media PRESUBMIT: add warning for V4L2 initialized as aggregate

V4L2 structs are often composed of unions of other structs. When such a
struct is initialized as an aggregate with a braced-init-list, only the
first union member is actually initialized. If posterior union members
are larger, they are left partially initialized. This CL adds a
presubmit for users to avoid such ={} initialization.

Bug: b:153935975
Change-Id: If52bb7b670fe5914e864a6d840f6064cae8b7baf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2300274
Commit-Queue: Miguel Casas <mcasas@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Reviewed-by: Alexandre Courbot <acourbot@chromium.org>
Cr-Commit-Position: refs/heads/master@{#790835}

media/PRESUBMIT.py

@@ -205,6 +205,29 @@ def _CheckNoLoggingOverrideInHeaders(input_api, output_api):
         files) ]
   return []
 
+def _CheckForNoV4L2AggregateInitialization(input_api, output_api):
+  """Check that struct v4l2_* are not initialized as aggregates with a
+  braced-init-list"""
+
+  problems = []
+
+  v4l2_aggregate_initializer_re = re.compile(r'(^|\W)struct.+v4l2_.+=.+{+}+;')
+
+  for f in input_api.AffectedSourceFiles(_FilterFile):
+    for line_number, line in f.ChangedContents():
+      if v4l2_aggregate_initializer_re.search(line):
+        problems.append('%s:%d' % (f, line_number))
+
+  if problems:
+    return [output_api.PresubmitPromptWarning(
+      'Avoid initializing V4L2 structures with braced-init-lists, i.e. as '
+      'aggregates. V4L2 structs often contain unions of various sized members: '
+      'when a union is initialized by aggregate initialization, only the first '
+      'non-static member is initialized, leaving other members unitialized if '
+      'they are larger. Use memset instead.',
+      problems)]
+  return []
+
 def _CheckChange(input_api, output_api):
   results = []
   results.extend(_CheckForUseOfWrongClock(input_api, output_api))
@@ -212,6 +235,7 @@ def _CheckChange(input_api, output_api):
   results.extend(_CheckForHistogramOffByOne(input_api, output_api))
   results.extend(_CheckForUseOfLazyInstance(input_api, output_api))
   results.extend(_CheckNoLoggingOverrideInHeaders(input_api, output_api))
+  results.extend(_CheckForNoV4L2AggregateInitialization(input_api, output_api))
   return results
 
 

media/PRESUBMIT_test.py

@@ -147,5 +147,28 @@ class HistogramOffByOneTest(unittest.TestCase):
                      '                          kFooMax + 2 /* The max */ );',
                      1)
 
+class NoV4L2AggregateInitializationTest(unittest.TestCase):
+
+  def testValid(self):
+    self._testChange(['struct v4l2_format_ format;'], 0)
+
+  def testInvalid(self):
+    self._testChange(['struct v4l2_format format = {};'], 1)
+    self._testChange(['  struct v4l2_format format = {};'], 1)
+    self._testChange(['  struct std::vector<v4l2_format> format[] = {};'], 1)
+    self._testChange(['  struct std::vector<v4l2_format> format[] = {{}};'], 1)
+
+  def _testChange(self, content, expected_warnings):
+    mock_input_api = MockInputApi()
+    mock_input_api.files.append(MockFile('test.cc', content))
+    results = PRESUBMIT._CheckForNoV4L2AggregateInitialization(mock_input_api,
+                                                               MockOutputApi())
+    if expected_warnings:
+      self.assertEqual(1, len(results))
+      self.assertEqual(expected_warnings, len(results[0].items))
+    else:
+      self.assertEqual(0, len(results))
+
+
 if __name__ == '__main__':
   unittest.main()