Arbitrary self types v2: simulated stabilization, do not merge

compiler/rustc_codegen_cranelift/example/arbitrary_self_types_pointers_and_wrappers.rs

@@ -1,6 +1,6 @@
 // Adapted from rustc run-pass test suite
 
-#![feature(arbitrary_self_types, unsize, coerce_unsized, dispatch_from_dyn)]
+#![feature(unsize, coerce_unsized, dispatch_from_dyn)]
 
 use std::marker::Unsize;
 use std::ops::{CoerceUnsized, Deref, DispatchFromDyn};

compiler/rustc_codegen_cranelift/example/mini_core.rs

@@ -47,13 +47,6 @@ impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<*const U> for *const T {}
 impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<*mut U> for *mut T {}
 impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Box<U>> for Box<T> {}
 
-#[lang = "legacy_receiver"]
-pub trait LegacyReceiver {}
-
-impl<T: ?Sized> LegacyReceiver for &T {}
-impl<T: ?Sized> LegacyReceiver for &mut T {}
-impl<T: ?Sized> LegacyReceiver for Box<T> {}
-
 #[lang = "copy"]
 pub unsafe trait Copy {}
 

compiler/rustc_codegen_gcc/example/arbitrary_self_types_pointers_and_wrappers.rs

@@ -1,6 +1,6 @@
 // Adapted from rustc run-pass test suite
 
-#![feature(arbitrary_self_types, unsize, coerce_unsized, dispatch_from_dyn)]
+#![feature(unsize, coerce_unsized, dispatch_from_dyn)]
 #![feature(rustc_attrs)]
 #![allow(internal_features)]
 

compiler/rustc_codegen_gcc/example/mini_core.rs

@@ -44,13 +44,6 @@ impl<T: ?Sized+Unsize<U>, U: ?Sized> DispatchFromDyn<*const U> for *const T {}
 impl<T: ?Sized+Unsize<U>, U: ?Sized> DispatchFromDyn<*mut U> for *mut T {}
 impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Box<U, ()>> for Box<T, ()> {}
 
-#[lang = "legacy_receiver"]
-pub trait LegacyReceiver {}
-
-impl<T: ?Sized> LegacyReceiver for &T {}
-impl<T: ?Sized> LegacyReceiver for &mut T {}
-impl<T: ?Sized, A: Allocator> LegacyReceiver for Box<T, A> {}
-
 #[lang = "copy"]
 pub unsafe trait Copy {}
 

compiler/rustc_error_codes/src/error_codes/E0307.md

@@ -65,8 +65,10 @@ impl Trait for Foo {
 ```
 
 The nightly feature [Arbitrary self types][AST] extends the accepted
-set of receiver types to also include any type that can dereference to
-`Self`:
+set of receiver types to also include any type that implements the
+`Receiver` trait and can follow its chain of `Target` types to `Self`.
+There's a blanket implementation of `Receiver` for `T: Deref`, so any
+type which dereferences to `Self` can be used.
 
 ```
 #![feature(arbitrary_self_types)]

compiler/rustc_feature/src/accepted.rs

@@ -60,6 +60,8 @@ declare_features! (
     (accepted, adx_target_feature, "1.61.0", Some(44839)),
     /// Allows explicit discriminants on non-unit enum variants.
     (accepted, arbitrary_enum_discriminant, "1.66.0", Some(60553)),
+    /// Allows inherent and trait methods with arbitrary self types.
+    (accepted, arbitrary_self_types, "CURRENT_RUSTC_VERSION", Some(44874)),
     /// Allows using `const` operands in inline assembly.
     (accepted, asm_const, "1.82.0", Some(93332)),
     /// Allows using `sym` operands in inline assembly.

compiler/rustc_feature/src/unstable.rs

@@ -370,8 +370,6 @@ declare_features! (
     (unstable, adt_const_params, "1.56.0", Some(95174)),
     /// Allows defining an `#[alloc_error_handler]`.
     (unstable, alloc_error_handler, "1.29.0", Some(51540)),
-    /// Allows inherent and trait methods with arbitrary self types.
-    (unstable, arbitrary_self_types, "1.23.0", Some(44874)),
     /// Allows inherent and trait methods with arbitrary self types that are raw pointers.
     (unstable, arbitrary_self_types_pointers, "1.83.0", Some(44874)),
     /// Enables experimental inline assembly support for additional architectures.

compiler/rustc_hir/src/lang_items.rs

@@ -243,7 +243,6 @@ language_item_table! {
     DerefTarget,             sym::deref_target,        deref_target,               Target::AssocTy,        GenericRequirement::None;
     Receiver,                sym::receiver,            receiver_trait,             Target::Trait,          GenericRequirement::None;
     ReceiverTarget,          sym::receiver_target,     receiver_target,            Target::AssocTy,        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/messages.ftl

@@ -241,10 +241,14 @@ hir_analysis_invalid_generic_receiver_ty_help =
     use a concrete type such as `self`, `&self`, `&mut self`, `self: Box<Self>`, `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one of the previous types except `Self`)
 
 hir_analysis_invalid_receiver_ty = invalid `self` parameter type: `{$receiver_ty}`
-    .note = type of `self` must be `Self` or a type that dereferences to it
+    .note = type of `self` must be `Self` or some type implementing Receiver
 
 hir_analysis_invalid_receiver_ty_help =
-    consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one of the previous types except `Self`)
+    consider changing to `self`, `&self`, `&mut self`, or a type implementing `Receiver` such as `self: Box<Self>`, `self: Rc<Self>`, or `self: Arc<Self>`
+
+hir_analysis_invalid_receiver_ty_help_pointer_note =
+    Raw pointers do not implement Receiver. Consider wrapping your pointer in
+    a newtype wrapper for which you implement Receiver
 
 hir_analysis_invalid_union_field =
     field must implement `Copy` or be wrapped in `ManuallyDrop<...>` to be used in a union

compiler/rustc_hir_analysis/src/autoderef.rs

@@ -18,7 +18,6 @@ pub enum AutoderefKind {
     /// A type which must dispatch to a `Deref` implementation.
     Overloaded,
 }
-
 struct AutoderefSnapshot<'tcx> {
     at_start: bool,
     reached_recursion_limit: bool,
@@ -27,6 +26,10 @@ struct AutoderefSnapshot<'tcx> {
     obligations: PredicateObligations<'tcx>,
 }
 
+/// Recursively dereference a type, considering both built-in
+/// dereferences (`*`) and the `Deref` trait.
+/// Although called `Autoderef` it can be configured to use the
+/// `Receiver` trait instead of the `Deref` trait.
 pub struct Autoderef<'a, 'tcx> {
     // Meta infos:
     infcx: &'a InferCtxt<'tcx>,
@@ -39,6 +42,7 @@ pub struct Autoderef<'a, 'tcx> {
 
     // Configurations:
     include_raw_pointers: bool,
+    use_receiver_trait: bool,
     silence_errors: bool,
 }
 
@@ -69,6 +73,10 @@ impl<'a, 'tcx> Iterator for Autoderef<'a, 'tcx> {
         }
 
         // Otherwise, deref if type is derefable:
+        // NOTE: in the case of self.use_receiver_trait = true, you might think it would
+        // be better to skip this clause and use the Overloaded case only, since &T
+        // and &mut T implement Receiver. But built-in derefs apply equally to Receiver
+        // and Deref, and this has benefits for const and the emitted MIR.
         let (kind, new_ty) =
             if let Some(ty) = self.state.cur_ty.builtin_deref(self.include_raw_pointers) {
                 debug_assert_eq!(ty, self.infcx.resolve_vars_if_possible(ty));
@@ -111,7 +119,7 @@ impl<'a, 'tcx> Autoderef<'a, 'tcx> {
         body_def_id: LocalDefId,
         span: Span,
         base_ty: Ty<'tcx>,
-    ) -> Autoderef<'a, 'tcx> {
+    ) -> Self {
         Autoderef {
             infcx,
             span,
@@ -125,6 +133,7 @@ impl<'a, 'tcx> Autoderef<'a, 'tcx> {
                 reached_recursion_limit: false,
             },
             include_raw_pointers: false,
+            use_receiver_trait: false,
             silence_errors: false,
         }
     }
@@ -137,8 +146,13 @@ impl<'a, 'tcx> Autoderef<'a, 'tcx> {
             return None;
         }
 
-        // <ty as Deref>
-        let trait_ref = ty::TraitRef::new(tcx, tcx.lang_items().deref_trait()?, [ty]);
+        // <ty as Deref>, or whatever the equivalent trait is that we've been asked to walk.
+        let (trait_def_id, trait_target_def_id) = if self.use_receiver_trait {
+            (tcx.lang_items().receiver_trait()?, tcx.lang_items().receiver_target()?)
+        } else {
+            (tcx.lang_items().deref_trait()?, tcx.lang_items().deref_target()?)
+        };
+        let trait_ref = ty::TraitRef::new(tcx, trait_def_id, [ty]);
         let cause = traits::ObligationCause::misc(self.span, self.body_id);
         let obligation = traits::Obligation::new(
             tcx,
@@ -151,11 +165,8 @@ impl<'a, 'tcx> Autoderef<'a, 'tcx> {
             return None;
         }
 
-        let (normalized_ty, obligations) = self.structurally_normalize(Ty::new_projection(
-            tcx,
-            tcx.lang_items().deref_target()?,
-            [ty],
-        ))?;
+        let (normalized_ty, obligations) =
+            self.structurally_normalize(Ty::new_projection(tcx, trait_target_def_id, [ty]))?;
         debug!("overloaded_deref_ty({:?}) = ({:?}, {:?})", ty, normalized_ty, obligations);
         self.state.obligations.extend(obligations);
 
@@ -234,6 +245,14 @@ impl<'a, 'tcx> Autoderef<'a, 'tcx> {
         self
     }
 
+    /// Use `core::ops::Receiver` and `core::ops::Receiver::Target` as
+    /// the trait and associated type to iterate, instead of
+    /// `core::ops::Deref` and `core::ops::Deref::Target`
+    pub fn use_receiver_trait(mut self) -> Self {
+        self.use_receiver_trait = true;
+        self
+    }
+
     pub fn silence_errors(mut self) -> Self {
         self.silence_errors = true;
         self