Auto merge of rust-lang#86041 - bstrie:unmagic-array-copy, r=jackh726

Replace Copy/Clone compiler magic on arrays with library impls

With const generics the compiler no longer needs to fake these impls.

Author: bors

core/src/array/mod.rs

@@ -330,6 +330,26 @@ impl<T: Ord, const N: usize> Ord for [T; N] {
     }
 }
 
+#[cfg(not(bootstrap))]
+#[stable(feature = "copy_clone_array_lib", since = "1.58.0")]
+impl<T: Copy, const N: usize> Copy for [T; N] {}
+
+#[cfg(not(bootstrap))]
+#[stable(feature = "copy_clone_array_lib", since = "1.58.0")]
+impl<T: Clone, const N: usize> Clone for [T; N] {
+    #[inline]
+    fn clone(&self) -> Self {
+        // SAFETY: we know for certain that this iterator will yield exactly `N`
+        // items.
+        unsafe { collect_into_array_unchecked(&mut self.iter().cloned()) }
+    }
+
+    #[inline]
+    fn clone_from(&mut self, other: &Self) {
+        self.clone_from_slice(other);
+    }
+}
+
 // The Default impls cannot be done with const generics because `[T; 0]` doesn't
 // require Default to be implemented, and having different impl blocks for
 // different numbers isn't supported yet.

core/src/clone.rs

@@ -93,7 +93,6 @@
 ///
 /// * Function item types (i.e., the distinct types defined for each function)
 /// * Function pointer types (e.g., `fn() -> i32`)
-/// * Array types, for all sizes, if the item type also implements `Clone` (e.g., `[i32; 123456]`)
 /// * Tuple types, if each component also implements `Clone` (e.g., `()`, `(i32, bool)`)
 /// * Closure types, if they capture no value from the environment
 ///   or if all such captured values implement `Clone` themselves.

core/src/marker.rs

@@ -359,7 +359,6 @@ pub trait StructuralEq {
 ///
 /// * Function item types (i.e., the distinct types defined for each function)
 /// * Function pointer types (e.g., `fn() -> i32`)
-/// * Array types, for all sizes, if the item type also implements `Copy` (e.g., `[i32; 123456]`)
 /// * Tuple types, if each component also implements `Copy` (e.g., `()`, `(i32, bool)`)
 /// * Closure types, if they capture no value from the environment
 ///   or if all such captured values implement `Copy` themselves.