WP: extend search results including tags

wp_extend_search_results_including_tags.php

<?php
/**
 * Extend search results query including tags.
 *
 * @hook   posts_where, posts_join, posts_groupby
 *
 * @param  string
 * @return string
 */
function my_theme_search_where_clause_include_tags( string $where ) : string
{
	if ( is_search() ) {
		global $wpdb;
		$where .= "OR (t.name LIKE '%".get_search_query()."%' AND {$wpdb->posts}.post_status = 'publish')";
	}
	return $where;
}
function my_theme_search_join_clause_include_tags( string $join ) : string
{
	if ( is_search() ) {
		global $wpdb;
		$join .= "LEFT JOIN {$wpdb->term_relationships} tr ON {$wpdb->posts}.ID = tr.object_id INNER JOIN {$wpdb->term_taxonomy} tt ON tt.term_taxonomy_id=tr.term_taxonomy_id INNER JOIN {$wpdb->terms} t ON t.term_id = tt.term_id";
	}
	return $join;
}
function my_theme_search_groupby_clause_group_by_post_id( string $groupby ) : string
{
	// we need to group on post ID
	global $wpdb;
	$groupby_id = "{$wpdb->posts}.ID";

	// on normal query (not search), or if the clause is already present, do nothing
	if( !is_search() || strpos( $groupby, $groupby_id ) !== false ) {
		return $groupby;
	}

	// groupby was empty, use ours
	if( !strlen( trim( $groupby ) ) ) {
		return $groupby_id;
	}

	// wasn't empty, append ours
	return $groupby . ", " . $groupby_id;
}
add_filter( 'posts_where','my_theme_search_where_clause_include_tags' );
add_filter( 'posts_join', 'my_theme_search_join_clause_include_tags' );
add_filter( 'posts_groupby', 'my_theme_search_groupby_clause_group_by_post_id' );