Steps to replicate the issue:

• Create 3 wikis, wiki_a, wiki_b and wiki_c
• Set $wgSharedDB = 'wiki_a'; on all wikis
• Set $wgSharedTables[] = 'actor'; on all wikis
• Set up file sharing between wiki_b and wiki_c
• Try using files from wiki_b on wiki_c

What happens?: The files appear as red links.

This is because FileSelectQueryBuilder queries the actor table on the shared repository database, as returned by ForeignDBRepo::getDBFactory(). But shared repository's database has an empty actor table, because the actor table actually resides in wiki_a's database.

I fixed this for myself by setting table aliases on the database returned from ::getDBFactory(). But this could be implemented in MediaWiki by allowing a configuration option for shared tables directly in $wgForeignFileRepos. Unless there is an existent configuration option that I'm missing?

What should have happened instead?: The files work.

Software version: 1.44.2 (bc12cea)