Route external versions to the queue where default version was built

When a build for an external version is triggered, we find the the last build
for the default version and use the same queue for this version.

This should make the build to always succeed when it's merged into the default
version since it's using the same build queue.

I thought this was fixed originally in
#7912 but that PR was wrong.

Author: humitos

readthedocs/builds/tasks.py

@@ -82,6 +82,24 @@ def route_for_task(self, task, args, kwargs, **__):
             )
             return project.build_queue
 
+        # Use last queue used by the default version for external versions
+        if version.type == EXTERNAL:
+            last_build_for_default_version = (
+                project.builds
+                .filter(version__slug=project.get_default_version())
+                .order_by('-date')
+                .first()
+            )
+            if 'default' in last_build_for_default_version.builder:
+                routing_queue = self.BUILD_DEFAULT_QUEUE
+            else:
+                routing_queue = self.BUILD_LARGE_QUEUE
+            log.info(
+                'Routing task because is a external version. project=%s queue=%s',
+                project.slug, routing_queue,
+            )
+            return routing_queue
+
         queryset = version.builds.filter(success=True).order_by('-date')
         last_builds = queryset[:self.N_LAST_BUILDS]
 
@@ -94,16 +112,6 @@ def route_for_task(self, task, args, kwargs, **__):
                 )
                 return self.BUILD_LARGE_QUEUE
 
-        # Use last queue used for external versions
-        if version.type == EXTERNAL:
-            for build in last_builds.iterator():
-                if not build.builder:
-                    continue
-
-                if 'default' in build.builder:
-                    return self.BUILD_DEFAULT_QUEUE
-                return self.BUILD_LARGE_QUEUE
-
         # We do not have enough builds for this version yet
         if queryset.count() < self.N_BUILDS:
             log.info(

readthedocs/builds/tests/test_celery_task_router.py

@@ -70,21 +70,31 @@ def test_no_build_pk(self):
         )
 
     def test_external_version(self):
-        self.version.type = EXTERNAL
-        self.version.save()
-
-        self.build.builder = 'build-default-a1b2c3'
-        self.build.save()
+        external_version = fixture.get(
+            Version,
+            project=self.project,
+            slug='pull-request',
+            type=EXTERNAL,
+        )
+        default_version = self.project.versions.get(slug=self.project.get_default_version())
+        default_version_build = fixture.get(
+            Build,
+            version=default_version,
+            project=self.project,
+            builder='build-default-a1b2c3',
+        )
+        args = (external_version.pk,)
+        kwargs = {'build_pk': default_version_build.pk}
 
         self.assertEqual(
-            self.router.route_for_task(self.task, self.args, self.kwargs),
+            self.router.route_for_task(self.task, args, kwargs),
             TaskRouter.BUILD_DEFAULT_QUEUE,
         )
 
-        self.build.builder = 'build-large-a1b2c3'
-        self.build.save()
+        default_version_build.builder = 'build-large-a1b2c3'
+        default_version_build.save()
 
         self.assertEqual(
-            self.router.route_for_task(self.task, self.args, self.kwargs),
+            self.router.route_for_task(self.task, args, kwargs),
             TaskRouter.BUILD_LARGE_QUEUE,
         )