[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):
+  _COMMAND_TEMPLATE = str('src/ $ python tools/json_schema_compiler/compiler.py'
+                          ' %s --root=. --generator=externs > %s')

[Dan Beam, 2016/02/23 23:26:17]

why can't we combine the strings in _GetWarningText and _GetCommand?

_UPDATE_MESSAGE = """
To update the externs, run:
src/ $ python tools/json_schema_compiler/compiler.py \
    %s --root. --generator=externs > %s
"""

or something

[Devlin, 2016/02/24 00:05:06]

Done.

+
+  def __init__(self, input_api, output_api, api_pairs):
+    self._api_pairs = api_pairs

[Dan Beam, 2016/02/23 23:26:17]

why are you initializing members in a different order than receiving them as
arguments?  alphabetizing members?  a little confusing

[Devlin, 2016/02/24 00:05:06]

Didn't even notice.  Done.

+    self._input_api = input_api
+    self._output_api = output_api
+
+  def _GetCommand(self, source, dest):
+    return self._COMMAND_TEMPLATE % (source, dest)
+
+  def _GetWarningText(self, entries):
+    if len(entries) == 1:
+      return str('To update the externs, run "%s"' %
+                     self._GetCommand(entries[0]['source'],
+                                      entries[0]['extern']))
+    return str('To update the externs, run "%s"' %
+                     self._GetCommand('<source_file>', '<output_file>'))

[Dan Beam, 2016/02/23 23:26:17]

# or source, dest = ... if you want

replacements = ('<source_file>', '<output_file>') if len(entries) > 1 else
    (entries[0]['source'], entries[0]['extern'])
return self._UPDATE_MESSAGE % replacements

[Devlin, 2016/02/24 00:05:06]

Done.

+
+  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