chore(libmain): license it under LGPL-2.1-only

Progress towards REUSE compliance.

Change-Id: I2991234cfd193773a377d2f1735b9974918b8138
Signed-off-by: Raito Bezarius <raito@lix.systems>

doc/manual/change-authors.yml

@@ -44,6 +44,11 @@ cole-h:
   display_name: Cole Helbling
   github: cole-h
 
+delan:
+  display_name: delan
+  forgejo: delan
+  github: delan
+
 edolstra:
   display_name: Eelco Dolstra
   github: edolstra
@@ -91,6 +96,10 @@ puck:
   forgejo: puck
   github: puckipedia
 
+quantumjump:
+  display_name: Quantum Jump
+  github: QuantumBJump
+
 r-vdp:
   github: r-vdp
 

doc/manual/rl-next/better-attrpath-errors.md

@@ -0,0 +1,90 @@
+---
+synopsis: "Trace which part of a `foo.bar.baz` expression errors"
+cls: 1505, 1506
+credits: Qyriad
+category: Improvements
+---
+
+Previously, if an attribute path selection expression like `linux_4_9.meta.description` it wouldn't show you which one of those parts in the attribute path, or even that that line of code is what caused evaluation of the failing expression.
+The previous error looks like this:
+
+```
+pkgs.linuxKernel.kernels.linux_4_9.meta.description
+
+error:
+       … while evaluating the attribute 'linuxKernel.kernels.linux_4_9.meta.description'
+         at /nix/store/dk2rpyb6ndvfbf19bkb2plcz5y3k8i5v-source/pkgs/top-level/linux-kernels.nix:278:5:
+          277|   } // lib.optionalAttrs config.allowAliases {
+          278|     linux_4_9 = throw "linux 4.9 was removed because it will reach its end of life within 22.11";
+             |     ^
+          279|     linux_4_14 = throw "linux 4.14 was removed because it will reach its end of life within 23.11";
+
+       … while calling the 'throw' builtin
+         at /nix/store/dk2rpyb6ndvfbf19bkb2plcz5y3k8i5v-source/pkgs/top-level/linux-kernels.nix:278:17:
+          277|   } // lib.optionalAttrs config.allowAliases {
+          278|     linux_4_9 = throw "linux 4.9 was removed because it will reach its end of life within 22.11";
+             |                 ^
+          279|     linux_4_14 = throw "linux 4.14 was removed because it will reach its end of life within 23.11";
+
+       error: linux 4.9 was removed because it will reach its end of life within 22.11
+```
+
+Now, the error will look like this:
+
+```
+pkgs.linuxKernel.kernels.linux_4_9.meta.description
+
+error:
+       … while evaluating the attribute 'linuxKernel.kernels.linux_4_9.meta.description'
+         at /nix/store/dk2rpyb6ndvfbf19bkb2plcz5y3k8i5v-source/pkgs/top-level/linux-kernels.nix:278:5:
+          277|   } // lib.optionalAttrs config.allowAliases {
+          278|     linux_4_9 = throw "linux 4.9 was removed because it will reach its end of life within 22.11";
+             |     ^
+          279|     linux_4_14 = throw "linux 4.14 was removed because it will reach its end of life within 23.11";
+
+       … while evaluating 'pkgs.linuxKernel.kernels.linux_4_9' to select 'meta' on it
+         at «string»:1:1:
+            1| pkgs.linuxKernel.kernels.linux_4_9.meta.description
+             | ^
+
+       … caused by explicit throw
+         at /nix/store/dk2rpyb6ndvfbf19bkb2plcz5y3k8i5v-source/pkgs/top-level/linux-kernels.nix:278:17:
+          277|   } // lib.optionalAttrs config.allowAliases {
+          278|     linux_4_9 = throw "linux 4.9 was removed because it will reach its end of life within 22.11";
+             |                 ^
+          279|     linux_4_14 = throw "linux 4.14 was removed because it will reach its end of life within 23.11";
+
+       error: linux 4.9 was removed because it will reach its end of life within 22.11
+```
+
+Not only does the line of code that referenced the failing attribute show up in the trace, it also tells you that it was specifically the `linux_4_9` part that failed.
+
+This includes if the failing part is a top-level binding:
+
+```
+let
+  inherit (pkgs.linuxKernel.kernels) linux_4_9;
+in linux_4_9.meta.description
+error:
+       … while evaluating 'linux_4_9' to select 'meta.description' on it
+         at «string»:3:4:
+            2|   inherit (pkgs.linuxKernel.kernels) linux_4_9;
+            3| in linux_4_9.meta.description
+             |    ^
+
+       … while evaluating the attribute 'linux_4_9'
+         at /nix/store/dk2rpyb6ndvfbf19bkb2plcz5y3k8i5v-source/pkgs/top-level/linux-kernels.nix:278:5:
+          277|   } // lib.optionalAttrs config.allowAliases {
+          278|     linux_4_9 = throw "linux 4.9 was removed because it will reach its end of life within 22.11";
+             |     ^
+          279|     linux_4_14 = throw "linux 4.14 was removed because it will reach its end of life within 23.11";
+
+       … caused by explicit throw
+         at /nix/store/dk2rpyb6ndvfbf19bkb2plcz5y3k8i5v-source/pkgs/top-level/linux-kernels.nix:278:17:
+          277|   } // lib.optionalAttrs config.allowAliases {
+          278|     linux_4_9 = throw "linux 4.9 was removed because it will reach its end of life within 22.11";
+             |                 ^
+          279|     linux_4_14 = throw "linux 4.14 was removed because it will reach its end of life within 23.11";
+
+       error: linux 4.9 was removed because it will reach its end of life within 22.11
+```

doc/manual/rl-next/distinguish-throw-errors.md

@@ -0,0 +1,70 @@
+---
+synopsis: "Distinguish between explicit throws and errors that happened while evaluating a throw"
+cls: 1511
+credits: Qyriad
+category: Improvements
+---
+
+Previously, errors caused by an expression like `throw "invalid argument"` were treated like an error that happened simply while some builtin function was being called:
+
+```
+let
+  throwMsg = p: throw "${p} isn't the right package";
+in throwMsg "linuz"
+
+error:
+       … while calling the 'throw' builtin
+         at «string»:2:17:
+            1| let
+            2|   throwMsg = p: throw "${p} isn't the right package";
+             |                 ^
+            3| in throwMsg "linuz"
+
+       error: linuz isn't the right package
+```
+
+But the error didn't just happen "while" calling the `throw` builtin — it's a throw error!
+Now it looks like this:
+
+```
+let
+  throwMsg = p: throw "${p} isn't the right package";
+in throwMsg "linuz"
+
+error:
+       … caused by explicit throw
+         at «string»:2:17:
+            1| let
+            2|   throwMsg = p: throw "${p} isn't the right package";
+             |                 ^
+            3| in throwMsg "linuz"
+
+       error: linuz isn't the right package
+```
+
+This also means that incorrect usage of `throw` or errors evaluating its arguments are easily distinguishable from explicit throws:
+
+```
+let
+  throwMsg = p: throw "${p} isn't the right package";
+in throwMsg { attrs = "error when coerced in string interpolation"; }
+
+error:
+       … while calling the 'throw' builtin
+         at «string»:2:17:
+            1| let
+            2|   throwMsg = p: throw "${p} isn't the right package";
+             |                 ^
+            3| in throwMsg { attrs = "error when coerced in string interpolation"; }
+
+       … while evaluating a path segment
+         at «string»:2:24:
+            1| let
+            2|   throwMsg = p: throw "${p} isn't the right package";
+             |                        ^
+            3| in throwMsg { attrs = "error when coerced in string interpolation"; }
+
+       error: cannot coerce a set to a string: { attrs = "error when coerced in string interpolation"; }
+```
+
+Here, instead of an actual thrown error, a type error happens first (trying to coerce an attribute set to a string), but that type error happened *while* calling `throw`.

doc/manual/rl-next/fix-gc-dry-run.md

@@ -0,0 +1,29 @@
+---
+synopsis: Fix nix-collect-garbage --dry-run
+issues: [fj#432]
+cls: [1566]
+category: Fixes
+credits: [quantumjump]
+---
+
+`nix-collect-garbage --dry-run` did not previously give any output - it simply
+exited without even checking to see what paths would be deleted.
+
+```
+$ nix-collect-garbage --dry-run
+$
+```
+
+We updated the behaviour of the flag such that instead it prints out how many
+paths it *would* delete, but doesn't actually delete them.
+
+```
+$ nix-collect-garbage --dry-run
+finding garbage collector roots...
+determining live/dead paths...
+...
+<nix store paths>
+...
+2670 store paths deleted, 0.00MiB freed
+$
+```

doc/manual/rl-next/fod-failure-includes-url.md

@@ -0,0 +1,16 @@
+---
+synopsis: "Hash mismatch diagnostics for fixed-output derivations include the URL"
+cls: [1536]
+credits: [jade]
+category: Improvements
+---
+
+Now, when building fixed-output derivations, Lix will guess the URL that was used in the derivation using the `url` or `urls` properties in the derivation environment.
+This is a layering violation but making these diagnostics tractable when there are multiple instances of the `AAAA` hash is too significant of an improvement to pass it up.
+
+```
+error: hash mismatch in fixed-output derivation '/nix/store/sjfw324j4533lwnpmr5z4icpb85r63ai-x1.drv':
+        likely URL: https://meow.puppy.forge/puppy.tar.gz
+         specified: sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=
+            got:    sha256-a1Qvp3FOOkWpL9kFHgugU1ok5UtRPSu+NwCZKbbaEro=
+```

doc/manual/rl-next/registry-add-shorthand-only.md

@@ -0,0 +1,10 @@
+---
+synopsis: "`nix registry add` now requires a shorthand flakeref on the 'from' side"
+cls: 1494
+credits: delan
+category: Improvements
+---
+
+The 'from' argument must now be a shorthand flakeref like `nixpkgs` or `nixpkgs/nixos-20.03`, making it harder to accidentally swap the 'from' and 'to' arguments.
+
+Registry entries that map from other flake URLs can still be specified in registry.json, the `nix.registry` option in NixOS, or the `--override-flake` option in the CLI, but they are not guaranteed to work correctly.

doc/manual/rl-next/reject-flake-config.md

@@ -0,0 +1,9 @@
+---
+synopsis: Allow automatic rejection of configuration options from flakes
+cls: [1541]
+credits: [alois31]
+category: Improvements
+---
+
+Setting `accept-flake-config` to `false` now respects user choice by automatically rejecting configuration options set by flakes.
+The old behaviour of asking each time is still available (and default) by setting it to the special value `ask`.

doc/manual/src/contributing/testing.md

@@ -433,9 +433,6 @@ I grepped `src/` for `get[eE]nv\("` to find the mentions in Lix code.
 - `NIX_PROFILE` - Selects which profile `nix-env` will operate on. Documented elsewhere.
 - `NIX_SSHOPTS` - Options passed to `ssh(1)` when using a ssh remote store.
   Incorrectly documented on `nix-copy-closure` which is *surely* not the only place they are used??
-- `_NIX_TEST_NO_LSOF` - Used on non-Linux, non-macOS platforms to disable using `lsof` when finding gc roots.
-
-  Since https://git.lix.systems/lix-project/lix/issues/156 was fixed, this should probably just be removed as it was a bad workaround for a macOS issue.
 - `_NIX_TEST_GC_SYNC_1` - Path to a pipe that is used to block the GC briefly to validate invariants from the test suite.
 - `_NIX_TEST_GC_SYNC_2` - Path to a pipe that is used to block the GC briefly to validate invariants from the test suite.
 - `_NIX_TEST_FREE_SPACE_FILE` - Path to a file containing a decimal number with the free space that the GC is to believe it has.

meson.build

@@ -142,6 +142,16 @@ else
   cpp_pch = []
 endif
 
+# gcc 12 is known to miscompile some coroutine-based code quite horribly,
+# causing (among other things) copies of move-only objects and the double
+# frees one would expect when the objects are unique_ptrs. these problems
+# often show up as memory corruption when nesting generators (since we do
+# treat generators like owned memory) and will cause inexplicable crashs.
+assert(
+  cxx.get_id() != 'gcc' or cxx.version().version_compare('>=13'),
+  'GCC 12 and earlier are known to miscompile lix coroutines, use GCC 13 or clang.'
+)
+
 
 # Translate some historical and Mesony CPU names to Lixy CPU names.
 # FIXME(Qyriad): the 32-bit x86 code is not tested right now, because cross compilation for Lix
@@ -432,6 +442,7 @@ add_project_arguments(
   '-Wimplicit-fallthrough',
   '-Werror=switch',
   '-Werror=switch-enum',
+  '-Werror=unused-result',
   '-Wdeprecated-copy',
   '-Wignored-qualifiers',
   # Enable assertions in libstdc++ by default. Harmless on libc++. Benchmarked

perl/meson.build

@@ -65,5 +65,6 @@ if cxx.get_linker_id() in ['ld.bfd', 'ld.gold']
 endif
 
 libstore = dependency('lixstore', 'lix-store', required : true)
+libutil = dependency('lixutil', 'lix-util', required : true)
 
 subdir('lib/Nix')

src/libcmd/built-path.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "built-path.hh"
 #include "derivations.hh"
 #include "store-api.hh"

src/libcmd/built-path.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 #include "derived-path.hh"

src/libcmd/cmd-profiles.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include <set>
 
 #include "cmd-profiles.hh"
@@ -244,7 +248,7 @@ StorePath ProfileManifest::build(ref<Store> store)
 
     /* Add the symlink tree to the store. */
     StringSink sink;
-    dumpPath(tempDir, sink);
+    sink << dumpPath(tempDir);
 
     auto narHash = hashString(htSHA256, sink.s);
 

src/libcmd/cmd-profiles.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 

src/libcmd/command.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "command.hh"
 #include "store-api.hh"
 #include "local-fs-store.hh"

src/libcmd/command.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 

src/libcmd/common-eval-args.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "eval-settings.hh"
 #include "common-eval-args.hh"
 #include "shared.hh"

src/libcmd/common-eval-args.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 

src/libcmd/editor-for.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "editor-for.hh"
 #include "environment-variables.hh"
 #include "source-path.hh"

src/libcmd/editor-for.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 

src/libcmd/installable-attr-path.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "globals.hh"
 #include "installable-attr-path.hh"
 #include "outputs-spec.hh"

src/libcmd/installable-attr-path.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 

src/libcmd/installable-derived-path.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "installable-derived-path.hh"
 #include "derivations.hh"
 

src/libcmd/installable-derived-path.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 

src/libcmd/installable-flake.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "globals.hh"
 #include "installable-flake.hh"
 #include "installable-derived-path.hh"

src/libcmd/installable-flake.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 

src/libcmd/installable-value.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "installable-value.hh"
 #include "eval-cache.hh"
 #include "fetch-to-store.hh"

src/libcmd/installable-value.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 

src/libcmd/installables.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "globals.hh"
 #include "installables.hh"
 #include "installable-derived-path.hh"

src/libcmd/installables.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 

src/libcmd/legacy.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "legacy.hh"
 
 namespace nix {

src/libcmd/legacy.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 

src/libcmd/markdown.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "markdown.hh"
 #include "error.hh"
 #include "finally.hh"

src/libcmd/markdown.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 

src/libcmd/meson.build

@@ -1,3 +1,7 @@
+# SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+#
+# SPDX-License-Identifier: LGPL-2.1-only
+
 libcmd_sources = files(
   'built-path.cc',
   'cmd-profiles.cc',

src/libcmd/repl-interacter.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "error.hh"
 #include "file-system.hh"
 #include "logging.hh"

src/libcmd/repl-interacter.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 /// @file
 

src/libcmd/repl-overlays.nix

@@ -1,3 +1,7 @@
+# SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+#
+# SPDX-License-Identifier: LGPL-2.1-only
+
 info: initial: functions:
 let
   final = builtins.foldl' (prev: function: prev // (function info final prev)) initial functions;

src/libcmd/repl.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include <cstdio>
 #include <editline.h>
 #include <iostream>
@@ -32,7 +36,6 @@
 #include "local-fs-store.hh"
 #include "signals.hh"
 #include "print.hh"
-#include "progress-bar.hh"
 #include "gc-small-vector.hh"
 #include "users.hh"
 
@@ -252,7 +255,7 @@ void runNix(Path program, const Strings & args)
         .program = settings.nixBinDir+ "/" + program,
         .args = args,
         .environment = subprocessEnv,
-    });
+    }).wait();
 
     return;
 }
@@ -300,7 +303,7 @@ ReplExitStatus NixRepl::mainLoop()
 
     /* Stop the progress bar because it interferes with the display of
        the repl. */
-    stopProgressBar();
+    logger->pause();
 
     std::string input;
 
@@ -651,7 +654,7 @@ ProcessLineResult NixRepl::processLine(std::string line)
 
         // runProgram redirects stdout to a StringSink,
         // using runProgram2 to allow editors to display their UI
-        runProgram2(RunOptions { .program = editor, .searchPath = true, .args = args });
+        runProgram2(RunOptions { .program = editor, .searchPath = true, .args = args }).wait();
 
         // Reload right after exiting the editor
         state->resetFileCache();
@@ -684,9 +687,10 @@ ProcessLineResult NixRepl::processLine(std::string line)
             // TODO: this only shows a progress bar for explicitly initiated builds,
             // not eval-time fetching or builds performed for IFD.
             // But we can't just show it everywhere, since that would erase partial output from evaluation.
-            startProgressBar();
+            logger->resetProgress();
+            logger->resume();
             Finally stopLogger([&]() {
-                stopProgressBar();
+                logger->pause();
             });
 
             state->store->buildPaths({

src/libcmd/repl.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 

src/libexpr/attr-path.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "attr-path.hh"
 #include "eval-inline.hh"
 

src/libexpr/attr-path.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 

src/libexpr/attr-set.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "attr-set.hh"
 #include "eval-inline.hh"
 

src/libexpr/attr-set.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 

src/libexpr/eval-cache.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "eval-cache.hh"
 #include "sqlite.hh"
 #include "eval.hh"

src/libexpr/eval-cache.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 

src/libexpr/eval-error.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "eval-error.hh"
 #include "eval.hh"
 #include "value.hh"

src/libexpr/eval-error.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 

src/libexpr/eval-inline.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 

src/libexpr/eval-settings.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "file-system.hh"
 #include "globals.hh"
 #include "profiles.hh"

src/libexpr/eval-settings.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 #include "config.hh"

src/libexpr/eval.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "eval.hh"
 #include "eval-settings.hh"
 #include "hash.hh"
@@ -1432,7 +1436,20 @@ void ExprSelect::eval(EvalState & state, Env & env, Value & v)
     Value * vCurrent = &vFirst;
     // Position for the current attrset Value in this select chain.
     PosIdx posCurrent;
-    e->eval(state, env, vFirst);
+
+    try {
+        e->eval(state, env, vFirst);
+    } catch (Error & e) {
+        assert(this->e != nullptr);
+        state.addErrorTrace(
+            e,
+            getPos(),
+            "while evaluating '%s' to select '%s' on it",
+            ExprPrinter(state, *this->e),
+            showAttrPath(state.symbols, this->attrPath)
+        );
+        throw;
+    }
 
     try {
         auto dts = state.debugRepl
@@ -1445,12 +1462,46 @@ void ExprSelect::eval(EvalState & state, Env & env, Value & v)
                 showAttrPath(state, env, attrPath))
             : nullptr;
 
-        for (auto const & currentAttrName : attrPath) {
+        for (auto const & [partIdx, currentAttrName] : enumerate(attrPath)) {
             state.nrLookups++;
 
             Symbol const name = getName(currentAttrName, state, env);
 
-            state.forceValue(*vCurrent, pos);
+            // For formatting errors, which should be done only when needed.
+            auto partsSoFar = [&]() -> std::string {
+                std::stringstream ss;
+                // We start with the base thing this ExprSelect is selecting on.
+                assert(this->e != nullptr);
+                this->e->show(state.symbols, ss);
+
+                // Then grab each part of the attr path up to this one.
+                assert(partIdx < attrPath.size());
+                std::span<AttrName> const parts(
+                    attrPath.begin(),
+                    attrPath.begin() + partIdx
+                );
+
+                // And convert them to strings and join them.
+                for (auto const & part : parts) {
+                    auto const partName = getName(part, state, env);
+                    ss << "." << state.symbols[partName];
+                }
+
+                return ss.str();
+            };
+
+            try {
+                state.forceValue(*vCurrent, pos);
+            } catch (Error & e) {
+                state.addErrorTrace(
+                    e,
+                    getPos(),
+                    "while evaluating '%s' to select '%s' on it",
+                    partsSoFar(),
+                    state.symbols[name]
+                );
+                throw;
+            }
 
             if (vCurrent->type() != nAttrs) {
 
@@ -1466,7 +1517,10 @@ void ExprSelect::eval(EvalState & state, Env & env, Value & v)
                     "expected a set but found %s: %s",
                     showType(*vCurrent),
                     ValuePrinter(state, *vCurrent, errorPrintOptions)
-                ).withTrace(pos, "while selecting an attribute").debugThrow();
+                ).addTrace(
+                    pos,
+                    HintFmt("while selecting '%s' on '%s'", state.symbols[name], partsSoFar())
+                ).debugThrow();
             }
 
             // Now that we know this is actually an attrset, try to find an attr
@@ -1757,6 +1811,15 @@ void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value &
 
                 try {
                     fn->fun(*this, vCur.determinePos(noPos), args, vCur);
+                } catch (ThrownError & e) {
+                    // Distinguish between an error that simply happened while "throw"
+                    // was being evaluated and an explicit thrown error.
+                    if (fn->name == "throw") {
+                        addErrorTrace(e, pos, "caused by explicit %s", "throw");
+                    } else {
+                        addErrorTrace(e, pos, "while calling the '%s' builtin", fn->name);
+                    }
+                    throw;
                 } catch (Error & e) {
                     addErrorTrace(e, pos, "while calling the '%1%' builtin", fn->name);
                     throw;

src/libexpr/eval.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 
@@ -9,14 +13,13 @@
 #include "symbol-table.hh"
 #include "config.hh"
 #include "experimental-features.hh"
-#include "input-accessor.hh"
 #include "search-path.hh"
 #include "repl-exit-status.hh"
 
+#include <gc/gc_allocator.h>
 #include <map>
 #include <optional>
 #include <unordered_map>
-#include <mutex>
 #include <functional>
 
 namespace nix {
@@ -38,11 +41,26 @@ namespace eval_cache {
     class EvalCache;
 }
 
+/** Alias for std::map which uses boehmgc's allocator conditional on us actually
+ * using boehmgc in this build.
+ */
+#if HAVE_BOEHMGC
+    template<typename KeyT, typename ValueT>
+    using GcMap = std::map<
+        KeyT,
+        ValueT,
+        std::less<KeyT>,
+        traceable_allocator<std::pair<KeyT const, ValueT>>
+    >;
+#else
+    using GcMap = std::map<KeyT, ValueT>
+#endif
+
 
 /**
  * Function that implements a primop.
  */
-typedef void (* PrimOpFun) (EvalState & state, const PosIdx pos, Value * * args, Value & v);
+using PrimOpImpl = void(EvalState & state, PosIdx pos, Value ** args, Value & v);
 
 /**
  * Info about a primitive operation, and its implementation
@@ -76,7 +94,7 @@ struct PrimOp
     /**
      * Implementation of the primop.
      */
-    std::function<std::remove_pointer<PrimOpFun>::type> fun;
+    std::function<PrimOpImpl> fun;
 
     /**
      * Optional experimental for this to be gated on.
@@ -115,11 +133,7 @@ struct Constant
     bool impureOnly = false;
 };
 
-#if HAVE_BOEHMGC
-    typedef std::map<std::string, Value *, std::less<std::string>, traceable_allocator<std::pair<const std::string, Value *> > > ValMap;
-#else
-    typedef std::map<std::string, Value *> ValMap;
-#endif
+using ValMap = GcMap<std::string, Value *>;
 
 struct Env
 {
@@ -214,7 +228,7 @@ public:
     /**
      * Debugger
      */
-    ReplExitStatus (* debugRepl)(ref<EvalState> es, const ValMap & extraEnv);
+    std::function<ReplExitStatus(ref<EvalState> es, ValMap const & extraEnv)> debugRepl;
     bool debugStop;
     bool inDebugger = false;
     int trylevel;
@@ -252,21 +266,13 @@ private:
     /**
      * A cache from path names to parse trees.
      */
-#if HAVE_BOEHMGC
-    typedef std::map<SourcePath, Expr *, std::less<SourcePath>, traceable_allocator<std::pair<const SourcePath, Expr *>>> FileParseCache;
-#else
-    typedef std::map<SourcePath, Expr *> FileParseCache;
-#endif
+    using FileParseCache = GcMap<SourcePath, Expr *>;
     FileParseCache fileParseCache;
 
     /**
      * A cache from path names to values.
      */
-#if HAVE_BOEHMGC
-    typedef std::map<SourcePath, Value, std::less<SourcePath>, traceable_allocator<std::pair<const SourcePath, Value>>> FileEvalCache;
-#else
-    typedef std::map<SourcePath, Value> FileEvalCache;
-#endif
+    using FileEvalCache = GcMap<SourcePath, Value>;
     FileEvalCache fileEvalCache;
 
     SearchPath searchPath;
@@ -737,15 +743,15 @@ private:
 
     bool countCalls;
 
-    typedef std::map<std::string, size_t> PrimOpCalls;
+    using PrimOpCalls = std::map<std::string, size_t>;
     PrimOpCalls primOpCalls;
 
-    typedef std::map<ExprLambda *, size_t> FunctionCalls;
+    using FunctionCalls = std::map<ExprLambda *, size_t>;
     FunctionCalls functionCalls;
 
     void incrFunctionCall(ExprLambda * fun);
 
-    typedef std::map<PosIdx, size_t> AttrSelects;
+    using AttrSelects = std::map<PosIdx, size_t>;
     AttrSelects attrSelects;
 
     friend struct ExprOpUpdate;
@@ -787,7 +793,7 @@ std::string showType(const Value & v);
  */
 SourcePath resolveExprPath(SourcePath path);
 
-static const std::string corepkgsPrefix{"/__corepkgs__/"};
+static constexpr std::string_view corepkgsPrefix{"/__corepkgs__/"};
 
 
 }

src/libexpr/fetchurl.nix

@@ -1,3 +1,7 @@
+# SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+#
+# SPDX-License-Identifier: LGPL-2.1-only
+
 {
   system ? "", # obsolete
   url,

src/libexpr/flake/call-flake.nix

@@ -1,3 +1,7 @@
+# SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+#
+# SPDX-License-Identifier: LGPL-2.1-only
+
 lockFileStr: rootSrc: rootSubdir:
 
 let

src/libexpr/flake/config.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "flake.hh"
 #include "logging.hh"
 #include "users.hh"
@@ -51,30 +55,46 @@ void ConfigFile::apply()
         else
             assert(false);
 
-        if (!whitelist.count(baseName) && !nix::fetchSettings.acceptFlakeConfig) {
-            bool trusted = false;
-            auto trustedList = readTrustedList();
-            auto tlname = get(trustedList, name);
-            if (auto saved = tlname ? get(*tlname, valueS) : nullptr) {
-                trusted = *saved;
-                printInfo("Using saved setting for '%s = %s' from ~/.local/share/nix/trusted-settings.json.", name, valueS);
-            } else {
-                // FIXME: filter ANSI escapes, newlines, \r, etc.
-                if (std::tolower(logger->ask(fmt("do you want to allow configuration setting '%s' to be set to '" ANSI_RED "%s" ANSI_NORMAL "' (y/N)?", name, valueS)).value_or('n')) == 'y') {
-                    trusted = true;
-                }
-                if (std::tolower(logger->ask(fmt("do you want to permanently mark this value as %s (y/N)?",  trusted ? "trusted": "untrusted" )).value_or('n')) == 'y') {
-                    trustedList[name][valueS] = trusted;
-                    writeTrustedList(trustedList);
-                }
+        bool trusted = whitelist.count(baseName);
+        if (!trusted) {
+            switch (nix::fetchSettings.acceptFlakeConfig) {
+            case AcceptFlakeConfig::True: {
+                trusted = true;
+                break;
             }
-            if (!trusted) {
-                warn("ignoring untrusted flake configuration setting '%s'.\nPass '%s' to trust it", name, "--accept-flake-config");
-                continue;
+            case AcceptFlakeConfig::Ask: {
+                auto trustedList = readTrustedList();
+                auto tlname = get(trustedList, name);
+                if (auto saved = tlname ? get(*tlname, valueS) : nullptr) {
+                    trusted = *saved;
+                    printInfo("Using saved setting for '%s = %s' from ~/.local/share/nix/trusted-settings.json.", name, valueS);
+                } else {
+                    // FIXME: filter ANSI escapes, newlines, \r, etc.
+                    if (std::tolower(logger->ask(fmt("Do you want to allow configuration setting '%s' to be set to '" ANSI_RED "%s" ANSI_NORMAL "' (y/N)? This may allow the flake to gain root, see the nix.conf manual page.", name, valueS)).value_or('n')) == 'y') {
+                        trusted = true;
+                    } else {
+                        warn("you can set '%s' to '%b' to automatically reject configuration options supplied by flakes", "accept-flake-config", false);
+                    }
+                    if (std::tolower(logger->ask(fmt("do you want to permanently mark this value as %s (y/N)?",  trusted ? "trusted": "untrusted" )).value_or('n')) == 'y') {
+                        trustedList[name][valueS] = trusted;
+                        writeTrustedList(trustedList);
+                    }
+                }
+                break;
+            }
+            case nix::AcceptFlakeConfig::False: {
+                trusted = false;
+                break;
+            };
             }
         }
 
-        globalConfig.set(name, valueS);
+        if (trusted) {
+            debug("accepting trusted flake configuration setting '%s'", name);
+            globalConfig.set(name, valueS);
+        } else {
+            warn("ignoring untrusted flake configuration setting '%s', pass '%s' to trust it (may allow the flake to gain root, see the nix.conf manual page)", name, "--accept-flake-config");
+        }
     }
 }
 

src/libexpr/flake/flake.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "flake.hh"
 #include "eval.hh"
 #include "eval-settings.hh"

src/libexpr/flake/flake.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 

src/libexpr/flake/flakeref.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "flakeref.hh"
 #include "store-api.hh"
 #include "url.hh"
@@ -85,8 +89,8 @@ std::pair<FlakeRef, std::string> parseFlakeRefWithFragment(
         + "(?:#(" + queryRegex + "))?",
         std::regex::ECMAScript);
 
-    static std::regex flakeRegex(
-        "((" + flakeIdRegexS + ")(?:/(?:" + refAndOrRevRegex + "))?)"
+    static std::regex flakeShorthandRegex(
+        flakeShorthandRegexS
         + "(?:#(" + queryRegex + "))?",
         std::regex::ECMAScript);
 
@@ -95,7 +99,7 @@ std::pair<FlakeRef, std::string> parseFlakeRefWithFragment(
     /* Check if 'url' is a flake ID. This is an abbreviated syntax for
        'flake:<flake-id>?ref=<ref>&rev=<rev>'. */
 
-    if (std::regex_match(url, match, flakeRegex)) {
+    if (std::regex_match(url, match, flakeShorthandRegex)) {
         auto parsedURL = ParsedURL{
             .url = url,
             .base = "flake:" + match.str(1),

src/libexpr/flake/flakeref.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 

src/libexpr/flake/lockfile.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "lockfile.hh"
 #include "store-api.hh"
 #include "url-parts.hh"

src/libexpr/flake/lockfile.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 

src/libexpr/flake/meson.build

@@ -1,3 +1,7 @@
+# SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+#
+# SPDX-License-Identifier: LGPL-2.1-only
+
 libexpr_generated_headers += custom_target(
   command : [ 'bash', '-c', 'echo \'R"__NIX_STR(\' | cat - @INPUT@ && echo \')__NIX_STR"\'' ],
   input : 'call-flake.nix',

src/libexpr/function-trace.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "function-trace.hh"
 #include "logging.hh"
 

src/libexpr/function-trace.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 

src/libexpr/gc-small-vector.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 

src/libexpr/get-drvs.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "get-drvs.hh"
 #include "eval-inline.hh"
 #include "derivations.hh"
@@ -45,7 +49,7 @@ DrvInfo::DrvInfo(EvalState & state, ref<Store> store, const std::string & drvPat
 }
 
 
-std::string DrvInfo::queryName() const
+std::string DrvInfo::queryName()
 {
     if (name == "" && attrs) {
         auto i = attrs->find(state->sName);
@@ -56,7 +60,7 @@ std::string DrvInfo::queryName() const
 }
 
 
-std::string DrvInfo::querySystem() const
+std::string DrvInfo::querySystem()
 {
     if (system == "" && attrs) {
         auto i = attrs->find(state->sSystem);
@@ -66,7 +70,7 @@ std::string DrvInfo::querySystem() const
 }
 
 
-std::optional<StorePath> DrvInfo::queryDrvPath() const
+std::optional<StorePath> DrvInfo::queryDrvPath()
 {
     if (!drvPath && attrs) {
         Bindings::iterator i = attrs->find(state->sDrvPath);
@@ -80,7 +84,7 @@ std::optional<StorePath> DrvInfo::queryDrvPath() const
 }
 
 
-StorePath DrvInfo::requireDrvPath() const
+StorePath DrvInfo::requireDrvPath()
 {
     if (auto drvPath = queryDrvPath())
         return *drvPath;
@@ -88,7 +92,7 @@ StorePath DrvInfo::requireDrvPath() const
 }
 
 
-StorePath DrvInfo::queryOutPath() const
+StorePath DrvInfo::queryOutPath()
 {
     if (!outPath && attrs) {
         Bindings::iterator i = attrs->find(state->sOutPath);
@@ -164,7 +168,7 @@ DrvInfo::Outputs DrvInfo::queryOutputs(bool withPaths, bool onlyOutputsToInstall
 }
 
 
-std::string DrvInfo::queryOutputName() const
+std::string DrvInfo::queryOutputName()
 {
     if (outputName == "" && attrs) {
         Bindings::iterator i = attrs->find(state->sOutputName);

src/libexpr/get-drvs.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 
@@ -19,11 +23,11 @@ public:
 private:
     EvalState * state;
 
-    mutable std::string name;
-    mutable std::string system;
-    mutable std::optional<std::optional<StorePath>> drvPath;
-    mutable std::optional<StorePath> outPath;
-    mutable std::string outputName;
+    std::string name;
+    std::string system;
+    std::optional<std::optional<StorePath>> drvPath;
+    std::optional<StorePath> outPath;
+    std::string outputName;
     Outputs outputs;
 
     /**
@@ -47,12 +51,12 @@ public:
     DrvInfo(EvalState & state, std::string attrPath, Bindings * attrs);
     DrvInfo(EvalState & state, ref<Store> store, const std::string & drvPathWithOutputs);
 
-    std::string queryName() const;
-    std::string querySystem() const;
-    std::optional<StorePath> queryDrvPath() const;
-    StorePath requireDrvPath() const;
-    StorePath queryOutPath() const;
-    std::string queryOutputName() const;
+    std::string queryName();
+    std::string querySystem();
+    std::optional<StorePath> queryDrvPath();
+    StorePath requireDrvPath();
+    StorePath queryOutPath();
+    std::string queryOutputName();
     /**
      * Return the unordered map of output names to (optional) output paths.
      * The "outputs to install" are determined by `meta.outputsToInstall`.

src/libexpr/imported-drv-to-derivation.nix

@@ -1,3 +1,7 @@
+# SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+#
+# SPDX-License-Identifier: LGPL-2.1-only
+
 attrs@{
   drvPath,
   outputs,

src/libexpr/json-to-value.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "json-to-value.hh"
 #include "value.hh"
 #include "eval.hh"

src/libexpr/json-to-value.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 

src/libexpr/meson.build

@@ -1,3 +1,7 @@
+# SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+#
+# SPDX-License-Identifier: LGPL-2.1-only
+
 libexpr_generated_headers = [
   gen_header.process('primops/derivation.nix', preserve_path_from : meson.current_source_dir()),
 ]

src/libexpr/nixexpr.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "nixexpr.hh"
 #include "derivations.hh"
 #include "eval.hh"
@@ -50,6 +54,13 @@ void ExprVar::show(const SymbolTable & symbols, std::ostream & str) const
     str << symbols[name];
 }
 
+void ExprInheritFrom::show(SymbolTable const & symbols, std::ostream & str) const
+{
+    str << "(/* expanded inherit (expr) */ ";
+    fromExpr->show(symbols, str);
+    str << ")";
+}
+
 void ExprSelect::show(const SymbolTable & symbols, std::ostream & str) const
 {
     str << "(";

src/libexpr/nixexpr.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 
@@ -144,14 +148,18 @@ struct ExprVar : Expr
  */
 struct ExprInheritFrom : ExprVar
 {
-    ExprInheritFrom(PosIdx pos, Displacement displ): ExprVar(pos, {})
+    ref<Expr> fromExpr;
+
+    ExprInheritFrom(PosIdx pos, Displacement displ, ref<Expr> fromExpr)
+          : ExprVar(pos, {}), fromExpr(fromExpr)
     {
         this->level = 0;
         this->displ = displ;
         this->fromWith = nullptr;
     }
 
-    void bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env);
+    void show(SymbolTable const & symbols, std::ostream & str) const override;
+    void bindVars(EvalState & es, const std::shared_ptr<const StaticEnv> & env) override;
 };
 
 struct ExprSelect : Expr
@@ -222,7 +230,7 @@ struct ExprAttrs : Expr
     };
     typedef std::map<Symbol, AttrDef> AttrDefs;
     AttrDefs attrs;
-    std::unique_ptr<std::vector<std::unique_ptr<Expr>>> inheritFromExprs;
+    std::unique_ptr<std::vector<ref<Expr>>> inheritFromExprs;
     struct DynamicAttrDef {
         std::unique_ptr<Expr> nameExpr, valueExpr;
         PosIdx pos;

src/libexpr/parser/change_head.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 

src/libexpr/parser/grammar.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 

src/libexpr/parser/parser.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "attr-set.hh"
 #include "error.hh"
 #include "eval-settings.hh"
@@ -317,18 +321,23 @@ template<> struct BuildAST<grammar::inherit> : change_head<InheritState> {
                 });
             }
         }
-        if (auto fromE = std::move(s.from)) {
+        if (s.from != nullptr) {
             if (!b.attrs.inheritFromExprs)
-                b.attrs.inheritFromExprs = std::make_unique<std::vector<std::unique_ptr<Expr>>>();
-            b.attrs.inheritFromExprs->push_back(std::move(fromE));
+                b.attrs.inheritFromExprs = std::make_unique<std::vector<ref<Expr>>>();
+            auto fromExpr = ref<Expr>(std::move(s.from));
+            b.attrs.inheritFromExprs->push_back(fromExpr);
             for (auto & [i, iPos] : s.attrs) {
                 if (attrs.find(i.symbol) != attrs.end())
                     ps.dupAttr(i.symbol, iPos, attrs[i.symbol].pos);
-                auto from = std::make_unique<ExprInheritFrom>(s.fromPos, b.attrs.inheritFromExprs->size() - 1);
+                auto inheritFrom = std::make_unique<ExprInheritFrom>(
+                    s.fromPos,
+                    b.attrs.inheritFromExprs->size() - 1,
+                    fromExpr
+                );
                 attrs.emplace(
                     i.symbol,
                     ExprAttrs::AttrDef(
-                        std::make_unique<ExprSelect>(iPos, std::move(from), i.symbol),
+                        std::make_unique<ExprSelect>(iPos, std::move(inheritFrom), i.symbol),
                         iPos,
                         ExprAttrs::AttrDef::Kind::InheritedFrom));
             }

src/libexpr/parser/state.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 
@@ -103,7 +107,7 @@ inline void State::addAttr(ExprAttrs * attrs, AttrPath && attrPath, std::unique_
             auto * jAttrs = dynamic_cast<ExprAttrs *>(j->second.e.get());
             if (jAttrs && ae) {
                 if (ae->inheritFromExprs && !jAttrs->inheritFromExprs)
-                    jAttrs->inheritFromExprs = std::make_unique<std::vector<std::unique_ptr<Expr>>>();
+                    jAttrs->inheritFromExprs = std::make_unique<std::vector<ref<Expr>>>();
                 for (auto & ad : ae->attrs) {
                     auto j2 = jAttrs->attrs.find(ad.first);
                     if (j2 != jAttrs->attrs.end()) // Attr already defined in iAttrs, error.

src/libexpr/paths.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "eval.hh"
 
 namespace nix {

src/libexpr/pos-idx.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 

src/libexpr/pos-table.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 

src/libexpr/primops.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "archive.hh"
 #include "derivations.hh"
 #include "downstream-placeholder.hh"
@@ -866,7 +870,7 @@ static void prim_tryEval(EvalState & state, const PosIdx pos, Value * * args, Va
     /* increment state.trylevel, and decrement it when this function returns. */
     MaintainCount trylevel(state.trylevel);
 
-    ReplExitStatus (* savedDebugRepl)(ref<EvalState> es, const ValMap & extraEnv) = nullptr;
+    std::function<ReplExitStatus(ref<EvalState> es, ValMap const & extraEnv)> savedDebugRepl;
     if (state.debugRepl && evalSettings.ignoreExceptionsDuringTry)
     {
         /* to prevent starting the repl from exceptions withing a tryEval, null it. */

src/libexpr/primops.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 

src/libexpr/primops/context.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "primops.hh"
 #include "eval-inline.hh"
 #include "derivations.hh"

src/libexpr/primops/derivation.nix

@@ -1,3 +1,7 @@
+# SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+#
+# SPDX-License-Identifier: LGPL-2.1-only
+
 /*
   This is the implementation of the ‘derivation’ builtin function.
   It's actually a wrapper around the ‘derivationStrict’ primop.

src/libexpr/primops/fetchClosure.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "primops.hh"
 #include "store-api.hh"
 #include "make-content-addressed.hh"

src/libexpr/primops/fetchMercurial.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "primops.hh"
 #include "eval-inline.hh"
 #include "eval-settings.hh"

src/libexpr/primops/fetchTree.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "primops.hh"
 #include "eval-inline.hh"
 #include "eval-settings.hh"

src/libexpr/primops/fromTOML.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "primops.hh"
 #include "eval-inline.hh"
 

src/libexpr/print-ambiguous.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "print-ambiguous.hh"
 #include "attr-set.hh"
 #include "logging.hh"

src/libexpr/print-ambiguous.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 

src/libexpr/print-options.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 /**
  * @file

src/libexpr/print.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include <limits>
 #include <span>
 #include <unordered_set>
@@ -574,4 +578,10 @@ fmt_internal::HintFmt & fmt_internal::HintFmt::operator%(const ValuePrinter & va
         return *this;
 }
 
+std::ostream & operator<<(std::ostream & output, ExprPrinter const & printer)
+{
+    printer.expr.show(printer.state.symbols, output);
+    return output;
+}
+
 }

src/libexpr/print.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 /**
  * @file
@@ -15,6 +19,8 @@
 
 namespace nix {
 
+struct Expr;
+
 class EvalState;
 struct Value;
 
@@ -50,6 +56,12 @@ void printValue(EvalState & state, std::ostream & str, Value & v, PrintOptions o
 /**
  * A partially-applied form of `printValue` which can be formatted using `<<`
  * without allocating an intermediate string.
+ * This class should not outlive the eval state or it will UAF.
+ * FIXME: This should take `nix::ref`s, to avoid that, but our eval methods all have
+ * EvalState &, not ref<EvalState>, and constructing a new shared_ptr to data that
+ * already has a shared_ptr is a much bigger footgun. In the current architecture of
+ * libexpr, using a ValuePrinter after an EvalState has been destroyed would be
+ * pretty hard.
  */
 class ValuePrinter {
     friend std::ostream & operator << (std::ostream & output, const ValuePrinter & printer);
@@ -73,4 +85,26 @@ std::ostream & operator<<(std::ostream & output, const ValuePrinter & printer);
 template<>
 fmt_internal::HintFmt & fmt_internal::HintFmt::operator%(const ValuePrinter & value);
 
+/**
+ * A partially-applied form of Expr::show(), which can be formatted using `<<`
+ * without allocating an intermediate string.
+ * This class should not outlive the eval state or it will UAF.
+ * FIXME: This should take `nix::ref`s, to avoid that, but our eval methods all have
+ * EvalState &, not ref<EvalState>, and constructing a new shared_ptr to data that
+ * already has a shared_ptr is a much bigger footgun. In the current architecture of
+ * libexpr, using an ExprPrinter after an EvalState has been destroyed would be
+ * pretty hard.
+ */
+class ExprPrinter
+{
+    /** The eval state used to get symbols. */
+    EvalState const & state;
+    /** The expression to print. */
+    Expr const & expr;
+
+public:
+    ExprPrinter(EvalState const & state, Expr const & expr) : state(state), expr(expr) { }
+    friend std::ostream & operator << (std::ostream & output, ExprPrinter const & printer);
+};
+
 }

src/libexpr/repl-exit-status.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 

src/libexpr/search-path.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "search-path.hh"
 
 namespace nix {

src/libexpr/search-path.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 

src/libexpr/symbol-table.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file
 

src/libexpr/value-to-json.cc

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #include "value-to-json.hh"
 #include "eval-inline.hh"
 #include "signals.hh"

src/libexpr/value-to-json.hh

@@ -1,3 +1,7 @@
+// SPDX-FileCopyrightText: 2024 Nix and Lix Authors
+//
+// SPDX-License-Identifier: LGPL-2.1-only
+
 #pragma once
 ///@file