@Krinkle I repeated your actions from T258199 and here are the answers to the same questions:

This happens both with Firefox and with Chrome. Screenshot of warning for https://fa.wikipedia.org/wiki/Special:Search?debug=true

And what I get to when I click on the ...:530 link:

This is one is queued by SpecialSearch.php.

@matmarex given your success with the other task, can I ask you to kindly take a look at this one too?

SpecialSearch.php loads it.

I totally misunderstood @Krinkle's comment until you repeated it!

The only actual use cases of mediawiki.ui that I can find, as it relates to Special:Search, are these two:

• In resources/src/mediawiki.special.search.interwikiwidget.styles.less which references mediawiki.ui\variables.less. The only variable it actually uses is @colorGray15 (here) for the background color of the interwiki search results (that is the sister project results, see the screenshot below).
• Vector (legacy skin) also references the variables.less file in resources/skins.vector.styles/SearchBox.less but I would argue that eliminating Vector's dependency on mediawiki.ui should be addressed in a separate task, because Vector may use it in other places too.

Going back to the first item, the interwiki one, what I don't know is how to do away with the dependency. The script is not loading mediawiki.ui for the sake of JS; it is only loading it for the sake of CSS. The grey background makes sense from a UI perspective so I don't think we should just eliminate it.

@Huji The @import statement for mediawiki.ui/variables is not the cause of these deprecation warnings. That file is not deprecated, and is not part of the mediawiki.ui module.

I realize this is confusing, but that is how it is.

What is deprecated is not the mediawiki.ui import directory, but the mediawiki.ui module, as defined in Resources.php, and as loaded by the following PHP code:

		$out->addModuleStyles( [
			… 'mediawiki.ui', 'mediawiki.ui.button',
			'mediawiki.ui.input', …
		] );

Re-using mediawiki.ui/variables internally within another module is fine. What we have deprecated is not the Less utilities for building styles, but rather the concrete class names and styles produced by the mediawiki.ui modules. In other words, the styles produced by src/mediawiki.ui/*. The importable Less utilities from /mediawiki.less/mediawiki.ui` are still stable and fine to use.

@Krinkle the explanation was helpful. But I am still unsure as to what is the correct solution for making the warning go away.

Hi !
I just want to add that if you open the Console on Main Page of the French Wikinews, you still get this error/warning :

VM41:1 This page is using the deprecated ResourceLoader module "mediawiki.ui".
Please use OOUI instead.

Is the problem patched ?

Change 963163 had a related patch set uploaded (by Jdlrobson; author: Jdlrobson):

[mediawiki/core@master] Drop unused mediawiki ui styles

https://gerrit.wikimedia.org/r/963163

Change 963163 merged by jenkins-bot:

[mediawiki/core@master] SpecialSearch: Drop unused mediawiki ui styles

https://gerrit.wikimedia.org/r/963163