Merging upstream version 1.72.1+dfsg1.

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

35 files changed, 2595 insertions, 2009 deletions

diff --git a/compiler/rustc_hir_analysis/src/astconv/bounds.rs b/compiler/rustc_hir_analysis/src/astconv/bounds.rs
new file mode 100644
index 000000000..b13de7701
--- /dev/null
+++ b/compiler/rustc_hir_analysis/src/astconv/bounds.rs
@@ -0,0 +1,575 @@
+use rustc_data_structures::fx::FxHashMap;
+use rustc_errors::struct_span_err;
+use rustc_hir as hir;
+use rustc_hir::def::{DefKind, Res};
+use rustc_hir::def_id::{DefId, LocalDefId};
+use rustc_lint_defs::Applicability;
+use rustc_middle::ty::{self as ty, Ty, TypeVisitableExt};
+use rustc_span::symbol::Ident;
+use rustc_span::{ErrorGuaranteed, Span};
+use rustc_trait_selection::traits;
+
+use crate::astconv::{
+    AstConv, ConvertedBinding, ConvertedBindingKind, OnlySelfBounds, PredicateFilter,
+};
+use crate::bounds::Bounds;
+use crate::errors::{MultipleRelaxedDefaultBounds, ValueOfAssociatedStructAlreadySpecified};
+
+impl<'tcx> dyn AstConv<'tcx> + '_ {
+    /// 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<'_>],
+        filter: PredicateFilter,
+    ) -> Bounds<'tcx> {
+        let mut bounds = Bounds::default();
+
+        let only_self_bounds = match filter {
+            PredicateFilter::All | PredicateFilter::SelfAndAssociatedTypeBounds => {
+                OnlySelfBounds(false)
+            }
+            PredicateFilter::SelfOnly | PredicateFilter::SelfThatDefines(_) => OnlySelfBounds(true),
+        };
+
+        self.add_bounds(
+            param_ty,
+            ast_bounds.iter().filter(|bound| {
+                match filter {
+                PredicateFilter::All
+                | PredicateFilter::SelfOnly
+                | PredicateFilter::SelfAndAssociatedTypeBounds => true,
+                PredicateFilter::SelfThatDefines(assoc_name) => {
+                    if let Some(trait_ref) = bound.trait_ref()
+                        && let Some(trait_did) = trait_ref.trait_def_id()
+                        && self.tcx().trait_may_define_assoc_item(trait_did, assoc_name)
+                    {
+                        true
+                    } else {
+                        false
+                    }
+                }
+            }
+            }),
+            &mut bounds,
+            ty::List::empty(),
+            only_self_bounds,
+        );
+        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))]
+    pub(super) 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 {
+            let mut emitted_bad_param_err = false;
+            // 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 {
+                        ty::GenericParamDefKind::Lifetime => ty::Region::new_late_bound(
+                            tcx,
+                            ty::INNERMOST,
+                            ty::BoundRegion {
+                                var: ty::BoundVar::from_usize(num_bound_vars),
+                                kind: ty::BoundRegionKind::BrNamed(param.def_id, param.name),
+                            },
+                        )
+                        .into(),
+                        ty::GenericParamDefKind::Type { .. } => {
+                            if !emitted_bad_param_err {
+                                tcx.sess.emit_err(
+                                    crate::errors::ReturnTypeNotationIllegalParam::Type {
+                                        span: path_span,
+                                        param_span: tcx.def_span(param.def_id),
+                                    },
+                                );
+                                emitted_bad_param_err = true;
+                            }
+                            Ty::new_bound(
+                                tcx,
+                                ty::INNERMOST,
+                                ty::BoundTy {
+                                    var: ty::BoundVar::from_usize(num_bound_vars),
+                                    kind: ty::BoundTyKind::Param(param.def_id, param.name),
+                                },
+                            )
+                            .into()
+                        }
+                        ty::GenericParamDefKind::Const { .. } => {
+                            if !emitted_bad_param_err {
+                                tcx.sess.emit_err(
+                                    crate::errors::ReturnTypeNotationIllegalParam::Const {
+                                        span: path_span,
+                                        param_span: tcx.def_span(param.def_id),
+                                    },
+                                );
+                                emitted_bad_param_err = true;
+                            }
+                            let ty = tcx
+                                .type_of(param.def_id)
+                                .no_bound_vars()
+                                .expect("ct params cannot have early bound vars");
+                            ty::Const::new_bound(
+                                tcx,
+                                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.is_impl_trait_in_trait(alias_ty.def_id)
+            {
+                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::bind(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 => Ty::new_error(tcx, reported).into(),
+                            hir::def::DefKind::AssocConst => ty::Const::new_error(
+                                tcx,
+                                reported,
+                                tcx.type_of(assoc_item_def_id)
+                                    .subst(tcx, projection_ty.skip_binder().substs),
+                            )
+                            .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 = Ty::new_alias(tcx, ty::Projection, projection_ty.skip_binder());
+                    self.add_bounds(
+                        param_ty,
+                        ast_bounds.iter(),
+                        bounds,
+                        projection_ty.bound_vars(),
+                        only_self_bounds,
+                    );
+                }
+            }
+        }
+        Ok(())
+    }
+}
diff --git a/compiler/rustc_hir_analysis/src/astconv/errors.rs b/compiler/rustc_hir_analysis/src/astconv/errors.rs
index 7b922f5d5..ddf99853b 100644
--- a/compiler/rustc_hir_analysis/src/astconv/errors.rs
+++ b/compiler/rustc_hir_analysis/src/astconv/errors.rs
@@ -122,9 +122,13 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
 
         let all_candidate_names: Vec<_> = all_candidates()
             .flat_map(|r| self.tcx().associated_items(r.def_id()).in_definition_order())
-            .filter_map(
-                |item| if item.kind == ty::AssocKind::Type { Some(item.name) } else { None },
-            )
+            .filter_map(|item| {
+                if item.opt_rpitit_info.is_none() && item.kind == ty::AssocKind::Type {
+                    Some(item.name)
+                } else {
+                    None
+                }
+            })
             .collect();
 
         if let (Some(suggested_name), true) = (
@@ -159,9 +163,13 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             .flat_map(|trait_def_id| {
                 self.tcx().associated_items(*trait_def_id).in_definition_order()
             })
-            .filter_map(
-                |item| if item.kind == ty::AssocKind::Type { Some(item.name) } else { None },
-            )
+            .filter_map(|item| {
+                if item.opt_rpitit_info.is_none() && item.kind == ty::AssocKind::Type {
+                    Some(item.name)
+                } else {
+                    None
+                }
+            })
             .collect();
 
         if let (Some(suggested_name), true) = (
@@ -343,13 +351,13 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         let format_pred = |pred: ty::Predicate<'tcx>| {
             let bound_predicate = pred.kind();
             match bound_predicate.skip_binder() {
-                ty::PredicateKind::Clause(ty::Clause::Projection(pred)) => {
+                ty::PredicateKind::Clause(ty::ClauseKind::Projection(pred)) => {
                     let pred = bound_predicate.rebind(pred);
                     // `<Foo as Iterator>::Item = String`.
                     let projection_ty = pred.skip_binder().projection_ty;
 
                     let substs_with_infer_self = tcx.mk_substs_from_iter(
-                        std::iter::once(tcx.mk_ty_var(ty::TyVid::from_u32(0)).into())
+                        std::iter::once(Ty::new_var(tcx, ty::TyVid::from_u32(0)).into())
                             .chain(projection_ty.substs.iter().skip(1)),
                     );
 
@@ -364,7 +372,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     bound_span_label(projection_ty.self_ty(), &obligation, &quiet);
                     Some((obligation, projection_ty.self_ty()))
                 }
-                ty::PredicateKind::Clause(ty::Clause::Trait(poly_trait_ref)) => {
+                ty::PredicateKind::Clause(ty::ClauseKind::Trait(poly_trait_ref)) => {
                     let p = poly_trait_ref.trait_ref;
                     let self_ty = p.self_ty();
                     let path = p.print_only_trait_path();
diff --git a/compiler/rustc_hir_analysis/src/astconv/lint.rs b/compiler/rustc_hir_analysis/src/astconv/lint.rs
new file mode 100644
index 000000000..05a3ab63d
--- /dev/null
+++ b/compiler/rustc_hir_analysis/src/astconv/lint.rs
@@ -0,0 +1,124 @@
+use rustc_ast::TraitObjectSyntax;
+use rustc_errors::{Diagnostic, StashKey};
+use rustc_hir as hir;
+use rustc_lint_defs::{builtin::BARE_TRAIT_OBJECTS, Applicability};
+use rustc_trait_selection::traits::error_reporting::suggestions::NextTypeParamName;
+
+use super::AstConv;
+
+impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
+    /// Make sure that we are in the condition to suggest the blanket implementation.
+    pub(super) 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,
+            );
+        }
+    }
+
+    pub(super) 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
+                    },
+                );
+            }
+        }
+    }
+}
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()
-            }
-        })
-    }
 }
diff --git a/compiler/rustc_hir_analysis/src/astconv/object_safety.rs b/compiler/rustc_hir_analysis/src/astconv/object_safety.rs
new file mode 100644
index 000000000..9227ee934
--- /dev/null
+++ b/compiler/rustc_hir_analysis/src/astconv/object_safety.rs
@@ -0,0 +1,408 @@
+use crate::astconv::{GenericArgCountMismatch, GenericArgCountResult, OnlySelfBounds};
+use crate::bounds::Bounds;
+use crate::errors::TraitObjectDeclaredWithNoTraits;
+use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_errors::struct_span_err;
+use rustc_hir as hir;
+use rustc_hir::def::{DefKind, Res};
+use rustc_hir::def_id::DefId;
+use rustc_lint_defs::builtin::UNUSED_ASSOCIATED_TYPE_BOUNDS;
+use rustc_middle::ty::{self, Ty};
+use rustc_middle::ty::{DynKind, ToPredicate};
+use rustc_span::Span;
+use rustc_trait_selection::traits::error_reporting::report_object_safety_error;
+use rustc_trait_selection::traits::{self, astconv_object_safety_violations};
+
+use smallvec::{smallvec, SmallVec};
+use std::collections::BTreeSet;
+
+use super::AstConv;
+
+impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
+    pub(super) fn conv_object_ty_poly_trait_ref(
+        &self,
+        span: Span,
+        hir_id: hir::HirId,
+        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.clauses() {
+            let bound_pred = pred.kind();
+            match bound_pred.skip_binder() {
+                ty::ClauseKind::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::ClauseKind::Projection(proj) => {
+                    projection_bounds.push((bound_pred.rebind(proj), span));
+                }
+                ty::ClauseKind::TypeOutlives(_) => {
+                    // Do nothing, we deal with regions separately
+                }
+                ty::ClauseKind::RegionOutlives(_)
+                | ty::ClauseKind::ConstArgHasType(..)
+                | ty::ClauseKind::WellFormed(_)
+                | ty::ClauseKind::ConstEvaluatable(_) => {
+                    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 Ty::new_error(tcx, 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 Ty::new_error(tcx, 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::ClauseKind::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| item.opt_rpitit_info.is_none())
+                                .map(|item| item.def_id),
+                        );
+                    }
+                    ty::PredicateKind::Clause(ty::ClauseKind::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));
+                        }
+                    }
+                    _ => (),
+                }
+            }
+        }
+
+        // `dyn Trait<Assoc = Foo>` desugars to (not Rust syntax) `dyn Trait where <Self as Trait>::Assoc = Foo`.
+        // So every `Projection` clause is an `Assoc = Foo` bound. `associated_types` contains all associated
+        // types's `DefId`, so the following loop removes all the `DefIds` of the associated types that have a
+        // corresponding `Projection` clause
+        for def_ids in associated_types.values_mut() {
+            for (projection_bound, span) in &projection_bounds {
+                let def_id = projection_bound.projection_def_id();
+                def_ids.remove(&def_id);
+                if tcx.generics_require_sized_self(def_id) {
+                    tcx.emit_spanned_lint(
+                        UNUSED_ASSOCIATED_TYPE_BOUNDS,
+                        hir_id,
+                        *span,
+                        crate::errors::UnusedAssociatedTypeBounds { span: *span },
+                    );
+                }
+            }
+            // If the associated type has a `where Self: Sized` bound, we do not need to constrain the associated
+            // type in the `dyn Trait`.
+            def_ids.retain(|def_id| !tcx.generics_require_sized_self(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 Ty::new_misc_error(tcx).into();
+                        } else if arg.walk().any(|arg| arg == dummy_self.into()) {
+                            references_self = true;
+                            return Ty::new_misc_error(tcx).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,
+                );
+
+                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 Ty::new_error(tcx, 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)
+        } 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()
+                        };
+                        ty::Region::new_error(tcx, e)
+                    })
+                }
+            })
+        };
+        debug!("region_bound: {:?}", region_bound);
+
+        let ty = Ty::new_dynamic(tcx, existential_predicates, region_bound, representation);
+        debug!("trait_object_type: {:?}", ty);
+        ty
+    }
+}
diff --git a/compiler/rustc_hir_analysis/src/autoderef.rs b/compiler/rustc_hir_analysis/src/autoderef.rs
index d6d1498d7..c07ac35cb 100644
--- a/compiler/rustc_hir_analysis/src/autoderef.rs
+++ b/compiler/rustc_hir_analysis/src/autoderef.rs
@@ -73,7 +73,7 @@ impl<'a, 'tcx> Iterator for Autoderef<'a, 'tcx> {
             // NOTE: we may still need to normalize the built-in deref in case
             // we have some type like `&<Ty as Trait>::Assoc`, since users of
             // autoderef expect this type to have been structurally normalized.
-            if self.infcx.tcx.trait_solver_next()
+            if self.infcx.next_trait_solver()
                 && let ty::Alias(ty::Projection, _) = ty.kind()
             {
                 let (normalized_ty, obligations) = self.structurally_normalize(ty)?;
@@ -148,8 +148,11 @@ impl<'a, 'tcx> Autoderef<'a, 'tcx> {
             return None;
         }
 
-        let (normalized_ty, obligations) =
-            self.structurally_normalize(tcx.mk_projection(tcx.lang_items().deref_target()?, [ty]))?;
+        let (normalized_ty, obligations) = self.structurally_normalize(Ty::new_projection(
+            tcx,
+            tcx.lang_items().deref_target()?,
+            [ty],
+        ))?;
         debug!("overloaded_deref_ty({:?}) = ({:?}, {:?})", ty, normalized_ty, obligations);
         self.state.obligations.extend(obligations);
 
@@ -161,8 +164,7 @@ impl<'a, 'tcx> Autoderef<'a, 'tcx> {
         &self,
         ty: Ty<'tcx>,
     ) -> Option<(Ty<'tcx>, Vec<traits::PredicateObligation<'tcx>>)> {
-        let tcx = self.infcx.tcx;
-        let mut fulfill_cx = <dyn TraitEngine<'tcx>>::new_in_snapshot(tcx);
+        let mut fulfill_cx = <dyn TraitEngine<'tcx>>::new(self.infcx);
 
         let cause = traits::ObligationCause::misc(self.span, self.body_id);
         let normalized_ty = match self
diff --git a/compiler/rustc_hir_analysis/src/bounds.rs b/compiler/rustc_hir_analysis/src/bounds.rs
index 686066abb..531100e1f 100644
--- a/compiler/rustc_hir_analysis/src/bounds.rs
+++ b/compiler/rustc_hir_analysis/src/bounds.rs
@@ -23,7 +23,7 @@ use rustc_span::Span;
 /// include the self type (e.g., `trait_bounds`) but in others we do not
 #[derive(Default, PartialEq, Eq, Clone, Debug)]
 pub struct Bounds<'tcx> {
-    pub predicates: Vec<(ty::Predicate<'tcx>, Span)>,
+    pub clauses: Vec<(ty::Clause<'tcx>, Span)>,
 }
 
 impl<'tcx> Bounds<'tcx> {
@@ -33,7 +33,8 @@ impl<'tcx> Bounds<'tcx> {
         region: ty::PolyTypeOutlivesPredicate<'tcx>,
         span: Span,
     ) {
-        self.predicates.push((region.to_predicate(tcx), span));
+        self.clauses
+            .push((region.map_bound(|p| ty::ClauseKind::TypeOutlives(p)).to_predicate(tcx), span));
     }
 
     pub fn push_trait_bound(
@@ -44,9 +45,11 @@ impl<'tcx> Bounds<'tcx> {
         constness: ty::BoundConstness,
         polarity: ty::ImplPolarity,
     ) {
-        self.predicates.push((
+        self.clauses.push((
             trait_ref
-                .map_bound(|trait_ref| ty::TraitPredicate { trait_ref, constness, polarity })
+                .map_bound(|trait_ref| {
+                    ty::ClauseKind::Trait(ty::TraitPredicate { trait_ref, constness, polarity })
+                })
                 .to_predicate(tcx),
             span,
         ));
@@ -58,17 +61,20 @@ impl<'tcx> Bounds<'tcx> {
         projection: ty::PolyProjectionPredicate<'tcx>,
         span: Span,
     ) {
-        self.predicates.push((projection.to_predicate(tcx), span));
+        self.clauses.push((
+            projection.map_bound(|proj| ty::ClauseKind::Projection(proj)).to_predicate(tcx),
+            span,
+        ));
     }
 
     pub fn push_sized(&mut self, tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, span: Span) {
         let sized_def_id = tcx.require_lang_item(LangItem::Sized, Some(span));
         let trait_ref = ty::TraitRef::new(tcx, sized_def_id, [ty]);
         // Preferable to put this obligation first, since we report better errors for sized ambiguity.
-        self.predicates.insert(0, (trait_ref.without_const().to_predicate(tcx), span));
+        self.clauses.insert(0, (trait_ref.to_predicate(tcx), span));
     }
 
-    pub fn predicates(&self) -> impl Iterator<Item = (ty::Predicate<'tcx>, Span)> + '_ {
-        self.predicates.iter().cloned()
+    pub fn clauses(&self) -> impl Iterator<Item = (ty::Clause<'tcx>, Span)> + '_ {
+        self.clauses.iter().cloned()
     }
 }
diff --git a/compiler/rustc_hir_analysis/src/check/check.rs b/compiler/rustc_hir_analysis/src/check/check.rs
index 3b2c052e8..120545c8e 100644
--- a/compiler/rustc_hir_analysis/src/check/check.rs
+++ b/compiler/rustc_hir_analysis/src/check/check.rs
@@ -177,7 +177,7 @@ fn check_static_inhabited(tcx: TyCtxt<'_>, def_id: LocalDefId) {
         }
         // Generic statics are rejected, but we still reach this case.
         Err(e) => {
-            tcx.sess.delay_span_bug(span, e.to_string());
+            tcx.sess.delay_span_bug(span, format!("{e:?}"));
             return;
         }
     };
@@ -224,7 +224,8 @@ fn check_opaque(tcx: TyCtxt<'_>, id: hir::ItemId) {
     if check_opaque_for_cycles(tcx, item.owner_id.def_id, substs, span, &origin).is_err() {
         return;
     }
-    check_opaque_meets_bounds(tcx, item.owner_id.def_id, span, &origin);
+
+    let _ = check_opaque_meets_bounds(tcx, item.owner_id.def_id, span, &origin);
 }
 
 /// Checks that an opaque type does not use `Self` or `T::Foo` projections that would result
@@ -299,7 +300,7 @@ pub(super) fn check_opaque_for_inheriting_lifetimes(
         }
     }
 
-    if let ItemKind::OpaqueTy(hir::OpaqueTy {
+    if let ItemKind::OpaqueTy(&hir::OpaqueTy {
         origin: hir::OpaqueTyOrigin::AsyncFn(..) | hir::OpaqueTyOrigin::FnReturn(..),
         in_trait,
         ..
@@ -307,9 +308,9 @@ pub(super) fn check_opaque_for_inheriting_lifetimes(
     {
         let substs = InternalSubsts::identity_for_item(tcx, def_id);
         let opaque_identity_ty = if in_trait && !tcx.lower_impl_trait_in_trait_to_assoc_ty() {
-            tcx.mk_projection(def_id.to_def_id(), substs)
+            Ty::new_projection(tcx, def_id.to_def_id(), substs)
         } else {
-            tcx.mk_opaque(def_id.to_def_id(), substs)
+            Ty::new_opaque(tcx, def_id.to_def_id(), substs)
         };
         let mut visitor = ProhibitOpaqueVisitor {
             opaque_identity_ty,
@@ -395,7 +396,7 @@ fn check_opaque_meets_bounds<'tcx>(
     def_id: LocalDefId,
     span: Span,
     origin: &hir::OpaqueTyOrigin,
-) {
+) -> Result<(), ErrorGuaranteed> {
     let defining_use_anchor = match *origin {
         hir::OpaqueTyOrigin::FnReturn(did) | hir::OpaqueTyOrigin::AsyncFn(did) => did,
         hir::OpaqueTyOrigin::TyAlias { .. } => tcx.impl_trait_parent(def_id),
@@ -409,7 +410,7 @@ fn check_opaque_meets_bounds<'tcx>(
     let ocx = ObligationCtxt::new(&infcx);
 
     let substs = InternalSubsts::identity_for_item(tcx, def_id.to_def_id());
-    let opaque_ty = tcx.mk_opaque(def_id.to_def_id(), substs);
+    let opaque_ty = Ty::new_opaque(tcx, def_id.to_def_id(), substs);
 
     // `ReErased` regions appear in the "parent_substs" of closures/generators.
     // We're ignoring them here and replacing them with fresh region variables.
@@ -429,24 +430,26 @@ fn check_opaque_meets_bounds<'tcx>(
         Ok(()) => {}
         Err(ty_err) => {
             let ty_err = ty_err.to_string(tcx);
-            tcx.sess.delay_span_bug(
+            return Err(tcx.sess.delay_span_bug(
                 span,
                 format!("could not unify `{hidden_ty}` with revealed type:\n{ty_err}"),
-            );
+            ));
         }
     }
 
     // Additionally require the hidden type to be well-formed with only the generics of the opaque type.
     // Defining use functions may have more bounds than the opaque type, which is ok, as long as the
     // hidden type is well formed even without those bounds.
-    let predicate = ty::Binder::dummy(ty::PredicateKind::WellFormed(hidden_ty.into()));
+    let predicate =
+        ty::Binder::dummy(ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(hidden_ty.into())));
     ocx.register_obligation(Obligation::new(tcx, misc_cause, param_env, predicate));
 
     // Check that all obligations are satisfied by the implementation's
     // version.
     let errors = ocx.select_all_or_error();
     if !errors.is_empty() {
-        infcx.err_ctxt().report_fulfillment_errors(&errors);
+        let guar = infcx.err_ctxt().report_fulfillment_errors(&errors);
+        return Err(guar);
     }
     match origin {
         // Checked when type checking the function containing them.
@@ -460,14 +463,15 @@ fn check_opaque_meets_bounds<'tcx>(
             if tcx.def_kind(tcx.parent(def_id.to_def_id())) == DefKind::OpaqueTy => {}
         // Can have different predicates to their defining use
         hir::OpaqueTyOrigin::TyAlias { .. } => {
-            let wf_tys = ocx.assumed_wf_types(param_env, span, def_id);
+            let wf_tys = ocx.assumed_wf_types_and_report_errors(param_env, def_id)?;
             let implied_bounds = infcx.implied_bounds_tys(param_env, def_id, wf_tys);
             let outlives_env = OutlivesEnvironment::with_bounds(param_env, implied_bounds);
-            let _ = ocx.resolve_regions_and_report_errors(defining_use_anchor, &outlives_env);
+            ocx.resolve_regions_and_report_errors(defining_use_anchor, &outlives_env)?;
         }
     }
     // Clean up after ourselves
     let _ = infcx.take_opaque_types();
+    Ok(())
 }
 
 fn is_enum_of_nonnullable_ptr<'tcx>(
@@ -562,8 +566,8 @@ fn check_item_type(tcx: TyCtxt<'_>, id: hir::ItemId) {
             check_union(tcx, id.owner_id.def_id);
         }
         DefKind::OpaqueTy => {
-            let opaque = tcx.hir().expect_item(id.owner_id.def_id).expect_opaque_ty();
-            if let hir::OpaqueTyOrigin::FnReturn(fn_def_id) | hir::OpaqueTyOrigin::AsyncFn(fn_def_id) = opaque.origin
+            let origin = tcx.opaque_type_origin(id.owner_id.def_id);
+            if let hir::OpaqueTyOrigin::FnReturn(fn_def_id) | hir::OpaqueTyOrigin::AsyncFn(fn_def_id) = origin
                 && let hir::Node::TraitItem(trait_item) = tcx.hir().get_by_def_id(fn_def_id)
                 && let (_, hir::TraitFn::Required(..)) = trait_item.expect_fn()
             {
@@ -704,7 +708,7 @@ pub(super) fn check_specialization_validity<'tcx>(
             // grandparent. In that case, if parent is a `default impl`, inherited items use the
             // "defaultness" from the grandparent, else they are final.
             None => {
-                if tcx.impl_defaultness(parent_impl.def_id()).is_default() {
+                if tcx.defaultness(parent_impl.def_id()).is_default() {
                     None
                 } else {
                     Some(Err(parent_impl.def_id()))
@@ -718,7 +722,14 @@ pub(super) fn check_specialization_validity<'tcx>(
     let result = opt_result.unwrap_or(Ok(()));
 
     if let Err(parent_impl) = result {
-        report_forbidden_specialization(tcx, impl_item, parent_impl);
+        if !tcx.is_impl_trait_in_trait(impl_item) {
+            report_forbidden_specialization(tcx, impl_item, parent_impl);
+        } else {
+            tcx.sess.delay_span_bug(
+                DUMMY_SP,
+                format!("parent item: {:?} not marked as default", parent_impl),
+            );
+        }
     }
 }
 
@@ -803,7 +814,7 @@ fn check_impl_items_against_trait<'tcx>(
                 .as_ref()
                 .is_some_and(|node_item| node_item.item.defaultness(tcx).has_value());
 
-            if !is_implemented && tcx.impl_defaultness(impl_id).is_final() {
+            if !is_implemented && tcx.defaultness(impl_id).is_final() {
                 missing_items.push(tcx.associated_item(trait_item_id));
             }
 
@@ -1481,7 +1492,9 @@ fn opaque_type_cycle_error(
                 }
 
                 for closure_def_id in visitor.closures {
-                    let Some(closure_local_did) = closure_def_id.as_local() else { continue; };
+                    let Some(closure_local_did) = closure_def_id.as_local() else {
+                        continue;
+                    };
                     let typeck_results = tcx.typeck(closure_local_did);
 
                     let mut label_match = |ty: Ty<'_>, span| {
@@ -1549,7 +1562,7 @@ pub(super) fn check_generator_obligations(tcx: TyCtxt<'_>, def_id: LocalDefId) {
         .with_opaque_type_inference(DefiningAnchor::Bind(def_id))
         .build();
 
-    let mut fulfillment_cx = <dyn TraitEngine<'_>>::new(infcx.tcx);
+    let mut fulfillment_cx = <dyn TraitEngine<'_>>::new(&infcx);
     for (predicate, cause) in generator_interior_predicates {
         let obligation = Obligation::new(tcx, cause.clone(), param_env, *predicate);
         fulfillment_cx.register_predicate_obligation(&infcx, obligation);
diff --git a/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs b/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
index 8bf1e0e84..22e576e34 100644
--- a/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
+++ b/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
@@ -19,12 +19,13 @@ use rustc_middle::ty::{
     self, InternalSubsts, Ty, TypeFoldable, TypeFolder, TypeSuperFoldable, TypeVisitableExt,
 };
 use rustc_middle::ty::{GenericParamDefKind, ToPredicate, TyCtxt};
-use rustc_span::Span;
+use rustc_span::{Span, DUMMY_SP};
 use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt;
 use rustc_trait_selection::traits::outlives_bounds::InferCtxtExt as _;
 use rustc_trait_selection::traits::{
     self, ObligationCause, ObligationCauseCode, ObligationCtxt, Reveal,
 };
+use std::borrow::Cow;
 use std::iter;
 
 /// Checks that a method from an impl conforms to the signature of
@@ -44,12 +45,7 @@ pub(super) fn compare_impl_method<'tcx>(
     debug!("compare_impl_method(impl_trait_ref={:?})", impl_trait_ref);
 
     let _: Result<_, ErrorGuaranteed> = try {
-        compare_self_type(tcx, impl_m, trait_m, impl_trait_ref)?;
-        compare_number_of_generics(tcx, impl_m, trait_m, false)?;
-        compare_generic_param_kinds(tcx, impl_m, trait_m, false)?;
-        compare_number_of_method_arguments(tcx, impl_m, trait_m)?;
-        compare_synthetic_generics(tcx, impl_m, trait_m)?;
-        compare_asyncness(tcx, impl_m, trait_m)?;
+        check_method_is_structurally_compatible(tcx, impl_m, trait_m, impl_trait_ref, false)?;
         compare_method_predicate_entailment(
             tcx,
             impl_m,
@@ -60,6 +56,26 @@ pub(super) fn compare_impl_method<'tcx>(
     };
 }
 
+/// Checks a bunch of different properties of the impl/trait methods for
+/// compatibility, such as asyncness, number of argument, self receiver kind,
+/// and number of early- and late-bound generics.
+fn check_method_is_structurally_compatible<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    impl_m: ty::AssocItem,
+    trait_m: ty::AssocItem,
+    impl_trait_ref: ty::TraitRef<'tcx>,
+    delay: bool,
+) -> Result<(), ErrorGuaranteed> {
+    compare_self_type(tcx, impl_m, trait_m, impl_trait_ref, delay)?;
+    compare_number_of_generics(tcx, impl_m, trait_m, delay)?;
+    compare_generic_param_kinds(tcx, impl_m, trait_m, delay)?;
+    compare_number_of_method_arguments(tcx, impl_m, trait_m, delay)?;
+    compare_synthetic_generics(tcx, impl_m, trait_m, delay)?;
+    compare_asyncness(tcx, impl_m, trait_m, delay)?;
+    check_region_bounds_on_impl_item(tcx, impl_m, trait_m, delay)?;
+    Ok(())
+}
+
 /// This function is best explained by example. Consider a trait with it's implementation:
 ///
 /// ```rust
@@ -176,9 +192,6 @@ fn compare_method_predicate_entailment<'tcx>(
     let impl_m_predicates = tcx.predicates_of(impl_m.def_id);
     let trait_m_predicates = tcx.predicates_of(trait_m.def_id);
 
-    // Check region bounds.
-    check_region_bounds_on_impl_item(tcx, impl_m, trait_m, false)?;
-
     // Create obligations for each predicate declared by the impl
     // definition in the context of the trait's parameter
     // environment. We can't just use `impl_env.caller_bounds`,
@@ -207,7 +220,7 @@ fn compare_method_predicate_entailment<'tcx>(
     // the new hybrid bounds we computed.
     let normalize_cause = traits::ObligationCause::misc(impl_m_span, impl_m_def_id);
     let param_env = ty::ParamEnv::new(
-        tcx.mk_predicates(&hybrid_preds.predicates),
+        tcx.mk_clauses(&hybrid_preds.predicates),
         Reveal::UserFacing,
         hir::Constness::NotConst,
     );
@@ -258,7 +271,7 @@ fn compare_method_predicate_entailment<'tcx>(
         infer::HigherRankedType,
         tcx.fn_sig(impl_m.def_id).subst_identity(),
     );
-    let unnormalized_impl_fty = tcx.mk_fn_ptr(ty::Binder::dummy(unnormalized_impl_sig));
+    let unnormalized_impl_fty = Ty::new_fn_ptr(tcx, ty::Binder::dummy(unnormalized_impl_sig));
 
     let norm_cause = ObligationCause::misc(impl_m_span, impl_m_def_id);
     let impl_sig = ocx.normalize(&norm_cause, param_env, unnormalized_impl_sig);
@@ -275,7 +288,7 @@ fn compare_method_predicate_entailment<'tcx>(
     // We also have to add the normalized trait signature
     // as we don't normalize during implied bounds computation.
     wf_tys.extend(trait_sig.inputs_and_output.iter());
-    let trait_fty = tcx.mk_fn_ptr(ty::Binder::dummy(trait_sig));
+    let trait_fty = Ty::new_fn_ptr(tcx, ty::Binder::dummy(trait_sig));
 
     debug!("compare_impl_method: trait_fty={:?}", trait_fty);
 
@@ -301,14 +314,16 @@ fn compare_method_predicate_entailment<'tcx>(
         return Err(emitted);
     }
 
-    if check_implied_wf == CheckImpliedWfMode::Check {
+    if check_implied_wf == CheckImpliedWfMode::Check && !(impl_sig, trait_sig).references_error() {
         // We need to check that the impl's args are well-formed given
         // the hybrid param-env (impl + trait method where-clauses).
         ocx.register_obligation(traits::Obligation::new(
             infcx.tcx,
             ObligationCause::dummy(),
             param_env,
-            ty::Binder::dummy(ty::PredicateKind::WellFormed(unnormalized_impl_fty.into())),
+            ty::Binder::dummy(ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(
+                unnormalized_impl_fty.into(),
+            ))),
         ));
     }
 
@@ -471,7 +486,8 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for RemapLateBound<'_, 'tcx> {
 
     fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
         if let ty::ReFree(fr) = *r {
-            self.tcx.mk_re_free(
+            ty::Region::new_free(
+                self.tcx,
                 fr.scope,
                 self.mapping.get(&fr.bound_region).copied().unwrap_or(fr.bound_region),
             )
@@ -532,6 +548,7 @@ fn compare_asyncness<'tcx>(
     tcx: TyCtxt<'tcx>,
     impl_m: ty::AssocItem,
     trait_m: ty::AssocItem,
+    delay: bool,
 ) -> Result<(), ErrorGuaranteed> {
     if tcx.asyncness(trait_m.def_id) == hir::IsAsync::Async {
         match tcx.fn_sig(impl_m.def_id).skip_binder().skip_binder().output().kind() {
@@ -542,11 +559,14 @@ fn compare_asyncness<'tcx>(
                 // We don't know if it's ok, but at least it's already an error.
             }
             _ => {
-                return Err(tcx.sess.emit_err(crate::errors::AsyncTraitImplShouldBeAsync {
-                    span: tcx.def_span(impl_m.def_id),
-                    method_name: trait_m.name,
-                    trait_item_span: tcx.hir().span_if_local(trait_m.def_id),
-                }));
+                return Err(tcx
+                    .sess
+                    .create_err(crate::errors::AsyncTraitImplShouldBeAsync {
+                        span: tcx.def_span(impl_m.def_id),
+                        method_name: trait_m.name,
+                        trait_item_span: tcx.hir().span_if_local(trait_m.def_id),
+                    })
+                    .emit_unless(delay));
             }
         };
     }
@@ -600,9 +620,7 @@ pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>(
 
     // First, check a few of the same things as `compare_impl_method`,
     // just so we don't ICE during substitution later.
-    compare_number_of_generics(tcx, impl_m, trait_m, true)?;
-    compare_generic_param_kinds(tcx, impl_m, trait_m, true)?;
-    check_region_bounds_on_impl_item(tcx, impl_m, trait_m, true)?;
+    check_method_is_structurally_compatible(tcx, impl_m, trait_m, impl_trait_ref, true)?;
 
     let trait_to_impl_substs = impl_trait_ref.substs;
 
@@ -633,11 +651,7 @@ pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>(
     let impl_sig = ocx.normalize(
         &norm_cause,
         param_env,
-        infcx.instantiate_binder_with_fresh_vars(
-            return_span,
-            infer::HigherRankedType,
-            tcx.fn_sig(impl_m.def_id).subst_identity(),
-        ),
+        tcx.liberate_late_bound_regions(impl_m.def_id, tcx.fn_sig(impl_m.def_id).subst_identity()),
     );
     impl_sig.error_reported()?;
     let impl_return_ty = impl_sig.output();
@@ -647,18 +661,21 @@ pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>(
     // them with inference variables.
     // We will use these inference variables to collect the hidden types of RPITITs.
     let mut collector = ImplTraitInTraitCollector::new(&ocx, return_span, param_env, impl_m_def_id);
-    let unnormalized_trait_sig = tcx
-        .liberate_late_bound_regions(
-            impl_m.def_id,
+    let unnormalized_trait_sig = infcx
+        .instantiate_binder_with_fresh_vars(
+            return_span,
+            infer::HigherRankedType,
             tcx.fn_sig(trait_m.def_id).subst(tcx, trait_to_placeholder_substs),
         )
         .fold_with(&mut collector);
 
-    debug_assert_ne!(
-        collector.types.len(),
-        0,
-        "expect >1 RPITITs in call to `collect_return_position_impl_trait_in_trait_tys`"
-    );
+    if !unnormalized_trait_sig.output().references_error() {
+        debug_assert_ne!(
+            collector.types.len(),
+            0,
+            "expect >1 RPITITs in call to `collect_return_position_impl_trait_in_trait_tys`"
+        );
+    }
 
     let trait_sig = ocx.normalize(&norm_cause, param_env, unnormalized_trait_sig);
     trait_sig.error_reported()?;
@@ -684,7 +701,7 @@ pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>(
                 &cause,
                 hir.get_if_local(impl_m.def_id)
                     .and_then(|node| node.fn_decl())
-                    .map(|decl| (decl.output.span(), "return type in trait".to_owned())),
+                    .map(|decl| (decl.output.span(), Cow::from("return type in trait"))),
                 Some(infer::ValuePairs::Terms(ExpectedFound {
                     expected: trait_return_ty.into(),
                     found: impl_return_ty.into(),
@@ -742,15 +759,17 @@ pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>(
 
     let mut collected_tys = FxHashMap::default();
     for (def_id, (ty, substs)) in collected_types {
-        match infcx.fully_resolve(ty) {
-            Ok(ty) => {
+        match infcx.fully_resolve((ty, substs)) {
+            Ok((ty, substs)) => {
                 // `ty` contains free regions that we created earlier while liberating the
                 // trait fn signature. However, projection normalization expects `ty` to
                 // contains `def_id`'s early-bound regions.
                 let id_substs = InternalSubsts::identity_for_item(tcx, def_id);
                 debug!(?id_substs, ?substs);
-                let map: FxHashMap<ty::GenericArg<'tcx>, ty::GenericArg<'tcx>> =
-                    std::iter::zip(substs, id_substs).collect();
+                let map: FxHashMap<_, _> = std::iter::zip(substs, id_substs)
+                    .skip(tcx.generics_of(trait_m.def_id).count())
+                    .filter_map(|(a, b)| Some((a.as_region()?, b.as_region()?)))
+                    .collect();
                 debug!(?map);
 
                 // NOTE(compiler-errors): RPITITs, like all other RPITs, have early-bound
@@ -775,33 +794,27 @@ pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>(
                 // same generics.
                 let num_trait_substs = trait_to_impl_substs.len();
                 let num_impl_substs = tcx.generics_of(impl_m.container_id(tcx)).params.len();
-                let ty = tcx.fold_regions(ty, |region, _| {
-                    match region.kind() {
-                        // Remap all free regions, which correspond to late-bound regions in the function.
-                        ty::ReFree(_) => {}
-                        // Remap early-bound regions as long as they don't come from the `impl` itself.
-                        ty::ReEarlyBound(ebr) if tcx.parent(ebr.def_id) != impl_m.container_id(tcx) => {}
-                        _ => return region,
-                    }
-                    let Some(ty::ReEarlyBound(e)) = map.get(&region.into()).map(|r| r.expect_region().kind())
-                    else {
-                        return tcx.mk_re_error_with_message(return_span, "expected ReFree to map to ReEarlyBound")
-                    };
-                    tcx.mk_re_early_bound(ty::EarlyBoundRegion {
-                        def_id: e.def_id,
-                        name: e.name,
-                        index: (e.index as usize - num_trait_substs + num_impl_substs) as u32,
-                    })
-                });
-                debug!(%ty);
-                collected_tys.insert(def_id, ty::EarlyBinder(ty));
+                let ty = match ty.try_fold_with(&mut RemapHiddenTyRegions {
+                    tcx,
+                    map,
+                    num_trait_substs,
+                    num_impl_substs,
+                    def_id,
+                    impl_def_id: impl_m.container_id(tcx),
+                    ty,
+                    return_span,
+                }) {
+                    Ok(ty) => ty,
+                    Err(guar) => Ty::new_error(tcx, guar),
+                };
+                collected_tys.insert(def_id, ty::EarlyBinder::bind(ty));
             }
             Err(err) => {
                 let reported = tcx.sess.delay_span_bug(
                     return_span,
                     format!("could not fully resolve: {ty} => {err:?}"),
                 );
-                collected_tys.insert(def_id, ty::EarlyBinder(tcx.ty_error(reported)));
+                collected_tys.insert(def_id, ty::EarlyBinder::bind(Ty::new_error(tcx, reported)));
             }
         }
     }
@@ -877,6 +890,97 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for ImplTraitInTraitCollector<'_, 'tcx> {
     }
 }
 
+struct RemapHiddenTyRegions<'tcx> {
+    tcx: TyCtxt<'tcx>,
+    map: FxHashMap<ty::Region<'tcx>, ty::Region<'tcx>>,
+    num_trait_substs: usize,
+    num_impl_substs: usize,
+    def_id: DefId,
+    impl_def_id: DefId,
+    ty: Ty<'tcx>,
+    return_span: Span,
+}
+
+impl<'tcx> ty::FallibleTypeFolder<TyCtxt<'tcx>> for RemapHiddenTyRegions<'tcx> {
+    type Error = ErrorGuaranteed;
+
+    fn interner(&self) -> TyCtxt<'tcx> {
+        self.tcx
+    }
+
+    fn try_fold_ty(&mut self, t: Ty<'tcx>) -> Result<Ty<'tcx>, Self::Error> {
+        if let ty::Alias(ty::Opaque, ty::AliasTy { substs, def_id, .. }) = *t.kind() {
+            let mut mapped_substs = Vec::with_capacity(substs.len());
+            for (arg, v) in std::iter::zip(substs, self.tcx.variances_of(def_id)) {
+                mapped_substs.push(match (arg.unpack(), v) {
+                    // Skip uncaptured opaque substs
+                    (ty::GenericArgKind::Lifetime(_), ty::Bivariant) => arg,
+                    _ => arg.try_fold_with(self)?,
+                });
+            }
+            Ok(Ty::new_opaque(self.tcx, def_id, self.tcx.mk_substs(&mapped_substs)))
+        } else {
+            t.try_super_fold_with(self)
+        }
+    }
+
+    fn try_fold_region(
+        &mut self,
+        region: ty::Region<'tcx>,
+    ) -> Result<ty::Region<'tcx>, Self::Error> {
+        match region.kind() {
+            // Remap all free regions, which correspond to late-bound regions in the function.
+            ty::ReFree(_) => {}
+            // Remap early-bound regions as long as they don't come from the `impl` itself,
+            // in which case we don't really need to renumber them.
+            ty::ReEarlyBound(ebr) if self.tcx.parent(ebr.def_id) != self.impl_def_id => {}
+            _ => return Ok(region),
+        }
+
+        let e = if let Some(region) = self.map.get(&region) {
+            if let ty::ReEarlyBound(e) = region.kind() { e } else { bug!() }
+        } else {
+            let guar = match region.kind() {
+                ty::ReEarlyBound(ty::EarlyBoundRegion { def_id, .. })
+                | ty::ReFree(ty::FreeRegion {
+                    bound_region: ty::BoundRegionKind::BrNamed(def_id, _),
+                    ..
+                }) => {
+                    let return_span = if let ty::Alias(ty::Opaque, opaque_ty) = self.ty.kind() {
+                        self.tcx.def_span(opaque_ty.def_id)
+                    } else {
+                        self.return_span
+                    };
+                    self.tcx
+                        .sess
+                        .struct_span_err(
+                            return_span,
+                            "return type captures more lifetimes than trait definition",
+                        )
+                        .span_label(self.tcx.def_span(def_id), "this lifetime was captured")
+                        .span_note(
+                            self.tcx.def_span(self.def_id),
+                            "hidden type must only reference lifetimes captured by this impl trait",
+                        )
+                        .note(format!("hidden type inferred to be `{}`", self.ty))
+                        .emit()
+                }
+                _ => self.tcx.sess.delay_span_bug(DUMMY_SP, "should've been able to remap region"),
+            };
+            return Err(guar);
+        };
+
+        Ok(ty::Region::new_early_bound(
+            self.tcx,
+            ty::EarlyBoundRegion {
+                def_id: e.def_id,
+                name: e.name,
+                index: (e.index as usize - self.num_trait_substs + self.num_impl_substs) as u32,
+            },
+        ))
+    }
+}
+
 fn report_trait_method_mismatch<'tcx>(
     infcx: &InferCtxt<'tcx>,
     mut cause: ObligationCause<'tcx>,
@@ -901,7 +1005,7 @@ fn report_trait_method_mismatch<'tcx>(
             if trait_m.fn_has_self_parameter =>
         {
             let ty = trait_sig.inputs()[0];
-            let sugg = match ExplicitSelf::determine(ty, |_| ty == impl_trait_ref.self_ty()) {
+            let sugg = match ExplicitSelf::determine(ty, |ty| ty == impl_trait_ref.self_ty()) {
                 ExplicitSelf::ByValue => "self".to_owned(),
                 ExplicitSelf::ByReference(_, hir::Mutability::Not) => "&self".to_owned(),
                 ExplicitSelf::ByReference(_, hir::Mutability::Mut) => "&mut self".to_owned(),
@@ -963,7 +1067,7 @@ fn report_trait_method_mismatch<'tcx>(
     infcx.err_ctxt().note_type_err(
         &mut diag,
         &cause,
-        trait_err_span.map(|sp| (sp, "type in trait".to_owned())),
+        trait_err_span.map(|sp| (sp, Cow::from("type in trait"))),
         Some(infer::ValuePairs::Sigs(ExpectedFound { expected: trait_sig, found: impl_sig })),
         terr,
         false,
@@ -1095,6 +1199,7 @@ fn compare_self_type<'tcx>(
     impl_m: ty::AssocItem,
     trait_m: ty::AssocItem,
     impl_trait_ref: ty::TraitRef<'tcx>,
+    delay: bool,
 ) -> Result<(), ErrorGuaranteed> {
     // Try to give more informative error messages about self typing
     // mismatches. Note that any mismatch will also be detected
@@ -1143,7 +1248,7 @@ fn compare_self_type<'tcx>(
             } else {
                 err.note_trait_signature(trait_m.name, trait_m.signature(tcx));
             }
-            return Err(err.emit());
+            return Err(err.emit_unless(delay));
         }
 
         (true, false) => {
@@ -1164,7 +1269,7 @@ fn compare_self_type<'tcx>(
                 err.note_trait_signature(trait_m.name, trait_m.signature(tcx));
             }
 
-            return Err(err.emit());
+            return Err(err.emit_unless(delay));
         }
     }
 
@@ -1214,7 +1319,7 @@ fn compare_number_of_generics<'tcx>(
     // has mismatched type or const generic arguments, then the method that it's
     // inheriting the generics from will also have mismatched arguments, and
     // we'll report an error for that instead. Delay a bug for safety, though.
-    if tcx.opt_rpitit_info(trait_.def_id).is_some() {
+    if trait_.opt_rpitit_info.is_some() {
         return Err(tcx.sess.delay_span_bug(
             rustc_span::DUMMY_SP,
             "errors comparing numbers of generics of trait/impl functions were not emitted",
@@ -1350,6 +1455,7 @@ fn compare_number_of_method_arguments<'tcx>(
     tcx: TyCtxt<'tcx>,
     impl_m: ty::AssocItem,
     trait_m: ty::AssocItem,
+    delay: bool,
 ) -> Result<(), ErrorGuaranteed> {
     let impl_m_fty = tcx.fn_sig(impl_m.def_id);
     let trait_m_fty = tcx.fn_sig(trait_m.def_id);
@@ -1420,7 +1526,7 @@ fn compare_number_of_method_arguments<'tcx>(
             ),
         );
 
-        return Err(err.emit());
+        return Err(err.emit_unless(delay));
     }
 
     Ok(())
@@ -1430,6 +1536,7 @@ fn compare_synthetic_generics<'tcx>(
     tcx: TyCtxt<'tcx>,
     impl_m: ty::AssocItem,
     trait_m: ty::AssocItem,
+    delay: bool,
 ) -> Result<(), ErrorGuaranteed> {
     // FIXME(chrisvittal) Clean up this function, list of FIXME items:
     //     1. Better messages for the span labels
@@ -1549,7 +1656,7 @@ fn compare_synthetic_generics<'tcx>(
                 }
                 _ => unreachable!(),
             }
-            error_found = Some(err.emit());
+            error_found = Some(err.emit_unless(delay));
         }
     }
     if let Some(reported) = error_found { Err(reported) } else { Ok(()) }
@@ -1731,7 +1838,7 @@ pub(super) fn compare_impl_const_raw(
         infcx.err_ctxt().note_type_err(
             &mut diag,
             &cause,
-            trait_c_span.map(|span| (span, "type in trait".to_owned())),
+            trait_c_span.map(|span| (span, Cow::from("type in trait"))),
             Some(infer::ValuePairs::Terms(ExpectedFound {
                 expected: trait_ty.into(),
                 found: impl_ty.into(),
@@ -1814,7 +1921,7 @@ fn compare_type_predicate_entailment<'tcx>(
     let impl_ty_span = tcx.def_span(impl_ty_def_id);
     let normalize_cause = traits::ObligationCause::misc(impl_ty_span, impl_ty_def_id);
     let param_env = ty::ParamEnv::new(
-        tcx.mk_predicates(&hybrid_preds.predicates),
+        tcx.mk_clauses(&hybrid_preds.predicates),
         Reveal::UserFacing,
         hir::Constness::NotConst,
     );
@@ -1922,7 +2029,8 @@ pub(super) fn check_type_bounds<'tcx>(
                 let kind = ty::BoundTyKind::Param(param.def_id, param.name);
                 let bound_var = ty::BoundVariableKind::Ty(kind);
                 bound_vars.push(bound_var);
-                tcx.mk_bound(
+                Ty::new_bound(
+                    tcx,
                     ty::INNERMOST,
                     ty::BoundTy { var: ty::BoundVar::from_usize(bound_vars.len() - 1), kind },
                 )
@@ -1932,7 +2040,8 @@ pub(super) fn check_type_bounds<'tcx>(
                 let kind = ty::BoundRegionKind::BrNamed(param.def_id, param.name);
                 let bound_var = ty::BoundVariableKind::Region(kind);
                 bound_vars.push(bound_var);
-                tcx.mk_re_late_bound(
+                ty::Region::new_late_bound(
+                    tcx,
                     ty::INNERMOST,
                     ty::BoundRegion { var: ty::BoundVar::from_usize(bound_vars.len() - 1), kind },
                 )
@@ -1941,11 +2050,10 @@ pub(super) fn check_type_bounds<'tcx>(
             GenericParamDefKind::Const { .. } => {
                 let bound_var = ty::BoundVariableKind::Const;
                 bound_vars.push(bound_var);
-                tcx.mk_const(
-                    ty::ConstKind::Bound(
-                        ty::INNERMOST,
-                        ty::BoundVar::from_usize(bound_vars.len() - 1),
-                    ),
+                ty::Const::new_bound(
+                    tcx,
+                    ty::INNERMOST,
+                    ty::BoundVar::from_usize(bound_vars.len() - 1),
                     tcx.type_of(param.def_id)
                         .no_bound_vars()
                         .expect("const parameter types cannot be generic"),
@@ -1989,7 +2097,7 @@ pub(super) fn check_type_bounds<'tcx>(
                 .to_predicate(tcx),
             ),
         };
-        ty::ParamEnv::new(tcx.mk_predicates(&predicates), Reveal::UserFacing, param_env.constness())
+        ty::ParamEnv::new(tcx.mk_clauses(&predicates), Reveal::UserFacing, param_env.constness())
     };
     debug!(?normalize_param_env);
 
@@ -2003,7 +2111,7 @@ pub(super) fn check_type_bounds<'tcx>(
     // A synthetic impl Trait for RPITIT desugaring has no HIR, which we currently use to get the
     // span for an impl's associated type. Instead, for these, use the def_span for the synthesized
     // associated type.
-    let impl_ty_span = if tcx.opt_rpitit_info(impl_ty.def_id).is_some() {
+    let impl_ty_span = if impl_ty.opt_rpitit_info.is_some() {
         tcx.def_span(impl_ty_def_id)
     } else {
         match tcx.hir().get_by_def_id(impl_ty_def_id) {
@@ -2015,7 +2123,7 @@ pub(super) fn check_type_bounds<'tcx>(
             _ => bug!(),
         }
     };
-    let assumed_wf_types = ocx.assumed_wf_types(param_env, impl_ty_span, impl_ty_def_id);
+    let assumed_wf_types = ocx.assumed_wf_types_and_report_errors(param_env, impl_ty_def_id)?;
 
     let normalize_cause = ObligationCause::new(
         impl_ty_span,
diff --git a/compiler/rustc_hir_analysis/src/check/dropck.rs b/compiler/rustc_hir_analysis/src/check/dropck.rs
index e0ba255cc..13d1abe2a 100644
--- a/compiler/rustc_hir_analysis/src/check/dropck.rs
+++ b/compiler/rustc_hir_analysis/src/check/dropck.rs
@@ -128,7 +128,7 @@ fn ensure_drop_predicates_are_implied_by_item_defn<'tcx>(
     // We don't need to normalize this param-env or anything, since we're only
     // substituting it with free params, so no additional param-env normalization
     // can occur on top of what has been done in the param_env query itself.
-    let param_env = ty::EarlyBinder(tcx.param_env(adt_def_id))
+    let param_env = ty::EarlyBinder::bind(tcx.param_env(adt_def_id))
         .subst(tcx, adt_to_impl_substs)
         .with_constness(tcx.constness(drop_impl_def_id));
 
@@ -183,7 +183,7 @@ fn ensure_drop_predicates_are_implied_by_item_defn<'tcx>(
                 }
                 RegionResolutionError::SubSupConflict(_, _, _, a, _, b, _) => format!("{b}: {a}"),
                 RegionResolutionError::UpperBoundUniverseConflict(a, _, _, _, b) => {
-                    format!("{b}: {a}", a = tcx.mk_re_var(a))
+                    format!("{b}: {a}", a = ty::Region::new_var(tcx, a))
                 }
             };
             guar = Some(
diff --git a/compiler/rustc_hir_analysis/src/check/intrinsic.rs b/compiler/rustc_hir_analysis/src/check/intrinsic.rs
index e8785235c..1248f991c 100644
--- a/compiler/rustc_hir_analysis/src/check/intrinsic.rs
+++ b/compiler/rustc_hir_analysis/src/check/intrinsic.rs
@@ -11,7 +11,7 @@ use hir::def_id::DefId;
 use rustc_errors::{struct_span_err, DiagnosticMessage};
 use rustc_hir as hir;
 use rustc_middle::traits::{ObligationCause, ObligationCauseCode};
-use rustc_middle::ty::{self, TyCtxt};
+use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_span::symbol::{kw, sym, Symbol};
 use rustc_target::spec::abi::Abi;
 
@@ -53,14 +53,14 @@ fn equate_intrinsic_type<'tcx>(
         && gen_count_ok(own_counts.types, n_tps, "type")
         && gen_count_ok(own_counts.consts, 0, "const")
     {
-        let fty = tcx.mk_fn_ptr(sig);
+        let fty = Ty::new_fn_ptr(tcx, sig);
         let it_def_id = it.owner_id.def_id;
         let cause = ObligationCause::new(it.span, it_def_id, ObligationCauseCode::IntrinsicType);
         require_same_types(
             tcx,
             &cause,
             ty::ParamEnv::empty(), // FIXME: do all intrinsics have an empty param env?
-            tcx.mk_fn_ptr(tcx.fn_sig(it.owner_id).subst_identity()),
+            Ty::new_fn_ptr(tcx, tcx.fn_sig(it.owner_id).subst_identity()),
             fty,
         );
     }
@@ -121,10 +121,11 @@ pub fn intrinsic_operation_unsafety(tcx: TyCtxt<'_>, intrinsic_id: DefId) -> hir
     if has_safe_attr != is_in_list {
         tcx.sess.struct_span_err(
             tcx.def_span(intrinsic_id),
-            DiagnosticMessage::Str(format!(
-                    "intrinsic safety mismatch between list of intrinsics within the compiler and core library intrinsics for intrinsic `{}`",
-                    tcx.item_name(intrinsic_id)
-        ))).emit();
+            DiagnosticMessage::from(format!(
+                "intrinsic safety mismatch between list of intrinsics within the compiler and core library intrinsics for intrinsic `{}`",
+                tcx.item_name(intrinsic_id)
+            )
+        )).emit();
     }
 
     is_in_list
@@ -133,7 +134,7 @@ pub fn intrinsic_operation_unsafety(tcx: TyCtxt<'_>, intrinsic_id: DefId) -> hir
 /// Remember to add all intrinsics here, in `compiler/rustc_codegen_llvm/src/intrinsic.rs`,
 /// and in `library/core/src/intrinsics.rs`.
 pub fn check_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>) {
-    let param = |n| tcx.mk_ty_param(n, Symbol::intern(&format!("P{}", n)));
+    let param = |n| Ty::new_param(tcx, n, Symbol::intern(&format!("P{}", n)));
     let intrinsic_id = it.owner_id.to_def_id();
     let intrinsic_name = tcx.item_name(intrinsic_id);
     let name_str = intrinsic_name.as_str();
@@ -144,16 +145,18 @@ pub fn check_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>) {
     ]);
     let mk_va_list_ty = |mutbl| {
         tcx.lang_items().va_list().map(|did| {
-            let region = tcx.mk_re_late_bound(
+            let region = ty::Region::new_late_bound(
+                tcx,
                 ty::INNERMOST,
                 ty::BoundRegion { var: ty::BoundVar::from_u32(0), kind: ty::BrAnon(None) },
             );
-            let env_region = tcx.mk_re_late_bound(
+            let env_region = ty::Region::new_late_bound(
+                tcx,
                 ty::INNERMOST,
                 ty::BoundRegion { var: ty::BoundVar::from_u32(1), kind: ty::BrEnv },
             );
             let va_list_ty = tcx.type_of(did).subst(tcx, &[region.into()]);
-            (tcx.mk_ref(env_region, ty::TypeAndMut { ty: va_list_ty, mutbl }), va_list_ty)
+            (Ty::new_ref(tcx, env_region, ty::TypeAndMut { ty: va_list_ty, mutbl }), va_list_ty)
         })
     };
 
@@ -165,15 +168,15 @@ pub fn check_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>) {
         let (n_tps, inputs, output) = match split[1] {
             "cxchg" | "cxchgweak" => (
                 1,
-                vec![tcx.mk_mut_ptr(param(0)), param(0), param(0)],
-                tcx.mk_tup(&[param(0), tcx.types.bool]),
+                vec![Ty::new_mut_ptr(tcx, param(0)), param(0), param(0)],
+                Ty::new_tup(tcx, &[param(0), tcx.types.bool]),
             ),
-            "load" => (1, vec![tcx.mk_imm_ptr(param(0))], param(0)),
-            "store" => (1, vec![tcx.mk_mut_ptr(param(0)), param(0)], tcx.mk_unit()),
+            "load" => (1, vec![Ty::new_imm_ptr(tcx, param(0))], param(0)),
+            "store" => (1, vec![Ty::new_mut_ptr(tcx, param(0)), param(0)], Ty::new_unit(tcx)),
 
             "xchg" | "xadd" | "xsub" | "and" | "nand" | "or" | "xor" | "max" | "min" | "umax"
-            | "umin" => (1, vec![tcx.mk_mut_ptr(param(0)), param(0)], param(0)),
-            "fence" | "singlethreadfence" => (0, Vec::new(), tcx.mk_unit()),
+            | "umin" => (1, vec![Ty::new_mut_ptr(tcx, param(0)), param(0)], param(0)),
+            "fence" | "singlethreadfence" => (0, Vec::new(), Ty::new_unit(tcx)),
             op => {
                 tcx.sess.emit_err(UnrecognizedAtomicOperation { span: it.span, op });
                 return;
@@ -185,19 +188,19 @@ pub fn check_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>) {
         let (n_tps, inputs, output) = match intrinsic_name {
             sym::abort => (0, Vec::new(), tcx.types.never),
             sym::unreachable => (0, Vec::new(), tcx.types.never),
-            sym::breakpoint => (0, Vec::new(), tcx.mk_unit()),
+            sym::breakpoint => (0, Vec::new(), Ty::new_unit(tcx)),
             sym::size_of | sym::pref_align_of | sym::min_align_of | sym::variant_count => {
                 (1, Vec::new(), tcx.types.usize)
             }
             sym::size_of_val | sym::min_align_of_val => {
-                (1, vec![tcx.mk_imm_ptr(param(0))], tcx.types.usize)
+                (1, vec![Ty::new_imm_ptr(tcx, param(0))], tcx.types.usize)
             }
             sym::rustc_peek => (1, vec![param(0)], param(0)),
             sym::caller_location => (0, vec![], tcx.caller_location_ty()),
             sym::assert_inhabited
             | sym::assert_zero_valid
-            | sym::assert_mem_uninitialized_valid => (1, Vec::new(), tcx.mk_unit()),
-            sym::forget => (1, vec![param(0)], tcx.mk_unit()),
+            | sym::assert_mem_uninitialized_valid => (1, Vec::new(), Ty::new_unit(tcx)),
+            sym::forget => (1, vec![param(0)], Ty::new_unit(tcx)),
             sym::transmute | sym::transmute_unchecked => (2, vec![param(0)], param(1)),
             sym::prefetch_read_data
             | sym::prefetch_write_data
@@ -205,75 +208,79 @@ pub fn check_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>) {
             | sym::prefetch_write_instruction => (
                 1,
                 vec![
-                    tcx.mk_ptr(ty::TypeAndMut { ty: param(0), mutbl: hir::Mutability::Not }),
+                    Ty::new_ptr(tcx, ty::TypeAndMut { ty: param(0), mutbl: hir::Mutability::Not }),
                     tcx.types.i32,
                 ],
-                tcx.mk_unit(),
+                Ty::new_unit(tcx),
             ),
-            sym::drop_in_place => (1, vec![tcx.mk_mut_ptr(param(0))], tcx.mk_unit()),
+            sym::drop_in_place => (1, vec![Ty::new_mut_ptr(tcx, param(0))], Ty::new_unit(tcx)),
             sym::needs_drop => (1, Vec::new(), tcx.types.bool),
 
-            sym::type_name => (1, Vec::new(), tcx.mk_static_str()),
-            sym::type_id => (1, Vec::new(), tcx.types.u64),
+            sym::type_name => (1, Vec::new(), Ty::new_static_str(tcx)),
+            sym::type_id => (1, Vec::new(), tcx.types.u128),
             sym::offset => (2, vec![param(0), param(1)], param(0)),
             sym::arith_offset => (
                 1,
                 vec![
-                    tcx.mk_ptr(ty::TypeAndMut { ty: param(0), mutbl: hir::Mutability::Not }),
+                    Ty::new_ptr(tcx, ty::TypeAndMut { ty: param(0), mutbl: hir::Mutability::Not }),
                     tcx.types.isize,
                 ],
-                tcx.mk_ptr(ty::TypeAndMut { ty: param(0), mutbl: hir::Mutability::Not }),
+                Ty::new_ptr(tcx, ty::TypeAndMut { ty: param(0), mutbl: hir::Mutability::Not }),
             ),
             sym::option_payload_ptr => {
                 let option_def_id = tcx.require_lang_item(hir::LangItem::Option, None);
                 let p0 = param(0);
                 (
                     1,
-                    vec![tcx.mk_ptr(ty::TypeAndMut {
-                        ty: tcx.mk_adt(
-                            tcx.adt_def(option_def_id),
-                            tcx.mk_substs_from_iter([ty::GenericArg::from(p0)].into_iter()),
-                        ),
-                        mutbl: hir::Mutability::Not,
-                    })],
-                    tcx.mk_ptr(ty::TypeAndMut { ty: p0, mutbl: hir::Mutability::Not }),
+                    vec![Ty::new_ptr(
+                        tcx,
+                        ty::TypeAndMut {
+                            ty: Ty::new_adt(
+                                tcx,
+                                tcx.adt_def(option_def_id),
+                                tcx.mk_substs_from_iter([ty::GenericArg::from(p0)].into_iter()),
+                            ),
+                            mutbl: hir::Mutability::Not,
+                        },
+                    )],
+                    Ty::new_ptr(tcx, ty::TypeAndMut { ty: p0, mutbl: hir::Mutability::Not }),
                 )
             }
             sym::ptr_mask => (
                 1,
                 vec![
-                    tcx.mk_ptr(ty::TypeAndMut { ty: param(0), mutbl: hir::Mutability::Not }),
+                    Ty::new_ptr(tcx, ty::TypeAndMut { ty: param(0), mutbl: hir::Mutability::Not }),
                     tcx.types.usize,
                 ],
-                tcx.mk_ptr(ty::TypeAndMut { ty: param(0), mutbl: hir::Mutability::Not }),
+                Ty::new_ptr(tcx, ty::TypeAndMut { ty: param(0), mutbl: hir::Mutability::Not }),
             ),
 
             sym::copy | sym::copy_nonoverlapping => (
                 1,
                 vec![
-                    tcx.mk_ptr(ty::TypeAndMut { ty: param(0), mutbl: hir::Mutability::Not }),
-                    tcx.mk_ptr(ty::TypeAndMut { ty: param(0), mutbl: hir::Mutability::Mut }),
+                    Ty::new_ptr(tcx, ty::TypeAndMut { ty: param(0), mutbl: hir::Mutability::Not }),
+                    Ty::new_ptr(tcx, ty::TypeAndMut { ty: param(0), mutbl: hir::Mutability::Mut }),
                     tcx.types.usize,
                 ],
-                tcx.mk_unit(),
+                Ty::new_unit(tcx),
             ),
             sym::volatile_copy_memory | sym::volatile_copy_nonoverlapping_memory => (
                 1,
                 vec![
-                    tcx.mk_ptr(ty::TypeAndMut { ty: param(0), mutbl: hir::Mutability::Mut }),
-                    tcx.mk_ptr(ty::TypeAndMut { ty: param(0), mutbl: hir::Mutability::Not }),
+                    Ty::new_ptr(tcx, ty::TypeAndMut { ty: param(0), mutbl: hir::Mutability::Mut }),
+                    Ty::new_ptr(tcx, ty::TypeAndMut { ty: param(0), mutbl: hir::Mutability::Not }),
                     tcx.types.usize,
                 ],
-                tcx.mk_unit(),
+                Ty::new_unit(tcx),
             ),
             sym::write_bytes | sym::volatile_set_memory => (
                 1,
                 vec![
-                    tcx.mk_ptr(ty::TypeAndMut { ty: param(0), mutbl: hir::Mutability::Mut }),
+                    Ty::new_ptr(tcx, ty::TypeAndMut { ty: param(0), mutbl: hir::Mutability::Mut }),
                     tcx.types.u8,
                     tcx.types.usize,
                 ],
-                tcx.mk_unit(),
+                Ty::new_unit(tcx),
             ),
             sym::sqrtf32 => (0, vec![tcx.types.f32], tcx.types.f32),
             sym::sqrtf64 => (0, vec![tcx.types.f64], tcx.types.f64),
@@ -321,10 +328,10 @@ pub fn check_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>) {
             sym::roundevenf64 => (0, vec![tcx.types.f64], tcx.types.f64),
 
             sym::volatile_load | sym::unaligned_volatile_load => {
-                (1, vec![tcx.mk_imm_ptr(param(0))], param(0))
+                (1, vec![Ty::new_imm_ptr(tcx, param(0))], param(0))
             }
             sym::volatile_store | sym::unaligned_volatile_store => {
-                (1, vec![tcx.mk_mut_ptr(param(0)), param(0)], tcx.mk_unit())
+                (1, vec![Ty::new_mut_ptr(tcx, param(0)), param(0)], Ty::new_unit(tcx))
             }
 
             sym::ctpop
@@ -336,28 +343,34 @@ pub fn check_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>) {
             | sym::bitreverse => (1, vec![param(0)], param(0)),
 
             sym::add_with_overflow | sym::sub_with_overflow | sym::mul_with_overflow => {
-                (1, vec![param(0), param(0)], tcx.mk_tup(&[param(0), tcx.types.bool]))
+                (1, vec![param(0), param(0)], Ty::new_tup(tcx, &[param(0), tcx.types.bool]))
             }
 
-            sym::ptr_guaranteed_cmp => {
-                (1, vec![tcx.mk_imm_ptr(param(0)), tcx.mk_imm_ptr(param(0))], tcx.types.u8)
-            }
+            sym::ptr_guaranteed_cmp => (
+                1,
+                vec![Ty::new_imm_ptr(tcx, param(0)), Ty::new_imm_ptr(tcx, param(0))],
+                tcx.types.u8,
+            ),
 
             sym::const_allocate => {
-                (0, vec![tcx.types.usize, tcx.types.usize], tcx.mk_mut_ptr(tcx.types.u8))
+                (0, vec![tcx.types.usize, tcx.types.usize], Ty::new_mut_ptr(tcx, tcx.types.u8))
             }
             sym::const_deallocate => (
                 0,
-                vec![tcx.mk_mut_ptr(tcx.types.u8), tcx.types.usize, tcx.types.usize],
-                tcx.mk_unit(),
+                vec![Ty::new_mut_ptr(tcx, tcx.types.u8), tcx.types.usize, tcx.types.usize],
+                Ty::new_unit(tcx),
             ),
 
-            sym::ptr_offset_from => {
-                (1, vec![tcx.mk_imm_ptr(param(0)), tcx.mk_imm_ptr(param(0))], tcx.types.isize)
-            }
-            sym::ptr_offset_from_unsigned => {
-                (1, vec![tcx.mk_imm_ptr(param(0)), tcx.mk_imm_ptr(param(0))], tcx.types.usize)
-            }
+            sym::ptr_offset_from => (
+                1,
+                vec![Ty::new_imm_ptr(tcx, param(0)), Ty::new_imm_ptr(tcx, param(0))],
+                tcx.types.isize,
+            ),
+            sym::ptr_offset_from_unsigned => (
+                1,
+                vec![Ty::new_imm_ptr(tcx, param(0)), Ty::new_imm_ptr(tcx, param(0))],
+                tcx.types.usize,
+            ),
             sym::unchecked_div | sym::unchecked_rem | sym::exact_div => {
                 (1, vec![param(0), param(0)], param(0))
             }
@@ -376,12 +389,14 @@ pub fn check_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>) {
             }
             sym::float_to_int_unchecked => (2, vec![param(0)], param(1)),
 
-            sym::assume => (0, vec![tcx.types.bool], tcx.mk_unit()),
+            sym::assume => (0, vec![tcx.types.bool], Ty::new_unit(tcx)),
             sym::likely => (0, vec![tcx.types.bool], tcx.types.bool),
             sym::unlikely => (0, vec![tcx.types.bool], tcx.types.bool),
 
-            sym::read_via_copy => (1, vec![tcx.mk_imm_ptr(param(0))], param(0)),
-            sym::write_via_move => (1, vec![tcx.mk_mut_ptr(param(0)), param(0)], tcx.mk_unit()),
+            sym::read_via_copy => (1, vec![Ty::new_imm_ptr(tcx, param(0))], param(0)),
+            sym::write_via_move => {
+                (1, vec![Ty::new_mut_ptr(tcx, param(0)), param(0)], Ty::new_unit(tcx))
+            }
 
             sym::discriminant_value => {
                 let assoc_items = tcx.associated_item_def_ids(
@@ -392,43 +407,47 @@ pub fn check_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>) {
                 let br = ty::BoundRegion { var: ty::BoundVar::from_u32(0), kind: ty::BrAnon(None) };
                 (
                     1,
-                    vec![tcx.mk_imm_ref(tcx.mk_re_late_bound(ty::INNERMOST, br), param(0))],
-                    tcx.mk_projection(discriminant_def_id, tcx.mk_substs(&[param(0).into()])),
+                    vec![Ty::new_imm_ref(
+                        tcx,
+                        ty::Region::new_late_bound(tcx, ty::INNERMOST, br),
+                        param(0),
+                    )],
+                    Ty::new_projection(tcx, discriminant_def_id, tcx.mk_substs(&[param(0).into()])),
                 )
             }
 
             kw::Try => {
-                let mut_u8 = tcx.mk_mut_ptr(tcx.types.u8);
+                let mut_u8 = Ty::new_mut_ptr(tcx, tcx.types.u8);
                 let try_fn_ty = ty::Binder::dummy(tcx.mk_fn_sig(
                     [mut_u8],
-                    tcx.mk_unit(),
+                    Ty::new_unit(tcx),
                     false,
                     hir::Unsafety::Normal,
                     Abi::Rust,
                 ));
                 let catch_fn_ty = ty::Binder::dummy(tcx.mk_fn_sig(
                     [mut_u8, mut_u8],
-                    tcx.mk_unit(),
+                    Ty::new_unit(tcx),
                     false,
                     hir::Unsafety::Normal,
                     Abi::Rust,
                 ));
                 (
                     0,
-                    vec![tcx.mk_fn_ptr(try_fn_ty), mut_u8, tcx.mk_fn_ptr(catch_fn_ty)],
+                    vec![Ty::new_fn_ptr(tcx, try_fn_ty), mut_u8, Ty::new_fn_ptr(tcx, catch_fn_ty)],
                     tcx.types.i32,
                 )
             }
 
             sym::va_start | sym::va_end => match mk_va_list_ty(hir::Mutability::Mut) {
-                Some((va_list_ref_ty, _)) => (0, vec![va_list_ref_ty], tcx.mk_unit()),
+                Some((va_list_ref_ty, _)) => (0, vec![va_list_ref_ty], Ty::new_unit(tcx)),
                 None => bug!("`va_list` language item needed for C-variadic intrinsics"),
             },
 
             sym::va_copy => match mk_va_list_ty(hir::Mutability::Not) {
                 Some((va_list_ref_ty, va_list_ty)) => {
-                    let va_list_ptr_ty = tcx.mk_mut_ptr(va_list_ty);
-                    (0, vec![va_list_ptr_ty, va_list_ref_ty], tcx.mk_unit())
+                    let va_list_ptr_ty = Ty::new_mut_ptr(tcx, va_list_ty);
+                    (0, vec![va_list_ptr_ty, va_list_ref_ty], Ty::new_unit(tcx))
                 }
                 None => bug!("`va_list` language item needed for C-variadic intrinsics"),
             },
@@ -438,11 +457,17 @@ pub fn check_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>) {
                 None => bug!("`va_list` language item needed for C-variadic intrinsics"),
             },
 
-            sym::nontemporal_store => (1, vec![tcx.mk_mut_ptr(param(0)), param(0)], tcx.mk_unit()),
+            sym::nontemporal_store => {
+                (1, vec![Ty::new_mut_ptr(tcx, param(0)), param(0)], Ty::new_unit(tcx))
+            }
 
             sym::raw_eq => {
                 let br = ty::BoundRegion { var: ty::BoundVar::from_u32(0), kind: ty::BrAnon(None) };
-                let param_ty = tcx.mk_imm_ref(tcx.mk_re_late_bound(ty::INNERMOST, br), param(0));
+                let param_ty = Ty::new_imm_ref(
+                    tcx,
+                    ty::Region::new_late_bound(tcx, ty::INNERMOST, br),
+                    param(0),
+                );
                 (1, vec![param_ty; 2], tcx.types.bool)
             }
 
@@ -451,7 +476,7 @@ pub fn check_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>) {
             sym::const_eval_select => (4, vec![param(0), param(1), param(2)], param(3)),
 
             sym::vtable_size | sym::vtable_align => {
-                (0, vec![tcx.mk_imm_ptr(tcx.mk_unit())], tcx.types.usize)
+                (0, vec![Ty::new_imm_ptr(tcx, Ty::new_unit(tcx))], tcx.types.usize)
             }
 
             other => {
@@ -470,7 +495,7 @@ pub fn check_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>) {
 pub fn check_platform_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>) {
     let param = |n| {
         let name = Symbol::intern(&format!("P{}", n));
-        tcx.mk_ty_param(n, name)
+        Ty::new_param(tcx, n, name)
     };
 
     let name = it.ident.name;
@@ -512,7 +537,7 @@ pub fn check_platform_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>)
         sym::simd_fpowi => (1, vec![param(0), tcx.types.i32], param(0)),
         sym::simd_fma => (1, vec![param(0), param(0), param(0)], param(0)),
         sym::simd_gather => (3, vec![param(0), param(1), param(2)], param(0)),
-        sym::simd_scatter => (3, vec![param(0), param(1), param(2)], tcx.mk_unit()),
+        sym::simd_scatter => (3, vec![param(0), param(1), param(2)], Ty::new_unit(tcx)),
         sym::simd_insert => (2, vec![param(0), tcx.types.u32, param(1)], param(0)),
         sym::simd_extract => (2, vec![param(0), tcx.types.u32], param(1)),
         sym::simd_cast
@@ -541,7 +566,7 @@ pub fn check_platform_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>)
         name if name.as_str().starts_with("simd_shuffle") => {
             match name.as_str()["simd_shuffle".len()..].parse() {
                 Ok(n) => {
-                    let params = vec![param(0), param(0), tcx.mk_array(tcx.types.u32, n)];
+                    let params = vec![param(0), param(0), Ty::new_array(tcx, tcx.types.u32, n)];
                     (2, params, param(1))
                 }
                 Err(_) => {
diff --git a/compiler/rustc_hir_analysis/src/check/mod.rs b/compiler/rustc_hir_analysis/src/check/mod.rs
index 3971a4c01..ce2da7cb1 100644
--- a/compiler/rustc_hir_analysis/src/check/mod.rs
+++ b/compiler/rustc_hir_analysis/src/check/mod.rs
@@ -188,7 +188,7 @@ fn missing_items_err(
     full_impl_span: Span,
 ) {
     let missing_items =
-        missing_items.iter().filter(|trait_item| tcx.opt_rpitit_info(trait_item.def_id).is_none());
+        missing_items.iter().filter(|trait_item| trait_item.opt_rpitit_info.is_none());
 
     let missing_items_msg = missing_items
         .clone()
@@ -296,7 +296,7 @@ fn default_body_is_unstable(
 /// Re-sugar `ty::GenericPredicates` in a way suitable to be used in structured suggestions.
 fn bounds_from_generic_predicates<'tcx>(
     tcx: TyCtxt<'tcx>,
-    predicates: impl IntoIterator<Item = (ty::Predicate<'tcx>, Span)>,
+    predicates: impl IntoIterator<Item = (ty::Clause<'tcx>, Span)>,
 ) -> (String, String) {
     let mut types: FxHashMap<Ty<'tcx>, Vec<DefId>> = FxHashMap::default();
     let mut projections = vec![];
@@ -304,7 +304,7 @@ fn bounds_from_generic_predicates<'tcx>(
         debug!("predicate {:?}", predicate);
         let bound_predicate = predicate.kind();
         match bound_predicate.skip_binder() {
-            ty::PredicateKind::Clause(ty::Clause::Trait(trait_predicate)) => {
+            ty::ClauseKind::Trait(trait_predicate) => {
                 let entry = types.entry(trait_predicate.self_ty()).or_default();
                 let def_id = trait_predicate.def_id();
                 if Some(def_id) != tcx.lang_items().sized_trait() {
@@ -313,7 +313,7 @@ fn bounds_from_generic_predicates<'tcx>(
                     entry.push(trait_predicate.def_id());
                 }
             }
-            ty::PredicateKind::Clause(ty::Clause::Projection(projection_pred)) => {
+            ty::ClauseKind::Projection(projection_pred) => {
                 projections.push(bound_predicate.rebind(projection_pred));
             }
             _ => {}
@@ -362,7 +362,7 @@ fn fn_sig_suggestion<'tcx>(
     tcx: TyCtxt<'tcx>,
     sig: ty::FnSig<'tcx>,
     ident: Ident,
-    predicates: impl IntoIterator<Item = (ty::Predicate<'tcx>, Span)>,
+    predicates: impl IntoIterator<Item = (ty::Clause<'tcx>, Span)>,
     assoc: ty::AssocItem,
 ) -> String {
     let args = sig
@@ -403,7 +403,30 @@ fn fn_sig_suggestion<'tcx>(
         .flatten()
         .collect::<Vec<String>>()
         .join(", ");
-    let output = sig.output();
+    let mut output = sig.output();
+
+    let asyncness = if tcx.asyncness(assoc.def_id).is_async() {
+        output = if let ty::Alias(_, alias_ty) = *output.kind() {
+            tcx.explicit_item_bounds(alias_ty.def_id)
+                .subst_iter_copied(tcx, alias_ty.substs)
+                .find_map(|(bound, _)| bound.as_projection_clause()?.no_bound_vars()?.term.ty())
+                .unwrap_or_else(|| {
+                    span_bug!(
+                        ident.span,
+                        "expected async fn to have `impl Future` output, but it returns {output}"
+                    )
+                })
+        } else {
+            span_bug!(
+                ident.span,
+                "expected async fn to have `impl Future` output, but it returns {output}"
+            )
+        };
+        "async "
+    } else {
+        ""
+    };
+
     let output = if !output.is_unit() { format!(" -> {output}") } else { String::new() };
 
     let unsafety = sig.unsafety.prefix_str();
@@ -414,7 +437,9 @@ fn fn_sig_suggestion<'tcx>(
     // lifetimes between the `impl` and the `trait`, but this should be good enough to
     // fill in a significant portion of the missing code, and other subsequent
     // suggestions can help the user fix the code.
-    format!("{unsafety}fn {ident}{generics}({args}){output}{where_clauses} {{ todo!() }}")
+    format!(
+        "{unsafety}{asyncness}fn {ident}{generics}({args}){output}{where_clauses} {{ todo!() }}"
+    )
 }
 
 pub fn ty_kind_suggestion(ty: Ty<'_>) -> Option<&'static str> {
@@ -443,19 +468,16 @@ fn suggestion_signature<'tcx>(
     );
 
     match assoc.kind {
-        ty::AssocKind::Fn => {
-            // We skip the binder here because the binder would deanonymize all
-            // late-bound regions, and we don't want method signatures to show up
-            // `as for<'r> fn(&'r MyType)`. Pretty-printing handles late-bound
-            // regions just fine, showing `fn(&MyType)`.
-            fn_sig_suggestion(
-                tcx,
-                tcx.fn_sig(assoc.def_id).subst(tcx, substs).skip_binder(),
-                assoc.ident(tcx),
-                tcx.predicates_of(assoc.def_id).instantiate_own(tcx, substs),
-                assoc,
-            )
-        }
+        ty::AssocKind::Fn => fn_sig_suggestion(
+            tcx,
+            tcx.liberate_late_bound_regions(
+                assoc.def_id,
+                tcx.fn_sig(assoc.def_id).subst(tcx, substs),
+            ),
+            assoc.ident(tcx),
+            tcx.predicates_of(assoc.def_id).instantiate_own(tcx, substs),
+            assoc,
+        ),
         ty::AssocKind::Type => {
             let (generics, where_clauses) = bounds_from_generic_predicates(
                 tcx,
diff --git a/compiler/rustc_hir_analysis/src/check/region.rs b/compiler/rustc_hir_analysis/src/check/region.rs
index 6ab5556e9..5bd6fcb96 100644
--- a/compiler/rustc_hir_analysis/src/check/region.rs
+++ b/compiler/rustc_hir_analysis/src/check/region.rs
@@ -392,7 +392,7 @@ fn resolve_expr<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, expr: &'tcx h
         // Manually recurse over closures and inline consts, because they are the only
         // case of nested bodies that share the parent environment.
         hir::ExprKind::Closure(&hir::Closure { body, .. })
-        | hir::ExprKind::ConstBlock(hir::AnonConst { body, .. }) => {
+        | hir::ExprKind::ConstBlock(hir::ConstBlock { body, .. }) => {
             let body = visitor.tcx.hir().body(body);
             visitor.visit_body(body);
         }
diff --git a/compiler/rustc_hir_analysis/src/check/wfcheck.rs b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
index b403ee96b..d4748b7ef 100644
--- a/compiler/rustc_hir_analysis/src/check/wfcheck.rs
+++ b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
@@ -15,7 +15,7 @@ use rustc_middle::mir::ConstraintCategory;
 use rustc_middle::query::Providers;
 use rustc_middle::ty::trait_def::TraitSpecializationKind;
 use rustc_middle::ty::{
-    self, AdtKind, GenericParamDefKind, Ty, TyCtxt, TypeFoldable, TypeSuperVisitable,
+    self, AdtKind, GenericParamDefKind, ToPredicate, Ty, TyCtxt, TypeFoldable, TypeSuperVisitable,
     TypeVisitable, TypeVisitableExt, TypeVisitor,
 };
 use rustc_middle::ty::{GenericArgKind, InternalSubsts};
@@ -81,7 +81,7 @@ impl<'tcx> WfCheckingCtxt<'_, 'tcx> {
             self.tcx(),
             cause,
             param_env,
-            ty::Binder::dummy(ty::PredicateKind::WellFormed(arg)),
+            ty::Binder::dummy(ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(arg))),
         ));
     }
 }
@@ -105,7 +105,12 @@ pub(super) fn enter_wf_checking_ctxt<'tcx, F>(
     }
     f(&mut wfcx);
 
-    let assumed_wf_types = wfcx.ocx.assumed_wf_types(param_env, span, body_def_id);
+    let assumed_wf_types = match wfcx.ocx.assumed_wf_types_and_report_errors(param_env, body_def_id)
+    {
+        Ok(wf_types) => wf_types,
+        Err(_guar) => return,
+    };
+
     let implied_bounds = infcx.implied_bounds_tys(param_env, body_def_id, assumed_wf_types);
 
     let errors = wfcx.select_all_or_error();
@@ -217,10 +222,10 @@ fn check_item<'tcx>(tcx: TyCtxt<'tcx>, item: &'tcx hir::Item<'tcx>) {
             check_item_fn(tcx, def_id, item.ident, item.span, sig.decl);
         }
         hir::ItemKind::Static(ty, ..) => {
-            check_item_type(tcx, def_id, ty.span, false);
+            check_item_type(tcx, def_id, ty.span, UnsizedHandling::Forbid);
         }
         hir::ItemKind::Const(ty, ..) => {
-            check_item_type(tcx, def_id, ty.span, false);
+            check_item_type(tcx, def_id, ty.span, UnsizedHandling::Forbid);
         }
         hir::ItemKind::Struct(_, ast_generics) => {
             check_type_defn(tcx, item, false);
@@ -242,6 +247,12 @@ fn check_item<'tcx>(tcx: TyCtxt<'tcx>, item: &'tcx hir::Item<'tcx>) {
         }
         // `ForeignItem`s are handled separately.
         hir::ItemKind::ForeignMod { .. } => {}
+        hir::ItemKind::TyAlias(hir_ty, ..) => {
+            if tcx.type_of(item.owner_id.def_id).skip_binder().has_opaque_types() {
+                // Bounds are respected for `type X = impl Trait` and `type X = (impl Trait, Y);`
+                check_item_type(tcx, def_id, hir_ty.span, UnsizedHandling::Allow);
+            }
+        }
         _ => {}
     }
 }
@@ -258,7 +269,9 @@ fn check_foreign_item(tcx: TyCtxt<'_>, item: &hir::ForeignItem<'_>) {
         hir::ForeignItemKind::Fn(decl, ..) => {
             check_item_fn(tcx, def_id, item.ident, item.span, decl)
         }
-        hir::ForeignItemKind::Static(ty, ..) => check_item_type(tcx, def_id, ty.span, true),
+        hir::ForeignItemKind::Static(ty, ..) => {
+            check_item_type(tcx, def_id, ty.span, UnsizedHandling::AllowIfForeignTail)
+        }
         hir::ForeignItemKind::Type => (),
     }
 }
@@ -314,7 +327,7 @@ fn check_gat_where_clauses(tcx: TyCtxt<'_>, associated_items: &[hir::TraitItemRe
             // Gather the bounds with which all other items inside of this trait constrain the GAT.
             // This is calculated by taking the intersection of the bounds that each item
             // constrains the GAT with individually.
-            let mut new_required_bounds: Option<FxHashSet<ty::Predicate<'_>>> = None;
+            let mut new_required_bounds: Option<FxHashSet<ty::Clause<'_>>> = None;
             for item in associated_items {
                 let item_def_id = item.id.owner_id;
                 // Skip our own GAT, since it does not constrain itself at all.
@@ -411,21 +424,17 @@ fn check_gat_where_clauses(tcx: TyCtxt<'_>, associated_items: &[hir::TraitItemRe
         let mut unsatisfied_bounds: Vec<_> = required_bounds
             .into_iter()
             .filter(|clause| match clause.kind().skip_binder() {
-                ty::PredicateKind::Clause(ty::Clause::RegionOutlives(ty::OutlivesPredicate(
-                    a,
-                    b,
-                ))) => !region_known_to_outlive(
-                    tcx,
-                    gat_def_id.def_id,
-                    param_env,
-                    &FxIndexSet::default(),
-                    a,
-                    b,
-                ),
-                ty::PredicateKind::Clause(ty::Clause::TypeOutlives(ty::OutlivesPredicate(
-                    a,
-                    b,
-                ))) => !ty_known_to_outlive(
+                ty::ClauseKind::RegionOutlives(ty::OutlivesPredicate(a, b)) => {
+                    !region_known_to_outlive(
+                        tcx,
+                        gat_def_id.def_id,
+                        param_env,
+                        &FxIndexSet::default(),
+                        a,
+                        b,
+                    )
+                }
+                ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(a, b)) => !ty_known_to_outlive(
                     tcx,
                     gat_def_id.def_id,
                     param_env,
@@ -433,7 +442,7 @@ fn check_gat_where_clauses(tcx: TyCtxt<'_>, associated_items: &[hir::TraitItemRe
                     a,
                     b,
                 ),
-                _ => bug!("Unexpected PredicateKind"),
+                _ => bug!("Unexpected ClauseKind"),
             })
             .map(|clause| clause.to_string())
             .collect();
@@ -481,7 +490,7 @@ fn check_gat_where_clauses(tcx: TyCtxt<'_>, associated_items: &[hir::TraitItemRe
 fn augment_param_env<'tcx>(
     tcx: TyCtxt<'tcx>,
     param_env: ty::ParamEnv<'tcx>,
-    new_predicates: Option<&FxHashSet<ty::Predicate<'tcx>>>,
+    new_predicates: Option<&FxHashSet<ty::Clause<'tcx>>>,
 ) -> ty::ParamEnv<'tcx> {
     let Some(new_predicates) = new_predicates else {
         return param_env;
@@ -491,7 +500,7 @@ fn augment_param_env<'tcx>(
         return param_env;
     }
 
-    let bounds = tcx.mk_predicates_from_iter(
+    let bounds = tcx.mk_clauses_from_iter(
         param_env.caller_bounds().iter().chain(new_predicates.iter().cloned()),
     );
     // FIXME(compiler-errors): Perhaps there is a case where we need to normalize this
@@ -517,7 +526,7 @@ fn gather_gat_bounds<'tcx, T: TypeFoldable<TyCtxt<'tcx>>>(
     wf_tys: &FxIndexSet<Ty<'tcx>>,
     gat_def_id: LocalDefId,
     gat_generics: &'tcx ty::Generics,
-) -> Option<FxHashSet<ty::Predicate<'tcx>>> {
+) -> Option<FxHashSet<ty::Clause<'tcx>>> {
     // The bounds we that we would require from `to_check`
     let mut bounds = FxHashSet::default();
 
@@ -552,22 +561,24 @@ fn gather_gat_bounds<'tcx, T: TypeFoldable<TyCtxt<'tcx>>>(
                 // our example, the type was `Self`, which will also be
                 // `Self` in the GAT.
                 let ty_param = gat_generics.param_at(*ty_idx, tcx);
-                let ty_param = tcx.mk_ty_param(ty_param.index, ty_param.name);
+                let ty_param = Ty::new_param(tcx, ty_param.index, ty_param.name);
                 // Same for the region. In our example, 'a corresponds
                 // to the 'me parameter.
                 let region_param = gat_generics.param_at(*region_a_idx, tcx);
-                let region_param = tcx.mk_re_early_bound(ty::EarlyBoundRegion {
-                    def_id: region_param.def_id,
-                    index: region_param.index,
-                    name: region_param.name,
-                });
+                let region_param = ty::Region::new_early_bound(
+                    tcx,
+                    ty::EarlyBoundRegion {
+                        def_id: region_param.def_id,
+                        index: region_param.index,
+                        name: region_param.name,
+                    },
+                );
                 // The predicate we expect to see. (In our example,
                 // `Self: 'me`.)
-                let clause = ty::PredicateKind::Clause(ty::Clause::TypeOutlives(
-                    ty::OutlivesPredicate(ty_param, region_param),
-                ));
-                let clause = tcx.mk_predicate(ty::Binder::dummy(clause));
-                bounds.insert(clause);
+                bounds.insert(
+                    ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(ty_param, region_param))
+                        .to_predicate(tcx),
+                );
             }
         }
 
@@ -593,24 +604,32 @@ fn gather_gat_bounds<'tcx, T: TypeFoldable<TyCtxt<'tcx>>>(
                 debug!("required clause: {region_a} must outlive {region_b}");
                 // Translate into the generic parameters of the GAT.
                 let region_a_param = gat_generics.param_at(*region_a_idx, tcx);
-                let region_a_param = tcx.mk_re_early_bound(ty::EarlyBoundRegion {
-                    def_id: region_a_param.def_id,
-                    index: region_a_param.index,
-                    name: region_a_param.name,
-                });
+                let region_a_param = ty::Region::new_early_bound(
+                    tcx,
+                    ty::EarlyBoundRegion {
+                        def_id: region_a_param.def_id,
+                        index: region_a_param.index,
+                        name: region_a_param.name,
+                    },
+                );
                 // Same for the region.
                 let region_b_param = gat_generics.param_at(*region_b_idx, tcx);
-                let region_b_param = tcx.mk_re_early_bound(ty::EarlyBoundRegion {
-                    def_id: region_b_param.def_id,
-                    index: region_b_param.index,
-                    name: region_b_param.name,
-                });
+                let region_b_param = ty::Region::new_early_bound(
+                    tcx,
+                    ty::EarlyBoundRegion {
+                        def_id: region_b_param.def_id,
+                        index: region_b_param.index,
+                        name: region_b_param.name,
+                    },
+                );
                 // The predicate we expect to see.
-                let clause = ty::PredicateKind::Clause(ty::Clause::RegionOutlives(
-                    ty::OutlivesPredicate(region_a_param, region_b_param),
-                ));
-                let clause = tcx.mk_predicate(ty::Binder::dummy(clause));
-                bounds.insert(clause);
+                bounds.insert(
+                    ty::ClauseKind::RegionOutlives(ty::OutlivesPredicate(
+                        region_a_param,
+                        region_b_param,
+                    ))
+                    .to_predicate(tcx),
+                );
             }
         }
     }
@@ -820,83 +839,20 @@ fn check_param_wf(tcx: TyCtxt<'_>, param: &hir::GenericParam<'_>) {
             let ty = tcx.type_of(param.def_id).subst_identity();
 
             if tcx.features().adt_const_params {
-                if let Some(non_structural_match_ty) =
-                    traits::search_for_adt_const_param_violation(param.span, tcx, ty)
-                {
-                    // We use the same error code in both branches, because this is really the same
-                    // issue: we just special-case the message for type parameters to make it
-                    // clearer.
-                    match non_structural_match_ty.kind() {
-                        ty::Param(_) => {
-                            // Const parameters may not have type parameters as their types,
-                            // because we cannot be sure that the type parameter derives `PartialEq`
-                            // and `Eq` (just implementing them is not enough for `structural_match`).
-                            struct_span_err!(
-                                tcx.sess,
-                                hir_ty.span,
-                                E0741,
-                                "`{ty}` is not guaranteed to `#[derive(PartialEq, Eq)]`, so may not be \
-                                used as the type of a const parameter",
-                            )
-                            .span_label(
-                                hir_ty.span,
-                                format!("`{ty}` may not derive both `PartialEq` and `Eq`"),
-                            )
-                            .note(
-                                "it is not currently possible to use a type parameter as the type of a \
-                                const parameter",
-                            )
-                            .emit();
-                        }
-                        ty::Float(_) => {
-                            struct_span_err!(
-                                tcx.sess,
-                                hir_ty.span,
-                                E0741,
-                                "`{ty}` is forbidden as the type of a const generic parameter",
-                            )
-                            .note("floats do not derive `Eq` or `Ord`, which are required for const parameters")
-                            .emit();
-                        }
-                        ty::FnPtr(_) => {
-                            struct_span_err!(
-                                tcx.sess,
-                                hir_ty.span,
-                                E0741,
-                                "using function pointers as const generic parameters is forbidden",
-                            )
-                            .emit();
-                        }
-                        ty::RawPtr(_) => {
-                            struct_span_err!(
-                                tcx.sess,
-                                hir_ty.span,
-                                E0741,
-                                "using raw pointers as const generic parameters is forbidden",
-                            )
-                            .emit();
-                        }
-                        _ => {
-                            let mut diag = struct_span_err!(
-                                tcx.sess,
-                                hir_ty.span,
-                                E0741,
-                                "`{}` must be annotated with `#[derive(PartialEq, Eq)]` to be used as \
-                                the type of a const parameter",
-                                non_structural_match_ty,
-                            );
-
-                            if ty == non_structural_match_ty {
-                                diag.span_label(
-                                    hir_ty.span,
-                                    format!("`{ty}` doesn't derive both `PartialEq` and `Eq`"),
-                                );
-                            }
-
-                            diag.emit();
-                        }
-                    }
-                }
+                enter_wf_checking_ctxt(tcx, hir_ty.span, param.def_id, |wfcx| {
+                    let trait_def_id =
+                        tcx.require_lang_item(LangItem::ConstParamTy, Some(hir_ty.span));
+                    wfcx.register_bound(
+                        ObligationCause::new(
+                            hir_ty.span,
+                            param.def_id,
+                            ObligationCauseCode::ConstParam(ty),
+                        ),
+                        wfcx.param_env,
+                        ty,
+                        trait_def_id,
+                    );
+                });
             } else {
                 let err_ty_str;
                 let mut is_ptr = true;
@@ -1025,7 +981,7 @@ fn check_type_defn<'tcx>(tcx: TyCtxt<'tcx>, item: &hir::Item<'tcx>, all_sized: b
             // intermediate types must be sized.
             let needs_drop_copy = || {
                 packed && {
-                    let ty = tcx.type_of(variant.fields.raw.last().unwrap().did).subst_identity();
+                    let ty = tcx.type_of(variant.tail().did).subst_identity();
                     let ty = tcx.erase_regions(ty);
                     if ty.has_infer() {
                         tcx.sess
@@ -1078,9 +1034,9 @@ fn check_type_defn<'tcx>(tcx: TyCtxt<'tcx>, item: &hir::Item<'tcx>, all_sized: b
                     tcx,
                     cause,
                     wfcx.param_env,
-                    ty::Binder::dummy(ty::PredicateKind::ConstEvaluatable(
+                    ty::Binder::dummy(ty::PredicateKind::Clause(ty::ClauseKind::ConstEvaluatable(
                         ty::Const::from_anon_const(tcx, discr_def_id.expect_local()),
-                    )),
+                    ))),
                 ));
             }
         }
@@ -1133,7 +1089,7 @@ fn check_associated_type_bounds(wfcx: &WfCheckingCtxt<'_, '_>, item: ty::AssocIt
             wfcx.infcx,
             wfcx.param_env,
             wfcx.body_def_id,
-            normalized_bound,
+            normalized_bound.as_predicate(),
             bound_span,
         )
     });
@@ -1154,20 +1110,32 @@ fn check_item_fn(
     })
 }
 
-fn check_item_type(tcx: TyCtxt<'_>, item_id: LocalDefId, ty_span: Span, allow_foreign_ty: bool) {
+enum UnsizedHandling {
+    Forbid,
+    Allow,
+    AllowIfForeignTail,
+}
+
+fn check_item_type(
+    tcx: TyCtxt<'_>,
+    item_id: LocalDefId,
+    ty_span: Span,
+    unsized_handling: UnsizedHandling,
+) {
     debug!("check_item_type: {:?}", item_id);
 
     enter_wf_checking_ctxt(tcx, ty_span, item_id, |wfcx| {
         let ty = tcx.type_of(item_id).subst_identity();
         let item_ty = wfcx.normalize(ty_span, Some(WellFormedLoc::Ty(item_id)), ty);
 
-        let mut forbid_unsized = true;
-        if allow_foreign_ty {
-            let tail = tcx.struct_tail_erasing_lifetimes(item_ty, wfcx.param_env);
-            if let ty::Foreign(_) = tail.kind() {
-                forbid_unsized = false;
+        let forbid_unsized = match unsized_handling {
+            UnsizedHandling::Forbid => true,
+            UnsizedHandling::Allow => false,
+            UnsizedHandling::AllowIfForeignTail => {
+                let tail = tcx.struct_tail_erasing_lifetimes(item_ty, wfcx.param_env);
+                !matches!(tail.kind(), ty::Foreign(_))
             }
-        }
+        };
 
         wfcx.register_wf_obligation(ty_span, Some(WellFormedLoc::Ty(item_id)), item_ty.into());
         if forbid_unsized {
@@ -1398,7 +1366,7 @@ fn check_where_clauses<'tcx>(wfcx: &WfCheckingCtxt<'_, 'tcx>, span: Span, def_id
             }
             let mut param_count = CountParams::default();
             let has_region = pred.visit_with(&mut param_count).is_break();
-            let substituted_pred = ty::EarlyBinder(pred).subst(tcx, substs);
+            let substituted_pred = ty::EarlyBinder::bind(pred).subst(tcx, substs);
             // Don't check non-defaulted params, dependent defaults (including lifetimes)
             // or preds with multiple params.
             if substituted_pred.has_non_region_param() || param_count.params.len() > 1 || has_region
@@ -1441,7 +1409,7 @@ fn check_where_clauses<'tcx>(wfcx: &WfCheckingCtxt<'_, 'tcx>, span: Span, def_id
             infcx,
             wfcx.param_env.without_const(),
             wfcx.body_def_id,
-            p,
+            p.as_predicate(),
             sp,
         )
     });
@@ -1503,7 +1471,7 @@ fn check_fn_or_method<'tcx>(
         let span = tcx.def_span(def_id);
         let has_implicit_self = hir_decl.implicit_self != hir::ImplicitSelfKind::None;
         let mut inputs = sig.inputs().iter().skip(if has_implicit_self { 1 } else { 0 });
-        // Check that the argument is a tuple
+        // Check that the argument is a tuple and is sized
         if let Some(ty) = inputs.next() {
             wfcx.register_bound(
                 ObligationCause::new(span, wfcx.body_def_id, ObligationCauseCode::RustCall),
@@ -1511,6 +1479,12 @@ fn check_fn_or_method<'tcx>(
                 *ty,
                 tcx.require_lang_item(hir::LangItem::Tuple, Some(span)),
             );
+            wfcx.register_bound(
+                ObligationCause::new(span, wfcx.body_def_id, ObligationCauseCode::RustCall),
+                wfcx.param_env,
+                *ty,
+                tcx.require_lang_item(hir::LangItem::Sized, Some(span)),
+            );
         } else {
             tcx.sess.span_err(
                 hir_decl.inputs.last().map_or(span, |input| input.span),
@@ -1572,13 +1546,13 @@ impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for ImplTraitInTraitFinder<'_, 'tcx> {
         if let ty::Alias(ty::Opaque, unshifted_opaque_ty) = *ty.kind()
             && self.seen.insert(unshifted_opaque_ty.def_id)
             && let Some(opaque_def_id) = unshifted_opaque_ty.def_id.as_local()
-            && let opaque = tcx.hir().expect_item(opaque_def_id).expect_opaque_ty()
-            && let hir::OpaqueTyOrigin::FnReturn(source) | hir::OpaqueTyOrigin::AsyncFn(source) = opaque.origin
+            && let origin = tcx.opaque_type_origin(opaque_def_id)
+            && let hir::OpaqueTyOrigin::FnReturn(source) | hir::OpaqueTyOrigin::AsyncFn(source) = origin
             && source == self.fn_def_id
         {
             let opaque_ty = tcx.fold_regions(unshifted_opaque_ty, |re, _depth| {
                 match re.kind() {
-                    ty::ReEarlyBound(_) | ty::ReFree(_) | ty::ReError(_) => re,
+                    ty::ReEarlyBound(_) | ty::ReFree(_) | ty::ReError(_) | ty::ReStatic => re,
                     r => bug!("unexpected region: {r:?}"),
                 }
             });
@@ -1591,7 +1565,7 @@ impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for ImplTraitInTraitFinder<'_, 'tcx> {
                     self.wfcx.infcx,
                     self.wfcx.param_env,
                     self.wfcx.body_def_id,
-                    bound,
+                    bound.as_predicate(),
                     bound_span,
                 ));
                 // Set the debruijn index back to innermost here, since we already eagerly
@@ -1799,9 +1773,11 @@ fn check_variances_for_type_defn<'tcx>(
     item: &hir::Item<'tcx>,
     hir_generics: &hir::Generics<'_>,
 ) {
-    let ty = tcx.type_of(item.owner_id).subst_identity();
-    if tcx.has_error_field(ty) {
-        return;
+    let identity_substs = ty::InternalSubsts::identity_for_item(tcx, item.owner_id);
+    for field in tcx.adt_def(item.owner_id).all_fields() {
+        if field.ty(tcx, identity_substs).references_error() {
+            return;
+        }
     }
 
     let ty_predicates = tcx.predicates_of(item.owner_id);
@@ -1902,7 +1878,7 @@ impl<'tcx> WfCheckingCtxt<'_, 'tcx> {
             // We lower empty bounds like `Vec<dyn Copy>:` as
             // `WellFormed(Vec<dyn Copy>)`, which will later get checked by
             // regular WF checking
-            if let ty::PredicateKind::WellFormed(..) = pred.kind().skip_binder() {
+            if let ty::ClauseKind::WellFormed(..) = pred.kind().skip_binder() {
                 continue;
             }
             // Match the existing behavior.
diff --git a/compiler/rustc_hir_analysis/src/coherence/builtin.rs b/compiler/rustc_hir_analysis/src/coherence/builtin.rs
index a98d8e171..79cc43edf 100644
--- a/compiler/rustc_hir_analysis/src/coherence/builtin.rs
+++ b/compiler/rustc_hir_analysis/src/coherence/builtin.rs
@@ -336,15 +336,17 @@ pub fn coerce_unsized_info<'tcx>(tcx: TyCtxt<'tcx>, impl_did: LocalDefId) -> Coe
             infcx.sub_regions(infer::RelateObjectBound(span), r_b, r_a);
             let mt_a = ty::TypeAndMut { ty: ty_a, mutbl: mutbl_a };
             let mt_b = ty::TypeAndMut { ty: ty_b, mutbl: mutbl_b };
-            check_mutbl(mt_a, mt_b, &|ty| tcx.mk_imm_ref(r_b, ty))
+            check_mutbl(mt_a, mt_b, &|ty| Ty::new_imm_ref(tcx, r_b, ty))
         }
 
         (&ty::Ref(_, ty_a, mutbl_a), &ty::RawPtr(mt_b)) => {
             let mt_a = ty::TypeAndMut { ty: ty_a, mutbl: mutbl_a };
-            check_mutbl(mt_a, mt_b, &|ty| tcx.mk_imm_ptr(ty))
+            check_mutbl(mt_a, mt_b, &|ty| Ty::new_imm_ptr(tcx, ty))
         }
 
-        (&ty::RawPtr(mt_a), &ty::RawPtr(mt_b)) => check_mutbl(mt_a, mt_b, &|ty| tcx.mk_imm_ptr(ty)),
+        (&ty::RawPtr(mt_a), &ty::RawPtr(mt_b)) => {
+            check_mutbl(mt_a, mt_b, &|ty| Ty::new_imm_ptr(tcx, ty))
+        }
 
         (&ty::Adt(def_a, substs_a), &ty::Adt(def_b, substs_b))
             if def_a.is_struct() && def_b.is_struct() =>
@@ -571,7 +573,7 @@ fn infringing_fields_error(
                             .or_default()
                             .push(error.obligation.cause.span);
                     }
-                    if let ty::PredicateKind::Clause(ty::Clause::Trait(ty::TraitPredicate {
+                    if let ty::PredicateKind::Clause(ty::ClauseKind::Trait(ty::TraitPredicate {
                         trait_ref,
                         polarity: ty::ImplPolarity::Positive,
                         ..
diff --git a/compiler/rustc_hir_analysis/src/coherence/inherent_impls_overlap.rs b/compiler/rustc_hir_analysis/src/coherence/inherent_impls_overlap.rs
index bd6252344..3bd293126 100644
--- a/compiler/rustc_hir_analysis/src/coherence/inherent_impls_overlap.rs
+++ b/compiler/rustc_hir_analysis/src/coherence/inherent_impls_overlap.rs
@@ -140,7 +140,7 @@ impl<'tcx> InherentOverlapChecker<'tcx> {
         impl1_def_id: DefId,
         impl2_def_id: DefId,
     ) {
-        traits::overlapping_impls(
+        let maybe_overlap = traits::overlapping_impls(
             self.tcx,
             impl1_def_id,
             impl2_def_id,
@@ -148,11 +148,11 @@ impl<'tcx> InherentOverlapChecker<'tcx> {
             // inherent impls without warning.
             SkipLeakCheck::Yes,
             overlap_mode,
-        )
-        .map_or(true, |overlap| {
+        );
+
+        if let Some(overlap) = maybe_overlap {
             self.check_for_common_items_in_impls(impl1_def_id, impl2_def_id, overlap);
-            false
-        });
+        }
     }
 
     fn check_item(&mut self, id: hir::ItemId) {
diff --git a/compiler/rustc_hir_analysis/src/coherence/mod.rs b/compiler/rustc_hir_analysis/src/coherence/mod.rs
index 4524b87a4..5097f4360 100644
--- a/compiler/rustc_hir_analysis/src/coherence/mod.rs
+++ b/compiler/rustc_hir_analysis/src/coherence/mod.rs
@@ -10,7 +10,6 @@ use rustc_errors::{error_code, struct_span_err};
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_middle::query::Providers;
 use rustc_middle::ty::{self, TyCtxt, TypeVisitableExt};
-use rustc_span::sym;
 use rustc_trait_selection::traits;
 
 mod builtin;
@@ -44,7 +43,7 @@ fn enforce_trait_manually_implementable(
     let impl_header_span = tcx.def_span(impl_def_id);
 
     // Disallow *all* explicit impls of traits marked `#[rustc_deny_explicit_impl]`
-    if tcx.has_attr(trait_def_id, sym::rustc_deny_explicit_impl) {
+    if tcx.trait_def(trait_def_id).deny_explicit_impl {
         let trait_name = tcx.item_name(trait_def_id);
         let mut err = struct_span_err!(
             tcx.sess,
diff --git a/compiler/rustc_hir_analysis/src/coherence/orphan.rs b/compiler/rustc_hir_analysis/src/coherence/orphan.rs
index 23beacd2a..025bab140 100644
--- a/compiler/rustc_hir_analysis/src/coherence/orphan.rs
+++ b/compiler/rustc_hir_analysis/src/coherence/orphan.rs
@@ -200,35 +200,32 @@ fn do_orphan_check_impl<'tcx>(
                 NonlocalImpl::DisallowOther,
             ),
 
-            // trait Id { type This: ?Sized; }
-            // impl<T: ?Sized> Id for T {
-            //     type This = T;
-            // }
-            // impl<T: ?Sized> AutoTrait for <T as Id>::This {}
-            ty::Alias(AliasKind::Projection, _) => (
-                LocalImpl::Disallow { problematic_kind: "associated type" },
-                NonlocalImpl::DisallowOther,
-            ),
-
-            // ```
-            // struct S<T>(T);
-            // impl<T: ?Sized> S<T> {
-            //     type This = T;
-            // }
-            // impl<T: ?Sized> AutoTrait for S<T>::This {}
-            // ```
-            // FIXME(inherent_associated_types): The example code above currently leads to a cycle
-            ty::Alias(AliasKind::Inherent, _) => (
-                LocalImpl::Disallow { problematic_kind: "associated type" },
-                NonlocalImpl::DisallowOther,
-            ),
-
-            // type Opaque = impl Trait;
-            // impl AutoTrait for Opaque {}
-            ty::Alias(AliasKind::Opaque, _) => (
-                LocalImpl::Disallow { problematic_kind: "opaque type" },
-                NonlocalImpl::DisallowOther,
-            ),
+            ty::Alias(kind, _) => {
+                let problematic_kind = match kind {
+                    // trait Id { type This: ?Sized; }
+                    // impl<T: ?Sized> Id for T {
+                    //     type This = T;
+                    // }
+                    // impl<T: ?Sized> AutoTrait for <T as Id>::This {}
+                    AliasKind::Projection => "associated type",
+                    // type Foo = (impl Sized, bool)
+                    // impl AutoTrait for Foo {}
+                    AliasKind::Weak => "type alias",
+                    // type Opaque = impl Trait;
+                    // impl AutoTrait for Opaque {}
+                    AliasKind::Opaque => "opaque type",
+                    // ```
+                    // struct S<T>(T);
+                    // impl<T: ?Sized> S<T> {
+                    //     type This = T;
+                    // }
+                    // impl<T: ?Sized> AutoTrait for S<T>::This {}
+                    // ```
+                    // FIXME(inherent_associated_types): The example code above currently leads to a cycle
+                    AliasKind::Inherent => "associated type",
+                };
+                (LocalImpl::Disallow { problematic_kind }, NonlocalImpl::DisallowOther)
+            }
 
             ty::Bool
             | ty::Char
@@ -346,7 +343,7 @@ fn emit_orphan_check_error<'tcx>(
                     // That way if we had `Vec<MyType>`, we will properly attribute the
                     // problem to `Vec<T>` and avoid confusing the user if they were to see
                     // `MyType` in the error.
-                    ty::Adt(def, _) => tcx.mk_adt(*def, ty::List::empty()),
+                    ty::Adt(def, _) => Ty::new_adt(tcx, *def, ty::List::empty()),
                     _ => ty,
                 };
                 let msg = |ty: &str, postfix: &str| {
@@ -608,7 +605,9 @@ fn fast_reject_auto_impl<'tcx>(tcx: TyCtxt<'tcx>, trait_def_id: DefId, self_ty:
     }
 
     let self_ty_root = match self_ty.kind() {
-        ty::Adt(def, _) => tcx.mk_adt(*def, InternalSubsts::identity_for_item(tcx, def.did())),
+        ty::Adt(def, _) => {
+            Ty::new_adt(tcx, *def, InternalSubsts::identity_for_item(tcx, def.did()))
+        }
         _ => unimplemented!("unexpected self ty {:?}", self_ty),
     };
 
diff --git a/compiler/rustc_hir_analysis/src/collect.rs b/compiler/rustc_hir_analysis/src/collect.rs
index ca0d5509c..f47df4f21 100644
--- a/compiler/rustc_hir_analysis/src/collect.rs
+++ b/compiler/rustc_hir_analysis/src/collect.rs
@@ -380,7 +380,7 @@ impl<'tcx> AstConv<'tcx> for ItemCtxt<'tcx> {
     }
 
     fn ty_infer(&self, _: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx> {
-        self.tcx().ty_error_with_message(span, "bad placeholder type")
+        Ty::new_error_with_message(self.tcx(), span, "bad placeholder type")
     }
 
     fn ct_infer(&self, ty: Ty<'tcx>, _: Option<&ty::GenericParamDef>, span: Span) -> Const<'tcx> {
@@ -390,7 +390,7 @@ impl<'tcx> AstConv<'tcx> for ItemCtxt<'tcx> {
             // left alone.
             r => bug!("unexpected region: {r:?}"),
         });
-        self.tcx().const_error_with_message(ty, span, "bad placeholder constant")
+        ty::Const::new_error_with_message(self.tcx(), ty, span, "bad placeholder constant")
     }
 
     fn projected_ty_from_poly_trait_ref(
@@ -407,7 +407,7 @@ impl<'tcx> AstConv<'tcx> for ItemCtxt<'tcx> {
                 item_segment,
                 trait_ref.substs,
             );
-            self.tcx().mk_projection(item_def_id, item_substs)
+            Ty::new_projection(self.tcx(), item_def_id, item_substs)
         } else {
             // There are no late-bound regions; we can just ignore the binder.
             let (mut mpart_sugg, mut inferred_sugg) = (None, None);
@@ -440,7 +440,7 @@ impl<'tcx> AstConv<'tcx> for ItemCtxt<'tcx> {
                                     self.tcx.replace_late_bound_regions_uncached(
                                         poly_trait_ref,
                                         |_| {
-                                            self.tcx.mk_re_early_bound(ty::EarlyBoundRegion {
+                                            ty::Region::new_early_bound(self.tcx, ty::EarlyBoundRegion {
                                                 def_id: item_def_id,
                                                 index: 0,
                                                 name: Symbol::intern(&lt_name),
@@ -471,14 +471,15 @@ impl<'tcx> AstConv<'tcx> for ItemCtxt<'tcx> {
                 }
                 _ => {}
             }
-            self.tcx().ty_error(self.tcx().sess.emit_err(
-                errors::AssociatedTypeTraitUninferredGenericParams {
+            Ty::new_error(
+                self.tcx(),
+                self.tcx().sess.emit_err(errors::AssociatedTypeTraitUninferredGenericParams {
                     span,
                     inferred_sugg,
                     bound,
                     mpart_sugg,
-                },
-            ))
+                }),
+            )
         }
     }
 
@@ -666,17 +667,15 @@ fn convert_trait_item(tcx: TyCtxt<'_>, trait_item_id: hir::TraitItemId) {
             tcx.ensure().fn_sig(def_id);
         }
 
-        hir::TraitItemKind::Const(.., Some(_)) => {
-            tcx.ensure().type_of(def_id);
-        }
-
-        hir::TraitItemKind::Const(hir_ty, _) => {
+        hir::TraitItemKind::Const(ty, body_id) => {
             tcx.ensure().type_of(def_id);
-            // Account for `const C: _;`.
-            let mut visitor = HirPlaceholderCollector::default();
-            visitor.visit_trait_item(trait_item);
-            if !tcx.sess.diagnostic().has_stashed_diagnostic(hir_ty.span, StashKey::ItemNoType) {
-                placeholder_type_error(tcx, None, visitor.0, false, None, "constant");
+            if !tcx.sess.diagnostic().has_stashed_diagnostic(ty.span, StashKey::ItemNoType)
+                && !(is_suggestable_infer_ty(ty) && body_id.is_some())
+            {
+                // Account for `const C: _;`.
+                let mut visitor = HirPlaceholderCollector::default();
+                visitor.visit_trait_item(trait_item);
+                placeholder_type_error(tcx, None, visitor.0, false, None, "associated constant");
             }
         }
 
@@ -721,7 +720,14 @@ fn convert_impl_item(tcx: TyCtxt<'_>, impl_item_id: hir::ImplItemId) {
 
             placeholder_type_error(tcx, None, visitor.0, false, None, "associated type");
         }
-        hir::ImplItemKind::Const(..) => {}
+        hir::ImplItemKind::Const(ty, _) => {
+            // Account for `const T: _ = ..;`
+            if !is_suggestable_infer_ty(ty) {
+                let mut visitor = HirPlaceholderCollector::default();
+                visitor.visit_impl_item(impl_item);
+                placeholder_type_error(tcx, None, visitor.0, false, None, "associated constant");
+            }
+        }
     }
 }
 
@@ -941,7 +947,7 @@ fn trait_def(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::TraitDef {
 
                 match item {
                     Some(item) if matches!(item.kind, hir::AssocItemKind::Fn { .. }) => {
-                        if !tcx.impl_defaultness(item.id.owner_id).has_value() {
+                        if !tcx.defaultness(item.id.owner_id).has_value() {
                             tcx.sess.emit_err(errors::FunctionNotHaveDefaultImplementation {
                                 span: item.span,
                                 note_span: attr_span,
@@ -986,6 +992,50 @@ fn trait_def(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::TraitDef {
             no_dups.then_some(list)
         });
 
+    let mut deny_explicit_impl = false;
+    let mut implement_via_object = true;
+    if let Some(attr) = tcx.get_attr(def_id, sym::rustc_deny_explicit_impl) {
+        deny_explicit_impl = true;
+        let mut seen_attr = false;
+        for meta in attr.meta_item_list().iter().flatten() {
+            if let Some(meta) = meta.meta_item()
+                && meta.name_or_empty() == sym::implement_via_object
+                && let Some(lit) = meta.name_value_literal()
+            {
+                if seen_attr {
+                    tcx.sess.span_err(
+                        meta.span,
+                        "duplicated `implement_via_object` meta item",
+                    );
+                }
+                seen_attr = true;
+
+                match lit.symbol {
+                    kw::True => {
+                        implement_via_object = true;
+                    }
+                    kw::False => {
+                        implement_via_object = false;
+                    }
+                    _ => {
+                        tcx.sess.span_err(
+                            meta.span,
+                            format!("unknown literal passed to `implement_via_object` attribute: {}", lit.symbol),
+                        );
+                    }
+                }
+            } else {
+                tcx.sess.span_err(
+                    meta.span(),
+                    format!("unknown meta item passed to `rustc_deny_explicit_impl` {:?}", meta),
+                );
+            }
+        }
+        if !seen_attr {
+            tcx.sess.span_err(attr.span, "missing `implement_via_object` meta item");
+        }
+    }
+
     ty::TraitDef {
         def_id: def_id.to_def_id(),
         unsafety,
@@ -996,6 +1046,8 @@ fn trait_def(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::TraitDef {
         skip_array_during_method_dispatch,
         specialization_kind,
         must_implement_one_of,
+        implement_via_object,
+        deny_explicit_impl,
     }
 }
 
@@ -1124,7 +1176,7 @@ fn fn_sig(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<ty::PolyFnSig<
             bug!("unexpected sort of node in fn_sig(): {:?}", x);
         }
     };
-    ty::EarlyBinder(output)
+    ty::EarlyBinder::bind(output)
 }
 
 fn infer_return_ty_for_fn_sig<'tcx>(
@@ -1188,7 +1240,7 @@ fn infer_return_ty_for_fn_sig<'tcx>(
             } else {
                 ty::Binder::dummy(tcx.mk_fn_sig(
                     fn_sig.inputs().iter().copied(),
-                    tcx.ty_error(guar),
+                    Ty::new_error(tcx, guar),
                     fn_sig.c_variadic,
                     fn_sig.unsafety,
                     fn_sig.abi,
@@ -1277,11 +1329,11 @@ fn suggest_impl_trait<'tcx>(
         {
             continue;
         }
-        let ocx = ObligationCtxt::new_in_snapshot(&infcx);
+        let ocx = ObligationCtxt::new(&infcx);
         let item_ty = ocx.normalize(
             &ObligationCause::misc(span, def_id),
             param_env,
-            tcx.mk_projection(assoc_item_def_id, substs),
+            Ty::new_projection(tcx, assoc_item_def_id, substs),
         );
         // FIXME(compiler-errors): We may benefit from resolving regions here.
         if ocx.select_where_possible().is_empty()
@@ -1312,7 +1364,7 @@ fn impl_trait_ref(
                 check_impl_constness(tcx, impl_.constness, ast_trait_ref),
             )
         })
-        .map(ty::EarlyBinder)
+        .map(ty::EarlyBinder::bind)
 }
 
 fn check_impl_constness(
diff --git a/compiler/rustc_hir_analysis/src/collect/generics_of.rs b/compiler/rustc_hir_analysis/src/collect/generics_of.rs
index ed60998ec..ccc9f8084 100644
--- a/compiler/rustc_hir_analysis/src/collect/generics_of.rs
+++ b/compiler/rustc_hir_analysis/src/collect/generics_of.rs
@@ -9,7 +9,7 @@ use rustc_hir::def_id::LocalDefId;
 use rustc_middle::ty::{self, TyCtxt};
 use rustc_session::lint;
 use rustc_span::symbol::{kw, Symbol};
-use rustc_span::Span;
+use rustc_span::{sym, Span};
 
 pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
     use rustc_hir::*;
@@ -50,7 +50,7 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
                 // We do not allow generic parameters in anon consts if we are inside
                 // of a const parameter type, e.g. `struct Foo<const N: usize, const M: [u8; N]>` is not allowed.
                 None
-            } else if tcx.lazy_normalization() {
+            } else if tcx.features().generic_const_exprs {
                 let parent_node = tcx.hir().get_parent(hir_id);
                 if let Node::Variant(Variant { disr_expr: Some(constant), .. }) = parent_node
                     && constant.hir_id == hir_id
@@ -101,6 +101,7 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
                         param_def_id_to_index,
                         has_self: generics.has_self,
                         has_late_bound_regions: generics.has_late_bound_regions,
+                        host_effect_index: None,
                     };
                 } else {
                     // HACK(eddyb) this provides the correct generics when
@@ -123,9 +124,6 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
                     {
                         Some(parent_def_id.to_def_id())
                     }
-                    Node::Expr(&Expr { kind: ExprKind::ConstBlock(_), .. }) => {
-                        Some(tcx.typeck_root_def_id(def_id.to_def_id()))
-                    }
                     // Exclude `GlobalAsm` here which cannot have generics.
                     Node::Expr(&Expr { kind: ExprKind::InlineAsm(asm), .. })
                         if asm.operands.iter().any(|(op, _op_sp)| match op {
@@ -142,11 +140,12 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
                 }
             }
         }
-        Node::Expr(&hir::Expr { kind: hir::ExprKind::Closure { .. }, .. }) => {
+        Node::ConstBlock(_)
+        | Node::Expr(&hir::Expr { kind: hir::ExprKind::Closure { .. }, .. }) => {
             Some(tcx.typeck_root_def_id(def_id.to_def_id()))
         }
         Node::Item(item) => match item.kind {
-            ItemKind::OpaqueTy(hir::OpaqueTy {
+            ItemKind::OpaqueTy(&hir::OpaqueTy {
                 origin:
                     hir::OpaqueTyOrigin::FnReturn(fn_def_id) | hir::OpaqueTyOrigin::AsyncFn(fn_def_id),
                 in_trait,
@@ -228,10 +227,12 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
     let has_self = opt_self.is_some();
     let mut parent_has_self = false;
     let mut own_start = has_self as u32;
+    let mut host_effect_index = None;
     let parent_count = parent_def_id.map_or(0, |def_id| {
         let generics = tcx.generics_of(def_id);
         assert!(!has_self);
         parent_has_self = generics.has_self;
+        host_effect_index = generics.host_effect_index;
         own_start = generics.count() as u32;
         generics.parent_count + generics.params.len()
     });
@@ -253,11 +254,11 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
 
     // Now create the real type and const parameters.
     let type_start = own_start - has_self as u32 + params.len() as u32;
-    let mut i = 0;
+    let mut i: u32 = 0;
     let mut next_index = || {
         let prev = i;
         i += 1;
-        prev as u32 + type_start
+        prev + type_start
     };
 
     const TYPE_DEFAULT_NOT_ALLOWED: &'static str = "defaults for type parameters are only allowed in \
@@ -297,7 +298,13 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
             })
         }
         GenericParamKind::Const { default, .. } => {
-            if !matches!(allow_defaults, Defaults::Allowed) && default.is_some() {
+            let is_host_param = tcx.has_attr(param.def_id, sym::rustc_host);
+
+            if !matches!(allow_defaults, Defaults::Allowed)
+                && default.is_some()
+                // `rustc_host` effect params are allowed to have defaults.
+                && !is_host_param
+            {
                 tcx.sess.span_err(
                     param.span,
                     "defaults for const parameters are only allowed in \
@@ -305,8 +312,18 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
                 );
             }
 
+            let index = next_index();
+
+            if is_host_param {
+                if let Some(idx) = host_effect_index {
+                    bug!("parent also has host effect param? index: {idx}, def: {def_id:?}");
+                }
+
+                host_effect_index = Some(parent_count + index as usize);
+            }
+
             Some(ty::GenericParamDef {
-                index: next_index(),
+                index,
                 name: param.name.ident().name,
                 def_id: param.def_id.to_def_id(),
                 pure_wrt_drop: param.pure_wrt_drop,
@@ -339,17 +356,14 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
     }
 
     // provide junk type parameter defs for const blocks.
-    if let Node::AnonConst(_) = node {
-        let parent_node = tcx.hir().get_parent(hir_id);
-        if let Node::Expr(&Expr { kind: ExprKind::ConstBlock(_), .. }) = parent_node {
-            params.push(ty::GenericParamDef {
-                index: next_index(),
-                name: Symbol::intern("<const_ty>"),
-                def_id: def_id.to_def_id(),
-                pure_wrt_drop: false,
-                kind: ty::GenericParamDefKind::Type { has_default: false, synthetic: false },
-            });
-        }
+    if let Node::ConstBlock(_) = node {
+        params.push(ty::GenericParamDef {
+            index: next_index(),
+            name: Symbol::intern("<const_ty>"),
+            def_id: def_id.to_def_id(),
+            pure_wrt_drop: false,
+            kind: ty::GenericParamDefKind::Type { has_default: false, synthetic: false },
+        });
     }
 
     let param_def_id_to_index = params.iter().map(|param| (param.def_id, param.index)).collect();
@@ -361,6 +375,7 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
         param_def_id_to_index,
         has_self: has_self || parent_has_self,
         has_late_bound_regions: has_late_bound_regions(tcx, node),
+        host_effect_index,
     }
 }
 
diff --git a/compiler/rustc_hir_analysis/src/collect/item_bounds.rs b/compiler/rustc_hir_analysis/src/collect/item_bounds.rs
index 948b903e5..57f74172e 100644
--- a/compiler/rustc_hir_analysis/src/collect/item_bounds.rs
+++ b/compiler/rustc_hir_analysis/src/collect/item_bounds.rs
@@ -1,5 +1,5 @@
 use super::ItemCtxt;
-use crate::astconv::{AstConv, OnlySelfBounds};
+use crate::astconv::{AstConv, PredicateFilter};
 use rustc_hir as hir;
 use rustc_infer::traits::util;
 use rustc_middle::ty::subst::InternalSubsts;
@@ -19,32 +19,34 @@ fn associated_type_bounds<'tcx>(
     assoc_item_def_id: LocalDefId,
     ast_bounds: &'tcx [hir::GenericBound<'tcx>],
     span: Span,
-) -> &'tcx [(ty::Predicate<'tcx>, Span)] {
-    let item_ty = tcx.mk_projection(
+) -> &'tcx [(ty::Clause<'tcx>, Span)] {
+    let item_ty = Ty::new_projection(
+        tcx,
         assoc_item_def_id.to_def_id(),
         InternalSubsts::identity_for_item(tcx, assoc_item_def_id),
     );
 
     let icx = ItemCtxt::new(tcx, assoc_item_def_id);
-    let mut bounds = icx.astconv().compute_bounds(item_ty, ast_bounds, OnlySelfBounds(false));
+    let mut bounds = icx.astconv().compute_bounds(item_ty, ast_bounds, PredicateFilter::All);
     // Associated types are implicitly sized unless a `?Sized` bound is found
     icx.astconv().add_implicitly_sized(&mut bounds, item_ty, ast_bounds, None, span);
 
     let trait_def_id = tcx.local_parent(assoc_item_def_id);
     let trait_predicates = tcx.trait_explicit_predicates_and_bounds(trait_def_id);
 
-    let bounds_from_parent = trait_predicates.predicates.iter().copied().filter(|(pred, _)| {
-        match pred.kind().skip_binder() {
-            ty::PredicateKind::Clause(ty::Clause::Trait(tr)) => tr.self_ty() == item_ty,
-            ty::PredicateKind::Clause(ty::Clause::Projection(proj)) => {
-                proj.projection_ty.self_ty() == item_ty
-            }
-            ty::PredicateKind::Clause(ty::Clause::TypeOutlives(outlives)) => outlives.0 == item_ty,
+    let bounds_from_parent = trait_predicates
+        .predicates
+        .iter()
+        .copied()
+        .filter(|(pred, _)| match pred.kind().skip_binder() {
+            ty::ClauseKind::Trait(tr) => tr.self_ty() == item_ty,
+            ty::ClauseKind::Projection(proj) => proj.projection_ty.self_ty() == item_ty,
+            ty::ClauseKind::TypeOutlives(outlives) => outlives.0 == item_ty,
             _ => false,
-        }
-    });
+        })
+        .map(|(clause, span)| (clause, span));
 
-    let all_bounds = tcx.arena.alloc_from_iter(bounds.predicates().chain(bounds_from_parent));
+    let all_bounds = tcx.arena.alloc_from_iter(bounds.clauses().chain(bounds_from_parent));
     debug!(
         "associated_type_bounds({}) = {:?}",
         tcx.def_path_str(assoc_item_def_id.to_def_id()),
@@ -64,33 +66,34 @@ fn opaque_type_bounds<'tcx>(
     ast_bounds: &'tcx [hir::GenericBound<'tcx>],
     item_ty: Ty<'tcx>,
     span: Span,
-) -> &'tcx [(ty::Predicate<'tcx>, Span)] {
+) -> &'tcx [(ty::Clause<'tcx>, Span)] {
     ty::print::with_no_queries!({
         let icx = ItemCtxt::new(tcx, opaque_def_id);
-        let mut bounds = icx.astconv().compute_bounds(item_ty, ast_bounds, OnlySelfBounds(false));
+        let mut bounds = icx.astconv().compute_bounds(item_ty, ast_bounds, PredicateFilter::All);
         // Opaque types are implicitly sized unless a `?Sized` bound is found
         icx.astconv().add_implicitly_sized(&mut bounds, item_ty, ast_bounds, None, span);
         debug!(?bounds);
 
-        tcx.arena.alloc_from_iter(bounds.predicates())
+        tcx.arena.alloc_from_iter(bounds.clauses())
     })
 }
 
 pub(super) fn explicit_item_bounds(
     tcx: TyCtxt<'_>,
     def_id: LocalDefId,
-) -> ty::EarlyBinder<&'_ [(ty::Predicate<'_>, Span)]> {
+) -> ty::EarlyBinder<&'_ [(ty::Clause<'_>, Span)]> {
     match tcx.opt_rpitit_info(def_id.to_def_id()) {
         // RPITIT's bounds are the same as opaque type bounds, but with
         // a projection self type.
         Some(ty::ImplTraitInTraitData::Trait { opaque_def_id, .. }) => {
             let item = tcx.hir().get_by_def_id(opaque_def_id.expect_local()).expect_item();
             let opaque_ty = item.expect_opaque_ty();
-            return ty::EarlyBinder(opaque_type_bounds(
+            return ty::EarlyBinder::bind(opaque_type_bounds(
                 tcx,
                 opaque_def_id.expect_local(),
                 opaque_ty.bounds,
-                tcx.mk_projection(
+                Ty::new_projection(
+                    tcx,
                     def_id.to_def_id(),
                     ty::InternalSubsts::identity_for_item(tcx, def_id),
                 ),
@@ -116,25 +119,23 @@ pub(super) fn explicit_item_bounds(
         }) => {
             let substs = InternalSubsts::identity_for_item(tcx, def_id);
             let item_ty = if *in_trait && !tcx.lower_impl_trait_in_trait_to_assoc_ty() {
-                tcx.mk_projection(def_id.to_def_id(), substs)
+                Ty::new_projection(tcx, def_id.to_def_id(), substs)
             } else {
-                tcx.mk_opaque(def_id.to_def_id(), substs)
+                Ty::new_opaque(tcx, def_id.to_def_id(), substs)
             };
             opaque_type_bounds(tcx, def_id, bounds, item_ty, *span)
         }
+        hir::Node::Item(hir::Item { kind: hir::ItemKind::TyAlias(..), .. }) => &[],
         _ => bug!("item_bounds called on {:?}", def_id),
     };
-    ty::EarlyBinder(bounds)
+    ty::EarlyBinder::bind(bounds)
 }
 
 pub(super) fn item_bounds(
     tcx: TyCtxt<'_>,
     def_id: DefId,
-) -> ty::EarlyBinder<&'_ ty::List<ty::Predicate<'_>>> {
+) -> ty::EarlyBinder<&'_ ty::List<ty::Clause<'_>>> {
     tcx.explicit_item_bounds(def_id).map_bound(|bounds| {
-        tcx.mk_predicates_from_iter(util::elaborate(
-            tcx,
-            bounds.iter().map(|&(bound, _span)| bound),
-        ))
+        tcx.mk_clauses_from_iter(util::elaborate(tcx, bounds.iter().map(|&(bound, _span)| bound)))
     })
 }
diff --git a/compiler/rustc_hir_analysis/src/collect/predicates_of.rs b/compiler/rustc_hir_analysis/src/collect/predicates_of.rs
index e5b5dae55..129366641 100644
--- a/compiler/rustc_hir_analysis/src/collect/predicates_of.rs
+++ b/compiler/rustc_hir_analysis/src/collect/predicates_of.rs
@@ -1,8 +1,8 @@
-use crate::astconv::{AstConv, OnlySelfBounds};
+use crate::astconv::{AstConv, OnlySelfBounds, PredicateFilter};
 use crate::bounds::Bounds;
 use crate::collect::ItemCtxt;
 use crate::constrained_generic_params as cgp;
-use hir::{HirId, Node};
+use hir::{HirId, Lifetime, Node};
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_hir as hir;
 use rustc_hir::def::DefKind;
@@ -10,9 +10,9 @@ use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::intravisit::{self, Visitor};
 use rustc_middle::ty::subst::InternalSubsts;
 use rustc_middle::ty::{self, Ty, TyCtxt};
-use rustc_middle::ty::{GenericPredicates, ToPredicate};
+use rustc_middle::ty::{GenericPredicates, Generics, ImplTraitInTraitData, ToPredicate};
 use rustc_span::symbol::{sym, Ident};
-use rustc_span::{Span, DUMMY_SP};
+use rustc_span::{Span, Symbol, DUMMY_SP};
 
 /// Returns a list of all type predicates (explicit and implicit) for the definition with
 /// ID `def_id`. This includes all predicates returned by `predicates_defined_on`, plus
@@ -62,6 +62,67 @@ pub(super) fn predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredic
 fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::GenericPredicates<'_> {
     use rustc_hir::*;
 
+    match tcx.opt_rpitit_info(def_id.to_def_id()) {
+        Some(ImplTraitInTraitData::Trait { opaque_def_id, fn_def_id }) => {
+            let opaque_ty_id = tcx.hir().local_def_id_to_hir_id(opaque_def_id.expect_local());
+            let opaque_ty_node = tcx.hir().get(opaque_ty_id);
+            let Node::Item(&Item { kind: ItemKind::OpaqueTy(OpaqueTy { lifetime_mapping, .. }), .. }) = opaque_ty_node else {
+                bug!("unexpected {opaque_ty_node:?}")
+            };
+
+            let mut predicates = Vec::new();
+
+            // RPITITs should inherit the predicates of their parent. This is
+            // both to ensure that the RPITITs are only instantiated when the
+            // parent predicates would hold, and also so that the param-env
+            // inherits these predicates as assumptions.
+            let identity_substs = InternalSubsts::identity_for_item(tcx, def_id);
+            predicates.extend(
+                tcx.explicit_predicates_of(fn_def_id).instantiate_own(tcx, identity_substs),
+            );
+
+            // We also install bidirectional outlives predicates for the RPITIT
+            // to keep the duplicates lifetimes from opaque lowering in sync.
+            compute_bidirectional_outlives_predicates(
+                tcx,
+                def_id,
+                lifetime_mapping.iter().map(|(lifetime, def_id)| {
+                    (*lifetime, (*def_id, lifetime.ident.name, lifetime.ident.span))
+                }),
+                tcx.generics_of(def_id.to_def_id()),
+                &mut predicates,
+            );
+
+            return ty::GenericPredicates {
+                parent: Some(tcx.parent(def_id.to_def_id())),
+                predicates: tcx.arena.alloc_from_iter(predicates),
+            };
+        }
+
+        Some(ImplTraitInTraitData::Impl { fn_def_id }) => {
+            let assoc_item = tcx.associated_item(def_id);
+            let trait_assoc_predicates =
+                tcx.explicit_predicates_of(assoc_item.trait_item_def_id.unwrap());
+
+            let impl_assoc_identity_substs = InternalSubsts::identity_for_item(tcx, def_id);
+            let impl_def_id = tcx.parent(fn_def_id);
+            let impl_trait_ref_substs =
+                tcx.impl_trait_ref(impl_def_id).unwrap().subst_identity().substs;
+
+            let impl_assoc_substs =
+                impl_assoc_identity_substs.rebase_onto(tcx, impl_def_id, impl_trait_ref_substs);
+
+            let impl_predicates = trait_assoc_predicates.instantiate_own(tcx, impl_assoc_substs);
+
+            return ty::GenericPredicates {
+                parent: Some(impl_def_id),
+                predicates: tcx.arena.alloc_from_iter(impl_predicates),
+            };
+        }
+
+        None => {}
+    }
+
     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
     let node = tcx.hir().get(hir_id);
 
@@ -75,7 +136,7 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
 
     // We use an `IndexSet` to preserve order of insertion.
     // Preserving the order of insertion is important here so as not to break UI tests.
-    let mut predicates: FxIndexSet<(ty::Predicate<'_>, Span)> = FxIndexSet::default();
+    let mut predicates: FxIndexSet<(ty::Clause<'_>, Span)> = FxIndexSet::default();
 
     let ast_generics = match node {
         Node::TraitItem(item) => item.generics,
@@ -125,8 +186,8 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
     if let Some(self_bounds) = is_trait {
         predicates.extend(
             icx.astconv()
-                .compute_bounds(tcx.types.self_param, self_bounds, OnlySelfBounds(false))
-                .predicates(),
+                .compute_bounds(tcx.types.self_param, self_bounds, PredicateFilter::All)
+                .clauses(),
         );
     }
 
@@ -175,22 +236,24 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
                     param.span,
                 );
                 trace!(?bounds);
-                predicates.extend(bounds.predicates());
+                predicates.extend(bounds.clauses());
                 trace!(?predicates);
             }
             GenericParamKind::Const { .. } => {
                 let name = param.name.ident().name;
                 let param_const = ty::ParamConst::new(index, name);
 
-                let ct_ty = tcx.type_of(param.def_id.to_def_id()).subst_identity();
+                let ct_ty = tcx
+                    .type_of(param.def_id.to_def_id())
+                    .no_bound_vars()
+                    .expect("const parameters cannot be generic");
 
-                let ct = tcx.mk_const(param_const, ct_ty);
+                let ct = ty::Const::new_param(tcx, param_const, ct_ty);
 
-                let predicate = ty::Binder::dummy(ty::PredicateKind::Clause(
-                    ty::Clause::ConstArgHasType(ct, ct_ty),
-                ))
-                .to_predicate(tcx);
-                predicates.insert((predicate, param.span));
+                predicates.insert((
+                    ty::ClauseKind::ConstArgHasType(ct, ct_ty).to_predicate(tcx),
+                    param.span,
+                ));
 
                 index += 1;
             }
@@ -219,7 +282,7 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
                     } else {
                         let span = bound_pred.bounded_ty.span;
                         let predicate = ty::Binder::bind_with_vars(
-                            ty::PredicateKind::WellFormed(ty.into()),
+                            ty::ClauseKind::WellFormed(ty.into()),
                             bound_vars,
                         );
                         predicates.insert((predicate.to_predicate(tcx), span));
@@ -234,7 +297,7 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
                     bound_vars,
                     OnlySelfBounds(false),
                 );
-                predicates.extend(bounds.predicates());
+                predicates.extend(bounds.clauses());
             }
 
             hir::WherePredicate::RegionPredicate(region_pred) => {
@@ -246,11 +309,8 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
                         }
                         _ => bug!(),
                     };
-                    let pred = ty::Binder::dummy(ty::PredicateKind::Clause(
-                        ty::Clause::RegionOutlives(ty::OutlivesPredicate(r1, r2)),
-                    ))
-                    .to_predicate(icx.tcx);
-
+                    let pred = ty::ClauseKind::RegionOutlives(ty::OutlivesPredicate(r1, r2))
+                        .to_predicate(icx.tcx);
                     (pred, span)
                 }))
             }
@@ -293,39 +353,22 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
             bug!("unexpected {opaque_ty_node:?}")
         };
         debug!(?lifetimes);
-        for (arg, duplicate) in std::iter::zip(lifetimes, ast_generics.params) {
-            let hir::GenericArg::Lifetime(arg) = arg else { bug!() };
-            let orig_region = icx.astconv().ast_region_to_region(&arg, None);
-            if !matches!(orig_region.kind(), ty::ReEarlyBound(..)) {
-                // Only early-bound regions can point to the original generic parameter.
-                continue;
-            }
 
-            let hir::GenericParamKind::Lifetime { .. } = duplicate.kind else { continue };
-            let dup_def = duplicate.def_id.to_def_id();
-
-            let Some(dup_index) = generics.param_def_id_to_index(tcx, dup_def) else { bug!() };
-
-            let dup_region = tcx.mk_re_early_bound(ty::EarlyBoundRegion {
-                def_id: dup_def,
-                index: dup_index,
-                name: duplicate.name.ident().name,
-            });
-            predicates.push((
-                ty::Binder::dummy(ty::PredicateKind::Clause(ty::Clause::RegionOutlives(
-                    ty::OutlivesPredicate(orig_region, dup_region),
-                )))
-                .to_predicate(icx.tcx),
-                duplicate.span,
-            ));
-            predicates.push((
-                ty::Binder::dummy(ty::PredicateKind::Clause(ty::Clause::RegionOutlives(
-                    ty::OutlivesPredicate(dup_region, orig_region),
-                )))
-                .to_predicate(icx.tcx),
-                duplicate.span,
-            ));
-        }
+        let lifetime_mapping = std::iter::zip(lifetimes, ast_generics.params)
+            .map(|(arg, dup)| {
+                let hir::GenericArg::Lifetime(arg) = arg else { bug!() };
+                (**arg, dup)
+            })
+            .filter(|(_, dup)| matches!(dup.kind, hir::GenericParamKind::Lifetime { .. }))
+            .map(|(lifetime, dup)| (lifetime, (dup.def_id, dup.name.ident().name, dup.span)));
+
+        compute_bidirectional_outlives_predicates(
+            tcx,
+            def_id,
+            lifetime_mapping,
+            generics,
+            &mut predicates,
+        );
         debug!(?predicates);
     }
 
@@ -335,13 +378,53 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
     }
 }
 
+/// Opaques have duplicated lifetimes and we need to compute bidirectional outlives predicates to
+/// enforce that these lifetimes stay in sync.
+fn compute_bidirectional_outlives_predicates<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    item_def_id: LocalDefId,
+    lifetime_mapping: impl Iterator<Item = (Lifetime, (LocalDefId, Symbol, Span))>,
+    generics: &Generics,
+    predicates: &mut Vec<(ty::Clause<'tcx>, Span)>,
+) {
+    let icx = ItemCtxt::new(tcx, item_def_id);
+
+    for (arg, (dup_def, name, span)) in lifetime_mapping {
+        let orig_region = icx.astconv().ast_region_to_region(&arg, None);
+        if !matches!(orig_region.kind(), ty::ReEarlyBound(..)) {
+            // There is no late-bound lifetime to actually match up here, since the lifetime doesn't
+            // show up in the opaque's parent's substs.
+            continue;
+        }
+
+        let Some(dup_index) = generics.param_def_id_to_index(icx.tcx, dup_def.to_def_id()) else { bug!() };
+
+        let dup_region = ty::Region::new_early_bound(
+            tcx,
+            ty::EarlyBoundRegion { def_id: dup_def.to_def_id(), index: dup_index, name },
+        );
+
+        predicates.push((
+            ty::ClauseKind::RegionOutlives(ty::OutlivesPredicate(orig_region, dup_region))
+                .to_predicate(tcx),
+            span,
+        ));
+
+        predicates.push((
+            ty::ClauseKind::RegionOutlives(ty::OutlivesPredicate(dup_region, orig_region))
+                .to_predicate(tcx),
+            span,
+        ));
+    }
+}
+
 fn const_evaluatable_predicates_of(
     tcx: TyCtxt<'_>,
     def_id: LocalDefId,
-) -> FxIndexSet<(ty::Predicate<'_>, Span)> {
+) -> FxIndexSet<(ty::Clause<'_>, Span)> {
     struct ConstCollector<'tcx> {
         tcx: TyCtxt<'tcx>,
-        preds: FxIndexSet<(ty::Predicate<'tcx>, Span)>,
+        preds: FxIndexSet<(ty::Clause<'tcx>, Span)>,
     }
 
     impl<'tcx> intravisit::Visitor<'tcx> for ConstCollector<'tcx> {
@@ -349,11 +432,8 @@ fn const_evaluatable_predicates_of(
             let ct = ty::Const::from_anon_const(self.tcx, c.def_id);
             if let ty::ConstKind::Unevaluated(_) = ct.kind() {
                 let span = self.tcx.def_span(c.def_id);
-                self.preds.insert((
-                    ty::Binder::dummy(ty::PredicateKind::ConstEvaluatable(ct))
-                        .to_predicate(self.tcx),
-                    span,
-                ));
+                self.preds
+                    .insert((ty::ClauseKind::ConstEvaluatable(ct).to_predicate(self.tcx), span));
             }
         }
 
@@ -441,13 +521,9 @@ pub(super) fn explicit_predicates_of<'tcx>(
             .iter()
             .copied()
             .filter(|(pred, _)| match pred.kind().skip_binder() {
-                ty::PredicateKind::Clause(ty::Clause::Trait(tr)) => !is_assoc_item_ty(tr.self_ty()),
-                ty::PredicateKind::Clause(ty::Clause::Projection(proj)) => {
-                    !is_assoc_item_ty(proj.projection_ty.self_ty())
-                }
-                ty::PredicateKind::Clause(ty::Clause::TypeOutlives(outlives)) => {
-                    !is_assoc_item_ty(outlives.0)
-                }
+                ty::ClauseKind::Trait(tr) => !is_assoc_item_ty(tr.self_ty()),
+                ty::ClauseKind::Projection(proj) => !is_assoc_item_ty(proj.projection_ty.self_ty()),
+                ty::ClauseKind::TypeOutlives(outlives) => !is_assoc_item_ty(outlives.0),
                 _ => true,
             })
             .collect();
@@ -460,7 +536,7 @@ pub(super) fn explicit_predicates_of<'tcx>(
             }
         }
     } else {
-        if matches!(def_kind, DefKind::AnonConst) && tcx.lazy_normalization() {
+        if matches!(def_kind, DefKind::AnonConst) && tcx.features().generic_const_exprs {
             let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
             let parent_def_id = tcx.hir().get_parent_item(hir_id);
 
@@ -488,9 +564,7 @@ pub(super) fn explicit_predicates_of<'tcx>(
                     .predicates
                     .into_iter()
                     .filter(|(pred, _)| {
-                        if let ty::PredicateKind::Clause(ty::Clause::ConstArgHasType(ct, _)) =
-                            pred.kind().skip_binder()
-                        {
+                        if let ty::ClauseKind::ConstArgHasType(ct, _) = pred.kind().skip_binder() {
                             match ct.kind() {
                                 ty::ConstKind::Param(param_const) => {
                                     let defaulted_param_idx = tcx
@@ -544,19 +618,6 @@ pub(super) fn explicit_predicates_of<'tcx>(
     }
 }
 
-#[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),
-}
-
 /// Ensures that the super-predicates of the trait with a `DefId`
 /// of `trait_def_id` are converted and stored. This also ensures that
 /// the transitive super-predicates are converted.
@@ -578,11 +639,15 @@ pub(super) fn implied_predicates_of(
     tcx: TyCtxt<'_>,
     trait_def_id: LocalDefId,
 ) -> ty::GenericPredicates<'_> {
-    if tcx.is_trait_alias(trait_def_id.to_def_id()) {
-        implied_predicates_with_filter(tcx, trait_def_id.to_def_id(), PredicateFilter::All)
-    } else {
-        tcx.super_predicates_of(trait_def_id)
-    }
+    implied_predicates_with_filter(
+        tcx,
+        trait_def_id.to_def_id(),
+        if tcx.is_trait_alias(trait_def_id.to_def_id()) {
+            PredicateFilter::All
+        } else {
+            PredicateFilter::SelfAndAssociatedTypeBounds
+        },
+    )
 }
 
 /// Ensures that the super-predicates of the trait with a `DefId`
@@ -615,48 +680,18 @@ pub(super) fn implied_predicates_with_filter(
     let icx = ItemCtxt::new(tcx, trait_def_id);
 
     let self_param_ty = tcx.types.self_param;
-    let (superbounds, where_bounds_that_match) = match filter {
-        PredicateFilter::All => (
-            // Convert the bounds that follow the colon (or equal in trait aliases)
-            icx.astconv().compute_bounds(self_param_ty, bounds, OnlySelfBounds(false)),
-            // Also include all where clause bounds
-            icx.type_parameter_bounds_in_generics(
-                generics,
-                item.owner_id.def_id,
-                self_param_ty,
-                OnlySelfBounds(false),
-                None,
-            ),
-        ),
-        PredicateFilter::SelfOnly => (
-            // Convert the bounds that follow the colon (or equal in trait aliases)
-            icx.astconv().compute_bounds(self_param_ty, bounds, OnlySelfBounds(true)),
-            // Include where clause bounds for `Self`
-            icx.type_parameter_bounds_in_generics(
-                generics,
-                item.owner_id.def_id,
-                self_param_ty,
-                OnlySelfBounds(true),
-                None,
-            ),
-        ),
-        PredicateFilter::SelfThatDefines(assoc_name) => (
-            // Convert the bounds that follow the colon (or equal) that reference the associated name
-            icx.astconv().compute_bounds_that_match_assoc_item(self_param_ty, bounds, assoc_name),
-            // Include where clause bounds for `Self` that reference the associated name
-            icx.type_parameter_bounds_in_generics(
-                generics,
-                item.owner_id.def_id,
-                self_param_ty,
-                OnlySelfBounds(true),
-                Some(assoc_name),
-            ),
-        ),
-    };
+    let superbounds = icx.astconv().compute_bounds(self_param_ty, bounds, filter);
+
+    let where_bounds_that_match = icx.type_parameter_bounds_in_generics(
+        generics,
+        item.owner_id.def_id,
+        self_param_ty,
+        filter,
+    );
 
     // Combine the two lists to form the complete set of superbounds:
     let implied_bounds =
-        &*tcx.arena.alloc_from_iter(superbounds.predicates().chain(where_bounds_that_match));
+        &*tcx.arena.alloc_from_iter(superbounds.clauses().chain(where_bounds_that_match));
     debug!(?implied_bounds);
 
     // Now require that immediate supertraits are converted, which will, in
@@ -665,7 +700,7 @@ pub(super) fn implied_predicates_with_filter(
     if matches!(filter, PredicateFilter::SelfOnly) {
         for &(pred, span) in implied_bounds {
             debug!("superbound: {:?}", pred);
-            if let ty::PredicateKind::Clause(ty::Clause::Trait(bound)) = pred.kind().skip_binder()
+            if let ty::ClauseKind::Trait(bound) = pred.kind().skip_binder()
                 && bound.polarity == ty::ImplPolarity::Positive
             {
                 tcx.at(span).super_predicates_of(bound.def_id());
@@ -684,6 +719,7 @@ pub(super) fn type_param_predicates(
     (item_def_id, def_id, assoc_name): (LocalDefId, LocalDefId, Ident),
 ) -> ty::GenericPredicates<'_> {
     use rustc_hir::*;
+    use rustc_middle::ty::Ty;
 
     // In the AST, bounds can derive from two places. Either
     // written inline like `<T: Foo>` or in a where-clause like
@@ -693,7 +729,7 @@ pub(super) fn type_param_predicates(
     let param_owner = tcx.hir().ty_param_owner(def_id);
     let generics = tcx.generics_of(param_owner);
     let index = generics.param_def_id_to_index[&def_id.to_def_id()];
-    let ty = tcx.mk_ty_param(index, tcx.hir().ty_param_name(def_id));
+    let ty = Ty::new_param(tcx, index, tcx.hir().ty_param_name(def_id));
 
     // Don't look for bounds where the type parameter isn't in scope.
     let parent = if item_def_id == param_owner {
@@ -721,7 +757,7 @@ pub(super) fn type_param_predicates(
                 ItemKind::Fn(.., generics, _)
                 | ItemKind::Impl(&hir::Impl { generics, .. })
                 | ItemKind::TyAlias(_, generics)
-                | ItemKind::OpaqueTy(OpaqueTy {
+                | ItemKind::OpaqueTy(&OpaqueTy {
                     generics,
                     origin: hir::OpaqueTyOrigin::TyAlias { .. },
                     ..
@@ -757,12 +793,11 @@ pub(super) fn type_param_predicates(
             ast_generics,
             def_id,
             ty,
-            OnlySelfBounds(true),
-            Some(assoc_name),
+            PredicateFilter::SelfThatDefines(assoc_name),
         )
         .into_iter()
         .filter(|(predicate, _)| match predicate.kind().skip_binder() {
-            ty::PredicateKind::Clause(ty::Clause::Trait(data)) => data.self_ty().is_param(index),
+            ty::ClauseKind::Trait(data) => data.self_ty().is_param(index),
             _ => false,
         }),
     );
@@ -782,9 +817,8 @@ impl<'tcx> ItemCtxt<'tcx> {
         ast_generics: &'tcx hir::Generics<'tcx>,
         param_def_id: LocalDefId,
         ty: Ty<'tcx>,
-        only_self_bounds: OnlySelfBounds,
-        assoc_name: Option<Ident>,
-    ) -> Vec<(ty::Predicate<'tcx>, Span)> {
+        filter: PredicateFilter,
+    ) -> Vec<(ty::Clause<'tcx>, Span)> {
         let mut bounds = Bounds::default();
 
         for predicate in ast_generics.predicates {
@@ -792,9 +826,23 @@ impl<'tcx> ItemCtxt<'tcx> {
                 continue;
             };
 
+            let (only_self_bounds, assoc_name) = match filter {
+                PredicateFilter::All | PredicateFilter::SelfAndAssociatedTypeBounds => {
+                    (OnlySelfBounds(false), None)
+                }
+                PredicateFilter::SelfOnly => (OnlySelfBounds(true), None),
+                PredicateFilter::SelfThatDefines(assoc_name) => {
+                    (OnlySelfBounds(true), Some(assoc_name))
+                }
+            };
+
+            // Subtle: If we're collecting `SelfAndAssociatedTypeBounds`, then we
+            // want to only consider predicates with `Self: ...`, but we don't want
+            // `OnlySelfBounds(true)` since we want to collect the nested associated
+            // type bound as well.
             let bound_ty = if predicate.is_param_bound(param_def_id.to_def_id()) {
                 ty
-            } else if !only_self_bounds.0 {
+            } else if matches!(filter, PredicateFilter::All) {
                 self.to_ty(predicate.bounded_ty)
             } else {
                 continue;
@@ -813,7 +861,7 @@ impl<'tcx> ItemCtxt<'tcx> {
             );
         }
 
-        bounds.predicates().collect()
+        bounds.clauses().collect()
     }
 
     #[instrument(level = "trace", skip(self))]
diff --git a/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs b/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs
index 794812a5c..acd0bcd8e 100644
--- a/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs
+++ b/compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs
@@ -22,7 +22,7 @@ use rustc_middle::ty::{self, TyCtxt, TypeSuperVisitable, TypeVisitor};
 use rustc_session::lint;
 use rustc_span::def_id::DefId;
 use rustc_span::symbol::{sym, Ident};
-use rustc_span::Span;
+use rustc_span::{Span, DUMMY_SP};
 use std::fmt;
 
 use crate::errors;
@@ -338,7 +338,17 @@ impl<'a, 'tcx> BoundVarContext<'a, 'tcx> {
 
                 Scope::TraitRefBoundary { .. } => {
                     // We should only see super trait lifetimes if there is a `Binder` above
-                    assert!(supertrait_bound_vars.is_empty());
+                    // though this may happen when we call `poly_trait_ref_binder_info` with
+                    // an (erroneous, #113423) associated return type bound in an impl header.
+                    if !supertrait_bound_vars.is_empty() {
+                        self.tcx.sess.delay_span_bug(
+                            DUMMY_SP,
+                            format!(
+                                "found supertrait lifetimes without a binder to append \
+                                them to: {supertrait_bound_vars:?}"
+                            ),
+                        );
+                    }
                     break (vec![], BinderScopeType::Normal);
                 }
 
@@ -556,7 +566,7 @@ impl<'a, 'tcx> Visitor<'tcx> for BoundVarContext<'a, 'tcx> {
                     });
                 }
             }
-            hir::ItemKind::OpaqueTy(hir::OpaqueTy {
+            hir::ItemKind::OpaqueTy(&hir::OpaqueTy {
                 origin: hir::OpaqueTyOrigin::FnReturn(parent) | hir::OpaqueTyOrigin::AsyncFn(parent),
                 generics,
                 ..
@@ -1344,12 +1354,10 @@ impl<'a, 'tcx> BoundVarContext<'a, 'tcx> {
                 Scope::Binder {
                     where_bound_origin: Some(hir::PredicateOrigin::ImplTrait), ..
                 } => {
-                    let mut err = self.tcx.sess.struct_span_err(
-                        lifetime_ref.ident.span,
-                        "`impl Trait` can only mention lifetimes bound at the fn or impl level",
-                    );
-                    err.span_note(self.tcx.def_span(region_def_id), "lifetime declared here");
-                    err.emit();
+                    self.tcx.sess.emit_err(errors::LateBoundInApit::Lifetime {
+                        span: lifetime_ref.ident.span,
+                        param_span: self.tcx.def_span(region_def_id),
+                    });
                     return;
                 }
                 Scope::Root { .. } => break,
@@ -1379,6 +1387,7 @@ impl<'a, 'tcx> BoundVarContext<'a, 'tcx> {
         let mut late_depth = 0;
         let mut scope = self.scope;
         let mut crossed_anon_const = false;
+
         let result = loop {
             match *scope {
                 Scope::Body { s, .. } => {
@@ -1446,6 +1455,50 @@ impl<'a, 'tcx> BoundVarContext<'a, 'tcx> {
             return;
         }
 
+        // We may fail to resolve higher-ranked ty/const vars that are mentioned by APIT.
+        // AST-based resolution does not care for impl-trait desugaring, which are the
+        // responsibility of lowering. This may create a mismatch between the resolution
+        // AST found (`param_def_id`) which points to HRTB, and what HIR allows.
+        // ```
+        // fn foo(x: impl for<T> Trait<Assoc = impl Trait2<T>>) {}
+        // ```
+        //
+        // In such case, walk back the binders to diagnose it properly.
+        let mut scope = self.scope;
+        loop {
+            match *scope {
+                Scope::Binder {
+                    where_bound_origin: Some(hir::PredicateOrigin::ImplTrait), ..
+                } => {
+                    let guar = self.tcx.sess.emit_err(match self.tcx.def_kind(param_def_id) {
+                        DefKind::TyParam => errors::LateBoundInApit::Type {
+                            span: self.tcx.hir().span(hir_id),
+                            param_span: self.tcx.def_span(param_def_id),
+                        },
+                        DefKind::ConstParam => errors::LateBoundInApit::Const {
+                            span: self.tcx.hir().span(hir_id),
+                            param_span: self.tcx.def_span(param_def_id),
+                        },
+                        kind => {
+                            bug!("unexpected def-kind: {}", kind.descr(param_def_id.to_def_id()))
+                        }
+                    });
+                    self.map.defs.insert(hir_id, ResolvedArg::Error(guar));
+                    return;
+                }
+                Scope::Root { .. } => break,
+                Scope::Binder { s, .. }
+                | Scope::Body { s, .. }
+                | Scope::Elision { s, .. }
+                | Scope::ObjectLifetimeDefault { s, .. }
+                | Scope::Supertrait { s, .. }
+                | Scope::TraitRefBoundary { s, .. }
+                | Scope::AnonConstBoundary { s } => {
+                    scope = s;
+                }
+            }
+        }
+
         self.tcx.sess.delay_span_bug(
             self.tcx.hir().span(hir_id),
             format!("could not resolve {param_def_id:?}"),
@@ -1761,7 +1814,7 @@ impl<'a, 'tcx> BoundVarContext<'a, 'tcx> {
             let obligations = predicates.predicates.iter().filter_map(|&(pred, _)| {
                 let bound_predicate = pred.kind();
                 match bound_predicate.skip_binder() {
-                    ty::PredicateKind::Clause(ty::Clause::Trait(data)) => {
+                    ty::ClauseKind::Trait(data) => {
                         // The order here needs to match what we would get from `subst_supertrait`
                         let pred_bound_vars = bound_predicate.bound_vars();
                         let mut all_bound_vars = bound_vars.clone();
diff --git a/compiler/rustc_hir_analysis/src/collect/type_of.rs b/compiler/rustc_hir_analysis/src/collect/type_of.rs
index 8e082d3c5..3755342ae 100644
--- a/compiler/rustc_hir_analysis/src/collect/type_of.rs
+++ b/compiler/rustc_hir_analysis/src/collect/type_of.rs
@@ -16,6 +16,7 @@ mod opaque;
 
 fn anon_const_type_of<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> Ty<'tcx> {
     use hir::*;
+    use rustc_middle::ty::Ty;
     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
 
     let Node::AnonConst(_) = tcx.hir().get(hir_id) else { panic!() };
@@ -25,21 +26,15 @@ fn anon_const_type_of<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> Ty<'tcx> {
 
     let (generics, arg_idx) = match parent_node {
         // Easy case: arrays repeat expressions.
-        Node::Ty(&Ty { kind: TyKind::Array(_, ref constant), .. })
+        Node::Ty(&hir::Ty { kind: TyKind::Array(_, ref constant), .. })
         | Node::Expr(&Expr { kind: ExprKind::Repeat(_, ref constant), .. })
             if constant.hir_id() == hir_id =>
         {
             return tcx.types.usize
         }
-        Node::Ty(&Ty { kind: TyKind::Typeof(ref e), .. }) if e.hir_id == hir_id => {
+        Node::Ty(&hir::Ty { kind: TyKind::Typeof(ref e), .. }) if e.hir_id == hir_id => {
             return tcx.typeck(def_id).node_type(e.hir_id)
         }
-        Node::Expr(&Expr { kind: ExprKind::ConstBlock(ref anon_const), .. })
-            if anon_const.hir_id == hir_id =>
-        {
-            let substs = InternalSubsts::identity_for_item(tcx, def_id.to_def_id());
-            return substs.as_inline_const().ty()
-        }
         Node::Expr(&Expr { kind: ExprKind::InlineAsm(asm), .. })
         | Node::Item(&Item { kind: ItemKind::GlobalAsm(asm), .. })
             if asm.operands.iter().any(|(op, _op_sp)| match op {
@@ -73,7 +68,7 @@ fn anon_const_type_of<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> Ty<'tcx> {
             ) =>
         {
             let Some(trait_def_id) = trait_ref.trait_def_id() else {
-                return tcx.ty_error_with_message(tcx.def_span(def_id), "Could not find trait");
+                return Ty::new_error_with_message(tcx,tcx.def_span(def_id), "Could not find trait");
             };
             let assoc_items = tcx.associated_items(trait_def_id);
             let assoc_item = assoc_items.find_by_name_and_kind(
@@ -85,7 +80,7 @@ fn anon_const_type_of<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> Ty<'tcx> {
                     .expect("const parameter types cannot be generic")
             } else {
                 // FIXME(associated_const_equality): add a useful error message here.
-                tcx.ty_error_with_message(tcx.def_span(def_id), "Could not find associated const on trait")
+                Ty::new_error_with_message(tcx,tcx.def_span(def_id), "Could not find associated const on trait")
             }
         }
 
@@ -105,7 +100,7 @@ fn anon_const_type_of<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> Ty<'tcx> {
         // arm would handle this.
         //
         // I believe this match arm is only needed for GAT but I am not 100% sure - BoxyUwU
-        Node::Ty(hir_ty @ Ty { kind: TyKind::Path(QPath::TypeRelative(_, segment)), .. }) => {
+        Node::Ty(hir_ty @ hir::Ty { kind: TyKind::Path(QPath::TypeRelative(_, segment)), .. }) => {
             // Find the Item containing the associated type so we can create an ItemCtxt.
             // Using the ItemCtxt convert the HIR for the unresolved assoc type into a
             // ty which is a fully resolved projection.
@@ -143,7 +138,7 @@ fn anon_const_type_of<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> Ty<'tcx> {
                 (generics, arg_index)
             } else {
                 // I dont think it's possible to reach this but I'm not 100% sure - BoxyUwU
-                return tcx.ty_error_with_message(
+                return Ty::new_error_with_message(tcx,
                     tcx.def_span(def_id),
                     "unexpected non-GAT usage of an anon const",
                 );
@@ -160,7 +155,7 @@ fn anon_const_type_of<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> Ty<'tcx> {
             // As there is no relevant param for `def_id`, we simply return
             // `None` here.
             let Some(type_dependent_def) = tables.type_dependent_def_id(parent_node_id) else {
-                return tcx.ty_error_with_message(
+                return Ty::new_error_with_message(tcx,
                     tcx.def_span(def_id),
                     format!("unable to find type-dependent def for {:?}", parent_node_id),
                 );
@@ -180,12 +175,12 @@ fn anon_const_type_of<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> Ty<'tcx> {
             (tcx.generics_of(type_dependent_def), idx)
         }
 
-        Node::Ty(&Ty { kind: TyKind::Path(_), .. })
+        Node::Ty(&hir::Ty { kind: TyKind::Path(_), .. })
         | Node::Expr(&Expr { kind: ExprKind::Path(_) | ExprKind::Struct(..), .. })
         | Node::TraitRef(..)
         | Node::Pat(_) => {
             let path = match parent_node {
-                Node::Ty(&Ty { kind: TyKind::Path(QPath::Resolved(_, path)), .. })
+                Node::Ty(&hir::Ty { kind: TyKind::Path(QPath::Resolved(_, path)), .. })
                 | Node::TraitRef(&TraitRef { path, .. }) => &*path,
                 Node::Expr(&Expr {
                     kind:
@@ -201,14 +196,14 @@ fn anon_const_type_of<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> Ty<'tcx> {
                     if let Some(path) = get_path_containing_arg_in_pat(pat, hir_id) {
                         path
                     } else {
-                        return tcx.ty_error_with_message(
+                        return Ty::new_error_with_message(tcx,
                             tcx.def_span(def_id),
                             format!("unable to find const parent for {} in pat {:?}", hir_id, pat),
                         );
                     }
                 }
                 _ => {
-                    return tcx.ty_error_with_message(
+                    return Ty::new_error_with_message(tcx,
                         tcx.def_span(def_id),
                         format!("unexpected const parent path {:?}", parent_node),
                     );
@@ -230,7 +225,7 @@ fn anon_const_type_of<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> Ty<'tcx> {
                     .position(|ct| ct.hir_id == hir_id)
                     .map(|idx| (idx, seg)))
             }) else {
-                return tcx.ty_error_with_message(
+                return Ty::new_error_with_message(tcx,
                     tcx.def_span(def_id),
                     "no arg matching AnonConst in path",
                 );
@@ -239,7 +234,7 @@ fn anon_const_type_of<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> Ty<'tcx> {
             let generics = match tcx.res_generics_def_id(segment.res) {
                 Some(def_id) => tcx.generics_of(def_id),
                 None => {
-                    return tcx.ty_error_with_message(
+                    return Ty::new_error_with_message(tcx,
                         tcx.def_span(def_id),
                         format!("unexpected anon const res {:?} in path: {:?}", segment.res, path),
                     );
@@ -249,7 +244,7 @@ fn anon_const_type_of<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> Ty<'tcx> {
             (generics, arg_index)
         }
 
-        _ => return tcx.ty_error_with_message(
+        _ => return Ty::new_error_with_message(tcx,
             tcx.def_span(def_id),
             format!("unexpected const parent in type_of(): {parent_node:?}"),
         ),
@@ -275,7 +270,8 @@ fn anon_const_type_of<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> Ty<'tcx> {
     {
         tcx.type_of(param_def_id).no_bound_vars().expect("const parameter types cannot be generic")
     } else {
-        return tcx.ty_error_with_message(
+        return Ty::new_error_with_message(
+            tcx,
             tcx.def_span(def_id),
             format!("const generic parameter not found in {generics:?} at position {arg_idx:?}"),
         );
@@ -311,6 +307,9 @@ fn get_path_containing_arg_in_pat<'hir>(
 }
 
 pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<Ty<'_>> {
+    use rustc_hir::*;
+    use rustc_middle::ty::Ty;
+
     // If we are computing `type_of` the synthesized associated type for an RPITIT in the impl
     // side, use `collect_return_position_impl_trait_in_trait_tys` to infer the value of the
     // associated type in the impl.
@@ -323,7 +322,8 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<Ty
                 return map[&assoc_item.trait_item_def_id.unwrap()];
             }
             Err(_) => {
-                return ty::EarlyBinder(tcx.ty_error_with_message(
+                return ty::EarlyBinder::bind(Ty::new_error_with_message(
+                    tcx,
                     DUMMY_SP,
                     "Could not collect return position impl trait in trait tys",
                 ));
@@ -331,8 +331,6 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<Ty
         }
     }
 
-    use rustc_hir::*;
-
     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
 
     let icx = ItemCtxt::new(tcx, def_id);
@@ -341,13 +339,18 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<Ty
         Node::TraitItem(item) => match item.kind {
             TraitItemKind::Fn(..) => {
                 let substs = InternalSubsts::identity_for_item(tcx, def_id);
-                tcx.mk_fn_def(def_id.to_def_id(), substs)
+                Ty::new_fn_def(tcx, def_id.to_def_id(), substs)
             }
             TraitItemKind::Const(ty, body_id) => body_id
                 .and_then(|body_id| {
                     is_suggestable_infer_ty(ty).then(|| {
                         infer_placeholder_type(
-                            tcx, def_id, body_id, ty.span, item.ident, "constant",
+                            tcx,
+                            def_id,
+                            body_id,
+                            ty.span,
+                            item.ident,
+                            "associated constant",
                         )
                     })
                 })
@@ -361,11 +364,18 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<Ty
         Node::ImplItem(item) => match item.kind {
             ImplItemKind::Fn(..) => {
                 let substs = InternalSubsts::identity_for_item(tcx, def_id);
-                tcx.mk_fn_def(def_id.to_def_id(), substs)
+                Ty::new_fn_def(tcx, def_id.to_def_id(), substs)
             }
             ImplItemKind::Const(ty, body_id) => {
                 if is_suggestable_infer_ty(ty) {
-                    infer_placeholder_type(tcx, def_id, body_id, ty.span, item.ident, "constant")
+                    infer_placeholder_type(
+                        tcx,
+                        def_id,
+                        body_id,
+                        ty.span,
+                        item.ident,
+                        "associated constant",
+                    )
                 } else {
                     icx.to_ty(ty)
                 }
@@ -411,31 +421,31 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<Ty
                             span: spans.into(),
                             note: (),
                         });
-                        tcx.ty_error(guar)
+                        Ty::new_error(tcx, guar)
                     }
                     _ => icx.to_ty(*self_ty),
                 },
                 ItemKind::Fn(..) => {
                     let substs = InternalSubsts::identity_for_item(tcx, def_id);
-                    tcx.mk_fn_def(def_id.to_def_id(), substs)
+                    Ty::new_fn_def(tcx, def_id.to_def_id(), substs)
                 }
                 ItemKind::Enum(..) | ItemKind::Struct(..) | ItemKind::Union(..) => {
                     let def = tcx.adt_def(def_id);
                     let substs = InternalSubsts::identity_for_item(tcx, def_id);
-                    tcx.mk_adt(def, substs)
+                    Ty::new_adt(tcx, def, substs)
                 }
                 ItemKind::OpaqueTy(OpaqueTy {
                     origin: hir::OpaqueTyOrigin::TyAlias { .. },
                     ..
                 }) => opaque::find_opaque_ty_constraints_for_tait(tcx, def_id),
                 // Opaque types desugared from `impl Trait`.
-                ItemKind::OpaqueTy(OpaqueTy {
+                ItemKind::OpaqueTy(&OpaqueTy {
                     origin:
                         hir::OpaqueTyOrigin::FnReturn(owner) | hir::OpaqueTyOrigin::AsyncFn(owner),
                     in_trait,
                     ..
                 }) => {
-                    if in_trait && !tcx.impl_defaultness(owner).has_value() {
+                    if in_trait && !tcx.defaultness(owner).has_value() {
                         span_bug!(
                             tcx.def_span(def_id),
                             "tried to get type of this RPITIT with no definition"
@@ -463,10 +473,10 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<Ty
         Node::ForeignItem(foreign_item) => match foreign_item.kind {
             ForeignItemKind::Fn(..) => {
                 let substs = InternalSubsts::identity_for_item(tcx, def_id);
-                tcx.mk_fn_def(def_id.to_def_id(), substs)
+                Ty::new_fn_def(tcx, def_id.to_def_id(), substs)
             }
             ForeignItemKind::Static(t, _) => icx.to_ty(t),
-            ForeignItemKind::Type => tcx.mk_foreign(def_id.to_def_id()),
+            ForeignItemKind::Type => Ty::new_foreign(tcx, def_id.to_def_id()),
         },
 
         Node::Ctor(def) | Node::Variant(Variant { data: def, .. }) => match def {
@@ -475,7 +485,7 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<Ty
             }
             VariantData::Tuple(..) => {
                 let substs = InternalSubsts::identity_for_item(tcx, def_id);
-                tcx.mk_fn_def(def_id.to_def_id(), substs)
+                Ty::new_fn_def(tcx, def_id.to_def_id(), substs)
             }
         },
 
@@ -487,6 +497,11 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<Ty
 
         Node::AnonConst(_) => anon_const_type_of(tcx, def_id),
 
+        Node::ConstBlock(_) => {
+            let substs = InternalSubsts::identity_for_item(tcx, def_id.to_def_id());
+            substs.as_inline_const().ty()
+        }
+
         Node::GenericParam(param) => match &param.kind {
             GenericParamKind::Type { default: Some(ty), .. }
             | GenericParamKind::Const { ty, .. } => icx.to_ty(ty),
@@ -497,7 +512,7 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<Ty
             bug!("unexpected sort of node in type_of(): {:?}", x);
         }
     };
-    ty::EarlyBinder(output)
+    ty::EarlyBinder::bind(output)
 }
 
 fn infer_placeholder_type<'a>(
diff --git a/compiler/rustc_hir_analysis/src/collect/type_of/opaque.rs b/compiler/rustc_hir_analysis/src/collect/type_of/opaque.rs
index f7c5b4467..957a6bb34 100644
--- a/compiler/rustc_hir_analysis/src/collect/type_of/opaque.rs
+++ b/compiler/rustc_hir_analysis/src/collect/type_of/opaque.rs
@@ -1,3 +1,4 @@
+use rustc_errors::StashKey;
 use rustc_hir::def_id::LocalDefId;
 use rustc_hir::intravisit::{self, Visitor};
 use rustc_hir::{self as hir, Expr, ImplItem, Item, Node, TraitItem};
@@ -5,7 +6,7 @@ use rustc_middle::hir::nested_filter;
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitableExt};
 use rustc_span::DUMMY_SP;
 
-use crate::errors::UnconstrainedOpaqueType;
+use crate::errors::{TaitForwardCompat, UnconstrainedOpaqueType};
 
 /// Checks "defining uses" of opaque `impl Trait` types to ensure that they meet the restrictions
 /// laid for "higher-order pattern unification".
@@ -59,7 +60,20 @@ pub(super) fn find_opaque_ty_constraints_for_tait(tcx: TyCtxt<'_>, def_id: Local
         }
     }
 
-    let Some(hidden) = locator.found else {
+    if let Some(hidden) = locator.found {
+        // Only check against typeck if we didn't already error
+        if !hidden.ty.references_error() {
+            for concrete_type in locator.typeck_types {
+                if concrete_type.ty != tcx.erase_regions(hidden.ty)
+                    && !(concrete_type, hidden).references_error()
+                {
+                    hidden.report_mismatch(&concrete_type, def_id, tcx).emit();
+                }
+            }
+        }
+
+        hidden.ty
+    } else {
         let reported = tcx.sess.emit_err(UnconstrainedOpaqueType {
             span: tcx.def_span(def_id),
             name: tcx.item_name(tcx.local_parent(def_id).to_def_id()),
@@ -70,21 +84,8 @@ pub(super) fn find_opaque_ty_constraints_for_tait(tcx: TyCtxt<'_>, def_id: Local
                 _ => "item",
             },
         });
-        return tcx.ty_error(reported);
-    };
-
-    // Only check against typeck if we didn't already error
-    if !hidden.ty.references_error() {
-        for concrete_type in locator.typeck_types {
-            if concrete_type.ty != tcx.erase_regions(hidden.ty)
-                && !(concrete_type, hidden).references_error()
-            {
-                hidden.report_mismatch(&concrete_type, def_id, tcx).emit();
-            }
-        }
+        Ty::new_error(tcx, reported)
     }
-
-    hidden.ty
 }
 
 struct TaitConstraintLocator<'tcx> {
@@ -127,16 +128,41 @@ impl TaitConstraintLocator<'_> {
         // ```
         let tables = self.tcx.typeck(item_def_id);
         if let Some(guar) = tables.tainted_by_errors {
-            self.found = Some(ty::OpaqueHiddenType { span: DUMMY_SP, ty: self.tcx.ty_error(guar) });
+            self.found =
+                Some(ty::OpaqueHiddenType { span: DUMMY_SP, ty: Ty::new_error(self.tcx, guar) });
             return;
         }
-        let Some(&typeck_hidden_ty) = tables.concrete_opaque_types.get(&self.def_id) else {
+
+        let mut constrained = false;
+        for (&opaque_type_key, &hidden_type) in &tables.concrete_opaque_types {
+            if opaque_type_key.def_id != self.def_id {
+                continue;
+            }
+            constrained = true;
+            if !self.tcx.opaque_types_defined_by(item_def_id).contains(&self.def_id) {
+                self.tcx.sess.emit_err(TaitForwardCompat {
+                    span: hidden_type.span,
+                    item_span: self
+                        .tcx
+                        .def_ident_span(item_def_id)
+                        .unwrap_or_else(|| self.tcx.def_span(item_def_id)),
+                });
+            }
+            let concrete_type =
+                self.tcx.erase_regions(hidden_type.remap_generic_params_to_declaration_params(
+                    opaque_type_key,
+                    self.tcx,
+                    true,
+                ));
+            if self.typeck_types.iter().all(|prev| prev.ty != concrete_type.ty) {
+                self.typeck_types.push(concrete_type);
+            }
+        }
+
+        if !constrained {
             debug!("no constraints in typeck results");
             return;
         };
-        if self.typeck_types.iter().all(|prev| prev.ty != typeck_hidden_ty.ty) {
-            self.typeck_types.push(typeck_hidden_ty);
-        }
 
         // Use borrowck to get the type with unerased regions.
         let concrete_opaque_types = &self.tcx.mir_borrowck(item_def_id).concrete_opaque_types;
@@ -146,7 +172,7 @@ impl TaitConstraintLocator<'_> {
             if let Some(prev) = &mut self.found {
                 if concrete_type.ty != prev.ty && !(concrete_type, prev.ty).references_error() {
                     let guar = prev.report_mismatch(&concrete_type, self.def_id, self.tcx).emit();
-                    prev.ty = self.tcx.ty_error(guar);
+                    prev.ty = Ty::new_error(self.tcx, guar);
                 }
             } else {
                 self.found = Some(concrete_type);
@@ -190,17 +216,45 @@ impl<'tcx> intravisit::Visitor<'tcx> for TaitConstraintLocator<'tcx> {
     }
 }
 
-pub(super) fn find_opaque_ty_constraints_for_rpit(
-    tcx: TyCtxt<'_>,
+pub(super) fn find_opaque_ty_constraints_for_rpit<'tcx>(
+    tcx: TyCtxt<'tcx>,
     def_id: LocalDefId,
     owner_def_id: LocalDefId,
 ) -> Ty<'_> {
-    let concrete = tcx.mir_borrowck(owner_def_id).concrete_opaque_types.get(&def_id).copied();
+    let tables = tcx.typeck(owner_def_id);
 
-    if let Some(concrete) = concrete {
+    // Check that all of the opaques we inferred during HIR are compatible.
+    // FIXME: We explicitly don't check that the types inferred during HIR
+    // typeck are compatible with the one that we infer during borrowck,
+    // because that one actually sometimes has consts evaluated eagerly so
+    // using strict type equality will fail.
+    let mut hir_opaque_ty: Option<ty::OpaqueHiddenType<'tcx>> = None;
+    if tables.tainted_by_errors.is_none() {
+        for (&opaque_type_key, &hidden_type) in &tables.concrete_opaque_types {
+            if opaque_type_key.def_id != def_id {
+                continue;
+            }
+            let concrete_type = tcx.erase_regions(
+                hidden_type.remap_generic_params_to_declaration_params(opaque_type_key, tcx, true),
+            );
+            if let Some(prev) = &mut hir_opaque_ty {
+                if concrete_type.ty != prev.ty && !(concrete_type, prev.ty).references_error() {
+                    prev.report_mismatch(&concrete_type, def_id, tcx).stash(
+                        tcx.def_span(opaque_type_key.def_id),
+                        StashKey::OpaqueHiddenTypeMismatch,
+                    );
+                }
+            } else {
+                hir_opaque_ty = Some(concrete_type);
+            }
+        }
+    }
+
+    let mir_opaque_ty = tcx.mir_borrowck(owner_def_id).concrete_opaque_types.get(&def_id).copied();
+    if let Some(mir_opaque_ty) = mir_opaque_ty {
         let scope = tcx.hir().local_def_id_to_hir_id(owner_def_id);
         debug!(?scope);
-        let mut locator = RpitConstraintChecker { def_id, tcx, found: concrete };
+        let mut locator = RpitConstraintChecker { def_id, tcx, found: mir_opaque_ty };
 
         match tcx.hir().get(scope) {
             Node::Item(it) => intravisit::walk_item(&mut locator, it),
@@ -208,27 +262,28 @@ pub(super) fn find_opaque_ty_constraints_for_rpit(
             Node::TraitItem(it) => intravisit::walk_trait_item(&mut locator, it),
             other => bug!("{:?} is not a valid scope for an opaque type item", other),
         }
-    }
 
-    concrete.map(|concrete| concrete.ty).unwrap_or_else(|| {
-        let table = tcx.typeck(owner_def_id);
-        if let Some(guar) = table.tainted_by_errors {
-            // Some error in the
-            // owner fn prevented us from populating
+        mir_opaque_ty.ty
+    } else {
+        if let Some(guar) = tables.tainted_by_errors {
+            // Some error in the owner fn prevented us from populating
             // the `concrete_opaque_types` table.
-            tcx.ty_error(guar)
+            Ty::new_error(tcx, guar)
         } else {
-            table.concrete_opaque_types.get(&def_id).map(|ty| ty.ty).unwrap_or_else(|| {
+            // Fall back to the RPIT we inferred during HIR typeck
+            if let Some(hir_opaque_ty) = hir_opaque_ty {
+                hir_opaque_ty.ty
+            } else {
                 // We failed to resolve the opaque type or it
                 // resolves to itself. We interpret this as the
                 // no values of the hidden type ever being constructed,
                 // so we can just make the hidden type be `!`.
                 // For backwards compatibility reasons, we fall back to
                 // `()` until we the diverging default is changed.
-                tcx.mk_diverging_default()
-            })
+                Ty::new_diverging_default(tcx)
+            }
         }
-    })
+    }
 }
 
 struct RpitConstraintChecker<'tcx> {
diff --git a/compiler/rustc_hir_analysis/src/constrained_generic_params.rs b/compiler/rustc_hir_analysis/src/constrained_generic_params.rs
index 9200c2aec..35882ad35 100644
--- a/compiler/rustc_hir_analysis/src/constrained_generic_params.rs
+++ b/compiler/rustc_hir_analysis/src/constrained_generic_params.rs
@@ -151,7 +151,7 @@ pub fn identify_constrained_generic_params<'tcx>(
 /// think of any.
 pub fn setup_constraining_predicates<'tcx>(
     tcx: TyCtxt<'tcx>,
-    predicates: &mut [(ty::Predicate<'tcx>, Span)],
+    predicates: &mut [(ty::Clause<'tcx>, Span)],
     impl_trait_ref: Option<ty::TraitRef<'tcx>>,
     input_parameters: &mut FxHashSet<Parameter>,
 ) {
@@ -187,9 +187,7 @@ pub fn setup_constraining_predicates<'tcx>(
         for j in i..predicates.len() {
             // Note that we don't have to care about binders here,
             // as the impl trait ref never contains any late-bound regions.
-            if let ty::PredicateKind::Clause(ty::Clause::Projection(projection)) =
-                predicates[j].0.kind().skip_binder()
-            {
+            if let ty::ClauseKind::Projection(projection) = predicates[j].0.kind().skip_binder() {
                 // Special case: watch out for some kind of sneaky attempt
                 // to project out an associated type defined by this very
                 // trait.
diff --git a/compiler/rustc_hir_analysis/src/errors.rs b/compiler/rustc_hir_analysis/src/errors.rs
index 6e7eb4f6c..c2d2e5f7e 100644
--- a/compiler/rustc_hir_analysis/src/errors.rs
+++ b/compiler/rustc_hir_analysis/src/errors.rs
@@ -5,7 +5,7 @@ use rustc_errors::{
     error_code, Applicability, DiagnosticBuilder, ErrorGuaranteed, Handler, IntoDiagnostic,
     MultiSpan,
 };
-use rustc_macros::{Diagnostic, Subdiagnostic};
+use rustc_macros::{Diagnostic, LintDiagnostic, Subdiagnostic};
 use rustc_middle::ty::{self, print::TraitRefPrintOnlyTraitPath, Ty};
 use rustc_span::{symbol::Ident, Span, Symbol};
 
@@ -184,6 +184,16 @@ pub struct UnconstrainedOpaqueType {
     pub what: &'static str,
 }
 
+#[derive(Diagnostic)]
+#[diag(hir_analysis_tait_forward_compat)]
+#[note]
+pub struct TaitForwardCompat {
+    #[primary_span]
+    pub span: Span,
+    #[note]
+    pub item_span: Span,
+}
+
 pub struct MissingTypeParams {
     pub span: Span,
     pub def_span: Span,
@@ -857,3 +867,54 @@ pub(crate) enum DropImplPolarity {
         span: Span,
     },
 }
+
+#[derive(Diagnostic)]
+pub(crate) enum ReturnTypeNotationIllegalParam {
+    #[diag(hir_analysis_return_type_notation_illegal_param_type)]
+    Type {
+        #[primary_span]
+        span: Span,
+        #[label]
+        param_span: Span,
+    },
+    #[diag(hir_analysis_return_type_notation_illegal_param_const)]
+    Const {
+        #[primary_span]
+        span: Span,
+        #[label]
+        param_span: Span,
+    },
+}
+
+#[derive(Diagnostic)]
+pub(crate) enum LateBoundInApit {
+    #[diag(hir_analysis_late_bound_type_in_apit)]
+    Type {
+        #[primary_span]
+        span: Span,
+        #[label]
+        param_span: Span,
+    },
+    #[diag(hir_analysis_late_bound_const_in_apit)]
+    Const {
+        #[primary_span]
+        span: Span,
+        #[label]
+        param_span: Span,
+    },
+    #[diag(hir_analysis_late_bound_lifetime_in_apit)]
+    Lifetime {
+        #[primary_span]
+        span: Span,
+        #[label]
+        param_span: Span,
+    },
+}
+
+#[derive(LintDiagnostic)]
+#[diag(hir_analysis_unused_associated_type_bounds)]
+#[note]
+pub struct UnusedAssociatedTypeBounds {
+    #[suggestion(code = "")]
+    pub span: Span,
+}
diff --git a/compiler/rustc_hir_analysis/src/hir_wf_check.rs b/compiler/rustc_hir_analysis/src/hir_wf_check.rs
index e4c6e6e39..f1765174d 100644
--- a/compiler/rustc_hir_analysis/src/hir_wf_check.rs
+++ b/compiler/rustc_hir_analysis/src/hir_wf_check.rs
@@ -79,7 +79,7 @@ fn diagnostic_hir_wf_check<'tcx>(
                 self.tcx,
                 cause,
                 self.param_env,
-                ty::PredicateKind::WellFormed(tcx_ty.into()),
+                ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(tcx_ty.into())),
             ));
 
             for error in ocx.select_all_or_error() {
@@ -128,7 +128,9 @@ fn diagnostic_hir_wf_check<'tcx>(
                 ref item => bug!("Unexpected TraitItem {:?}", item),
             },
             hir::Node::Item(item) => match item.kind {
-                hir::ItemKind::Static(ty, _, _) | hir::ItemKind::Const(ty, _) => vec![ty],
+                hir::ItemKind::TyAlias(ty, _)
+                | hir::ItemKind::Static(ty, _, _)
+                | hir::ItemKind::Const(ty, _) => vec![ty],
                 hir::ItemKind::Impl(impl_) => match &impl_.of_trait {
                     Some(t) => t
                         .path
diff --git a/compiler/rustc_hir_analysis/src/impl_wf_check.rs b/compiler/rustc_hir_analysis/src/impl_wf_check.rs
index 612d4ff3d..5526dd4b0 100644
--- a/compiler/rustc_hir_analysis/src/impl_wf_check.rs
+++ b/compiler/rustc_hir_analysis/src/impl_wf_check.rs
@@ -106,10 +106,23 @@ fn enforce_impl_params_are_constrained(tcx: TyCtxt<'_>, impl_def_id: LocalDefId)
                     if item.defaultness(tcx).has_value() {
                         cgp::parameters_for(&tcx.type_of(def_id).subst_identity(), true)
                     } else {
-                        Vec::new()
+                        vec![]
                     }
                 }
-                ty::AssocKind::Fn | ty::AssocKind::Const => Vec::new(),
+                ty::AssocKind::Fn => {
+                    if !tcx.lower_impl_trait_in_trait_to_assoc_ty()
+                        && item.defaultness(tcx).has_value()
+                        && tcx.impl_method_has_trait_impl_trait_tys(item.def_id)
+                        && let Ok(table) = tcx.collect_return_position_impl_trait_in_trait_tys(def_id)
+                    {
+                        table.values().copied().flat_map(|ty| {
+                            cgp::parameters_for(&ty.subst_identity(), true)
+                        }).collect()
+                    } else {
+                        vec![]
+                    }
+                }
+                ty::AssocKind::Const => vec![],
             }
         })
         .collect();
diff --git a/compiler/rustc_hir_analysis/src/impl_wf_check/min_specialization.rs b/compiler/rustc_hir_analysis/src/impl_wf_check/min_specialization.rs
index e84da2519..c64fb469b 100644
--- a/compiler/rustc_hir_analysis/src/impl_wf_check/min_specialization.rs
+++ b/compiler/rustc_hir_analysis/src/impl_wf_check/min_specialization.rs
@@ -77,7 +77,7 @@ use rustc_infer::traits::specialization_graph::Node;
 use rustc_middle::ty::subst::{GenericArg, InternalSubsts, SubstsRef};
 use rustc_middle::ty::trait_def::TraitSpecializationKind;
 use rustc_middle::ty::{self, TyCtxt, TypeVisitableExt};
-use rustc_span::Span;
+use rustc_span::{ErrorGuaranteed, Span};
 use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt;
 use rustc_trait_selection::traits::outlives_bounds::InferCtxtExt as _;
 use rustc_trait_selection::traits::{self, translate_substs_with_cause, wf, ObligationCtxt};
@@ -113,7 +113,7 @@ fn check_always_applicable(tcx: TyCtxt<'_>, impl1_def_id: LocalDefId, impl2_node
     let span = tcx.def_span(impl1_def_id);
     check_has_items(tcx, impl1_def_id, impl2_node, span);
 
-    if let Some((impl1_substs, impl2_substs)) = get_impl_substs(tcx, impl1_def_id, impl2_node) {
+    if let Ok((impl1_substs, impl2_substs)) = get_impl_substs(tcx, impl1_def_id, impl2_node) {
         let impl2_def_id = impl2_node.def_id();
         debug!(?impl2_def_id, ?impl2_substs);
 
@@ -171,16 +171,14 @@ fn get_impl_substs(
     tcx: TyCtxt<'_>,
     impl1_def_id: LocalDefId,
     impl2_node: Node,
-) -> Option<(SubstsRef<'_>, SubstsRef<'_>)> {
+) -> Result<(SubstsRef<'_>, SubstsRef<'_>), ErrorGuaranteed> {
     let infcx = &tcx.infer_ctxt().build();
     let ocx = ObligationCtxt::new(infcx);
     let param_env = tcx.param_env(impl1_def_id);
-
-    let assumed_wf_types =
-        ocx.assumed_wf_types(param_env, tcx.def_span(impl1_def_id), impl1_def_id);
+    let impl1_span = tcx.def_span(impl1_def_id);
+    let assumed_wf_types = ocx.assumed_wf_types_and_report_errors(param_env, impl1_def_id)?;
 
     let impl1_substs = InternalSubsts::identity_for_item(tcx, impl1_def_id);
-    let impl1_span = tcx.def_span(impl1_def_id);
     let impl2_substs = translate_substs_with_cause(
         infcx,
         param_env,
@@ -198,8 +196,8 @@ fn get_impl_substs(
 
     let errors = ocx.select_all_or_error();
     if !errors.is_empty() {
-        ocx.infcx.err_ctxt().report_fulfillment_errors(&errors);
-        return None;
+        let guar = ocx.infcx.err_ctxt().report_fulfillment_errors(&errors);
+        return Err(guar);
     }
 
     let implied_bounds = infcx.implied_bounds_tys(param_env, impl1_def_id, assumed_wf_types);
@@ -207,10 +205,10 @@ fn get_impl_substs(
     let _ = ocx.resolve_regions_and_report_errors(impl1_def_id, &outlives_env);
     let Ok(impl2_substs) = infcx.fully_resolve(impl2_substs) else {
         let span = tcx.def_span(impl1_def_id);
-        tcx.sess.emit_err(SubstsOnOverriddenImpl { span });
-        return None;
+        let guar = tcx.sess.emit_err(SubstsOnOverriddenImpl { span });
+        return Err(guar);
     };
-    Some((impl1_substs, impl2_substs))
+    Ok((impl1_substs, impl2_substs))
 }
 
 /// Returns a list of all of the unconstrained subst of the given impl.
@@ -235,10 +233,8 @@ fn unconstrained_parent_impl_substs<'tcx>(
     // what we want here. We want only a list of constrained parameters while
     // the functions in `cgp` add the constrained parameters to a list of
     // unconstrained parameters.
-    for (predicate, _) in impl_generic_predicates.predicates.iter() {
-        if let ty::PredicateKind::Clause(ty::Clause::Projection(proj)) =
-            predicate.kind().skip_binder()
-        {
+    for (clause, _) in impl_generic_predicates.predicates.iter() {
+        if let ty::ClauseKind::Projection(proj) = clause.kind().skip_binder() {
             let projection_ty = proj.projection_ty;
             let projected_ty = proj.term;
 
@@ -340,8 +336,11 @@ fn check_predicates<'tcx>(
     impl2_substs: SubstsRef<'tcx>,
     span: Span,
 ) {
-    let instantiated = tcx.predicates_of(impl1_def_id).instantiate(tcx, impl1_substs);
-    let impl1_predicates: Vec<_> = traits::elaborate(tcx, instantiated.into_iter()).collect();
+    let impl1_predicates: Vec<_> = traits::elaborate(
+        tcx,
+        tcx.predicates_of(impl1_def_id).instantiate(tcx, impl1_substs).into_iter(),
+    )
+    .collect();
 
     let mut impl2_predicates = if impl2_node.is_from_trait() {
         // Always applicable traits have to be always applicable without any
@@ -352,8 +351,8 @@ fn check_predicates<'tcx>(
             tcx,
             tcx.predicates_of(impl2_node.def_id())
                 .instantiate(tcx, impl2_substs)
-                .predicates
-                .into_iter(),
+                .into_iter()
+                .map(|(c, _s)| c.as_predicate()),
         )
         .collect()
     };
@@ -377,13 +376,13 @@ fn check_predicates<'tcx>(
     let always_applicable_traits = impl1_predicates
         .iter()
         .copied()
-        .filter(|&(predicate, _)| {
+        .filter(|(clause, _span)| {
             matches!(
-                trait_predicate_kind(tcx, predicate),
+                trait_predicate_kind(tcx, clause.as_predicate()),
                 Some(TraitSpecializationKind::AlwaysApplicable)
             )
         })
-        .map(|(pred, _span)| pred);
+        .map(|(c, _span)| c.as_predicate());
 
     // Include the well-formed predicates of the type parameters of the impl.
     for arg in tcx.impl_trait_ref(impl1_def_id).unwrap().subst_identity().substs {
@@ -398,9 +397,12 @@ fn check_predicates<'tcx>(
     }
     impl2_predicates.extend(traits::elaborate(tcx, always_applicable_traits));
 
-    for (predicate, span) in impl1_predicates {
-        if !impl2_predicates.iter().any(|pred2| trait_predicates_eq(tcx, predicate, *pred2, span)) {
-            check_specialization_on(tcx, predicate, span)
+    for (clause, span) in impl1_predicates {
+        if !impl2_predicates
+            .iter()
+            .any(|pred2| trait_predicates_eq(tcx, clause.as_predicate(), *pred2, span))
+        {
+            check_specialization_on(tcx, clause.as_predicate(), span)
         }
     }
 }
@@ -438,8 +440,8 @@ fn trait_predicates_eq<'tcx>(
     let pred2_kind = predicate2.kind().skip_binder();
     let (trait_pred1, trait_pred2) = match (pred1_kind, pred2_kind) {
         (
-            ty::PredicateKind::Clause(ty::Clause::Trait(pred1)),
-            ty::PredicateKind::Clause(ty::Clause::Trait(pred2)),
+            ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred1)),
+            ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred2)),
         ) => (pred1, pred2),
         // Just use plain syntactic equivalence if either of the predicates aren't
         // trait predicates or have bound vars.
@@ -478,7 +480,7 @@ fn check_specialization_on<'tcx>(tcx: TyCtxt<'tcx>, predicate: ty::Predicate<'tc
         _ if predicate.is_global() => (),
         // We allow specializing on explicitly marked traits with no associated
         // items.
-        ty::PredicateKind::Clause(ty::Clause::Trait(ty::TraitPredicate {
+        ty::PredicateKind::Clause(ty::ClauseKind::Trait(ty::TraitPredicate {
             trait_ref,
             constness: _,
             polarity: _,
@@ -498,7 +500,7 @@ fn check_specialization_on<'tcx>(tcx: TyCtxt<'tcx>, predicate: ty::Predicate<'tc
                     .emit();
             }
         }
-        ty::PredicateKind::Clause(ty::Clause::Projection(ty::ProjectionPredicate {
+        ty::PredicateKind::Clause(ty::ClauseKind::Projection(ty::ProjectionPredicate {
             projection_ty,
             term,
         })) => {
@@ -509,7 +511,7 @@ fn check_specialization_on<'tcx>(tcx: TyCtxt<'tcx>, predicate: ty::Predicate<'tc
                 )
                 .emit();
         }
-        ty::PredicateKind::Clause(ty::Clause::ConstArgHasType(..)) => {
+        ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType(..)) => {
             // FIXME(min_specialization), FIXME(const_generics):
             // It probably isn't right to allow _every_ `ConstArgHasType` but I am somewhat unsure
             // about the actual rules that would be sound. Can't just always error here because otherwise
@@ -532,24 +534,23 @@ fn trait_predicate_kind<'tcx>(
     predicate: ty::Predicate<'tcx>,
 ) -> Option<TraitSpecializationKind> {
     match predicate.kind().skip_binder() {
-        ty::PredicateKind::Clause(ty::Clause::Trait(ty::TraitPredicate {
+        ty::PredicateKind::Clause(ty::ClauseKind::Trait(ty::TraitPredicate {
             trait_ref,
             constness: _,
             polarity: _,
         })) => Some(tcx.trait_def(trait_ref.def_id).specialization_kind),
-        ty::PredicateKind::Clause(ty::Clause::RegionOutlives(_))
-        | ty::PredicateKind::Clause(ty::Clause::TypeOutlives(_))
-        | ty::PredicateKind::Clause(ty::Clause::Projection(_))
-        | ty::PredicateKind::Clause(ty::Clause::ConstArgHasType(..))
+        ty::PredicateKind::Clause(ty::ClauseKind::RegionOutlives(_))
+        | ty::PredicateKind::Clause(ty::ClauseKind::TypeOutlives(_))
+        | ty::PredicateKind::Clause(ty::ClauseKind::Projection(_))
+        | ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType(..))
         | ty::PredicateKind::AliasRelate(..)
-        | ty::PredicateKind::WellFormed(_)
+        | ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(_))
         | ty::PredicateKind::Subtype(_)
         | ty::PredicateKind::Coerce(_)
         | ty::PredicateKind::ObjectSafe(_)
         | ty::PredicateKind::ClosureKind(..)
-        | ty::PredicateKind::ConstEvaluatable(..)
+        | ty::PredicateKind::Clause(ty::ClauseKind::ConstEvaluatable(..))
         | ty::PredicateKind::ConstEquate(..)
-        | ty::PredicateKind::Ambiguous
-        | ty::PredicateKind::TypeWellFormedFromEnv(..) => None,
+        | ty::PredicateKind::Ambiguous => None,
     }
 }
diff --git a/compiler/rustc_hir_analysis/src/lib.rs b/compiler/rustc_hir_analysis/src/lib.rs
index 5cd2cd50c..a68832d96 100644
--- a/compiler/rustc_hir_analysis/src/lib.rs
+++ b/compiler/rustc_hir_analysis/src/lib.rs
@@ -59,8 +59,6 @@ This API is completely unstable and subject to change.
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![feature(box_patterns)]
 #![feature(control_flow_enum)]
-#![feature(drain_filter)]
-#![feature(hash_drain_filter)]
 #![feature(if_let_guard)]
 #![feature(is_sorted)]
 #![feature(iter_intersperse)]
@@ -321,16 +319,19 @@ fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
         expected_return_type = main_fnsig.output();
     } else {
         // standard () main return type
-        expected_return_type = ty::Binder::dummy(tcx.mk_unit());
+        expected_return_type = ty::Binder::dummy(Ty::new_unit(tcx));
     }
 
     if error {
         return;
     }
 
-    let se_ty = tcx.mk_fn_ptr(expected_return_type.map_bound(|expected_return_type| {
-        tcx.mk_fn_sig([], expected_return_type, false, hir::Unsafety::Normal, Abi::Rust)
-    }));
+    let se_ty = Ty::new_fn_ptr(
+        tcx,
+        expected_return_type.map_bound(|expected_return_type| {
+            tcx.mk_fn_sig([], expected_return_type, false, hir::Unsafety::Normal, Abi::Rust)
+        }),
+    );
 
     require_same_types(
         tcx,
@@ -341,7 +342,7 @@ fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
         ),
         param_env,
         se_ty,
-        tcx.mk_fn_ptr(main_fnsig),
+        Ty::new_fn_ptr(tcx, main_fnsig),
     );
 }
 fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: DefId) {
@@ -399,13 +400,16 @@ fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: DefId) {
                 }
             }
 
-            let se_ty = tcx.mk_fn_ptr(ty::Binder::dummy(tcx.mk_fn_sig(
-                [tcx.types.isize, tcx.mk_imm_ptr(tcx.mk_imm_ptr(tcx.types.u8))],
-                tcx.types.isize,
-                false,
-                hir::Unsafety::Normal,
-                Abi::Rust,
-            )));
+            let se_ty = Ty::new_fn_ptr(
+                tcx,
+                ty::Binder::dummy(tcx.mk_fn_sig(
+                    [tcx.types.isize, Ty::new_imm_ptr(tcx, Ty::new_imm_ptr(tcx, tcx.types.u8))],
+                    tcx.types.isize,
+                    false,
+                    hir::Unsafety::Normal,
+                    Abi::Rust,
+                )),
+            );
 
             require_same_types(
                 tcx,
@@ -416,7 +420,7 @@ fn check_start_fn_ty(tcx: TyCtxt<'_>, start_def_id: DefId) {
                 ),
                 ty::ParamEnv::empty(), // start should not have any where bounds.
                 se_ty,
-                tcx.mk_fn_ptr(tcx.fn_sig(start_def_id).subst_identity()),
+                Ty::new_fn_ptr(tcx, tcx.fn_sig(start_def_id).subst_identity()),
             );
         }
         _ => {
diff --git a/compiler/rustc_hir_analysis/src/outlives/explicit.rs b/compiler/rustc_hir_analysis/src/outlives/explicit.rs
index 357deb07b..a7fca41f8 100644
--- a/compiler/rustc_hir_analysis/src/outlives/explicit.rs
+++ b/compiler/rustc_hir_analysis/src/outlives/explicit.rs
@@ -30,45 +30,34 @@ impl<'tcx> ExplicitPredicatesMap<'tcx> {
             // process predicates and convert to `RequiredPredicates` entry, see below
             for &(predicate, span) in predicates.predicates {
                 match predicate.kind().skip_binder() {
-                    ty::PredicateKind::Clause(ty::Clause::TypeOutlives(OutlivesPredicate(
-                        ty,
-                        reg,
-                    ))) => insert_outlives_predicate(
-                        tcx,
-                        ty.into(),
-                        reg,
-                        span,
-                        &mut required_predicates,
-                    ),
-
-                    ty::PredicateKind::Clause(ty::Clause::RegionOutlives(OutlivesPredicate(
-                        reg1,
-                        reg2,
-                    ))) => insert_outlives_predicate(
-                        tcx,
-                        reg1.into(),
-                        reg2,
-                        span,
-                        &mut required_predicates,
-                    ),
-
-                    ty::PredicateKind::Clause(ty::Clause::Trait(..))
-                    | ty::PredicateKind::Clause(ty::Clause::Projection(..))
-                    | ty::PredicateKind::Clause(ty::Clause::ConstArgHasType(..))
-                    | 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::Ambiguous
-                    | ty::PredicateKind::TypeWellFormedFromEnv(..) => (),
+                    ty::ClauseKind::TypeOutlives(OutlivesPredicate(ty, reg)) => {
+                        insert_outlives_predicate(
+                            tcx,
+                            ty.into(),
+                            reg,
+                            span,
+                            &mut required_predicates,
+                        )
+                    }
+
+                    ty::ClauseKind::RegionOutlives(OutlivesPredicate(reg1, reg2)) => {
+                        insert_outlives_predicate(
+                            tcx,
+                            reg1.into(),
+                            reg2,
+                            span,
+                            &mut required_predicates,
+                        )
+                    }
+                    ty::ClauseKind::Trait(_)
+                    | ty::ClauseKind::Projection(_)
+                    | ty::ClauseKind::ConstArgHasType(_, _)
+                    | ty::ClauseKind::WellFormed(_)
+                    | ty::ClauseKind::ConstEvaluatable(_) => {}
                 }
             }
 
-            ty::EarlyBinder(required_predicates)
+            ty::EarlyBinder::bind(required_predicates)
         })
     }
 }
diff --git a/compiler/rustc_hir_analysis/src/outlives/implicit_infer.rs b/compiler/rustc_hir_analysis/src/outlives/implicit_infer.rs
index 0cd2fc1aa..71dca918f 100644
--- a/compiler/rustc_hir_analysis/src/outlives/implicit_infer.rs
+++ b/compiler/rustc_hir_analysis/src/outlives/implicit_infer.rs
@@ -68,12 +68,13 @@ pub(super) fn infer_predicates(
             // Therefore mark `predicates_added` as true and which will ensure
             // we walk the crates again and re-calculate predicates for all
             // items.
-            let item_predicates_len: usize =
-                global_inferred_outlives.get(&item_did.to_def_id()).map_or(0, |p| p.0.len());
+            let item_predicates_len: usize = global_inferred_outlives
+                .get(&item_did.to_def_id())
+                .map_or(0, |p| p.as_ref().skip_binder().len());
             if item_required_predicates.len() > item_predicates_len {
                 predicates_added = true;
                 global_inferred_outlives
-                    .insert(item_did.to_def_id(), ty::EarlyBinder(item_required_predicates));
+                    .insert(item_did.to_def_id(), ty::EarlyBinder::bind(item_required_predicates));
             }
         }
 
@@ -137,7 +138,9 @@ fn insert_required_predicates_to_be_wf<'tcx>(
                 // 'a` holds for `Foo`.
                 debug!("Adt");
                 if let Some(unsubstituted_predicates) = global_inferred_outlives.get(&def.did()) {
-                    for (unsubstituted_predicate, &span) in &unsubstituted_predicates.0 {
+                    for (unsubstituted_predicate, &span) in
+                        unsubstituted_predicates.as_ref().skip_binder()
+                    {
                         // `unsubstituted_predicate` is `U: 'b` in the
                         // example above. So apply the substitution to
                         // get `T: 'a` (or `predicate`):
@@ -251,7 +254,7 @@ fn check_explicit_predicates<'tcx>(
     );
     let explicit_predicates = explicit_map.explicit_predicates_of(tcx, def_id);
 
-    for (outlives_predicate, &span) in &explicit_predicates.0 {
+    for (outlives_predicate, &span) in explicit_predicates.as_ref().skip_binder() {
         debug!("outlives_predicate = {:?}", &outlives_predicate);
 
         // Careful: If we are inferring the effects of a `dyn Trait<..>`
diff --git a/compiler/rustc_hir_analysis/src/outlives/mod.rs b/compiler/rustc_hir_analysis/src/outlives/mod.rs
index a8596c707..48624cefe 100644
--- a/compiler/rustc_hir_analysis/src/outlives/mod.rs
+++ b/compiler/rustc_hir_analysis/src/outlives/mod.rs
@@ -3,7 +3,7 @@ use rustc_hir as hir;
 use rustc_hir::def_id::LocalDefId;
 use rustc_middle::query::Providers;
 use rustc_middle::ty::subst::GenericArgKind;
-use rustc_middle::ty::{self, CratePredicatesMap, TyCtxt};
+use rustc_middle::ty::{self, CratePredicatesMap, ToPredicate, TyCtxt};
 use rustc_span::symbol::sym;
 use rustc_span::Span;
 
@@ -20,7 +20,8 @@ pub fn provide(providers: &mut Providers) {
 fn inferred_outlives_of(tcx: TyCtxt<'_>, item_def_id: LocalDefId) -> &[(ty::Clause<'_>, Span)] {
     let id = tcx.hir().local_def_id_to_hir_id(item_def_id);
 
-    if matches!(tcx.def_kind(item_def_id), hir::def::DefKind::AnonConst) && tcx.lazy_normalization()
+    if matches!(tcx.def_kind(item_def_id), hir::def::DefKind::AnonConst)
+        && tcx.features().generic_const_exprs
     {
         if tcx.hir().opt_const_param_default_param_def_id(id).is_some() {
             // In `generics_of` we set the generics' parent to be our parent's parent which means that
@@ -51,9 +52,9 @@ fn inferred_outlives_of(tcx: TyCtxt<'_>, item_def_id: LocalDefId) -> &[(ty::Clau
                 if tcx.has_attr(item_def_id, sym::rustc_outlives) {
                     let mut pred: Vec<String> = predicates
                         .iter()
-                        .map(|(out_pred, _)| match out_pred {
-                            ty::Clause::RegionOutlives(p) => p.to_string(),
-                            ty::Clause::TypeOutlives(p) => p.to_string(),
+                        .map(|(out_pred, _)| match out_pred.kind().skip_binder() {
+                            ty::ClauseKind::RegionOutlives(p) => p.to_string(),
+                            ty::ClauseKind::TypeOutlives(p) => p.to_string(),
                             err => bug!("unexpected clause {:?}", err),
                         })
                         .collect();
@@ -98,24 +99,29 @@ fn inferred_outlives_crate(tcx: TyCtxt<'_>, (): ()) -> CratePredicatesMap<'_> {
     let predicates = global_inferred_outlives
         .iter()
         .map(|(&def_id, set)| {
-            let predicates = &*tcx.arena.alloc_from_iter(set.0.iter().filter_map(
-                |(ty::OutlivesPredicate(kind1, region2), &span)| {
-                    match kind1.unpack() {
-                        GenericArgKind::Type(ty1) => Some((
-                            ty::Clause::TypeOutlives(ty::OutlivesPredicate(ty1, *region2)),
-                            span,
-                        )),
-                        GenericArgKind::Lifetime(region1) => Some((
-                            ty::Clause::RegionOutlives(ty::OutlivesPredicate(region1, *region2)),
-                            span,
-                        )),
-                        GenericArgKind::Const(_) => {
-                            // Generic consts don't impose any constraints.
-                            None
+            let predicates =
+                &*tcx.arena.alloc_from_iter(set.as_ref().skip_binder().iter().filter_map(
+                    |(ty::OutlivesPredicate(kind1, region2), &span)| {
+                        match kind1.unpack() {
+                            GenericArgKind::Type(ty1) => Some((
+                                ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(ty1, *region2))
+                                    .to_predicate(tcx),
+                                span,
+                            )),
+                            GenericArgKind::Lifetime(region1) => Some((
+                                ty::ClauseKind::RegionOutlives(ty::OutlivesPredicate(
+                                    region1, *region2,
+                                ))
+                                .to_predicate(tcx),
+                                span,
+                            )),
+                            GenericArgKind::Const(_) => {
+                                // Generic consts don't impose any constraints.
+                                None
+                            }
                         }
-                    }
-                },
-            ));
+                    },
+                ));
             (def_id, predicates)
         })
         .collect();
diff --git a/compiler/rustc_hir_analysis/src/variance/mod.rs b/compiler/rustc_hir_analysis/src/variance/mod.rs
index 3ebd9e134..066e74491 100644
--- a/compiler/rustc_hir_analysis/src/variance/mod.rs
+++ b/compiler/rustc_hir_analysis/src/variance/mod.rs
@@ -51,20 +51,19 @@ fn variances_of(tcx: TyCtxt<'_>, item_def_id: LocalDefId) -> &[ty::Variance] {
         | DefKind::Struct
         | DefKind::Union
         | DefKind::Variant
-        | DefKind::Ctor(..) => {}
+        | DefKind::Ctor(..) => {
+            // These are inferred.
+            let crate_map = tcx.crate_variances(());
+            return crate_map.variances.get(&item_def_id.to_def_id()).copied().unwrap_or(&[]);
+        }
         DefKind::OpaqueTy | DefKind::ImplTraitPlaceholder => {
             return variance_of_opaque(tcx, item_def_id);
         }
-        _ => {
-            // Variance not relevant.
-            span_bug!(tcx.def_span(item_def_id), "asked to compute variance for wrong kind of item")
-        }
+        _ => {}
     }
 
-    // Everything else must be inferred.
-
-    let crate_map = tcx.crate_variances(());
-    crate_map.variances.get(&item_def_id.to_def_id()).copied().unwrap_or(&[])
+    // Variance not relevant.
+    span_bug!(tcx.def_span(item_def_id), "asked to compute variance for wrong kind of item");
 }
 
 #[instrument(level = "trace", skip(tcx), ret)]
@@ -119,7 +118,8 @@ fn variance_of_opaque(tcx: TyCtxt<'_>, item_def_id: LocalDefId) -> &[ty::Varianc
                 // FIXME(-Zlower-impl-trait-in-trait-to-assoc-ty) check whether this is necessary
                 // at all for RPITITs.
                 ty::Alias(_, ty::AliasTy { def_id, substs, .. })
-                    if self.tcx.is_impl_trait_in_trait(*def_id) =>
+                    if self.tcx.is_impl_trait_in_trait(*def_id)
+                        && !self.tcx.lower_impl_trait_in_trait_to_assoc_ty() =>
                 {
                     self.visit_opaque(*def_id, substs)
                 }
@@ -162,28 +162,25 @@ fn variance_of_opaque(tcx: TyCtxt<'_>, item_def_id: LocalDefId) -> &[ty::Varianc
         // which thus mentions `'a` and should thus accept hidden types that borrow 'a
         // instead of requiring an additional `+ 'a`.
         match pred.kind().skip_binder() {
-            ty::PredicateKind::Clause(ty::Clause::Trait(ty::TraitPredicate {
+            ty::ClauseKind::Trait(ty::TraitPredicate {
                 trait_ref: ty::TraitRef { def_id: _, substs, .. },
                 constness: _,
                 polarity: _,
-            })) => {
+            }) => {
                 for subst in &substs[1..] {
                     subst.visit_with(&mut collector);
                 }
             }
-            ty::PredicateKind::Clause(ty::Clause::Projection(ty::ProjectionPredicate {
+            ty::ClauseKind::Projection(ty::ProjectionPredicate {
                 projection_ty: ty::AliasTy { substs, .. },
                 term,
-            })) => {
+            }) => {
                 for subst in &substs[1..] {
                     subst.visit_with(&mut collector);
                 }
                 term.visit_with(&mut collector);
             }
-            ty::PredicateKind::Clause(ty::Clause::TypeOutlives(ty::OutlivesPredicate(
-                _,
-                region,
-            ))) => {
+            ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(_, region)) => {
                 region.visit_with(&mut collector);
             }
             _ => {