build: use gnullvm for Windows Rust exec tools

.github/scripts/run-argument-comment-lint-bazel.sh

@@ -3,36 +3,6 @@
 set -euo pipefail
 
 bazel_lint_args=("$@")
-if [[ "${RUNNER_OS:-}" == "Windows" ]]; then
-  has_host_platform_override=0
-  for arg in "${bazel_lint_args[@]}"; do
-    if [[ "$arg" == --host_platform=* ]]; then
-      has_host_platform_override=1
-      break
-    fi
-  done
-
-  if [[ $has_host_platform_override -eq 0 ]]; then
-    # The nightly Windows lint toolchain is registered with an MSVC exec
-    # platform even though the lint target platform stays on `windows-gnullvm`.
-    # Override the host platform here so the exec-side helper binaries actually
-    # match the registered toolchain set.
-    bazel_lint_args+=("--host_platform=//:local_windows_msvc")
-  fi
-
-  # Native Windows lint runs need exec-side Rust helper binaries and proc-macros
-  # to use rust-lld instead of the C++ linker path. The default `none`
-  # preference resolves to `cc` when a cc_toolchain is present, which currently
-  # routes these exec actions through clang++ with an argument shape it cannot
-  # consume.
-  bazel_lint_args+=("--@rules_rust//rust/settings:toolchain_linker_preference=rust")
-
-  # Some Rust top-level targets are still intentionally incompatible with the
-  # local Windows MSVC exec platform. Skip those explicit targets so the native
-  # lint aspect can run across the compatible crate graph instead of failing the
-  # whole build after analysis.
-  bazel_lint_args+=("--skip_incompatible_explicit_targets")
-fi
 
 read_query_labels() {
   local query="$1"

MODULE.bazel

@@ -136,34 +136,26 @@ nightly_rust.toolchain(
     versions = ["nightly/2025-09-18"],
 )
 
-# Keep Windows exec tools on MSVC so Bazel helper binaries link correctly, but
-# lint crate targets as `windows-gnullvm` to preserve the repo's actual cfgs.
+# Build Windows exec tools and lint targets with the same `windows-gnullvm`
+# ABI so proc macros, build scripts, and the lint driver share one hermetic
+# LLVM/MinGW toolchain.
 nightly_rust.repository_set(
-    name = "rust_windows_x86_64",
+    name = "rust_windows_x86_64_gnullvm",
     dev_components = True,
     edition = "2024",
     exec_compatible_with = [
         "@platforms//cpu:x86_64",
         "@platforms//os:windows",
-        "@rules_rs//rs/experimental/platforms/constraints:windows_msvc",
+        "@rules_rs//rs/experimental/platforms/constraints:windows_gnullvm",
     ],
-    exec_triple = "x86_64-pc-windows-msvc",
-    target_compatible_with = [
-        "@platforms//cpu:x86_64",
-        "@platforms//os:windows",
-        "@rules_rs//rs/experimental/platforms/constraints:windows_msvc",
-    ],
-    target_triple = "x86_64-pc-windows-msvc",
-    versions = ["nightly/2025-09-18"],
-)
-nightly_rust.repository_set(
-    name = "rust_windows_x86_64",
+    exec_triple = "x86_64-pc-windows-gnullvm",
     target_compatible_with = [
         "@platforms//cpu:x86_64",
         "@platforms//os:windows",
         "@rules_rs//rs/experimental/platforms/constraints:windows_gnullvm",
     ],
     target_triple = "x86_64-pc-windows-gnullvm",
+    versions = ["nightly/2025-09-18"],
 )
 use_repo(nightly_rust, "rust_toolchains")
 

patches/rules_rs_windows_exec_linker.patch

@@ -1,6 +1,7 @@
-# What: use a working Windows direct linker for `rules_rs` exec toolchains and
+# What: use Rust's bundled direct linker for Windows MSVC exec toolchains and
 # preserve the Windows stdlib link flags the stable wrapper was dropping.
-# Scope: Windows-only linker metadata for the generated `rules_rs` toolchains.
+# Scope: Windows-only linker metadata for the generated `rules_rs` toolchains;
+# Windows gnullvm keeps using the selected hermetic C++ toolchain driver.
 
 diff --git a/rs/experimental/toolchains/declare_rustc_toolchains.bzl b/rs/experimental/toolchains/declare_rustc_toolchains.bzl
 --- a/rs/experimental/toolchains/declare_rustc_toolchains.bzl
@@ -9,8 +10,8 @@ diff --git a/rs/experimental/toolchains/declare_rustc_toolchains.bzl b/rs/experi
          rust_toolchain(
              name = rust_toolchain_name,
              rust_doc = "{}rustdoc".format(rustc_repo_label),
-+            linker = "{}rust-lld".format(rustc_repo_label) if exec_triple.system == "windows" else None,
-+            linker_type = "direct" if exec_triple.system == "windows" else None,
++            linker = "{}rust-lld".format(rustc_repo_label) if exec_triple.abi == "msvc" else None,
++            linker_type = "direct" if exec_triple.abi == "msvc" else None,
              rust_std = select(rust_std_select),
              rustc = "{}rustc".format(rustc_repo_label),
              cargo = "{}cargo".format(cargo_repo_label),
@@ -39,7 +40,7 @@ diff --git a/rs/experimental/toolchains/declare_rustc_toolchains.bzl b/rs/experi
 diff --git a/rs/private/rustc_repository.bzl b/rs/private/rustc_repository.bzl
 --- a/rs/private/rustc_repository.bzl
 +++ b/rs/private/rustc_repository.bzl
-@@ -7,10 +7,24 @@ load(
+@@ -7,10 +7,26 @@ load(
  )
  load(":rust_repository_utils.bzl", "RUST_REPOSITORY_COMMON_ATTR", "download_and_extract")
 +
@@ -55,11 +56,13 @@ diff --git a/rs/private/rustc_repository.bzl b/rs/private/rustc_repository.bzl
      exec_triple = triple(rctx.attr.triple)
      download_and_extract(rctx, "rustc", "rustc", exec_triple)
      build_content = [BUILD_for_compiler(exec_triple)]
-+    if exec_triple.system == "windows":
-+        lld_link = rctx.which("lld-link.exe")
-+        if lld_link == None:
-+            fail("lld-link.exe not found on PATH")
-+        rctx.symlink(lld_link, "bin/lld-link.exe")
++    if exec_triple.abi == "msvc":
++        # Keep the `lld-link.exe` basename so the multi-call Rust LLD binary
++        # selects its COFF driver without importing a linker from PATH.
++        rctx.symlink(
++            "lib/rustlib/{}/bin/rust-lld.exe".format(exec_triple.str),
++            "bin/lld-link.exe",
++        )
 +        build_content.append(_WINDOWS_EXEC_LINKER_BUILD)
      if includes_rust_analyzer_proc_macro_srv(rctx.attr.version, rctx.attr.iso_date):
          build_content.append(BUILD_for_rust_analyzer_proc_macro_srv(exec_triple))