I was working on T249167 and T258337 and found what causes this: Never call setLabel() with anything but plain text. When you want a more complex HTML label, do it like this:

new OO.ui.…Widget( {
	label: 'Plain text',
	$label: $( '<a>' ).attr( { 'href': '…' } ),
} );

Or like this:

// This is exactly what the LabelElement constructor does
widget.setLabel( 'Plain text' );
widget.setLabelElement( $( '<a>' ).attr( { 'href': '…' } ) );

In both cases the plain text label and the HTML element that wraps the text are passed in separately.

This is a workaround that avoids any of the broken code in setLabel().

Change 618729 had a related patch set uploaded (by Thiemo Kreuz (WMDE); owner: Thiemo Kreuz (WMDE)):
[oojs/ui@master] Fix several broken code paths related to LabelElement#getLabel

https://gerrit.wikimedia.org/r/618729

Change 811308 had a related patch set uploaded (by Guergana Tzatchkova; author: Guergana Tzatchkova):

[oojs/ui@master] Fix Lexemes: Grammatical form can render as `[object Object]`

https://gerrit.wikimedia.org/r/811308

An easy way to test this patch is to directly edit the JS files in MediaWiki, copying the portion added in the patch to mediawiki/core/resources/lib/ooui/oojs-ui-widgets.js

Once this is merged, we could mark T220093 as solved because it wouldn't be an issue if the jquery object is passed. The uploaded patch adds the case that a jquery object.

Change 811308 merged by jenkins-bot:

[oojs/ui@master] TagMultiselectWidget: Support editing tags with jQuery-formatted labels

https://gerrit.wikimedia.org/r/811308

Gerrit patch 811308 has been merged, the next step for fixing this bug is to create a release so we can update the current version of oojs/ui in mediawiki. @Jdforrester-WMF @matmarex should I upload a patch requesting a release or when do you estimate that a new release will be made? :)

In T239208#8068539, @guergana.tzatchkova wrote:

Gerrit patch 811308 has been merged, the next step for fixing this bug is to create a release so we can update the current version of oojs/ui in mediawiki. @Jdforrester-WMF @matmarex should I upload a patch requesting a release or when do you estimate that a new release will be made? :)

I don't know, @Jdforrester-WMF and @Volker_E do the releases.

If you need the fix urgently, you could also manually backport the patch to the vendored copy of OOUI we have in mediawiki/core, by building it locally and copying the result over to resources/lib/ooui/oojs-ui-widgets.js (or manually applying the changes there if you have trouble building it for any reason).

Change 813630 had a related patch set uploaded (by Jforrester; author: Jforrester):

[mediawiki/core@master] Update OOUI to v0.44.1

https://gerrit.wikimedia.org/r/813630

Change 813630 merged by jenkins-bot:

[mediawiki/core@master] Update OOUI to v0.44.1

https://gerrit.wikimedia.org/r/813630

Change 813905 had a related patch set uploaded (by Guergana Tzatchkova; author: Guergana Tzatchkova):

[mediawiki/extensions/WikibaseLexeme@master] Remove TODO comment since T239208 allows for labels to be Objects

https://gerrit.wikimedia.org/r/813905

Change 813905 merged by jenkins-bot:

[mediawiki/extensions/WikibaseLexeme@master] Remove TODO comment since T239208 allows for labels to be Objects

https://gerrit.wikimedia.org/r/813905