add impl const for Clone

Author: Randl

library/core/src/clone.rs

@@ -543,7 +543,8 @@ mod impls {
         ($($t:ty)*) => {
             $(
                 #[stable(feature = "rust1", since = "1.0.0")]
-                impl Clone for $t {
+                #[rustc_const_unstable(feature = "const_clone", issue = "142757")]
+                impl const Clone for $t {
                     #[inline(always)]
                     fn clone(&self) -> Self {
                         *self
@@ -561,23 +562,26 @@ mod impls {
     }
 
     #[unstable(feature = "never_type", issue = "35121")]
-    impl Clone for ! {
+    #[rustc_const_unstable(feature = "const_clone", issue = "142757")]
+    impl const Clone for ! {
         #[inline]
         fn clone(&self) -> Self {
             *self
         }
     }
 
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<T: PointeeSized> Clone for *const T {
+    #[rustc_const_unstable(feature = "const_clone", issue = "142757")]
+    impl<T: PointeeSized> const Clone for *const T {
         #[inline(always)]
         fn clone(&self) -> Self {
             *self
         }
     }
 
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<T: PointeeSized> Clone for *mut T {
+    #[rustc_const_unstable(feature = "const_clone", issue = "142757")]
+    impl<T: PointeeSized> const Clone for *mut T {
         #[inline(always)]
         fn clone(&self) -> Self {
             *self
@@ -586,7 +590,8 @@ mod impls {
 
     /// Shared references can be cloned, but mutable references *cannot*!
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<T: PointeeSized> Clone for &T {
+    #[rustc_const_unstable(feature = "const_clone", issue = "142757")]
+    impl<T: PointeeSized> const Clone for &T {
         #[inline(always)]
         #[rustc_diagnostic_item = "noop_method_clone"]
         fn clone(&self) -> Self {

library/core/src/marker.rs

@@ -462,7 +462,9 @@ marker_impls! {
 // library, and there's no way to safely have this behavior right now.
 #[rustc_unsafe_specialization_marker]
 #[rustc_diagnostic_item = "Copy"]
-pub trait Copy: Clone {
+#[const_trait]
+#[rustc_const_unstable(feature = "const_clone", issue = "142757")]
+pub trait Copy: [const] Clone {
     // Empty.
 }
 
@@ -852,10 +854,12 @@ impl<T: PointeeSized> cmp::Ord for PhantomData<T> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: PointeeSized> Copy for PhantomData<T> {}
+#[rustc_const_unstable(feature = "const_clone", issue = "142757")]
+impl<T: PointeeSized> const Copy for PhantomData<T> {}
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: PointeeSized> Clone for PhantomData<T> {
+#[rustc_const_unstable(feature = "const_clone", issue = "142757")]
+impl<T: PointeeSized> const Clone for PhantomData<T> {
     fn clone(&self) -> Self {
         Self
     }

library/core/src/num/bignum.rs

@@ -398,7 +398,8 @@ macro_rules! define_bignum {
             }
         }
 
-        impl crate::clone::Clone for $name {
+        #[rustc_const_unstable(feature = "const_clone", issue = "142757")]
+        impl const crate::clone::Clone for $name {
             fn clone(&self) -> Self {
                 Self { size: self.size, base: self.base }
             }

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);
     )+) => {$(
-        #[derive(Clone, Copy, Eq)]
+        #[derive(Eq)]
+        #[derive_const(Clone, Copy)]
         #[repr(transparent)]
         #[rustc_layout_scalar_valid_range_start($low)]
         #[rustc_layout_scalar_valid_range_end($high)]

library/core/src/ops/control_flow.rs

@@ -83,7 +83,8 @@ use crate::{convert, ops};
 #[must_use]
 // ControlFlow should not implement PartialOrd or Ord, per RFC 3058:
 // https://rust-lang.github.io/rfcs/3058-try-trait-v2.html#traits-for-controlflow
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+#[derive(Debug, Eq, Hash)]
+#[derive_const(Clone, Copy, PartialEq)]
 pub enum ControlFlow<B, C = ()> {
     /// Move on to the next phase of the operation as normal.
     #[stable(feature = "control_flow_enum_type", since = "1.55.0")]

library/core/src/ops/index_range.rs

@@ -9,7 +9,8 @@ use crate::ub_checks;
 ///
 /// (Normal `Range` code needs to handle degenerate ranges like `10..0`,
 ///  which takes extra checks compared to only handling the canonical form.)
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive(Debug, Eq)]
+#[derive_const(Clone, PartialEq)]
 pub(crate) struct IndexRange {
     start: usize,
     end: usize,

library/core/src/ops/range.rs

@@ -38,7 +38,8 @@ use crate::hash::Hash;
 /// [slicing index]: crate::slice::SliceIndex
 #[lang = "RangeFull"]
 #[doc(alias = "..")]
-#[derive(Copy, Clone, Default, PartialEq, Eq, Hash)]
+#[derive(Eq, Hash)]
+#[derive_const(Copy, Clone, Default, PartialEq)]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct RangeFull;
 
@@ -75,7 +76,8 @@ impl fmt::Debug for RangeFull {
 /// ```
 #[lang = "Range"]
 #[doc(alias = "..")]
-#[derive(Clone, Default, PartialEq, Eq, Hash)] // not Copy -- see #27186
+#[derive(Eq, Hash)]
+#[derive_const(Clone, Default, PartialEq)] // not Copy -- see #27186
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct Range<Idx> {
     /// The lower bound of the range (inclusive).
@@ -184,7 +186,8 @@ impl<Idx: PartialOrd<Idx>> Range<Idx> {
 /// ```
 #[lang = "RangeFrom"]
 #[doc(alias = "..")]
-#[derive(Clone, PartialEq, Eq, Hash)] // not Copy -- see #27186
+#[derive(Eq, Hash)]
+#[derive_const(Clone, PartialEq)] // not Copy -- see #27186
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct RangeFrom<Idx> {
     /// The lower bound of the range (inclusive).
@@ -266,7 +269,8 @@ impl<Idx: PartialOrd<Idx>> RangeFrom<Idx> {
 /// [slicing index]: crate::slice::SliceIndex
 #[lang = "RangeTo"]
 #[doc(alias = "..")]
-#[derive(Copy, Clone, PartialEq, Eq, Hash)]
+#[derive(Eq, Hash)]
+#[derive_const(Copy, Clone, PartialEq)]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct RangeTo<Idx> {
     /// The upper bound of the range (exclusive).
@@ -340,7 +344,8 @@ impl<Idx: PartialOrd<Idx>> RangeTo<Idx> {
 /// ```
 #[lang = "RangeInclusive"]
 #[doc(alias = "..=")]
-#[derive(Clone, PartialEq, Eq, Hash)] // not Copy -- see #27186
+#[derive(Eq, Hash)]
+#[derive_const(Clone, PartialEq)] // not Copy -- see #27186
 #[stable(feature = "inclusive_range", since = "1.26.0")]
 pub struct RangeInclusive<Idx> {
     // Note that the fields here are not public to allow changing the
@@ -587,7 +592,8 @@ impl<Idx: PartialOrd<Idx>> RangeInclusive<Idx> {
 /// [slicing index]: crate::slice::SliceIndex
 #[lang = "RangeToInclusive"]
 #[doc(alias = "..=")]
-#[derive(Copy, Clone, PartialEq, Eq, Hash)]
+#[derive(Hash)]
+#[derive(Copy, Clone, PartialEq, Eq)]
 #[stable(feature = "inclusive_range", since = "1.26.0")]
 pub struct RangeToInclusive<Idx> {
     /// The upper bound of the range (inclusive)
@@ -668,7 +674,8 @@ impl<Idx: PartialOrd<Idx>> RangeToInclusive<Idx> {
 ///
 /// [`BTreeMap::range`]: ../../std/collections/btree_map/struct.BTreeMap.html#method.range
 #[stable(feature = "collections_bound", since = "1.17.0")]
-#[derive(Clone, Copy, Debug, Hash, PartialEq, Eq)]
+#[derive(Debug, Eq, Hash)]
+#[derive_const(Clone, Copy, PartialEq)]
 pub enum Bound<T> {
     /// An inclusive bound.
     #[stable(feature = "collections_bound", since = "1.17.0")]

library/core/src/slice/mod.rs

@@ -8,6 +8,7 @@
 
 use crate::cmp::Ordering::{self, Equal, Greater, Less};
 use crate::intrinsics::{exact_div, unchecked_sub};
+use crate::marker::Destruct;
 use crate::mem::{self, MaybeUninit, SizedTypeProperties};
 use crate::num::NonZero;
 use crate::ops::{OneSidedRange, OneSidedRangeBound, Range, RangeBounds, RangeInclusive};
@@ -3785,10 +3786,12 @@ impl<T> [T] {
     /// [`copy_from_slice`]: slice::copy_from_slice
     /// [`split_at_mut`]: slice::split_at_mut
     #[stable(feature = "clone_from_slice", since = "1.7.0")]
+    #[rustc_const_unstable(feature = "const_clone", issue = "142757")]
+    #[rustc_allow_const_fn_unstable(const_precise_live_drops)]
     #[track_caller]
-    pub fn clone_from_slice(&mut self, src: &[T])
+    pub const fn clone_from_slice(&mut self, src: &[T])
     where
-        T: Clone,
+        T: [const] Clone + [const] Destruct,
     {
         self.spec_clone_from(src);
     }
@@ -5089,31 +5092,43 @@ impl [f64] {
     }
 }
 
+#[const_trait]
+#[rustc_const_unstable(feature = "const_clone", issue = "142757")]
 trait CloneFromSpec<T> {
-    fn spec_clone_from(&mut self, src: &[T]);
+    fn spec_clone_from(&mut self, src: &[T])
+    where
+        T: [const] Destruct;
 }
 
-impl<T> CloneFromSpec<T> for [T]
+#[rustc_const_unstable(feature = "const_clone", issue = "142757")]
+impl<T> const CloneFromSpec<T> for [T]
 where
-    T: Clone,
+    T: [const] Clone,
 {
     #[track_caller]
-    default fn spec_clone_from(&mut self, src: &[T]) {
+    default fn spec_clone_from(&mut self, src: &[T])
+    where
+        T: [const] Destruct,
+    {
         assert!(self.len() == src.len(), "destination and source slices have different lengths");
         // NOTE: We need to explicitly slice them to the same length
         // to make it easier for the optimizer to elide bounds checking.
         // But since it can't be relied on we also have an explicit specialization for T: Copy.
         let len = self.len();
         let src = &src[..len];
-        for i in 0..len {
-            self[i].clone_from(&src[i]);
+        // FIXME(const_hack): make this a `for idx in 0..self.len()` loop.
+        let mut idx = 0;
+        while idx < self.len() {
+            self[idx].clone_from(&src[idx]);
+            idx += 1;
         }
     }
 }
 
-impl<T> CloneFromSpec<T> for [T]
+#[rustc_const_unstable(feature = "const_clone", issue = "142757")]
+impl<T> const CloneFromSpec<T> for [T]
 where
-    T: Copy,
+    T: [const] Copy,
 {
     #[track_caller]
     fn spec_clone_from(&mut self, src: &[T]) {

library/core/src/tuple.rs

@@ -122,7 +122,8 @@ macro_rules! tuple_impls {
         maybe_tuple_doc! {
             $($T)+ @
             #[stable(feature = "rust1", since = "1.0.0")]
-            impl<$($T: Default),+> Default for ($($T,)+) {
+            #[rustc_const_unstable(feature = "const_default", issue = "143894")]
+            impl<$($T: ~const Default),+> const Default for ($($T,)+) {
                 #[inline]
                 fn default() -> ($($T,)+) {
                     ($({ let x: $T = Default::default(); x},)+)