Detect whether Gazelle itself is a Bazel module

Previously, we gated certain Bzlmod-specific behavior behind a general
check for `--enable_bzlmod`, but even with that flag, Gazelle may still
be a regular WORKSPACE dependency.

BUILD.bazel

@@ -1,7 +1,7 @@
+load("@bazel_gazelle_is_bazel_module//:defs.bzl", "GAZELLE_IS_BAZEL_MODULE")
 load("@bazel_skylib//:bzl_library.bzl", "bzl_library")
 load("@io_bazel_rules_go//go:def.bzl", "nogo")
 load("//:def.bzl", "gazelle", "gazelle_binary")
-load("//internal:common.bzl", "IS_BZLMOD_ENABLED")
 
 # gazelle:prefix github.com/bazelbuild/bazel-gazelle
 # gazelle:exclude vendor
@@ -32,7 +32,7 @@ gazelle_binary(
         "//language/proto",
         "//language/go",
         "//internal/language/test_filegroup",
-        "@bazel_skylib_gazelle_plugin//bzl" if IS_BZLMOD_ENABLED else "@bazel_skylib//gazelle/bzl",
+        "@bazel_skylib_gazelle_plugin//bzl" if GAZELLE_IS_BAZEL_MODULE else "@bazel_skylib//gazelle/bzl",
     ],
 )
 

MODULE.bazel

@@ -22,6 +22,7 @@ use_repo(
     non_module_deps,
     "bazel_gazelle_go_repository_cache",
     "bazel_gazelle_go_repository_tools",
+    "bazel_gazelle_is_bazel_module",
 )
 
 go_deps = use_extension("//:extensions.bzl", "go_deps")

def.bzl

@@ -17,8 +17,8 @@ load(
     "shell",
 )
 load(
-    "//internal:common.bzl",
-    "IS_BZLMOD_ENABLED",
+    "@bazel_gazelle_is_bazel_module//:defs.bzl",
+    "GAZELLE_IS_BAZEL_MODULE",
 )
 load(
     "//internal:go_repository.bzl",
@@ -79,7 +79,7 @@ def _gazelle_runner_impl(ctx):
         args.extend(["-go_prefix", ctx.attr.prefix])
     if ctx.attr.build_tags:
         args.extend(["-build_tags", ",".join(ctx.attr.build_tags)])
-    if IS_BZLMOD_ENABLED:
+    if GAZELLE_IS_BAZEL_MODULE:
         args.append("-bzlmod")
     args.extend([ctx.expand_location(arg, ctx.attr.data) for arg in ctx.attr.extra_args])
 
@@ -153,7 +153,7 @@ _gazelle_runner = rule(
         "data": attr.label_list(allow_files = True),
         "env": attr.string_dict(),
         "_repo_config": attr.label(
-            default = "@bazel_gazelle_go_repository_config//:WORKSPACE" if IS_BZLMOD_ENABLED else None,
+            default = "@bazel_gazelle_go_repository_config//:WORKSPACE" if GAZELLE_IS_BAZEL_MODULE else None,
             allow_single_file = True,
         ),
         "_template": attr.label(

deps.bzl

@@ -32,6 +32,10 @@ load(
     "//internal:go_repository_config.bzl",
     "go_repository_config",
 )
+load(
+    "//internal:is_bazel_module.bzl",
+    "is_bazel_module",
+)
 
 # Re-export go_repository . Users should get it from this file.
 go_repository = _go_repository
@@ -84,6 +88,12 @@ def gazelle_dependencies(
         name = "bazel_gazelle_go_repository_config",
         config = go_repository_default_config,
     )
+
+    is_bazel_module(
+        name = "bazel_gazelle_is_bazel_module",
+        is_bazel_module = False,
+    )
+
     _maybe(
         go_repository,
         name = "co_honnef_go_tools",

internal/BUILD.bazel

@@ -46,6 +46,7 @@ filegroup(
         "go_repository_config.bzl",
         "go_repository_tools.bzl",
         "go_repository_tools_srcs.bzl",
+        "is_bazel_module.bzl",
         "list_repository_tools_srcs.go",
         "overlay_repository.bzl",
         "repository_docs.bzl",
@@ -139,6 +140,12 @@ bzl_library(
     visibility = ["//:__subpackages__"],
 )
 
+bzl_library(
+    name = "is_bazel_module",
+    srcs = ["is_bazel_module.bzl"],
+    visibility = ["//:__subpackages__"],
+)
+
 bzl_library(
     name = "overlay_repository",
     srcs = ["overlay_repository.bzl"],

internal/bzlmod/non_module_deps.bzl

@@ -6,6 +6,10 @@ load(
     "//internal:go_repository_tools.bzl",
     "go_repository_tools",
 )
+load(
+    "//internal:is_bazel_module.bzl",
+    "is_bazel_module",
+)
 load(
     "@go_host_compatible_sdk_label//:defs.bzl",
     "HOST_COMPATIBLE_SDK",
@@ -24,6 +28,10 @@ def _non_module_deps_impl(_):
         name = "bazel_gazelle_go_repository_tools",
         go_cache = Label("@bazel_gazelle_go_repository_cache//:go.env"),
     )
+    is_bazel_module(
+        name = "bazel_gazelle_is_bazel_module",
+        is_bazel_module = True,
+    )
 
 non_module_deps = module_extension(
     _non_module_deps_impl,

internal/common.bzl

@@ -36,7 +36,3 @@ def executable_extension(ctx):
     if ctx.os.name.startswith("windows"):
         extension = ".exe"
     return extension
-
-# Label instances stringify to a canonical label if and only if Bzlmod is
-# enabled.
-IS_BZLMOD_ENABLED = str(Label("//:bogus")).startswith("@@")

internal/go_repository.bzl

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-load("//internal:common.bzl", "IS_BZLMOD_ENABLED", "env_execute", "executable_extension")
+load("//internal:common.bzl", "env_execute", "executable_extension")
 load("//internal:go_repository_cache.bzl", "read_cache_env")
 load("@bazel_tools//tools/build_defs/repo:utils.bzl", "patch", "read_user_netrc", "use_netrc")
 
@@ -284,7 +284,8 @@ def _go_repository_impl(ctx):
         # ctx.attr.name is the canonical name of this repository, which contains a '~' if and only
         # if this repository is generated by a module extension rather than an invocation in
         # WORKSPACE.
-        if "~" in ctx.attr.name:
+        is_module_extension_repo = "~" in ctx.attr.name
+        if is_module_extension_repo:
             # TODO: In Bazel 6.3.0 and earlier, there is no way to obtain a label referencing a repo
             # generated by an extension from within that extension. We thus have to manually
             # construct such a label pointing to the sibling `_go_repository_config` repo created by
@@ -318,7 +319,7 @@ def _go_repository_impl(ctx):
             cmd.extend(["-proto", ctx.attr.build_file_proto_mode])
         if ctx.attr.build_naming_convention:
             cmd.extend(["-go_naming_convention", ctx.attr.build_naming_convention])
-        if IS_BZLMOD_ENABLED:
+        if is_module_extension_repo:
             cmd.append("-bzlmod")
         cmd.extend(ctx.attr.build_extra_args)
         cmd.append(ctx.path(""))

internal/is_bazel_module.bzl

@@ -0,0 +1,27 @@
+# Copyright 2023 The Bazel Authors. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+def _is_bazel_module_impl(repository_ctx):
+    repository_ctx.file("WORKSPACE")
+    repository_ctx.file("BUILD")
+    repository_ctx.file("defs.bzl", "GAZELLE_IS_BAZEL_MODULE = {}".format(
+        repr(repository_ctx.attr.is_bazel_module),
+    ))
+
+is_bazel_module = repository_rule(
+    implementation = _is_bazel_module_impl,
+    attrs = {
+        "is_bazel_module": attr.bool(mandatory = True),
+    },
+)