Merge pull request #247 from GaloisInc/T245-box-clone-patch

Specialize `Clone` impl for `Box` to use Crucible's allocator

Author: RyanGlScott

libs/Patches.md

@@ -90,6 +90,15 @@ into the main commit for that patch, and then the *Update* line can be removed.
   functions to call built-in Crucible allocation functions instead (e.g.
   `crucible::alloc::allocate`).
 
+* Specialize `Clone` impl for `Box` to use Crucible's allocator (last applied: Feburary 26, 2026)
+
+  The default `Clone` impl for `Box` is parameterized over an arbitrary
+  allocator, and as a result, it has to call the `new_uninit_in` function,
+  which `crucible-mir` cannot easily support. We add a specialized version of
+  the `Clone` impl for the `Global` allocator that instead calls the more
+  Crucible-friendly `new_uninit` function. (See also the `` Use crucible's
+  allocator in `Box` constructors `` patch above.)
+
 * Define `Arc`/`Rc` constructors in terms of `{Arc,Rc}::new` (last applied: January 20, 2026)
 
   This ensures that all `Arc`/`Rc` constructors are defined in terms of

libs/alloc/src/boxed.rs

@@ -1755,7 +1755,7 @@ impl<T: Clone, A: Allocator + Clone> Clone for Box<T, A> {
     /// assert_ne!(&*x as *const i32, &*y as *const i32);
     /// ```
     #[inline]
-    fn clone(&self) -> Self {
+    default fn clone(&self) -> Self {
         // Pre-allocate memory to allow writing the cloned value directly.
         let mut boxed = Self::new_uninit_in(self.1.clone());
         unsafe {
@@ -1782,11 +1782,27 @@ impl<T: Clone, A: Allocator + Clone> Clone for Box<T, A> {
     /// assert_eq!(yp, &*y);
     /// ```
     #[inline]
-    fn clone_from(&mut self, source: &Self) {
+    default fn clone_from(&mut self, source: &Self) {
         (**self).clone_from(&(**source));
     }
 }
 
+// A specialized version of the Clone impl that uses new_uninit() instead of
+// new_uninit_in(), as the former is more Crucible-friendly.
+#[cfg(not(no_global_oom_handling))]
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: Clone> Clone for Box<T, Global> {
+    #[inline]
+    fn clone(&self) -> Self {
+        // Pre-allocate memory to allow writing the cloned value directly.
+        let mut boxed = Self::new_uninit();
+        unsafe {
+            (**self).clone_to_uninit(boxed.as_mut_ptr().cast());
+            boxed.assume_init()
+        }
+    }
+}
+
 #[cfg(not(no_global_oom_handling))]
 #[stable(feature = "box_slice_clone", since = "1.3.0")]
 impl<T: Clone, A: Allocator + Clone> Clone for Box<[T], A> {