Skip subject line length check for merge commits

Some merge requests (e.g. those created for release branches) include
merge commits.  Prevent Danger from warning about excessive subject line
length for merge commits.  (While the proper way to detect a merge
commit would be to check the 'parents' attribute of a commit object,
Danger Python does not seem to populate that attribute, so a simple
string search is performed on the commit subject instead.)

diff --git a/dangerfile.py b/dangerfile.py
index 1943df62b112698430b71e3c7c0d0e3a83eff3a3..f9db5bd7d7eac97be9030608a5b461dc3513ba8c 100644 (file)
--- a/dangerfile.py
+++ b/dangerfile.py
@@ -49,7 +49,8 @@ target_branch = danger.gitlab.mr.target_branch
 #
 # - WARN if any of the following is true for any commit on the MR branch:
 #
-#     * The length of the subject line exceeds 72 characters.
+#     * The length of the subject line for a non-merge commit exceeds 72
+#       characters.
 #
 #     * There is no log message present (i.e. commit only has a subject) and
 #       the subject line does not contain any of the following strings:
@@ -77,7 +78,7 @@ for commit in danger.git.commits:
         fail('Fixup commits are still present in this merge request. '
              'Please squash them before merging.')
         fixup_error_logged = True
-    if len(subject) > 72:
+    if len(subject) > 72 and not subject.startswith('Merge branch '):
         warn(
             f'Subject line for commit {commit.sha} is too long: '
             f'```{subject}``` ({len(subject)} > 72 characters).'