BUILD.gn: Delete stale generated files in Dawn's gen dir.

This normalizes even more the directory structure of generated files in
Dawn and removes stale autogenerated files that could be included
wrongly using a GN action.

See comment on top of dawn_generator.gni in this commit for more
context.

BUG=dawn:22

Change-Id: I8ec038f949c048431b2b643af4462f98c4ae610b
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/11361
Reviewed-by: Austin Eng <enga@chromium.org>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>

generator/remove_files.py

@@ -0,0 +1,70 @@
+# Copyright 2019 The Dawn 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 argparse, glob, os, sys
+
+def check_in_subdirectory(path, directory):
+    return path.startswith(directory) and not '/' in path[len(directory):]
+
+def check_is_allowed(path, allowed_dirs):
+    return any(check_in_subdirectory(path, directory) for directory in allowed_dirs)
+
+def get_all_files_in_dir(find_directory):
+    result = []
+    for (directory, _, files) in os.walk(find_directory):
+        result += [os.path.join(directory, filename) for filename in files]
+    return result
+
+def run():
+    # Parse command line arguments
+    parser = argparse.ArgumentParser(
+        description = "Removes stale autogenerated files from gen/ directories."
+    )
+    parser.add_argument('--root-dir', type=str, help='The root directory, all other paths in files are relative to it.')
+    parser.add_argument('--allowed-output-dirs-file', type=str, help='The file containing a list of allowed directories')
+    parser.add_argument('--stale-dirs-file', type=str, help='The file containing a list of directories to check for stale files')
+    parser.add_argument('--stamp', type=str, help='A stamp written once this script completes')
+    args = parser.parse_args()
+
+    root_dir = args.root_dir
+    stamp_file = args.stamp
+
+    # Load the list of allowed and stale directories
+    with open(args.allowed_output_dirs_file) as f:
+        allowed_dirs = set([os.path.join(root_dir, line.strip()) for line in f.readlines()])
+
+    for directory in allowed_dirs:
+        if not directory.endswith('/'):
+            print('Allowed directory entry "{}" doesn\'t end with /'.format(directory))
+            return 1
+
+    with open(args.stale_dirs_file) as f:
+        stale_dirs = set([line.strip() for line in f.readlines()])
+
+    # Remove all files in stale dirs that aren't in the allowed dirs.
+    for stale_dir in stale_dirs:
+        stale_dir = os.path.join(root_dir, stale_dir)
+
+        for candidate in get_all_files_in_dir(stale_dir):
+            if not check_is_allowed(candidate, allowed_dirs):
+                os.remove(candidate)
+
+    # Finished! Write the stamp file so ninja knows to not run this again.
+    with open(stamp_file, "w") as f:
+        f.write("")
+
+    return 0
+
+if __name__ == "__main__":
+    sys.exit(run())