struct FragIn {
  @location(0)
  a : f32;
  @builtin(sample_mask)
  mask : u32;
}

@stage(fragment)
fn main(in : FragIn, @location(1) b : f32) -> FragIn {
  if ((in.mask == 0u)) {
    return in;
  }
  return FragIn(b, 1u);
}