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

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/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,
@@ -1630,13 +1629,6 @@ 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>,
@@ -1669,55 +1661,21 @@ 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);
 
-    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(
@@ -1726,15 +1684,13 @@ 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 => {
                         let hint = match receiver_ty
@@ -1748,7 +1704,7 @@ fn check_method_receiver<'tcx>(
                                     wfcx,
                                     span,
                                     receiver_ty,
-                                    arbitrary_self_types_level,
+                                    arbitrary_self_types_pointers_enabled,
                                 );
                                 None
                             }
@@ -1760,8 +1716,8 @@ fn check_method_receiver<'tcx>(
                         tcx.dcx().emit_err(errors::InvalidGenericReceiverTy { span, receiver_ty })
                     }
                 }
-            }
-        });
+            },
+        );
     }
     Ok(())
 }
@@ -1805,11 +1761,10 @@ 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);
 
@@ -1824,17 +1779,11 @@ 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();
     }
 
@@ -1857,58 +1806,12 @@ 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
-    }
-}
-
 /// Determine whether it _would have_ been possible to use `receiver_ty` as
 /// a self type if it had been `Sized`, so we can show a specialized diagnostic.
 /// This is because it's an easy mistake to `impl<T> Receiver` instead of
@@ -1917,16 +1820,13 @@ fn emit_receiver_not_implemented_errors<'tcx>(
     wfcx: &WfCheckingCtxt<'_, 'tcx>,
     span: Span,
     receiver_ty: Ty<'tcx>,
-    arbitrary_self_types_enabled: Option<ArbitrarySelfTypesLevel>,
+    arbitrary_self_types_pointers_enabled: bool,
 ) {
     let infcx = wfcx.infcx;
     let mut autoderef = Autoderef::new(infcx, wfcx.param_env, wfcx.body_def_id, span, receiver_ty)
         .use_receiver_trait();
 
-    if arbitrary_self_types_enabled.is_some() {
-        autoderef = autoderef.use_receiver_trait();
-    }
-    if arbitrary_self_types_enabled == Some(ArbitrarySelfTypesLevel::WithPointers) {
+    if arbitrary_self_types_pointers_enabled {
         autoderef = autoderef.include_raw_pointers();
     }
 

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();
             }
         }
     }