We took an initial look at this during the task breakdown today and came to the following conclutions:

We looked at doHtmlPageLinkRendererBegin in HtmlPageLinkRendererBeginHookHandler and we probably need to implement or alter the logic here for the title -> entity Id bit, or implement one of these using the API? does that make sense? what is this title? abusing this mediawiki hook in this way for federated properties feels quite evil.

		$entityId = $foreignEntityId ?: $this->entityIdLookup->getEntityIdForTitle( $target );

We also spotted a title existence check:

		if ( $isLocal && !$target->exists() ) {

For which we might be able to use another one of our new services (if we have the entity id)

The other part of this is:

		$labelDescriptionLookup = $this->getLabelDescriptionLookup( $context );

which we should(tm) get for free once T249797 and T249799 are done.

This first area of wikitext -> title -> entityid needs to be thought about more.

We might need to rewrite most of doHtmlPageLinkRendererBegin to use our new services.
This would essentially move away from Title and towards LinkTarget and Entity based checks.
We might still need a LinkTarget -> EntityId service?

We will need to look at this more to perform an actual breakdown.

During the today's task breakdown we came up with the following rough steps:

• Create a service that can go from a Title / LinkTarget object to an EntityId object.
  • This is essentially the reverse of TitleLookupBasedEntityTitleTextLookup with some more logic
  • The extra logic would be that from HtmlPageLinkRendererBeginHookHandler::doHtmlPageLinkRendererBegin
• Alter ApiPrefetchingTermLookup to also allow fetching of descriptions

• Rewrite HtmlPageLinkRendererBeginHookHandler::doHtmlPageLinkRendererBegin to use the new service
  • This hook handler would use an EntityId throughout rather than messing about with a Title object
  • This should allow the links to be rendered with labels and descriptions as expected
  • Alter DefaultEntityLinkFormatter to not use Title, instead use and EntityId and EntityTitleTextLookup

• Use HtmlPageLinkRendererEnd in wikibase repo to override the href of property links for federated properties only (using a EntityUrlLookup service)