[grrr] Add a test that BUILD.gn does not exist (#29498)

* Add a test that BUILD.gn does not exist

* fix copyright

* review feedback

tools/run_tests/sanity/check_banned_filenames.py

@@ -0,0 +1,34 @@
+#!/usr/bin/env python3
+
+# Copyright 2022 gRPC authors.
+#
+# 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.
+
+import os
+import sys
+
+BANNED_FILENAMES = [
+    'BUILD.gn',
+]
+
+os.chdir(os.path.join(os.path.dirname(sys.argv[0]), '../../..'))
+
+bad = []
+for filename in BANNED_FILENAMES:
+    if os.path.exists(filename):
+        bad.append(filename)
+
+if bad:
+    for file in bad:
+        print("%s should not exist" % file)
+    sys.exit(1)

tools/run_tests/sanity/sanity_tests.yaml

@@ -2,6 +2,7 @@
 - script: tools/run_tests/sanity/check_absl_mutex.sh
 - script: tools/run_tests/sanity/check_bad_dependencies.sh
 - script: tools/run_tests/sanity/check_bazel_workspace.py
+- script: tools/run_tests/sanity/check_banned_filenames.py
 - script: tools/run_tests/sanity/check_buildifier.sh
 - script: tools/run_tests/sanity/check_cache_mk.sh
 - script: tools/run_tests/sanity/check_deprecated_grpc++.py