rust: hooks: fix cross compilation

Currently there is a state of severe confusion in
pkgs/build-support/rust/hooks/ regarding host vs target; right now
there is only "host" defined, but whether it means "host" or
"target" seems to fluctuate.

This commit corrects that, ensuring that all variables come in all
three flavors (build, host, target) and are used consistently with
the nixpkgs convention.

This also fixes the cross-compilation of packages which use
`maturinBuildHook` -- hooks go in `nativeBuildInputs` and are
phase-shifted backwards by one platform, so they need to be careful
about distinguishing between build and host.

Closes #247441

pkgs/build-support/rust/hooks/cargo-build-hook.sh

@@ -30,13 +30,8 @@ cargoBuildHook() {
 
     (
     set -x
-    env \
-      "CC_@rustBuildPlatform@=@ccForBuild@" \
-      "CXX_@rustBuildPlatform@=@cxxForBuild@" \
-      "CC_@rustTargetPlatform@=@ccForHost@" \
-      "CXX_@rustTargetPlatform@=@cxxForHost@" \
-      cargo build -j $NIX_BUILD_CORES \
-        --target @rustTargetPlatformSpec@ \
+    @setEnv@ cargo build -j $NIX_BUILD_CORES \
+        --target @rustHostPlatformSpec@ \
         --frozen \
         ${cargoBuildProfileFlag} \
         ${cargoBuildNoDefaultFeaturesFlag} \

pkgs/build-support/rust/hooks/cargo-check-hook.sh

@@ -29,7 +29,7 @@ cargoCheckHook() {
     fi
 
     argstr="${cargoCheckProfileFlag} ${cargoCheckNoDefaultFeaturesFlag} ${cargoCheckFeaturesFlag}
-        --target @rustTargetPlatformSpec@ --frozen ${cargoTestFlags}"
+        --target @rustHostPlatformSpec@ --frozen ${cargoTestFlags}"
 
     (
         set -x

pkgs/build-support/rust/hooks/cargo-install-hook.sh

@@ -1,7 +1,7 @@
 cargoInstallPostBuildHook() {
     echo "Executing cargoInstallPostBuildHook"
 
-    releaseDir=target/@shortTarget@/$cargoBuildType
+    releaseDir=target/@targetSubdirectory@/$cargoBuildType
     tmpDir="${releaseDir}-tmp";
 
     mkdir -p $tmpDir
@@ -21,7 +21,7 @@ cargoInstallHook() {
 
     # rename the output dir to a architecture independent one
 
-    releaseDir=target/@shortTarget@/$cargoBuildType
+    releaseDir=target/@targetSubdirectory@/$cargoBuildType
     tmpDir="${releaseDir}-tmp";
 
     mapfile -t targets < <(find "$NIX_BUILD_TOP" -type d | grep "${tmpDir}$")

pkgs/build-support/rust/hooks/cargo-nextest-hook.sh

@@ -29,7 +29,7 @@ cargoNextestHook() {
     fi
 
     argstr="${cargoCheckProfileFlag} ${cargoCheckNoDefaultFeaturesFlag} ${cargoCheckFeaturesFlag}
-        --target @rustTargetPlatformSpec@ --frozen ${cargoTestFlags}"
+        --target @rustHostPlatformSpec@ --frozen ${cargoTestFlags}"
 
     (
         set -x

pkgs/build-support/rust/hooks/default.nix

@@ -9,6 +9,10 @@
 , rust
 , rustc
 , stdenv
+
+# This confusingly-named parameter indicates the *subdirectory of
+# `target/` from which to copy the build artifacts.  It is derived
+# from a stdenv platform (or a JSON file; see below).
 , target ? rust.toRustTargetSpec stdenv.hostPlatform
 }:
 
@@ -17,24 +21,17 @@ let
 
   # see https://github.com/rust-lang/cargo/blob/964a16a28e234a3d397b2a7031d4ab4a428b1391/src/cargo/core/compiler/compile_kind.rs#L151-L168
   # the "${}" is needed to transform the path into a /nix/store path before baseNameOf
-  shortTarget = if targetIsJSON then
+  targetSubdirectory = if targetIsJSON then
       (lib.removeSuffix ".json" (builtins.baseNameOf "${target}"))
     else target;
-  ccForBuild = "${buildPackages.stdenv.cc}/bin/${buildPackages.stdenv.cc.targetPrefix}cc";
-  cxxForBuild = "${buildPackages.stdenv.cc}/bin/${buildPackages.stdenv.cc.targetPrefix}c++";
-  ccForHost = "${stdenv.cc}/bin/${stdenv.cc.targetPrefix}cc";
-  cxxForHost = "${stdenv.cc}/bin/${stdenv.cc.targetPrefix}c++";
-  rustBuildPlatform = rust.toRustTarget stdenv.buildPlatform;
-  rustTargetPlatform = rust.toRustTarget stdenv.hostPlatform;
-  rustTargetPlatformSpec = rust.toRustTargetSpec stdenv.hostPlatform;
+
 in {
   cargoBuildHook = callPackage ({ }:
     makeSetupHook {
       name = "cargo-build-hook.sh";
       propagatedBuildInputs = [ cargo ];
       substitutions = {
-        inherit ccForBuild ccForHost cxxForBuild cxxForHost
-          rustBuildPlatform rustTargetPlatform rustTargetPlatformSpec;
+        inherit (rust.envVars) rustHostPlatformSpec setEnv;
       };
     } ./cargo-build-hook.sh) {};
 
@@ -43,7 +40,7 @@ in {
       name = "cargo-check-hook.sh";
       propagatedBuildInputs = [ cargo ];
       substitutions = {
-        inherit rustTargetPlatformSpec;
+        inherit (rust.envVars) rustHostPlatformSpec;
       };
     } ./cargo-check-hook.sh) {};
 
@@ -52,7 +49,7 @@ in {
       name = "cargo-install-hook.sh";
       propagatedBuildInputs = [ ];
       substitutions = {
-        inherit shortTarget;
+        inherit targetSubdirectory;
       };
     } ./cargo-install-hook.sh) {};
 
@@ -61,7 +58,7 @@ in {
       name = "cargo-nextest-hook.sh";
       propagatedBuildInputs = [ cargo cargo-nextest ];
       substitutions = {
-        inherit rustTargetPlatformSpec;
+        inherit (rust.envVars) rustHostPlatformSpec;
       };
     } ./cargo-nextest-hook.sh) {};
 
@@ -78,23 +75,26 @@ in {
 
         cargoConfig = ''
           [target."${rust.toRustTarget stdenv.buildPlatform}"]
-          "linker" = "${ccForBuild}"
-          ${lib.optionalString (stdenv.buildPlatform.config != stdenv.hostPlatform.config) ''
-            [target."${shortTarget}"]
-            "linker" = "${ccForHost}"
+          "linker" = "${rust.envVars.ccForBuild}"
+          ${lib.optionalString (stdenv.hostPlatform.config != stdenv.targetPlatform.config) ''
+            [target."${rust.toRustTarget stdenv.targetPlatform}"]
+            "linker" = "${rust.envVars.ccForTarget}"
           ''}
           "rustflags" = [ "-C", "target-feature=${if stdenv.hostPlatform.isStatic then "+" else "-"}crt-static" ]
         '';
       };
     } ./cargo-setup-hook.sh) {};
 
-  maturinBuildHook = callPackage ({ }:
+  maturinBuildHook = callPackage ({ pkgsHostTarget }:
     makeSetupHook {
       name = "maturin-build-hook.sh";
-      propagatedBuildInputs = [ cargo maturin rustc ];
+      propagatedBuildInputs = [
+        pkgsHostTarget.maturin
+        pkgsHostTarget.cargo
+        pkgsHostTarget.rustc
+      ];
       substitutions = {
-        inherit ccForBuild ccForHost cxxForBuild cxxForHost
-          rustBuildPlatform rustTargetPlatform rustTargetPlatformSpec;
+        inherit (rust.envVars) rustTargetPlatformSpec setEnv;
       };
     } ./maturin-build-hook.sh) {};
 

pkgs/build-support/rust/hooks/maturin-build-hook.sh

@@ -9,12 +9,7 @@ maturinBuildHook() {
 
     (
     set -x
-    env \
-      "CC_@rustBuildPlatform@=@ccForBuild@" \
-      "CXX_@rustBuildPlatform@=@cxxForBuild@" \
-      "CC_@rustTargetPlatform@=@ccForHost@" \
-      "CXX_@rustTargetPlatform@=@cxxForHost@" \
-      maturin build \
+    @setEnv@ maturin build \
         --jobs=$NIX_BUILD_CORES \
         --frozen \
         --target @rustTargetPlatformSpec@ \