gistfile1.php

<?php

add_action( 'wp_loaded', function() {
	global $wp_rewrite;
	$wp_rewrite->matches = 'matches';
	$rules = $wp_rewrite->rewrite_rules( true );

	if ( update_option('rewrite_rules', $rules) ) {
		$title = 'Rewrites: Flushed';
	}
	else {
		$title = 'Rewrites: Cached';
	}

	add_action( 'admin_bar_menu', function ( $wp_admin_bar ) use ( $title ) {
		$wp_admin_bar->add_menu( array(
			'id'    => 'rewrite-flush',
			'title' => $title,
			'parent' => 'top-secondary',
		) );
	}, 150 );
}, 9999 );