Custom classes and IDs are removed from admin notices

[desrosj]

Companion ticket for Trac-45418.

Custom classes and IDs are stripped from admin notices, making it impossible for plugin and theme developers to specifically target their notices.

Describe the bug
A clear and concise description of what the bug is.

To Reproduce
Add an admin notice using the admin_notices action hook that has custom classes and an ID attribute.

add_action( 'admin_notices', function() {
	?>
	<div id="my-plugin-error-notice" class="notice notice-error my-plugins-custom-class"><p>This is a custom error notice for my plugin.</p></div>
	<?php
});

Open the editor screen and inspect the notice. It has the Gutenberg notice class (components-notice is-error), and nothing else.

Expected behavior
The custom classes and ID should be preserved.

[chrisvanpatten]

I think this was an intentional change, although there are definitely back-compat implications. I think the long term idea is for core to limit the amount of customisation to notices, so we can build out a better system for managing and displaying notifications. @aduth can probably add more context here :)

[aduth]

This is a consequence of the notices module being more constrained in its understanding of a "notice" entity, and thus prone to lossy conversion in the upgrade for admin_notices backwards-compatibility (#11604).

An interim workaround can be to leverage the fact that the inner markup of a notice is preserved verbatim, and thus it's possible to include a wrapping element within the .notice upon which an ID is applied.

add_action( 'admin_notices', function() {
	?><div class="notice notice-error"><div id="my-plugin-error-notice" class="my-plugins-custom-class"><p>This is a custom error notice for my plugin.</p></div></div><?php
} );

As to a general solution? To the use-case of Trac-45418, ideally the dismiss remembrance is something which could be baked into the default notices behavior. Other ideas to explore could include:

• Detect whether there are attributes or classes assigned to the admin_notices notice and, if present, create some wrapping element automatically
• Enhance notices module to support "attributes" broadly, and pass through all attributes of the admin_notices notice

These should be tempered by an understanding that the implementation of preserving markup in #11604 via __unstableHTML is intended to serve as a stop-gap solution.

[desrosj]

I am going to close this. Legacy admin notices are no longer being consumed and displayed by Gutenberg as of #12444.