastModified": 1757198069,
+        "narHash": "sha256-m3VUcOD4rTs8J7S+3dOjWMrAjw6RcITC3XYQ98zhEFs=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "3f00d36f15e16e0471d9ca1e8f88958941fa970a",
+        "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.
@@ -259,6 +260,19 @@
             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
     {
@@ -371,7 +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.

lix/legacy/build-remote.cc

@@ -1,15 +1,18 @@
 #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"
+#include "lix/libutil/types-rpc.hh" // IWYU pragma: keep
+#include "lix/libutil/types.hh"
 #include <algorithm>
 #include <capnp/rpc-twoparty.h>
-#include <chrono>
 #include <cstring>
-#include <future>
+#include <exception>
+#include <kj/async.h>
 #include <kj/time.h>
 #include <set>
 #include <memory>
@@ -43,9 +46,11 @@ namespace {
 struct Instance final : rpc::build_remote::HookInstance::Server
 {
     unsigned int maxBuildJobs;
+    bool initialized = false, used = false;
 
-    Instance(unsigned int maxBuildJobs) : maxBuildJobs(maxBuildJobs) {}
+    kj::Promise<void> init(InitContext context) override;
 
+    kj::Promise<void> buildImpl(BuildContext context);
     kj::Promise<void> build(BuildContext context) override;
 };
 }
@@ -183,27 +188,62 @@ struct BuilderConnection
 
     // start the thread that reads ssh stderr and turns it into log items.
     // this future *must* outlive sshStore, otherwise it will never finish
-    std::future<void> startLogThread(int intoFD)
-    {
+    kj::Promise<Result<void>> startLogThread(std::string buildDescription, std::string drvPath)
+    try {
         if (!logPipe.readSide) {
-            return {};
+            co_return result::success();
         }
 
         logPipe.writeSide.close();
 
-        return std::async(
-            std::launch::async,
-            [](int from, int to) {
-                AsyncIoRoot aio;
-
-                auto reader = AIO().lowLevelProvider.wrapInputFd(from);
-                auto writer = AIO().lowLevelProvider.wrapOutputFd(to);
-
-                reader->pumpTo(*writer).wait(aio.kj.waitScope);
-            },
-            logPipe.readSide.get(),
-            intoFD
+        // 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();
     }
 };
 
@@ -212,21 +252,16 @@ struct AcceptedBuild final : rpc::build_remote::HookInstance::AcceptedBuild::Ser
     ref<Store> store;
     StorePath drvPath;
     BuilderConnection builder;
-    rpc::build_remote::HookInstance::BuildLogger::Client buildLogger;
+    bool used = false;
 
-    AcceptedBuild(
-        ref<Store> store,
-        StorePath drvPath,
-        BuilderConnection builder,
-        rpc::build_remote::HookInstance::BuildLogger::Client buildLogger
-    )
+    AcceptedBuild(ref<Store> store, StorePath drvPath, BuilderConnection builder)
         : store(store)
         , drvPath(drvPath)
         , builder(std::move(builder))
-        , buildLogger(std::move(buildLogger))
     {
     }
 
+    kj::Promise<void> runImpl(RunContext context);
     kj::Promise<void> run(RunContext context) override;
 };
 
@@ -235,7 +270,7 @@ enum class BuildRejected { Temporarily, Permanently };
 
 static kj::Promise<Result<std::variant<BuildRejected, BuilderConnection>>> connectToBuilder(
     const ref<Store> & store,
-    const std::optional<StorePath> & drvPath,
+    const StorePath & drvPath,
     Machines & machines,
     const unsigned int maxBuildJobs,
     const bool amWilling,
@@ -255,7 +290,7 @@ try {
     bool canBuildLocally = amWilling && couldBuildLocally;
 
     /* Error ignored here, will be caught later */
-    mkdir(currentLoad.c_str(), 0777);
+    (void) sys::mkdir(currentLoad, 0777);
 
     while (true) {
         bestSlotLock.reset();
@@ -272,7 +307,7 @@ try {
             } else {
                 printSelectionFailureMessage(
                     couldBuildLocally ? lvlChatty : lvlWarn,
-                    drvPath ? drvPath->to_string() : "<unknown>",
+                    drvPath.to_string(),
                     machines,
                     neededSystem,
                     requiredFeatures
@@ -294,8 +329,8 @@ try {
         Pipe logPipe;
 
         try {
-            Activity act(
-                *logger, lvlTalkative, actUnknown, fmt("connecting to '%s'", bestMachine->storeUri)
+            auto act = logger->startActivity(
+                lvlTalkative, actUnknown, fmt("connecting to '%s'", bestMachine->storeUri)
             );
 
             std::tie(sshStore, logPipe) = TRY_AWAIT(bestMachine->openStore());
@@ -321,8 +356,6 @@ try {
 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");
@@ -335,104 +368,146 @@ static int main_build_remote(AsyncIoRoot & aio, std::string programName, Strings
 
         verbosity = (Verbosity) std::stoll(argv.front());
 
-        FdSource source(STDIN_FILENO);
-
-        /* Read the parent's settings. */
-        while (readNum<unsigned>(source)) {
-            auto name = readString(source);
-            auto value = readString(source);
-            settings.set(name, value);
-        }
-
-        auto maxBuildJobs = settings.maxBuildJobs;
-        settings.maxBuildJobs.set("1"); // hack to make tests with local?root= work
-
-        initPlugins();
-
         auto conn = aio.kj.lowLevelProvider->wrapUnixSocketFd(1);
-        capnp::TwoPartyServer srv(kj::heap<Instance>(maxBuildJobs));
+        capnp::TwoPartyServer srv(kj::heap<Instance>());
         srv.accept(*conn, 1).wait(aio.kj.waitScope);
         return 0;
     }
 }
 
-kj::Promise<void> Instance::build(BuildContext context)
+kj::Promise<void> Instance::init(InitContext context)
 {
     try {
-        // 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;
+        if (initialized) {
+            throw Error("build hook can only be initialized once");
         }
 
-        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 buildLogger = context.getParams().getBuildLogger();
+        logger = rpc::log::makeRpcLoggerClient(context.getParams().getLogger());
 
-        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;
-            }
+        /* Read the parent's settings. */
+        for (const auto & [name, value] : rpc::to<StringMap>(context.getParams().getSettings())) {
+            settings.set(name, value);
         }
 
-        auto builder = std::get_if<BuilderConnection>(&result);
-        assert(builder);
+        maxBuildJobs = settings.maxBuildJobs;
+        settings.maxBuildJobs.set("1"); // hack to make tests with local?root= work
 
-        auto ac = context.getResults().initResult().initGood().initAccept();
-        RPC_FILL(ac, setMachineName, builder->storeUri);
-        ac.setMachine(kj::heap<AcceptedBuild>(store, drvPath, std::move(*builder), buildLogger));
+        initPlugins();
+
+        initialized = true;
+
+        context.getResults().initResult().setGood();
     } catch (...) {
         RPC_FILL(context.getResults(), initResult, std::current_exception());
     }
+
+    return kj::READY_NOW;
+}
+
+kj::Promise<void> Instance::buildImpl(BuildContext context)
+{
+    if (!initialized) {
+        throw Error("build hook not fully initialized");
+    }
+
+    // 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;
+        }
+    }
+
+    auto builder = std::get_if<BuilderConnection>(&result);
+    assert(builder);
+
+    auto ac = context.getResults().initResult().initGood().initAccept();
+    ac.setMachine(kj::heap<AcceptedBuild>(store, drvPath, std::move(*builder)));
+}
+
+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());
 }
 
 kj::Promise<void> AcceptedBuild::run(RunContext context)
 {
     try {
-        const int logFD = (co_await buildLogger.getFd()).orDefault(-1);
-        if (logFD < 0) {
-            throw Error("build-hook needs a logFD from the builder to build");
-        }
-
-        auto logThread = builder.startLogThread(logFD);
+        auto oldLogger = logger;
+        logger = rpc::log::makeRpcLoggerClient(context.getParams().getLogger());
+        TRY_AWAIT(oldLogger->flush());
         KJ_DEFER({
-            // drop any existing ssh connection so the log thread can exit
-            builder.sshStore = nullptr;
-            if (logThread.valid()) {
-                logThread.get();
-            }
+            delete logger;
+            logger = oldLogger;
         });
 
+        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());
+    }
+}
+
+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)
+        );
+
         auto & sshStore = builder.sshStore;
         auto & storeUri = builder.storeUri;
 
@@ -444,7 +519,9 @@ kj::Promise<void> AcceptedBuild::run(RunContext context)
         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)
+            );
 
             auto result = TRY_AWAIT(
                 AIO().timeoutAfter(15 * kj::MINUTES, lockFileAsync(uploadLock.get(), ltWrite))
@@ -457,7 +534,9 @@ kj::Promise<void> AcceptedBuild::run(RunContext context)
         auto substitute = settings.buildersUseSubstitutes ? Substitute : NoSubstitute;
 
         {
-            Activity act(*logger, lvlTalkative, actUnknown, fmt("copying dependencies to '%s'", storeUri));
+            auto act = logger->startActivity(
+                lvlTalkative, actUnknown, fmt("copying dependencies to '%s'", storeUri)
+            );
             TRY_AWAIT(copyPaths(*store, *sshStore, inputs, NoRepair, NoCheckSigs, substitute));
         }
 
@@ -527,7 +606,9 @@ kj::Promise<void> AcceptedBuild::run(RunContext context)
         }
 
         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 */
@@ -536,6 +617,10 @@ kj::Promise<void> AcceptedBuild::run(RunContext context)
             );
         }
 
+        // 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; "
@@ -526,29 +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();
 
         printMsg(lvlChatty, "running shell: %s", concatMapStringsSep(" ", args, shellEscape));
 
-        execvp(shell->c_str(), argPtrs.data());
+        RunningProgram proc = runProgram2(
+            {.program = *shell,
+             .searchPath = true,
+             .args = args,
+             .environment = env,
+             .dieWithParent = true}
+        );
 
-        throw SysError("executing shell '%s'", *shell);
+        // 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 {
@@ -582,7 +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;
 
@@ -611,6 +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

@@ -8,6 +8,7 @@
 #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"
@@ -44,7 +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)
@@ -174,11 +175,12 @@ static void update(AsyncIoRoot & aio, const StringSet & channelNames)
 
     // 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);
     }

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();

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);
 
@@ -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);
 }
 
@@ -1275,35 +1277,39 @@ static void opQuery(Globals & globals, Strings opFlags, Strings opArgs)
                                 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->str();
+                                    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) {
                                     const Attr & a(*attrs.get(i.name));
-                                    if(a.value->type() != nString) continue;
+                                    if (a.value.type() != nString) {
+                                        continue;
+                                    }
                                     XMLAttrs attrs3;
                                     attrs3["type"] = globals.state->symbols[i.name];
-                                    attrs3["value"] = a.value->str();
+                                    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

@@ -25,6 +25,7 @@
 #include <iostream>
 #include <algorithm>
 
+#include <ranges>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>
@@ -88,6 +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) {

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;
-    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, "");
+    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

@@ -5,6 +5,8 @@
 #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));
 
@@ -303,8 +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);
@@ -314,7 +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/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-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

@@ -235,14 +235,13 @@ 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) {
+                for (auto & i : *v2.attrs()) {
                     std::string name{evaluator->symbols[i.name]};
                     if (name.find(searchWord) == 0) {
                         if (prefix_ == "")
@@ -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/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) {

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,
@@ -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
@@ -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();
@@ -963,9 +967,9 @@ void NixRepl::loadReplOverlays()
     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;
 }
 
@@ -1090,7 +1099,7 @@ void NixRepl::addAttrsToScope(Value & attrs)
 {
     state.forceAttrs(attrs, noPos, "while evaluating an attribute set to be merged in the global scope");
     addToScope(
-        *attrs.attrs, [](const Attr & a) { return a.name; }, [](const Attr & a) { return a.value; }
+        *attrs.attrs(), [](const Attr & a) { return a.name; }, [](const Attr & a) { return a.value; }
     );
 }
 
@@ -1112,19 +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;
 }
 
@@ -1147,12 +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();
             }
 
-            auto a = v->attrs->get(state.ctx.symbols.create(attr));
+            auto a = v.attrs()->get(state.ctx.symbols.create(attr));
             if (!a) {
                 std::set<std::string> attrNames;
-                for (auto & attr : *v->attrs)
+                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

@@ -20,15 +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();
+    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;
@@ -73,7 +72,7 @@ public:
 
     const 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;
@@ -136,7 +135,7 @@ public:
     {
     }
 
-    void insert(Symbol name, Value * value, PosIdx pos = noPos)
+    void insert(Symbol name, Value value, PosIdx pos = noPos)
     {
         insert(Attr(name, value, pos));
     }

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
@@ -438,16 +439,16 @@ 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.str(), v.string.context), string_t{v.str(), {}}
+                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
@@ -500,7 +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) {
@@ -519,7 +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)
@@ -633,7 +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)
@@ -655,7 +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)
@@ -682,11 +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;
 }
@@ -711,7 +717,7 @@ 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)
+    for (auto & attr : *getValue(state).attrs())
         attrs.p.emplace_back(state.ctx.symbols[attr.name]);
     std::sort(attrs.p.begin(), attrs.p.end());
 

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 +5,105 @@
 #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)
+    : Value(app_t{}, mem, lhs, args, {})
+{
+}
+
+inline Value::Value(
+    app_t, EvalMemory & mem, const Value & lhs, std::span<Value> baseArgs, std::span<Value> moreArgs
+)
+{
+    auto app = static_cast<Value::App *>(
+        mem.allocBytes(sizeof(Value::App) + baseArgs.size_bytes() + moreArgs.size_bytes())
+    );
+    app->_left = lhs;
+    app->_n = baseArgs.size() + moreArgs.size();
+    std::copy(baseArgs.begin(), baseArgs.end(), app->_args);
+    std::copy(moreArgs.begin(), moreArgs.end(), app->_args + baseArgs.size());
+    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 +115,38 @@ 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);
@@ -224,39 +179,40 @@ 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)
     {
@@ -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/flake.cc

@@ -96,7 +96,7 @@ static void expectType(EvalState & state, ValueType type,
 
 static std::pair<std::map<FlakeId, FlakeInput>, std::optional<fetchers::Attrs>> parseFlakeInputs(
     EvalState & state,
-    Value * value,
+    Value & value,
     const PosIdx pos,
     const std::optional<Path> & baseDir,
     InputPath lockRootPath,
@@ -109,15 +109,15 @@ static void parseFlakeInputAttr(EvalState & state, const Attr & attr, fetchers::
 // Allow selecting a subset of enum values
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Wswitch-enum"
-    switch (attr.value->type()) {
+    switch (attr.value.type()) {
     case 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()));
         break;
     case 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()});
         break;
     case nInt: {
-        auto intValue = attr.value->integer.value;
+        auto intValue = attr.value.integer().value;
 
         if (intValue < 0) {
             state.ctx.errors
@@ -137,18 +137,24 @@ static void parseFlakeInputAttr(EvalState & state, const Attr & attr, fetchers::
             .make<TypeError>(
                 "flake input attribute '%s' is %s while a string, Boolean, or integer is expected",
                 state.ctx.symbols[attr.name],
-                showType(*attr.value)
+                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)
+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);
+    expectType(state, nAttrs, value, pos);
 
     FlakeInput input;
 
@@ -160,15 +166,15 @@ 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->str();
+                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(
@@ -176,8 +182,8 @@ static FlakeInput parseFlakeInput(EvalState & state,
                     )
                         .first;
             } else if (attr.name == sFollows) {
-                expectType(state, nString, *attr.value, attr.pos);
-                auto follows(parseInputPath(attr.value->str()));
+                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 {
@@ -218,7 +224,7 @@ static FlakeInput parseFlakeInput(EvalState & state,
 
 static std::pair<std::map<FlakeId, FlakeInput>, std::optional<fetchers::Attrs>> parseFlakeInputs(
     EvalState & state,
-    Value * value,
+    Value & value,
     const PosIdx pos,
     const std::optional<Path> & baseDir,
     InputPath lockRootPath,
@@ -228,10 +234,10 @@ static std::pair<std::map<FlakeId, FlakeInput>, std::optional<fetchers::Attrs>>
 {
     std::map<FlakeId, FlakeInput> inputs;
 
-    expectType(state, nAttrs, *value, pos);
+    expectType(state, nAttrs, value, pos);
 
     std::optional<fetchers::Attrs> selfAttrs = std::nullopt;
-    for (const nix::Attr & inputAttr : *(*value).attrs) {
+    for (const nix::Attr & inputAttr : *value.attrs()) {
         std::string inputName{state.ctx.symbols[inputAttr.name]};
         if (inputName == "self") {
             experimentalFeatureSettings.require(Xp::FlakeSelfAttrs);
@@ -241,10 +247,10 @@ static std::pair<std::map<FlakeId, FlakeInput>, std::optional<fetchers::Attrs>>
                     "'self' input attributes not allowed at %s", state.ctx.positions[inputAttr.pos]
                 );
             }
-            expectType(state, nAttrs, *inputAttr.value, inputAttr.pos);
+            expectType(state, nAttrs, inputAttr.value, inputAttr.pos);
 
             selfAttrs = selfAttrs.value_or(fetchers::Attrs{});
-            for (auto & attr : *inputAttr.value->attrs) {
+            for (auto & attr : *inputAttr.value.attrs()) {
                 parseFlakeInputAttr(state, attr, *selfAttrs);
             }
         } else {
@@ -328,14 +334,14 @@ 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->str();
+    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)) {
+    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);
@@ -361,11 +367,14 @@ static Flake getFlake(
         flake.resolvedRef = resolvedRef;
     }
 
-    if (auto outputs = vInfo.attrs->get(state.ctx.s.outputs)) {
-        expectType(state, nFunction, *outputs->value, outputs->pos);
+    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) {
+        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(
@@ -383,46 +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 &&
@@ -907,34 +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)
@@ -984,10 +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();
@@ -996,17 +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/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

@@ -68,7 +68,9 @@ std::string DrvInfo::queryName(EvalState & state)
         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");
+        name = state.forceStringNoCtx(
+            i->value, noPos, "while evaluating the 'name' attribute of a derivation"
+        );
     }
     return name;
 }
@@ -81,7 +83,7 @@ std::string DrvInfo::querySystem(EvalState & state)
         system = !i
             ? "unknown"
             : state.forceStringNoCtx(
-                  *i->value, i->pos, "while evaluating the 'system' attribute of a derivation"
+                  i->value, i->pos, "while evaluating the 'system' attribute of a derivation"
               );
     }
     return system;
@@ -98,7 +100,7 @@ std::optional<StorePath> DrvInfo::queryDrvPath(EvalState & state)
         } else {
             drvPath = {state.coerceToStorePath(
                 i->pos,
-                *i->value,
+                i->value,
                 context,
                 "while evaluating the 'drvPath' attribute of a derivation"
             )};
@@ -123,7 +125,7 @@ StorePath DrvInfo::queryOutPath(EvalState & state)
         NixStringContext context;
         if (i) {
             outPath = state.coerceToStorePath(
-                i->pos, *i->value, context, "while evaluating the output path of a derivation"
+                i->pos, i->value, context, "while evaluating the output path of a derivation"
             );
         }
     }
@@ -156,23 +158,17 @@ 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...
@@ -184,10 +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.
-            const 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?
@@ -196,12 +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);
@@ -233,7 +224,7 @@ DrvInfo::Outputs DrvInfo::queryOutputs(EvalState & state, bool withPaths, bool o
     // explicitly selected-into output.
     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"
         );
@@ -253,15 +244,16 @@ 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(std::string(elem->str()));
+        }
+        auto out = outputs.find(std::string(elem.str()));
         if (out == outputs.end()) {
-            throw Error(errMsg + "output '%s' does not exist", elem->str());
+            throw Error(errMsg + "output '%s' does not exist", elem.str());
         }
         result.insert(*out);
     }
@@ -274,7 +266,7 @@ std::string DrvInfo::queryOutputName(EvalState & state)
     if (outputName == "" && attrs) {
         auto i = attrs->get(state.ctx.s.outputName);
         outputName = i ? state.forceStringNoCtx(
-                             *i->value, noPos, "while evaluating the output name of a derivation"
+                             i->value, noPos, "while evaluating the output name of a derivation"
                          )
                        : "";
     }
@@ -290,8 +282,8 @@ Bindings * DrvInfo::getMeta(EvalState & state)
     if (!a) {
         return 0;
     }
-    state.forceAttrs(*a->value, a->pos, "while evaluating the 'meta' attribute of a derivation");
-    meta = a->value->attrs;
+    state.forceAttrs(a->value, a->pos, "while evaluating the 'meta' attribute of a derivation");
+    meta = a->value.attrs();
     return meta;
 }
 
@@ -310,17 +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) {
-        auto i = v.attrs->get(state.ctx.s.outPath);
+        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;
+        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 ||
@@ -332,10 +330,10 @@ Value * DrvInfo::queryMeta(EvalState & state, const std::string & name)
 {
     if (!getMeta(state)) return 0;
     auto a = meta->get(state.ctx.symbols.create(name));
-    if (!a || !checkMeta(state, *a->value)) {
+    if (!a || !checkMeta(state, a->value)) {
         return 0;
     }
-    return a->value;
+    return &a->value;
 }
 
 
@@ -351,7 +349,9 @@ 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. */
@@ -366,7 +366,9 @@ 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. */
@@ -380,8 +382,7 @@ bool DrvInfo::queryMetaBool(EvalState & state, const std::string & name, bool de
     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));
@@ -390,7 +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();
 }
 
@@ -409,7 +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);
 
@@ -462,19 +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
                 );
             }
         }
@@ -489,7 +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;
     }
@@ -497,14 +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->get(state.ctx.symbols.create("_combineChannels"));
+    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)) {
@@ -514,7 +509,7 @@ static void getDerivations(EvalState & state, Value & vIn, PosIdx pos,
         if (combineChannels) {
             getDerivations(
                 state,
-                *attr->value,
+                attr->value,
                 attr->pos,
                 joinedAttrPath,
                 autoArgs,
@@ -522,18 +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) {
+            if (attr->value.type() == nAttrs) {
                 const Attr * recurseForDrvs =
-                    attr->value->attrs->get(state.ctx.s.recurseForDerivations);
+                    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"))
                 );
@@ -543,7 +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;
     }
@@ -113,21 +121,21 @@ public:
             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;
     }
@@ -178,10 +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/nixexpr.cc

@@ -9,7 +9,9 @@
 namespace nix {
 
 ExprBlackHole eBlackHole;
-Expr *eBlackHoleAddr = &eBlackHole;
+
+static Env nullEnv;
+Value::Thunk Value::blackHole{{&nullEnv}, &eBlackHole};
 
 // FIXME: remove, because *symbols* are abstract and do not have a single
 //        textual representation; see printIdentifier()
@@ -47,11 +49,11 @@ JSON ExprLiteral::toJSON(const SymbolTable & symbols) const
     switch (v.type()) {
         case nInt:
             valueType = "Int";
-            value = v.integer.value;
+            value = v.integer().value;
             break;
         case nFloat:
             valueType = "Float";
-            value = v.fpoint;
+            value = v.fpoint();
             break;
         case nString:
             valueType = "String";

lix/libexpr/nixexpr.hh

@@ -127,7 +127,7 @@ public:
     virtual JSON toJSON(const SymbolTable & symbols) const;
     virtual void accept(ExprVisitor & ev, std::unique_ptr<Expr> & ptr) = 0;
     virtual void eval(EvalState & state, Env & env, Value & v);
-    virtual Value * maybeThunk(EvalState & state, Env & env);
+    virtual Value maybeThunk(EvalState & state, Env & env);
     virtual void setName(Symbol name);
     PosIdx getPos() const { return pos; }
 
@@ -175,26 +175,61 @@ protected:
     Value v;
     ExprLiteral(const PosIdx pos) : Expr(pos) {};
 public:
-
-    ExprLiteral(const PosIdx pos, NewValueAs::integer_t, NixInt n) : Expr(pos) { v.mkInt(n); };
-    ExprLiteral(const PosIdx pos, NewValueAs::integer_t, NixInt::Inner n) : Expr(pos) { v.mkInt(n); };
-    ExprLiteral(const PosIdx pos, NewValueAs::floating_t, NixFloat nf) : Expr(pos) { v.mkFloat(nf); };
-    Value * maybeThunk(EvalState & state, Env & env) override;
+    Value maybeThunk(EvalState & state, Env & env) override;
     JSON toJSON(const SymbolTable & symbols) const override;
     void eval(EvalState & state, Env & env, Value & v) override;
     void accept(ExprVisitor & ev, std::unique_ptr<Expr> & ptr) override { ev.visit(*this, ptr); }
 };
 
+struct ExprInt : ExprLiteral
+{
+    Value::Int i;
+    ExprInt(const PosIdx pos, NixInt n) : ExprLiteral(pos), i{{Value::Acb::tInt}, n}
+    {
+        v = Value::isTaggableInteger(n) ? Value{NewValueAs::integer, n} : Value(i);
+    }
+    ExprInt(const PosIdx pos, NixInt::Inner n) : ExprInt(pos, NixInt(n)) {}
+};
+
+struct ExprFloat : ExprLiteral
+{
+    Value::Float f;
+    ExprFloat(const PosIdx pos, NewValueAs::floating_t, double f)
+        : ExprLiteral(pos)
+        , f{{Value::Acb::tFloat}, f}
+    {
+        v = Value(this->f);
+    }
+};
+
 struct ExprString : ExprLiteral
 {
-    std::string s;
-    ExprString(const PosIdx pos, std::string &&s) : ExprLiteral(pos), s(std::move(s)) { v.mkString(this->s.data()); };
+    std::unique_ptr<Value::Str, Value::Str::Deleter> contents;
+    Value::String strcb{.content = contents.get(), .context = nullptr};
+    ExprString(const PosIdx pos, std::string s) : ExprLiteral(pos), contents(Value::Str::copy(s))
+    {
+        v = {NewValueAs::string, &strcb};
+    }
+
+    std::string_view str() const
+    {
+        return contents->str();
+    }
 };
 
 struct ExprPath : ExprLiteral
 {
-    std::string s;
-    ExprPath(const PosIdx pos, std::string s) : ExprLiteral(pos), s(std::move(s)) { v.mkPath(this->s.c_str()); };
+    std::unique_ptr<Value::Str, Value::Str::Deleter> contents;
+    Value::String strcb{.content = contents.get(), .context = Value::String::path};
+    ExprPath(const PosIdx pos, std::string s) : ExprLiteral(pos), contents(Value::Str::copy(s))
+    {
+        v = Value{NewValueAs::path, &strcb};
+    }
+
+    std::string_view str() const
+    {
+        return contents->str();
+    }
 };
 
 typedef uint32_t Level;
@@ -228,7 +263,7 @@ struct ExprVar : Expr
 
     ExprVar(Symbol name) : name(name), needsRoot(false) { };
     ExprVar(const PosIdx & pos, Symbol name, bool needsRoot = false) : Expr(pos), name(name), needsRoot(needsRoot) { };
-    Value * maybeThunk(EvalState & state, Env & env) override;
+    Value maybeThunk(EvalState & state, Env & env) override;
     JSON toJSON(const SymbolTable & symbols) const override;
     void eval(EvalState & state, Env & env, Value & v) override;
     void accept(ExprVisitor & ev, std::unique_ptr<Expr> & ptr) override { ev.visit(*this, ptr); }
@@ -254,6 +289,8 @@ struct ExprInheritFrom : Expr
     void accept(ExprVisitor & ev, std::unique_ptr<Expr> & ptr) override { ev.visit(*this, ptr); }
 };
 
+struct Attr;
+
 struct ExprSelect : Expr
 {
     /** The expression attributes are being selected on. e.g. `foo` in `foo.bar.baz`. */
@@ -272,6 +309,9 @@ struct ExprSelect : Expr
     JSON toJSON(const SymbolTable & symbols) const override;
     void eval(EvalState & state, Env & env, Value & v) override;
     void accept(ExprVisitor & ev, std::unique_ptr<Expr> & ptr) override { ev.visit(*this, ptr); }
+
+private:
+    Attr const * selectSingleAttr(EvalState & state, Env & env, AttrName const & attrName, Value & vCurrent);
 };
 
 struct ExprOpHasAttr : Expr
@@ -370,7 +410,7 @@ struct ExprList : Expr
     JSON toJSON(const SymbolTable & symbols) const override;
     void eval(EvalState & state, Env & env, Value & v) override;
     void accept(ExprVisitor & ev, std::unique_ptr<Expr> & ptr) override { ev.visit(*this, ptr); }
-    Value * maybeThunk(EvalState & state, Env & env) override;
+    Value maybeThunk(EvalState & state, Env & env) override;
 };
 
 struct Pattern {
@@ -384,7 +424,8 @@ struct Pattern {
 
     virtual std::shared_ptr<const StaticEnv> buildEnv(const StaticEnv * up) = 0;
     virtual void accept(ExprVisitor & ev) = 0;
-    virtual Env & match(ExprLambda & lambda, EvalState & state, Env & up, Value * arg, const PosIdx pos) = 0;
+    virtual Env &
+    match(ExprLambda & lambda, EvalState & state, Env & up, Value & arg, const PosIdx pos) = 0;
 
     virtual void addBindingsToJSON(JSON & out, const SymbolTable & symbols) const = 0;
 };
@@ -399,7 +440,8 @@ struct SimplePattern : Pattern
 
     virtual std::shared_ptr<const StaticEnv> buildEnv(const StaticEnv * up) override;
     virtual void accept(ExprVisitor & ev) override;
-    virtual Env & match(ExprLambda & lambda, EvalState & state, Env & up, Value * arg, const PosIdx pos) override;
+    virtual Env &
+    match(ExprLambda & lambda, EvalState & state, Env & up, Value & arg, const PosIdx pos) override;
 
     virtual void addBindingsToJSON(JSON & out, const SymbolTable & symbols) const override;
 };
@@ -420,7 +462,8 @@ struct AttrsPattern : Pattern
 
     virtual std::shared_ptr<const StaticEnv> buildEnv(const StaticEnv * up) override;
     virtual void accept(ExprVisitor & ev) override;
-    virtual Env & match(ExprLambda & lambda, EvalState & state, Env & up, Value * arg, const PosIdx pos) override;
+    virtual Env &
+    match(ExprLambda & lambda, EvalState & state, Env & up, Value & arg, const PosIdx pos) override;
 
     virtual void addBindingsToJSON(JSON & out, const SymbolTable & symbols) const override;
 

lix/libexpr/parser/parser-impl1.inc.cc

@@ -148,7 +148,7 @@ struct ExprState
     std::unique_ptr<Expr> negate(PosIdx pos, State & state)
     {
         std::vector<std::unique_ptr<Expr>> args(2);
-        args[0] = std::make_unique<ExprLiteral>(pos, NewValueAs::integer, 0);
+        args[0] = std::make_unique<ExprInt>(pos, 0);
         args[1] = popExprOnly();
         return std::make_unique<ExprCall>(pos, state.mkInternalVar(pos, state.s.sub), std::move(args));
     }
@@ -326,10 +326,11 @@ template<> struct BuildAST<grammar::v1::attr::simple> {
 template<> struct BuildAST<grammar::v1::attr::string> {
     static void apply(const auto & in, auto & s, State & ps) {
         auto e = s->popExprOnly();
-        if (auto str = dynamic_cast<ExprString *>(e.get()))
-            s.pushAttr(ps.symbols.create(str->s), ps.at(in));
-        else
+        if (auto estr = dynamic_cast<ExprString *>(e.get())) {
+            s.pushAttr(ps.symbols.create(estr->str()), ps.at(in));
+        } else {
             s.pushAttr(std::move(e), ps.at(in));
+        }
     }
 };
 
@@ -387,9 +388,9 @@ template<> struct BuildAST<grammar::v1::inherit> : change_head<InheritState> {
         for (auto & i : s.attrs) {
             if (i.symbol)
                 continue;
-            if (auto str = dynamic_cast<ExprString *>(i.expr.get()))
-                i = AttrName(i.pos, ps.symbols.create(str->s));
-            else {
+            if (auto estr = dynamic_cast<ExprString *>(i.expr.get())) {
+                i = AttrName(i.pos, ps.symbols.create(estr->str()));
+            } else {
                 throw ParseError({
                     .msg = HintFmt("dynamic attributes not allowed in inherit"),
                     .pos = ps.positions[i.pos]
@@ -507,7 +508,7 @@ template<> struct BuildAST<grammar::v1::expr::int_> {
                 .pos = ps.positions[ps.at(in)],
             });
         }
-        s.emplaceExpr<ExprLiteral>(ps.at(in), NewValueAs::integer, v);
+        s.emplaceExpr<ExprInt>(ps.at(in), v);
     }
 };
 
@@ -542,7 +543,7 @@ template<> struct BuildAST<grammar::v1::expr::float_> {
                 });
             }
         }();
-        s.emplaceExpr<ExprLiteral>(ps.at(in), NewValueAs::floating, v);
+        s.emplaceExpr<ExprFloat>(ps.at(in), NewValueAs::floating, v);
     }
 };
 
@@ -770,13 +771,15 @@ template<> struct BuildAST<grammar::v1::path> : change_head<StringState> {
     template<typename E>
     static void check_slash(PosIdx end, StringState & s, State & ps) {
         auto e = dynamic_cast<E *>(s.parts.back().second.get());
-        if (!e || !e->s.ends_with('/'))
+        if (!e || !e->str().ends_with('/')) {
             return;
-        if (s.parts.size() > 1 || e->s != "/")
+        }
+        if (s.parts.size() > 1 || e->str() != "/") {
             throw ParseError({
                 .msg = HintFmt("path has a trailing slash"),
                 .pos = ps.positions[end],
             });
+        }
     }
 
     static void success(const auto & in, StringState & s, ExprState & e, State & ps) {

lix/libexpr/primops.hh

@@ -33,7 +33,7 @@ struct RegisterPrimOp
      * will get called during EvalState initialization, so there
      * may be primops not yet added and builtins is not yet sorted.
      */
-    RegisterPrimOp(PrimOp && primOp);
+    RegisterPrimOp(PrimOpDetails && primOp);
 };
 
 /* These primops are disabled without enableNativeCode, but plugins

lix/libexpr/primops/context.cc

@@ -3,6 +3,7 @@
 #include "lix/libstore/derivations.hh"
 #include "lix/libstore/store-api.hh"
 #include "lix/libutil/types.hh"
+#include "value.hh"
 
 namespace nix {
 
@@ -147,9 +148,10 @@ void prim_getContext(EvalState & state, Value * * args, Value & v)
             infoAttrs.alloc(sAllOutputs).mkBool(true);
         if (!info.second.outputs.empty()) {
             auto & outputsVal = infoAttrs.alloc(state.ctx.s.outputs);
-            outputsVal = state.ctx.mem.newList(info.second.outputs.size());
+            auto content = state.ctx.mem.newList(info.second.outputs.size());
+            outputsVal = {NewValueAs::list, content};
             for (const auto & [i, output] : enumerate(info.second.outputs))
-                (outputsVal.listElems()[i] = state.ctx.mem.allocValue())->mkString(output);
+                content->elems[i].mkString(output);
         }
         attrs.alloc(state.ctx.store->printStorePath(info.first)).mkAttrs(infoAttrs);
     }
@@ -171,7 +173,7 @@ static void prim_appendContext(EvalState & state, Value * * args, Value & v)
     state.forceAttrs(*args[1], noPos, "while evaluating the second argument passed to builtins.appendContext");
 
     auto sAllOutputs = state.ctx.symbols.create("allOutputs");
-    for (auto & i : *args[1]->attrs) {
+    for (auto & i : *args[1]->attrs()) {
         const auto & name = state.ctx.symbols[i.name];
         if (!state.ctx.store->isStorePath(name))
             state.ctx.errors.make<EvalError>(
@@ -181,11 +183,11 @@ static void prim_appendContext(EvalState & state, Value * * args, Value & v)
         auto namePath = state.ctx.store->parseStorePath(name);
         if (!settings.readOnlyMode)
             state.aio.blockOn(state.ctx.store->ensurePath(namePath));
-        state.forceAttrs(*i.value, i.pos, "while evaluating the value of a string context");
-        auto a = i.value->attrs->get(state.ctx.s.path);
+        state.forceAttrs(i.value, i.pos, "while evaluating the value of a string context");
+        auto a = i.value.attrs()->get(state.ctx.s.path);
         if (a) {
             if (state.forceBool(
-                    *a->value, a->pos, "while evaluating the `path` attribute of a string context"
+                    a->value, a->pos, "while evaluating the `path` attribute of a string context"
                 ))
             {
                 context.emplace(NixStringContextElem::Opaque{
@@ -194,10 +196,10 @@ static void prim_appendContext(EvalState & state, Value * * args, Value & v)
             }
         }
 
-        a = i.value->attrs->get(sAllOutputs);
+        a = i.value.attrs()->get(sAllOutputs);
         if (a) {
             if (state.forceBool(
-                    *a->value,
+                    a->value,
                     a->pos,
                     "while evaluating the `allOutputs` attribute of a string context"
                 ))
@@ -214,20 +216,20 @@ static void prim_appendContext(EvalState & state, Value * * args, Value & v)
             }
         }
 
-        a = i.value->attrs->get(state.ctx.s.outputs);
+        a = i.value.attrs()->get(state.ctx.s.outputs);
         if (a) {
             state.forceList(
-                *a->value, a->pos, "while evaluating the `outputs` attribute of a string context"
+                a->value, a->pos, "while evaluating the `outputs` attribute of a string context"
             );
-            if (a->value->listSize() && !isDerivation(name)) {
+            if (a->value.listSize() && !isDerivation(name)) {
                 state.ctx.errors.make<EvalError>(
                     "tried to add derivation output context of %s, which is not a derivation, to a string",
                     name
                 ).atPos(i.pos).debugThrow();
             }
-            for (auto elem : a->value->listItems()) {
+            for (auto & elem : a->value.listItems()) {
                 auto outputName = state.forceStringNoCtx(
-                    *elem, a->pos, "while evaluating an output name within a string context"
+                    elem, a->pos, "while evaluating an output name within a string context"
                 );
                 context.emplace(NixStringContextElem::Built {
                     .drvPath = makeConstantStorePath(namePath),

lix/libexpr/primops/fetchClosure.cc

@@ -118,7 +118,7 @@ void prim_fetchClosure(EvalState & state, Value * * args, Value & v)
     std::optional<StorePathOrGap> toPath;
     std::optional<bool> inputAddressedMaybe;
 
-    for (auto & attr : *args[0]->attrs) {
+    for (auto & attr : *args[0]->attrs()) {
         const auto & attrName = state.ctx.symbols[attr.name];
         auto attrHint = [&]() -> std::string {
             return "while evaluating the '" + attrName + "' attribute passed to builtins.fetchClosure";
@@ -126,27 +126,26 @@ void prim_fetchClosure(EvalState & state, Value * * args, Value & v)
 
         if (attrName == "fromPath") {
             NixStringContext context;
-            fromPath = state.coerceToStorePath(attr.pos, *attr.value, context, attrHint());
+            fromPath = state.coerceToStorePath(attr.pos, attr.value, context, attrHint());
         }
 
         else if (attrName == "toPath") {
-            state.forceValue(*attr.value, attr.pos);
-            bool isEmptyString = attr.value->type() == nString && attr.value->str().empty();
+            state.forceValue(attr.value, attr.pos);
+            bool isEmptyString = attr.value.type() == nString && attr.value.str().empty();
             if (isEmptyString) {
                 toPath = StorePathOrGap {};
             }
             else {
                 NixStringContext context;
-                toPath = state.coerceToStorePath(attr.pos, *attr.value, context, attrHint());
+                toPath = state.coerceToStorePath(attr.pos, attr.value, context, attrHint());
             }
         }
 
         else if (attrName == "fromStore")
-            fromStoreUrl = state.forceStringNoCtx(*attr.value, attr.pos,
-                    attrHint());
+            fromStoreUrl = state.forceStringNoCtx(attr.value, attr.pos, attrHint());
 
         else if (attrName == "inputAddressed")
-            inputAddressedMaybe = state.forceBool(*attr.value, attr.pos, attrHint());
+            inputAddressedMaybe = state.forceBool(attr.value, attr.pos, attrHint());
 
         else
             throw Error({