Make some `Clone` impls `const`

7 files changed, 33 insertions, 11 deletions

diff --git a/library/core/src/clone.rs b/library/core/src/clone.rs
index 6f9579043c3..1912694412b 100644
--- a/library/core/src/clone.rs
+++ b/library/core/src/clone.rs
@@ -127,7 +127,11 @@ pub trait Clone: Sized {
     /// allocations.
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
-    fn clone_from(&mut self, source: &Self) {
+    #[default_method_body_is_const]
+    fn clone_from(&mut self, source: &Self)
+    where
+        Self: ~const Drop,
+    {
         *self = source.clone()
     }
 }
@@ -178,7 +182,8 @@ mod impls {
         ($($t:ty)*) => {
             $(
                 #[stable(feature = "rust1", since = "1.0.0")]
-                impl Clone for $t {
+                #[rustc_const_unstable(feature = "const_clone", issue = "91805")]
+                impl const Clone for $t {
                     #[inline]
                     fn clone(&self) -> Self {
                         *self
@@ -196,7 +201,8 @@ mod impls {
     }
 
     #[unstable(feature = "never_type", issue = "35121")]
-    impl Clone for ! {
+    #[rustc_const_unstable(feature = "const_clone", issue = "91805")]
+    impl const Clone for ! {
         #[inline]
         fn clone(&self) -> Self {
             *self
@@ -204,7 +210,8 @@ mod impls {
     }
 
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<T: ?Sized> Clone for *const T {
+    #[rustc_const_unstable(feature = "const_clone", issue = "91805")]
+    impl<T: ?Sized> const Clone for *const T {
         #[inline]
         fn clone(&self) -> Self {
             *self
@@ -212,7 +219,8 @@ mod impls {
     }
 
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<T: ?Sized> Clone for *mut T {
+    #[rustc_const_unstable(feature = "const_clone", issue = "91805")]
+    impl<T: ?Sized> const Clone for *mut T {
         #[inline]
         fn clone(&self) -> Self {
             *self
@@ -221,7 +229,8 @@ mod impls {
 
     /// Shared references can be cloned, but mutable references *cannot*!
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<T: ?Sized> Clone for &T {
+    #[rustc_const_unstable(feature = "const_clone", issue = "91805")]
+    impl<T: ?Sized> const Clone for &T {
         #[inline]
         #[rustc_diagnostic_item = "noop_method_clone"]
         fn clone(&self) -> Self {
diff --git a/library/core/src/convert/mod.rs b/library/core/src/convert/mod.rs
index 5aa53deee34..a50b8904b59 100644
--- a/library/core/src/convert/mod.rs
+++ b/library/core/src/convert/mod.rs
@@ -683,7 +683,8 @@ impl AsMut<str> for str {
 pub enum Infallible {}
 
 #[stable(feature = "convert_infallible", since = "1.34.0")]
-impl Clone for Infallible {
+#[rustc_const_unstable(feature = "const_clone", issue = "91805")]
+impl const Clone for Infallible {
     fn clone(&self) -> Infallible {
         match *self {}
     }
diff --git a/library/core/src/lib.rs b/library/core/src/lib.rs
index 78383b54c5d..4ef4740799a 100644
--- a/library/core/src/lib.rs
+++ b/library/core/src/lib.rs
@@ -106,6 +106,7 @@
 #![feature(const_caller_location)]
 #![feature(const_cell_into_inner)]
 #![feature(const_char_convert)]
+#![feature(const_clone)]
 #![feature(const_discriminant)]
 #![feature(const_eval_select)]
 #![feature(const_float_bits_conv)]
diff --git a/library/core/src/option.rs b/library/core/src/option.rs
index 7b9c6e43960..941d7e07926 100644
--- a/library/core/src/option.rs
+++ b/library/core/src/option.rs
@@ -1668,7 +1668,11 @@ const fn expect_failed(msg: &str) -> ! {
 /////////////////////////////////////////////////////////////////////////////
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: Clone> Clone for Option<T> {
+#[rustc_const_unstable(feature = "const_clone", issue = "91805")]
+impl<T> const Clone for Option<T>
+where
+    T: ~const Clone + ~const Drop,
+{
     #[inline]
     fn clone(&self) -> Self {
         match self {
diff --git a/library/core/src/ptr/non_null.rs b/library/core/src/ptr/non_null.rs
index 58110b06809..cb268abc8ee 100644
--- a/library/core/src/ptr/non_null.rs
+++ b/library/core/src/ptr/non_null.rs
@@ -635,7 +635,8 @@ impl<T> NonNull<[T]> {
 }
 
 #[stable(feature = "nonnull", since = "1.25.0")]
-impl<T: ?Sized> Clone for NonNull<T> {
+#[rustc_const_unstable(feature = "const_clone", issue = "91805")]
+impl<T: ?Sized> const Clone for NonNull<T> {
     #[inline]
     fn clone(&self) -> Self {
         *self
diff --git a/library/core/src/ptr/unique.rs b/library/core/src/ptr/unique.rs
index d650a6f974b..ee984b7b5a4 100644
--- a/library/core/src/ptr/unique.rs
+++ b/library/core/src/ptr/unique.rs
@@ -146,7 +146,8 @@ impl<T: ?Sized> Unique<T> {
 }
 
 #[unstable(feature = "ptr_internals", issue = "none")]
-impl<T: ?Sized> Clone for Unique<T> {
+#[rustc_const_unstable(feature = "const_clone", issue = "91805")]
+impl<T: ?Sized> const Clone for Unique<T> {
     #[inline]
     fn clone(&self) -> Self {
         *self
diff --git a/library/core/src/result.rs b/library/core/src/result.rs
index e6b8c8ec338..d639c7188c1 100644
--- a/library/core/src/result.rs
+++ b/library/core/src/result.rs
@@ -1665,7 +1665,12 @@ fn unwrap_failed(msg: &str, error: &dyn fmt::Debug) -> ! {
 /////////////////////////////////////////////////////////////////////////////
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: Clone, E: Clone> Clone for Result<T, E> {
+#[rustc_const_unstable(feature = "const_clone", issue = "91805")]
+impl<T, E> const Clone for Result<T, E>
+where
+    T: ~const Clone + ~const Drop,
+    E: ~const Clone + ~const Drop,
+{
     #[inline]
     fn clone(&self) -> Self {
         match self {