remapPathPrefixHook: make opt-in

CHANGELOG.md

@@ -6,6 +6,13 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## Unreleased
 
+### Changed
+* **Breaking**: `mkCargoDerivation` now no longer automatically includes the
+  `remapPathPrefixHook` as a nativeBuildInput. Unfortunately, this hook's
+  implementation will lead to cache invalidation if built on a Nix
+  implementation outside of NixOS (see the API documentation for more details).
+  Thus using this hook is now *opt-in*.
+
 ## [0.22.0] - 2025-12-26
 
 ### Changed

checks/default.nix

@@ -272,10 +272,6 @@ onlyDrvs (
         asdf = 1;
         CARGO_TARGET_DIR = "target/foo";
       };
-      compilesFreshStrip = self.compilesFresh "simple" (myLib.buildPackage) {
-        src = ./simple;
-        dontStrip = true;
-      };
       compilesFreshWorkspace =
         self.compilesFresh
           {
@@ -674,10 +670,6 @@ onlyDrvs (
         src = ./simple;
         CARGO_PROFILE = "";
       };
-      simpleNoStrip = myLib.buildPackage {
-        src = ./simple;
-        dontStrip = true;
-      };
       simpleOnlyTests = myLib.buildPackage {
         src = myLib.cleanCargoSource ./simple-only-tests;
       };

docs/API.md

@@ -135,10 +135,6 @@ to influence its behavior.
 * `checkPhaseCargoCommand`: A command to run during the derivation's check
   phase. Pre and post check hooks will automatically be run.
   - Default value: `"${cargoTestCommand} ${cargoExtraArgs}"`
-* `noCompressDebugSectionsSet`: Controls whether (DWARF) debug sections are
-  compressed via the `remapPathPrefixHook`.
-  - Default value: `''` if the `stdenv.hostPlatform` uses ELF as the execution
-    format, `'1'` otherwise.
 * `doCheck`: whether the derivation's check phase should be run
   - Default value: `true`
 * `dummySrc`: the "dummy" source to use when building this derivation.
@@ -1262,7 +1258,6 @@ input to any other `nativeBuildInputs` specified by the caller:
 * `configureCargoVendoredDepsHook`
 * `inheritCargoArtifactsHook`
 * `installCargoArtifactsHook`
-* `remapPathPrefixHook`
 * `replaceCargoLockHook`
 * `rustc`
 * `rsync`
@@ -1938,9 +1933,17 @@ a temporary location defined by `$postBuildInstallFromCargoBuildLogOut`
 
 **Required nativeBuildInputs**: assumes `cargo` is available on the `$PATH`
 
-### `craneLib.remapSourcePathPrefixHook`
-
-> Note: this hook is not supported when building on Darwin and will do nothing
+### `craneLib.remapPathPrefixHook`
+
+> Note: this hook's implementation relies on the derivation source path being
+> mounted on the same location between the `buildDepsOnly` and the "real" build.
+> On NixOS, this happens to be something like `/build/${drv.src.name}`, but
+> *outside* of NixOS (e.g. Nix installations on Darwin or any other Linux
+> distro, including things like GitHub Actions installs) this path will look
+> something like `/nix/var/nix/builds/${drv.name}.drv`, where the derivation's
+> name *does differ* on the `buildDepsOnly` build. Because of this, cargo will
+> observe a change in `CARGO_BUILD_RUSTFLAGS` and result in external
+> (dependency) crates being recompiled from scratch!
 
 Defines `configureRustcRemapPathPrefix()` which can be used to set up a source
 map using the [`--remap-path-prefix`] option. The output of the derivation gains

lib/mkCargoDerivation.nix

@@ -9,7 +9,6 @@
   lib,
   mkCrossToolchainEnv,
   pkgs,
-  remapPathPrefixHook,
   replaceCargoLockHook,
   rsync,
   rustc,
@@ -100,11 +99,6 @@ chosenStdenv.mkDerivation (
     # access. Directory structure should basically follow the output of `cargo vendor`.
     cargoVendorDir = args.cargoVendorDir or (vendorCargoDeps args);
 
-    # compressing debug sections is only supported on elf formats (i.e. not darwin)
-    noCompressDebugSectionsSet =
-      args.noCompressDebugSectionsSet
-        or (lib.optionalString (chosenStdenv.hostPlatform.parsed.kernel.execFormat.name != "elf") "1");
-
     nativeBuildInputs =
       (args.nativeBuildInputs or [ ])
       ++ (crossEnv.nativeBuildInputs or [ ])
@@ -115,7 +109,6 @@ chosenStdenv.mkDerivation (
         configureCargoVendoredDepsHook
         inheritCargoArtifactsHook
         installCargoArtifactsHook
-        remapPathPrefixHook
         replaceCargoLockHook
         rsync
         rustc

lib/setupHooks/remapPathPrefixHook.nix

@@ -1,27 +1,9 @@
 {
-  lib,
   makeSetupHook,
-  stdenv,
 }:
 makeSetupHook {
   name = "remapPathPrefixHook";
   substitutions = {
     storeDir = builtins.storeDir;
-
-    # Unfortunately, we cannot support automatic path remapping on Darwin. The remap paths option
-    # requires absolute paths (since rustc will basically do a blind substitution). On Linux builds,
-    # each derivation is chrooted to `/build/{name-of-src}` which ends up being the same string for
-    # both the real and the deps-only derivations. On Darwin, however, this ends up being
-    # `/nix/var/nix/builds/{name-of-derivation}` which *is* different between the main and deps-only
-    # derivations. Since this value ends up in CARGO_BUILD_RUSTFLAGS, it effectively will lead to
-    # cache invalidation when the real derivation runs if the values differ.
-    #
-    # Moreover, we can't "just" replace the bytes ourselves since there's no guarantee that the
-    # original build path is the same length as the un-neutered store path. Thus we'll noop this for
-    # now on Darwin builders and leave it up to the caller to handle path remap if needed...
-    isDarwin = lib.optionalString stdenv.buildPlatform.isDarwin /* bash */ ''
-      echo 'automatic path remapping not supported on Darwin'
-      return 0
-    '';
   };
 } ./remapPathPrefixHook.sh

lib/setupHooks/remapPathPrefixHook.sh

@@ -1,6 +1,4 @@
 configureRustcRemapPathPrefix() {
-  @isDarwin@
-
   local remapTo="${1:-${src:?not defined}}"
   local remapFrom="${2:-$(pwd)}"
   local doNeuter="${3:-neuter}"