WordPress Filter for changing author list in edit post Authors box

Question

I want to change the list of users in the Author select dropdown on the edit post page for a custom post type. Is there a filter hook I can use for this? I haven't been able to find any information on a filter hook that does what I want.

The hook should (in theory) let me return a user array and those will be the users that populate the select box at the bottom. The reason I want to do this is so I can conditionally filter out users by their role for different post types. As an admin (or other admins) I don't want to have to check if user has certain role before making them the author.

Example of code:

add_filter('example_filter', 'my_custom_function');
function my_custom_function ( $users ){

    // Get users with role 'my_role' for post type 'my_post_type'
    if( 'my_post_type' == get_post_type() ){
        $users = get_users( ['role' => 'my_role'] );
    }

    // Get users with role 'other_role' for post type 'other_post_type'
    if( 'other_post_type' == get_post_type() ){
        $users = get_users( ['role' => 'other_role'] );
    }

    return $users;
}

Answer 1

You can use hook 'wp_dropdown_users_args'.

Add below code snippet in your theme's functions.php file.

add_filter( 'wp_dropdown_users_args', 'change_user_dropdown', 10, 2 );

function change_user_dropdown( $query_args, $r ){
    // get screen object
    $screen = get_current_screen();

    // list users whose role is e.g. 'Editor' for 'post' post type
    if( $screen->post_type == 'post' ):
        $query_args['role'] = array('Editor');

        // unset default role 
        unset( $query_args['who'] );
    endif;

    // list users whose role is e.g. 'Administrator' for 'page' post type
    if( $screen->post_type == 'page' ):
        $query_args['role'] = array('Administrator');

        // unset default role 
        unset( $query_args['who'] );
    endif;

    return $query_args;
}

Let me know if this works for you or not.