by alexander.surma:

I build a small testcase for this particular problem:
https://gist.github.com/1514784

If you compile as is, the following error occurs:
unrecognized Go type *ast.StructType
unrecognized Go type *ast.StructType

If you comment out the current `Callback` implementation, and uncomment the other one
(as well as the import of the unsafe package). It will compile (and work as expected).

The problem does NOT occur, when:
* the function is not exported
* the parameter is not a struct (e.g. *C.int as a parameter type works just fine)

The problem does ALSO occur:
* when the using a pointer to a C struct as a return type
* when the parameter is just a C struct (i.e. NOT a pointer)

I'm on Mac OS 10.7.2, using weekly-2011-12-22 darwin/amd64. Same error on tip.