Rename Receiver -> LegacyReceiver

As part of the "arbitrary self types v2" project, we are going to
replace the current `Receiver` trait with a new mechanism based on a
new, different `Receiver` trait.

This PR renames the old trait to get it out the way. Naming is hard.
Options considered included:
* HardCodedReceiver (because it should only be used for things in the
  standard library, and hence is sort-of hard coded)
* LegacyReceiver
* TargetLessReceiver
* OldReceiver

These are all bad names, but fortunately this will be temporary.
Assuming the new mechanism proceeds to stabilization as intended, the
legacy trait will be removed altogether.

Although we expect this trait to be used only in the standard library,
we suspect it may be in use elsehwere, so we're landing this change
separately to identify any surprising breakages.

It's known that this trait is used within the Rust for Linux project; a
patch is in progress to remove their dependency.

This is a part of the arbitrary self types v2 project,
rust-lang/rfcs#3519
#44874

r? @wesleywiser

compiler/rustc_hir/src/lang_items.rs

@@ -232,7 +232,7 @@ language_item_table! {
     DerefMut,                sym::deref_mut,           deref_mut_trait,            Target::Trait,          GenericRequirement::Exact(0);
     DerefPure,               sym::deref_pure,          deref_pure_trait,           Target::Trait,          GenericRequirement::Exact(0);
     DerefTarget,             sym::deref_target,        deref_target,               Target::AssocTy,        GenericRequirement::None;
-    Receiver,                sym::receiver,            receiver_trait,             Target::Trait,          GenericRequirement::None;
+    LegacyReceiver,          sym::legacy_receiver,     legacy_receiver_trait,      Target::Trait,          GenericRequirement::None;
 
     Fn,                      kw::Fn,                   fn_trait,                   Target::Trait,          GenericRequirement::Exact(1);
     FnMut,                   sym::fn_mut,              fn_mut_trait,               Target::Trait,          GenericRequirement::Exact(1);

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -1794,7 +1794,7 @@ fn receiver_is_valid<'tcx>(
         autoderef = autoderef.include_raw_pointers();
     }
 
-    let receiver_trait_def_id = tcx.require_lang_item(LangItem::Receiver, Some(span));
+    let receiver_trait_def_id = tcx.require_lang_item(LangItem::LegacyReceiver, Some(span));
 
     // Keep dereferencing `receiver_ty` until we get to `self_ty`.
     while let Some((potential_self_ty, _)) = autoderef.next() {

compiler/rustc_span/src/symbol.rs

@@ -1096,6 +1096,7 @@ symbols! {
         lazy_normalization_consts,
         lazy_type_alias,
         le,
+        legacy_receiver,
         len,
         let_chains,
         let_else,
@@ -1524,7 +1525,6 @@ symbols! {
         readonly,
         realloc,
         reason,
-        receiver,
         recursion_limit,
         reexport_test_harness_main,
         ref_pat_eat_one_layer_2024,

library/alloc/src/boxed.rs

@@ -196,7 +196,7 @@ use core::marker::{Tuple, Unsize};
 use core::mem::{self, SizedTypeProperties};
 use core::ops::{
     AsyncFn, AsyncFnMut, AsyncFnOnce, CoerceUnsized, Coroutine, CoroutineState, Deref, DerefMut,
-    DerefPure, DispatchFromDyn, Receiver,
+    DerefPure, DispatchFromDyn, LegacyReceiver,
 };
 use core::pin::{Pin, PinCoerceUnsized};
 use core::ptr::{self, addr_of_mut, NonNull, Unique};
@@ -2153,8 +2153,8 @@ impl<T: ?Sized, A: Allocator> DerefMut for Box<T, A> {
 #[unstable(feature = "deref_pure_trait", issue = "87121")]
 unsafe impl<T: ?Sized, A: Allocator> DerefPure for Box<T, A> {}
 
-#[unstable(feature = "receiver_trait", issue = "none")]
-impl<T: ?Sized, A: Allocator> Receiver for Box<T, A> {}
+#[unstable(feature = "legacy_receiver_trait", issue = "none")]
+impl<T: ?Sized, A: Allocator> LegacyReceiver for Box<T, A> {}
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<I: Iterator + ?Sized, A: Allocator> Iterator for Box<I, A> {

library/alloc/src/lib.rs

@@ -131,6 +131,7 @@
 #![feature(iter_advance_by)]
 #![feature(iter_next_chunk)]
 #![feature(layout_for_ptr)]
+#![feature(legacy_receiver_trait)]
 #![feature(local_waker)]
 #![feature(maybe_uninit_slice)]
 #![feature(maybe_uninit_uninit_array_transpose)]
@@ -140,7 +141,6 @@
 #![feature(ptr_internals)]
 #![feature(ptr_metadata)]
 #![feature(ptr_sub_ptr)]
-#![feature(receiver_trait)]
 #![feature(set_ptr_value)]
 #![feature(sized_type_properties)]
 #![feature(slice_from_ptr_range)]

library/alloc/src/rc.rs

@@ -252,7 +252,7 @@ use core::intrinsics::abort;
 use core::iter;
 use core::marker::{PhantomData, Unsize};
 use core::mem::{self, align_of_val_raw, ManuallyDrop};
-use core::ops::{CoerceUnsized, Deref, DerefMut, DerefPure, DispatchFromDyn, Receiver};
+use core::ops::{CoerceUnsized, Deref, DerefMut, DerefPure, DispatchFromDyn, LegacyReceiver};
 use core::panic::{RefUnwindSafe, UnwindSafe};
 #[cfg(not(no_global_oom_handling))]
 use core::pin::Pin;
@@ -2179,8 +2179,8 @@ unsafe impl<T: ?Sized, A: Allocator> PinCoerceUnsized for Weak<T, A> {}
 #[unstable(feature = "deref_pure_trait", issue = "87121")]
 unsafe impl<T: ?Sized, A: Allocator> DerefPure for Rc<T, A> {}
 
-#[unstable(feature = "receiver_trait", issue = "none")]
-impl<T: ?Sized> Receiver for Rc<T> {}
+#[unstable(feature = "legacy_receiver_trait", issue = "none")]
+impl<T: ?Sized> LegacyReceiver for Rc<T> {}
 
 #[stable(feature = "rust1", since = "1.0.0")]
 unsafe impl<#[may_dangle] T: ?Sized, A: Allocator> Drop for Rc<T, A> {

library/alloc/src/sync.rs

@@ -18,7 +18,7 @@ use core::intrinsics::abort;
 use core::iter;
 use core::marker::{PhantomData, Unsize};
 use core::mem::{self, align_of_val_raw, ManuallyDrop};
-use core::ops::{CoerceUnsized, Deref, DerefPure, DispatchFromDyn, Receiver};
+use core::ops::{CoerceUnsized, Deref, DerefPure, DispatchFromDyn, LegacyReceiver};
 use core::panic::{RefUnwindSafe, UnwindSafe};
 use core::pin::{Pin, PinCoerceUnsized};
 use core::ptr::{self, NonNull};
@@ -2143,8 +2143,8 @@ unsafe impl<T: ?Sized, A: Allocator> PinCoerceUnsized for Weak<T, A> {}
 #[unstable(feature = "deref_pure_trait", issue = "87121")]
 unsafe impl<T: ?Sized, A: Allocator> DerefPure for Arc<T, A> {}
 
-#[unstable(feature = "receiver_trait", issue = "none")]
-impl<T: ?Sized> Receiver for Arc<T> {}
+#[unstable(feature = "legacy_receiver_trait", issue = "none")]
+impl<T: ?Sized> LegacyReceiver for Arc<T> {}
 
 #[cfg(not(no_global_oom_handling))]
 impl<T: ?Sized + CloneToUninit, A: Allocator + Clone> Arc<T, A> {

library/core/src/ops/deref.rs

@@ -297,15 +297,21 @@ unsafe impl<T: ?Sized> DerefPure for &mut T {}
 /// Indicates that a struct can be used as a method receiver, without the
 /// `arbitrary_self_types` feature. This is implemented by stdlib pointer types like `Box<T>`,
 /// `Rc<T>`, `&T`, and `Pin<P>`.
-#[lang = "receiver"]
-#[unstable(feature = "receiver_trait", issue = "none")]
+///
+/// This trait will shortly be removed and replaced with a more generic
+/// facility based around the current "arbitrary self types" unstable feature.
+/// That new facility will use a replacement trait called `Receiver` which is
+/// why this is now named `LegacyReceiver`.
+#[cfg_attr(bootstrap, lang = "receiver")]
+#[cfg_attr(not(bootstrap), lang = "legacy_receiver")]
+#[unstable(feature = "legacy_receiver_trait", issue = "none")]
 #[doc(hidden)]
-pub trait Receiver {
+pub trait LegacyReceiver {
     // Empty.
 }
 
-#[unstable(feature = "receiver_trait", issue = "none")]
-impl<T: ?Sized> Receiver for &T {}
+#[unstable(feature = "legacy_receiver_trait", issue = "none")]
+impl<T: ?Sized> LegacyReceiver for &T {}
 
-#[unstable(feature = "receiver_trait", issue = "none")]
-impl<T: ?Sized> Receiver for &mut T {}
+#[unstable(feature = "legacy_receiver_trait", issue = "none")]
+impl<T: ?Sized> LegacyReceiver for &mut T {}

library/core/src/ops/mod.rs

@@ -168,8 +168,8 @@ pub use self::control_flow::ControlFlow;
 pub use self::coroutine::{Coroutine, CoroutineState};
 #[unstable(feature = "deref_pure_trait", issue = "87121")]
 pub use self::deref::DerefPure;
-#[unstable(feature = "receiver_trait", issue = "none")]
-pub use self::deref::Receiver;
+#[unstable(feature = "legacy_receiver_trait", issue = "none")]
+pub use self::deref::LegacyReceiver;
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use self::deref::{Deref, DerefMut};
 pub(crate) use self::drop::fallback_surface_drop;

library/core/src/pin.rs

@@ -921,7 +921,7 @@
 #![stable(feature = "pin", since = "1.33.0")]
 
 use crate::hash::{Hash, Hasher};
-use crate::ops::{CoerceUnsized, Deref, DerefMut, DerefPure, DispatchFromDyn, Receiver};
+use crate::ops::{CoerceUnsized, Deref, DerefMut, DerefPure, DispatchFromDyn, LegacyReceiver};
 #[allow(unused_imports)]
 use crate::{
     cell::{RefCell, UnsafeCell},
@@ -1692,8 +1692,8 @@ impl<Ptr: DerefMut<Target: Unpin>> DerefMut for Pin<Ptr> {
 #[unstable(feature = "deref_pure_trait", issue = "87121")]
 unsafe impl<Ptr: DerefPure> DerefPure for Pin<Ptr> {}
 
-#[unstable(feature = "receiver_trait", issue = "none")]
-impl<Ptr: Receiver> Receiver for Pin<Ptr> {}
+#[unstable(feature = "legacy_receiver_trait", issue = "none")]
+impl<Ptr: LegacyReceiver> LegacyReceiver for Pin<Ptr> {}
 
 #[stable(feature = "pin", since = "1.33.0")]
 impl<Ptr: fmt::Debug> fmt::Debug for Pin<Ptr> {

tests/ui/abi/compatibility.rs

@@ -80,10 +80,10 @@ mod prelude {
     #[lang = "sized"]
     pub trait Sized {}
 
-    #[lang = "receiver"]
-    pub trait Receiver {}
-    impl<T: ?Sized> Receiver for &T {}
-    impl<T: ?Sized> Receiver for &mut T {}
+    #[lang = "legacy_receiver"]
+    pub trait LegacyReceiver {}
+    impl<T: ?Sized> LegacyReceiver for &T {}
+    impl<T: ?Sized> LegacyReceiver for &mut T {}
 
     #[lang = "copy"]
     pub trait Copy: Sized {}

tests/ui/closures/closure-move-sync.rs

@@ -5,7 +5,7 @@ fn bar() {
     let (send, recv) = channel();
     let t = thread::spawn(|| {
         recv.recv().unwrap();
-        //~^^ ERROR `std::sync::mpsc::Receiver<()>` cannot be shared between threads safely
+        //~^^ ERROR `Receiver<()>` cannot be shared between threads safely
     });
 
     send.send(());

tests/ui/closures/closure-move-sync.stderr

@@ -1,4 +1,4 @@
-error[E0277]: `std::sync::mpsc::Receiver<()>` cannot be shared between threads safely
+error[E0277]: `Receiver<()>` cannot be shared between threads safely
   --> $DIR/closure-move-sync.rs:6:27
    |
 LL |       let t = thread::spawn(|| {
@@ -8,10 +8,10 @@ LL |       let t = thread::spawn(|| {
 LL | |         recv.recv().unwrap();
 LL | |
 LL | |     });
-   | |_____^ `std::sync::mpsc::Receiver<()>` cannot be shared between threads safely
+   | |_____^ `Receiver<()>` cannot be shared between threads safely
    |
-   = help: the trait `Sync` is not implemented for `std::sync::mpsc::Receiver<()>`, which is required by `{closure@$DIR/closure-move-sync.rs:6:27: 6:29}: Send`
-   = note: required for `&std::sync::mpsc::Receiver<()>` to implement `Send`
+   = help: the trait `Sync` is not implemented for `Receiver<()>`, which is required by `{closure@$DIR/closure-move-sync.rs:6:27: 6:29}: Send`
+   = note: required for `&Receiver<()>` to implement `Send`
 note: required because it's used within this closure
   --> $DIR/closure-move-sync.rs:6:27
    |

tests/ui/privacy/privacy1.rs

@@ -12,14 +12,14 @@ pub trait Deref {
     type Target;
 }
 
-#[lang="receiver"]
-pub trait Receiver: Deref {}
+#[lang="legacy_receiver"]
+pub trait LegacyReceiver: Deref {}
 
 impl<'a, T> Deref for &'a T {
     type Target = T;
 }
 
-impl<'a, T> Receiver for &'a T {}
+impl<'a, T> LegacyReceiver for &'a T {}
 
 mod bar {
     // shouldn't bring in too much

tests/ui/rfcs/rfc-2632-const-trait-impl/const-fns-are-early-bound.rs

@@ -82,12 +82,12 @@ trait Copy {}
 #[lang = "tuple_trait"]
 trait Tuple {}
 
-#[lang = "receiver"]
-trait Receiver {}
+#[lang = "legacy_receiver"]
+trait LegacyReceiver {}
 
-impl<T: ?Sized> Receiver for &T {}
+impl<T: ?Sized> LegacyReceiver for &T {}
 
-impl<T: ?Sized> Receiver for &mut T {}
+impl<T: ?Sized> LegacyReceiver for &mut T {}
 
 #[stable(feature = "minicore", since = "1.0.0")]
 pub mod effects {

tests/ui/rfcs/rfc-2632-const-trait-impl/effects/minicore.rs

@@ -137,12 +137,12 @@ macro_rules! impl_fn_mut_tuple {
 //impl_fn_mut_tuple!(A B C D);
 //impl_fn_mut_tuple!(A B C D E);
 
-#[lang = "receiver"]
-trait Receiver {}
+#[lang = "legacy_receiver"]
+trait LegacyReceiver {}
 
-impl<T: ?Sized> Receiver for &T {}
+impl<T: ?Sized> LegacyReceiver for &T {}
 
-impl<T: ?Sized> Receiver for &mut T {}
+impl<T: ?Sized> LegacyReceiver for &mut T {}
 
 #[lang = "destruct"]
 #[const_trait]
@@ -454,7 +454,7 @@ impl<T> /* const */ Deref for Option<T> {
     }
 }
 
-impl<P: Receiver> Receiver for Pin<P> {}
+impl<P: LegacyReceiver> LegacyReceiver for Pin<P> {}
 
 impl<T: Clone> Clone for RefCell<T> {
     fn clone(&self) -> RefCell<T> {

tests/ui/stdlib-unit-tests/not-sync.rs

@@ -16,5 +16,5 @@ fn main() {
     //~^ ERROR `std::rc::Weak<i32>` cannot be shared between threads safely [E0277]
 
     test::<Receiver<i32>>();
-    //~^ ERROR `std::sync::mpsc::Receiver<i32>` cannot be shared between threads safely [E0277]
+    //~^ ERROR `Receiver<i32>` cannot be shared between threads safely [E0277]
 }

tests/ui/stdlib-unit-tests/not-sync.stderr

@@ -52,13 +52,13 @@ note: required by a bound in `test`
 LL | fn test<T: Sync>() {}
    |            ^^^^ required by this bound in `test`
 
-error[E0277]: `std::sync::mpsc::Receiver<i32>` cannot be shared between threads safely
+error[E0277]: `Receiver<i32>` cannot be shared between threads safely
   --> $DIR/not-sync.rs:18:12
    |
 LL |     test::<Receiver<i32>>();
-   |            ^^^^^^^^^^^^^ `std::sync::mpsc::Receiver<i32>` cannot be shared between threads safely
+   |            ^^^^^^^^^^^^^ `Receiver<i32>` cannot be shared between threads safely
    |
-   = help: the trait `Sync` is not implemented for `std::sync::mpsc::Receiver<i32>`
+   = help: the trait `Sync` is not implemented for `Receiver<i32>`
 note: required by a bound in `test`
   --> $DIR/not-sync.rs:5:12
    |