Arbitrary self types v2: stabilize! [WIP]

Do not merge any time soon - just to see what blows up in test suites
when the old non-arbitrary-self-types paths are removed.

Author: adetaylor

Diff for: 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.

Diff for: 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.

Diff for: 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);

Diff for: compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -30,7 +30,6 @@ use rustc_trait_selection::traits::misc::{
     ConstParamTyImplementationError, type_allowed_to_implement_const_param_ty,
 };
 use rustc_trait_selection::traits::outlives_bounds::InferCtxtExt as _;
-use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt as _;
 use rustc_trait_selection::traits::{
     self, FulfillmentError, Obligation, ObligationCause, ObligationCauseCode, ObligationCtxt,
     WellFormedLoc,
@@ -1629,13 +1628,6 @@ fn check_fn_or_method<'tcx>(
     }
 }
 
-/// The `arbitrary_self_types_pointers` feature implies `arbitrary_self_types`.
-#[derive(Clone, Copy, PartialEq)]
-enum ArbitrarySelfTypesLevel {
-    Basic,        // just arbitrary_self_types
-    WithPointers, // both arbitrary_self_types and arbitrary_self_types_pointers
-}
-
 #[instrument(level = "debug", skip(wfcx))]
 fn check_method_receiver<'tcx>(
     wfcx: &WfCheckingCtxt<'_, 'tcx>,
@@ -1668,13 +1660,6 @@ fn check_method_receiver<'tcx>(
         return Ok(());
     }
 
-    let arbitrary_self_types_level = if tcx.features().arbitrary_self_types_pointers() {
-        Some(ArbitrarySelfTypesLevel::WithPointers)
-    } else if tcx.features().arbitrary_self_types() {
-        Some(ArbitrarySelfTypesLevel::Basic)
-    } else {
-        None
-    };
     let generics = tcx.generics_of(method.def_id);
 
     // yet to do: determine whether self_ty is Sized. If not (most commonly
@@ -1687,46 +1672,19 @@ fn check_method_receiver<'tcx>(
     // exist for this.
     let raw_pointer = is_raw_pointer(receiver_ty);
 
-    let receiver_validity =
-        receiver_is_valid(wfcx, span, receiver_ty, self_ty, arbitrary_self_types_level, generics);
+    let arbitrary_self_types_pointers_enabled = tcx.features().arbitrary_self_types_pointers();
+    let receiver_validity = receiver_is_valid(
+        wfcx,
+        span,
+        receiver_ty,
+        self_ty,
+        arbitrary_self_types_pointers_enabled,
+        generics,
+    );
     if let Err(receiver_validity_err) = receiver_validity {
-        return Err(match arbitrary_self_types_level {
-            // Wherever possible, emit a message advising folks that the features
-            // `arbitrary_self_types` or `arbitrary_self_types_pointers` might
-            // have helped.
-            None if receiver_is_valid(
-                wfcx,
-                span,
-                receiver_ty,
-                self_ty,
-                Some(ArbitrarySelfTypesLevel::Basic),
-                generics,
-            )
-            .is_ok() =>
-            {
-                // Report error; would have worked with `arbitrary_self_types`.
-                feature_err(
-                    &tcx.sess,
-                    sym::arbitrary_self_types,
-                    span,
-                    format!(
-                        "`{receiver_ty}` cannot be used as the type of `self` without \
-                            the `arbitrary_self_types` feature",
-                    ),
-                )
-                .with_help(fluent::hir_analysis_invalid_receiver_ty_help)
-                .emit()
-            }
-            None | Some(ArbitrarySelfTypesLevel::Basic)
-                if receiver_is_valid(
-                    wfcx,
-                    span,
-                    receiver_ty,
-                    self_ty,
-                    Some(ArbitrarySelfTypesLevel::WithPointers),
-                    generics,
-                )
-                .is_ok() =>
+        return Err(
+            if !arbitrary_self_types_pointers_enabled
+                && receiver_is_valid(wfcx, span, receiver_ty, self_ty, true, generics).is_ok()
             {
                 // Report error; would have worked with `arbitrary_self_types_pointers`.
                 feature_err(
@@ -1735,15 +1693,13 @@ fn check_method_receiver<'tcx>(
                     span,
                     format!(
                         "`{receiver_ty}` cannot be used as the type of `self` without \
-                            the `arbitrary_self_types_pointers` feature",
+                                the `arbitrary_self_types_pointers` feature",
                     ),
                 )
                 .with_help(fluent::hir_analysis_invalid_receiver_ty_help)
                 .emit()
-            }
-            _ =>
-            // Report error; would not have worked with `arbitrary_self_types[_pointers]`.
-            {
+            } else {
+                // Report error; would not have worked with `arbitrary_self_types[_pointers]`.
                 match receiver_validity_err {
                     ReceiverValidityError::DoesNotDeref => tcx
                         .dcx()
@@ -1752,8 +1708,8 @@ fn check_method_receiver<'tcx>(
                         tcx.dcx().emit_err(errors::InvalidGenericReceiverTy { span, receiver_ty })
                     }
                 }
-            }
-        });
+            },
+        );
     }
     Ok(())
 }
@@ -1801,11 +1757,10 @@ fn receiver_is_valid<'tcx>(
     span: Span,
     receiver_ty: Ty<'tcx>,
     self_ty: Ty<'tcx>,
-    arbitrary_self_types_enabled: Option<ArbitrarySelfTypesLevel>,
+    arbitrary_self_types_pointers_enabled: bool,
     method_generics: &ty::Generics,
 ) -> Result<(), ReceiverValidityError> {
     let infcx = wfcx.infcx;
-    let tcx = wfcx.tcx();
     let cause =
         ObligationCause::new(span, wfcx.body_def_id, traits::ObligationCauseCode::MethodReceiver);
 
@@ -1820,17 +1775,11 @@ fn receiver_is_valid<'tcx>(
 
     confirm_type_is_not_a_method_generic_param(receiver_ty, method_generics)?;
 
-    let mut autoderef = Autoderef::new(infcx, wfcx.param_env, wfcx.body_def_id, span, receiver_ty);
-
-    // The `arbitrary_self_types` feature allows custom smart pointer
-    // types to be method receivers, as identified by following the Receiver<Target=T>
-    // chain.
-    if arbitrary_self_types_enabled.is_some() {
-        autoderef = autoderef.use_receiver_trait();
-    }
+    let mut autoderef = Autoderef::new(infcx, wfcx.param_env, wfcx.body_def_id, span, receiver_ty)
+        .use_receiver_trait();
 
     // The `arbitrary_self_types_pointers` feature allows raw pointer receivers like `self: *const Self`.
-    if arbitrary_self_types_enabled == Some(ArbitrarySelfTypesLevel::WithPointers) {
+    if arbitrary_self_types_pointers_enabled {
         autoderef = autoderef.include_raw_pointers();
     }
 
@@ -1853,58 +1802,12 @@ fn receiver_is_valid<'tcx>(
             wfcx.register_obligations(autoderef.into_obligations());
             return Ok(());
         }
-
-        // Without `feature(arbitrary_self_types)`, we require that each step in the
-        // deref chain implement `LegacyReceiver`.
-        if arbitrary_self_types_enabled.is_none() {
-            let legacy_receiver_trait_def_id =
-                tcx.require_lang_item(LangItem::LegacyReceiver, Some(span));
-            if !legacy_receiver_is_implemented(
-                wfcx,
-                legacy_receiver_trait_def_id,
-                cause.clone(),
-                potential_self_ty,
-            ) {
-                // We cannot proceed.
-                break;
-            }
-
-            // Register the bound, in case it has any region side-effects.
-            wfcx.register_bound(
-                cause.clone(),
-                wfcx.param_env,
-                potential_self_ty,
-                legacy_receiver_trait_def_id,
-            );
-        }
     }
 
     debug!("receiver_is_valid: type `{:?}` does not deref to `{:?}`", receiver_ty, self_ty);
     Err(ReceiverValidityError::DoesNotDeref)
 }
 
-fn legacy_receiver_is_implemented<'tcx>(
-    wfcx: &WfCheckingCtxt<'_, 'tcx>,
-    legacy_receiver_trait_def_id: DefId,
-    cause: ObligationCause<'tcx>,
-    receiver_ty: Ty<'tcx>,
-) -> bool {
-    let tcx = wfcx.tcx();
-    let trait_ref = ty::TraitRef::new(tcx, legacy_receiver_trait_def_id, [receiver_ty]);
-
-    let obligation = Obligation::new(tcx, cause, wfcx.param_env, trait_ref);
-
-    if wfcx.infcx.predicate_must_hold_modulo_regions(&obligation) {
-        true
-    } else {
-        debug!(
-            "receiver_is_implemented: type `{:?}` does not implement `LegacyReceiver` trait",
-            receiver_ty
-        );
-        false
-    }
-}
-
 fn check_variances_for_type_defn<'tcx>(
     tcx: TyCtxt<'tcx>,
     item: &'tcx hir::Item<'tcx>,

Diff for: compiler/rustc_hir_typeck/src/method/confirm.rs

@@ -531,24 +531,9 @@ impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
                 self.register_predicates(obligations);
             }
             Err(terr) => {
-                if self.tcx.features().arbitrary_self_types() {
-                    self.err_ctxt()
-                        .report_mismatched_types(
-                            &cause,
-                            self.param_env,
-                            method_self_ty,
-                            self_ty,
-                            terr,
-                        )
-                        .emit();
-                } else {
-                    // This has/will have errored in wfcheck, which we cannot depend on from here, as typeck on functions
-                    // may run before wfcheck if the function is used in const eval.
-                    self.dcx().span_delayed_bug(
-                        cause.span,
-                        format!("{self_ty} was a subtype of {method_self_ty} but now is not?"),
-                    );
-                }
+                self.err_ctxt()
+                    .report_mismatched_types(&cause, self.param_env, method_self_ty, self_ty, terr)
+                    .emit();
             }
         }
     }

Diff for: compiler/rustc_hir_typeck/src/method/probe.rs

@@ -476,7 +476,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 let guar = match *ty.kind() {
                     ty::Infer(ty::TyVar(_)) => {
                         let raw_ptr_call = bad_ty.reached_raw_pointer
-                            && !self.tcx.features().arbitrary_self_types();
+                            && !self.tcx.features().arbitrary_self_types_pointers();
                         let mut err = self.err_ctxt().emit_inference_failure_err(
                             self.body_id,
                             span,
@@ -562,73 +562,38 @@ fn method_autoderef_steps<'tcx>(
     let (ref infcx, goal, inference_vars) = tcx.infer_ctxt().build_with_canonical(DUMMY_SP, &goal);
     let ParamEnvAnd { param_env, value: self_ty } = goal;
 
-    // If arbitrary self types is not enabled, we follow the chain of
-    // `Deref<Target=T>`. If arbitrary self types is enabled, we instead
-    // follow the chain of `Receiver<Target=T>`, but we also record whether
-    // such types are reachable by following the (potentially shorter)
-    // chain of `Deref<Target=T>`. We will use the first list when finding
-    // potentially relevant function implementations (e.g. relevant impl blocks)
-    // but the second list when determining types that the receiver may be
-    // converted to, in order to find out which of those methods might actually
-    // be callable.
     let mut autoderef_via_deref =
         Autoderef::new(infcx, param_env, hir::def_id::CRATE_DEF_ID, DUMMY_SP, self_ty)
             .include_raw_pointers()
             .silence_errors();
 
+    let mut autoderef_via_receiver =
+        Autoderef::new(infcx, param_env, hir::def_id::CRATE_DEF_ID, DUMMY_SP, self_ty)
+            .include_raw_pointers()
+            .use_receiver_trait()
+            .silence_errors();
+
     let mut reached_raw_pointer = false;
-    let arbitrary_self_types_enabled =
-        tcx.features().arbitrary_self_types() || tcx.features().arbitrary_self_types_pointers();
-    let (mut steps, reached_recursion_limit): (Vec<_>, bool) = if arbitrary_self_types_enabled {
-        let reachable_via_deref =
-            autoderef_via_deref.by_ref().map(|_| true).chain(std::iter::repeat(false));
-
-        let mut autoderef_via_receiver =
-            Autoderef::new(infcx, param_env, hir::def_id::CRATE_DEF_ID, DUMMY_SP, self_ty)
-                .include_raw_pointers()
-                .use_receiver_trait()
-                .silence_errors();
-        let steps = autoderef_via_receiver
-            .by_ref()
-            .zip(reachable_via_deref)
-            .map(|((ty, d), reachable_via_deref)| {
-                let step = CandidateStep {
-                    self_ty: infcx
-                        .make_query_response_ignoring_pending_obligations(inference_vars, ty),
-                    autoderefs: d,
-                    from_unsafe_deref: reached_raw_pointer,
-                    unsize: false,
-                    reachable_via_deref,
-                };
-                if let ty::RawPtr(_, _) = ty.kind() {
-                    // all the subsequent steps will be from_unsafe_deref
-                    reached_raw_pointer = true;
-                }
-                step
-            })
-            .collect();
-        (steps, autoderef_via_receiver.reached_recursion_limit())
-    } else {
-        let steps = autoderef_via_deref
-            .by_ref()
-            .map(|(ty, d)| {
-                let step = CandidateStep {
-                    self_ty: infcx
-                        .make_query_response_ignoring_pending_obligations(inference_vars, ty),
-                    autoderefs: d,
-                    from_unsafe_deref: reached_raw_pointer,
-                    unsize: false,
-                    reachable_via_deref: true,
-                };
-                if let ty::RawPtr(_, _) = ty.kind() {
-                    // all the subsequent steps will be from_unsafe_deref
-                    reached_raw_pointer = true;
-                }
-                step
-            })
-            .collect();
-        (steps, autoderef_via_deref.reached_recursion_limit())
-    };
+    let reachable_via_deref =
+        autoderef_via_deref.by_ref().map(|_| true).chain(std::iter::repeat(false));
+    let mut steps: Vec<_> = autoderef_via_receiver
+        .by_ref()
+        .zip(reachable_via_deref)
+        .map(|((ty, d), reachable_via_deref)| {
+            let step = CandidateStep {
+                self_ty: infcx.make_query_response_ignoring_pending_obligations(inference_vars, ty),
+                autoderefs: d,
+                from_unsafe_deref: reached_raw_pointer,
+                unsize: false,
+                reachable_via_deref,
+            };
+            if let ty::RawPtr(_, _) = ty.kind() {
+                // all the subsequent steps will be from_unsafe_deref
+                reached_raw_pointer = true;
+            }
+            step
+        })
+        .collect();
     let final_ty = autoderef_via_deref.final_ty(true);
     let opt_bad_ty = match final_ty.kind() {
         ty::Infer(ty::TyVar(_)) | ty::Error(_) => Some(MethodAutoderefBadTy {
@@ -661,7 +626,7 @@ fn method_autoderef_steps<'tcx>(
     MethodAutoderefStepsResult {
         steps: tcx.arena.alloc_from_iter(steps),
         opt_bad_ty: opt_bad_ty.map(|ty| &*tcx.arena.alloc(ty)),
-        reached_recursion_limit,
+        reached_recursion_limit: autoderef_via_receiver.reached_recursion_limit(),
     }
 }