[pixel shader]
struct apple
{
    struct
    {
        float4 a;
    } m;
    float4 b;
};

float4 main() : sv_target
{
    struct apple q, r, s;

    q.m.a = float4(0.1, 0.2, 0.3, 0.4);
    q.b = float4(0.5, 0.1, 0.4, 0.5);
    s = r = q;
    return s.m.a + s.b;
}

[test]
todo(msl) draw quad
probe (0, 0) rgba (0.6, 0.3, 0.7, 0.9) 1