test/bug/tint/1076.wgsl

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);
}