Is there any supported way to have shared sources between different modules? Imagine module_a and module_b defining their own content roots plus taking sources from one common content root.
Gradle works with such configuration just fine and IDEA happily imports and builds it, though editor isn't very happy when opening shared files. Main problem is I can't change module settings: IDEA refuses to save them with a "Two modules in a project cannot share the same content root" error.
I can't extract common part in a separate module because it won't even compile: there are a lot of missing classes that are provided (in different ways) by module_a and module_b. (It's an attempt to share Grammar-Kit generated parser by both idea plugin and a standalone parser; generated and most of surrounding hand-written classes are common, but stubs and some of the helpers are different)