Warn user in case they use commit messages with "Bug=" instead of "Bug:"

Chrome uses the syntax "Bug: xyz" in commit messages to attribute CLs
to bugs while Critique uses "BUG=xyz". As per
```
git log --grep '\(Bug\|Fixed\)=' --since=2021-01-01 --format=oneline \
| wc -l
```
we've had 27 CLs this year using the wrong syntax which led to crbug.com
not learning about the CLs <-> Bug attribution. Yours truly caused one
of them and wants to prevent the problem in the future.

We might relax the requirments in crbug.com or
chromium-review.googlesource.com but then anyone grepping through the
commit logs would need to deal with the ambiguity. Therefore, we can
just enforce the right syntax here.

https://chromium.googlesource.com/chromium/src/+/refs/heads/main/docs/contributing.md
contains the correct syntax.

Change-Id: I60ee579deac50a74e1a014ceb1d9744cbc10ab41
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3141567Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Dominic Battré <battre@chromium.org>

presubmit_canned_checks.py

@@ -109,6 +109,22 @@ def CheckChangeWasUploaded(input_api, output_api):
   return []
 
 
+def CheckDescriptionUsesColonInsteadOfEquals(input_api, output_api):
+  """Checks that the CL description uses a colon after 'Bug' and 'Fixed' tags
+  instead of equals.
+
+  crbug.com only interprets the lines "Bug: xyz" and "Fixed: xyz" but not
+  "Bug=xyz" or "Fixed=xyz".
+  """
+  text = input_api.change.DescriptionText()
+  if input_api.re.search(r'^(Bug|Fixed)=',
+                         text,
+                         flags=input_api.re.IGNORECASE
+                         | input_api.re.MULTILINE):
+    return [output_api.PresubmitError('Use Bug:/Fixed: instead of Bug=/Fixed=')]
+  return []
+
+
 ### Content checks
 
 

presubmit_canned_checks_test.py

@@ -9,6 +9,7 @@ import unittest
 
 from presubmit_canned_checks_test_mocks import MockFile, MockAffectedFile
 from presubmit_canned_checks_test_mocks import MockInputApi, MockOutputApi
+from presubmit_canned_checks_test_mocks import MockChange
 
 import presubmit_canned_checks
 
@@ -200,5 +201,45 @@ class InclusiveLanguageCheckTest(unittest.TestCase):
     self.assertEqual([], errors)
 
 
+class DescriptionChecksTest(unittest.TestCase):
+  def testCheckDescriptionUsesColonInsteadOfEquals(self):
+    input_api = MockInputApi()
+    input_api.change.RepositoryRoot = lambda: ''
+    input_api.presubmit_local_path = ''
+
+    # Verify error in case of the attempt to use "Bug=".
+    input_api.change = MockChange([], 'Broken description\nBug=123')
+    errors = presubmit_canned_checks.CheckDescriptionUsesColonInsteadOfEquals(
+        input_api, MockOutputApi())
+    self.assertEqual(1, len(errors))
+    self.assertTrue('Bug=' in errors[0].message)
+
+    # Verify error in case of the attempt to use "Fixed=".
+    input_api.change = MockChange([], 'Broken description\nFixed=123')
+    errors = presubmit_canned_checks.CheckDescriptionUsesColonInsteadOfEquals(
+        input_api, MockOutputApi())
+    self.assertEqual(1, len(errors))
+    self.assertTrue('Fixed=' in errors[0].message)
+
+    # Verify error in case of the attempt to use the lower case "bug=".
+    input_api.change = MockChange([], 'Broken description lowercase\nbug=123')
+    errors = presubmit_canned_checks.CheckDescriptionUsesColonInsteadOfEquals(
+        input_api, MockOutputApi())
+    self.assertEqual(1, len(errors))
+    self.assertTrue('Bug=' in errors[0].message)
+
+    # Verify no error in case of "Bug:"
+    input_api.change = MockChange([], 'Correct description\nBug: 123')
+    errors = presubmit_canned_checks.CheckDescriptionUsesColonInsteadOfEquals(
+        input_api, MockOutputApi())
+    self.assertEqual(0, len(errors))
+
+    # Verify no error in case of "Fixed:"
+    input_api.change = MockChange([], 'Correct description\nFixed: 123')
+    errors = presubmit_canned_checks.CheckDescriptionUsesColonInsteadOfEquals(
+        input_api, MockOutputApi())
+    self.assertEqual(0, len(errors))
+
+
 if __name__ == '__main__':
   unittest.main()

presubmit_canned_checks_test_mocks.py

@@ -119,7 +119,7 @@ class MockInputApi(object):
 
   def ReadFile(self, filename, mode='rU'):
     if hasattr(filename, 'AbsoluteLocalPath'):
-       filename = filename.AbsoluteLocalPath()
+      filename = filename.AbsoluteLocalPath()
     for file_ in self.files:
       if file_.LocalPath() == filename:
         return '\n'.join(file_.NewContents())
@@ -243,9 +243,10 @@ class MockChange(object):
   current change.
   """
 
-  def __init__(self, changed_files):
+  def __init__(self, changed_files, description=''):
     self._changed_files = changed_files
     self.footers = defaultdict(list)
+    self._description = description
 
   def LocalPaths(self):
     return self._changed_files
@@ -257,3 +258,5 @@ class MockChange(object):
   def GitFootersFromDescription(self):
     return self.footers
 
+  def DescriptionText(self):
+    return self._description