[Extern Generation] Add a presubmit script to check externs not being updated

extensions/common/api/externs_checker.py

+# Copyright 2016 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+class ExternsChecker(object):
+  _UPDATE_MESSAGE = """To update the externs, run:
+ src/ $ python tools/json_schema_compiler/compiler.py\
+ %s --root=. --generator=externs > %s"""
+
+  def __init__(self, input_api, output_api, api_pairs):
+    self._input_api = input_api
+    self._output_api = output_api
+    self._api_pairs = api_pairs
+
+  def _GetWarningText(self, entries):

[Dan Beam, 2016/02/24 19:06:49]

I don't really see the point of having this to only call once (nor pushing the
knowledge of how to act into here, sharing key names)

would probably be better to pass only the active replacements in from outer
scope or just do all of this there

[Devlin, 2016/02/25 01:14:11]

Done.

+    replacements = (('<source_file>', '<output_file>') if len(entries) > 1 else
+        (entries[0]['source'], entries[0]['extern']))
+    return self._UPDATE_MESSAGE % replacements
+
+  def RunChecks(self):
+    bad_files = []
+    affected = [f.AbsoluteLocalPath() for f in self._input_api.AffectedFiles()]
+    for path in affected:
+      pair = self._api_pairs.get(path)
+      if pair != None and pair not in affected:
+        bad_files.append({'source': path, 'extern': pair})
+    results = []
+    if bad_files:
+      results.append(self._output_api.PresubmitPromptWarning(
+          str('Found updated extension api files without updated extern files. '
+              'Please update the extern files.'),
+          [f['source'] for f in bad_files],
+          self._GetWarningText(bad_files)))
+    return results