[Issue 22981] Another forward reference bug involving a string mixin

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=22981

--- Comment #2 from Max Samukha <maxsamukha at gmail.com> ---

> However, it does if the template instance is aliased inside the type:

template E_()
{
        mixin ("enum E_ {", S.attr, "}");
}

struct S
{
    alias E = E_!();
    E e;
    enum attr = "a";
}

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