These are a little broken, as discussed in MDL-38515.

core_filepicker describes a file in /repository/filepicker.js which adds a YUI module called moodle-core_filepicker.

Because the YUI module is wrapped in a YUI.add line, it's contents are only added to the sandbox when a module depends on moodle-core_filepicker.

So in order to get this to work, core_filepicker depends on moodle-core_filepicker.
The inclusion of core_filepicker means that the JS file itself is included, and then the contents of it's YUI module are handled by our legacy code having it depend on it's own module.

This is really really broken and needs to be fixed as it prevents us from detecting and reporting other issues.

My suggested fix is to go over the existing code and convert all of the bits to appropriate YUI modules.

This may give us an opportunity to write a treeview based on the new YUI3 Y.Tree so we can remove the current dependence on yui2 here.

My guess is that this could be a week or two's work.