Between functions.php (theme), widgets, and plugins, which is loaded first?

Customer asks if a specific carousel plugin he uses can be widgetized. That means I should create a widget inside functions.php which calls the plugin’s function. That means that the plugin’s code has to be loaded first so that the function be available to WordPress when the functions.php file is loaded, right? Would that work?

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3 comments

  1. The plugins are loaded right before theme (yes, I’ve been looking for excuse to use this):

    enter image description here

    However it is wrong to think about either as point of code execution. For most cases everything should be hooked and executed no earlier than init hook. According to Codex widget registration with register_widget() should be hooked to widget_init.

    Because of that order of load doesn’t matter for this case, you will have everything loaded by the time widget needs it in any case.

  2. One interesting approach would be to list all hooks to a file in a sequence of execution.

    add_action( 'all', '_20161224_printer' );
    function _20161224_printer( $r ){
    
        $line =  microtime(true)*10000 . ' ' . $r .  "n";
        $fp = fopen( ABSPATH . 'hooks.txt', 'a+');
        fwrite($fp, $line);
        fclose($fp);
    
    }
    

    And you will get the output like this:

    14825992300742 pre_option_blog_charset
    14825992300743 option_blog_charset
    14825992300743 plugins_loaded
    14825992300744 load_default_widgets
    14825992300745 load_default_embeds
    14825992300745 wp_audio_extensions
    14825992300745 wp_audio_embed_handler
    14825992300746 wp_video_extensions
    14825992300746 wp_video_embed_handler
    14825992300746 sanitize_comment_cookies
    14825992300747 pre_option_permalink_structure
    14825992300747 option_permalink_structure
    14825992300748 pre_option_wp_user_roles
    14825992300748 option_wp_user_roles
    14825992300749 wp_roles_init
    14825992300749 setup_theme
    14825992300749 pre_option_template
    14825992300750 option_template
    14825992300750 template
    14825992300750 theme_root
    14825992300751 template_directory
    14825992300751 pre_option_stylesheet
    14825992300751 option_stylesheet
    14825992300751 stylesheet
    14825992300752 theme_root
    14825992300752 stylesheet_directory
    14825992300752 pre_option_WPLANG
    14825992300753 query
    14825992300754 default_option_WPLANG
    14825992300755 locale
    14825992300755 override_unload_textdomain
    14825992300755 unload_textdomain
    14825992300755 override_load_textdomain
    14825992300756 load_textdomain
    14825992300756 load_textdomain_mofile
    14825992300756 locale
    ...
    many many more action hooks
    ...
    14825992302886 wp_parse_str
    14825992302886 nonce_life
    14825992302886 salt
    14825992302886 wp_parse_str
    14825992302887 esc_html
    14825992302887 logout_url
    14825992302887 clean_url
    14825992302887 gettext
    14825992302887 wp_after_admin_bar_render
    14825992302888 pre_option_template
    14825992302888 option_template
    14825992302888 template
    14825992302888 theme_root
    14825992302888 template_directory
    14825992302889 parent_theme_file_path
    14825992302889 shutdown
    

    Note the full list simply could not fit the 30.000 characters limitation per WPSO post, so I removed many action hooks.

    Put the above code inside a plugin. If you do that from the themes functions.php you will not catch plugins_loaded. One another proof the plugins are loaded before the theme.

    The possible goodies of this check are many, but please note the output will be different for different page templates you will call, or if you are in a dashboard.

    I simply called this from /?p=1 or Hello World page.

    If you don’t have a single plugin activated, you may put this code into mu-plugins folder.

    It may be better to use WP FS API, but this way is realy concise.