1const Derp = opaque {};
 2const Wat = opaque {};
 3
 4extern fn bar(d: *Derp) void;
 5fn foo(w: *Wat) callconv(.c) void {
 6    bar(w);
 7}
 8
 9test "call foo" {
10    foo(undefined);
11}
12
13// test_error=expected type '*test_opaque.Derp', found '*test_opaque.Wat'