Only emit parent-change-enqueued if needed

When running with GitHub and many app installations emitting the
parent-change-enqueued event is very expensive. In most cases this
event will be used to enqueue downstream changes together with the
parent change into a gate queue. Currently this event is emitted if
any pipeline uses defined trigger regardless if the event will be
consumed or not.

Emitting this event only when there is a real user makes it possible
to use this event in the gate pipeline without overloading github by
depends-on search requests triggered by items enqueued into the check
pipeline.

Change-Id: Iadcfe9b96172dcc3d0affb252a542beed3b90831

tests/unit/test_zuultrigger.py

@@ -15,6 +15,7 @@
 # under the License.
 
 from tests.base import ZuulTestCase
+from zuul.driver.zuul.zuulmodel import ZuulTriggerEvent
 
 
 class TestZuulTriggerParentChangeEnqueued(ZuulTestCase):
@@ -61,6 +62,32 @@ class TestZuulTriggerParentChangeEnqueued(ZuulTestCase):
             else:
                 raise Exception("Unknown job")
 
+        # Now directly enqueue a change into the check. As no pipeline reacts
+        # on parent-change-enqueued from pipeline check no
+        # parent-change-enqueued event is expected.
+        zuultrigger_event_count = 0
+
+        def counting_put(*args, **kwargs):
+            nonlocal zuultrigger_event_count
+            if isinstance(args[0], ZuulTriggerEvent):
+                zuultrigger_event_count += 1
+            self.sched.trigger_event_queue.put_orig(*args, **kwargs)
+
+        self.sched.trigger_event_queue.put_orig = \
+            self.sched.trigger_event_queue.put
+        self.sched.trigger_event_queue.put = counting_put
+
+        C = self.fake_gerrit.addFakeChange('org/project', 'master', 'C')
+        C.addApproval('Verified', -1)
+        D = self.fake_gerrit.addFakeChange('org/project', 'master', 'D')
+        D.addApproval('Verified', -1)
+        D.setDependsOn(C, 1)
+        self.fake_gerrit.addEvent(C.getPatchsetCreatedEvent(1))
+
+        self.waitUntilSettled()
+        self.assertEqual(len(self.history), 4)
+        self.assertEqual(zuultrigger_event_count, 0)
+
 
 class TestZuulTriggerProjectChangeMerged(ZuulTestCase):
 

zuul/driver/zuul/__init__.py

@@ -28,26 +28,29 @@ class ZuulDriver(Driver, TriggerInterface):
     log = logging.getLogger("zuul.ZuulTrigger")
 
     def __init__(self):
-        self.tenant_events = {}
+        self.parent_change_enqueued_events = {}
+        self.project_change_merged_events = {}
 
     def registerScheduler(self, scheduler):
         self.sched = scheduler
 
     def reconfigure(self, tenant):
-        events = set()
-        self.tenant_events[tenant.name] = events
         for pipeline in tenant.layout.pipelines.values():
             for ef in pipeline.manager.event_filters:
                 if not isinstance(ef.trigger, zuultrigger.ZuulTrigger):
                     continue
                 if PARENT_CHANGE_ENQUEUED in ef._types:
-                    events.add(PARENT_CHANGE_ENQUEUED)
+                    # parent-change-enqueued events need to be filtered by
+                    # pipeline
+                    for pipeline in ef._pipelines:
+                        key = (tenant.name, pipeline)
+                        self.parent_change_enqueued_events[key] = True
                 elif PROJECT_CHANGE_MERGED in ef._types:
-                    events.add(PROJECT_CHANGE_MERGED)
+                    self.project_change_merged_events[tenant.name] = True
 
     def onChangeMerged(self, tenant, change, source):
         # Called each time zuul merges a change
-        if PROJECT_CHANGE_MERGED in self.tenant_events[tenant.name]:
+        if self.project_change_merged_events.get(tenant.name):
             try:
                 self._createProjectChangeMergedEvents(change, source)
             except Exception:
@@ -56,9 +59,11 @@ class ZuulDriver(Driver, TriggerInterface):
                     "%s" % (change,))
 
     def onChangeEnqueued(self, tenant, change, pipeline):
-        self.log.debug("onChangeEnqueued %s", self.tenant_events[tenant.name])
         # Called each time a change is enqueued in a pipeline
-        if PARENT_CHANGE_ENQUEUED in self.tenant_events[tenant.name]:
+        tenant_events = self.parent_change_enqueued_events.get(
+            (tenant.name, pipeline.name))
+        self.log.debug("onChangeEnqueued %s", tenant_events)
+        if tenant_events:
             try:
                 self._createParentChangeEnqueuedEvents(change, pipeline)
             except Exception: