Rollup of 9 pull requests

compiler/rustc_hir_analysis/src/check/check.rs

@@ -576,7 +576,6 @@ fn find_and_apply_rpit_args<'tcx>(
     struct Visitor<'tcx> {
         tcx: TyCtxt<'tcx>,
         opaque: DefId,
-        function: DefId,
         seen: FxHashSet<DefId>,
     }
     impl<'tcx> ty::TypeVisitor<TyCtxt<'tcx>> for Visitor<'tcx> {
@@ -601,19 +600,6 @@ fn find_and_apply_rpit_args<'tcx>(
                         }
                     }
                 }
-                ty::Alias(ty::Projection, alias) => {
-                    if self.tcx.is_impl_trait_in_trait(alias.def_id)
-                        && self.tcx.impl_trait_in_trait_parent_fn(alias.def_id) == self.function
-                    {
-                        // If we're lowering to associated item, install the opaque type which is just
-                        // the `type_of` of the trait's associated item. If we're using the old lowering
-                        // strategy, then just reinterpret the associated type like an opaque :^)
-                        self.tcx
-                            .type_of(alias.def_id)
-                            .instantiate(self.tcx, alias.args)
-                            .visit_with(self)?;
-                    }
-                }
                 ty::Alias(ty::Weak, alias) => {
                     self.tcx
                         .type_of(alias.def_id)
@@ -627,7 +613,7 @@ fn find_and_apply_rpit_args<'tcx>(
         }
     }
     if let ControlFlow::Break(args) =
-        ret.visit_with(&mut Visitor { tcx, function, opaque, seen: Default::default() })
+        ret.visit_with(&mut Visitor { tcx, opaque, seen: Default::default() })
     {
         trace!(?args);
         trace!("expected: {hidden_ty:#?}");

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -246,8 +246,11 @@ fn check_item<'tcx>(tcx: TyCtxt<'tcx>, item: &'tcx hir::Item<'tcx>) {
         // `ForeignItem`s are handled separately.
         hir::ItemKind::ForeignMod { .. } => {}
         hir::ItemKind::TyAlias(hir_ty, ..) => {
-            if tcx.type_of(item.owner_id.def_id).skip_binder().has_opaque_types() {
-                // Bounds are respected for `type X = impl Trait` and `type X = (impl Trait, Y);`
+            if tcx.features().lazy_type_alias
+                || tcx.type_of(item.owner_id).skip_binder().has_opaque_types()
+            {
+                // Bounds of lazy type aliases and of eager ones that contain opaque types are respected.
+                // E.g: `type X = impl Trait;`, `type X = (impl Trait, Y);`.
                 check_item_type(tcx, def_id, hir_ty.span, UnsizedHandling::Allow);
             }
         }

compiler/rustc_hir_analysis/src/collect/item_bounds.rs

@@ -3,7 +3,7 @@ use crate::astconv::{AstConv, PredicateFilter};
 use rustc_hir as hir;
 use rustc_infer::traits::util;
 use rustc_middle::ty::GenericArgs;
-use rustc_middle::ty::{self, Ty, TyCtxt};
+use rustc_middle::ty::{self, Ty, TyCtxt, TypeFoldable, TypeFolder};
 use rustc_span::def_id::{DefId, LocalDefId};
 use rustc_span::Span;
 
@@ -113,14 +113,35 @@ pub(super) fn explicit_item_bounds(
             ..
         }) => associated_type_bounds(tcx, def_id, bounds, *span),
         hir::Node::Item(hir::Item {
-            kind: hir::ItemKind::OpaqueTy(hir::OpaqueTy { bounds, .. }),
+            kind: hir::ItemKind::OpaqueTy(hir::OpaqueTy { bounds, in_trait: false, .. }),
             span,
             ..
         }) => {
             let args = GenericArgs::identity_for_item(tcx, def_id);
             let item_ty = Ty::new_opaque(tcx, def_id.to_def_id(), args);
             opaque_type_bounds(tcx, def_id, bounds, item_ty, *span)
         }
+        // Since RPITITs are astconv'd as projections in `ast_ty_to_ty`, when we're asking
+        // for the item bounds of the *opaques* in a trait's default method signature, we
+        // need to map these projections back to opaques.
+        hir::Node::Item(hir::Item {
+            kind: hir::ItemKind::OpaqueTy(hir::OpaqueTy { bounds, in_trait: true, origin, .. }),
+            span,
+            ..
+        }) => {
+            let (hir::OpaqueTyOrigin::FnReturn(fn_def_id)
+            | hir::OpaqueTyOrigin::AsyncFn(fn_def_id)) = *origin
+            else {
+                bug!()
+            };
+            let args = GenericArgs::identity_for_item(tcx, def_id);
+            let item_ty = Ty::new_opaque(tcx, def_id.to_def_id(), args);
+            tcx.arena.alloc_slice(
+                &opaque_type_bounds(tcx, def_id, bounds, item_ty, *span)
+                    .to_vec()
+                    .fold_with(&mut AssocTyToOpaque { tcx, fn_def_id: fn_def_id.to_def_id() }),
+            )
+        }
         hir::Node::Item(hir::Item { kind: hir::ItemKind::TyAlias(..), .. }) => &[],
         _ => bug!("item_bounds called on {:?}", def_id),
     };
@@ -135,3 +156,26 @@ pub(super) fn item_bounds(
         tcx.mk_clauses_from_iter(util::elaborate(tcx, bounds.iter().map(|&(bound, _span)| bound)))
     })
 }
+
+struct AssocTyToOpaque<'tcx> {
+    tcx: TyCtxt<'tcx>,
+    fn_def_id: DefId,
+}
+
+impl<'tcx> TypeFolder<TyCtxt<'tcx>> for AssocTyToOpaque<'tcx> {
+    fn interner(&self) -> TyCtxt<'tcx> {
+        self.tcx
+    }
+
+    fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
+        if let ty::Alias(ty::Projection, projection_ty) = ty.kind()
+            && let Some(ty::ImplTraitInTraitData::Trait { fn_def_id, .. })
+                = self.tcx.opt_rpitit_info(projection_ty.def_id)
+            && fn_def_id == self.fn_def_id
+        {
+            self.tcx.type_of(projection_ty.def_id).instantiate(self.tcx, projection_ty.args)
+        } else {
+            ty
+        }
+    }
+}

compiler/rustc_hir_typeck/src/_match.rs

@@ -558,18 +558,17 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     {
                         let pred = clause.kind().rebind(match clause.kind().skip_binder() {
                             ty::ClauseKind::Trait(trait_pred) => {
-                                // FIXME(rpitit): This will need to be fixed when we move to associated types
                                 assert!(matches!(
                                     *trait_pred.trait_ref.self_ty().kind(),
-                                    ty::Alias(_, ty::AliasTy { def_id, args: alias_args, .. })
+                                    ty::Alias(ty::Opaque, ty::AliasTy { def_id, args: alias_args, .. })
                                     if def_id == rpit_def_id && args == alias_args
                                 ));
                                 ty::ClauseKind::Trait(trait_pred.with_self_ty(self.tcx, ty))
                             }
                             ty::ClauseKind::Projection(mut proj_pred) => {
                                 assert!(matches!(
                                     *proj_pred.projection_ty.self_ty().kind(),
-                                    ty::Alias(_, ty::AliasTy { def_id, args: alias_args, .. })
+                                    ty::Alias(ty::Opaque, ty::AliasTy { def_id, args: alias_args, .. })
                                     if def_id == rpit_def_id && args == alias_args
                                 ));
                                 proj_pred = proj_pred.with_self_ty(self.tcx, ty);

compiler/rustc_hir_typeck/src/closure.rs

@@ -723,11 +723,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 .iter_instantiated_copied(self.tcx, args)
                 .find_map(|(p, s)| get_future_output(p.as_predicate(), s))?,
             ty::Error(_) => return None,
-            ty::Alias(ty::Projection, proj) if self.tcx.is_impl_trait_in_trait(proj.def_id) => self
-                .tcx
-                .explicit_item_bounds(proj.def_id)
-                .iter_instantiated_copied(self.tcx, proj.args)
-                .find_map(|(p, s)| get_future_output(p.as_predicate(), s))?,
             _ => span_bug!(
                 self.tcx.def_span(expr_def_id),
                 "async fn generator return type not an inference variable: {ret_ty}"

compiler/rustc_infer/src/infer/opaque_types.rs

@@ -619,13 +619,6 @@ impl<'tcx> InferCtxt<'tcx> {
                     {
                         hidden_ty
                     }
-                    // FIXME(RPITIT): This can go away when we move to associated types
-                    // FIXME(inherent_associated_types): Extend this to support `ty::Inherent`, too.
-                    ty::Alias(ty::Projection, ty::AliasTy { def_id: def_id2, args: args2, .. })
-                        if def_id == def_id2 && args == args2 =>
-                    {
-                        hidden_ty
-                    }
                     _ => ty,
                 },
                 lt_op: |lt| lt,

compiler/rustc_lint/src/builtin.rs

@@ -1458,15 +1458,20 @@ impl TypeAliasBounds {
 
 impl<'tcx> LateLintPass<'tcx> for TypeAliasBounds {
     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
-        let hir::ItemKind::TyAlias(ty, type_alias_generics) = &item.kind else { return };
-        if cx.tcx.type_of(item.owner_id.def_id).skip_binder().has_opaque_types() {
-            // Bounds are respected for `type X = impl Trait` and `type X = (impl Trait, Y);`
+        let hir::ItemKind::TyAlias(hir_ty, type_alias_generics) = &item.kind else { return };
+
+        if cx.tcx.features().lazy_type_alias {
+            // Bounds of lazy type aliases are respected.
             return;
         }
-        if cx.tcx.type_of(item.owner_id).skip_binder().has_inherent_projections() {
-            // Bounds are respected for `type X = … Type::Inherent …`
+
+        let ty = cx.tcx.type_of(item.owner_id).skip_binder();
+        if ty.has_opaque_types() || ty.has_inherent_projections() {
+            // Bounds of type aliases that contain opaque types or inherent projections are respected.
+            // E.g: `type X = impl Trait;`, `type X = (impl Trait, Y);`, `type X = Type::Inherent;`.
             return;
         }
+
         // There must not be a where clause
         if type_alias_generics.predicates.is_empty() {
             return;
@@ -1491,7 +1496,7 @@ impl<'tcx> LateLintPass<'tcx> for TypeAliasBounds {
         if !where_spans.is_empty() {
             let sub = (!suggested_changing_assoc_types).then(|| {
                 suggested_changing_assoc_types = true;
-                SuggestChangingAssocTypes { ty }
+                SuggestChangingAssocTypes { ty: hir_ty }
             });
             cx.emit_spanned_lint(
                 TYPE_ALIAS_BOUNDS,
@@ -1507,7 +1512,7 @@ impl<'tcx> LateLintPass<'tcx> for TypeAliasBounds {
             let suggestion = BuiltinTypeAliasGenericBoundsSuggestion { suggestions: inline_sugg };
             let sub = (!suggested_changing_assoc_types).then(|| {
                 suggested_changing_assoc_types = true;
-                SuggestChangingAssocTypes { ty }
+                SuggestChangingAssocTypes { ty: hir_ty }
             });
             cx.emit_spanned_lint(
                 TYPE_ALIAS_BOUNDS,

compiler/rustc_lint/src/multiple_supertrait_upcastable.rs

@@ -10,6 +10,7 @@ declare_lint! {
     /// ### Example
     ///
     /// ```rust
+    /// #![feature(multiple_supertrait_upcastable)]
     /// trait A {}
     /// trait B {}
     ///

compiler/rustc_middle/src/traits/solve.rs

@@ -57,6 +57,7 @@ pub enum Certainty {
 
 impl Certainty {
     pub const AMBIGUOUS: Certainty = Certainty::Maybe(MaybeCause::Ambiguity);
+    pub const OVERFLOW: Certainty = Certainty::Maybe(MaybeCause::Overflow);
 
     /// Use this function to merge the certainty of multiple nested subgoals.
     ///
@@ -66,7 +67,7 @@ impl Certainty {
     /// success, we merge these two responses. This results in ambiguity.
     ///
     /// If we unify ambiguity with overflow, we return overflow. This doesn't matter
-    /// inside of the solver as we distinguish ambiguity from overflow. It does
+    /// inside of the solver as we do not distinguish ambiguity from overflow. It does
     /// however matter for diagnostics. If `T: Foo` resulted in overflow and `T: Bar`
     /// in ambiguity without changing the inference state, we still want to tell the
     /// user that `T: Baz` results in overflow.

compiler/rustc_middle/src/ty/mod.rs

@@ -1359,12 +1359,24 @@ impl<'tcx> ToPredicate<'tcx, Clause<'tcx>> for PolyTraitPredicate<'tcx> {
     }
 }
 
+impl<'tcx> ToPredicate<'tcx> for OutlivesPredicate<ty::Region<'tcx>, ty::Region<'tcx>> {
+    fn to_predicate(self, tcx: TyCtxt<'tcx>) -> Predicate<'tcx> {
+        ty::Binder::dummy(PredicateKind::Clause(ClauseKind::RegionOutlives(self))).to_predicate(tcx)
+    }
+}
+
 impl<'tcx> ToPredicate<'tcx> for PolyRegionOutlivesPredicate<'tcx> {
     fn to_predicate(self, tcx: TyCtxt<'tcx>) -> Predicate<'tcx> {
         self.map_bound(|p| PredicateKind::Clause(ClauseKind::RegionOutlives(p))).to_predicate(tcx)
     }
 }
 
+impl<'tcx> ToPredicate<'tcx> for OutlivesPredicate<Ty<'tcx>, ty::Region<'tcx>> {
+    fn to_predicate(self, tcx: TyCtxt<'tcx>) -> Predicate<'tcx> {
+        ty::Binder::dummy(PredicateKind::Clause(ClauseKind::TypeOutlives(self))).to_predicate(tcx)
+    }
+}
+
 impl<'tcx> ToPredicate<'tcx> for PolyTypeOutlivesPredicate<'tcx> {
     fn to_predicate(self, tcx: TyCtxt<'tcx>) -> Predicate<'tcx> {
         self.map_bound(|p| PredicateKind::Clause(ClauseKind::TypeOutlives(p))).to_predicate(tcx)
@@ -2613,19 +2625,6 @@ impl<'tcx> TyCtxt<'tcx> {
         matches!(self.trait_of_item(def_id), Some(trait_id) if self.has_attr(trait_id, sym::const_trait))
     }
 
-    pub fn impl_trait_in_trait_parent_fn(self, mut def_id: DefId) -> DefId {
-        match self.opt_rpitit_info(def_id) {
-            Some(ImplTraitInTraitData::Trait { fn_def_id, .. })
-            | Some(ImplTraitInTraitData::Impl { fn_def_id, .. }) => fn_def_id,
-            None => {
-                while let def_kind = self.def_kind(def_id) && def_kind != DefKind::AssocFn {
-                    def_id = self.parent(def_id);
-                }
-                def_id
-            }
-        }
-    }
-
     /// Returns the `DefId` of the item within which the `impl Trait` is declared.
     /// For type-alias-impl-trait this is the `type` alias.
     /// For impl-trait-in-assoc-type this is the assoc type.

compiler/rustc_trait_selection/src/solve/assembly/mod.rs

@@ -7,7 +7,7 @@ use rustc_hir::def_id::DefId;
 use rustc_infer::traits::query::NoSolution;
 use rustc_infer::traits::Reveal;
 use rustc_middle::traits::solve::inspect::CandidateKind;
-use rustc_middle::traits::solve::{CanonicalResponse, Certainty, Goal, MaybeCause, QueryResult};
+use rustc_middle::traits::solve::{CanonicalResponse, Certainty, Goal, QueryResult};
 use rustc_middle::traits::BuiltinImplSource;
 use rustc_middle::ty::fast_reject::{SimplifiedType, TreatParams};
 use rustc_middle::ty::{self, Ty, TyCtxt};
@@ -299,7 +299,7 @@ pub(super) trait GoalKind<'tcx>:
     /// for unsize coercion in hir typeck and because it is difficult to
     /// otherwise recompute this for codegen. This is a bit of a mess but the
     /// easiest way to maintain the existing behavior for now.
-    fn consider_builtin_unsize_and_upcast_candidates(
+    fn consider_builtin_unsize_candidates(
         ecx: &mut EvalCtxt<'_, 'tcx>,
         goal: Goal<'tcx, Self>,
     ) -> Vec<(CanonicalResponse<'tcx>, BuiltinImplSource)>;
@@ -402,7 +402,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
                 ecx.with_incremented_depth(
                     |ecx| {
                         let result = ecx.evaluate_added_goals_and_make_canonical_response(
-                            Certainty::Maybe(MaybeCause::Overflow),
+                            Certainty::OVERFLOW,
                         )?;
                         Ok(vec![Candidate {
                             source: CandidateSource::BuiltinImpl(BuiltinImplSource::Misc),
@@ -624,7 +624,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
         // There may be multiple unsize candidates for a trait with several supertraits:
         // `trait Foo: Bar<A> + Bar<B>` and `dyn Foo: Unsize<dyn Bar<_>>`
         if lang_items.unsize_trait() == Some(trait_def_id) {
-            for (result, source) in G::consider_builtin_unsize_and_upcast_candidates(self, goal) {
+            for (result, source) in G::consider_builtin_unsize_candidates(self, goal) {
                 candidates.push(Candidate { source: CandidateSource::BuiltinImpl(source), result });
             }
         }

compiler/rustc_trait_selection/src/solve/eval_ctxt.rs

@@ -11,8 +11,8 @@ use rustc_infer::traits::ObligationCause;
 use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
 use rustc_middle::traits::solve::inspect;
 use rustc_middle::traits::solve::{
-    CanonicalInput, CanonicalResponse, Certainty, IsNormalizesToHack, MaybeCause,
-    PredefinedOpaques, PredefinedOpaquesData, QueryResult,
+    CanonicalInput, CanonicalResponse, Certainty, IsNormalizesToHack, PredefinedOpaques,
+    PredefinedOpaquesData, QueryResult,
 };
 use rustc_middle::traits::DefiningAnchor;
 use rustc_middle::ty::{
@@ -475,7 +475,7 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
         let mut new_goals = NestedGoals::new();
 
         let response = self.repeat_while_none(
-            |_| Ok(Certainty::Maybe(MaybeCause::Overflow)),
+            |_| Ok(Certainty::OVERFLOW),
             |this| {
                 this.inspect.evaluate_added_goals_loop_start();
 

compiler/rustc_trait_selection/src/solve/eval_ctxt/select.rs

@@ -338,7 +338,7 @@ fn rematch_unsize<'tcx>(
                     .into_obligations(),
             );
 
-            // Similar to ADTs, require that the rest of the fields are equal.
+            // Similar to ADTs, require that we can unsize the tail.
             nested.push(Obligation::new(
                 tcx,
                 ObligationCause::dummy(),

compiler/rustc_trait_selection/src/solve/project_goals.rs

@@ -503,7 +503,7 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> {
         )
     }
 
-    fn consider_builtin_unsize_and_upcast_candidates(
+    fn consider_builtin_unsize_candidates(
         _ecx: &mut EvalCtxt<'_, 'tcx>,
         goal: Goal<'tcx, Self>,
     ) -> Vec<(CanonicalResponse<'tcx>, BuiltinImplSource)> {

compiler/rustc_trait_selection/src/solve/search_graph/mod.rs

@@ -9,9 +9,7 @@ use cache::ProvisionalCache;
 use overflow::OverflowData;
 use rustc_index::IndexVec;
 use rustc_middle::dep_graph::DepKind;
-use rustc_middle::traits::solve::{
-    CanonicalInput, Certainty, EvaluationCache, MaybeCause, QueryResult,
-};
+use rustc_middle::traits::solve::{CanonicalInput, Certainty, EvaluationCache, QueryResult};
 use rustc_middle::ty::TyCtxt;
 use std::{collections::hash_map::Entry, mem};
 
@@ -146,11 +144,7 @@ impl<'tcx> SearchGraph<'tcx> {
                 {
                     Err(cache.provisional_result(entry_index))
                 } else {
-                    Err(super::response_no_constraints(
-                        tcx,
-                        input,
-                        Certainty::Maybe(MaybeCause::Overflow),
-                    ))
+                    Err(super::response_no_constraints(tcx, input, Certainty::OVERFLOW))
                 }
             }
         }

compiler/rustc_trait_selection/src/solve/search_graph/overflow.rs

@@ -1,6 +1,6 @@
 use rustc_infer::infer::canonical::Canonical;
 use rustc_infer::traits::query::NoSolution;
-use rustc_middle::traits::solve::{Certainty, MaybeCause, QueryResult};
+use rustc_middle::traits::solve::{Certainty, QueryResult};
 use rustc_middle::ty::TyCtxt;
 use rustc_session::Limit;
 
@@ -115,6 +115,6 @@ impl<'tcx> SearchGraph<'tcx> {
         goal: Canonical<'tcx, impl Sized>,
     ) -> QueryResult<'tcx> {
         self.overflow_data.deal_with_overflow();
-        response_no_constraints(tcx, goal, Certainty::Maybe(MaybeCause::Overflow))
+        response_no_constraints(tcx, goal, Certainty::OVERFLOW)
     }
 }