Dominik Schilling

<?php
/**
 * Debug WordPress filters.
 *
 * Use add_action( 'shutdown', 'ds_debug_filters' ) to display all used
 * filters with the functions hooked into the filter.
 *
 * @author Dominik Schilling
 * @license GPLv2
 * @link https://dominikschilling.de/262/
 *
 * @version 0.1.1
 *
 * Changelog:
 * Version 0.1.1 - Fixed string for more then 1 accepted arguments.
 *
 */
function ds_debug_filters( $custom_tags = array() ) {
	// $wp_filter Stores all of the filters
	global $wp_filter;

	if ( empty( $wp_filter ) )
		return false;

	// Check if custom tags are defined
	if ( ! empty( $custom_tags ) ) {
		// Check if custom tags are available
		$tags = array_intersect( array_keys( $wp_filter), (array) $custom_tags );

		if ( empty( $tags ) )
			return false;

		// Fill custom tags
		foreach ( $tags as $tag )
			$_wp_filter[$tag] = $wp_filter[$tag];
	} else {
		// Use default tags
		$_wp_filter = $wp_filter;
	}

	echo '<pre id="wp-debug-filters">';

	// Uncomment, if you want to sort by name of the filter hooks
	// ksort( $_wp_filter );

	foreach ( $_wp_filter as $tag => $data ) {
		// Print tag name
		printf(
			'<br /><strong>%s</strong><br />',
			esc_html( $tag )
		);

		// Sort by priority
		ksort( $data );

		foreach ( $data as $priority => $functions ) {
			// Print priority once
			printf(
				'%s',
				$priority
			);

			// Go through each function
			foreach ( $functions as $function ) {
				$_function = $function['function'];
				$_args = $function['accepted_args'];

				// Check function type
				if ( is_array( $_function ) ) {
					// Object class calling
					if ( is_object( $_function[0] ) )
						$class = get_class( $_function[0] );
					else
						$class = $_function[0];

					$name = $class . '::' . $_function[1];
				} else {
					// Static calling
					$name = $_function;
				}

				// Print function name and number of accepted arguments
				printf(
					"t%s() (%s)<br />",
					esc_html( $name ),
					sprintf(
						_n(
							'1 accepted argument',
							'%s accepted arguments',
							$_args
						),
						$_args
					)
				);
			}
		}
	}

	echo '</pre>';
}