Improve presubmit check for BUG line

PRESUBMIT.py

Index: PRESUBMIT.py
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index 34e09b8ec51b25ccc63f362fb66df403ec6dd0c4..b0b811dc41a82a74d099e7a1c5ce29f98630c28e 100644
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -209,28 +209,32 @@ def _SkipTreeCheck(input_api, output_api):
   return input_api.environ.get('PRESUBMIT_TREE_CHECK') == 'skip'
 
 
-def _CheckChangeLogFlag(input_api, output_api):
+def _CheckChangeLogFlag(input_api, output_api, warn):
   """Checks usage of LOG= flag in the commit message."""
   results = []
-  if input_api.change.BUG and not 'LOG' in input_api.change.tags:
-    results.append(output_api.PresubmitError(
-        'An issue reference (BUG=) requires a change log flag (LOG=). '
-        'Use LOG=Y for including this commit message in the change log. '
-        'Use LOG=N or leave blank otherwise.'))
+  if (input_api.change.BUG and input_api.change.BUG != 'none' and
+      not 'LOG' in input_api.change.tags):
+    text = ('An issue reference (BUG=) requires a change log flag (LOG=). '
+            'Use LOG=Y for including this commit message in the change log. '
+            'Use LOG=N or leave blank otherwise.')
+    if warn:
+      results.append(output_api.PresubmitPromptWarning(text))
+    else:
+      results.append(output_api.PresubmitError(text))
   return results
 
 
 def CheckChangeOnUpload(input_api, output_api):
   results = []
   results.extend(_CommonChecks(input_api, output_api))
-  results.extend(_CheckChangeLogFlag(input_api, output_api))
+  results.extend(_CheckChangeLogFlag(input_api, output_api, True))
   return results
 
 
 def CheckChangeOnCommit(input_api, output_api):
   results = []
   results.extend(_CommonChecks(input_api, output_api))
-  results.extend(_CheckChangeLogFlag(input_api, output_api))
+  results.extend(_CheckChangeLogFlag(input_api, output_api, False))

[Michael Achenbach, 2015/07/17 09:55:08]

Can you make a test CL with e.g. BUG=foo and see if the CQ blocks it?

   results.extend(input_api.canned_checks.CheckChangeHasDescription(
       input_api, output_api))
   if not _SkipTreeCheck(input_api, output_api):