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Currently, all paths passed to ResourceLoaderFileModule are prefixed with $IP before being used. This means extensions have to hardcode their location. because the more elegant solution of using paths relative to __FILE__ (resulting in absolute paths) won't work.

Example of bad code that works:
new ResourceLoaderFileModule( $resources, 'extensions/WikiEditor/modules/' )

Example of good code that breaks:
new ResourceLoaderFileModule( $resources, dirname( __FILE__ ) . '/modules/' )

$IP prefixing should be taken out of the software entirely, and be moved to the definition of core resources that specify paths relative to $IP (i.e. Resources.php) or be the default value for the $basepath parameter to ResourceLoaderFileModule::__construct().