We deprecated this in 1.37. It should be removed in 1.39. Removing it will not break anything, but skins using the feature which have not upgraded will likely see a slight degradation in skin styling on certain pages.
Outside Phabricator impacts: Citizen skin, Medik skin, mediawiki bootstrap, Chameleon
See https://www.mediawiki.org/wiki/Manual:ResourceLoaderSkinModule#For_skins_deprecating_the_legacy_feature for directions on how to fix this.
Impacted skins:
https://codesearch.wmcloud.org/search/?q=%22legacy%22&i=nope&files=skin.json&excludeFiles=&repos=
TODO
- Update all skins on Gerrit
- Raise issues for all skins not on Gerrit that are still maintained
sign off steps
- When all skins are updated create follow up ticket for making sure declaring the legacy feature throw an exception in Mediawiki core.