Shortcode to display all attribute terms in WooCommerce, including unused ones, with working filter links.

all-attribute-terms-shortcode.php

/**
 * Shortcode: [all_attribute_terms attribute="pa_size"]
 * Shows all terms for a product attribute, even if not assigned to products.
 * Links use WooCommerce's layered nav filter format.
 */
function show_all_attribute_terms( $atts ) {
    $atts = shortcode_atts( [
        'attribute' => '',
    ], $atts );

    if ( empty( $atts['attribute'] ) ) {
        return '';
    }

    $taxonomy = wc_sanitize_taxonomy_name( $atts['attribute'] );
    $attribute = wc_sanitize_taxonomy_name( str_replace( 'pa_', '', $taxonomy ) );
    $terms = get_terms( [
        'taxonomy'   => $taxonomy,
        'hide_empty' => false,
    ] );

    if ( is_wp_error( $terms ) || empty( $terms ) ) {
        return '';
    }

    // Get the shop page URL
    $shop_url = wc_get_page_permalink( 'shop' );

    $output = '<ul class="all-attribute-terms">';
    foreach ( $terms as $term ) {
        // Build WooCommerce layered nav filter URL
        $url = add_query_arg( [
            'filter_' . $attribute => $term->slug,
            'query_type_' . $attribute => 'or',
        ], $shop_url );

        $output .= sprintf(
            '<li><a href="%s">%s</a> (%d)</li>',
            esc_url( $url ),
            esc_html( $term->name ),
            intval( $term->count )
        );
    }
    $output .= '</ul>';

    return $output;
}
add_shortcode( 'all_attribute_terms', 'show_all_attribute_terms' );