PRESUBMIT: Add check for JSON parse errors + fix JSON

PRESUBMIT.py

 # Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 import json
 import os
@@ skipping 321 matching lines @@
         error_descriptions))
   if warning_descriptions:
     results.append(output_api.PresubmitPromptOrNotify(
         'You added one or more #includes of files that are temporarily\n'
         'allowed but being removed. Can you avoid introducing the\n'
         '#include? See relevant DEPS file(s) for details and contacts.',
         warning_descriptions))
   return results
 
 
+def _GetJSONParseError(input_api, filename):
+  try:
+    contents = input_api.ReadFile(filename)
+    input_api.json.loads(contents)
+  except ValueError as e:
+    return e
+  return None
+
+
+def _CheckJSONParseErrors(input_api, output_api):
+  """Check that JSON files do not contain syntax errors."""
+  actions = {

[phoglund, 2016/02/11 08:38:56]

Is this a pattern generally followed by all presubmits? It seems like
overengineering otherwise. You could just filter on extension in the for loop
and call _GetJsonParseError directly from there.

[kjellander_webrtc, 2016/02/11 09:24:15]

Chromium has IDL files as well
(https://code.google.com/p/chromium/codesearch#chromium/src/PRESUBMIT.py&l=1269)
but I only wanted JSON for now. I simplified it now since it's unlikely we'll
need IDL.

+    '.json': _GetJSONParseError,
+  }
+
+  def get_action(affected_file):
+    filename = affected_file.LocalPath()
+    return actions.get(input_api.os_path.splitext(filename)[1])
+
+  def FilterFile(affected_file):
+    action = get_action(affected_file)
+    if not action:
+      return False
+    return True
+
+  results = []
+  for affected_file in input_api.AffectedFiles(
+      file_filter=FilterFile, include_deletes=False):
+    action = get_action(affected_file)
+    parse_error = action(input_api, affected_file.AbsoluteLocalPath())
+    if parse_error:
+      results.append(output_api.PresubmitError('%s could not be parsed: %s' %
+          (affected_file.LocalPath(), parse_error)))
+  return results
+
+
 def _RunPythonTests(input_api, output_api):
   def join(*args):
     return input_api.os_path.join(input_api.PresubmitLocalPath(), *args)
 
   test_directories = [
     join('tools', 'autoroller', 'unittests'),
   ]
 
   tests = []
   for directory in test_directories:
@@ skipping 64 matching lines @@
       input_api, output_api))
   results.extend(input_api.canned_checks.CheckChangeHasNoStrayWhitespace(
       input_api, output_api))
   results.extend(input_api.canned_checks.CheckChangeTodoHasOwner(
       input_api, output_api))
   results.extend(_CheckNativeApiHeaderChanges(input_api, output_api))
   results.extend(_CheckNoIOStreamInHeaders(input_api, output_api))
   results.extend(_CheckNoFRIEND_TEST(input_api, output_api))
   results.extend(_CheckGypChanges(input_api, output_api))
   results.extend(_CheckUnwantedDependencies(input_api, output_api))
+  results.extend(_CheckJSONParseErrors(input_api, output_api))
   results.extend(_RunPythonTests(input_api, output_api))
   return results
 
 
 def CheckChangeOnUpload(input_api, output_api):
   results = []
   results.extend(_CommonChecks(input_api, output_api))
   results.extend(
       input_api.canned_checks.CheckGNFormatted(input_api, output_api))
   return results
@@ skipping 34 matching lines @@
     for builder in masters[master]:
       if 'presubmit' in builder:
         # Do not trigger presubmit builders, since they're likely to fail
         # (e.g. OWNERS checks before finished code review), and we're running
         # local presubmit anyway.
         pass
       else:
         try_config[master][builder] = ['defaulttests']
 
   return try_config