Add a test for enqueuing complex dependencies

To fully validate that the logic in enqueueChangesAhead and
enqueueChangesBehind is working as intended, create a complex
graph of dependent changes and ensure that even when a change
in the middle is the triggering change, the whole graph is
enqueued in the correct order.

This also adds a missing return statement from the addChange
method.  It does not actually alter the result in this case as
the current code has enough repitition in walking up and down
the tree to eventually enqueue everything, however, it might
be possible for it to produce the wrong result in some cases,
or perhaps do so in a less efficient way.  At any rate, I
believe the added return value is more correct.

Also, this adjusts one of the most annoying log messages, where
a perfectly normal false condition was being logged at error
level.

Change-Id: Ie39f24943d878ae7510736250fb3c43c53649de0

tests/test_scheduler.py

@@ -601,6 +601,91 @@ class TestScheduler(ZuulTestCase):
         self.assertEqual(B.reported, 2)
         self.assertEqual(C.reported, 2)
 
+    def test_needed_changes_enqueue(self):
+        "Test that a needed change is enqueued ahead"
+        #          A      Given a git tree like this, if we enqueue
+        #         / \     change C, we should walk up and down the tree
+        #        B   G    and enqueue changes in the order ABCDEFG.
+        #       /|\       This is also the order that you would get if
+        #     *C E F      you enqueued changes in the order ABCDEFG, so
+        #     /           the ordering is stable across re-enqueue events.
+        #    D
+
+        A = self.fake_gerrit.addFakeChange('org/project', 'master', 'A')
+        B = self.fake_gerrit.addFakeChange('org/project', 'master', 'B')
+        C = self.fake_gerrit.addFakeChange('org/project', 'master', 'C')
+        D = self.fake_gerrit.addFakeChange('org/project', 'master', 'D')
+        E = self.fake_gerrit.addFakeChange('org/project', 'master', 'E')
+        F = self.fake_gerrit.addFakeChange('org/project', 'master', 'F')
+        G = self.fake_gerrit.addFakeChange('org/project', 'master', 'G')
+        B.setDependsOn(A, 1)
+        C.setDependsOn(B, 1)
+        D.setDependsOn(C, 1)
+        E.setDependsOn(B, 1)
+        F.setDependsOn(B, 1)
+        G.setDependsOn(A, 1)
+
+        A.addApproval('CRVW', 2)
+        B.addApproval('CRVW', 2)
+        C.addApproval('CRVW', 2)
+        D.addApproval('CRVW', 2)
+        E.addApproval('CRVW', 2)
+        F.addApproval('CRVW', 2)
+        G.addApproval('CRVW', 2)
+        self.fake_gerrit.addEvent(C.addApproval('APRV', 1))
+
+        self.waitUntilSettled()
+
+        self.assertEqual(A.data['status'], 'NEW')
+        self.assertEqual(B.data['status'], 'NEW')
+        self.assertEqual(C.data['status'], 'NEW')
+        self.assertEqual(D.data['status'], 'NEW')
+        self.assertEqual(E.data['status'], 'NEW')
+        self.assertEqual(F.data['status'], 'NEW')
+        self.assertEqual(G.data['status'], 'NEW')
+
+        # We're about to add approvals to changes without adding the
+        # triggering events to Zuul, so that we can be sure that it is
+        # enqueing the changes based on dependencies, not because of
+        # triggering events.  Since it will have the changes cached
+        # already (without approvals), we need to clear the cache
+        # first.
+        source = self.sched.layout.pipelines['gate'].source
+        source.maintainCache([])
+
+        self.worker.hold_jobs_in_build = True
+        A.addApproval('APRV', 1)
+        B.addApproval('APRV', 1)
+        D.addApproval('APRV', 1)
+        E.addApproval('APRV', 1)
+        F.addApproval('APRV', 1)
+        G.addApproval('APRV', 1)
+        self.fake_gerrit.addEvent(C.addApproval('APRV', 1))
+
+        for x in range(8):
+            self.worker.release('.*-merge')
+            self.waitUntilSettled()
+        self.worker.hold_jobs_in_build = False
+        self.worker.release()
+        self.waitUntilSettled()
+
+        self.assertEqual(A.data['status'], 'MERGED')
+        self.assertEqual(B.data['status'], 'MERGED')
+        self.assertEqual(C.data['status'], 'MERGED')
+        self.assertEqual(D.data['status'], 'MERGED')
+        self.assertEqual(E.data['status'], 'MERGED')
+        self.assertEqual(F.data['status'], 'MERGED')
+        self.assertEqual(G.data['status'], 'MERGED')
+        self.assertEqual(A.reported, 2)
+        self.assertEqual(B.reported, 2)
+        self.assertEqual(C.reported, 2)
+        self.assertEqual(D.reported, 2)
+        self.assertEqual(E.reported, 2)
+        self.assertEqual(F.reported, 2)
+        self.assertEqual(G.reported, 2)
+        self.assertEqual(self.history[6].changes,
+                         '1,1 2,1 3,1 4,1 5,1 6,1 7,1')
+
     def test_trigger_cache(self):
         "Test that the trigger cache operates correctly"
         self.worker.hold_jobs_in_build = True

zuul/scheduler.py

@@ -1166,9 +1166,11 @@ class BasePipelineManager(object):
             self.enqueueChangesBehind(change, quiet, ignore_requirements)
             self.sched.triggers['zuul'].onChangeEnqueued(item.change,
                                                          self.pipeline)
+            return True
         else:
-            self.log.error("Unable to find change queue for project %s" %
-                           change.project)
+            self.log.debug("Unable to find change queue for "
+                           "change %s in project %s" %
+                           (change, change.project))
             return False
 
     def dequeueItem(self, item):