git_cl: Add JSON output flag for `git cl presubmit`

This allows scripts to use `git cl presubmit` to get JSON output from
the presubmit hook.

See https://crrev.com/c/5302055/comment/5b78090c_24935055/ for more
context.

Bug: None
Change-Id: I5aaee016b74f8b7375eaf9c5d10cb0af8d86bad8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/5320109
Commit-Queue: Michael Cui <mlcui@google.com>
Reviewed-by: Scott Lee <ddoman@chromium.org>

git_cl.py

@@ -4665,6 +4665,9 @@ def CMDpresubmit(parser, args):
                       help='Run presubmit checks in the ResultSink environment '
                       'and send results to the ResultDB database.')
     parser.add_option('--realm', help='LUCI realm if reporting to ResultDB')
+    parser.add_option('-j',
+                      '--json',
+                      help='File to write JSON results to, or "-" for stdout')
     options, args = parser.parse_args(args)
 
     if not options.force and git_common.is_dirty_git_tree('presubmit'):
@@ -4697,16 +4700,18 @@ def CMDpresubmit(parser, args):
             return 1
         base_branch = 'HEAD'
 
-    cl.RunHook(committing=not options.upload,
-               may_prompt=False,
-               verbose=options.verbose,
-               parallel=options.parallel,
-               upstream=base_branch,
-               description=description,
-               all_files=options.all,
-               files=options.files,
-               resultdb=options.resultdb,
-               realm=options.realm)
+    result = cl.RunHook(committing=not options.upload,
+                        may_prompt=False,
+                        verbose=options.verbose,
+                        parallel=options.parallel,
+                        upstream=base_branch,
+                        description=description,
+                        all_files=options.all,
+                        files=options.files,
+                        resultdb=options.resultdb,
+                        realm=options.realm)
+    if options.json:
+        write_json(options.json, result)
     return 0
 
 

tests/git_cl_test.py

@@ -4268,6 +4268,13 @@ class CMDTestCaseBase(unittest.TestCase):
 
 
 class CMDPresubmitTestCase(CMDTestCaseBase):
+    _RUN_HOOK_RETURN = {
+        'errors': [],
+        'more_cc': [],
+        'notifications': [],
+        'warnings': []
+    }
+
     def setUp(self):
         super(CMDPresubmitTestCase, self).setUp()
         mock.patch('git_cl.Changelist.GetCommonAncestorWithUpstream',
@@ -4276,7 +4283,8 @@ class CMDPresubmitTestCase(CMDTestCaseBase):
                    return_value='fetch description').start()
         mock.patch('git_cl._create_description_from_log',
                    return_value='get description').start()
-        mock.patch('git_cl.Changelist.RunHook').start()
+        mock.patch('git_cl.Changelist.RunHook',
+                   return_value=self._RUN_HOOK_RETURN).start()
 
     def testDefaultCase(self):
         self.assertEqual(0, git_cl.main(['presubmit']))
@@ -4340,6 +4348,12 @@ class CMDPresubmitTestCase(CMDTestCaseBase):
             resultdb=True,
             realm='chromium:public')
 
+    @mock.patch('git_cl.write_json')
+    def testJson(self, mock_write_json):
+        self.assertEqual(0, git_cl.main(['presubmit', '--json', 'file.json']))
+        mock_write_json.assert_called_once_with('file.json',
+                                                self._RUN_HOOK_RETURN)
+
 
 class CMDTryResultsTestCase(CMDTestCaseBase):
     _DEFAULT_REQUEST = {