]> git.proxmox.com Git - rustc.git/blobdiff - compiler/rustc_hir_analysis/src/astconv/mod.rs
New upstream version 1.68.2+dfsg1
[rustc.git] / compiler / rustc_hir_analysis / src / astconv / mod.rs
index 78d204d470d32ebea861f0d0fb49341435d4e86a..6435b05cef8a8bac5041a2fe8db5207c5d9b86d9 100644 (file)
@@ -3,8 +3,11 @@
 //! instance of `AstConv`.
 
 mod errors;
-mod generics;
+pub mod generics;
 
+use crate::astconv::generics::{
+    check_generic_arg_count, create_substs_for_generic_args, prohibit_assoc_ty_binding,
+};
 use crate::bounds::Bounds;
 use crate::collect::HirPlaceholderCollector;
 use crate::errors::{
@@ -24,13 +27,12 @@ use rustc_hir::def::{CtorOf, DefKind, Namespace, Res};
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::intravisit::{walk_generics, Visitor as _};
 use rustc_hir::{GenericArg, GenericArgs, OpaqueTyOrigin};
+use rustc_infer::infer::TyCtxtInferExt;
 use rustc_middle::middle::stability::AllowUnstable;
 use rustc_middle::ty::subst::{self, GenericArgKind, InternalSubsts, SubstsRef};
-use rustc_middle::ty::DynKind;
 use rustc_middle::ty::GenericParamDefKind;
-use rustc_middle::ty::{
-    self, Const, DefIdTree, EarlyBinder, IsSuggestable, Ty, TyCtxt, TypeVisitable,
-};
+use rustc_middle::ty::{self, Const, DefIdTree, IsSuggestable, Ty, TyCtxt, TypeVisitable};
+use rustc_middle::ty::{DynKind, EarlyBinder};
 use rustc_session::lint::builtin::{AMBIGUOUS_ASSOCIATED_ITEMS, BARE_TRAIT_OBJECTS};
 use rustc_span::edition::Edition;
 use rustc_span::lev_distance::find_best_match_for_name;
@@ -108,11 +110,12 @@ pub trait AstConv<'tcx> {
         poly_trait_ref: ty::PolyTraitRef<'tcx>,
     ) -> Ty<'tcx>;
 
-    /// Normalize an associated type coming from the user.
-    ///
-    /// This should only be used by astconv. Use `FnCtxt::normalize`
-    /// or `ObligationCtxt::normalize` in downstream crates.
-    fn normalize_ty(&self, span: Span, ty: Ty<'tcx>) -> Ty<'tcx>;
+    /// Returns `AdtDef` if `ty` is an ADT.
+    /// Note that `ty` might be a projection type that needs normalization.
+    /// This used to get the enum variants in scope of the type.
+    /// For example, `Self::A` could refer to an associated type
+    /// or to an enum variant depending on the result of this function.
+    fn probe_adt(&self, span: Span, ty: Ty<'tcx>) -> Option<ty::AdtDef<'tcx>>;
 
     /// Invoked when we encounter an error from some prior pass
     /// (e.g., resolve) that is translated into a ty-error. This is
@@ -121,6 +124,13 @@ pub trait AstConv<'tcx> {
     fn set_tainted_by_errors(&self, e: ErrorGuaranteed);
 
     fn record_ty(&self, hir_id: hir::HirId, ty: Ty<'tcx>, span: Span);
+
+    fn astconv(&self) -> &dyn AstConv<'tcx>
+    where
+        Self: Sized,
+    {
+        self
+    }
 }
 
 #[derive(Debug)]
@@ -280,7 +290,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             ty::BoundConstness::NotConst,
         );
         if let Some(b) = item_segment.args().bindings.first() {
-            Self::prohibit_assoc_ty_binding(self.tcx(), b.span);
+            prohibit_assoc_ty_binding(self.tcx(), b.span);
         }
 
         substs
@@ -350,7 +360,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             assert!(self_ty.is_none());
         }
 
-        let arg_count = Self::check_generic_arg_count(
+        let arg_count = check_generic_arg_count(
             tcx,
             span,
             def_id,
@@ -487,13 +497,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                                 // Avoid ICE #86756 when type error recovery goes awry.
                                 return tcx.ty_error().into();
                             }
-                            self.astconv
-                                .normalize_ty(
-                                    self.span,
-                                    EarlyBinder(tcx.at(self.span).type_of(param.def_id))
-                                        .subst(tcx, substs),
-                                )
-                                .into()
+                            tcx.at(self.span).bound_type_of(param.def_id).subst(tcx, substs).into()
                         } else if infer_args {
                             self.astconv.ty_infer(Some(param), self.span).into()
                         } else {
@@ -507,9 +511,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                             return tcx.const_error(ty).into();
                         }
                         if !infer_args && has_default {
-                            tcx.bound_const_param_default(param.def_id)
-                                .subst(tcx, substs.unwrap())
-                                .into()
+                            tcx.const_param_default(param.def_id).subst(tcx, substs.unwrap()).into()
                         } else {
                             if infer_args {
                                 self.astconv.ct_infer(ty, Some(param), self.span).into()
@@ -531,7 +533,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             inferred_params: vec![],
             infer_args,
         };
-        let substs = Self::create_substs_for_generic_args(
+        let substs = create_substs_for_generic_args(
             tcx,
             def_id,
             parent_substs,
@@ -567,17 +569,17 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             .bindings
             .iter()
             .map(|binding| {
-                let kind = match binding.kind {
-                    hir::TypeBindingKind::Equality { ref term } => match term {
-                        hir::Term::Ty(ref ty) => {
+                let kind = match &binding.kind {
+                    hir::TypeBindingKind::Equality { term } => match term {
+                        hir::Term::Ty(ty) => {
                             ConvertedBindingKind::Equality(self.ast_ty_to_ty(ty).into())
                         }
-                        hir::Term::Const(ref c) => {
+                        hir::Term::Const(c) => {
                             let c = Const::from_anon_const(self.tcx(), c.def_id);
                             ConvertedBindingKind::Equality(c.into())
                         }
                     },
-                    hir::TypeBindingKind::Constraint { ref bounds } => {
+                    hir::TypeBindingKind::Constraint { bounds } => {
                         ConvertedBindingKind::Constraint(bounds)
                     }
                 };
@@ -617,7 +619,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         );
 
         if let Some(b) = item_segment.args().bindings.first() {
-            Self::prohibit_assoc_ty_binding(self.tcx(), b.span);
+            prohibit_assoc_ty_binding(self.tcx(), b.span);
         }
 
         args
@@ -680,10 +682,10 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         let assoc_bindings = self.create_assoc_bindings_for_generic_args(args);
 
         let poly_trait_ref =
-            ty::Binder::bind_with_vars(ty::TraitRef::new(trait_def_id, substs), bound_vars);
+            ty::Binder::bind_with_vars(tcx.mk_trait_ref(trait_def_id, substs), bound_vars);
 
         debug!(?poly_trait_ref, ?assoc_bindings);
-        bounds.trait_bounds.push((poly_trait_ref, span, constness));
+        bounds.push_trait_bound(tcx, poly_trait_ref, span, constness);
 
         let mut dup_bindings = FxHashMap::default();
         for binding in &assoc_bindings {
@@ -811,9 +813,9 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             constness,
         );
         if let Some(b) = trait_segment.args().bindings.first() {
-            Self::prohibit_assoc_ty_binding(self.tcx(), b.span);
+            prohibit_assoc_ty_binding(self.tcx(), b.span);
         }
-        ty::TraitRef::new(trait_def_id, substs)
+        self.tcx().mk_trait_ref(trait_def_id, substs)
     }
 
     #[instrument(level = "debug", skip(self, span))]
@@ -854,18 +856,19 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
     }
 
     /// Sets `implicitly_sized` to true on `Bounds` if necessary
-    pub(crate) fn add_implicitly_sized<'hir>(
+    pub(crate) fn add_implicitly_sized(
         &self,
-        bounds: &mut Bounds<'hir>,
-        ast_bounds: &'hir [hir::GenericBound<'hir>],
-        self_ty_where_predicates: Option<(LocalDefId, &'hir [hir::WherePredicate<'hir>])>,
+        bounds: &mut Bounds<'tcx>,
+        self_ty: Ty<'tcx>,
+        ast_bounds: &'tcx [hir::GenericBound<'tcx>],
+        self_ty_where_predicates: Option<(LocalDefId, &'tcx [hir::WherePredicate<'tcx>])>,
         span: Span,
     ) {
         let tcx = self.tcx();
 
         // Try to find an unbound in bounds.
         let mut unbound = None;
-        let mut search_bounds = |ast_bounds: &'hir [hir::GenericBound<'hir>]| {
+        let mut search_bounds = |ast_bounds: &'tcx [hir::GenericBound<'tcx>]| {
             for ab in ast_bounds {
                 if let hir::GenericBound::Trait(ptr, hir::TraitBoundModifier::Maybe) = ab {
                     if unbound.is_none() {
@@ -913,7 +916,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             // No lang item for `Sized`, so we can't add it as a bound.
             return;
         }
-        bounds.implicitly_sized = Some(span);
+        bounds.push_sized(tcx, self_ty, span);
     }
 
     /// This helper takes a *converted* parameter type (`param_ty`)
@@ -964,10 +967,14 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 }
                 hir::GenericBound::Outlives(lifetime) => {
                     let region = self.ast_region_to_region(lifetime, None);
-                    bounds.region_bounds.push((
-                        ty::Binder::bind_with_vars(region, bound_vars),
+                    bounds.push_region_bound(
+                        self.tcx(),
+                        ty::Binder::bind_with_vars(
+                            ty::OutlivesPredicate(param_ty, region),
+                            bound_vars,
+                        ),
                         lifetime.ident.span,
-                    ));
+                    );
                 }
             }
         }
@@ -985,7 +992,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
     /// ```
     ///
     /// The `sized_by_default` parameter indicates if, in this context, the `param_ty` should be
-    /// considered `Sized` unless there is an explicit `?Sized` bound.  This would be true in the
+    /// considered `Sized` unless there is an explicit `?Sized` bound. This would be true in the
     /// example above, but is not true in supertrait listings like `trait Foo: Bar + Baz`.
     ///
     /// `span` should be the declaration size of the parameter.
@@ -1146,10 +1153,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
 
             debug!(?substs_trait_ref_and_assoc_item);
 
-            ty::ProjectionTy {
-                item_def_id: assoc_item.def_id,
-                substs: substs_trait_ref_and_assoc_item,
-            }
+            self.tcx().mk_alias_ty(assoc_item.def_id, substs_trait_ref_and_assoc_item)
         });
 
         if !speculative {
@@ -1195,7 +1199,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 // the "projection predicate" for:
                 //
                 // `<T as Iterator>::Item = u32`
-                let assoc_item_def_id = projection_ty.skip_binder().item_def_id;
+                let assoc_item_def_id = projection_ty.skip_binder().def_id;
                 let def_kind = tcx.def_kind(assoc_item_def_id);
                 match (def_kind, term.unpack()) {
                     (hir::def::DefKind::AssocTy, ty::TermKind::Ty(_))
@@ -1203,17 +1207,26 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     (_, _) => {
                         let got = if let Some(_) = term.ty() { "type" } else { "constant" };
                         let expected = def_kind.descr(assoc_item_def_id);
-                        let reported = tcx
-                            .sess
-                            .struct_span_err(
+                        let mut err = tcx.sess.struct_span_err(
+                            binding.span,
+                            &format!("expected {expected} bound, found {got}"),
+                        );
+                        err.span_note(
+                            tcx.def_span(assoc_item_def_id),
+                            &format!("{expected} defined here"),
+                        );
+
+                        if let hir::def::DefKind::AssocConst = def_kind
+                          && let Some(t) = term.ty() && (t.is_enum() || t.references_error())
+                          && tcx.features().associated_const_equality {
+                            err.span_suggestion(
                                 binding.span,
-                                &format!("expected {expected} bound, found {got}"),
-                            )
-                            .span_note(
-                                tcx.def_span(assoc_item_def_id),
-                                &format!("{expected} defined here"),
-                            )
-                            .emit();
+                                "if equating a const, try wrapping with braces",
+                                format!("{} = {{ const }}", binding.item_name),
+                                Applicability::HasPlaceholders,
+                            );
+                        }
+                        let reported = err.emit();
                         term = match def_kind {
                             hir::def::DefKind::AssocTy => {
                                 tcx.ty_error_with_guaranteed(reported).into()
@@ -1229,13 +1242,12 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                         };
                     }
                 }
-                bounds.projection_bounds.push((
-                    projection_ty.map_bound(|projection_ty| ty::ProjectionPredicate {
-                        projection_ty,
-                        term: term,
-                    }),
+                bounds.push_projection_bound(
+                    tcx,
+                    projection_ty
+                        .map_bound(|projection_ty| ty::ProjectionPredicate { projection_ty, term }),
                     binding.span,
-                ));
+                );
             }
             ConvertedBindingKind::Constraint(ast_bounds) => {
                 // "Desugar" a constraint like `T: Iterator<Item: Debug>` to
@@ -1244,7 +1256,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 //
                 // Calling `skip_binder` is okay, because `add_bounds` expects the `param_ty`
                 // parameter to have a skipped binder.
-                let param_ty = tcx.mk_ty(ty::Projection(projection_ty.skip_binder()));
+                let param_ty = tcx.mk_ty(ty::Alias(ty::Projection, projection_ty.skip_binder()));
                 self.add_bounds(param_ty, ast_bounds.iter(), bounds, candidate.bound_vars());
             }
         }
@@ -1258,16 +1270,13 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         item_segment: &hir::PathSegment<'_>,
     ) -> Ty<'tcx> {
         let substs = self.ast_path_substs_for_ty(span, did, item_segment);
-        self.normalize_ty(
-            span,
-            EarlyBinder(self.tcx().at(span).type_of(did)).subst(self.tcx(), substs),
-        )
+        self.tcx().at(span).bound_type_of(did).subst(self.tcx(), substs)
     }
 
     fn conv_object_ty_poly_trait_ref(
         &self,
         span: Span,
-        trait_bounds: &[hir::PolyTraitRef<'_>],
+        hir_trait_bounds: &[hir::PolyTraitRef<'_>],
         lifetime: &hir::Lifetime,
         borrowed: bool,
         representation: DynKind,
@@ -1277,7 +1286,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         let mut bounds = Bounds::default();
         let mut potential_assoc_types = Vec::new();
         let dummy_self = self.tcx().types.trait_object_dummy_self;
-        for trait_bound in trait_bounds.iter().rev() {
+        for trait_bound in hir_trait_bounds.iter().rev() {
             if let GenericArgCountResult {
                 correct:
                     Err(GenericArgCountMismatch { invalid_args: cur_potential_assoc_types, .. }),
@@ -1294,10 +1303,45 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             }
         }
 
+        let mut trait_bounds = vec![];
+        let mut projection_bounds = vec![];
+        for (pred, span) in bounds.predicates() {
+            let bound_pred = pred.kind();
+            match bound_pred.skip_binder() {
+                ty::PredicateKind::Clause(clause) => match clause {
+                    ty::Clause::Trait(trait_pred) => {
+                        assert_eq!(trait_pred.polarity, ty::ImplPolarity::Positive);
+                        trait_bounds.push((
+                            bound_pred.rebind(trait_pred.trait_ref),
+                            span,
+                            trait_pred.constness,
+                        ));
+                    }
+                    ty::Clause::Projection(proj) => {
+                        projection_bounds.push((bound_pred.rebind(proj), span));
+                    }
+                    ty::Clause::TypeOutlives(_) => {
+                        // Do nothing, we deal with regions separately
+                    }
+                    ty::Clause::RegionOutlives(_) => bug!(),
+                },
+                ty::PredicateKind::WellFormed(_)
+                | ty::PredicateKind::ObjectSafe(_)
+                | ty::PredicateKind::ClosureKind(_, _, _)
+                | ty::PredicateKind::Subtype(_)
+                | ty::PredicateKind::Coerce(_)
+                | ty::PredicateKind::ConstEvaluatable(_)
+                | ty::PredicateKind::ConstEquate(_, _)
+                | ty::PredicateKind::TypeWellFormedFromEnv(_)
+                | ty::PredicateKind::Ambiguous => bug!(),
+            }
+        }
+
         // Expand trait aliases recursively and check that only one regular (non-auto) trait
         // is used and no 'maybe' bounds are used.
         let expanded_traits =
-            traits::expand_trait_aliases(tcx, bounds.trait_bounds.iter().map(|&(a, b, _)| (a, b)));
+            traits::expand_trait_aliases(tcx, trait_bounds.iter().map(|&(a, b, _)| (a, b)));
+
         let (mut auto_traits, regular_traits): (Vec<_>, Vec<_>) = expanded_traits
             .filter(|i| i.trait_ref().self_ty().skip_binder() == dummy_self)
             .partition(|i| tcx.trait_is_auto(i.trait_ref().def_id()));
@@ -1334,8 +1378,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         }
 
         if regular_traits.is_empty() && auto_traits.is_empty() {
-            let trait_alias_span = bounds
-                .trait_bounds
+            let trait_alias_span = trait_bounds
                 .iter()
                 .map(|&(trait_ref, _, _)| trait_ref.def_id())
                 .find(|&trait_ref| tcx.is_trait_alias(trait_ref))
@@ -1366,8 +1409,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         // Use a `BTreeSet` to keep output in a more consistent order.
         let mut associated_types: FxHashMap<Span, BTreeSet<DefId>> = FxHashMap::default();
 
-        let regular_traits_refs_spans = bounds
-            .trait_bounds
+        let regular_traits_refs_spans = trait_bounds
             .into_iter()
             .filter(|(trait_ref, _, _)| !tcx.trait_is_auto(trait_ref.def_id()));
 
@@ -1421,7 +1463,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                         // the discussion in #56288 for alternatives.
                         if !references_self {
                             // Include projections defined on supertraits.
-                            bounds.projection_bounds.push((pred, span));
+                            projection_bounds.push((pred, span));
                         }
                     }
                     _ => (),
@@ -1429,7 +1471,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             }
         }
 
-        for (projection_bound, _) in &bounds.projection_bounds {
+        for (projection_bound, _) in &projection_bounds {
             for def_ids in associated_types.values_mut() {
                 def_ids.remove(&projection_bound.projection_def_id());
             }
@@ -1438,7 +1480,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         self.complain_about_missing_associated_types(
             associated_types,
             potential_assoc_types,
-            trait_bounds,
+            hir_trait_bounds,
         );
 
         // De-duplicate auto traits so that, e.g., `dyn Trait + Send + Send` is the same as
@@ -1455,7 +1497,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             i.trait_ref().map_bound(|trait_ref: ty::TraitRef<'tcx>| {
                 assert_eq!(trait_ref.self_ty(), dummy_self);
 
-                // Verify that `dummy_self` did not leak inside default type parameters.  This
+                // Verify that `dummy_self` did not leak inside default type parameters. This
                 // could not be done at path creation, since we need to see through trait aliases.
                 let mut missing_type_params = vec![];
                 let mut references_self = false;
@@ -1480,7 +1522,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 let substs = tcx.intern_substs(&substs[..]);
 
                 let span = i.bottom().1;
-                let empty_generic_args = trait_bounds.iter().any(|hir_bound| {
+                let empty_generic_args = hir_trait_bounds.iter().any(|hir_bound| {
                     hir_bound.trait_ref.path.res == Res::Def(DefKind::Trait, trait_ref.def_id)
                         && hir_bound.span.contains(span)
                 });
@@ -1512,7 +1554,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             })
         });
 
-        let existential_projections = bounds.projection_bounds.iter().map(|(bound, _)| {
+        let existential_projections = projection_bounds.iter().map(|(bound, _)| {
             bound.map_bound(|mut b| {
                 assert_eq!(b.projection_ty.self_ty(), dummy_self);
 
@@ -1600,8 +1642,8 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
     fn report_ambiguous_associated_type(
         &self,
         span: Span,
-        type_str: &str,
-        trait_str: &str,
+        types: &[String],
+        traits: &[String],
         name: Symbol,
     ) -> ErrorGuaranteed {
         let mut err = struct_span_err!(self.tcx().sess, span, E0223, "ambiguous associated type");
@@ -1612,19 +1654,92 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             .keys()
             .any(|full_span| full_span.contains(span))
         {
-            err.span_suggestion(
+            err.span_suggestion_verbose(
                 span.shrink_to_lo(),
                 "you are looking for the module in `std`, not the primitive type",
                 "std::",
                 Applicability::MachineApplicable,
             );
         } else {
-            err.span_suggestion(
-                span,
-                "use fully-qualified syntax",
-                format!("<{} as {}>::{}", type_str, trait_str, name),
-                Applicability::HasPlaceholders,
-            );
+            match (types, traits) {
+                ([], []) => {
+                    err.span_suggestion_verbose(
+                        span,
+                        &format!(
+                            "if there were a type named `Type` that implements a trait named \
+                             `Trait` with associated type `{name}`, you could use the \
+                             fully-qualified path",
+                        ),
+                        format!("<Type as Trait>::{name}"),
+                        Applicability::HasPlaceholders,
+                    );
+                }
+                ([], [trait_str]) => {
+                    err.span_suggestion_verbose(
+                        span,
+                        &format!(
+                            "if there were a type named `Example` that implemented `{trait_str}`, \
+                             you could use the fully-qualified path",
+                        ),
+                        format!("<Example as {trait_str}>::{name}"),
+                        Applicability::HasPlaceholders,
+                    );
+                }
+                ([], traits) => {
+                    err.span_suggestions(
+                        span,
+                        &format!(
+                            "if there were a type named `Example` that implemented one of the \
+                             traits with associated type `{name}`, you could use the \
+                             fully-qualified path",
+                        ),
+                        traits
+                            .iter()
+                            .map(|trait_str| format!("<Example as {trait_str}>::{name}"))
+                            .collect::<Vec<_>>(),
+                        Applicability::HasPlaceholders,
+                    );
+                }
+                ([type_str], []) => {
+                    err.span_suggestion_verbose(
+                        span,
+                        &format!(
+                            "if there were a trait named `Example` with associated type `{name}` \
+                             implemented for `{type_str}`, you could use the fully-qualified path",
+                        ),
+                        format!("<{type_str} as Example>::{name}"),
+                        Applicability::HasPlaceholders,
+                    );
+                }
+                (types, []) => {
+                    err.span_suggestions(
+                        span,
+                        &format!(
+                            "if there were a trait named `Example` with associated type `{name}` \
+                             implemented for one of the types, you could use the fully-qualified \
+                             path",
+                        ),
+                        types
+                            .into_iter()
+                            .map(|type_str| format!("<{type_str} as Example>::{name}")),
+                        Applicability::HasPlaceholders,
+                    );
+                }
+                (types, traits) => {
+                    let mut suggestions = vec![];
+                    for type_str in types {
+                        for trait_str in traits {
+                            suggestions.push(format!("<{type_str} as {trait_str}>::{name}"));
+                        }
+                    }
+                    err.span_suggestions(
+                        span,
+                        "use the fully-qualified path",
+                        suggestions,
+                        Applicability::MachineApplicable,
+                    );
+                }
+            }
         }
         err.emit()
     }
@@ -1793,7 +1908,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         Ok(bound)
     }
 
-    // Create a type from a path to an associated type.
+    // Create a type from a path to an associated type or to an enum variant.
     // For a path `A::B::C::D`, `qself_ty` and `qself_def` are the type and def for `A::B::C`
     // and item_segment is the path segment for `D`. We return a type and a def for
     // the whole path.
@@ -1813,7 +1928,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
     ) -> Result<(Ty<'tcx>, DefKind, DefId), ErrorGuaranteed> {
         let tcx = self.tcx();
         let assoc_ident = assoc_segment.ident;
-        let qself_res = if let hir::TyKind::Path(hir::QPath::Resolved(_, ref path)) = qself.kind {
+        let qself_res = if let hir::TyKind::Path(hir::QPath::Resolved(_, path)) = &qself.kind {
             path.res
         } else {
             Res::Err
@@ -1821,7 +1936,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
 
         // Check if we have an enum variant.
         let mut variant_resolution = None;
-        if let ty::Adt(adt_def, adt_substs) = qself_ty.kind() {
+        if let Some(adt_def) = self.probe_adt(span, qself_ty) {
             if adt_def.is_enum() {
                 let variant_def = adt_def
                     .variants()
@@ -1856,8 +1971,8 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                                 return;
                             };
                             let (qself_sugg_span, is_self) = if let hir::TyKind::Path(
-                                hir::QPath::Resolved(_, ref path)
-                            ) = qself.kind {
+                                hir::QPath::Resolved(_, path)
+                            ) = &qself.kind {
                                 // If the path segment already has type params, we want to overwrite
                                 // them.
                                 match &path.segments[..] {
@@ -1923,6 +2038,10 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 let Some(assoc_ty_did) = self.lookup_assoc_ty(assoc_ident, hir_ref_id, span, impl_) else {
                     continue;
                 };
+                let ty::Adt(_, adt_substs) = qself_ty.kind() else {
+                    // FIXME(inherent_associated_types)
+                    bug!("unimplemented: non-adt self of inherent assoc ty");
+                };
                 let item_substs = self.create_substs_for_associated_item(
                     span,
                     assoc_ty_did,
@@ -1930,7 +2049,6 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     adt_substs,
                 );
                 let ty = tcx.bound_type_of(assoc_ty_did).subst(tcx, item_substs);
-                let ty = self.normalize_ty(span, ty);
                 return Ok((ty, DefKind::AssocTy, assoc_ty_did));
             }
         }
@@ -1948,7 +2066,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 };
 
                 self.one_bound_for_assoc_type(
-                    || traits::supertraits(tcx, ty::Binder::dummy(trait_ref)),
+                    || traits::supertraits(tcx, ty::Binder::dummy(trait_ref.subst_identity())),
                     || "Self".to_string(),
                     assoc_ident,
                     span,
@@ -2004,12 +2122,64 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     err.emit()
                 } else if let Err(reported) = qself_ty.error_reported() {
                     reported
+                } else if let ty::Alias(ty::Opaque, alias_ty) = qself_ty.kind() {
+                    // `<impl Trait as OtherTrait>::Assoc` makes no sense.
+                    struct_span_err!(
+                        tcx.sess,
+                        tcx.def_span(alias_ty.def_id),
+                        E0667,
+                        "`impl Trait` is not allowed in path parameters"
+                    )
+                    .emit() // Already reported in an earlier stage.
                 } else {
+                    // Find all the `impl`s that `qself_ty` has for any trait that has the
+                    // associated type, so that we suggest the right one.
+                    let infcx = tcx.infer_ctxt().build();
+                    // We create a fresh `ty::ParamEnv` instead of the one for `self.item_def_id()`
+                    // to avoid a cycle error in `src/test/ui/resolve/issue-102946.rs`.
+                    let param_env = ty::ParamEnv::empty();
+                    let traits: Vec<_> = self
+                        .tcx()
+                        .all_traits()
+                        .filter(|trait_def_id| {
+                            // Consider only traits with the associated type
+                            tcx.associated_items(*trait_def_id)
+                                .in_definition_order()
+                                .any(|i| {
+                                    i.kind.namespace() == Namespace::TypeNS
+                                        && i.ident(tcx).normalize_to_macros_2_0() == assoc_ident
+                                        && matches!(i.kind, ty::AssocKind::Type)
+                                })
+                            // Consider only accessible traits
+                            && tcx.visibility(*trait_def_id)
+                                .is_accessible_from(self.item_def_id(), tcx)
+                            && tcx.all_impls(*trait_def_id)
+                                .any(|impl_def_id| {
+                                    let trait_ref = tcx.impl_trait_ref(impl_def_id);
+                                    trait_ref.map_or(false, |trait_ref| {
+                                        let impl_ = trait_ref.subst(
+                                            tcx,
+                                            infcx.fresh_substs_for_item(span, impl_def_id),
+                                        );
+                                        infcx
+                                            .can_eq(
+                                                param_env,
+                                                tcx.erase_regions(impl_.self_ty()),
+                                                tcx.erase_regions(qself_ty),
+                                            )
+                                            .is_ok()
+                                    })
+                                    && tcx.impl_polarity(impl_def_id) != ty::ImplPolarity::Negative
+                                })
+                        })
+                        .map(|trait_def_id| tcx.def_path_str(trait_def_id))
+                        .collect();
+
                     // Don't print `TyErr` to the user.
                     self.report_ambiguous_associated_type(
                         span,
-                        &qself_ty.to_string(),
-                        "Trait",
+                        &[qself_ty.to_string()],
+                        &traits,
                         assoc_ident.name,
                     )
                 };
@@ -2027,7 +2197,6 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         };
 
         let ty = self.projected_ty_from_poly_trait_ref(span, assoc_ty_did, assoc_segment, bound);
-        let ty = self.normalize_ty(span, ty);
 
         if let Some(variant_def_id) = variant_resolution {
             tcx.struct_span_lint_hir(
@@ -2128,16 +2297,30 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             let is_part_of_self_trait_constraints = def_id == trait_def_id;
             let is_part_of_fn_in_self_trait = parent_def_id == Some(trait_def_id);
 
-            let type_name = if is_part_of_self_trait_constraints || is_part_of_fn_in_self_trait {
-                "Self"
+            let type_names = if is_part_of_self_trait_constraints || is_part_of_fn_in_self_trait {
+                vec!["Self".to_string()]
             } else {
-                "Type"
+                // Find all the types that have an `impl` for the trait.
+                tcx.all_impls(trait_def_id)
+                    .filter(|impl_def_id| {
+                        // Consider only accessible traits
+                        tcx.visibility(*impl_def_id).is_accessible_from(self.item_def_id(), tcx)
+                            && tcx.impl_polarity(impl_def_id) != ty::ImplPolarity::Negative
+                    })
+                    .filter_map(|impl_def_id| tcx.impl_trait_ref(impl_def_id))
+                    .map(|impl_| impl_.subst_identity().self_ty())
+                    // We don't care about blanket impls.
+                    .filter(|self_ty| !self_ty.has_non_region_param())
+                    .map(|self_ty| tcx.erase_regions(self_ty).to_string())
+                    .collect()
             };
-
+            // FIXME: also look at `tcx.generics_of(self.item_def_id()).params` any that
+            // references the trait. Relevant for the first case in
+            // `src/test/ui/associated-types/associated-types-in-ambiguous-context.rs`
             let reported = self.report_ambiguous_associated_type(
                 span,
-                type_name,
-                &path_str,
+                &type_names,
+                &[path_str],
                 item_segment.ident.name,
             );
             return tcx.ty_error_with_guaranteed(reported)
@@ -2163,7 +2346,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
 
         debug!("qpath_to_ty: trait_ref={:?}", trait_ref);
 
-        self.normalize_ty(span, tcx.mk_projection(item_def_id, item_substs))
+        tcx.mk_projection(item_def_id, item_substs)
     }
 
     pub fn prohibit_generics<'a>(
@@ -2243,7 +2426,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     ),
                     "s",
                 ),
-                [only] => (format!("{only}"), ""),
+                [only] => (only.to_string(), ""),
                 [] => unreachable!(),
             };
             let last_span = *arg_spans.last().unwrap();
@@ -2266,7 +2449,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         for segment in segments {
             // Only emit the first error to avoid overloading the user with error messages.
             if let Some(b) = segment.args().bindings.first() {
-                Self::prohibit_assoc_ty_binding(self.tcx(), b.span);
+                prohibit_assoc_ty_binding(self.tcx(), b.span);
                 return true;
             }
         }
@@ -2280,6 +2463,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         self_ty: Option<Ty<'tcx>>,
         kind: DefKind,
         def_id: DefId,
+        span: Span,
     ) -> Vec<PathSeg> {
         // We need to extract the type parameters supplied by the user in
         // the path `path`. Due to the current setup, this is a bit of a
@@ -2347,8 +2531,8 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
 
             // Case 2. Reference to a variant constructor.
             DefKind::Ctor(CtorOf::Variant, ..) | DefKind::Variant => {
-                let adt_def = self_ty.map(|t| t.ty_adt_def().unwrap());
-                let (generics_def_id, index) = if let Some(adt_def) = adt_def {
+                let (generics_def_id, index) = if let Some(self_ty) = self_ty {
+                    let adt_def = self.probe_adt(span, self_ty).unwrap();
                     debug_assert!(adt_def.is_enum());
                     (adt_def.did(), last)
                 } else if last >= 1 && segments[last - 1].args.is_some() {
@@ -2424,7 +2608,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     err.note("`impl Trait` types can't have type parameters");
                 });
                 let substs = self.ast_path_substs_for_ty(span, did, item_segment.0);
-                self.normalize_ty(span, tcx.mk_opaque(did, substs))
+                tcx.mk_opaque(did, substs)
             }
             Res::Def(
                 DefKind::Enum
@@ -2444,7 +2628,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 assert_eq!(opt_self_ty, None);
 
                 let path_segs =
-                    self.def_ids_for_value_path_segments(path.segments, None, kind, def_id);
+                    self.def_ids_for_value_path_segments(path.segments, None, kind, def_id, span);
                 let generic_segs: FxHashSet<_> =
                     path_segs.iter().map(|PathSeg(_, index)| index).collect();
                 self.prohibit_generics(
@@ -2576,7 +2760,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                         "generic `Self` types are currently not permitted in anonymous constants",
                     );
                     if let Some(hir::Node::Item(&hir::Item {
-                        kind: hir::ItemKind::Impl(ref impl_),
+                        kind: hir::ItemKind::Impl(impl_),
                         ..
                     })) = tcx.hir().get_if_local(def_id)
                     {
@@ -2584,7 +2768,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     }
                     tcx.ty_error_with_guaranteed(err.emit())
                 } else {
-                    self.normalize_ty(span, ty)
+                    ty
                 }
             }
             Res::Def(DefKind::AssocTy, def_id) => {
@@ -2633,7 +2817,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 let e = self
                     .tcx()
                     .sess
-                    .delay_span_bug(path.span, "path with `Res:Err` but no error emitted");
+                    .delay_span_bug(path.span, "path with `Res::Err` but no error emitted");
                 self.set_tainted_by_errors(e);
                 self.tcx().ty_error_with_guaranteed(e)
             }
@@ -2648,7 +2832,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
     }
 
     /// Parses the programmer's textual representation of a type into our
-    /// internal notion of a type.  This is meant to be used within a path.
+    /// internal notion of a type. This is meant to be used within a path.
     pub fn ast_ty_to_ty_in_path(&self, ast_ty: &hir::Ty<'_>) -> Ty<'tcx> {
         self.ast_ty_to_ty_inner(ast_ty, false, true)
     }
@@ -2659,12 +2843,12 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
     fn ast_ty_to_ty_inner(&self, ast_ty: &hir::Ty<'_>, borrowed: bool, in_path: bool) -> Ty<'tcx> {
         let tcx = self.tcx();
 
-        let result_ty = match ast_ty.kind {
-            hir::TyKind::Slice(ref ty) => tcx.mk_slice(self.ast_ty_to_ty(ty)),
-            hir::TyKind::Ptr(ref mt) => {
+        let result_ty = match &ast_ty.kind {
+            hir::TyKind::Slice(ty) => tcx.mk_slice(self.ast_ty_to_ty(ty)),
+            hir::TyKind::Ptr(mt) => {
                 tcx.mk_ptr(ty::TypeAndMut { ty: self.ast_ty_to_ty(mt.ty), mutbl: mt.mutbl })
             }
-            hir::TyKind::Rptr(ref region, ref mt) => {
+            hir::TyKind::Ref(region, mt) => {
                 let r = self.ast_region_to_region(region, None);
                 debug!(?r);
                 let t = self.ast_ty_to_ty_inner(mt.ty, true, false);
@@ -2684,7 +2868,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     Some(ast_ty),
                 ))
             }
-            hir::TyKind::TraitObject(bounds, ref lifetime, repr) => {
+            hir::TyKind::TraitObject(bounds, lifetime, repr) => {
                 self.maybe_lint_bare_trait(ast_ty, in_path);
                 let repr = match repr {
                     TraitObjectSyntax::Dyn | TraitObjectSyntax::None => ty::Dyn,
@@ -2692,12 +2876,12 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 };
                 self.conv_object_ty_poly_trait_ref(ast_ty.span, bounds, lifetime, borrowed, repr)
             }
-            hir::TyKind::Path(hir::QPath::Resolved(ref maybe_qself, ref path)) => {
+            hir::TyKind::Path(hir::QPath::Resolved(maybe_qself, path)) => {
                 debug!(?maybe_qself, ?path);
                 let opt_self_ty = maybe_qself.as_ref().map(|qself| self.ast_ty_to_ty(qself));
                 self.res_to_ty(opt_self_ty, path, false)
             }
-            hir::TyKind::OpaqueDef(item_id, lifetimes, in_trait) => {
+            &hir::TyKind::OpaqueDef(item_id, lifetimes, in_trait) => {
                 let opaque_ty = tcx.hir().item(item_id);
                 let def_id = item_id.owner_id.to_def_id();
 
@@ -2708,14 +2892,14 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     ref i => bug!("`impl Trait` pointed to non-opaque type?? {:#?}", i),
                 }
             }
-            hir::TyKind::Path(hir::QPath::TypeRelative(ref qself, ref segment)) => {
+            hir::TyKind::Path(hir::QPath::TypeRelative(qself, segment)) => {
                 debug!(?qself, ?segment);
                 let ty = self.ast_ty_to_ty_inner(qself, false, true);
                 self.associated_path_to_ty(ast_ty.hir_id, ast_ty.span, ty, qself, segment, false)
                     .map(|(ty, _, _)| ty)
                     .unwrap_or_else(|_| tcx.ty_error())
             }
-            hir::TyKind::Path(hir::QPath::LangItem(lang_item, span, _)) => {
+            &hir::TyKind::Path(hir::QPath::LangItem(lang_item, span, _)) => {
                 let def_id = tcx.require_lang_item(lang_item, Some(span));
                 let (substs, _) = self.create_substs_for_ast_path(
                     span,
@@ -2727,10 +2911,9 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     None,
                     ty::BoundConstness::NotConst,
                 );
-                EarlyBinder(self.normalize_ty(span, tcx.at(span).type_of(def_id)))
-                    .subst(tcx, substs)
+                EarlyBinder(tcx.at(span).type_of(def_id)).subst(tcx, substs)
             }
-            hir::TyKind::Array(ref ty, ref length) => {
+            hir::TyKind::Array(ty, length) => {
                 let length = match length {
                     &hir::ArrayLen::Infer(_, span) => self.ct_infer(tcx.types.usize, None, span),
                     hir::ArrayLen::Body(constant) => {
@@ -2738,10 +2921,9 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     }
                 };
 
-                let array_ty = tcx.mk_ty(ty::Array(self.ast_ty_to_ty(ty), length));
-                self.normalize_ty(ast_ty.span, array_ty)
+                tcx.mk_ty(ty::Array(self.ast_ty_to_ty(ty), length))
             }
-            hir::TyKind::Typeof(ref e) => {
+            hir::TyKind::Typeof(e) => {
                 let ty_erased = tcx.type_of(e.def_id);
                 let ty = tcx.fold_regions(ty_erased, |r, _| {
                     if r.is_erased() { tcx.lifetimes.re_static } else { r }
@@ -2943,7 +3125,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         let hir::Node::ImplItem(hir::ImplItem { kind: hir::ImplItemKind::Fn(..), ident, .. }) =
             hir.get(fn_hir_id) else { return None };
         let hir::Node::Item(hir::Item { kind: hir::ItemKind::Impl(i), .. }) =
-                hir.get(hir.get_parent_node(fn_hir_id)) else { bug!("ImplItem should have Impl parent") };
+                hir.get_parent(fn_hir_id) else { bug!("ImplItem should have Impl parent") };
 
         let trait_ref = self.instantiate_mono_trait_ref(
             i.of_trait.as_ref()?,
@@ -3123,7 +3305,13 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 let label = "add `dyn` keyword before this trait";
                 let mut diag =
                     rustc_errors::struct_span_err!(tcx.sess, self_ty.span, E0782, "{}", msg);
-                diag.multipart_suggestion_verbose(label, sugg, Applicability::MachineApplicable);
+                if self_ty.span.can_be_used_for_suggestions() {
+                    diag.multipart_suggestion_verbose(
+                        label,
+                        sugg,
+                        Applicability::MachineApplicable,
+                    );
+                }
                 // check if the impl trait that we are considering is a impl of a local trait
                 self.maybe_lint_blanket_trait_impl(&self_ty, &mut diag);
                 diag.emit();