PRESUBMIT: Add check for JSON parse errors + fix JSON

PRESUBMIT.py

Index: PRESUBMIT.py
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index 7388cf8b61307a043e8f06ccdf3e164e357f0002..7a9c6fd98e1c11c757e0f221ee8139b4c69ce199 100755
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -339,6 +339,42 @@ def _CheckUnwantedDependencies(input_api, output_api):
   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)
@@ -423,6 +459,7 @@ def _CommonChecks(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