Add buf_format rule

buf/BUILD.bazel

@@ -21,6 +21,7 @@ bzl_library(
     srcs = ["defs.bzl"],
     deps = [
         "//buf/internal:breaking",
+        "//buf/internal:format",
         "//buf/internal:lint",
         "//buf/internal:repo",
     ],

buf/defs.bzl

@@ -29,7 +29,9 @@ Use [gazelle](/gazelle/buf) to auto generate all of these rules based on `buf.ya
 load("//buf/internal:breaking.bzl", _buf_breaking_test = "buf_breaking_test")
 load("//buf/internal:lint.bzl", _buf_lint_test = "buf_lint_test")
 load("//buf/internal:repo.bzl", _buf_dependencies = "buf_dependencies")
+load("//buf/internal:format.bzl", _buf_format = "buf_format")
 
+buf_format = _buf_format
 buf_dependencies = _buf_dependencies
 
 def buf_breaking_test(timeout = "short", **kwargs):

buf/internal/BUILD.bazel

@@ -16,6 +16,11 @@ load("@bazel_skylib//:bzl_library.bzl", "bzl_library")
 
 package(default_visibility = ["//:__subpackages__"])
 
+bzl_library(
+    name = "format",
+    srcs = ["format.bzl"],
+)
+
 bzl_library(
     name = "breaking",
     srcs = ["breaking.bzl"],

buf/internal/format.bzl

@@ -0,0 +1,38 @@
+_DOC = """
+buf_format rule formats Protobuf files.
+"""
+
+_TEMPLATE = """
+buf=$(readlink "{}")
+if ! cd "$BUILD_WORKSPACE_DIRECTORY"; then
+  echo "Unable to change to workspace (BUILD_WORKSPACE_DIRECTORY: $BUILD_WORKSPACE_DIRECTORY)"
+  exit 1
+fi
+
+$buf format {} .
+"""
+
+_TOOLCHAIN = str(Label("//tools/buf:toolchain_type"))
+
+def _buf_format_impl(ctx):
+    ctx.actions.write(
+        output = ctx.outputs.executable,
+        is_executable = True,
+        content = _TEMPLATE.format(ctx.toolchains[_TOOLCHAIN].cli.short_path, "-w"),
+    )
+
+    return [
+        DefaultInfo(
+            runfiles = ctx.runfiles(
+                files = [ctx.toolchains[_TOOLCHAIN].cli],
+            ),
+        ),
+    ]
+
+buf_format = rule(
+    implementation = _buf_format_impl,
+    doc = _DOC,
+    attrs = {},
+    toolchains = [_TOOLCHAIN],
+    executable = True,
+)

examples/bzlmod/BUILD.bazel

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-load("@rules_buf//buf:defs.bzl", "buf_lint_test")
+load("@rules_buf//buf:defs.bzl", "buf_format", "buf_lint_test")
 load("@rules_proto//proto:defs.bzl", "proto_library")
 load("@gazelle//:def.bzl", "gazelle", "gazelle_binary")
 
@@ -51,3 +51,7 @@ buf_lint_test(
     config = "//:buf.yaml",
     targets = [":root_proto"],
 )
+
+buf_format(
+    name = "buf_format",
+)

examples/bzlmod/unused.proto

@@ -12,4 +12,4 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-syntax = "proto3";
+syntax = "proto3";