[REG master] Wrong associative array access with alias this for key

[tim-dlang]

The following code fails on DMD master:

struct A
{
    bool extra;
    uint id;
}

struct B
{
    uint id;

    A toA() const pure nothrow
    {
        return A(false, id);
    }

    alias toA this;
}

void main()
{
    bool[A] aa;
    aa[B(5)] = true;
    assert(A(false, 5) in aa);
    assert(B(5) in aa);
}

The code fails since commit c31f959, but worked before.