Support for mu-plugins folder, when using plugins_url()

plugins_url() is supposed to work for plugins or mu-plugins, the code inside it supports both. But the filter inside this plugin forces one, and if it’s an mu-plugin, it breaks all of the URLs.

Problem code in the plugin itself stems from this:

add_filter( 'plugins_url', 'domain_mapping_plugins_uri', 1 );

which calls:

function domain_mapping_plugins_uri( $full_url, $path=NULL, $plugin=NULL ) {
	return get_option( 'siteurl' ) . substr( $full_url, stripos( $full_url, PLUGINDIR ) - 1 );
}

I think this would be better, but I’m not sure if this plugin will get future updates:

function domain_mapping_plugins_uri( $full_url, $path=NULL, $plugin=NULL ) {

	$siteurl = get_site_url();

	if ( false !== stripos( $full_url, PLUGINDIR ) ) {
		$full_url = $siteurl . substr( $full_url, stripos( $full_url, PLUGINDIR ) - 1 );
	} elseif ( false !== stripos( $full_url, MUPLUGINDIR ) ) {
		$full_url = $siteurl . substr( $full_url, stripos( $full_url, MUPLUGINDIR ) - 1 );
	}

	return $full_url;

}

The code above is backwards compatible with WP 3.0+

• PLUGINDIR was added in 2.1
• MUPLUGINDIR was added in 2.8
• get_site_url() was added in 3.0

Given that the plugin states support for 3.1+, this should be acceptable. Even though the two constants referenced here are deprecated, it at least resolves the issues using the plugin presents for those using mu-plugins files as well.

https://wordpress.org/plugins/wordpress-mu-domain-mapping/