[do not merge] Add a Move marker trait

library/alloc/src/boxed.rs

@@ -191,7 +191,7 @@ use core::error::{self, Error};
 use core::fmt;
 use core::future::Future;
 use core::hash::{Hash, Hasher};
-use core::marker::{Tuple, Unsize};
+use core::marker::{Tuple, Move, Unsize};
 use core::mem::{self, SizedTypeProperties};
 use core::ops::{
     AsyncFn, AsyncFnMut, AsyncFnOnce, CoerceUnsized, Coroutine, CoroutineState, Deref, DerefMut,
@@ -2132,3 +2132,6 @@ impl<E: Error> Error for Box<E> {
         Error::provide(&**self, request);
     }
 }
+
+#[unstable(feature = "move_trait", issue = "none")]
+unsafe impl<T: ?Sized> Move for Box<T> {}

library/alloc/src/collections/btree/map.rs

@@ -190,6 +190,9 @@ unsafe impl<#[may_dangle] K, #[may_dangle] V, A: Allocator + Clone> Drop for BTr
     }
 }
 
+#[unstable(feature = "move_trait", issue = "none")]
+unsafe impl<K, V, A: Allocator + Clone> core::marker::Move for BTreeMap<K, V, A> {}
+
 // FIXME: This implementation is "wrong", but changing it would be a breaking change.
 // (The bounds of the automatic `UnwindSafe` implementation have been like this since Rust 1.50.)
 // Maybe we can fix it nonetheless with a crater run, or if the `UnwindSafe`

library/alloc/src/collections/vec_deque/mod.rs

@@ -3025,6 +3025,9 @@ impl<T, A: Allocator> IndexMut<usize> for VecDeque<T, A> {
     }
 }
 
+#[unstable(feature = "move_trait", issue = "none")]
+unsafe impl<T, A: Allocator> core::marker::Move for VecDeque<T, A> {}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T> FromIterator<T> for VecDeque<T> {
     #[track_caller]

library/alloc/src/lib.rs

@@ -132,6 +132,7 @@
 #![feature(local_waker)]
 #![feature(maybe_uninit_slice)]
 #![feature(maybe_uninit_uninit_array_transpose)]
+#![feature(move_trait)]
 #![feature(panic_internals)]
 #![feature(pattern)]
 #![feature(pin_coerce_unsized_trait)]

library/alloc/src/rc.rs

@@ -251,7 +251,7 @@ use core::hash::{Hash, Hasher};
 use core::intrinsics::abort;
 #[cfg(not(no_global_oom_handling))]
 use core::iter;
-use core::marker::{PhantomData, Unsize};
+use core::marker::{PhantomData, Move, Unsize};
 use core::mem::{self, ManuallyDrop, align_of_val_raw};
 use core::num::NonZeroUsize;
 use core::ops::{CoerceUnsized, Deref, DerefMut, DerefPure, DispatchFromDyn, LegacyReceiver};
@@ -2277,6 +2277,9 @@ unsafe impl<T: ?Sized, A: Allocator> DerefPure for UniqueRc<T, A> {}
 #[unstable(feature = "legacy_receiver_trait", issue = "none")]
 impl<T: ?Sized> LegacyReceiver for Rc<T> {}
 
+#[unstable(feature = "move_trait", issue = "none")]
+unsafe impl<T: ?Sized, A: Allocator> Move for Rc<T, A> {}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 unsafe impl<#[may_dangle] T: ?Sized, A: Allocator> Drop for Rc<T, A> {
     /// Drops the `Rc`.

library/alloc/src/sync.rs

@@ -17,7 +17,7 @@ use core::hash::{Hash, Hasher};
 use core::intrinsics::abort;
 #[cfg(not(no_global_oom_handling))]
 use core::iter;
-use core::marker::{PhantomData, Unsize};
+use core::marker::{PhantomData, Unsize, Move};
 use core::mem::{self, ManuallyDrop, align_of_val_raw};
 use core::num::NonZeroUsize;
 use core::ops::{CoerceUnsized, Deref, DerefMut, DerefPure, DispatchFromDyn, LegacyReceiver};
@@ -271,6 +271,8 @@ pub struct Arc<
 unsafe impl<T: ?Sized + Sync + Send, A: Allocator + Send> Send for Arc<T, A> {}
 #[stable(feature = "rust1", since = "1.0.0")]
 unsafe impl<T: ?Sized + Sync + Send, A: Allocator + Sync> Sync for Arc<T, A> {}
+#[unstable(feature = "move_trait", issue = "none")]
+unsafe impl<T: ?Sized, A: Allocator> Move for Arc<T, A> {}
 
 #[stable(feature = "catch_unwind", since = "1.9.0")]
 impl<T: RefUnwindSafe + ?Sized, A: Allocator + UnwindSafe> UnwindSafe for Arc<T, A> {}

library/alloc/src/vec/mod.rs

@@ -59,7 +59,7 @@ use core::cmp::Ordering;
 use core::hash::{Hash, Hasher};
 #[cfg(not(no_global_oom_handling))]
 use core::iter;
-use core::marker::PhantomData;
+use core::marker::{PhantomData, Move};
 use core::mem::{self, ManuallyDrop, MaybeUninit, SizedTypeProperties};
 use core::ops::{self, Index, IndexMut, Range, RangeBounds};
 use core::ptr::{self, NonNull};
@@ -3908,6 +3908,9 @@ unsafe impl<#[may_dangle] T, A: Allocator> Drop for Vec<T, A> {
     }
 }
 
+#[unstable(feature = "move_trait", issue = "none")]
+unsafe impl<T> Move for Vec<T> {}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_const_unstable(feature = "const_default", issue = "143894")]
 impl<T> const Default for Vec<T> {

library/core/src/marker.rs

@@ -1366,3 +1366,19 @@ pub macro CoercePointee($item:item) {
 pub trait CoercePointeeValidated {
     /* compiler built-in */
 }
+
+/// Types that do not require a stable memory address, and so can be freely
+/// `move`d.
+#[unstable(feature = "move_trait", issue = "none")]
+pub unsafe auto trait Move {
+    // empty.
+}
+marker_impls! {
+    #[unstable(feature = "move_trait", issue = "none")]
+    unsafe Move for
+        {T: ?Sized} PhantomData<T>,
+        {T: ?Sized} *const T,
+        {T: ?Sized} *mut T,
+        {T: ?Sized} &T,
+        {T: ?Sized} &mut T,
+}

library/std/src/collections/hash/map.rs

@@ -1327,6 +1327,15 @@ where
     }
 }
 
+#[unstable(feature = "move_trait", issue = "none")]
+unsafe impl<K, V, S> core::marker::Move for HashMap<K, V, S>
+where
+    K: Eq + Hash,
+    V: Eq,
+    S: BuildHasher,
+{
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<K, V, S> Eq for HashMap<K, V, S>
 where

library/std/src/collections/hash/set.rs

@@ -1046,6 +1046,14 @@ where
 {
 }
 
+#[unstable(feature = "move_trait", issue = "none")]
+unsafe impl<T, S> core::marker::Move for HashSet<T, S>
+where
+    T: Eq + Hash,
+    S: BuildHasher,
+{
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T, S> fmt::Debug for HashSet<T, S>
 where

library/std/src/lib.rs

@@ -349,6 +349,7 @@
 #![feature(lazy_get)]
 #![feature(maybe_uninit_slice)]
 #![feature(maybe_uninit_write_slice)]
+#![feature(move_trait)]
 #![feature(panic_can_unwind)]
 #![feature(panic_internals)]
 #![feature(pin_coerce_unsized_trait)]