How to avoid manage posts screen duplicates when two plugins use the same library

Question

In your code, you add the filter like this:

add_action( 'restrict_manage_posts', array( $this, 'restrict_log_posts' ) );

Which adds a function that starts like this:

public function restrict_log_posts() {
    $type="wp_log";
    $taxonomy = 'wp_log_type';
    // only add filter to post type you want
    if ( isset( $_GET['post_type'] ) && esc_attr( $_GET['post_type'] ) === $type ) {
        // get wp_log_type
        $terms = get_terms(

First, this action passes the post type so it can be simplified by adjusting the add_action and using the first parameter it passes:

public function restrict_log_posts( $post_type ) {
    $type="wp_log";
    $taxonomy = 'wp_log_type';
    // only add filter to post type you want
    if ( 'wp_log' === $post_type ) {
        // get wp_log_type
        $terms = get_terms(

Then we could use did_action to only run it the first time:

public function restrict_log_posts( $post_type ) {
    if ( did_action( 'restrict_manage_posts' ) ) {
        return;
    }
....

But this might not have the desired effect, and it’s crude. Instead, this action doesn’t belong in this class at all, and should be a standalone action. Then we can define the function only if it isn’t already defined:


if ( !function_exists('restrict_logs_by_type') ) {
    add_action( 'restrict_manage_posts', 'restrict_logs_by_type', 10, 1 );
    /**
     * Add a filter form for the log admin so we can filter by wp_log_type taxonomy values
     *
     */
    function restrict_logs_by_type( $post_type ) {
        $type="wp_log";
        $taxonomy = 'wp_log_type';
        // only add filter to post type you want
        if ( $type !== $post_type ) {
            return;
        }
        // get wp_log_type
        $terms = get_terms([
                'taxonomy'   => $taxonomy,
                'hide_empty' => true,
        ]);
        if ( is_wp_error( $terms ) || empty( $terms ) ) {
            // no terms, or the taxonomy doesn't exist, skip
            return;
        }

        ?>
        <select name="wp_log_type">
            <option value=""><?php esc_html_e( 'All log types ', 'form-processor-mailchimp' ); ?></option>
            <?php
            $current_log_type = isset( $_GET[ $taxonomy ] ) ? esc_attr( $_GET[ $taxonomy ] ) : '';
            foreach ( $terms as $key => $term ) {
                printf(
                    '<option value="%s"%s>%s</option>',
                    esc_attr( $term->slug ),
                    selected( $term->slug, $current_log_type, false ),
                    esc_html( $term->name )
                );
            }
            ?>
        </select>
        <?php
    }
}

Note that I made a number of significant improvements:

I fixed a major security hole by adding escaping to your option tags
I replaced the ugly ternary operator with the selected function provided by WP
I replaced the if check with a !==, making it a guard. Now the entire function can be unindented by 1, and is more readable. Additionally both the Cyclomatic and NPath complexity have been reduced
The function is now standalone, there was never any need for it to be part of an object or class
I renamed the function to describe what it does
If no terms are found, or the taxonomy doesn’t exist, this version skips displaying the dropdown entirely. No sense having a dropdown if the only item is “All”. Without this, the log screen would crash if there were no log types or entries
The entire snippet is wrapped in a function_exists call, if the function is loaded by the first plugin, the second plugin won’t bother defining and adding it

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