Change #1251196 had a related patch set uploaded (by Jdlrobson; author: Jdlrobson):

[operations/mediawiki-config@master] Limit and standardize thumbnail options

https://gerrit.wikimedia.org/r/1251196

@MSantos is this still blocked?

Is there a plan yet for how existing values are migrated, who will do so, and when to do this? (in relation to when this patch would be deployed). Ref T106640#10761152

In T376152#11787751, @Krinkle wrote:

Is there a plan yet for how existing values are migrated, who will do so, and when to do this? (in relation to when this patch would be deployed). Ref T106640#10761152

Parsoid is using a CSS-based approach for thumbnail preference with three options using same parser cache for all variants. @cscott and I were talking about whether we should apply this to legacy parser to avoid this being conflated with the roll out but Content-Transform-Team haven't made any decisions around if we'll do this and when.

If we wanted to push ahead I think we could use the following rough plan:

• T417513: Switch to CSS/JS solution for thumbnail size in legacy parser - which would effectively limit preferences to three values backwards compatible with existing preferences, sharing the same parser cache. However it would limit options to three sizes e.g. 300px would become 400px - this would allow us to see how a wider set of users react to this and if the solution needs further improvements.
• We would update Special:Preferences to surface three options with labels "Small", "Medium" and "Large" with logic that handles old values. (https://gerrit.wikimedia.org/r/c/mediawiki/core/+/1256553)
• We would then work with @Ladsgroup to remap the existing preferences to the new values, after which we can reduce config to 3 options (in core), T106640: Choose a sensible set of thumbnail sizes for Special:Preferences
• We would remove thumbsize from parser cache T417514: Remove `thumbsize` from ParserOptions
• Optionally: we could limit wgThumbLimits to three values to reflect these flags (e.g. warning/runtime exception when you add more)

Let me know if you think this is missing a step or wouldn't work for some reason and have a counterproposal.