Extending zig structs at compile time

gistfile1.txt

const S1 = struct {
  n: u32,
}

fn S2() type {
  return S1 {
    m: u64,
  };
}

test "t" {
  const x = S2() {
    .n = 1,
    .m = 2,
  };
  assert(x.n == 1);
  assert(x.m == 2);
}