Add canned presubmit check for GN formatting

Requires https://codereview.chromium.org/779883002/ to be landed/rolled before it's useful.

R=dpranke@chromium.org
BUG=348474

Review URL: https://codereview.chromium.org/779513005

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@293269 0039d316-1c4b-4281-b951-d872f2087c98

gn.py

@@ -30,7 +30,7 @@ def main(args):
     print >> sys.stderr, 'gn.py: Could not find gn executable at: %s' % gn_path
     return 2
   else:
-    return subprocess.call([gn_path] + sys.argv[1:])
+    return subprocess.call([gn_path] + args[1:])
 
 
 if __name__ == '__main__':

presubmit_canned_checks.py

@@ -1113,3 +1113,22 @@ def CheckPatchFormatted(input_api, output_api):
   # As this is just a warning, ignore all other errors if the user
   # happens to have a broken clang-format, doesn't use git, etc etc.
   return []
+
+
+def CheckGNFormatted(input_api, output_api):
+  import gn
+  affected_files = input_api.AffectedFiles(
+      include_deletes=False,
+      file_filter=lambda x: x.LocalPath().endswith('.gn') or
+                            x.LocalPath().endswith('.gni'))
+  warnings = []
+  for f in affected_files:
+    cmd = ['gn', 'format', '--dry-run', f.AbsoluteLocalPath()]
+    rc = gn.main(cmd)
+    if rc == 2:
+      warnings.append(output_api.PresubmitPromptWarning(
+          '%s requires formatting. Please run `gn format --in-place %s`.' % (
+              f.AbsoluteLocalPath(), f.LocalPath())))
+  # It's just a warning, so ignore other types of failures assuming they'll be
+  # caught elsewhere.
+  return warnings

tests/presubmit_unittest.py

@@ -1878,6 +1878,7 @@ class CannedChecksUnittest(PresubmitTestsBase):
       'CheckLicense',
       'CheckOwners',
       'CheckPatchFormatted',
+      'CheckGNFormatted',
       'CheckRietveldTryJobExecution',
       'CheckSingletonInHeaders',
       'CheckSvnModifiedDirectories',