Expose bindgen toolchain through bzlmod

MODULE.bazel

@@ -175,8 +175,11 @@ register_toolchains(
     "//proto/prost:default_prost_toolchain",
 )
 
+bindgen = use_extension("//bindgen:extension.bzl", "bindgen")
+use_repo(bindgen, "bindgen_toolchains")
+
 register_toolchains(
-    "//bindgen:default_bindgen_toolchain",
+    "@bindgen_toolchains//:default_bindgen_toolchain",
 )
 
 rust_host_tools = use_extension("//rust:extensions.bzl", "rust_host_tools")

bindgen/BUILD.bazel

@@ -1,5 +1,4 @@
 load("@bazel_skylib//:bzl_library.bzl", "bzl_library")
-load("//bindgen:defs.bzl", "rust_bindgen_toolchain")
 
 package(default_visibility = ["//visibility:public"])
 
@@ -11,21 +10,18 @@ bzl_library(
     name = "bzl_lib",
     srcs = glob(["**/*.bzl"]),
     deps = [
-        "//bindgen/3rdparty:bzl_lib",
-        "//bindgen/private:bzl_lib",
-        "//rust:bzl_lib",
+        "@rules_rust//bindgen/3rdparty:bzl_lib",
+        "@rules_rust//bindgen/private:bzl_lib",
+        "@rules_rust//rust:bzl_lib",
     ],
 )
 
-rust_bindgen_toolchain(
+alias(
     name = "default_bindgen_toolchain_impl",
-    bindgen = "//bindgen/3rdparty:bindgen",
-    clang = "@llvm-project//clang:clang",
-    libclang = "@llvm-project//clang:libclang",
+    actual = "//bindgen/toolchain:default_bindgen_toolchain_impl",
 )
 
-toolchain(
+alias(
     name = "default_bindgen_toolchain",
-    toolchain = "default_bindgen_toolchain_impl",
-    toolchain_type = "//bindgen:toolchain_type",
+    actual = "//bindgen/toolchain:default_bindgen_toolchain",
 )

bindgen/extension.bzl

@@ -0,0 +1,47 @@
+"""Module extension for accessing a bindgen toolchain"""
+
+load(":repositories.bzl", "rust_bindgen_dependencies")
+load(":transitive_repositories.bzl", "rust_bindgen_transitive_dependencies")
+
+def _bindgen_impl(_):
+    rust_bindgen_transitive_dependencies(repo_mapping = None)
+    rust_bindgen_dependencies()
+    bindgen_toolchains(
+        name = "bindgen_toolchains",
+        build_file = "//bindgen/toolchain:BUILD.bazel",
+    )
+
+bindgen = module_extension(implementation = _bindgen_impl)
+
+def _bindgen_toolchains_impl(rctx):
+    if (rctx.attr.build_file == None) == (rctx.attr.build_file_content == "_UNSET"):
+        fail("exactly one of `build_file` or `build_file_content` must be specified")
+
+    if rctx.attr.build_file != None:
+        rctx.file("BUILD.bazel", rctx.read(rctx.attr.build_file))
+    else:
+        rctx.file("BUILD.bazel", rctx.attr.build_file_content)
+
+bindgen_toolchains = repository_rule(
+    implementation = _bindgen_toolchains_impl,
+    attrs = {
+        "build_file": attr.label(
+            doc =
+                "A file to use as a BUILD file for this repo." +
+                "<p>Exactly one of <code>build_file</code> or <code>build_file_content</code>" +
+                "must be specified.",
+        ),
+        "build_file_content": attr.string(
+            doc =
+                "The content of a BUILD file to be created for this repo." +
+                "<p>Exactly one of <code>build_file</code> or <code>build_file_content</code>" +
+                "must be specified.",
+            default = "_UNSET",
+        ),
+    },
+    doc =
+        "Creates a local repository containing a provided BUILD file to be used for defining " +
+        "bindgen toolchains." +
+        "<p>This rule is a replacement for the <code>local_repository</code> rule available " +
+        "in later supported versions of Bazel.",
+)

bindgen/toolchain/BUILD.bazel

@@ -0,0 +1,16 @@
+load("@rules_rust//bindgen:defs.bzl", "rust_bindgen_toolchain")
+
+package(default_visibility = ["//visibility:public"])
+
+rust_bindgen_toolchain(
+    name = "default_bindgen_toolchain_impl",
+    bindgen = "@rules_rust//bindgen/3rdparty:bindgen",
+    clang = "@llvm-project//clang:clang",
+    libclang = "@llvm-project//clang:libclang",
+)
+
+toolchain(
+    name = "default_bindgen_toolchain",
+    toolchain = "default_bindgen_toolchain_impl",
+    toolchain_type = "@rules_rust//bindgen:toolchain_type",
+)