Parsoid is moving to a CSS/JS solution for thumbnail size (T375981); we probably want to use the same solution for the legacy parser as well to reduce the variance between legacy and Parsoid output.
TODO
- Update legacy parser to support upscaling/downscaling of upright images
- Wait 2 weeks (23rd April 2026)
- Disable parser cache variance on thumbsize and apply Parsoid JavaScript and CSS to legacy parser [in wmf.1.47.0]
- Create a follow up task for limiting user preferences to three values (https://gerrit.wikimedia.org/r/c/mediawiki/core/+/1256553) > T424910: Limit Special:Preferences thumbnail option to three options - small, regular and large
Rollback plan
While this has been in Parsoid for some time, this will expand the feature to a much larger audience. Differences in rendering may be noticed by eagle-eyed users. It is important that we do not rollback if the complaints are about minor changes (e.g. an image is more pixelated than before or the image is 20px smaller than before)
We should only consider rollback in the following situations:
- Images are appearing as a completely different size for logged out users
- Logged in users are seeing images in sizes different to the wikitext e.g. [[File:Foo.jpg|600px]] is not rendering at 600px.
If we do need to rollback, logged in users will need to purge the page and cache to revert to previous rendering.