Merging upstream version 1.72.1+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 151 insertions, 1145 deletions

diff --git a/compiler/rustc_hir_analysis/src/astconv/mod.rs b/compiler/rustc_hir_analysis/src/astconv/mod.rs
index 2c60a0624..3d6984628 100644
--- a/compiler/rustc_hir_analysis/src/astconv/mod.rs
+++ b/compiler/rustc_hir_analysis/src/astconv/mod.rs
@@ -2,53 +2,45 @@
 //! The main routine here is `ast_ty_to_ty()`; each use is parameterized by an
 //! instance of `AstConv`.
 
+mod bounds;
 mod errors;
 pub mod generics;
+mod lint;
+mod object_safety;
 
 use crate::astconv::errors::prohibit_assoc_ty_binding;
 use crate::astconv::generics::{check_generic_arg_count, create_substs_for_generic_args};
 use crate::bounds::Bounds;
 use crate::collect::HirPlaceholderCollector;
-use crate::errors::{
-    AmbiguousLifetimeBound, MultipleRelaxedDefaultBounds, TraitObjectDeclaredWithNoTraits,
-    TypeofReservedKeywordUsed, ValueOfAssociatedStructAlreadySpecified,
-};
+use crate::errors::{AmbiguousLifetimeBound, TypeofReservedKeywordUsed};
 use crate::middle::resolve_bound_vars as rbv;
 use crate::require_c_abi_if_c_variadic;
 use rustc_ast::TraitObjectSyntax;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_errors::{
     struct_span_err, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed, FatalError,
-    MultiSpan, StashKey,
+    MultiSpan,
 };
 use rustc_hir as hir;
 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::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
-use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
+use rustc_infer::infer::{InferCtxt, InferOk, TyCtxtInferExt};
 use rustc_infer::traits::ObligationCause;
-use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
 use rustc_middle::middle::stability::AllowUnstable;
-use rustc_middle::ty::fold::FnMutDelegate;
 use rustc_middle::ty::subst::{self, GenericArgKind, InternalSubsts, SubstsRef};
 use rustc_middle::ty::GenericParamDefKind;
 use rustc_middle::ty::{self, Const, IsSuggestable, Ty, TyCtxt, TypeVisitableExt};
-use rustc_middle::ty::{DynKind, ToPredicate};
-use rustc_session::lint::builtin::{AMBIGUOUS_ASSOCIATED_ITEMS, BARE_TRAIT_OBJECTS};
+use rustc_session::lint::builtin::AMBIGUOUS_ASSOCIATED_ITEMS;
 use rustc_span::edit_distance::find_best_match_for_name;
 use rustc_span::symbol::{kw, Ident, Symbol};
 use rustc_span::{sym, Span, DUMMY_SP};
 use rustc_target::spec::abi;
-use rustc_trait_selection::traits::error_reporting::{
-    report_object_safety_error, suggestions::NextTypeParamName,
-};
 use rustc_trait_selection::traits::wf::object_region_bounds;
-use rustc_trait_selection::traits::{self, astconv_object_safety_violations, ObligationCtxt};
+use rustc_trait_selection::traits::{self, NormalizeExt, ObligationCtxt};
+use rustc_type_ir::fold::{TypeFoldable, TypeFolder, TypeSuperFoldable};
 
-use smallvec::{smallvec, SmallVec};
-use std::collections::BTreeSet;
 use std::fmt::Display;
 use std::slice;
 
@@ -58,6 +50,24 @@ pub struct PathSeg(pub DefId, pub usize);
 #[derive(Copy, Clone, Debug)]
 pub struct OnlySelfBounds(pub bool);
 
+#[derive(Copy, Clone, Debug)]
+pub enum PredicateFilter {
+    /// All predicates may be implied by the trait.
+    All,
+
+    /// Only traits that reference `Self: ..` are implied by the trait.
+    SelfOnly,
+
+    /// Only traits that reference `Self: ..` and define an associated type
+    /// with the given ident are implied by the trait.
+    SelfThatDefines(Ident),
+
+    /// Only traits that reference `Self: ..` and their associated type bounds.
+    /// For example, given `Self: Tr<A: B>`, this would expand to `Self: Tr`
+    /// and `<Self as Tr>::A: B`.
+    SelfAndAssociatedTypeBounds,
+}
+
 pub trait AstConv<'tcx> {
     fn tcx(&self) -> TyCtxt<'tcx>;
 
@@ -239,7 +249,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     var: ty::BoundVar::from_u32(index),
                     kind: ty::BrNamed(def_id, name),
                 };
-                tcx.mk_re_late_bound(debruijn, br)
+                ty::Region::new_late_bound(tcx, debruijn, br)
             }
 
             Some(rbv::ResolvedArg::EarlyBound(def_id)) => {
@@ -247,12 +257,12 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 let item_def_id = tcx.hir().ty_param_owner(def_id.expect_local());
                 let generics = tcx.generics_of(item_def_id);
                 let index = generics.param_def_id_to_index[&def_id];
-                tcx.mk_re_early_bound(ty::EarlyBoundRegion { def_id, index, name })
+                ty::Region::new_early_bound(tcx, ty::EarlyBoundRegion { def_id, index, name })
             }
 
             Some(rbv::ResolvedArg::Free(scope, id)) => {
                 let name = lifetime_name(id.expect_local());
-                tcx.mk_re_free(scope, ty::BrNamed(id, name))
+                ty::Region::new_free(tcx, scope, ty::BrNamed(id, name))
 
                 // (*) -- not late-bound, won't change
             }
@@ -269,7 +279,8 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     // elision. `resolve_lifetime` should have
                     // reported an error in this case -- but if
                     // not, let's error out.
-                    tcx.mk_re_error_with_message(
+                    ty::Region::new_error_with_message(
+                        tcx,
                         lifetime.ident.span,
                         "unelided lifetime in signature",
                     )
@@ -432,7 +443,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     }
                     if let (hir::TyKind::Infer, false) = (&ty.kind, self.astconv.allow_ty_infer()) {
                         self.inferred_params.push(ty.span);
-                        tcx.ty_error_misc().into()
+                        Ty::new_misc_error(tcx).into()
                     } else {
                         self.astconv.ast_ty_to_ty(ty).into()
                     }
@@ -463,7 +474,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                             self.astconv.ct_infer(ty, Some(param), inf.span).into()
                         } else {
                             self.inferred_params.push(inf.span);
-                            tcx.const_error_misc(ty).into()
+                            ty::Const::new_misc_error(tcx, ty).into()
                         }
                     }
                     _ => unreachable!(),
@@ -485,7 +496,8 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                             debug!(?param, "unelided lifetime in signature");
 
                             // This indicates an illegal lifetime in a non-assoc-trait position
-                            tcx.mk_re_error_with_message(
+                            ty::Region::new_error_with_message(
+                                tcx,
                                 self.span,
                                 "unelided lifetime in signature",
                             )
@@ -500,14 +512,14 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                                 _ => false,
                             }) {
                                 // Avoid ICE #86756 when type error recovery goes awry.
-                                return tcx.ty_error_misc().into();
+                                return Ty::new_misc_error(tcx).into();
                             }
                             tcx.at(self.span).type_of(param.def_id).subst(tcx, substs).into()
                         } else if infer_args {
                             self.astconv.ty_infer(Some(param), self.span).into()
                         } else {
                             // We've already errored above about the mismatch.
-                            tcx.ty_error_misc().into()
+                            Ty::new_misc_error(tcx).into()
                         }
                     }
                     GenericParamDefKind::Const { has_default } => {
@@ -517,7 +529,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                             .no_bound_vars()
                             .expect("const parameter types cannot be generic");
                         if let Err(guar) = ty.error_reported() {
-                            return tcx.const_error(ty, guar).into();
+                            return ty::Const::new_error(tcx, guar, ty).into();
                         }
                         if !infer_args && has_default {
                             tcx.const_param_default(param.def_id).subst(tcx, substs.unwrap()).into()
@@ -526,7 +538,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                                 self.astconv.ct_infer(ty, Some(param), self.span).into()
                             } else {
                                 // We've already errored above about the mismatch.
-                                tcx.const_error_misc(ty).into()
+                                ty::Const::new_misc_error(tcx, ty).into()
                             }
                         }
                     }
@@ -884,551 +896,6 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             .is_some()
     }
 
-    /// Sets `implicitly_sized` to true on `Bounds` if necessary
-    pub(crate) fn add_implicitly_sized(
-        &self,
-        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: &'tcx [hir::GenericBound<'tcx>]| {
-            for ab in ast_bounds {
-                if let hir::GenericBound::Trait(ptr, hir::TraitBoundModifier::Maybe) = ab {
-                    if unbound.is_none() {
-                        unbound = Some(&ptr.trait_ref);
-                    } else {
-                        tcx.sess.emit_err(MultipleRelaxedDefaultBounds { span });
-                    }
-                }
-            }
-        };
-        search_bounds(ast_bounds);
-        if let Some((self_ty, where_clause)) = self_ty_where_predicates {
-            for clause in where_clause {
-                if let hir::WherePredicate::BoundPredicate(pred) = clause {
-                    if pred.is_param_bound(self_ty.to_def_id()) {
-                        search_bounds(pred.bounds);
-                    }
-                }
-            }
-        }
-
-        let sized_def_id = tcx.lang_items().sized_trait();
-        match (&sized_def_id, unbound) {
-            (Some(sized_def_id), Some(tpb))
-                if tpb.path.res == Res::Def(DefKind::Trait, *sized_def_id) =>
-            {
-                // There was in fact a `?Sized` bound, return without doing anything
-                return;
-            }
-            (_, Some(_)) => {
-                // There was a `?Trait` bound, but it was not `?Sized`; warn.
-                tcx.sess.span_warn(
-                    span,
-                    "default bound relaxed for a type parameter, but \
-                        this does nothing because the given bound is not \
-                        a default; only `?Sized` is supported",
-                );
-                // Otherwise, add implicitly sized if `Sized` is available.
-            }
-            _ => {
-                // There was no `?Sized` bound; add implicitly sized if `Sized` is available.
-            }
-        }
-        if sized_def_id.is_none() {
-            // No lang item for `Sized`, so we can't add it as a bound.
-            return;
-        }
-        bounds.push_sized(tcx, self_ty, span);
-    }
-
-    /// This helper takes a *converted* parameter type (`param_ty`)
-    /// and an *unconverted* list of bounds:
-    ///
-    /// ```text
-    /// fn foo<T: Debug>
-    ///        ^  ^^^^^ `ast_bounds` parameter, in HIR form
-    ///        |
-    ///        `param_ty`, in ty form
-    /// ```
-    ///
-    /// It adds these `ast_bounds` into the `bounds` structure.
-    ///
-    /// **A note on binders:** there is an implied binder around
-    /// `param_ty` and `ast_bounds`. See `instantiate_poly_trait_ref`
-    /// for more details.
-    #[instrument(level = "debug", skip(self, ast_bounds, bounds))]
-    pub(crate) fn add_bounds<'hir, I: Iterator<Item = &'hir hir::GenericBound<'hir>>>(
-        &self,
-        param_ty: Ty<'tcx>,
-        ast_bounds: I,
-        bounds: &mut Bounds<'tcx>,
-        bound_vars: &'tcx ty::List<ty::BoundVariableKind>,
-        only_self_bounds: OnlySelfBounds,
-    ) {
-        for ast_bound in ast_bounds {
-            match ast_bound {
-                hir::GenericBound::Trait(poly_trait_ref, modifier) => {
-                    let (constness, polarity) = match modifier {
-                        hir::TraitBoundModifier::MaybeConst => {
-                            (ty::BoundConstness::ConstIfConst, ty::ImplPolarity::Positive)
-                        }
-                        hir::TraitBoundModifier::None => {
-                            (ty::BoundConstness::NotConst, ty::ImplPolarity::Positive)
-                        }
-                        hir::TraitBoundModifier::Negative => {
-                            (ty::BoundConstness::NotConst, ty::ImplPolarity::Negative)
-                        }
-                        hir::TraitBoundModifier::Maybe => continue,
-                    };
-                    let _ = self.instantiate_poly_trait_ref(
-                        &poly_trait_ref.trait_ref,
-                        poly_trait_ref.span,
-                        constness,
-                        polarity,
-                        param_ty,
-                        bounds,
-                        false,
-                        only_self_bounds,
-                    );
-                }
-                &hir::GenericBound::LangItemTrait(lang_item, span, hir_id, args) => {
-                    self.instantiate_lang_item_trait_ref(
-                        lang_item,
-                        span,
-                        hir_id,
-                        args,
-                        param_ty,
-                        bounds,
-                        only_self_bounds,
-                    );
-                }
-                hir::GenericBound::Outlives(lifetime) => {
-                    let region = self.ast_region_to_region(lifetime, None);
-                    bounds.push_region_bound(
-                        self.tcx(),
-                        ty::Binder::bind_with_vars(
-                            ty::OutlivesPredicate(param_ty, region),
-                            bound_vars,
-                        ),
-                        lifetime.ident.span,
-                    );
-                }
-            }
-        }
-    }
-
-    /// Translates a list of bounds from the HIR into the `Bounds` data structure.
-    /// The self-type for the bounds is given by `param_ty`.
-    ///
-    /// Example:
-    ///
-    /// ```ignore (illustrative)
-    /// fn foo<T: Bar + Baz>() { }
-    /// //     ^  ^^^^^^^^^ ast_bounds
-    /// //     param_ty
-    /// ```
-    ///
-    /// 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
-    /// example above, but is not true in supertrait listings like `trait Foo: Bar + Baz`.
-    ///
-    /// `span` should be the declaration size of the parameter.
-    pub(crate) fn compute_bounds(
-        &self,
-        param_ty: Ty<'tcx>,
-        ast_bounds: &[hir::GenericBound<'_>],
-        only_self_bounds: OnlySelfBounds,
-    ) -> Bounds<'tcx> {
-        let mut bounds = Bounds::default();
-        self.add_bounds(
-            param_ty,
-            ast_bounds.iter(),
-            &mut bounds,
-            ty::List::empty(),
-            only_self_bounds,
-        );
-        debug!(?bounds);
-
-        bounds
-    }
-
-    /// Convert the bounds in `ast_bounds` that refer to traits which define an associated type
-    /// named `assoc_name` into ty::Bounds. Ignore the rest.
-    pub(crate) fn compute_bounds_that_match_assoc_item(
-        &self,
-        param_ty: Ty<'tcx>,
-        ast_bounds: &[hir::GenericBound<'_>],
-        assoc_name: Ident,
-    ) -> Bounds<'tcx> {
-        let mut result = Vec::new();
-
-        for ast_bound in ast_bounds {
-            if let Some(trait_ref) = ast_bound.trait_ref()
-                && let Some(trait_did) = trait_ref.trait_def_id()
-                && self.tcx().trait_may_define_assoc_item(trait_did, assoc_name)
-            {
-                result.push(ast_bound.clone());
-            }
-        }
-
-        let mut bounds = Bounds::default();
-        self.add_bounds(
-            param_ty,
-            result.iter(),
-            &mut bounds,
-            ty::List::empty(),
-            OnlySelfBounds(true),
-        );
-        debug!(?bounds);
-
-        bounds
-    }
-
-    /// Given an HIR binding like `Item = Foo` or `Item: Foo`, pushes the corresponding predicates
-    /// onto `bounds`.
-    ///
-    /// **A note on binders:** given something like `T: for<'a> Iterator<Item = &'a u32>`, the
-    /// `trait_ref` here will be `for<'a> T: Iterator`. The `binding` data however is from *inside*
-    /// the binder (e.g., `&'a u32`) and hence may reference bound regions.
-    #[instrument(level = "debug", skip(self, bounds, speculative, dup_bindings, path_span))]
-    fn add_predicates_for_ast_type_binding(
-        &self,
-        hir_ref_id: hir::HirId,
-        trait_ref: ty::PolyTraitRef<'tcx>,
-        binding: &ConvertedBinding<'_, 'tcx>,
-        bounds: &mut Bounds<'tcx>,
-        speculative: bool,
-        dup_bindings: &mut FxHashMap<DefId, Span>,
-        path_span: Span,
-        constness: ty::BoundConstness,
-        only_self_bounds: OnlySelfBounds,
-        polarity: ty::ImplPolarity,
-    ) -> Result<(), ErrorGuaranteed> {
-        // Given something like `U: SomeTrait<T = X>`, we want to produce a
-        // predicate like `<U as SomeTrait>::T = X`. This is somewhat
-        // subtle in the event that `T` is defined in a supertrait of
-        // `SomeTrait`, because in that case we need to upcast.
-        //
-        // That is, consider this case:
-        //
-        // ```
-        // trait SubTrait: SuperTrait<i32> { }
-        // trait SuperTrait<A> { type T; }
-        //
-        // ... B: SubTrait<T = foo> ...
-        // ```
-        //
-        // We want to produce `<B as SuperTrait<i32>>::T == foo`.
-
-        let tcx = self.tcx();
-
-        let return_type_notation =
-            binding.gen_args.parenthesized == hir::GenericArgsParentheses::ReturnTypeNotation;
-
-        let candidate = if return_type_notation {
-            if self.trait_defines_associated_item_named(
-                trait_ref.def_id(),
-                ty::AssocKind::Fn,
-                binding.item_name,
-            ) {
-                trait_ref
-            } else {
-                self.one_bound_for_assoc_method(
-                    traits::supertraits(tcx, trait_ref),
-                    trait_ref.print_only_trait_path(),
-                    binding.item_name,
-                    path_span,
-                )?
-            }
-        } else if self.trait_defines_associated_item_named(
-            trait_ref.def_id(),
-            ty::AssocKind::Type,
-            binding.item_name,
-        ) {
-            // Simple case: X is defined in the current trait.
-            trait_ref
-        } else {
-            // Otherwise, we have to walk through the supertraits to find
-            // those that do.
-            self.one_bound_for_assoc_type(
-                || traits::supertraits(tcx, trait_ref),
-                trait_ref.skip_binder().print_only_trait_name(),
-                binding.item_name,
-                path_span,
-                match binding.kind {
-                    ConvertedBindingKind::Equality(term) => Some(term),
-                    _ => None,
-                },
-            )?
-        };
-
-        let (assoc_ident, def_scope) =
-            tcx.adjust_ident_and_get_scope(binding.item_name, candidate.def_id(), hir_ref_id);
-
-        // We have already adjusted the item name above, so compare with `ident.normalize_to_macros_2_0()` instead
-        // of calling `filter_by_name_and_kind`.
-        let find_item_of_kind = |kind| {
-            tcx.associated_items(candidate.def_id())
-                .filter_by_name_unhygienic(assoc_ident.name)
-                .find(|i| i.kind == kind && i.ident(tcx).normalize_to_macros_2_0() == assoc_ident)
-        };
-        let assoc_item = if return_type_notation {
-            find_item_of_kind(ty::AssocKind::Fn)
-        } else {
-            find_item_of_kind(ty::AssocKind::Type)
-                .or_else(|| find_item_of_kind(ty::AssocKind::Const))
-        }
-        .expect("missing associated type");
-
-        if !assoc_item.visibility(tcx).is_accessible_from(def_scope, tcx) {
-            tcx.sess
-                .struct_span_err(
-                    binding.span,
-                    format!("{} `{}` is private", assoc_item.kind, binding.item_name),
-                )
-                .span_label(binding.span, format!("private {}", assoc_item.kind))
-                .emit();
-        }
-        tcx.check_stability(assoc_item.def_id, Some(hir_ref_id), binding.span, None);
-
-        if !speculative {
-            dup_bindings
-                .entry(assoc_item.def_id)
-                .and_modify(|prev_span| {
-                    tcx.sess.emit_err(ValueOfAssociatedStructAlreadySpecified {
-                        span: binding.span,
-                        prev_span: *prev_span,
-                        item_name: binding.item_name,
-                        def_path: tcx.def_path_str(assoc_item.container_id(tcx)),
-                    });
-                })
-                .or_insert(binding.span);
-        }
-
-        let projection_ty = if return_type_notation {
-            // If we have an method return type bound, then we need to substitute
-            // the method's early bound params with suitable late-bound params.
-            let mut num_bound_vars = candidate.bound_vars().len();
-            let substs =
-                candidate.skip_binder().substs.extend_to(tcx, assoc_item.def_id, |param, _| {
-                    let subst = match param.kind {
-                        GenericParamDefKind::Lifetime => tcx
-                            .mk_re_late_bound(
-                                ty::INNERMOST,
-                                ty::BoundRegion {
-                                    var: ty::BoundVar::from_usize(num_bound_vars),
-                                    kind: ty::BoundRegionKind::BrNamed(param.def_id, param.name),
-                                },
-                            )
-                            .into(),
-                        GenericParamDefKind::Type { .. } => tcx
-                            .mk_bound(
-                                ty::INNERMOST,
-                                ty::BoundTy {
-                                    var: ty::BoundVar::from_usize(num_bound_vars),
-                                    kind: ty::BoundTyKind::Param(param.def_id, param.name),
-                                },
-                            )
-                            .into(),
-                        GenericParamDefKind::Const { .. } => {
-                            let ty = tcx
-                                .type_of(param.def_id)
-                                .no_bound_vars()
-                                .expect("ct params cannot have early bound vars");
-                            tcx.mk_const(
-                                ty::ConstKind::Bound(
-                                    ty::INNERMOST,
-                                    ty::BoundVar::from_usize(num_bound_vars),
-                                ),
-                                ty,
-                            )
-                            .into()
-                        }
-                    };
-                    num_bound_vars += 1;
-                    subst
-                });
-
-            // Next, we need to check that the return-type notation is being used on
-            // an RPITIT (return-position impl trait in trait) or AFIT (async fn in trait).
-            let output = tcx.fn_sig(assoc_item.def_id).skip_binder().output();
-            let output = if let ty::Alias(ty::Projection, alias_ty) = *output.skip_binder().kind()
-                && tcx.def_kind(alias_ty.def_id) == DefKind::ImplTraitPlaceholder
-            {
-                alias_ty
-            } else {
-                return Err(self.tcx().sess.emit_err(
-                    crate::errors::ReturnTypeNotationOnNonRpitit {
-                        span: binding.span,
-                        ty: tcx.liberate_late_bound_regions(assoc_item.def_id, output),
-                        fn_span: tcx.hir().span_if_local(assoc_item.def_id),
-                        note: (),
-                    },
-                ));
-            };
-
-            // Finally, move the fn return type's bound vars over to account for the early bound
-            // params (and trait ref's late bound params). This logic is very similar to
-            // `Predicate::subst_supertrait`, and it's no coincidence why.
-            let shifted_output = tcx.shift_bound_var_indices(num_bound_vars, output);
-            let subst_output = ty::EarlyBinder(shifted_output).subst(tcx, substs);
-
-            let bound_vars = tcx.late_bound_vars(binding.hir_id);
-            ty::Binder::bind_with_vars(subst_output, bound_vars)
-        } else {
-            // Include substitutions for generic parameters of associated types
-            candidate.map_bound(|trait_ref| {
-                let ident = Ident::new(assoc_item.name, binding.item_name.span);
-                let item_segment = hir::PathSegment {
-                    ident,
-                    hir_id: binding.hir_id,
-                    res: Res::Err,
-                    args: Some(binding.gen_args),
-                    infer_args: false,
-                };
-
-                let substs_trait_ref_and_assoc_item = self.create_substs_for_associated_item(
-                    path_span,
-                    assoc_item.def_id,
-                    &item_segment,
-                    trait_ref.substs,
-                );
-
-                debug!(?substs_trait_ref_and_assoc_item);
-
-                tcx.mk_alias_ty(assoc_item.def_id, substs_trait_ref_and_assoc_item)
-            })
-        };
-
-        if !speculative {
-            // Find any late-bound regions declared in `ty` that are not
-            // declared in the trait-ref or assoc_item. These are not well-formed.
-            //
-            // Example:
-            //
-            //     for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad
-            //     for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok
-            if let ConvertedBindingKind::Equality(ty) = binding.kind {
-                let late_bound_in_trait_ref =
-                    tcx.collect_constrained_late_bound_regions(&projection_ty);
-                let late_bound_in_ty =
-                    tcx.collect_referenced_late_bound_regions(&trait_ref.rebind(ty));
-                debug!(?late_bound_in_trait_ref);
-                debug!(?late_bound_in_ty);
-
-                // FIXME: point at the type params that don't have appropriate lifetimes:
-                // struct S1<F: for<'a> Fn(&i32, &i32) -> &'a i32>(F);
-                //                         ----  ----     ^^^^^^^
-                self.validate_late_bound_regions(
-                    late_bound_in_trait_ref,
-                    late_bound_in_ty,
-                    |br_name| {
-                        struct_span_err!(
-                            tcx.sess,
-                            binding.span,
-                            E0582,
-                            "binding for associated type `{}` references {}, \
-                             which does not appear in the trait input types",
-                            binding.item_name,
-                            br_name
-                        )
-                    },
-                );
-            }
-        }
-
-        match binding.kind {
-            ConvertedBindingKind::Equality(..) if return_type_notation => {
-                return Err(self.tcx().sess.emit_err(
-                    crate::errors::ReturnTypeNotationEqualityBound { span: binding.span },
-                ));
-            }
-            ConvertedBindingKind::Equality(mut term) => {
-                // "Desugar" a constraint like `T: Iterator<Item = u32>` this to
-                // the "projection predicate" for:
-                //
-                // `<T as Iterator>::Item = u32`
-                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(_))
-                    | (hir::def::DefKind::AssocConst, ty::TermKind::Const(_)) => (),
-                    (_, _) => {
-                        let got = if let Some(_) = term.ty() { "type" } else { "constant" };
-                        let expected = tcx.def_descr(assoc_item_def_id);
-                        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,
-                                "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(reported).into(),
-                            hir::def::DefKind::AssocConst => tcx
-                                .const_error(
-                                    tcx.type_of(assoc_item_def_id)
-                                        .subst(tcx, projection_ty.skip_binder().substs),
-                                    reported,
-                                )
-                                .into(),
-                            _ => unreachable!(),
-                        };
-                    }
-                }
-                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
-                //
-                // `<T as Iterator>::Item: Debug`
-                //
-                // Calling `skip_binder` is okay, because `add_bounds` expects the `param_ty`
-                // parameter to have a skipped binder.
-                //
-                // NOTE: If `only_self_bounds` is true, do NOT expand this associated
-                // type bound into a trait predicate, since we only want to add predicates
-                // for the `Self` type.
-                if !only_self_bounds.0 {
-                    let param_ty = tcx.mk_alias(ty::Projection, projection_ty.skip_binder());
-                    self.add_bounds(
-                        param_ty,
-                        ast_bounds.iter(),
-                        bounds,
-                        projection_ty.bound_vars(),
-                        only_self_bounds,
-                    );
-                }
-            }
-        }
-        Ok(())
-    }
-
     fn ast_path_to_ty(
         &self,
         span: Span,
@@ -1436,384 +903,19 @@ 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.tcx().at(span).type_of(did).subst(self.tcx(), substs)
-    }
-
-    fn conv_object_ty_poly_trait_ref(
-        &self,
-        span: Span,
-        hir_trait_bounds: &[hir::PolyTraitRef<'_>],
-        lifetime: &hir::Lifetime,
-        borrowed: bool,
-        representation: DynKind,
-    ) -> Ty<'tcx> {
-        let tcx = self.tcx();
-
-        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 hir_trait_bounds.iter().rev() {
-            if let GenericArgCountResult {
-                correct:
-                    Err(GenericArgCountMismatch { invalid_args: cur_potential_assoc_types, .. }),
-                ..
-            } = self.instantiate_poly_trait_ref(
-                &trait_bound.trait_ref,
-                trait_bound.span,
-                ty::BoundConstness::NotConst,
-                ty::ImplPolarity::Positive,
-                dummy_self,
-                &mut bounds,
-                false,
-                // FIXME: This should be `true`, but we don't really handle
-                // associated type bounds or type aliases in objects in a way
-                // that makes this meaningful, I think.
-                OnlySelfBounds(false),
-            ) {
-                potential_assoc_types.extend(cur_potential_assoc_types);
-            }
-        }
-
-        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(_) | ty::Clause::ConstArgHasType(..) => bug!(),
-                },
-                ty::PredicateKind::WellFormed(_)
-                | ty::PredicateKind::AliasRelate(..)
-                | 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, 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()));
-        if regular_traits.len() > 1 {
-            let first_trait = &regular_traits[0];
-            let additional_trait = &regular_traits[1];
-            let mut err = struct_span_err!(
-                tcx.sess,
-                additional_trait.bottom().1,
-                E0225,
-                "only auto traits can be used as additional traits in a trait object"
-            );
-            additional_trait.label_with_exp_info(
-                &mut err,
-                "additional non-auto trait",
-                "additional use",
-            );
-            first_trait.label_with_exp_info(&mut err, "first non-auto trait", "first use");
-            err.help(format!(
-                "consider creating a new trait with all of these as supertraits and using that \
-                 trait here instead: `trait NewTrait: {} {{}}`",
-                regular_traits
-                    .iter()
-                    .map(|t| t.trait_ref().print_only_trait_path().to_string())
-                    .collect::<Vec<_>>()
-                    .join(" + "),
-            ));
-            err.note(
-                "auto-traits like `Send` and `Sync` are traits that have special properties; \
-                 for more information on them, visit \
-                 <https://doc.rust-lang.org/reference/special-types-and-traits.html#auto-traits>",
-            );
-            err.emit();
-        }
-
-        if regular_traits.is_empty() && auto_traits.is_empty() {
-            let trait_alias_span = trait_bounds
-                .iter()
-                .map(|&(trait_ref, _, _)| trait_ref.def_id())
-                .find(|&trait_ref| tcx.is_trait_alias(trait_ref))
-                .map(|trait_ref| tcx.def_span(trait_ref));
-            let reported =
-                tcx.sess.emit_err(TraitObjectDeclaredWithNoTraits { span, trait_alias_span });
-            return tcx.ty_error(reported);
-        }
-
-        // Check that there are no gross object safety violations;
-        // most importantly, that the supertraits don't contain `Self`,
-        // to avoid ICEs.
-        for item in &regular_traits {
-            let object_safety_violations =
-                astconv_object_safety_violations(tcx, item.trait_ref().def_id());
-            if !object_safety_violations.is_empty() {
-                let reported = report_object_safety_error(
-                    tcx,
-                    span,
-                    item.trait_ref().def_id(),
-                    &object_safety_violations,
-                )
-                .emit();
-                return tcx.ty_error(reported);
-            }
-        }
-
-        // 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 = trait_bounds
-            .into_iter()
-            .filter(|(trait_ref, _, _)| !tcx.trait_is_auto(trait_ref.def_id()));
-
-        for (base_trait_ref, span, constness) in regular_traits_refs_spans {
-            assert_eq!(constness, ty::BoundConstness::NotConst);
-            let base_pred: ty::Predicate<'tcx> = base_trait_ref.to_predicate(tcx);
-            for pred in traits::elaborate(tcx, [base_pred]) {
-                debug!("conv_object_ty_poly_trait_ref: observing object predicate `{:?}`", pred);
-
-                let bound_predicate = pred.kind();
-                match bound_predicate.skip_binder() {
-                    ty::PredicateKind::Clause(ty::Clause::Trait(pred)) => {
-                        let pred = bound_predicate.rebind(pred);
-                        associated_types.entry(span).or_default().extend(
-                            tcx.associated_items(pred.def_id())
-                                .in_definition_order()
-                                .filter(|item| item.kind == ty::AssocKind::Type)
-                                .filter(|item| tcx.opt_rpitit_info(item.def_id).is_none())
-                                .map(|item| item.def_id),
-                        );
-                    }
-                    ty::PredicateKind::Clause(ty::Clause::Projection(pred)) => {
-                        let pred = bound_predicate.rebind(pred);
-                        // A `Self` within the original bound will be substituted with a
-                        // `trait_object_dummy_self`, so check for that.
-                        let references_self = match pred.skip_binder().term.unpack() {
-                            ty::TermKind::Ty(ty) => ty.walk().any(|arg| arg == dummy_self.into()),
-                            ty::TermKind::Const(c) => {
-                                c.ty().walk().any(|arg| arg == dummy_self.into())
-                            }
-                        };
-
-                        // If the projection output contains `Self`, force the user to
-                        // elaborate it explicitly to avoid a lot of complexity.
-                        //
-                        // The "classically useful" case is the following:
-                        // ```
-                        //     trait MyTrait: FnMut() -> <Self as MyTrait>::MyOutput {
-                        //         type MyOutput;
-                        //     }
-                        // ```
-                        //
-                        // Here, the user could theoretically write `dyn MyTrait<Output = X>`,
-                        // but actually supporting that would "expand" to an infinitely-long type
-                        // `fix $ τ → dyn MyTrait<MyOutput = X, Output = <τ as MyTrait>::MyOutput`.
-                        //
-                        // Instead, we force the user to write
-                        // `dyn MyTrait<MyOutput = X, Output = X>`, which is uglier but works. See
-                        // the discussion in #56288 for alternatives.
-                        if !references_self {
-                            // Include projections defined on supertraits.
-                            projection_bounds.push((pred, span));
-                        }
-                    }
-                    _ => (),
-                }
-            }
-        }
-
-        for (projection_bound, _) in &projection_bounds {
-            for def_ids in associated_types.values_mut() {
-                def_ids.remove(&projection_bound.projection_def_id());
-            }
-        }
-
-        self.complain_about_missing_associated_types(
-            associated_types,
-            potential_assoc_types,
-            hir_trait_bounds,
-        );
-
-        // De-duplicate auto traits so that, e.g., `dyn Trait + Send + Send` is the same as
-        // `dyn Trait + Send`.
-        // We remove duplicates by inserting into a `FxHashSet` to avoid re-ordering
-        // the bounds
-        let mut duplicates = FxHashSet::default();
-        auto_traits.retain(|i| duplicates.insert(i.trait_ref().def_id()));
-        debug!("regular_traits: {:?}", regular_traits);
-        debug!("auto_traits: {:?}", auto_traits);
-
-        // Erase the `dummy_self` (`trait_object_dummy_self`) used above.
-        let existential_trait_refs = regular_traits.iter().map(|i| {
-            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
-                // 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;
-                let generics = tcx.generics_of(trait_ref.def_id);
-                let substs: Vec<_> = trait_ref
-                    .substs
-                    .iter()
-                    .enumerate()
-                    .skip(1) // Remove `Self` for `ExistentialPredicate`.
-                    .map(|(index, arg)| {
-                        if arg == dummy_self.into() {
-                            let param = &generics.params[index];
-                            missing_type_params.push(param.name);
-                            return tcx.ty_error_misc().into();
-                        } else if arg.walk().any(|arg| arg == dummy_self.into()) {
-                            references_self = true;
-                            return tcx.ty_error_misc().into();
-                        }
-                        arg
-                    })
-                    .collect();
-                let substs = tcx.mk_substs(&substs);
-
-                let span = i.bottom().1;
-                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)
-                });
-                self.complain_about_missing_type_params(
-                    missing_type_params,
-                    trait_ref.def_id,
-                    span,
-                    empty_generic_args,
-                );
+        let ty = self.tcx().at(span).type_of(did);
 
-                if references_self {
-                    let def_id = i.bottom().0.def_id();
-                    let mut err = struct_span_err!(
-                        tcx.sess,
-                        i.bottom().1,
-                        E0038,
-                        "the {} `{}` cannot be made into an object",
-                        tcx.def_descr(def_id),
-                        tcx.item_name(def_id),
-                    );
-                    err.note(
-                        rustc_middle::traits::ObjectSafetyViolation::SupertraitSelf(smallvec![])
-                            .error_msg(),
-                    );
-                    err.emit();
-                }
-
-                ty::ExistentialTraitRef { def_id: trait_ref.def_id, substs }
-            })
-        });
-
-        let existential_projections = projection_bounds
-            .iter()
-            // We filter out traits that don't have `Self` as their self type above,
-            // we need to do the same for projections.
-            .filter(|(bound, _)| bound.skip_binder().self_ty() == dummy_self)
-            .map(|(bound, _)| {
-                bound.map_bound(|mut b| {
-                    assert_eq!(b.projection_ty.self_ty(), dummy_self);
-
-                    // Like for trait refs, verify that `dummy_self` did not leak inside default type
-                    // parameters.
-                    let references_self = b.projection_ty.substs.iter().skip(1).any(|arg| {
-                        if arg.walk().any(|arg| arg == dummy_self.into()) {
-                            return true;
-                        }
-                        false
-                    });
-                    if references_self {
-                        let guar = tcx.sess.delay_span_bug(
-                            span,
-                            "trait object projection bounds reference `Self`",
-                        );
-                        let substs: Vec<_> = b
-                            .projection_ty
-                            .substs
-                            .iter()
-                            .map(|arg| {
-                                if arg.walk().any(|arg| arg == dummy_self.into()) {
-                                    return tcx.ty_error(guar).into();
-                                }
-                                arg
-                            })
-                            .collect();
-                        b.projection_ty.substs = tcx.mk_substs(&substs);
-                    }
-
-                    ty::ExistentialProjection::erase_self_ty(tcx, b)
-                })
-            });
-
-        let regular_trait_predicates = existential_trait_refs
-            .map(|trait_ref| trait_ref.map_bound(ty::ExistentialPredicate::Trait));
-        let auto_trait_predicates = auto_traits.into_iter().map(|trait_ref| {
-            ty::Binder::dummy(ty::ExistentialPredicate::AutoTrait(trait_ref.trait_ref().def_id()))
-        });
-        // N.b. principal, projections, auto traits
-        // FIXME: This is actually wrong with multiple principals in regards to symbol mangling
-        let mut v = regular_trait_predicates
-            .chain(
-                existential_projections.map(|x| x.map_bound(ty::ExistentialPredicate::Projection)),
-            )
-            .chain(auto_trait_predicates)
-            .collect::<SmallVec<[_; 8]>>();
-        v.sort_by(|a, b| a.skip_binder().stable_cmp(tcx, &b.skip_binder()));
-        v.dedup();
-        let existential_predicates = tcx.mk_poly_existential_predicates(&v);
-
-        // Use explicitly-specified region bound.
-        let region_bound = if !lifetime.is_elided() {
-            self.ast_region_to_region(lifetime, None)
+        if matches!(self.tcx().def_kind(did), DefKind::TyAlias)
+            && (ty.skip_binder().has_opaque_types() || self.tcx().features().lazy_type_alias)
+        {
+            // Type aliases referring to types that contain opaque types (but aren't just directly
+            // referencing a single opaque type) get encoded as a type alias that normalization will
+            // then actually instantiate the where bounds of.
+            let alias_ty = self.tcx().mk_alias_ty(did, substs);
+            Ty::new_alias(self.tcx(), ty::Weak, alias_ty)
         } else {
-            self.compute_object_lifetime_bound(span, existential_predicates).unwrap_or_else(|| {
-                if tcx.named_bound_var(lifetime.hir_id).is_some() {
-                    self.ast_region_to_region(lifetime, None)
-                } else {
-                    self.re_infer(None, span).unwrap_or_else(|| {
-                        let mut err = struct_span_err!(
-                            tcx.sess,
-                            span,
-                            E0228,
-                            "the lifetime bound for this object type cannot be deduced \
-                             from context; please supply an explicit bound"
-                        );
-                        let e = if borrowed {
-                            // We will have already emitted an error E0106 complaining about a
-                            // missing named lifetime in `&dyn Trait`, so we elide this one.
-                            err.delay_as_bug()
-                        } else {
-                            err.emit()
-                        };
-                        tcx.mk_re_error(e)
-                    })
-                }
-            })
-        };
-        debug!("region_bound: {:?}", region_bound);
-
-        let ty = tcx.mk_dynamic(existential_predicates, region_bound, representation);
-        debug!("trait_object_type: {:?}", ty);
-        ty
+            ty.subst(self.tcx(), substs)
+        }
     }
 
     fn report_ambiguous_associated_type(
@@ -1948,9 +1050,9 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             || {
                 traits::transitive_bounds_that_define_assoc_item(
                     tcx,
-                    predicates.iter().filter_map(|(p, _)| {
-                        Some(p.to_opt_poly_trait_pred()?.map_bound(|t| t.trait_ref))
-                    }),
+                    predicates
+                        .iter()
+                        .filter_map(|(p, _)| Some(p.as_trait_clause()?.map_bound(|t| t.trait_ref))),
                     assoc_name,
                 )
             },
@@ -2408,6 +1510,15 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
     ) -> Result<Option<(Ty<'tcx>, DefId)>, ErrorGuaranteed> {
         let tcx = self.tcx();
 
+        // Don't attempt to look up inherent associated types when the feature is not enabled.
+        // Theoretically it'd be fine to do so since we feature-gate their definition site.
+        // However, due to current limitations of the implementation (caused by us performing
+        // selection in AstConv), IATs can lead to cycle errors (#108491, #110106) which mask the
+        // feature-gate error, needlessly confusing users that use IATs by accident (#113265).
+        if !tcx.features().inherent_associated_types {
+            return Ok(None);
+        }
+
         let candidates: Vec<_> = tcx
             .inherent_impls(adt_did)
             .iter()
@@ -2441,32 +1552,64 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
 
         let mut fulfillment_errors = Vec::new();
         let mut applicable_candidates: Vec<_> = infcx.probe(|_| {
-            let universe = infcx.create_next_universe();
-
             // Regions are not considered during selection.
-            // FIXME(non_lifetime_binders): Here we are "truncating" or "flattening" the universes
-            // of type and const binders. Is that correct in the selection phase? See also #109505.
-            let self_ty = tcx.replace_escaping_bound_vars_uncached(
-                self_ty,
-                FnMutDelegate {
-                    regions: &mut |_| tcx.lifetimes.re_erased,
-                    types: &mut |bv| {
-                        tcx.mk_placeholder(ty::PlaceholderType { universe, bound: bv })
-                    },
-                    consts: &mut |bv, ty| {
-                        tcx.mk_const(ty::PlaceholderConst { universe, bound: bv }, ty)
-                    },
-                },
-            );
+            let self_ty = self_ty
+                .fold_with(&mut BoundVarEraser { tcx, universe: infcx.create_next_universe() });
+
+            struct BoundVarEraser<'tcx> {
+                tcx: TyCtxt<'tcx>,
+                universe: ty::UniverseIndex,
+            }
+
+            // FIXME(non_lifetime_binders): Don't assign the same universe to each placeholder.
+            impl<'tcx> TypeFolder<TyCtxt<'tcx>> for BoundVarEraser<'tcx> {
+                fn interner(&self) -> TyCtxt<'tcx> {
+                    self.tcx
+                }
+
+                fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
+                    if r.is_late_bound() { self.tcx.lifetimes.re_erased } else { r }
+                }
+
+                fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
+                    match *ty.kind() {
+                        ty::Bound(_, bv) => Ty::new_placeholder(
+                            self.tcx,
+                            ty::PlaceholderType { universe: self.universe, bound: bv },
+                        ),
+                        _ => ty.super_fold_with(self),
+                    }
+                }
+
+                fn fold_const(
+                    &mut self,
+                    ct: ty::Const<'tcx>,
+                ) -> <TyCtxt<'tcx> as rustc_type_ir::Interner>::Const {
+                    assert!(!ct.ty().has_escaping_bound_vars());
+
+                    match ct.kind() {
+                        ty::ConstKind::Bound(_, bv) => ty::Const::new_placeholder(
+                            self.tcx,
+                            ty::PlaceholderConst { universe: self.universe, bound: bv },
+                            ct.ty(),
+                        ),
+                        _ => ct.super_fold_with(self),
+                    }
+                }
+            }
+
+            let InferOk { value: self_ty, obligations } =
+                infcx.at(&cause, param_env).normalize(self_ty);
 
             candidates
                 .iter()
                 .copied()
                 .filter(|&(impl_, _)| {
                     infcx.probe(|_| {
-                        let ocx = ObligationCtxt::new_in_snapshot(&infcx);
+                        let ocx = ObligationCtxt::new(&infcx);
+                        ocx.register_obligations(obligations.clone());
 
-                        let impl_substs = infcx.fresh_item_substs(impl_);
+                        let impl_substs = infcx.fresh_substs_for_item(span, impl_);
                         let impl_ty = tcx.type_of(impl_).subst(tcx, impl_substs);
                         let impl_ty = ocx.normalize(&cause, param_env, impl_ty);
 
@@ -2522,7 +1665,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     .chain(substs.into_iter().skip(parent_substs.len())),
             );
 
-            let ty = tcx.mk_alias(ty::Inherent, tcx.mk_alias_ty(assoc_item, substs));
+            let ty = Ty::new_alias(tcx, ty::Inherent, tcx.mk_alias_ty(assoc_item, substs));
 
             return Ok(Some((ty, assoc_item)));
         }
@@ -2707,7 +1850,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 &[path_str],
                 item_segment.ident.name,
             );
-            return tcx.ty_error(reported)
+            return Ty::new_error(tcx,reported)
         };
 
         debug!("qpath_to_ty: self_type={:?}", self_ty);
@@ -2730,7 +1873,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
 
         debug!("qpath_to_ty: trait_ref={:?}", trait_ref);
 
-        tcx.mk_projection(item_def_id, item_substs)
+        Ty::new_projection(tcx, item_def_id, item_substs)
     }
 
     pub fn prohibit_generics<'a>(
@@ -2993,7 +2136,7 @@ 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);
-                tcx.mk_opaque(did, substs)
+                Ty::new_opaque(tcx, did, substs)
             }
             Res::Def(
                 DefKind::Enum
@@ -3045,16 +2188,16 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                             var: ty::BoundVar::from_u32(index),
                             kind: ty::BoundTyKind::Param(def_id, name),
                         };
-                        tcx.mk_bound(debruijn, br)
+                        Ty::new_bound(tcx, debruijn, br)
                     }
                     Some(rbv::ResolvedArg::EarlyBound(_)) => {
                         let def_id = def_id.expect_local();
                         let item_def_id = tcx.hir().ty_param_owner(def_id);
                         let generics = tcx.generics_of(item_def_id);
                         let index = generics.param_def_id_to_index[&def_id.to_def_id()];
-                        tcx.mk_ty_param(index, tcx.hir().ty_param_name(def_id))
+                        Ty::new_param(tcx, index, tcx.hir().ty_param_name(def_id))
                     }
-                    Some(rbv::ResolvedArg::Error(guar)) => tcx.ty_error(guar),
+                    Some(rbv::ResolvedArg::Error(guar)) => Ty::new_error(tcx, guar),
                     arg => bug!("unexpected bound var resolution for {hir_id:?}: {arg:?}"),
                 }
             }
@@ -3166,7 +2309,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     {
                         err.span_note(impl_.self_ty.span, "not a concrete type");
                     }
-                    tcx.ty_error(err.emit())
+                    Ty::new_error(tcx, err.emit())
                 } else {
                     ty
                 }
@@ -3207,9 +2350,9 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 match prim_ty {
                     hir::PrimTy::Bool => tcx.types.bool,
                     hir::PrimTy::Char => tcx.types.char,
-                    hir::PrimTy::Int(it) => tcx.mk_mach_int(ty::int_ty(it)),
-                    hir::PrimTy::Uint(uit) => tcx.mk_mach_uint(ty::uint_ty(uit)),
-                    hir::PrimTy::Float(ft) => tcx.mk_mach_float(ty::float_ty(ft)),
+                    hir::PrimTy::Int(it) => Ty::new_int(tcx, ty::int_ty(it)),
+                    hir::PrimTy::Uint(uit) => Ty::new_uint(tcx, ty::uint_ty(uit)),
+                    hir::PrimTy::Float(ft) => Ty::new_float(tcx, ty::float_ty(ft)),
                     hir::PrimTy::Str => tcx.types.str_,
                 }
             }
@@ -3219,7 +2362,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     .sess
                     .delay_span_bug(path.span, "path with `Res::Err` but no error emitted");
                 self.set_tainted_by_errors(e);
-                self.tcx().ty_error(e)
+                Ty::new_error(self.tcx(), e)
             }
             _ => span_bug!(span, "unexpected resolution: {:?}", path.res),
         }
@@ -3244,31 +2387,27 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         let tcx = self.tcx();
 
         let result_ty = match &ast_ty.kind {
-            hir::TyKind::Slice(ty) => tcx.mk_slice(self.ast_ty_to_ty(ty)),
+            hir::TyKind::Slice(ty) => Ty::new_slice(tcx, 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 })
+                Ty::new_ptr(tcx, ty::TypeAndMut { ty: self.ast_ty_to_ty(mt.ty), mutbl: mt.mutbl })
             }
             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);
-                tcx.mk_ref(r, ty::TypeAndMut { ty: t, mutbl: mt.mutbl })
+                Ty::new_ref(tcx, r, ty::TypeAndMut { ty: t, mutbl: mt.mutbl })
             }
             hir::TyKind::Never => tcx.types.never,
             hir::TyKind::Tup(fields) => {
-                tcx.mk_tup_from_iter(fields.iter().map(|t| self.ast_ty_to_ty(t)))
+                Ty::new_tup_from_iter(tcx, fields.iter().map(|t| self.ast_ty_to_ty(t)))
             }
             hir::TyKind::BareFn(bf) => {
                 require_c_abi_if_c_variadic(tcx, bf.decl, bf.abi, ast_ty.span);
 
-                tcx.mk_fn_ptr(self.ty_of_fn(
-                    ast_ty.hir_id,
-                    bf.unsafety,
-                    bf.abi,
-                    bf.decl,
-                    None,
-                    Some(ast_ty),
-                ))
+                Ty::new_fn_ptr(
+                    tcx,
+                    self.ty_of_fn(ast_ty.hir_id, bf.unsafety, bf.abi, bf.decl, None, Some(ast_ty)),
+                )
             }
             hir::TyKind::TraitObject(bounds, lifetime, repr) => {
                 self.maybe_lint_bare_trait(ast_ty, in_path);
@@ -3277,7 +2416,14 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     TraitObjectSyntax::DynStar => ty::DynStar,
                 };
 
-                self.conv_object_ty_poly_trait_ref(ast_ty.span, bounds, lifetime, borrowed, repr)
+                self.conv_object_ty_poly_trait_ref(
+                    ast_ty.span,
+                    ast_ty.hir_id,
+                    bounds,
+                    lifetime,
+                    borrowed,
+                    repr,
+                )
             }
             hir::TyKind::Path(hir::QPath::Resolved(maybe_qself, path)) => {
                 debug!(?maybe_qself, ?path);
@@ -3288,7 +2434,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 let opaque_ty = tcx.hir().item(item_id);
 
                 match opaque_ty.kind {
-                    hir::ItemKind::OpaqueTy(hir::OpaqueTy { origin, .. }) => {
+                    hir::ItemKind::OpaqueTy(&hir::OpaqueTy { origin, .. }) => {
                         let local_def_id = item_id.owner_id.def_id;
                         // If this is an RPITIT and we are using the new RPITIT lowering scheme, we
                         // generate the def_id of an associated type for the trait and return as
@@ -3308,7 +2454,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 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(|guar| tcx.ty_error(guar))
+                    .unwrap_or_else(|guar| Ty::new_error(tcx, guar))
             }
             &hir::TyKind::Path(hir::QPath::LangItem(lang_item, span, _)) => {
                 let def_id = tcx.require_lang_item(lang_item, Some(span));
@@ -3332,7 +2478,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     }
                 };
 
-                tcx.mk_array_with_const_len(self.ast_ty_to_ty(ty), length)
+                Ty::new_array_with_const_len(tcx, self.ast_ty_to_ty(ty), length)
             }
             hir::TyKind::Typeof(e) => {
                 let ty_erased = tcx.type_of(e.def_id).subst_identity();
@@ -3356,7 +2502,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 // handled specially and will not descend into this routine.
                 self.ty_infer(None, ast_ty.span)
             }
-            hir::TyKind::Err(guar) => tcx.ty_error(*guar),
+            hir::TyKind::Err(guar) => Ty::new_error(tcx, *guar),
         };
 
         self.record_ty(ast_ty.hir_id, result_ty, ast_ty.span);
@@ -3393,7 +2539,11 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         });
         debug!("impl_trait_ty_to_ty: substs={:?}", substs);
 
-        if in_trait { tcx.mk_projection(def_id, substs) } else { tcx.mk_opaque(def_id, substs) }
+        if in_trait {
+            Ty::new_projection(tcx, def_id, substs)
+        } else {
+            Ty::new_opaque(tcx, def_id, substs)
+        }
     }
 
     pub fn ty_of_arg(&self, ty: &hir::Ty<'_>, expected_ty: Option<Ty<'tcx>>) -> Ty<'tcx> {
@@ -3462,7 +2612,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     self.ast_ty_to_ty(output)
                 }
             }
-            hir::FnRetTy::DefaultReturn(..) => tcx.mk_unit(),
+            hir::FnRetTy::DefaultReturn(..) => Ty::new_unit(tcx,),
         };
 
         debug!(?output_ty);
@@ -3641,148 +2791,4 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         }
         Some(r)
     }
-
-    /// Make sure that we are in the condition to suggest the blanket implementation.
-    fn maybe_lint_blanket_trait_impl(&self, self_ty: &hir::Ty<'_>, diag: &mut Diagnostic) {
-        let tcx = self.tcx();
-        let parent_id = tcx.hir().get_parent_item(self_ty.hir_id).def_id;
-        if let hir::Node::Item(hir::Item {
-            kind:
-                hir::ItemKind::Impl(hir::Impl {
-                    self_ty: impl_self_ty, of_trait: Some(of_trait_ref), generics, ..
-                }),
-            ..
-        }) = tcx.hir().get_by_def_id(parent_id) && self_ty.hir_id == impl_self_ty.hir_id
-        {
-            if !of_trait_ref.trait_def_id().is_some_and(|def_id| def_id.is_local()) {
-                return;
-            }
-            let of_trait_span = of_trait_ref.path.span;
-            // make sure that we are not calling unwrap to abort during the compilation
-            let Ok(impl_trait_name) = tcx.sess.source_map().span_to_snippet(self_ty.span) else { return; };
-            let Ok(of_trait_name) = tcx.sess.source_map().span_to_snippet(of_trait_span) else { return; };
-            // check if the trait has generics, to make a correct suggestion
-            let param_name = generics.params.next_type_param_name(None);
-
-            let add_generic_sugg = if let Some(span) = generics.span_for_param_suggestion() {
-                (span, format!(", {}: {}", param_name, impl_trait_name))
-            } else {
-                (generics.span, format!("<{}: {}>", param_name, impl_trait_name))
-            };
-            diag.multipart_suggestion(
-            format!("alternatively use a blanket \
-                     implementation to implement `{of_trait_name}` for \
-                     all types that also implement `{impl_trait_name}`"),
-                vec![
-                    (self_ty.span, param_name),
-                    add_generic_sugg,
-                ],
-                Applicability::MaybeIncorrect,
-            );
-        }
-    }
-
-    fn maybe_lint_bare_trait(&self, self_ty: &hir::Ty<'_>, in_path: bool) {
-        let tcx = self.tcx();
-        if let hir::TyKind::TraitObject([poly_trait_ref, ..], _, TraitObjectSyntax::None) =
-            self_ty.kind
-        {
-            let needs_bracket = in_path
-                && !tcx
-                    .sess
-                    .source_map()
-                    .span_to_prev_source(self_ty.span)
-                    .ok()
-                    .is_some_and(|s| s.trim_end().ends_with('<'));
-
-            let is_global = poly_trait_ref.trait_ref.path.is_global();
-
-            let mut sugg = Vec::from_iter([(
-                self_ty.span.shrink_to_lo(),
-                format!(
-                    "{}dyn {}",
-                    if needs_bracket { "<" } else { "" },
-                    if is_global { "(" } else { "" },
-                ),
-            )]);
-
-            if is_global || needs_bracket {
-                sugg.push((
-                    self_ty.span.shrink_to_hi(),
-                    format!(
-                        "{}{}",
-                        if is_global { ")" } else { "" },
-                        if needs_bracket { ">" } else { "" },
-                    ),
-                ));
-            }
-
-            if self_ty.span.edition().rust_2021() {
-                let msg = "trait objects must include the `dyn` keyword";
-                let label = "add `dyn` keyword before this trait";
-                let mut diag =
-                    rustc_errors::struct_span_err!(tcx.sess, self_ty.span, E0782, "{}", msg);
-                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.stash(self_ty.span, StashKey::TraitMissingMethod);
-            } else {
-                let msg = "trait objects without an explicit `dyn` are deprecated";
-                tcx.struct_span_lint_hir(
-                    BARE_TRAIT_OBJECTS,
-                    self_ty.hir_id,
-                    self_ty.span,
-                    msg,
-                    |lint| {
-                        lint.multipart_suggestion_verbose(
-                            "use `dyn`",
-                            sugg,
-                            Applicability::MachineApplicable,
-                        );
-                        self.maybe_lint_blanket_trait_impl(&self_ty, lint);
-                        lint
-                    },
-                );
-            }
-        }
-    }
-}
-
-pub trait InferCtxtExt<'tcx> {
-    fn fresh_item_substs(&self, def_id: DefId) -> SubstsRef<'tcx>;
-}
-
-impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
-    fn fresh_item_substs(&self, def_id: DefId) -> SubstsRef<'tcx> {
-        InternalSubsts::for_item(self.tcx, def_id, |param, _| match param.kind {
-            GenericParamDefKind::Lifetime => self.tcx.lifetimes.re_erased.into(),
-            GenericParamDefKind::Type { .. } => self
-                .next_ty_var(TypeVariableOrigin {
-                    kind: TypeVariableOriginKind::SubstitutionPlaceholder,
-                    span: self.tcx.def_span(def_id),
-                })
-                .into(),
-            GenericParamDefKind::Const { .. } => {
-                let span = self.tcx.def_span(def_id);
-                let origin = ConstVariableOrigin {
-                    kind: ConstVariableOriginKind::SubstitutionPlaceholder,
-                    span,
-                };
-                self.next_const_var(
-                    self.tcx
-                        .type_of(param.def_id)
-                        .no_bound_vars()
-                        .expect("const parameter types cannot be generic"),
-                    origin,
-                )
-                .into()
-            }
-        })
-    }
 }