Add cache clearing mechanisms

[g-elwell]

What problem does this address?

When working with theme.json, patterns, and templates, changes are often not visible immediately due to caching which is employed by WordPress.

You can set the WP_DEVELOPMENT_MODE constant to disable this - https://make.wordpress.org/core/2023/07/14/configuring-development-mode-in-6-3/

However this is sometimes missed, especially on hosted dev environments.

What is your proposed solution?

Investigate possible approaches for setting WP_DEVELOPMENT_MODE and/or clearing caches within themer.

Potentially - have an option in the 'more menu' for enabling theme dev mode, and display a persistent notification in WP Admin to alert users that this is active.

[con322]

Would it be possible to change the WP_DEVELOPMENT_MODE constant via some user action? since that's usually defined very early on.

Wondering it calling wp_clean_theme_json_cache on save_post_wp_global_styles hook would work.

Something like:

add_action('save_post_wp_global_styles', function () {
	wp_clean_theme_json_cache();
});

Is there a scenario you know of where caching is causing a problem locally that one could try to see if the above would be enough?

[g-elwell]

I haven't got a reproducible example but the main pain point I know people have hit appears to be around patterns rather than theme.json - I've experienced situations where a new pattern or template may take several minutes or longer to appear within the site editor and it's tripped quite a few people up.

I think this is the scenario we're hitting but as I say would need to check if it's reproducible:

• user is developing a theme
• a new pattern file is added to the theme (eg patterns/my-new-pattern.php)
• this doesn't show in the site editor
• the user has no idea why so assumes they have done something wrong

Setting WP_DEVELOPMENT_MODE locally is the true solution, this seems to resolve things immediately as well as disabling some other caching, but if it's not possible to pass control to set this to the user via UI then we might need to dig deeper into what it actually does and configure something with similar behaviour.

I suppose we might also have the situation where we deploy code to production which includes new patterns, and need to clear the caches but not set WP_DEVELOPMENT_MODE, so maybe a cache clear action is along the right lines?

[ampersarnie]

Moved to Needs Refinement - Discussion to be had on whether Themer is the right place for this feature, and what the future of Themer is going to be. To be discussed more as part of focus groups.

cc: @scottblackburn @balw