Example to reproduce is to comment out the struct in object.d and try compiling: int[int] foo; foreach(k; foo.keys) {} Regards
https://github.com/D-Programming-Language/dmd/pull/295
https://github.com/D-Programming-Language/dmd/commit/5a5defb9d34a3d6b1dd87cb5e6c5f234f7e562aa