Add sanity linter to catch future use

tools/run_tests/sanity/check_channel_arg_usage.py

@@ -0,0 +1,53 @@
+#!/usr/bin/env python
+
+# Copyright 2018 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.
+
+from __future__ import print_function
+
+import os
+import sys
+
+os.chdir(os.path.join(os.path.dirname(sys.argv[0]), '../../..'))
+
+# set of files that are allowed to use the raw GRPC_ARG_* types
+_EXCEPTIONS = set([
+    'src/core/lib/channel/channel_args.cc',
+    'src/core/lib/channel/channel_args.h',
+])
+
+_BANNED = set([
+    "GRPC_ARG_POINTER",
+])
+
+errors = 0
+num_files = 0
+for root, dirs, files in os.walk('src/core'):
+    for filename in files:
+        num_files += 1
+        path = os.path.join(root, filename)
+        if path in _EXCEPTIONS: continue
+        with open(path) as f:
+            text = f.read()
+        for banned in _BANNED:
+            if banned in text:
+                print('Illegal use of "%s" in %s' % (banned, path))
+                errors += 1
+
+assert errors == 0
+# This check comes about from this issue:
+# https://github.com/grpc/grpc/issues/15381
+# Basically, a change rendered this script useless and we did not realize it.
+# This dumb check ensures that this type of issue doesn't occur again.
+assert num_files > 300  # we definitely have more than 300 files