AMP: last AMP compatibility changes impact CSS concatenation

[jeherve]

In #10945, we made changes to our AMP compatibility file that impact the way we load CSS. Unfortunately, this change impacts all site owners currently using the jetpack_implode_frontend_css filter

Steps to reproduce the issue

1. Start from a site using Jetpack 6.8.1 and with the following code snippet: add_filter( 'jetpack_implode_frontend_css', '__return_false' );
2. Separate CSS files are loaded by Jetpack on the frontend.
3. Update to Jetpack 6.9
4. Your code snippet does not have any impact anymore, the concatenated jetpack.css is loaded instead. You have to change the priority for it to start working again, like add_filter( 'jetpack_implode_frontend_css', '__return_false', 99 );.

I have not tested, but I suspect this also impacts the other filters in use by the AMP compatibility file.

Reported here:
https://jetpack.com/2019/01/10/jetpack-6-9-introducing-more-tools-for-the-new-block-editor/#comment-193496

[superpoincare]

add_filter( 'jetpack_implode_frontend_css', '__return_false', 11 );

itself works, not just 99.

[jeherve]

@macmanx2 confirmed this also impacts another filter on that list, jetpack_sharing_counts

[macmanx2]

Thanks, Jeremy!

Confirming that add_filter( 'jetpack_sharing_counts', '__return_false', 99 ); does indeed work.

If you're using the Code Snippets plugin, simply setting the priority there to 99 doesn't seem to fix the problem, but if you change your snippet to add_filter( 'jetpack_sharing_counts', '__return_false', 99 ); and set whatever priority level you want in the plugin, it works perfectly.

[chriscoyier]

Hey gang! Just noting I got burned by this. It's a heck of a thing to have essentially dequeued Jetpack CSS only to have it show up all the sudden by upgrading a version with no warning.

[Garconis]

It would be nice if your plugin would first check to see if any of the modules need to have your jetpack.css and devicepx-jetpack.js loaded. Right now, none of the modules that we have active within Jetpack require those files to be loaded on the frontend. Rather than having to remove those via PHP snippets, it would be good if your plugin removed them automatically when they aren't needed.