id	summary	reporter	owner	description	type	status	priority	milestone	component	version	severity	resolution	keywords	cc
21412	Hookable dropins	mikeschinkel		"This ticket is the result of a discussion on the wp-hackers list where I proposed the idea in [http://lists.automattic.com/pipermail/wp-hackers/2012-July/043772.html 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 ''""[http://wordpress.org/about/philosophy/#decisions 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] [http://www.urbandictionary.com/define.php?term=%22there%20can%20only%20be%20one%22%20 Gratuitous Highlander reference]."	enhancement	new	normal	Awaiting Review	Cache		normal		has-patch dev-feedback	mikeschinkel@… ashishsainiashfame@… kpayne@… whsatterwhite@… beau@… mike.schroder@…