howdy. I finally managed to get a separate library together that adapts ANTLR stuff to intellij. note that I copied over a lot of support for trees from ANTLR, such as Xpath. For example, here is how you get the name nodes for all functions assuming a tree structure from sample grammar.
Collection<? extends PsiElement> allfuncs =
XPath.findAll(SampleLanguage.INSTANCE, tree, "/script/function/ID");
Here is the library and a sample plug-in (screenshot attached)
I gave up trying to force fit ANTLR parse trees into intellij. Once I embraced PSI, I made rapid progress by simply adapting my favorite tree stuff to PSI types.
@jetbrains guys: any interest in formally accepting the ANTLR support lib as part of the standard plug-in SDK? It's quite small and would provide an excellent service to plug-in developers.