Support bug prefixes when stripping away empty bug in git-cl-upload.

For instance, if the bug-prefix is set to "b/", git cl upload will offer a
line with "Bug: b/", however it won't get stripped away if it's left blank,
unlike the default "Bug:" line. This change fixes that inconsistency by
also taking the bug-prefix into account when stripping.

Change-Id: Ib6e4d18c1ff52ec77cd1422be15b1e6920332238
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1528972Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Jonas Termansen <sortie@google.com>

git_cl.py

@@ -3083,8 +3083,8 @@ class ChangeDescription(object):
     ] + self._description_lines)
 
     regexp = re.compile(self.BUG_LINE)
+    prefix = settings.GetBugPrefix()
     if not any((regexp.match(line) for line in self._description_lines)):
-      prefix = settings.GetBugPrefix()
       values = list(_get_bug_line_values(prefix, bug or '')) or [prefix]
       if git_footer:
         self.append_footer('Bug: %s' % ', '.join(values))
@@ -3100,7 +3100,9 @@ class ChangeDescription(object):
 
     # Strip off comments and default inserted "Bug:" line.
     clean_lines = [line.rstrip() for line in lines if not
-                   (line.startswith('#') or line.rstrip() == "Bug:")]
+                   (line.startswith('#') or
+                    line.rstrip() == "Bug:" or
+                    line.rstrip() == "Bug: " + prefix)]
     if not clean_lines:
       DieWithError('No CL description, aborting')
     self.set_description(clean_lines)

tests/git_cl_test.py

@@ -964,6 +964,7 @@ class TestGitCl(TestCase):
       if not issue:
         # Prompting to edit description on first upload.
         calls += [
+          ((['git', 'config', 'rietveld.bug-prefix'],), ''),
           ((['git', 'config', 'core.editor'],), ''),
           ((['RunEditor'],), description),
         ]