Make truncate and extend use const traits to work in const contexts

Author: joshtriplett

library/core/src/num/int_macros.rs

@@ -3958,9 +3958,10 @@ macro_rules! int_impl {
         /// ```
         #[must_use = "this returns the truncated value and does not modify the original"]
         #[unstable(feature = "integer_extend_truncate", issue = "154330")]
+        #[rustc_const_unstable(feature = "integer_truncate_extend", issue = "154330")]
         #[inline]
-        pub fn truncate<Target>(self) -> Target
-            where Self: traits::TruncateTarget<Target>
+        pub const fn truncate<Target>(self) -> Target
+            where Self: [const] traits::TruncateTarget<Target>
         {
             traits::TruncateTarget::internal_truncate(self)
         }
@@ -3979,9 +3980,10 @@ macro_rules! int_impl {
         /// ```
         #[must_use = "this returns the truncated value and does not modify the original"]
         #[unstable(feature = "integer_extend_truncate", issue = "154330")]
+        #[rustc_const_unstable(feature = "integer_truncate_extend", issue = "154330")]
         #[inline]
-        pub fn saturating_truncate<Target>(self) -> Target
-            where Self: traits::TruncateTarget<Target>
+        pub const fn saturating_truncate<Target>(self) -> Target
+            where Self: [const] traits::TruncateTarget<Target>
         {
             traits::TruncateTarget::internal_saturating_truncate(self)
         }
@@ -4000,9 +4002,10 @@ macro_rules! int_impl {
         /// ```
         #[must_use = "this returns the truncated value and does not modify the original"]
         #[unstable(feature = "integer_extend_truncate", issue = "154330")]
+        #[rustc_const_unstable(feature = "integer_truncate_extend", issue = "154330")]
         #[inline]
-        pub fn checked_truncate<Target>(self) -> Option<Target>
-            where Self: traits::TruncateTarget<Target>
+        pub const fn checked_truncate<Target>(self) -> Option<Target>
+            where Self: [const] traits::TruncateTarget<Target>
         {
             traits::TruncateTarget::internal_checked_truncate(self)
         }
@@ -4018,9 +4021,10 @@ macro_rules! int_impl {
         /// ```
         #[must_use = "this returns the extended value and does not modify the original"]
         #[unstable(feature = "integer_extend_truncate", issue = "154330")]
+        #[rustc_const_unstable(feature = "integer_truncate_extend", issue = "154330")]
         #[inline]
-        pub fn extend<Target>(self) -> Target
-            where Self: traits::ExtendTarget<Target>
+        pub const fn extend<Target>(self) -> Target
+            where Self: [const] traits::ExtendTarget<Target>
         {
             traits::ExtendTarget::internal_extend(self)
         }

library/core/src/num/traits.rs

@@ -3,7 +3,8 @@
 
 /// Trait for types that this type can be truncated to
 #[unstable(feature = "num_internals", reason = "internal implementation detail", issue = "none")]
-pub trait TruncateTarget<Target>: crate::sealed::Sealed {
+#[rustc_const_unstable(feature = "integer_truncate_extend", issue = "154330")]
+pub const trait TruncateTarget<Target>: crate::sealed::Sealed {
     #[doc(hidden)]
     fn internal_truncate(self) -> Target;
 
@@ -16,7 +17,8 @@ pub trait TruncateTarget<Target>: crate::sealed::Sealed {
 
 /// Trait for types that this type can be truncated to
 #[unstable(feature = "num_internals", reason = "internal implementation detail", issue = "none")]
-pub trait ExtendTarget<Target>: crate::sealed::Sealed {
+#[rustc_const_unstable(feature = "integer_truncate_extend", issue = "154330")]
+pub const trait ExtendTarget<Target>: crate::sealed::Sealed {
     #[doc(hidden)]
     fn internal_extend(self) -> Target;
 }
@@ -38,7 +40,8 @@ macro_rules! impl_truncate {
         );
 
         #[unstable(feature = "num_internals", reason = "internal implementation detail", issue = "none")]
-        impl TruncateTarget<$to> for $from {
+        #[rustc_const_unstable(feature = "integer_truncate_extend", issue = "154330")]
+        impl const TruncateTarget<$to> for $from {
             #[inline]
             fn internal_truncate(self) -> $to {
                 self as _
@@ -84,7 +87,8 @@ macro_rules! impl_extend {
         );
 
         #[unstable(feature = "num_internals", reason = "internal implementation detail", issue = "none")]
-        impl ExtendTarget<$to> for $from {
+        #[rustc_const_unstable(feature = "integer_truncate_extend", issue = "154330")]
+        impl const ExtendTarget<$to> for $from {
             fn internal_extend(self) -> $to {
                 self as _
             }

library/core/src/num/uint_macros.rs

@@ -4120,9 +4120,10 @@ macro_rules! uint_impl {
         /// ```
         #[must_use = "this returns the truncated value and does not modify the original"]
         #[unstable(feature = "integer_extend_truncate", issue = "154330")]
+        #[rustc_const_unstable(feature = "integer_truncate_extend", issue = "154330")]
         #[inline]
-        pub fn truncate<Target>(self) -> Target
-            where Self: traits::TruncateTarget<Target>
+        pub const fn truncate<Target>(self) -> Target
+            where Self: [const] traits::TruncateTarget<Target>
         {
             traits::TruncateTarget::internal_truncate(self)
         }
@@ -4139,9 +4140,10 @@ macro_rules! uint_impl {
         /// ```
         #[must_use = "this returns the truncated value and does not modify the original"]
         #[unstable(feature = "integer_extend_truncate", issue = "154330")]
+        #[rustc_const_unstable(feature = "integer_truncate_extend", issue = "154330")]
         #[inline]
-        pub fn saturating_truncate<Target>(self) -> Target
-            where Self: traits::TruncateTarget<Target>
+        pub const fn saturating_truncate<Target>(self) -> Target
+            where Self: [const] traits::TruncateTarget<Target>
         {
             traits::TruncateTarget::internal_saturating_truncate(self)
         }
@@ -4158,9 +4160,10 @@ macro_rules! uint_impl {
         /// ```
         #[must_use = "this returns the truncated value and does not modify the original"]
         #[unstable(feature = "integer_extend_truncate", issue = "154330")]
+        #[rustc_const_unstable(feature = "integer_truncate_extend", issue = "154330")]
         #[inline]
-        pub fn checked_truncate<Target>(self) -> Option<Target>
-            where Self: traits::TruncateTarget<Target>
+        pub const fn checked_truncate<Target>(self) -> Option<Target>
+            where Self: [const] traits::TruncateTarget<Target>
         {
             traits::TruncateTarget::internal_checked_truncate(self)
         }
@@ -4175,9 +4178,10 @@ macro_rules! uint_impl {
         /// ```
         #[must_use = "this returns the extended value and does not modify the original"]
         #[unstable(feature = "integer_extend_truncate", issue = "154330")]
+        #[rustc_const_unstable(feature = "integer_truncate_extend", issue = "154330")]
         #[inline]
-        pub fn extend<Target>(self) -> Target
-            where Self: traits::ExtendTarget<Target>
+        pub const fn extend<Target>(self) -> Target
+            where Self: [const] traits::ExtendTarget<Target>
         {
             traits::ExtendTarget::internal_extend(self)
         }