For Parsoid purposes, the interwiki mapping needs to be bidirectional -- that is, we need to be able not just to go from enwiki:$1 to //en.wikipedia.org/wiki/$1 but also given a URL https://en.wkipedia.org/wiki/Foo we need to lookup that this matches the enwiki prefix and that the Title part should be Foo.
We are currently doing this by calling the InterwikiLookup::getAllPrefixes() method *but* this doesn't play nicely with the InterwikiLoadPrefix hook. That is, InterwikiLoadPrefix is demand-driven, but extensions can add new prefixes via InterwikiLoadPrefix (and the used-in-WMF-production Extension:Interwiki does so, as does the parser test infrastructure) without them showing up in ::getAllPrefixes(). In fact, Extension:Interwiki explicitly requires that the new prefixes *not* show up in ::getAllPrefixes, as its implementation of the InterwikiLoadPrefix hook recursively calls ::getAllPrefixes to avoid delegating lookup of prefixes defined locally.
One solution is to add a "reverse mapping" API and hook to InterwikiLookup, say:
public function match( $url ): string {
if ( !$this->hookRunner->onInterwikiMatchPrefix( $url, $result ) ) {
return $result;
}
// else....
}This would allow Parsoid to call *just* InterwikiLookup::fetch and InterwikiLookup::match and avoid calling the problematic ::getAllPrefixes method (or indeed, avoid enumerating all prefixes at all).
The Extension:Interwiki could continue to recursively invoke ::getAllPrefixes to determine what prefixes the base wiki supports. It would implement the new InterwikiMatchPrefix hook by enumerating the interwiki table from the central DB (caching would help here!) and then returning true to indicate that any matches from the local DB should take precedence.
T113034: RFC: Overhaul Interwiki map, unify with Sites and WikiMap proposes to overhaul and unify the interwiki map; it's possible that would lead to a better solution. Putting in an ad-hoc match hook now would at least guide that work by making concrete the requirement that the mapping be bidirectional.