rustPlatform: don't install artifacts modified by checkPhase

While the artifacts from `buildPhase` should be used for testing as
well, it should be avoided that those are modified during `checkPhase`.

This can happen if a package is built e.g. with special
`cargoBuildFlags` that don't apply to the `checkPhase`. In that case, a
binary would be installed into `$out` without those flags since
`checkPhase` overrides the binary in the `target`-directory.

This patch copies the state of `target/release` into a temporary
location at the end of the `buildPhase` and installs the results from
that temporary directory into `$out` while `checkPhase` can continue
using the configured build-dir.

cc #91689
Closes #93119
Closes #91191

pkgs/build-support/rust/default.nix

@@ -74,6 +74,7 @@ let
   ccForHost="${stdenv.cc}/bin/${stdenv.cc.targetPrefix}cc";
   cxxForHost="${stdenv.cc}/bin/${stdenv.cc.targetPrefix}c++";
   releaseDir = "target/${rustTarget}/${buildType}";
+  tmpDir = "${releaseDir}-tmp";
 
   # Specify the stdenv's `diff` by abspath to ensure that the user's build
   # inputs do not cause us to find the wrong `diff`.
@@ -193,7 +194,9 @@ stdenv.mkDerivation (args // {
     # This needs to be done after postBuild: packages like `cargo` do a pushd/popd in
     # the pre/postBuild-hooks that need to be taken into account before gathering
     # all binaries to install.
-    bins=$(find $releaseDir \
+    mkdir -p $tmpDir
+    cp -r $releaseDir/* $tmpDir/
+    bins=$(find $tmpDir \
       -maxdepth 1 \
       -type f \
       -executable ! \( -regex ".*\.\(so.[0-9.]+\|so\|a\|dylib\)" \))
@@ -214,13 +217,13 @@ stdenv.mkDerivation (args // {
 
   strictDeps = true;
 
-  inherit releaseDir;
+  inherit releaseDir tmpDir;
 
   installPhase = args.installPhase or ''
     runHook preInstall
 
     # rename the output dir to a architecture independent one
-    mapfile -t targets < <(find "$NIX_BUILD_TOP" -type d | grep '${releaseDir}$')
+    mapfile -t targets < <(find "$NIX_BUILD_TOP" -type d | grep '${tmpDir}$')
     for target in "''${targets[@]}"; do
       rm -rf "$target/../../${buildType}"
       ln -srf "$target" "$target/../../"
@@ -228,7 +231,7 @@ stdenv.mkDerivation (args // {
     mkdir -p $out/bin $out/lib
 
     xargs -r cp -t $out/bin <<< $bins
-    find $releaseDir \
+    find $tmpDir \
       -maxdepth 1 \
       -regex ".*\.\(so.[0-9.]+\|so\|a\|dylib\)" \
       -print0 | xargs -r -0 cp -t $out/lib