Per https://www.mediawiki.org/wiki/Manual:Hooks/LoadExtensionSchemaUpdates documentation, and code search: https://codesearch.wmflabs.org/deployed/?q=onLoadExtensionSchemaUpdates%5C(%20%5C%24&i=nope&files=&repos=, the idea here is to type hint all WMF deployed repos hook handler function $updater parameter with DatabaseUpdater
See example patch: https://gerrit.wikimedia.org/r/#/c/511602/
All extensions with unknown name of hook functions
https://codesearch.wmflabs.org/search/?q=function%5Cs%2B%5Cw%2B%5Cs*%5C(%20%5C%24updater&i=nope&files=&repos=
Remove also = null and return true for such hook functions