test/shader_io/fragment_input_builtins.wgsl

@stage(fragment)
fn main(
  @builtin(position) position : vec4<f32>,
  @builtin(front_facing) front_facing : bool,
  @builtin(sample_index) sample_index : u32,
  @builtin(sample_mask) sample_mask : u32,
) {
  if (front_facing) {
    let foo : vec4<f32> = position;
    let bar : u32 = sample_index + sample_mask;
  }
}