is_main_query()

function is_main_query() {
	if ( 'pre_get_posts' === current_filter() ) {
		$message = sprintf(
			/* translators: 1: pre_get_posts 2: WP_Query->is_main_query() 3: is_main_query() 4: link to codex is_main_query() page. */
			__( 'In %1$s, use the %2$s method, not the %3$s function. See %4$s.' ),
			'<code>pre_get_posts</code>',
			'<code>WP_Query->is_main_query()</code>',
			'<code>is_main_query()</code>',
			__( 'https://codex.wordpress.org/Function_Reference/is_main_query' )
		);
		_doing_it_wrong( __FUNCTION__, $message, 'WP-3.7.0' );
	}

	global $wp_query;
	return $wp_query->is_main_query();
}