Auto merge of #146201 - lcnr:move-trait, r=<try>

[DO NOT MERGE] `Move` trait perf test

Author: rust-bors[bot]

compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs

@@ -231,7 +231,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         }
     }
 
-    /// Adds `experimental_default_bounds` bounds to the supertrait bounds.
+    /// Sets `experimental_default_bounds` to true on trait super bounds.
     pub(crate) fn add_default_super_traits(
         &self,
         trait_def_id: LocalDefId,
@@ -242,8 +242,6 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
     ) {
         assert_matches!(self.tcx().def_kind(trait_def_id), DefKind::Trait | DefKind::TraitAlias);
 
-        // Supertraits for auto trait are unsound according to the unstable book:
-        // https://doc.rust-lang.org/beta/unstable-book/language-features/auto-traits.html#supertraits
         if self.tcx().trait_is_auto(trait_def_id.to_def_id()) {
             return;
         }

compiler/rustc_session/src/options.rs

@@ -2307,7 +2307,7 @@ options! {
         "Use WebAssembly error handling for wasm32-unknown-emscripten"),
     enforce_type_length_limit: bool = (false, parse_bool, [TRACKED],
         "enforce the type length limit when monomorphizing instances in codegen"),
-    experimental_default_bounds: bool = (false, parse_bool, [TRACKED],
+    experimental_default_bounds: bool = (true, parse_bool, [TRACKED],
         "enable default bounds for experimental group of auto traits"),
     export_executable_symbols: bool = (false, parse_bool, [TRACKED],
         "export symbols from executables, as if they were dynamic libraries"),

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -474,7 +474,13 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             }
         } else {
             let has_non_region_infer = stack.obligation.predicate.has_non_region_infer();
-            if let Some(candidate) = self.winnow_candidates(has_non_region_infer, candidates) {
+            let is_default_auto_trait = self
+                .tcx()
+                .as_lang_item(stack.obligation.predicate.def_id())
+                .is_some_and(|lang_item| matches!(lang_item, LangItem::DefaultTrait1));
+            if let Some(candidate) =
+                self.winnow_candidates(has_non_region_infer, is_default_auto_trait, candidates)
+            {
                 self.filter_reservation_impls(candidate)
             } else {
                 Ok(None)
@@ -1821,15 +1827,19 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
     fn winnow_candidates(
         &mut self,
         has_non_region_infer: bool,
+        is_default_auto_trait: bool,
         mut candidates: Vec<EvaluatedCandidate<'tcx>>,
     ) -> Option<SelectionCandidate<'tcx>> {
         if candidates.len() == 1 {
             return Some(candidates.pop().unwrap().candidate);
         }
 
         // We prefer `Sized` candidates over everything.
-        let mut sized_candidates =
-            candidates.iter().filter(|c| matches!(c.candidate, SizedCandidate));
+        let mut sized_candidates = candidates.iter().filter(|c| {
+            matches!(c.candidate, SizedCandidate)
+                || (is_default_auto_trait
+                    && matches!(c.candidate, AutoImplCandidate | ImplCandidate(..)))
+        });
         if let Some(sized_candidate) = sized_candidates.next() {
             // There should only ever be a single sized candidate
             // as they would otherwise overlap.

library/alloc/src/boxed.rs

@@ -2039,7 +2039,10 @@ unsafe impl<T: ?Sized, A: Allocator> PinCoerceUnsized for Box<T, A> {}
 // Handling arbitrary custom allocators (which can affect the `Box` layout heavily!)
 // would need a lot of codegen and interpreter adjustments.
 #[unstable(feature = "dispatch_from_dyn", issue = "none")]
-impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Box<U>> for Box<T, Global> {}
+impl<T: ?Sized + Unsize<U> + ?core::marker::Move, U: ?Sized + ?core::marker::Move>
+    DispatchFromDyn<Box<U>> for Box<T, Global>
+{
+}
 
 #[stable(feature = "box_borrow", since = "1.1.0")]
 impl<T: ?Sized, A: Allocator> Borrow<T> for Box<T, A> {
@@ -2141,3 +2144,6 @@ impl<E: Error> Error for Box<E> {
         Error::provide(&**self, request);
     }
 }
+
+#[unstable(feature = "move_trait", issue = "none")]
+unsafe impl<T: ?Sized + ?core::marker::Move, A: Allocator> core::marker::Move for Box<T, A> {}

library/alloc/src/lib.rs

@@ -133,6 +133,7 @@
 #![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/alloctests/tests/lib.rs

@@ -13,6 +13,7 @@
 #![feature(int_format_into)]
 #![feature(linked_list_cursors)]
 #![feature(map_try_insert)]
+#![feature(move_trait)]
 #![feature(pattern)]
 #![feature(trusted_len)]
 #![feature(try_reserve_kind)]

library/core/src/cell.rs

@@ -252,7 +252,7 @@
 
 use crate::cmp::Ordering;
 use crate::fmt::{self, Debug, Display};
-use crate::marker::{PhantomData, Unsize};
+use crate::marker::{Move, PhantomData, Unsize};
 use crate::mem;
 use crate::ops::{CoerceUnsized, Deref, DerefMut, DerefPure, DispatchFromDyn};
 use crate::panic::const_panic;
@@ -309,7 +309,7 @@ pub use once::OnceCell;
 #[stable(feature = "rust1", since = "1.0.0")]
 #[repr(transparent)]
 #[rustc_pub_transparent]
-pub struct Cell<T: ?Sized> {
+pub struct Cell<T: ?Sized + ?Move> {
     value: UnsafeCell<T>,
 }
 
@@ -322,7 +322,7 @@ unsafe impl<T: ?Sized> Send for Cell<T> where T: Send {}
 // having an explicit negative impl is nice for documentation purposes
 // and results in nicer error messages.
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized> !Sync for Cell<T> {}
+impl<T: ?Sized + ?Move> !Sync for Cell<T> {}
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: Copy> Clone for Cell<T> {
@@ -669,7 +669,7 @@ impl<T: CoerceUnsized<U>, U> CoerceUnsized<Cell<U>> for Cell<T> {}
 // `self: Cell<&Self>` won't work
 // `self: CellWrapper<Self>` becomes possible
 #[unstable(feature = "dispatch_from_dyn", issue = "none")]
-impl<T: DispatchFromDyn<U>, U> DispatchFromDyn<Cell<U>> for Cell<T> {}
+impl<T: DispatchFromDyn<U> + ?Move, U: ?Move> DispatchFromDyn<Cell<U>> for Cell<T> {}
 
 impl<T> Cell<[T]> {
     /// Returns a `&[Cell<T>]` from a `&Cell<[T]>`
@@ -2185,12 +2185,12 @@ impl<T: ?Sized + fmt::Display> fmt::Display for RefMut<'_, T> {
 #[stable(feature = "rust1", since = "1.0.0")]
 #[repr(transparent)]
 #[rustc_pub_transparent]
-pub struct UnsafeCell<T: ?Sized> {
+pub struct UnsafeCell<T: ?Sized + ?Move> {
     value: T,
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized> !Sync for UnsafeCell<T> {}
+impl<T: ?Sized + ?Move> !Sync for UnsafeCell<T> {}
 
 impl<T> UnsafeCell<T> {
     /// Constructs a new instance of `UnsafeCell` which will wrap the specified
@@ -2455,7 +2455,7 @@ impl<T: CoerceUnsized<U>, U> CoerceUnsized<UnsafeCell<U>> for UnsafeCell<T> {}
 // `self: UnsafeCell<&Self>` won't work
 // `self: UnsafeCellWrapper<Self>` becomes possible
 #[unstable(feature = "dispatch_from_dyn", issue = "none")]
-impl<T: DispatchFromDyn<U>, U> DispatchFromDyn<UnsafeCell<U>> for UnsafeCell<T> {}
+impl<T: DispatchFromDyn<U> + ?Move, U: ?Move> DispatchFromDyn<UnsafeCell<U>> for UnsafeCell<T> {}
 
 /// [`UnsafeCell`], but [`Sync`].
 ///
@@ -2473,7 +2473,7 @@ impl<T: DispatchFromDyn<U>, U> DispatchFromDyn<UnsafeCell<U>> for UnsafeCell<T>
 #[repr(transparent)]
 #[rustc_diagnostic_item = "SyncUnsafeCell"]
 #[rustc_pub_transparent]
-pub struct SyncUnsafeCell<T: ?Sized> {
+pub struct SyncUnsafeCell<T: ?Sized + ?Move> {
     value: UnsafeCell<T>,
 }
 
@@ -2563,7 +2563,10 @@ impl<T: CoerceUnsized<U>, U> CoerceUnsized<SyncUnsafeCell<U>> for SyncUnsafeCell
 // `self: SyncUnsafeCellWrapper<Self>` becomes possible
 #[unstable(feature = "dispatch_from_dyn", issue = "none")]
 //#[unstable(feature = "sync_unsafe_cell", issue = "95439")]
-impl<T: DispatchFromDyn<U>, U> DispatchFromDyn<SyncUnsafeCell<U>> for SyncUnsafeCell<T> {}
+impl<T: DispatchFromDyn<U> + ?Move, U: ?Move> DispatchFromDyn<SyncUnsafeCell<U>>
+    for SyncUnsafeCell<T>
+{
+}
 
 #[allow(unused)]
 fn assert_coerce_unsized(

library/core/src/marker.rs

@@ -236,7 +236,7 @@ pub trait PointeeSized {
 #[lang = "unsize"]
 #[rustc_deny_explicit_impl]
 #[rustc_do_not_implement_via_object]
-pub trait Unsize<T: PointeeSized>: PointeeSized {
+pub trait Unsize<T: PointeeSized + ?crate::marker::Move>: PointeeSized {
     // Empty.
 }
 
@@ -819,7 +819,7 @@ impl<T: PointeeSized> !Sync for *mut T {}
 /// [drop check]: Drop#drop-check
 #[lang = "phantom_data"]
 #[stable(feature = "rust1", since = "1.0.0")]
-pub struct PhantomData<T: PointeeSized>;
+pub struct PhantomData<T: PointeeSized + ?crate::marker::Move>;
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: PointeeSized> Hash for PhantomData<T> {
@@ -913,7 +913,7 @@ pub trait DiscriminantKind {
 pub unsafe auto trait Freeze {}
 
 #[unstable(feature = "freeze", issue = "121675")]
-impl<T: PointeeSized> !Freeze for UnsafeCell<T> {}
+impl<T: PointeeSized + ?crate::marker::Move> !Freeze for UnsafeCell<T> {}
 marker_impls! {
     #[unstable(feature = "freeze", issue = "121675")]
     unsafe Freeze for
@@ -933,7 +933,7 @@ marker_impls! {
 #[lang = "unsafe_unpin"]
 pub(crate) unsafe auto trait UnsafeUnpin {}
 
-impl<T: ?Sized> !UnsafeUnpin for UnsafePinned<T> {}
+impl<T: ?Sized + ?crate::marker::Move> !UnsafeUnpin for UnsafePinned<T> {}
 unsafe impl<T: ?Sized> UnsafeUnpin for PhantomData<T> {}
 unsafe impl<T: ?Sized> UnsafeUnpin for *const T {}
 unsafe impl<T: ?Sized> UnsafeUnpin for *mut T {}
@@ -1372,3 +1372,20 @@ pub trait CoercePointeeValidated {
 pub trait Reborrow {
     // Empty.
 }
+
+/// Types that do not require a stable memory address, and so can be freely
+/// `move`d.
+#[lang = "default_trait1"]
+#[rustc_unsafe_specialization_marker]
+#[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 + PointeeSized} *const T,
+        {T: ?Sized + PointeeSized} *mut T,
+        {T: ?Sized + PointeeSized} &T,
+        {T: ?Sized + PointeeSized} &mut T,
+}

library/core/src/ops/unsize.rs

@@ -1,4 +1,4 @@
-use crate::marker::{PointeeSized, Unsize};
+use crate::marker::{Move, PointeeSized, Unsize};
 
 /// Trait that indicates that this is a pointer or a wrapper for one,
 /// where unsizing can be performed on the pointee.
@@ -39,34 +39,46 @@ pub trait CoerceUnsized<T: PointeeSized> {
 
 // &mut T -> &mut U
 #[unstable(feature = "coerce_unsized", issue = "18598")]
-impl<'a, T: PointeeSized + Unsize<U>, U: PointeeSized> CoerceUnsized<&'a mut U> for &'a mut T {}
+impl<'a, T: PointeeSized + ?Move + Unsize<U>, U: PointeeSized> CoerceUnsized<&'a mut U>
+    for &'a mut T
+{
+}
 // &mut T -> &U
 #[unstable(feature = "coerce_unsized", issue = "18598")]
-impl<'a, 'b: 'a, T: PointeeSized + Unsize<U>, U: PointeeSized> CoerceUnsized<&'a U> for &'b mut T {}
+impl<'a, 'b: 'a, T: PointeeSized + ?Move + Unsize<U>, U: PointeeSized> CoerceUnsized<&'a U>
+    for &'b mut T
+{
+}
 // &mut T -> *mut U
 #[unstable(feature = "coerce_unsized", issue = "18598")]
-impl<'a, T: PointeeSized + Unsize<U>, U: PointeeSized> CoerceUnsized<*mut U> for &'a mut T {}
+impl<'a, T: PointeeSized + ?Move + Unsize<U>, U: PointeeSized> CoerceUnsized<*mut U> for &'a mut T {}
 // &mut T -> *const U
 #[unstable(feature = "coerce_unsized", issue = "18598")]
-impl<'a, T: PointeeSized + Unsize<U>, U: PointeeSized> CoerceUnsized<*const U> for &'a mut T {}
+impl<'a, T: PointeeSized + ?Move + Unsize<U>, U: PointeeSized> CoerceUnsized<*const U>
+    for &'a mut T
+{
+}
 
 // &T -> &U
 #[unstable(feature = "coerce_unsized", issue = "18598")]
-impl<'a, 'b: 'a, T: PointeeSized + Unsize<U>, U: PointeeSized> CoerceUnsized<&'a U> for &'b T {}
+impl<'a, 'b: 'a, T: PointeeSized + ?Move + Unsize<U>, U: PointeeSized> CoerceUnsized<&'a U>
+    for &'b T
+{
+}
 // &T -> *const U
 #[unstable(feature = "coerce_unsized", issue = "18598")]
-impl<'a, T: PointeeSized + Unsize<U>, U: PointeeSized> CoerceUnsized<*const U> for &'a T {}
+impl<'a, T: PointeeSized + ?Move + Unsize<U>, U: PointeeSized> CoerceUnsized<*const U> for &'a T {}
 
 // *mut T -> *mut U
 #[unstable(feature = "coerce_unsized", issue = "18598")]
-impl<T: PointeeSized + Unsize<U>, U: PointeeSized> CoerceUnsized<*mut U> for *mut T {}
+impl<T: PointeeSized + ?Move + Unsize<U>, U: PointeeSized> CoerceUnsized<*mut U> for *mut T {}
 // *mut T -> *const U
 #[unstable(feature = "coerce_unsized", issue = "18598")]
-impl<T: PointeeSized + Unsize<U>, U: PointeeSized> CoerceUnsized<*const U> for *mut T {}
+impl<T: PointeeSized + ?Move + Unsize<U>, U: PointeeSized> CoerceUnsized<*const U> for *mut T {}
 
 // *const T -> *const U
 #[unstable(feature = "coerce_unsized", issue = "18598")]
-impl<T: PointeeSized + Unsize<U>, U: PointeeSized> CoerceUnsized<*const U> for *const T {}
+impl<T: PointeeSized + ?Move + Unsize<U>, U: PointeeSized> CoerceUnsized<*const U> for *const T {}
 
 /// `DispatchFromDyn` is used in the implementation of dyn-compatibility[^1] checks (specifically
 /// allowing arbitrary self types), to guarantee that a method's receiver type can be dispatched on.
@@ -116,19 +128,31 @@ impl<T: PointeeSized + Unsize<U>, U: PointeeSized> CoerceUnsized<*const U> for *
 /// [^1]: Formerly known as *object safety*.
 #[unstable(feature = "dispatch_from_dyn", issue = "none")]
 #[lang = "dispatch_from_dyn"]
-pub trait DispatchFromDyn<T> {
+pub trait DispatchFromDyn<T: ?Move> {
     // Empty.
 }
 
 // &T -> &U
 #[unstable(feature = "dispatch_from_dyn", issue = "none")]
-impl<'a, T: PointeeSized + Unsize<U>, U: PointeeSized> DispatchFromDyn<&'a U> for &'a T {}
+impl<'a, T: PointeeSized + ?Move + Unsize<U>, U: PointeeSized + ?Move> DispatchFromDyn<&'a U>
+    for &'a T
+{
+}
 // &mut T -> &mut U
 #[unstable(feature = "dispatch_from_dyn", issue = "none")]
-impl<'a, T: PointeeSized + Unsize<U>, U: PointeeSized> DispatchFromDyn<&'a mut U> for &'a mut T {}
+impl<'a, T: PointeeSized + ?Move + Unsize<U>, U: PointeeSized + ?Move> DispatchFromDyn<&'a mut U>
+    for &'a mut T
+{
+}
 // *const T -> *const U
 #[unstable(feature = "dispatch_from_dyn", issue = "none")]
-impl<T: PointeeSized + Unsize<U>, U: PointeeSized> DispatchFromDyn<*const U> for *const T {}
+impl<T: PointeeSized + ?Move + Unsize<U>, U: PointeeSized + ?Move> DispatchFromDyn<*const U>
+    for *const T
+{
+}
 // *mut T -> *mut U
 #[unstable(feature = "dispatch_from_dyn", issue = "none")]
-impl<T: PointeeSized + Unsize<U>, U: PointeeSized> DispatchFromDyn<*mut U> for *mut T {}
+impl<T: PointeeSized + ?Move + Unsize<U>, U: PointeeSized + ?Move> DispatchFromDyn<*mut U>
+    for *mut T
+{
+}

library/core/src/panic/unwind_safe.rs

@@ -197,7 +197,7 @@ impl<T> UnwindSafe for AssertUnwindSafe<T> {}
 // only thing which doesn't implement it (which then transitively applies to
 // everything else).
 #[stable(feature = "catch_unwind", since = "1.9.0")]
-impl<T: ?Sized> !RefUnwindSafe for UnsafeCell<T> {}
+impl<T: ?Sized + ?crate::marker::Move> !RefUnwindSafe for UnsafeCell<T> {}
 #[stable(feature = "catch_unwind", since = "1.9.0")]
 impl<T> RefUnwindSafe for AssertUnwindSafe<T> {}