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

extensions/common/api/externs_checker.py

Index: extensions/common/api/externs_checker.py
diff --git a/extensions/common/api/externs_checker.py b/extensions/common/api/externs_checker.py
new file mode 100644
index 0000000000000000000000000000000000000000..910c9a570d7a32219286c4221f8deb2f105e7200
--- /dev/null
+++ b/extensions/common/api/externs_checker.py
@@ -0,0 +1,43 @@
+# 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 _WarningEntry(object):

[Dan Beam, 2016/02/23 03:15:24]

nit: is this better than a dict or a tuple?  can this class be private inside of
ExternsChecker?

[Devlin, 2016/02/23 23:12:39]

Tuple yes (I originally had it like that and decided it was too easy to mix up
source and extern), dict, no.  Using dict now.

+  def __init__(self, source, extern):
+    self.source = source
+    self.extern = extern
+

[Dan Beam, 2016/02/23 03:15:24]

\n\n between file-level globals

[Devlin, 2016/02/23 23:12:39]

Moot

+class ExternsChecker(object):
+  COMMAND_STUB = str('src/ $ python tools/json_schema_compiler/compiler.py %s '

[Dan Beam, 2016/02/23 03:15:24]

nit: prefix with _ (also, STUB seems a bit odd... _COMMAND_TEMPLATE, just
_COMMAND?)

[Devlin, 2016/02/23 23:12:39]

I like _COMMAND_TEMPLATE, done.

+                     '--root=. --generator=externs > %s')
+
+  def __init__(self, input_api, output_api, api_pairs):
+    self._api_pairs = api_pairs
+    self._input_api = input_api
+    self._output_api = output_api
+
+  def _GetCommand(self, source, dest):
+    return self.COMMAND_STUB % (source, dest)
+
+  def _GetWarningText(self, entries):
+    if (len(entries) == 1):

[Dan Beam, 2016/02/23 03:15:24]

if len(entries) == 1:

[Devlin, 2016/02/23 23:12:39]

Done.

+      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>'))
+
+  def RunChecks(self):
+    bad_files = []
+    affected = [f.LocalPath() 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(_WarningEntry(path, pair))
+    results = []
+    if len(bad_files) > 0:

[Dan Beam, 2016/02/23 03:15:24]

nit: if bad_files:

[Devlin, 2016/02/23 23:12:39]

Ah, right, done.

+      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