Code review for 6.1.1 global stylesheet invalidation testing plugin

[ironprogrammer]

Creates a testing plugin to address issue described in Trac 56970.

Why a testing plugin?

Because the issue occurs after upgrade from WordPress 5.9/6.0 to 6.1.1 specifically, is hard to reproduce. Making a plugin available to the community allows for easier testing to validate whether this approach is works. If this plugin is found to address the reported issue, then the implementation may be adapted in an upcoming minor release.

Details

• Runs under WordPress 6.1.1.
• Hooks the transient_$transient_name filter to invalidate the cache for `'global_styles_'.
• Only runs the hook once. This is sufficient to force regeneration of the global stylesheet, which is subsequently cached.

Note that this is a different approach from that proposed in wp-hotfix-56970/pull/1. While the other plugin does resolve the issue in local controlled testing, it also introduces caching changes from Gutenberg to Core that should ideally ship with the next major after the code has had more time to bake in Gutenberg. 43%.

Testing

Tested with 5.9 and 6.0, and addresses issue described per the testing instructions.

More testing is needed by the community in different hosting environments, to determine whether it works when external caching is at play.

[azaozz]

LGTM, good job!

[anton-vlasenko]

I've tested this PR.
I installed this plugin, and updated WP 5.9.5 to 6.1.1 using the update button in the admin area.
The issue is that the wp_test_56970_transient_global_styles_stylesheet() callback function doesn't get called during the upgrade process (or later).
Are there any steps/prerequisites to make this work?

[ironprogrammer]

Thanks, @anton-vlasenko -- yes, the steps to test can be found here.

The global stylesheet transient is loaded on the frontend or in the editor, so the hook should only fire the first time either of those are loaded. Caching must not be disabled (e.g. WP_DEBUG must not be enabled).

[anton-vlasenko]

Thanks, @anton-vlasenko -- yes, the steps to test can be found here.

The global stylesheet transient is loaded on the frontend or in the editor, so the hook should only fire the first time either of those are loaded. Caching must not be disabled (e.g. WP_DEBUG must not be enabled).

Thanks, @ironprogrammer.
I've just tested it again and it worked.
Maybe it didn't work for me before because I was on the "Twenty Twenty Two" theme.
Anyway, I confirm that the plugin works as intended.
Great job.