Need help enabling post thumbnails for a custom post type in my plugin

[JLeuze]

I recently released my first plugin, Meteor Slides, which adds a custom post type for slides.

The slide images are managed using the Featured Image functionality. To ensure that this works with older themes, my plugin is adding support for post thumbnails like this:

 add_theme_support( 'post-thumbnails', array( 'slide' ) ); 
  

This has worked well so far to add thumbnail support for the slides post type, without adding it to posts and pages in themes that don't support this feature.

The above code works with themes that have no thumbnail support, and it works with themes that have it fully enabled like this:

 add_theme_support( 'post-thumbnails' ); 
  

But I just found out that when a theme enables this feature for a specific post type or types using an array, the featured image feature is disabled in my plugin.

Here is an example of how one theme that conflicts with my plugin adds post thumbnail support:

 add_theme_support( 'post-thumbnails', array( 'post' ) ); 
  

It doesn't matter if the theme is specifying support for posts, pages, or another custom post type; if an array is used like this there is a conflict.

I had thought that the two arrays were the source of the conflict, but even when I remove the array from my plugin and enable post thumbnails for all post types, the conflict remains unchanged.

So I am assuming that when a theme specifies certain post types to be enabled with this feature, it overrides that setting in plugins?

Does anyone know anything more about adding post-thumbnails that could help me with this problem?

My only idea right now would be to check if the theme or another plugin has added support for this already, and if it has added an array, filter that array to include my custom post type. Would something like this even be possible?

[JLeuze]

I did a bit more experimenting, figured out that the theme's settings for the post thumbnail doesn't necessarily have to override the plugin settings.

It's just a matter of timing, the themes that I tested are running this function on a later action than the function I have setup in my plugin.

I could run my function on a later action, but this is either going to override the theme or another plugin, or it is going to open up post thumbnails to all post types.

I'd prefer to cleanly add featured image support just to my own post type and not mess with any other post types, so I don't think the adjusting the timing of my function would be of much help.

[Rarst]

Run later, add whatever you need directly to global $_wp_theme_features (see add_theme_support() source) to what theme already did?

[JLeuze]

Thanks Rarst, that's a good idea, I didn't think to dig into theme.php to see what was going on.

Right now I am running this pretty early, on the "plugins_loaded" action. I guess I can't anticipate when every theme or plugin is running this, but timing my action to run after the theme's functions.php would cover the most common conflicts.

I can't find any info on when functions.php runs, I'm guessing "setup_theme", any know if that is right?

It looks like this is the bit of code in theme.php that is setting up the post thumbnails:

 function current_theme_supports( $feature ) {
            global $_wp_theme_features;
    
            if ( !isset( $_wp_theme_features[$feature] ) )
                    return false;
    
            // If no args passed then no extra checks need be performed
            if ( func_num_args() <= 1 )
                    return true;
    
            $args = array_slice( func_get_args(), 1 );
    
            // @todo Allow pluggable arg checking
            switch ( $feature ) {
                    case 'post-thumbnails':
                            // post-thumbnails can be registered for only certain content/post types by passing
                            // an array of types to add_theme_support().  If no array was passed, then
                            // any type is accepted
                            if ( true === $_wp_theme_features[$feature] )  // Registered for all types
                                    return true;
                            $content_type = $args[0];
                            if ( in_array($content_type, $_wp_theme_features[$feature][0]) )
                                    return true;
                            else
                                    return false;
                            break;
            }
    
            return true;
} 
  

Not exactly sure how to work directly with this, I'm pretty much a newbie when it comes to PHP, could anyone point me in the right direction?

[Rarst]

Right now I am running this pretty early, on the "plugins_loaded" action. I guess I can't anticipate when every theme or plugin is running this, but timing my action to run after the theme's functions.php would cover the most common conflicts.

functions.php is running earlier in same file (wp-settings.php).

 /**
 * Allows a theme to register its support of a certain feature
 *
 * Must be called in the theme's functions.php file to work.
 * If attached to a hook, it must be after_setup_theme.
 * The init hook may be too late for some features.
 *
 * @since 2.9.0
 * @param string $feature the feature being added
 */
function add_theme_support( $feature ) {
    global $_wp_theme_features;
 
    if ( func_num_args() == 1 )
        $_wp_theme_features[$feature] = true;
    else
        $_wp_theme_features[$feature] = array_slice( func_get_args(), 1 );
} 
  

Seems like you will need to check what $_wp_theme_features['post-thumbnails'] holds and modify accordingly. Also see comments for this function, might be better choice of hook to mess with this.

[JLeuze]

Thanks for pointing me at the right file, in wp-settings.php I found where it loads the theme's function file:

     // Load the functions for the active theme, for both parent and child theme if applicable.
    if ( TEMPLATEPATH !== STYLESHEETPATH && file_exists( STYLESHEETPATH . '/functions.php' ) )
            include( STYLESHEETPATH . '/functions.php' );
    if ( file_exists( TEMPLATEPATH . '/functions.php' ) )
            include( TEMPLATEPATH . '/functions.php' );
    
    do_action( 'after_setup_theme' );
    
    // Load any template functions the theme supports.
    require_if_theme_supports( 'post-thumbnails', ABSPATH . WPINC . '/post-thumbnail-template.php' ); 
  

So it looks like if I want to run my function after the theme and have the post thumbnails work, I need to use the "after_setup_theme" action.

At least when I setup my plugin to enable post-thumbnails for all post types and run on "after_setup_theme", it worked pretty well in my tests.

Now if I can just rein that in to work on just slides

[Rarst]

Purely theoretical code, but I imagine close to what you need

 function add_slide() {
    global $_wp_theme_features;
 
    if( !isset( $_wp_theme_features['post-thumbnails'] ) )
        $_wp_theme_features['post-thumbnails'] = array( array( 'slide' ) );
 
    elseif ( true === $_wp_theme_features['post-thumbnails'] )
        $_wp_theme_features['post-thumbnails'] = array( array( 'post','page', 'slide' ) );
 
    elseif ( is_array( $_wp_theme_features['post-thumbnails'] ) )
        $_wp_theme_features['post-thumbnails'][0][] = 'slide';
} 
  

No promises if it will work. :)

[JLeuze]

Awesome, that code worked perfectly Rarst, I didn't have to change a thing!

Works great with post thumbnails disabled, enabled, or any with any array I threw at it and totally fixed the specific theme conflict I was trying to fix for a user.

Only situation in which it didn't work strangely enough was with 2010. Checked it out, 2010 is running this on "after_setup_theme" as well. Tested my action, and "after_setup_theme" is the latest you can run this and get the post thumbnail template to be included.

So I set the priority of my action super low and it works just fine with 2010:

 add_action( 'after_setup_theme', 'meteorslides_featured_image_array', '9999' ); 
  

As long as no other themes or plugins try to come to the party even later than mine is, I think it should play nice with others

And I thought that moving the featured image box was a learning experience. I should really write a blog post about using featured images with a custom post type, it ended up being a lot trickier than I expected.