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
@@ -561,7 +562,8 @@ 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

tests/ui/traits/const-traits/const-clone.rs

@@ -0,0 +1,69 @@
+#![feature(
+    const_trait_impl, const_default, const_clone, ptr_alignment_type,
+    ascii_char, f16, f128, sync_unsafe_cell,
+)]
+#![allow(dead_code)]
+// core::default
+const UNIT: () = Default::default();
+const BOOL: bool = Default::default();
+const CHAR: char = Default::default();
+const ASCII_CHAR: std::ascii::Char = Default::default();
+const USIZE: usize = Default::default();
+const U8: u8 = Default::default();
+const U16: u16 = Default::default();
+const U32: u32 = Default::default();
+const U64: u64 = Default::default();
+const U128: u128 = Default::default();
+const I8: i8 = Default::default();
+const I16: i16 = Default::default();
+const I32: i32 = Default::default();
+const I64: i64 = Default::default();
+const I128: i128 = Default::default();
+const F16: f16 = Default::default();
+const F32: f32 = Default::default();
+const F64: f64 = Default::default();
+const F128: f128 = Default::default();
+// core::marker
+const PHANTOM: std::marker::PhantomData<()> = Default::default();
+// core::option
+const OPT: Option<i32> = Default::default();
+// core::iter::sources::empty
+const EMPTY: std::iter::Empty<()> = Default::default();
+// core::ptr::alignment
+const ALIGNMENT: std::ptr::Alignment = Default::default();
+// core::slice
+const SLICE: &[()] = Default::default();
+const MUT_SLICE: &mut [()] = Default::default();
+// core::str
+const STR: &str = Default::default();
+const MUT_STR: &mut str = Default::default();
+// core::cell
+const CELL: std::cell::Cell<()> = Default::default();
+const REF_CELL: std::cell::RefCell<()> = Default::default();
+const UNSAFE_CELL: std::cell::UnsafeCell<()> = Default::default();
+const SYNC_UNSAFE_CELL: std::cell::SyncUnsafeCell<()> = Default::default();
+
+// core::clone
+const UNIT_CLONE: () = UNIT.clone();
+//~^ ERROR: the trait bound `(): const Clone` is not satisfied
+const BOOL_CLONE: bool = BOOL.clone();
+const CHAR_CLONE: char = CHAR.clone();
+const ASCII_CHAR_CLONE: std::ascii::Char = ASCII_CHAR.clone();
+//~^ ERROR: the trait bound `Char: const Clone` is not satisfied
+const USIZE_CLONE: usize = USIZE.clone();
+const U8_CLONE: u8 = U8.clone();
+const U16_CLONE: u16 = U16.clone();
+const U32_CLONE: u32 = U32.clone();
+const U64_CLONE: u64 = U64.clone();
+const U128_CLONE: u128 = U128.clone();
+const I8_CLONE: i8 = I8.clone();
+const I16_CLONE: i16 = I16.clone();
+const I32_CLONE: i32 = I32.clone();
+const I64_CLONE: i64 = I64.clone();
+const I128_CLONE: i128 = I128.clone();
+const F16_CLONE: f16 = F16.clone();
+const F32_CLONE: f32 = F32.clone();
+const F64_CLONE: f64 = F64.clone();
+const F128_CLONE: f128 = F128.clone();
+
+fn main() {}

tests/ui/traits/const-traits/const-clone.stderr

@@ -0,0 +1,15 @@
+error[E0277]: the trait bound `(): const Clone` is not satisfied
+  --> $DIR/const-clone.rs:47:29
+   |
+LL | const UNIT_CLONE: () = UNIT.clone();
+   |                             ^^^^^
+
+error[E0277]: the trait bound `Char: const Clone` is not satisfied
+  --> $DIR/const-clone.rs:51:55
+   |
+LL | const ASCII_CHAR_CLONE: std::ascii::Char = ASCII_CHAR.clone();
+   |                                                       ^^^^^
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0277`.