Add bzlmod support

MODULE.bazel

@@ -0,0 +1,23 @@
+"Bazel module definition for bzlmod"
+module(
+    name = "rules_buf",
+    version = "0.0.0", # Replaced when publishing
+    compatibility_level = 1,
+)
+
+bazel_dep(name = "platforms", version = "0.0.4")
+# Only needed because rules_proto doesn't provide the protoc toolchain yet.
+# TODO: remove in the future
+bazel_dep(name = "protobuf", version = "21.7", repo_name = "com_google_protobuf")
+bazel_dep(name = "rules_proto", version = "5.3.0-21.7")
+
+# We depend on gazelle at runtime to generate our proto_library rules
+bazel_dep(name = "gazelle", version = "0.33.0")
+
+# ... and then reach inside to get the gazelle binary from this repository
+non_module_deps = use_extension("@gazelle//internal/bzlmod:non_module_deps.bzl", "non_module_deps")
+use_repo(non_module_deps, "bazel_gazelle_go_repository_tools")
+
+ext = use_extension("//buf:extensions.bzl", "buf")
+use_repo(ext, "rules_buf_toolchains")
+register_toolchains("@rules_buf_toolchains//:all")

buf/extensions.bzl

@@ -0,0 +1,78 @@
+"""Define module extensions for using rules_buf with bzlmod.
+See https://bazel.build/docs/bzlmod#extension-definition
+"""
+
+load("//buf/internal:toolchain.bzl", "buf_download_releases")
+load("//buf/internal:repo.bzl", "buf_dependencies")
+
+# NB: this should be updated periodically
+_DEFAULT_VERSION = "v1.27.0"
+_DEFAULT_TOOLCHAIN_NAME = "rules_buf_toolchains"
+_DEFAULT_DEPS = "buf_deps"
+
+dependency = tag_class(attrs = {
+    "name": attr.string(doc = "name of resulting deps repo", default = _DEFAULT_DEPS),
+    "module": attr.string(doc = "A module name from the Buf Schema Registry, see https://buf.build/docs/bsr/module/manage"),
+})
+
+toolchains = tag_class(attrs = {
+    "name": attr.string(doc = "name of resulting buf toolchains repo", default = _DEFAULT_TOOLCHAIN_NAME),
+    "version": attr.string(doc = "Version of the buf tool, see https://github.com/bufbuild/buf/releases"),
+})
+
+def _extension_impl(module_ctx):
+    registrations = {}
+    dependencies = {}
+
+    # Iterate over the global modules registered either directly by the user
+    # or transitively by some other bazel module they use.
+    for mod in module_ctx.modules:
+
+        # collect all buf.dependency tags, group by name of resulting buf_dependencies repo
+        for dependency in mod.tags.dependency:
+            if dependency.name not in dependencies.keys():
+                dependencies[dependency.name] = []
+            dependencies[dependency.name].append(dependency.module)
+
+        # collect all toolchain versions, group by name of toolchain repo
+        for toolchains in mod.tags.toolchains:
+            if toolchains.name != _DEFAULT_TOOLCHAIN_NAME and not mod.is_root:
+                fail("""\
+                Only the root module may override the default name for the buf toolchains.
+                This prevents conflicting registrations in the global namespace of external repos.
+                """)
+            if toolchains.name not in registrations.keys():
+                registrations[toolchains.name] = []
+            registrations[toolchains.name].append(toolchains.version)
+
+    # Don't require that the user manually registers a toolchain
+    if len(registrations) == 0:
+        registrations = {_DEFAULT_TOOLCHAIN_NAME: [_DEFAULT_VERSION]}
+
+    for name, versions in registrations.items():
+        if len(versions) > 1:
+            # TODO: should be semver-aware, using MVS
+            selected = sorted(versions, reverse = True)[0]
+
+            # buildifier: disable=print
+            print("NOTE: buf toolchains {} has multiple versions {}, selected {}".format(name, versions, selected))
+        else:
+            selected = versions[0]
+        buf_download_releases(
+            name = name,
+            version = selected,
+        )
+
+    for name, modules in dependencies.items():
+        buf_dependencies(
+            name = name,
+            modules = modules,
+        )
+
+buf = module_extension(
+    implementation = _extension_impl,
+    tag_classes = {
+        "dependency": dependency,
+        "toolchains": toolchains,
+    },
+)

buf/internal/toolchain.bzl

@@ -63,7 +63,7 @@ def declare_buf_toolchains(os, cpu, rules_buf_repo_name):
         native.toolchain(
             name = cmd + "_toolchain",
             toolchain = ":" + toolchain_impl,
-            toolchain_type = "@{}//tools/{}:toolchain_type".format(rules_buf_repo_name, cmd),
+            toolchain_type = "@@{}//tools/{}:toolchain_type".format(rules_buf_repo_name, cmd),
             exec_compatible_with = [
                 "@platforms//os:" + os,
                 "@platforms//cpu:" + cpu,
@@ -202,7 +202,7 @@ def _buf_download_releases_impl(ctx):
     )
     return update_attrs(ctx.attr, ["version", "sha256"], {"version": version, "sha256": sha256})
 
-_buf_download_releases = repository_rule(
+buf_download_releases = repository_rule(
     implementation = _buf_download_releases_impl,
     attrs = {
         "version": attr.string(
@@ -229,7 +229,7 @@ def rules_buf_toolchains(name = _TOOLCHAINS_REPO, version = None, sha256 = None,
         repository_url: The repository url base used for downloads. Defaults to "https://github.com/bufbuild/buf/releases/download"
     """
 
-    _buf_download_releases(name = name, version = version, sha256 = sha256, repository_url = repository_url)
+    buf_download_releases(name = name, version = version, sha256 = sha256, repository_url = repository_url)
 
     _register_toolchains(name, "buf")
     _register_toolchains(name, "protoc-gen-buf-breaking")

examples/bzlmod/.bazelrc

@@ -0,0 +1 @@
+common --enable_bzlmod

examples/bzlmod/BUILD.bazel

@@ -0,0 +1,25 @@
+load("@rules_buf//buf:defs.bzl", "buf_lint_test")
+load("@rules_proto//proto:defs.bzl", "proto_library")
+
+exports_files(["buf.yaml"], visibility = ["//visibility:public"])
+
+proto_library(
+    name = "unused",
+    srcs = ["unused.proto"],
+)
+
+proto_library(
+    name = "foo_proto",
+    srcs = ["file.proto"],
+    deps = [
+        # imports "validate/validate.proto"
+        "@buf_deps//validate:validate_proto",
+        ":unused",
+    ],
+)
+
+buf_lint_test(
+    name = "foo_proto_lint",
+    targets = [":foo_proto"],
+    config = "buf.yaml",
+)

examples/bzlmod/MODULE.bazel

@@ -0,0 +1,19 @@
+"Bazel dependencies"
+bazel_dep(name = "rules_buf", dev_dependency = True, version = "0.0.0")
+
+local_path_override(
+    module_name = "rules_buf",
+    path = "../..",
+)
+
+buf = use_extension("@rules_buf//buf:extensions.bzl", "buf")
+
+# Override the default version of buf
+buf.toolchains(version = "v1.26.0")
+
+# See https://buf.build/docs/build-systems/bazel#buf-dependencies
+buf.dependency(module = "buf.build/envoyproxy/protoc-gen-validate:eac44469a7af47e7839a7f1f3d7ac004")
+buf.dependency(module = "buf.build/acme/petapis:7abdb7802c8f4737a1a23a35ca8266ef")
+
+# Allow references to labels under @buf_deps
+use_repo(buf, "buf_deps")

examples/bzlmod/WORKSPACE

@@ -0,0 +1 @@
+# Marker that this folder is the root of a Bazel workspace

examples/bzlmod/buf.yaml

@@ -0,0 +1,4 @@
+version: v1
+lint:
+  use:
+    - IMPORT_USED

examples/bzlmod/file.proto

@@ -0,0 +1,4 @@
+syntax = "proto3";
+
+import "unused.proto";
+import "validate/validate.proto";

examples/bzlmod/unused.proto

@@ -0,0 +1 @@
+syntax = "proto3";