Remove const hack from impl Clone for Option

Author: ShoyuVanilla

library/core/src/option.rs

@@ -2147,9 +2147,7 @@ const fn expect_failed(msg: &str) -> ! {
 #[rustc_const_unstable(feature = "const_try", issue = "74935")]
 impl<T> const Clone for Option<T>
 where
-    // FIXME(const_hack): the T: ~const Destruct should be inferred from the Self: ~const Destruct in clone_from.
-    // See https://github.com/rust-lang/rust/issues/144207
-    T: ~const Clone + ~const Destruct,
+    T: ~const Clone,
 {
     #[inline]
     fn clone(&self) -> Self {
@@ -2160,7 +2158,10 @@ where
     }
 
     #[inline]
-    fn clone_from(&mut self, source: &Self) {
+    fn clone_from(&mut self, source: &Self)
+    where
+        Self: ~const Destruct,
+    {
         match (self, source) {
             (Some(to), Some(from)) => to.clone_from(from),
             (to, from) => *to = from.clone(),

tests/ui/traits/const-traits/conditionally-const-option-impl-clone.rs

@@ -0,0 +1,50 @@
+// Demonstrates that `impl<T> const Clone for Option<T>` does not require const_hack bounds.
+// See issue #144207.
+//@ revisions: next old
+//@ [next] compile-flags: -Znext-solver
+//@ check-pass
+
+#![feature(const_trait_impl, const_destruct)]
+
+use std::marker::Destruct;
+
+#[const_trait]
+pub trait CloneLike: Sized {
+    fn clone(&self) -> Self;
+
+    fn clone_from(&mut self, source: &Self)
+    where
+        Self: [const] Destruct,
+    {
+        *self = source.clone()
+    }
+}
+
+enum OptionLike<T> {
+    None,
+    Some(T),
+}
+
+impl<T> const CloneLike for OptionLike<T>
+where
+    T: [const] CloneLike,
+{
+    fn clone(&self) -> Self {
+        match self {
+            Self::Some(x) => Self::Some(x.clone()),
+            Self::None => Self::None,
+        }
+    }
+
+    fn clone_from(&mut self, source: &Self)
+    where
+        Self: [const] Destruct,
+    {
+        match (self, source) {
+            (Self::Some(to), Self::Some(from)) => to.clone_from(from),
+            (to, from) => *to = from.clone(),
+        }
+    }
+}
+
+fn main() {}