const stroo = extern struct {
    moo: ?[*c]u8,
};
export fn testf(fluff: *stroo) void {
    _ = fluff.*;
}

// error
//
// :2:10: error: extern structs cannot contain fields of type '?[*c]u8'
// :2:10: note: non-pointer optionals have no guaranteed in-memory representation
