message: Panic in debug build if unchecked cast fails
diff: @@ -71,6 +71,7 @@ macro_rules! sp_index_impl {
  #[inline(always)]
  fn index_unchecked(self) -> usize {
  + debug_assert!(num_traits::cast::<Self, usize>(self).is_some());
  self as usize
  }
  @@ -83,6 +84,7 @@ macro_rules! sp_index_impl {
  #[inline(always)]
  fn from_usize_unchecked(ind: usize) -> Self {
  + debug_assert!(num_traits::cast::<usize, Self>(ind).is_some());
  ind as $int
  }
  }
  