Report to pulls with identical SHAs

tests/test_github.py

@@ -527,3 +527,27 @@ def test_failed_change_at_head(self):
         self.assertNotIn('merge', A.labels)
         self.assertNotIn('merge', B.labels)
         self.assertNotIn('merge', C.labels)
+
+    def test_multiple_pulls(self):
+        self.worker.hold_jobs_in_build = True
+        self.create_branch('org/project', 'pr_branch_A')
+        self.create_branch('org/project', 'pr_branch_B')
+        A = self.fake_github.openFakePullRequest('org/project', 'pr_branch_A',
+                                                 'A')
+        B = self.fake_github.openFakePullRequest('org/project', 'pr_branch_B',
+                                                 'B')
+        self.fake_github.emitEvent(A.getPullRequestOpenedEvent())
+        self.fake_github.emitEvent(B.getPullRequestOpenedEvent())
+        self.waitUntilSettled()
+
+        self.worker.hold_jobs_in_build = False
+        self.worker.release()
+        self.waitUntilSettled()
+        self.fake_github.emitEvent(A.addLabel('merge'))
+        self.fake_github.emitEvent(B.addLabel('merge'))
+        self.waitUntilSettled()
+
+        self.assertThat(A.comments[0],
+                        MatchesRegex('.*Multiple pulls.*', re.DOTALL))
+        self.assertThat(B.comments[0],
+                        MatchesRegex('.*Multiple pulls.*', re.DOTALL))

zuul/connection/github.py

@@ -565,6 +565,10 @@ def getPullBySha(self, sha):
             pulls.append(pr.as_dict())
 
         if len(pulls) > 1:
+            for pull in pulls:
+                self.commentPull(pull.owner, pull.project, pull.pr_number,
+                                 'Multiple pulls found with head sha %s. '
+                                 'Please amend your change.' % sha)
             raise Exception('Multiple pulls found with head sha %s' % sha)
 
         log_rate_limit(self.log, github)