Add meta data to WordPress default search

search_all_w_meta.php

<?php

add_action( 'pre_get_posts', array( $this, 'search_metadata' ), 9 );
function search_metadata() {
	if ( ! is_main_query() || ! is_search() ) {
		return;
	}

	add_filter( 'posts_join', function( $join ) {
		global $wpdb;
		return $join .' LEFT JOIN ' . $wpdb->postmeta . ' ON '. $wpdb->posts . '.ID = ' . $wpdb->postmeta . '.post_id ';
	} );

	add_filter( 'posts_where', function ( $where ) {
		global $wpdb;

		$or = array(
			"(".$wpdb->posts.".post_title LIKE $1)",
			"(".$wpdb->postmeta.".meta_value LIKE $1)",
		);

		if ( is_main_query() && is_search() ) {
			$where = preg_replace(
				"/\(\s*".$wpdb->posts.".post_title\s+LIKE\s*(\'[^\']+\')\s*\)/",
				implode( ' OR ', $or ),
				$where
			);
		}

		return $where;
	} );

	add_filter( 'posts_distinct', function () {
		global $wpdb;
		return "DISTINCT";
	} );
}