I have implemented the import of NestedNameSpecifier. Patch attached.
I have only tested the NestedNameSpecifier::TypeSpec case. But also the other cases look sufficiently simple in order to do the right thing first hand. Then again, I don't know whether I've overlooked some pitfalls. At least it looks sufficiently simple to makes me wonder why it wasn't implemented yet.
ASTImporter.patch (1.64 KB)