Use coreutils hermetic symlink instead of host ln

Author: dzbarsky

MODULE.bazel

@@ -60,6 +60,18 @@ bazel_dep(name = "rules_proto", version = "7.1.0")
 bazel_dep(name = "llvm", version = "0.7.6")
 bazel_dep(name = "aspect_tools_telemetry", version = "0.3.3")
 
+bazel_lib_toolchains = use_extension("@bazel_lib//lib:extensions.bzl", "toolchains")
+bazel_lib_toolchains.coreutils(version = "0.5.0")
+use_repo(
+    bazel_lib_toolchains,
+    "coreutils_darwin_amd64",
+    "coreutils_darwin_arm64",
+    "coreutils_linux_amd64",
+    "coreutils_linux_arm64",
+    "coreutils_windows_amd64",
+    "coreutils_windows_arm64",
+)
+
 osx = use_extension("@llvm//extensions:osx.bzl", "osx")
 use_repo(osx, "macos_sdk")
 

rs/private/BUILD.bazel

@@ -208,6 +208,7 @@ bzl_library(
     deps = [
         "@bazel_features//:features",
         "@bazel_lib//lib:paths",
+        "@bazel_lib//lib:repo_utils",
     ],
 )
 

rs/private/symlink_utils.bzl

@@ -1,5 +1,11 @@
 load("@bazel_features//:features.bzl", "bazel_features")
 load("@bazel_lib//lib:paths.bzl", "relative_file")
+load("@bazel_lib//lib:repo_utils.bzl", "repo_utils")
+
+def _coreutils_label(rctx):
+    platform = repo_utils.platform(rctx)
+    binary = "coreutils.exe" if platform.startswith("windows_") else "coreutils"
+    return Label("@coreutils_%s//:%s" % (platform, binary))
 
 def relative_symlink(rctx, target, link_name):
     target_path = rctx.path(target)
@@ -16,6 +22,7 @@ def relative_symlink(rctx, target, link_name):
         return
 
     result = rctx.execute([
+        _coreutils_label(rctx),
         "ln",
         "-sf",
         relative_file(str(target_path), str(link_path)),