rust-lang · nia-e · Jun 4, 2026 · Jul 13, 2026 · Jul 13, 2026 · Jul 13, 2026
diff --git a/compiler/rustc_hir/src/lang_items.rs b/compiler/rustc_hir/src/lang_items.rs
@@ -345,6 +345,7 @@ language_item_table! {
 
     OwnedBox,                sym::owned_box,           owned_box,                  Target::Struct,         GenericRequirement::Minimum(1);
     GlobalAlloc,             sym::global_alloc_ty,     global_alloc_ty,            Target::Struct,         GenericRequirement::None;
+    NoaliasAllocator,        sym::noalias_allocator,   noalias_allocator_trait,         Target::Trait,          GenericRequirement::None;
 
     PhantomData,             sym::phantom_data,        phantom_data,               Target::Struct,         GenericRequirement::Exact(1);
 

diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
@@ -1434,6 +1434,7 @@ symbols! {
         no_sanitize,
         no_stack_check,
         no_std,
+        noalias_allocator,
         nomem,
         non_ascii_idents,
         non_exhaustive,

diff --git a/library/alloc/src/alloc.rs b/library/alloc/src/alloc.rs
@@ -54,9 +54,19 @@ unsafe extern "Rust" {
 #[unstable(feature = "allocator_api", issue = "32838")]
 #[derive(Copy, Clone, Default, Debug)]
 // the compiler needs to know when a Box uses the global allocator vs a custom one
+// FIXME(nia-e): change everything to use the noalias_allocator lang item instead
 #[lang = "global_alloc_ty"]
 pub struct Global;
 
+#[unstable(feature = "allocator_api", issue = "32838")]
+unsafe impl core::alloc::AllocatorClone for Global {}
+
+#[unstable(feature = "allocator_api", issue = "32838")]
+unsafe impl core::alloc::StaticAllocator for Global {}
+
+#[unstable(feature = "allocator_api", issue = "32838")]
+unsafe impl core::alloc::NoaliasAllocator for Global {}
+
 /// Allocates memory with the global allocator.
 ///
 /// This function forwards calls to the [`GlobalAlloc::alloc`] method

diff --git a/library/alloc/src/boxed.rs b/library/alloc/src/boxed.rs
@@ -206,10 +206,12 @@ use core::task::{Context, Poll};
 
 #[cfg(not(no_global_oom_handling))]
 use crate::alloc::handle_alloc_error;
-use crate::alloc::{AllocError, Allocator, Global, Layout};
+use crate::alloc::{
+    AllocError, Allocator, AllocatorClone, AllocatorEq, Global, Layout, StaticAllocator,
+};
 use crate::raw_vec::RawVec;
 #[cfg(not(no_global_oom_handling))]
-use crate::str::from_boxed_utf8_unchecked;
+use crate::str::from_boxed_utf8_unchecked_in;
 
 /// Conversion related impls for `Box<_>` (`From`, `downcast`, etc)
 mod convert;
@@ -712,7 +714,7 @@ impl<T, A: Allocator> Box<T, A> {
     #[inline(always)]
     pub fn pin_in(x: T, alloc: A) -> Pin<Self>
     where
-        A: 'static + Allocator,
+        A: StaticAllocator,
     {
         Self::into_pin(Self::new_in(x, alloc))
     }
@@ -1979,7 +1981,7 @@ impl<T: ?Sized, A: Allocator> Box<T, A> {
     #[stable(feature = "box_into_pin", since = "1.63.0")]
     pub fn into_pin(boxed: Self) -> Pin<Self>
     where
-        A: 'static,
+        A: StaticAllocator,
     {
         // It's not possible to move or replace the insides of a `Pin<Box<T>>`
         // when `T: !Unpin`, so it's safe to pin it directly without any
@@ -2153,11 +2155,10 @@ impl<T: Clone, A: Allocator + Clone> Clone for Box<[T], A> {
 
 #[cfg(not(no_global_oom_handling))]
 #[stable(feature = "box_slice_clone", since = "1.3.0")]
-impl Clone for Box<str> {
+impl<A: Allocator + Clone> Clone for Box<str, A> {
     fn clone(&self) -> Self {
-        // this makes a copy of the data
-        let buf: Box<[u8]> = self.as_bytes().into();
-        unsafe { from_boxed_utf8_unchecked(buf) }
+        let buf = Box::clone_from_ref_in(self.as_bytes(), self.1.clone());
+        unsafe { from_boxed_utf8_unchecked_in(buf) }
     }
 }
 
@@ -2529,3 +2530,21 @@ unsafe impl<T: ?Sized + Allocator, A: Allocator> Allocator for Box<T, A> {
         unsafe { (**self).shrink(ptr, old_layout, new_layout) }
     }
 }
+
+#[unstable(feature = "allocator_api", issue = "32838")]
+unsafe impl<T, A> AllocatorClone for Box<T, A>
+where
+    T: AllocatorClone,
+    // Otherwise, the clone impl *here* may unwind.
+    A: AllocatorClone,
+    Box<T, A>: Clone,
+{
+}
+
+#[unstable(feature = "allocator_api", issue = "32838")]
+unsafe impl<T, A> AllocatorEq for Box<T, A>
+where
+    T: AllocatorEq + ?Sized,
+    A: Allocator,
+{
+}
diff --git a/library/alloc/src/boxed/convert.rs b/library/alloc/src/boxed/convert.rs
@@ -5,7 +5,7 @@ use core::fmt;
 use core::mem;
 use core::pin::Pin;
 
-use crate::alloc::Allocator;
+use crate::alloc::{Allocator, StaticAllocator};
 #[cfg(not(no_global_oom_handling))]
 use crate::borrow::Cow;
 use crate::boxed::Box;
@@ -38,7 +38,7 @@ impl<T> From<T> for Box<T> {
 #[stable(feature = "pin", since = "1.33.0")]
 impl<T: ?Sized, A: Allocator> From<Box<T, A>> for Pin<Box<T, A>>
 where
-    A: 'static,
+    A: StaticAllocator,
 {
     /// Converts a `Box<T>` into a `Pin<Box<T>>`. If `T` does not implement [`Unpin`], then
     /// `*boxed` will be pinned in memory and unable to be moved.

diff --git a/library/alloc/src/collections/linked_list.rs b/library/alloc/src/collections/linked_list.rs
@@ -12,6 +12,7 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
+use core::alloc::AllocatorClone;
 use core::cmp::Ordering;
 use core::hash::{Hash, Hasher};
 use core::iter::FusedIterator;
@@ -136,7 +137,6 @@ impl<T: fmt::Debug> fmt::Debug for IterMut<'_, T> {
 /// (provided by the [`IntoIterator`] trait). See its documentation for more.
 ///
 /// [`into_iter`]: LinkedList::into_iter
-#[derive(Clone)]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct IntoIter<
     T,
@@ -145,6 +145,13 @@ pub struct IntoIter<
     list: LinkedList<T, A>,
 }
 
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: Clone, A: Allocator + Clone> Clone for IntoIter<T, A> {
+    fn clone(&self) -> Self {
+        Self { list: self.list.clone() }
+    }
+}
+
 #[stable(feature = "collection_debug", since = "1.17.0")]
 impl<T: fmt::Debug, A: Allocator> fmt::Debug for IntoIter<T, A> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
@@ -340,7 +347,7 @@ impl<T, A: Allocator> LinkedList<T, A> {
         at: usize,
     ) -> Self
     where
-        A: Clone,
+        A: AllocatorClone,
     {
         // The split node is the new head node of the second part
         if let Some(mut split_node) = split_node {
@@ -383,7 +390,7 @@ impl<T, A: Allocator> LinkedList<T, A> {
         at: usize,
     ) -> Self
     where
-        A: Clone,
+        A: AllocatorClone,
     {
         // The split node is the new tail node of the first part and owns
         // the head of the second part.
@@ -994,7 +1001,7 @@ impl<T, A: Allocator> LinkedList<T, A> {
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn split_off(&mut self, at: usize) -> LinkedList<T, A>
     where
-        A: Clone,
+        A: AllocatorClone,
     {
         let len = self.len();
         assert!(at <= len, "Cannot split off at a nonexistent index");
@@ -1748,7 +1755,7 @@ impl<'a, T, A: Allocator> CursorMut<'a, T, A> {
     #[unstable(feature = "linked_list_cursors", issue = "58533")]
     pub fn remove_current_as_list(&mut self) -> Option<LinkedList<T, A>>
     where
-        A: Clone,
+        A: AllocatorClone,
     {
         let mut unlinked_node = self.current?;
         unsafe {
@@ -1776,7 +1783,7 @@ impl<'a, T, A: Allocator> CursorMut<'a, T, A> {
     #[unstable(feature = "linked_list_cursors", issue = "58533")]
     pub fn split_after(&mut self) -> LinkedList<T, A>
     where
-        A: Clone,
+        A: AllocatorClone,
     {
         let split_off_idx = if self.index == self.list.len { 0 } else { self.index + 1 };
         if self.index == self.list.len {
@@ -1795,7 +1802,7 @@ impl<'a, T, A: Allocator> CursorMut<'a, T, A> {
     #[unstable(feature = "linked_list_cursors", issue = "58533")]
     pub fn split_before(&mut self) -> LinkedList<T, A>
     where
-        A: Clone,
+        A: AllocatorClone,
     {
         let split_off_idx = self.index;
         self.index = 0;
@@ -2151,6 +2158,7 @@ impl<T: Ord, A: Allocator> Ord for LinkedList<T, A> {
     }
 }
 
+// `AllocatorClone` bound is necessary due to the `split_off` in `clone_from`.
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: Clone, A: Allocator + Clone> Clone for LinkedList<T, A> {
     fn clone(&self) -> Self {
@@ -2167,12 +2175,15 @@ impl<T: Clone, A: Allocator + Clone> Clone for LinkedList<T, A> {
     /// resources of `self`'s elements as well.
     fn clone_from(&mut self, source: &Self) {
         let mut source_iter = source.iter();
-        if self.len() > source.len() {
-            self.split_off(source.len());
-        }
-        for (elem, source_elem) in self.iter_mut().zip(&mut source_iter) {
+        for elem in self.iter_mut() {
+            let Some(source_elem) = source_iter.next() else {
+                break;
+            };
             elem.clone_from(source_elem);
         }
+        while self.len() > source.len() {
+            self.pop_back();
+        }
         if !source_iter.is_empty() {
             self.extend(source_iter.cloned());
         }

diff --git a/library/alloc/src/rc.rs b/library/alloc/src/rc.rs
@@ -268,7 +268,7 @@ use core::{borrow, fmt, hint};
 
 #[cfg(not(no_global_oom_handling))]
 use crate::alloc::handle_alloc_error;
-use crate::alloc::{AllocError, Allocator, Global, Layout};
+use crate::alloc::{AllocError, Allocator, AllocatorClone, Global, Layout};
 use crate::borrow::{Cow, ToOwned};
 use crate::boxed::Box;
 #[cfg(not(no_global_oom_handling))]
@@ -1771,7 +1771,7 @@ impl<T: ?Sized, A: Allocator> Rc<T, A> {
     #[stable(feature = "rc_weak", since = "1.4.0")]
     pub fn downgrade(this: &Self) -> Weak<T, A>
     where
-        A: Clone,
+        A: AllocatorClone,
     {
         this.inner().inc_weak();
         // Make sure we do not create a dangling Weak
@@ -1852,7 +1852,7 @@ impl<T: ?Sized, A: Allocator> Rc<T, A> {
     #[unstable(feature = "allocator_api", issue = "32838")]
     pub unsafe fn increment_strong_count_in(ptr: *const T, alloc: A)
     where
-        A: Clone,
+        A: AllocatorClone,
     {
         // Retain Rc, but don't touch refcount by wrapping in ManuallyDrop
         let rc = unsafe { mem::ManuallyDrop::new(Rc::<T, A>::from_raw_in(ptr, alloc)) };
@@ -2028,7 +2028,7 @@ impl<T: ?Sized, A: Allocator> Rc<T, A> {
 }
 
 #[cfg(not(no_global_oom_handling))]
-impl<T: ?Sized + CloneToUninit, A: Allocator + Clone> Rc<T, A> {
+impl<T: ?Sized + CloneToUninit, A: AllocatorClone> Rc<T, A> {
     /// Makes a mutable reference into the given `Rc`.
     ///
     /// If there are other `Rc` pointers to the same allocation, then `make_mut` will
@@ -2309,7 +2309,7 @@ impl<T: ?Sized, A: Allocator> Rc<T, A> {
 
             // Free the allocation without dropping its contents
             let (bptr, alloc) = Box::into_raw_with_allocator(src);
-            let src = Box::from_raw_in(bptr as *mut mem::ManuallyDrop<T>, alloc.by_ref());
+            let src = Box::from_raw_in(bptr as *mut mem::ManuallyDrop<T>, &alloc);
             drop(src);
 
             Self::from_ptr_in(ptr, alloc)
@@ -2498,7 +2498,7 @@ unsafe impl<#[may_dangle] T: ?Sized, A: Allocator> Drop for Rc<T, A> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized, A: Allocator + Clone> Clone for Rc<T, A> {
+impl<T: ?Sized, A: AllocatorClone> Clone for Rc<T, A> {
     /// Makes a clone of the `Rc` pointer.
     ///
     /// This creates another pointer to the same allocation, increasing the
@@ -2523,10 +2523,10 @@ impl<T: ?Sized, A: Allocator + Clone> Clone for Rc<T, A> {
 }
 
 #[unstable(feature = "ergonomic_clones", issue = "132290")]
-impl<T: ?Sized, A: Allocator + Clone> UseCloned for Rc<T, A> {}
+impl<T: ?Sized, A: AllocatorClone> UseCloned for Rc<T, A> {}
 
 #[unstable(feature = "share_trait", issue = "156756")]
-impl<T: ?Sized, A: Allocator + Clone> Share for Rc<T, A> {}
+impl<T: ?Sized, A: AllocatorClone> Share for Rc<T, A> {}
 
 #[cfg(not(no_global_oom_handling))]
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -3547,7 +3547,7 @@ impl<T: ?Sized, A: Allocator> Weak<T, A> {
     #[stable(feature = "rc_weak", since = "1.4.0")]
     pub fn upgrade(&self) -> Option<Rc<T, A>>
     where
-        A: Clone,
+        A: AllocatorClone,
     {
         let inner = self.inner()?;
 
@@ -3692,7 +3692,7 @@ unsafe impl<#[may_dangle] T: ?Sized, A: Allocator> Drop for Weak<T, A> {
 }
 
 #[stable(feature = "rc_weak", since = "1.4.0")]
-impl<T: ?Sized, A: Allocator + Clone> Clone for Weak<T, A> {
+impl<T: ?Sized, A: AllocatorClone> Clone for Weak<T, A> {
     /// Makes a clone of the `Weak` pointer that points to the same allocation.
     ///
     /// # Examples
@@ -3714,7 +3714,7 @@ impl<T: ?Sized, A: Allocator + Clone> Clone for Weak<T, A> {
 }
 
 #[unstable(feature = "ergonomic_clones", issue = "132290")]
-impl<T: ?Sized, A: Allocator + Clone> UseCloned for Weak<T, A> {}
+impl<T: ?Sized, A: AllocatorClone> UseCloned for Weak<T, A> {}
 
 #[stable(feature = "rc_weak", since = "1.4.0")]
 impl<T: ?Sized, A: Allocator> fmt::Debug for Weak<T, A> {
@@ -4414,7 +4414,7 @@ impl<T: ?Sized, A: Allocator> UniqueRc<T, A> {
     }
 }
 
-impl<T: ?Sized, A: Allocator + Clone> UniqueRc<T, A> {
+impl<T: ?Sized, A: AllocatorClone> UniqueRc<T, A> {
     /// Creates a new weak reference to the `UniqueRc`.
     ///
     /// Attempting to upgrade this weak reference will fail before the `UniqueRc` has been converted
@@ -4603,3 +4603,6 @@ unsafe impl<T: ?Sized + Allocator, A: Allocator> Allocator for Rc<T, A> {
         unsafe { (**self).shrink(ptr, old_layout, new_layout) }
     }
 }
+
+#[unstable(feature = "allocator_api", issue = "32838")]
+unsafe impl<T: Allocator + ?Sized, A: AllocatorClone> AllocatorClone for Rc<T, A> {}
diff --git a/library/alloc/src/str.rs b/library/alloc/src/str.rs
@@ -896,6 +896,22 @@ pub unsafe fn from_boxed_utf8_unchecked(v: Box<[u8]>) -> Box<str> {
     unsafe { Box::from_raw(Box::into_raw(v) as *mut str) }
 }
 
+/// Converts a boxed slice of bytes to a boxed string slice without checking
+/// that the string contains valid UTF-8 generically over the box's allocator.
+///
+/// # Safety
+///
+/// * The provided bytes must contain a valid UTF-8 sequence.
+#[unstable(feature = "allocator_api", issue = "32838")]
+#[must_use]
+#[inline]
+pub unsafe fn from_boxed_utf8_unchecked_in<A: crate::alloc::Allocator>(
+    v: Box<[u8], A>,
+) -> Box<str, A> {
+    let (ptr, alloc) = Box::into_raw_with_allocator(v);
+    unsafe { Box::from_raw_in(ptr as *mut str, alloc) }
+}
+
 /// Converts leading ascii bytes in `s` by calling the `convert` function.
 ///
 /// For better average performance, this happens in chunks of `2*size_of::<usize>()`.