This is log message has severity NOTICE which means it is a non-error, however it seems either this is a real error with the wrong severity, or it should be disabled in production.
+145,000 hits in the last 24 hours, during enablement of 1.32.0-wmf.18. In the diff channel.
level=NOTICE type=mediawiki channel=diff Falling back to DifferenceEngineSlotDiffRenderer
Example url that triggers the message in the logs server-side, https://en.m.wikipedia.org/wiki/Special:MobileDiff/243891470.
| Subject | Repo | Branch | Lines +/- | |
|---|---|---|---|---|
| Make warning about deprecated SlotDiffRenderer wrapper less noisy | mediawiki/core | master | +1 -1 |
According to http://codesearch.wmflabs.org this message is from https://gerrit.wikimedia.org/g/mediawiki/core/+/master/includes/content/ContentHandler.php#668, introduced just recently (3 days ago) via https://gerrit.wikimedia.org/r/445200, linked to T194731: Show diffs for all slots [MCR], a Multi-Content-Revisions ticket.
I'm pretty sure this is unrelated to the changes we, the WMDE-TechWish, made to wikidiff2 the past weeks.
This is not an error. SlotDiffRenderer has been split out of DifferenceEngine for handling slot-level functionality (i.e. single-content diff, as opposed to full-page diff which can soon include multiple content slots), this is a warning when some extension still tries to use DifferenceEngine for slot-level functionality (so the ContentHandler puts it into a compatibility wrapper).
For now this is fully expected for extensions which provide custom diff implementations. Eventually it should become a deprecation warning but we need to update all extensions in WMF production first. Probably we should downgrade it to INFO?
Change 455403 had a related patch set uploaded (by Gergő Tisza; owner: Gergő Tisza):
[mediawiki/core@master] Make warning about deprecated SlotDiffRenderer wrapper less noisy
Change 455403 merged by jenkins-bot:
[mediawiki/core@master] Make warning about deprecated SlotDiffRenderer wrapper less noisy