build: select the gnullvm nightly toolchain

MODULE.bazel

@@ -112,6 +112,7 @@ rules_rust = use_extension("@rules_rs//rs/experimental:rules_rust.bzl", "rules_r
 # `libssp_nonshared`, so strip the forwarded stack-protector flags there.
 rules_rust.patch(
     patches = [
+        "//patches:rules_rust_repository_set_replacement.patch",
         "//patches:rules_rust_windows_gnullvm_build_script.patch",
         "//patches:rules_rust_windows_exec_msvc_build_script_env.patch",
         "//patches:rules_rust_windows_bootstrap_process_wrapper_linker.patch",
@@ -140,7 +141,7 @@ nightly_rust.toolchain(
 # 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_gnullvm",
+    name = "rust_windows_x86_64",
     dev_components = True,
     edition = "2024",
     exec_compatible_with = [

patches/BUILD.bazel

@@ -15,6 +15,7 @@ exports_files([
     "rules_rust_windows_msvc_direct_link_args.patch",
     "rules_rust_windows_gnullvm_build_script.patch",
     "rules_cc_rusty_v8_custom_libcxx.patch",
+    "rules_rust_repository_set_replacement.patch",
     "rules_rs_build_script_deps_annotation.patch",
     "rules_rs_windows_gnullvm_exec.patch",
     "rules_rs_windows_exec_linker.patch",

patches/rules_rs_windows_exec_linker.patch

@@ -21,10 +21,10 @@ diff --git a/rs/experimental/toolchains/declare_rustc_toolchains.bzl b/rs/experi
                  "@platforms//os:ios": ["-lSystem", "-lobjc", "-Wl,-framework,Security", "-Wl,-framework,Foundation", "-lresolv"],
 -                # TODO: windows
 +                "@rules_rs//rs/experimental/platforms/constraints:windows_gnullvm": [
-+                    "advapi32.lib",
-+                    "ws2_32.lib",
-+                    "userenv.lib",
-+                    "Bcrypt.lib",
++                    "-ladvapi32",
++                    "-lws2_32",
++                    "-luserenv",
++                    "-lbcrypt",
 +                ],
 +                "@rules_rs//rs/experimental/platforms/constraints:windows_msvc": [
 +                    "advapi32.lib",

patches/rules_rust_repository_set_replacement.patch

@@ -0,0 +1,24 @@
+# What: replace a default repository set by its documented repository name.
+# Why: changing the exec triple (for example, MSVC to gnullvm) also changes the
+# lookup key, so matching by both the old triple and name leaves the default
+# toolchain registered and lets it win toolchain resolution.
+
+diff --git a/rust/extensions.bzl b/rust/extensions.bzl
+--- a/rust/extensions.bzl
++++ b/rust/extensions.bzl
+@@ -100,8 +100,13 @@ def _rust_impl(module_ctx):
+             **repository_set
+         )
+         extra_toolchain_infos.update(**toolchain_infos)
+-        if toolchain_triples.get(repository_set["exec_triple"]) == repository_set["name"]:
+-            toolchain_triples.pop(repository_set["exec_triple"], None)
++        replaced_exec_triples = [
++            exec_triple
++            for exec_triple, name in toolchain_triples.items()
++            if name == repository_set["name"]
++        ]
++        for exec_triple in replaced_exec_triples:
++            toolchain_triples.pop(exec_triple)
+ 
+     toolchains = root.tags.toolchain
+     if not toolchains and rules_rust: