Hello,
We often have the case of a change to an extension depending on a pending patch to MediaWiki core. I have upgraded our CI scheduler - Zuul - a couple weeks ago and it now supports marking dependencies even in different repositories.
Why does it matter? To make sure the dependency is fulfilled one usually either:
* CR-2 the patch until dependent change is merged * write a test that exercise the required patch in MediaWiki.
With the first solution (lack of test), once both are merged, nothing prevent one from cherry picking a patch without its dependent patch. For example for MediaWiki minor releases or Wikimedia deployment branches.
When a test covers the dependency, it will fail until the dependent one is merged which is rather annoying.
Zuul now recognizes the header 'Depends-On' in git messages, similar to 'Change-Id' and 'Bug'. 'Depends-On' takes as parameter a change-id and multiple ones can be added.
When a patch is proposed in Gerrit, Zuul looks for Gerrit changes matching the 'Depends-On' and verify whether any are still open. In such a case, it will craft references for the open patches so all the dependencies can be tested as if they got merged.
Real world example ------------------
The ContentTranslation extension is tested with the Wikidata one and was not passing the test. Wikidata created a patch and we did not want to merge it until we confirm the ContentTranslation one is passing properly.
The Wikidata patch is https://gerrit.wikimedia.org/r/#/c/252227/ Change-Id: I0312c23628d706deb507b5534b868480945b6163
On ContentTranslation we indicated the dependency: https://gerrit.wikimedia.org/r/#/c/252172/1..2//COMMIT_MSG + Depends-On: I0312c23628d706deb507b5534b868480945b6163
Which is the Wikidata patch.
Zuul: * received the patch for ContentTranslation * looked up the change-id and found the Wikidata * created git references in both repo to point to the proper patches
Jenkins: * zuul-cloner cloned both repos and fetched the references created by the Zuul service * run tests * SUCCESS
That confirmed us the Wikidata patch was actually fixing the issue for ContentTranslation. Hence we CR+2 both and all merged fine.
Please take a moment to read upstream documentation:
http://docs.openstack.org/infra/zuul/gating.html#cross-repository-dependenci...
Wikidata/ContentTranslation task: https://phabricator.wikimedia.org/T118263