buildRustPackage: factor out check phase to cargoCheckHook

API change:

`cargoParallelTestThreads` suggests that this attribute sets the
number of threads used during tests, while it is actually a boolean
option (use 1 thread or NIX_BUILD_CORES threads). In the hook, this
is replaced by a more canonical name `dontUseCargoParallelTests`.

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

@@ -0,0 +1,37 @@
+cargoCheckHook() {
+    echo "Executing cargoCheckHook"
+
+    runHook preCheck
+
+    if [[ -n "${buildAndTestSubdir-}" ]]; then
+        pushd "${buildAndTestSubdir}"
+    fi
+
+    if [[ -z ${dontUseCargoParallelTests-} ]]; then
+        threads=$NIX_BUILD_CORES
+    else
+        threads=1
+    fi
+
+    argstr="--${cargoBuildType} --target @rustTargetPlatformSpec@ --frozen";
+
+    (
+        set -x
+        cargo test \
+              -j $NIX_BUILD_CORES \
+              ${argstr} -- \
+              --test-threads=${threads} \
+              ${checkFlags} \
+              ${checkFlagsArray+"${checkFlagsArray[@]}"}
+    )
+
+    if [[ -n "${buildAndTestSubdir-}" ]]; then
+        popd
+    fi
+
+    echo "Finished cargoCheckHook"
+
+    runHook postCheck
+}
+
+checkPhase=cargoCheckHook

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

@@ -36,6 +36,15 @@ in {
       };
     } ./cargo-build-hook.sh) {};
 
+  cargoCheckHook = callPackage ({ }:
+    makeSetupHook {
+      name = "cargo-check-hook.sh";
+      deps = [ cargo ];
+      substitutions = {
+        inherit rustTargetPlatformSpec;
+      };
+    } ./cargo-check-hook.sh) {};
+
   cargoInstallHook = callPackage ({ }:
     makeSetupHook {
       name = "cargo-install-hook.sh";