Hookable dropins

[mikeschinkel]

This ticket is the result of a discussion on the wp-hackers list where I proposed the idea in ​this message.

Currently for dropins there can be only one[1] per install which means that, especially for advanced-cache.php where multiple plugins cannot easily:

• Cache different mime types with different plugins
• Provide basic functionality and leave the complexity to other plugins because hooks are not available (this is likely needed for a good page caching API to ever emerge from the work of plugins.)

For caching this results in plugins like WP Super Cache and WP Total Cache that significantly violate a sancrosact WordPress philosophy of "​Decisions, not Options". To see what I mean, just visit the settings page for either of these plugins. (Note: I'm not criticizing the plugins or their developers, instead saying that WordPress doesn't give them much of a choice.)

It turns out however that fixing this is really lightweight and easy, at least for advanced-cache.php. I will attach the following files but here is the short list of changes to core required:

• Move the hooks-related function out of /wp-includes/plugin.php into another file which I called /wp-includes/hooks.php and include /wp-includes/hooks.php in /wp-settings.php close to the top after /wp-includes/versions.php is included.
• Include another new file /wp-includes/dropsin.php in /wp-settings.php after /wp-includes/hooks.php which contains a wp_load_dropins() function that include()s all .php files found in /wp-includes/dropins/.
• Lastly add the following two (2) lines before advanced-cache.php is included:

// Load any potential dropins found /wp-content/dropins/
wp_load_dropins();

// Run the hook-based page cache.
do_action( 'page_cache' );

With this future caching plugins can implement the page_cache hook by dropping a file into /wp-content/cache/ instead of adding an /wp-content/advanced-cache.php.

If this idea is blessed then we could add a deprecation notice for /wp-content/advanced-cache.php and also potentially replace (some of) the other dropins with do_actions( "{$dropin_hook}" ).

[1] ​Gratuitous Highlander reference.

[mikeschinkel]

hookable-dropins.diff

[mikeschinkel]

hooks.php which contains the files moved out of plugin.php.

[mikeschinkel]

dropins.php - To enable loading .php files from /wp-content/dropins/

[mikeschinkel]

Related #21401

[scribu]

Move the hooks-related function out of /wp-includes/plugin.php into another file which I called /wp-includes/hooks.php

If you do that, the plugin.php file is left with just a handful of functions (198 lines, mostly docs).

[mikeschinkel]

Replying to scribu:

If you do that, the plugin.php file is left with just a handful of functions (198 lines, mostly docs).

So what's your suggestion, just move where plugin.php is included?

[wonderboymusic]

19 months of silence. Most people just alter advanced-cache.php to suit their needs. Most widely-used dropins change infrequently and are flexible enough to allow changes without causing painful merges when a new version is released.