Run lint-luci-milo.py as presubmit on luci-milo.cfg changes.

Bug: none
Change-Id: I4cd719751f4962bd80c7f9b6531535e15a1d3d99
Reviewed-on: https://chromium-review.googlesource.com/c/1340520
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608943}

infra/config/global/PRESUBMIT.py

+# Copyright 2018 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.
+
+"""Enforces luci-milo.cfg consistency.
+
+See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
+for more details on the presubmit API built into depot_tools.
+"""
+
+
+def _CheckLintLuciMiloCfg(input_api, output_api):
+  if ('infra/config/global/luci-milo.cfg' not in input_api.LocalPaths() and
+      'infra/config/global/lint-luci-milo.py' not in input_api.LocalPaths()):
+    return []
+  return input_api.RunTests([input_api.Command(
+      name='lint-luci-milo',
+      cmd=[input_api.python_executable, 'lint-luci-milo.py'],
+      kwargs={},
+      message=output_api.PresubmitError)])
+
+
+def CheckChangeOnUpload(input_api, output_api):
+  return _CheckLintLuciMiloCfg(input_api, output_api)
+
+
+def CheckChangeOnCommit(input_api, output_api):
+  return _CheckLintLuciMiloCfg(input_api, output_api)

infra/config/global/lint-luci-milo.py

@@ -28,12 +28,14 @@ def compare_builders(name, main_builders, sub_builders):
   sub_names = [', '.join(builder.name) for builder in sub_builders]
 
   if main_names != sub_names:
-    print '%s: bot name lists different:' % name
+    print ('bot name lists different between main waterfall ' +
+           'and stand-alone %s waterfall:' % name)
     print '\n'.join(difflib.unified_diff(main_names, sub_names,
-                                         fromfile='main', tofile='sub',
+                                         fromfile='main', tofile=name,
                                          lineterm=''))
     print
-    return
+    return False
+  return True
 
 
 def main():
@@ -51,9 +53,13 @@ def main():
         subwaterfall = builder.category.split('|', 1)[0]
         subwaterfalls[subwaterfall].append(builder)
 
+  all_good = True
   for console in project.consoles:
     if console.id in subwaterfalls:
-      compare_builders(console.id, subwaterfalls[console.id], console.builders)
+      if not compare_builders(console.id, subwaterfalls[console.id],
+                              console.builders):
+        all_good = False
+  return 0 if all_good else 1
 
 
 if __name__ == '__main__':