clang AST doesn't carry source location of storage class like "extern"

Hi Clang-Devs,
I’m trying to do some c++ source modification work by using clang AST,
I found that source location for storage class like “extern”, are stored in parse phase only object DeclSpec, this source location is not passed to AST Decl nodes,
so I can’t get them in the AST traverse phase. I wonder is there a way to get source location of “extern” after AST is built?

Best Regards
cz