Fix ZUUL_COMMIT in certain conditions

In a dependent pipeline with changes to multiple branches of
a single project, ZUUL_COMMIT would sometimes point to a commit
further back in the series rather than the commit that should
be tested (ie, not the commit pointed to by ZUUL_REF).  It's
possible this situation could appear in other circumstances as
well.

The error was the re-use of a variable when creating Zuul refs
for the entire series.  The variable should have been reserved
to indicate the final commit but instead could end up containing
the most recent commit of another branch or even project.

A test case is updated to detect both the condition where the
ZUUL_COMMIT for two different changes are the same, as well as
when ZUUL_REF does not point to ZUUL_COMMIT.

Change-Id: I9074746070edeebdff9f2ef3c1bb00526c21cfee

tests/test_scheduler.py

@@ -1945,6 +1945,15 @@ class TestScheduler(testtools.TestCase):
         self.fake_gerrit.addEvent(B.addApproval('APRV', 1))
         self.fake_gerrit.addEvent(C.addApproval('APRV', 1))
         self.waitUntilSettled()
+        queue = self.gearman_server.getQueue()
+        job_A = None
+        for job in queue:
+            if 'project-merge' in job.name:
+                job_A = job
+        ref_A = self.getParameter(job_A, 'ZUUL_REF')
+        commit_A = self.getParameter(job_A, 'ZUUL_COMMIT')
+        self.log.debug("Got Zuul ref for change A: %s" % ref_A)
+        self.log.debug("Got Zuul commit for change A: %s" % commit_A)
 
         self.gearman_server.release('.*-merge')
         self.waitUntilSettled()
@@ -1954,7 +1963,10 @@ class TestScheduler(testtools.TestCase):
             if 'project-merge' in job.name:
                 job_B = job
         ref_B = self.getParameter(job_B, 'ZUUL_REF')
+        commit_B = self.getParameter(job_B, 'ZUUL_COMMIT')
         self.log.debug("Got Zuul ref for change B: %s" % ref_B)
+        self.log.debug("Got Zuul commit for change B: %s" % commit_B)
+
         self.gearman_server.release('.*-merge')
         self.waitUntilSettled()
         queue = self.gearman_server.getQueue()
@@ -1962,7 +1974,9 @@ class TestScheduler(testtools.TestCase):
             if 'project-merge' in job.name:
                 job_C = job
         ref_C = self.getParameter(job_C, 'ZUUL_REF')
+        commit_C = self.getParameter(job_C, 'ZUUL_COMMIT')
         self.log.debug("Got Zuul ref for change C: %s" % ref_C)
+        self.log.debug("Got Zuul commit for change C: %s" % commit_C)
         self.gearman_server.hold_jobs_in_queue = False
         self.gearman_server.release()
         self.waitUntilSettled()
@@ -1972,15 +1986,32 @@ class TestScheduler(testtools.TestCase):
 
         repo_messages = [c.message.strip()
                          for c in repo.iter_commits(ref_C)]
+        repo_shas = [c.hexsha for c in repo.iter_commits(ref_C)]
         repo_messages.reverse()
         correct_messages = ['initial commit', 'A-1', 'C-1']
+        # Ensure the right commits are in the history for this ref
         self.assertEqual(repo_messages, correct_messages)
+        # Ensure ZUUL_REF -> ZUUL_COMMIT
+        self.assertEqual(repo_shas[0], commit_C)
 
         repo_messages = [c.message.strip()
                          for c in repo.iter_commits(ref_B)]
+        repo_shas = [c.hexsha for c in repo.iter_commits(ref_B)]
         repo_messages.reverse()
         correct_messages = ['initial commit', 'mp commit', 'B-1']
         self.assertEqual(repo_messages, correct_messages)
+        self.assertEqual(repo_shas[0], commit_B)
+
+        repo_messages = [c.message.strip()
+                         for c in repo.iter_commits(ref_A)]
+        repo_shas = [c.hexsha for c in repo.iter_commits(ref_A)]
+        repo_messages.reverse()
+        correct_messages = ['initial commit', 'A-1']
+        self.assertEqual(repo_messages, correct_messages)
+        self.assertEqual(repo_shas[0], commit_A)
+
+        self.assertNotEqual(ref_A, ref_B, ref_C)
+        self.assertNotEqual(commit_A, commit_B, commit_C)
 
     def test_one_job_project(self):
         "Test that queueing works with one job"

zuul/merger/merger.py

@@ -266,12 +266,12 @@ class Merger(object):
         recent[key] = commit
         # Set the Zuul ref for this item to point to the most recent
         # commits of each project-branch
-        for key, commit in recent.items():
+        for key, mrc in recent.items():
             project, branch = key
             try:
                 repo = self.getRepo(project, None)
                 zuul_ref = branch + '/' + item['ref']
-                repo.createZuulRef(zuul_ref, commit)
+                repo.createZuulRef(zuul_ref, mrc)
             except Exception:
                 self.log.exception("Unable to set zuul ref %s for "
                                    "item %s" % (zuul_ref, item))