Set the Apple deployment target for rustc from the linker args

[drakeo338]

Fixes #4149.

Following keith's suggestion on the issue: when the link args carry an Apple -target triple with an OS version, rustc links now get the matching *_DEPLOYMENT_TARGET env var, so rustc's -m<os>-version-min agrees with the triple and clang stops warning. A value from --action_env, rustc_env or the toolchain's env still wins, and non-Apple targets are untouched.

Tests: a unit test for the triple parser, plus analysis tests for the linkopt case and the precedence rules. The two linkopt tests skip on macOS, because apple_support's toolchain appends its own -target after user linkopts there, so the last triple is the toolchain's. I'd be glad to swap that for a macOS-specific assertion if you prefer.

Verified locally on Linux with bazelisk: 20 passed, 2 unrelated skips. I don't have a Mac, so macOS coverage comes from CI.

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[drakeo338]

signed

[UebelAndre]

Thank you!

[UebelAndre]

@drakeo338 Looks like some of the tests need to be constrained to Apple platforms

(18:59:58) ERROR: /workdir/test/unit/apple_deployment_target/BUILD.bazel:3:35: Compiling Rust bin bin (1 file) failed: (Exit 1): process_wrapper failed: error executing Rustc command (from rust_binary rule target //test/unit/apple_deployment_target:bin)
  (cd /var/lib/buildkite-agent/.cache/bazel/_bazel_buildkite-agent/ec321eb2cc2d0f8f91b676b6d4c66c29/sandbox/linux-sandbox/3509/execroot/_main && \
  exec env - \
    CARGO_CFG_TARGET_ARCH=x86_64 \
    CARGO_CFG_TARGET_OS=linux \
    CARGO_CRATE_NAME=bin \
    CARGO_MANIFEST_DIR='${pwd}/test/unit/apple_deployment_target' \
    CARGO_PKG_AUTHORS='' \
    CARGO_PKG_DESCRIPTION='' \
    CARGO_PKG_HOMEPAGE='' \
    CARGO_PKG_NAME=bin \
    CARGO_PKG_VERSION=0.0.0 \
    CARGO_PKG_VERSION_MAJOR=0 \
    CARGO_PKG_VERSION_MINOR=0 \
    CARGO_PKG_VERSION_PATCH=0 \
    CARGO_PKG_VERSION_PRE='' \
    MACOSX_DEPLOYMENT_TARGET=15.0 \
    PATH=/bin:/usr/bin:/usr/local/bin \
    REPOSITORY_NAME='' \
    ZERO_AR_DATE=1 \
  bazel-out/k8-opt-exec/bin/util/process_wrapper/process_wrapper --subst 'pwd=${pwd}' --subst 'exec_root=${exec_root}' --subst 'output_base=${output_base}' -- bazel-out/k8-fastbuild-ST-f8e821cf2346/bin/external/+rust+rust_linux_x86_64__x86_64-unknown-linux-gnu__stable_tools/rust_toolchain/bin/rustc @bazel-out/k8-fastbuild-ST-f8e821cf2346/bin/test/unit/apple_deployment_target/bin-0.params)
# Configuration: 4c6a8e4a753b8c63d0debdffc22c59ca782f4054d6a72e018cf46fc9d9047f9d
# Execution platform: @@platforms//host:host
Use --sandbox_debug to see verbose messages from the sandbox and retain the sandbox build root for debugging
error: linking with `/usr/bin/gcc` failed: exit status: 1
  |
  = note:  "/usr/bin/gcc" "-m64" "/var/lib/buildkite-agent/.cache/bazel/_bazel_buildkite-agent/ec321eb2cc2d0f8f91b676b6d4c66c29/sandbox/linux-sandbox/3509/execroot/_main/bazel-out/k8-fastbuild-ST-f8e821cf2346/bin/test/unit/apple_deployment_target/rustcsDo5iP/symbols.o" "<2 object files omitted>" "-Wl,--as-needed" "-Wl,-Bstatic" "<sysroot>/lib/rustlib/x86_64-unknown-linux-gnu/lib/{libprofiler_builtins-*,libstd-*,libpanic_unwind-*,libobject-*,libmemchr-*,libaddr2line-*,libgimli-*,libcfg_if-*,librustc_demangle-*,libstd_detect-*,libhashbrown-*,librustc_std_workspace_alloc-*,libminiz_oxide-*,libadler2-*,libunwind-*,liblibc-*,librustc_std_workspace_core-*,liballoc-*,libcore-*,libcompiler_builtins-*}.rlib" "-Wl,-Bdynamic" "-lgcc_s" "-lutil" "-lrt" "-lpthread" "-lm" "-ldl" "-lc" "-L" "/var/lib/buildkite-agent/.cache/bazel/_bazel_buildkite-agent/ec321eb2cc2d0f8f91b676b6d4c66c29/sandbox/linux-sandbox/3509/execroot/_main/bazel-out/k8-fastbuild-ST-f8e821cf2346/bin/test/unit/apple_deployment_target/rustcsDo5iP/raw-dylibs" "-Wl,--eh-frame-hdr" "-Wl,-z,noexecstack" "-L" "<sysroot>/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-L" "<sysroot>/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-o" "bazel-out/k8-fastbuild-ST-f8e821cf2346/bin/test/unit/apple_deployment_target/bin" "-Wl,--gc-sections" "-pie" "-Wl,-z,relro,-z,now" "-nodefaultlibs" "-u" "__llvm_profile_runtime" "--coverage" "-fuse-ld=gold" "-B/usr/bin" "-Wl,-no-as-needed" "-Wl,-z,relro,-z,now" "-pass-exit-codes" "-target" "arm64-apple-macosx26.0" "-Wl,--push-state,-as-needed" "-lstdc++" "-Wl,--pop-state" "-Wl,--push-state,-as-needed" "-lm" "-Wl,--pop-state"
  = note: some arguments are omitted. use `--verbose` to show all linker arguments
  = note: gcc: error: unrecognized command-line option '-target'
error: aborting due to 1 previous error

[drakeo338]

Thanks! Fixed in 98e0081. The failure was bazel coverage linking the test binaries with the Apple -target linkopt on Linux. The tests now read the Rustc actions through a small wrapper that applies the link settings as a transition, so nothing gets linked. That keeps them running on Linux and Windows, and bazel coverage on the package passes locally. The two linkopt tests still skip on macOS, because apple_support appends its own -target there.