constify comparison traits on niche types

Author: npmccallum

library/core/src/num/niche_types.rs

@@ -14,7 +14,8 @@ macro_rules! define_valid_range_type {
         $(#[$m:meta])*
         $vis:vis struct $name:ident($int:ident as $uint:ident in $low:literal..=$high:literal);
     )+) => {$(
-        #[derive(Clone, Copy, Eq)]
+        #[derive(Copy)]
+        #[derive_const(Clone, Eq)]
         #[repr(transparent)]
         #[rustc_layout_scalar_valid_range_start($low)]
         #[rustc_layout_scalar_valid_range_end($high)]
@@ -67,21 +68,24 @@ macro_rules! define_valid_range_type {
         // by <https://github.com/rust-lang/compiler-team/issues/807>.
         impl StructuralPartialEq for $name {}
 
-        impl PartialEq for $name {
+        #[rustc_const_unstable(feature = "const_cmp", issue = "143800")]
+        impl const PartialEq for $name {
             #[inline]
             fn eq(&self, other: &Self) -> bool {
                 self.as_inner() == other.as_inner()
             }
         }
 
-        impl Ord for $name {
+        #[rustc_const_unstable(feature = "const_cmp", issue = "143800")]
+        impl const Ord for $name {
             #[inline]
             fn cmp(&self, other: &Self) -> Ordering {
                 Ord::cmp(&self.as_inner(), &other.as_inner())
             }
         }
 
-        impl PartialOrd for $name {
+        #[rustc_const_unstable(feature = "const_cmp", issue = "143800")]
+        impl const PartialOrd for $name {
             #[inline]
             fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
                 Some(Ord::cmp(self, other))