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);
}