[wp-trac] [WordPress Trac] #21412: Hookable dropins

[WordPress Trac]

#21412: Hookable dropins
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 Reporter:  mikeschinkel  |      Owner:
     Type:  enhancement   |     Status:  new
 Priority:  normal        |  Milestone:  Awaiting Review
Component:  Cache         |    Version:
 Severity:  normal        |   Keywords:  has-patch dev-feedback
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 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].

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Ticket URL: <http://core.trac.wordpress.org/ticket/21412>
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