file include fails when a template is overridden

I too have just noticed this issue. I however do not think this is a bug, but more by design.

I originally had my template preprocess functions in a separate file, which I had included by setting the 'file' and 'path' properties in my modules hook_theme. I got the idea to do this from the hook_theme documentation of the file property here.

The current implementation would allow the theme to set the 'file' and 'path' properties which allow's the theme to break all its stuff out into separate files. This of course, then breaks the module includes, which might be needed to ensure template preprocess functions are run.

There are several solutions and workarounds, and I'm not sure which one would be best, but at the very least, the documentation for hook_theme should be updated to indicate that if a module puts its template_preprocess_HOOK functions in a separate file, that the file will not be included if a theme overrides the template, and that the module will need to load the file itself.

Solutions could include:

• Making the file property in the registry an array, and loading up each include. Obviously the path property would probably need to be the same.
• Have modules ensure that any template preprocess hooks are loaded up. This seems to defeat the purpose of having the file and path properties, at least for modules.
• Have themes that override these templates, make sure that they include the needed module preprocess functions.

None of those options seem ideal. At the very least, this needs to be documented somewhere.
This is only a problem when include files contain the preprocess functions, normal theme function overrides will not cause this problem.