wp_mime_type_icon function fails to return non-SVG icons

[dglingren]

WordPress 6.5 added a new parameter, $preferred_ext, to the wp_mime_type_icon function in the /wp-includes/post.php file. It is described as "File format to prefer in return." In fact, it is the REQUIRED extension, not the preferred extension, and no other file extension is allowed. WordPress passes ".svg" in the argument and that prevents any other file type, e.g., a ".png" icon, from being returned.

You can reproduce the problem by activating a plugin that supplies a custom icon directory with non-SVG icon files, such as my own Media Library Assistant. Simply install and activate the plugin, then go to the Settings/Media Library Assistant Uploads tab. Check the "Enable MLA File Type Icons Support" box and click Save Changes. The go to the Media/Library or Media/Assistant admin screen and display a non-image item such as an audio or video item.

When this bug occurs the wp_mime_type_icon function causes a PHP Warning message. "Undefined variable $icon in ...\wp-includes\post.php on line 6940", and the function returns a NULL value. The function also caches an empty array for the $icon_files variable so subsequent function calls return a false value.

[joedolson]

Thanks for reporting!

Return the array of all icons found in icon directory if the preferred extension is not found.

Trac ticket: https://core.trac.wordpress.org/attachment/ticket/60740

[joedolson]

To test:

• Follow testing instructions provided by @dglingren. Observe the error or non-loading icons before patch, note properly loading icon after patch.
• Deactivate plugin and verify that the .svg icons appear as expected both before and after patch.

Properly based version of prior PR

Trac ticket: https://core.trac.wordpress.org/ticket/60740

[antpb]

I left an approval in the GitHub issue but echoing here that this working in my testing following the reproduction steps and the code looks good.

[joedolson]

In 57845:

Media: Fall back to available icons if SVG media icons not found.

Follow up to [57687]. If no icons of the preferred type are available, then the icon array should return the collection of valid icons found, rather than an empty array.

Props sabernhardt, swissspidy, sabernhardt, antpb, joedolson.
Fixes #60740.

[joedolson]

Re-opening for committing to 6.5 branch.

[sabernhardt]

I added dglingren's props manually.

[joedolson]

Thanks, @sabernhardt.

I *know* I added them when I wrote the commit message; but I must have accidentally pasted yours over them. Argh.

[joedolson]

I'll add them in the commit to the 6.5 branch, though.

[joedolson]

In 57846:

Media: Fall back to available icons if SVG media icons not found.

Follow up to [57687]. If no icons of the preferred type are available, then the icon array should return the collection of valid icons found, rather than an empty array.

Props dglingren, sabernhardt, swissspidy, sabernhardt, antpb, joedolson.
Reviewed by swissspidy.
Merges [57845] to the 6.5 branch.
Fixes #60740.