gcc/testsuite/gdc.test/fail_compilation/fail21206.d

// https://issues.dlang.org/show_bug.cgi?id=21206
/* TEST_OUTPUT:
---
fail_compilation/fail21206.d(9): Error: function `fail21206.Obj.toString` cannot return type `string` because its linkage is `extern(C++)`
---
*/
extern(C++) struct Obj
{
    string toString()
    {
        return "ret";
    }
}