parser: don't trigger database IntegrityErrors on duplicate comments

As we've done for the Patch model, this change prevents database errors
from duplicate Comments.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Reviewed-by: Stephen Finucane <stephen@that.guru>
(cherry picked from commit 55aa9cd)

Author: jk-ozlabs

patchwork/parser.py

@@ -1277,16 +1277,16 @@ def parse_mail(mail, list_id=None):
 
     author = get_or_create_author(mail, project)
 
-    try:
+    with transaction.atomic():
+        if Comment.objects.filter(submission=submission, msgid=msgid):
+            raise DuplicateMailError(msgid=msgid)
         comment = Comment.objects.create(
             submission=submission,
             msgid=msgid,
             date=date,
             headers=headers,
             submitter=author,
             content=message)
-    except IntegrityError:
-        raise DuplicateMailError(msgid=msgid)
 
     logger.debug('Comment saved')
 

patchwork/tests/test_parser.py

@@ -1168,3 +1168,15 @@ def test_duplicate_patch(self):
         self._test_duplicate_mail(m)
 
         self.assertEqual(Patch.objects.count(), 1)
+
+    def test_duplicate_comment(self):
+        diff = read_patch('0001-add-line.patch')
+        m1 = create_email(diff, listid=self.listid, msgid='1@example.com')
+        _parse_mail(m1)
+
+        m2 = create_email('test', listid=self.listid, msgid='2@example.com',
+                          in_reply_to='1@example.com')
+        self._test_duplicate_mail(m2)
+
+        self.assertEqual(Patch.objects.count(), 1)
+        self.assertEqual(Comment.objects.count(), 1)