In https://gerrit.wikimedia.org/r/#/c/396067/ @cscott exposed this,
$ echo "[[File:Foobar.jpg|alt=galleryalt|link=meatball:Link]]" | node bin/parse --normalize <p><figure-inline><a href="Meatball:Link"><img alt="galleryalt" src="//upload.wikimedia.org/wikipedia/commons/3/3a/Foobar.jpg" data-file-width="240" data-file-height="28" data-file-type="bitmap" height="28" width="240"/></a></figure-inline></p>
In handleInfo, the o.hasLink case (https://github.com/wikimedia/parsoid/blob/master/lib/wt2html/tt/LinkHandler.js#L1432-L1459) probably needs a call to getWikiLinkTargetInfo instead of just the makeTitleFromText