Merging upstream version 1.67.1+dfsg1.

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

34 files changed, 2867 insertions, 2844 deletions

diff --git a/compiler/rustc_trait_selection/src/autoderef.rs b/compiler/rustc_trait_selection/src/autoderef.rs
index 61cfeec4b..e988c77a0 100644
--- a/compiler/rustc_trait_selection/src/autoderef.rs
+++ b/compiler/rustc_trait_selection/src/autoderef.rs
@@ -1,10 +1,11 @@
 use crate::errors::AutoDerefReachedRecursionLimit;
 use crate::traits::query::evaluate_obligation::InferCtxtExt;
-use crate::traits::{self, TraitEngine};
+use crate::traits::NormalizeExt;
+use crate::traits::{self, TraitEngine, TraitEngineExt};
 use rustc_hir as hir;
 use rustc_infer::infer::InferCtxt;
-use rustc_middle::ty::{self, TraitRef, Ty, TyCtxt};
-use rustc_middle::ty::{ToPredicate, TypeVisitable};
+use rustc_middle::ty::TypeVisitable;
+use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_session::Limit;
 use rustc_span::def_id::LOCAL_CRATE;
 use rustc_span::Span;
@@ -27,7 +28,6 @@ pub struct Autoderef<'a, 'tcx> {
     // Meta infos:
     infcx: &'a InferCtxt<'tcx>,
     span: Span,
-    overloaded_span: Span,
     body_id: hir::HirId,
     param_env: ty::ParamEnv<'tcx>,
 
@@ -99,12 +99,10 @@ impl<'a, 'tcx> Autoderef<'a, 'tcx> {
         body_id: hir::HirId,
         span: Span,
         base_ty: Ty<'tcx>,
-        overloaded_span: Span,
     ) -> Autoderef<'a, 'tcx> {
         Autoderef {
             infcx,
             span,
-            overloaded_span,
             body_id,
             param_env,
             state: AutoderefSnapshot {
@@ -125,33 +123,28 @@ impl<'a, 'tcx> Autoderef<'a, 'tcx> {
         let tcx = self.infcx.tcx;
 
         // <ty as Deref>
-        let trait_ref = TraitRef {
-            def_id: tcx.lang_items().deref_trait()?,
-            substs: tcx.mk_substs_trait(ty, &[]),
-        };
+        let trait_ref = tcx.mk_trait_ref(tcx.lang_items().deref_trait()?, [ty]);
 
         let cause = traits::ObligationCause::misc(self.span, self.body_id);
 
         let obligation = traits::Obligation::new(
+            tcx,
             cause.clone(),
             self.param_env,
-            ty::Binder::dummy(trait_ref).without_const().to_predicate(tcx),
+            ty::Binder::dummy(trait_ref),
         );
         if !self.infcx.predicate_may_hold(&obligation) {
             debug!("overloaded_deref_ty: cannot match obligation");
             return None;
         }
 
-        let mut fulfillcx = traits::FulfillmentContext::new_in_snapshot();
-        let normalized_ty = fulfillcx.normalize_projection_type(
-            &self.infcx,
-            self.param_env,
-            ty::ProjectionTy {
-                item_def_id: tcx.lang_items().deref_target()?,
-                substs: trait_ref.substs,
-            },
-            cause,
-        );
+        let normalized_ty = self
+            .infcx
+            .at(&cause, self.param_env)
+            .normalize(tcx.mk_projection(tcx.lang_items().deref_target()?, trait_ref.substs));
+        let mut fulfillcx = <dyn TraitEngine<'tcx>>::new_in_snapshot(tcx);
+        let normalized_ty =
+            normalized_ty.into_value_registering_obligations(self.infcx, &mut *fulfillcx);
         let errors = fulfillcx.select_where_possible(&self.infcx);
         if !errors.is_empty() {
             // This shouldn't happen, except for evaluate/fulfill mismatches,
@@ -193,10 +186,6 @@ impl<'a, 'tcx> Autoderef<'a, 'tcx> {
         self.span
     }
 
-    pub fn overloaded_span(&self) -> Span {
-        self.overloaded_span
-    }
-
     pub fn reached_recursion_limit(&self) -> bool {
         self.state.reached_recursion_limit
     }
diff --git a/compiler/rustc_trait_selection/src/errors.rs b/compiler/rustc_trait_selection/src/errors.rs
index 7f8705824..19f404cb5 100644
--- a/compiler/rustc_trait_selection/src/errors.rs
+++ b/compiler/rustc_trait_selection/src/errors.rs
@@ -58,24 +58,25 @@ pub struct NoValueInOnUnimplemented {
     pub span: Span,
 }
 
-pub struct NegativePositiveConflict<'a> {
+pub struct NegativePositiveConflict<'tcx> {
     pub impl_span: Span,
-    pub trait_desc: &'a str,
-    pub self_desc: &'a Option<String>,
+    pub trait_desc: ty::TraitRef<'tcx>,
+    pub self_ty: Option<Ty<'tcx>>,
     pub negative_impl_span: Result<Span, Symbol>,
     pub positive_impl_span: Result<Span, Symbol>,
 }
 
 impl IntoDiagnostic<'_> for NegativePositiveConflict<'_> {
+    #[track_caller]
     fn into_diagnostic(
         self,
         handler: &Handler,
     ) -> rustc_errors::DiagnosticBuilder<'_, ErrorGuaranteed> {
         let mut diag = handler.struct_err(fluent::trait_selection_negative_positive_conflict);
-        diag.set_arg("trait_desc", self.trait_desc);
+        diag.set_arg("trait_desc", self.trait_desc.print_only_trait_path().to_string());
         diag.set_arg(
             "self_desc",
-            self.self_desc.clone().map_or_else(|| String::from("none"), |ty| ty),
+            self.self_ty.map_or_else(|| "none".to_string(), |ty| ty.to_string()),
         );
         diag.set_span(self.impl_span);
         diag.code(rustc_errors::error_code!(E0751));
diff --git a/compiler/rustc_trait_selection/src/infer.rs b/compiler/rustc_trait_selection/src/infer.rs
index a335f8e06..6c70bbf75 100644
--- a/compiler/rustc_trait_selection/src/infer.rs
+++ b/compiler/rustc_trait_selection/src/infer.rs
@@ -1,15 +1,13 @@
 use crate::traits::query::evaluate_obligation::InferCtxtExt as _;
-use crate::traits::{self, TraitEngine, TraitEngineExt};
+use crate::traits::{self, ObligationCtxt};
 
 use rustc_hir::def_id::DefId;
 use rustc_hir::lang_items::LangItem;
-use rustc_infer::traits::ObligationCause;
 use rustc_middle::arena::ArenaAllocatable;
 use rustc_middle::infer::canonical::{Canonical, CanonicalizedQueryResponse, QueryResponse};
 use rustc_middle::traits::query::Fallible;
-use rustc_middle::ty::subst::SubstsRef;
-use rustc_middle::ty::ToPredicate;
 use rustc_middle::ty::{self, Ty, TypeFoldable, TypeVisitable};
+use rustc_middle::ty::{GenericArg, ToPredicate};
 use rustc_span::{Span, DUMMY_SP};
 
 use std::fmt::Debug;
@@ -31,21 +29,11 @@ pub trait InferCtxtExt<'tcx> {
         span: Span,
     ) -> bool;
 
-    fn partially_normalize_associated_types_in<T>(
-        &self,
-        cause: ObligationCause<'tcx>,
-        param_env: ty::ParamEnv<'tcx>,
-        value: T,
-    ) -> InferOk<'tcx, T>
-    where
-        T: TypeFoldable<'tcx>;
-
     /// Check whether a `ty` implements given trait(trait_def_id).
     /// The inputs are:
     ///
     /// - the def-id of the trait
-    /// - the self type
-    /// - the *other* type parameters of the trait, excluding the self-type
+    /// - the type parameters of the trait, including the self-type
     /// - the parameter environment
     ///
     /// Invokes `evaluate_obligation`, so in the event that evaluating
@@ -54,8 +42,7 @@ pub trait InferCtxtExt<'tcx> {
     fn type_implements_trait(
         &self,
         trait_def_id: DefId,
-        ty: Ty<'tcx>,
-        params: SubstsRef<'tcx>,
+        params: impl IntoIterator<Item = impl Into<GenericArg<'tcx>>>,
         param_env: ty::ParamEnv<'tcx>,
     ) -> traits::EvaluationResult;
 }
@@ -91,42 +78,14 @@ impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
         traits::type_known_to_meet_bound_modulo_regions(self, param_env, ty, lang_item, span)
     }
 
-    /// Normalizes associated types in `value`, potentially returning
-    /// new obligations that must further be processed.
-    fn partially_normalize_associated_types_in<T>(
-        &self,
-        cause: ObligationCause<'tcx>,
-        param_env: ty::ParamEnv<'tcx>,
-        value: T,
-    ) -> InferOk<'tcx, T>
-    where
-        T: TypeFoldable<'tcx>,
-    {
-        debug!("partially_normalize_associated_types_in(value={:?})", value);
-        let mut selcx = traits::SelectionContext::new(self);
-        let traits::Normalized { value, obligations } =
-            traits::normalize(&mut selcx, param_env, cause, value);
-        debug!(
-            "partially_normalize_associated_types_in: result={:?} predicates={:?}",
-            value, obligations
-        );
-        InferOk { value, obligations }
-    }
-
+    #[instrument(level = "debug", skip(self, params), ret)]
     fn type_implements_trait(
         &self,
         trait_def_id: DefId,
-        ty: Ty<'tcx>,
-        params: SubstsRef<'tcx>,
+        params: impl IntoIterator<Item = impl Into<GenericArg<'tcx>>>,
         param_env: ty::ParamEnv<'tcx>,
     ) -> traits::EvaluationResult {
-        debug!(
-            "type_implements_trait: trait_def_id={:?}, type={:?}, params={:?}, param_env={:?}",
-            trait_def_id, ty, params, param_env
-        );
-
-        let trait_ref =
-            ty::TraitRef { def_id: trait_def_id, substs: self.tcx.mk_substs_trait(ty, params) };
+        let trait_ref = self.tcx.mk_trait_ref(trait_def_id, params);
 
         let obligation = traits::Obligation {
             cause: traits::ObligationCause::dummy(),
@@ -142,7 +101,7 @@ pub trait InferCtxtBuilderExt<'tcx> {
     fn enter_canonical_trait_query<K, R>(
         &mut self,
         canonical_key: &Canonical<'tcx, K>,
-        operation: impl FnOnce(&InferCtxt<'tcx>, &mut dyn TraitEngine<'tcx>, K) -> Fallible<R>,
+        operation: impl FnOnce(&ObligationCtxt<'_, 'tcx>, K) -> Fallible<R>,
     ) -> Fallible<CanonicalizedQueryResponse<'tcx, R>>
     where
         K: TypeFoldable<'tcx>,
@@ -170,17 +129,17 @@ impl<'tcx> InferCtxtBuilderExt<'tcx> for InferCtxtBuilder<'tcx> {
     fn enter_canonical_trait_query<K, R>(
         &mut self,
         canonical_key: &Canonical<'tcx, K>,
-        operation: impl FnOnce(&InferCtxt<'tcx>, &mut dyn TraitEngine<'tcx>, K) -> Fallible<R>,
+        operation: impl FnOnce(&ObligationCtxt<'_, 'tcx>, K) -> Fallible<R>,
     ) -> Fallible<CanonicalizedQueryResponse<'tcx, R>>
     where
         K: TypeFoldable<'tcx>,
         R: Debug + TypeFoldable<'tcx>,
         Canonical<'tcx, QueryResponse<'tcx, R>>: ArenaAllocatable<'tcx>,
     {
-        let (ref infcx, key, canonical_inference_vars) =
+        let (infcx, key, canonical_inference_vars) =
             self.build_with_canonical(DUMMY_SP, canonical_key);
-        let mut fulfill_cx = <dyn TraitEngine<'_>>::new(infcx.tcx);
-        let value = operation(infcx, &mut *fulfill_cx, key)?;
-        infcx.make_canonicalized_query_response(canonical_inference_vars, value, &mut *fulfill_cx)
+        let ocx = ObligationCtxt::new(&infcx);
+        let value = operation(&ocx, key)?;
+        ocx.make_canonicalized_query_response(canonical_inference_vars, value)
     }
 }
diff --git a/compiler/rustc_trait_selection/src/lib.rs b/compiler/rustc_trait_selection/src/lib.rs
index 5d52aa075..975ff31a6 100644
--- a/compiler/rustc_trait_selection/src/lib.rs
+++ b/compiler/rustc_trait_selection/src/lib.rs
@@ -10,8 +10,8 @@
 //!
 //! This API is completely unstable and subject to change.
 
-#![allow(rustc::potential_query_instability)]
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
+#![feature(associated_type_bounds)]
 #![feature(box_patterns)]
 #![feature(control_flow_enum)]
 #![feature(drain_filter)]
diff --git a/compiler/rustc_trait_selection/src/traits/auto_trait.rs b/compiler/rustc_trait_selection/src/traits/auto_trait.rs
index ed34ab95a..8e04da4f9 100644
--- a/compiler/rustc_trait_selection/src/traits/auto_trait.rs
+++ b/compiler/rustc_trait_selection/src/traits/auto_trait.rs
@@ -10,9 +10,9 @@ use crate::traits::project::ProjectAndUnifyResult;
 use rustc_middle::mir::interpret::ErrorHandled;
 use rustc_middle::ty::fold::{TypeFolder, TypeSuperFoldable};
 use rustc_middle::ty::visit::TypeVisitable;
-use rustc_middle::ty::{PolyTraitRef, Region, RegionVid};
+use rustc_middle::ty::{ImplPolarity, Region, RegionVid};
 
-use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet};
 
 use std::collections::hash_map::Entry;
 use std::collections::VecDeque;
@@ -27,8 +27,8 @@ pub enum RegionTarget<'tcx> {
 
 #[derive(Default, Debug, Clone)]
 pub struct RegionDeps<'tcx> {
-    larger: FxHashSet<RegionTarget<'tcx>>,
-    smaller: FxHashSet<RegionTarget<'tcx>>,
+    larger: FxIndexSet<RegionTarget<'tcx>>,
+    smaller: FxIndexSet<RegionTarget<'tcx>>,
 }
 
 pub enum AutoTraitResult<A> {
@@ -86,18 +86,25 @@ impl<'tcx> AutoTraitFinder<'tcx> {
     ) -> AutoTraitResult<A> {
         let tcx = self.tcx;
 
-        let trait_ref = ty::TraitRef { def_id: trait_did, substs: tcx.mk_substs_trait(ty, &[]) };
-
-        let trait_pred = ty::Binder::dummy(trait_ref);
+        let trait_ref = tcx.mk_trait_ref(trait_did, [ty]);
 
         let infcx = tcx.infer_ctxt().build();
         let mut selcx = SelectionContext::new(&infcx);
-        for f in [
-            PolyTraitRef::to_poly_trait_predicate,
-            PolyTraitRef::to_poly_trait_predicate_negative_polarity,
-        ] {
-            let result =
-                selcx.select(&Obligation::new(ObligationCause::dummy(), orig_env, f(&trait_pred)));
+        for polarity in [true, false] {
+            let result = selcx.select(&Obligation::new(
+                tcx,
+                ObligationCause::dummy(),
+                orig_env,
+                ty::Binder::dummy(ty::TraitPredicate {
+                    trait_ref,
+                    constness: ty::BoundConstness::NotConst,
+                    polarity: if polarity {
+                        ImplPolarity::Positive
+                    } else {
+                        ImplPolarity::Negative
+                    },
+                }),
+            ));
             if let Ok(Some(ImplSource::UserDefined(_))) = result {
                 debug!(
                     "find_auto_trait_generics({:?}): \
@@ -256,17 +263,15 @@ impl<'tcx> AutoTraitFinder<'tcx> {
         let mut already_visited = FxHashSet::default();
         let mut predicates = VecDeque::new();
         predicates.push_back(ty::Binder::dummy(ty::TraitPredicate {
-            trait_ref: ty::TraitRef {
-                def_id: trait_did,
-                substs: infcx.tcx.mk_substs_trait(ty, &[]),
-            },
+            trait_ref: infcx.tcx.mk_trait_ref(trait_did, [ty]),
+
             constness: ty::BoundConstness::NotConst,
             // Auto traits are positive
             polarity: ty::ImplPolarity::Positive,
         }));
 
         let computed_preds = param_env.caller_bounds().iter();
-        let mut user_computed_preds: FxHashSet<_> = user_env.caller_bounds().iter().collect();
+        let mut user_computed_preds: FxIndexSet<_> = user_env.caller_bounds().iter().collect();
 
         let mut new_env = param_env;
         let dummy_cause = ObligationCause::dummy();
@@ -280,8 +285,12 @@ impl<'tcx> AutoTraitFinder<'tcx> {
 
             // Call `infcx.resolve_vars_if_possible` to see if we can
             // get rid of any inference variables.
-            let obligation =
-                infcx.resolve_vars_if_possible(Obligation::new(dummy_cause.clone(), new_env, pred));
+            let obligation = infcx.resolve_vars_if_possible(Obligation::new(
+                tcx,
+                dummy_cause.clone(),
+                new_env,
+                pred,
+            ));
             let result = select.select(&obligation);
 
             match result {
@@ -389,13 +398,15 @@ impl<'tcx> AutoTraitFinder<'tcx> {
     /// not just one specific lifetime (e.g., `'static`).
     fn add_user_pred(
         &self,
-        user_computed_preds: &mut FxHashSet<ty::Predicate<'tcx>>,
+        user_computed_preds: &mut FxIndexSet<ty::Predicate<'tcx>>,
         new_pred: ty::Predicate<'tcx>,
     ) {
         let mut should_add_new = true;
         user_computed_preds.retain(|&old_pred| {
-            if let (ty::PredicateKind::Trait(new_trait), ty::PredicateKind::Trait(old_trait)) =
-                (new_pred.kind().skip_binder(), old_pred.kind().skip_binder())
+            if let (
+                ty::PredicateKind::Clause(ty::Clause::Trait(new_trait)),
+                ty::PredicateKind::Clause(ty::Clause::Trait(old_trait)),
+            ) = (new_pred.kind().skip_binder(), old_pred.kind().skip_binder())
             {
                 if new_trait.def_id() == old_trait.def_id() {
                     let new_substs = new_trait.trait_ref.substs;
@@ -585,20 +596,20 @@ impl<'tcx> AutoTraitFinder<'tcx> {
         &self,
         ty: Ty<'_>,
         nested: impl Iterator<Item = Obligation<'tcx, ty::Predicate<'tcx>>>,
-        computed_preds: &mut FxHashSet<ty::Predicate<'tcx>>,
+        computed_preds: &mut FxIndexSet<ty::Predicate<'tcx>>,
         fresh_preds: &mut FxHashSet<ty::Predicate<'tcx>>,
         predicates: &mut VecDeque<ty::PolyTraitPredicate<'tcx>>,
-        select: &mut SelectionContext<'_, 'tcx>,
+        selcx: &mut SelectionContext<'_, 'tcx>,
         only_projections: bool,
     ) -> bool {
         let dummy_cause = ObligationCause::dummy();
 
         for obligation in nested {
             let is_new_pred =
-                fresh_preds.insert(self.clean_pred(select.infcx(), obligation.predicate));
+                fresh_preds.insert(self.clean_pred(selcx.infcx, obligation.predicate));
 
             // Resolve any inference variables that we can, to help selection succeed
-            let predicate = select.infcx().resolve_vars_if_possible(obligation.predicate);
+            let predicate = selcx.infcx.resolve_vars_if_possible(obligation.predicate);
 
             // We only add a predicate as a user-displayable bound if
             // it involves a generic parameter, and doesn't contain
@@ -615,14 +626,14 @@ impl<'tcx> AutoTraitFinder<'tcx> {
 
             let bound_predicate = predicate.kind();
             match bound_predicate.skip_binder() {
-                ty::PredicateKind::Trait(p) => {
+                ty::PredicateKind::Clause(ty::Clause::Trait(p)) => {
                     // Add this to `predicates` so that we end up calling `select`
                     // with it. If this predicate ends up being unimplemented,
                     // then `evaluate_predicates` will handle adding it the `ParamEnv`
                     // if possible.
                     predicates.push_back(bound_predicate.rebind(p));
                 }
-                ty::PredicateKind::Projection(p) => {
+                ty::PredicateKind::Clause(ty::Clause::Projection(p)) => {
                     let p = bound_predicate.rebind(p);
                     debug!(
                         "evaluate_nested_obligations: examining projection predicate {:?}",
@@ -706,7 +717,8 @@ impl<'tcx> AutoTraitFinder<'tcx> {
                     // and turn them into an explicit negative impl for our type.
                     debug!("Projecting and unifying projection predicate {:?}", predicate);
 
-                    match project::poly_project_and_unify_type(select, &obligation.with(p)) {
+                    match project::poly_project_and_unify_type(selcx, &obligation.with(self.tcx, p))
+                    {
                         ProjectAndUnifyResult::MismatchedProjectionTypes(e) => {
                             debug!(
                                 "evaluate_nested_obligations: Unable to unify predicate \
@@ -731,7 +743,7 @@ impl<'tcx> AutoTraitFinder<'tcx> {
                                     computed_preds,
                                     fresh_preds,
                                     predicates,
-                                    select,
+                                    selcx,
                                     only_projections,
                                 ) {
                                     return false;
@@ -752,25 +764,25 @@ impl<'tcx> AutoTraitFinder<'tcx> {
                         }
                     }
                 }
-                ty::PredicateKind::RegionOutlives(binder) => {
+                ty::PredicateKind::Clause(ty::Clause::RegionOutlives(binder)) => {
                     let binder = bound_predicate.rebind(binder);
-                    select.infcx().region_outlives_predicate(&dummy_cause, binder)
+                    selcx.infcx.region_outlives_predicate(&dummy_cause, binder)
                 }
-                ty::PredicateKind::TypeOutlives(binder) => {
+                ty::PredicateKind::Clause(ty::Clause::TypeOutlives(binder)) => {
                     let binder = bound_predicate.rebind(binder);
                     match (
                         binder.no_bound_vars(),
                         binder.map_bound_ref(|pred| pred.0).no_bound_vars(),
                     ) {
                         (None, Some(t_a)) => {
-                            select.infcx().register_region_obligation_with_cause(
+                            selcx.infcx.register_region_obligation_with_cause(
                                 t_a,
-                                select.infcx().tcx.lifetimes.re_static,
+                                selcx.infcx.tcx.lifetimes.re_static,
                                 &dummy_cause,
                             );
                         }
                         (Some(ty::OutlivesPredicate(t_a, r_b)), _) => {
-                            select.infcx().register_region_obligation_with_cause(
+                            selcx.infcx.register_region_obligation_with_cause(
                                 t_a,
                                 r_b,
                                 &dummy_cause,
@@ -782,14 +794,12 @@ impl<'tcx> AutoTraitFinder<'tcx> {
                 ty::PredicateKind::ConstEquate(c1, c2) => {
                     let evaluate = |c: ty::Const<'tcx>| {
                         if let ty::ConstKind::Unevaluated(unevaluated) = c.kind() {
-                            match select.infcx().const_eval_resolve(
+                            match selcx.infcx.const_eval_resolve(
                                 obligation.param_env,
                                 unevaluated,
                                 Some(obligation.cause.span),
                             ) {
-                                Ok(Some(valtree)) => {
-                                    Ok(ty::Const::from_value(select.tcx(), valtree, c.ty()))
-                                }
+                                Ok(Some(valtree)) => Ok(selcx.tcx().mk_const(valtree, c.ty())),
                                 Ok(None) => {
                                     let tcx = self.tcx;
                                     let def_id = unevaluated.def.did;
@@ -809,10 +819,7 @@ impl<'tcx> AutoTraitFinder<'tcx> {
 
                     match (evaluate(c1), evaluate(c2)) {
                         (Ok(c1), Ok(c2)) => {
-                            match select
-                                .infcx()
-                                .at(&obligation.cause, obligation.param_env)
-                                .eq(c1, c2)
+                            match selcx.infcx.at(&obligation.cause, obligation.param_env).eq(c1, c2)
                             {
                                 Ok(_) => (),
                                 Err(_) => return false,
@@ -832,6 +839,7 @@ impl<'tcx> AutoTraitFinder<'tcx> {
                 | ty::PredicateKind::ConstEvaluatable(..)
                 | ty::PredicateKind::Coerce(..)
                 | ty::PredicateKind::TypeWellFormedFromEnv(..) => {}
+                ty::PredicateKind::Ambiguous => return false,
             };
         }
         true
@@ -846,7 +854,7 @@ impl<'tcx> AutoTraitFinder<'tcx> {
     }
 }
 
-// Replaces all ReVars in a type with ty::Region's, using the provided map
+/// Replaces all ReVars in a type with ty::Region's, using the provided map
 pub struct RegionReplacer<'a, 'tcx> {
     vid_to_region: &'a FxHashMap<ty::RegionVid, ty::Region<'tcx>>,
     tcx: TyCtxt<'tcx>,
diff --git a/compiler/rustc_trait_selection/src/traits/chalk_fulfill.rs b/compiler/rustc_trait_selection/src/traits/chalk_fulfill.rs
index 81e1d6449..e88950523 100644
--- a/compiler/rustc_trait_selection/src/traits/chalk_fulfill.rs
+++ b/compiler/rustc_trait_selection/src/traits/chalk_fulfill.rs
@@ -4,44 +4,43 @@ use crate::infer::canonical::OriginalQueryValues;
 use crate::infer::InferCtxt;
 use crate::traits::query::NoSolution;
 use crate::traits::{
-    ChalkEnvironmentAndGoal, FulfillmentError, FulfillmentErrorCode, ObligationCause,
-    PredicateObligation, SelectionError, TraitEngine,
+    ChalkEnvironmentAndGoal, FulfillmentError, FulfillmentErrorCode, PredicateObligation,
+    SelectionError, TraitEngine,
 };
 use rustc_data_structures::fx::{FxHashMap, FxIndexSet};
-use rustc_middle::ty::{self, Ty, TypeVisitable};
+use rustc_middle::ty::{self, TypeVisitable};
 
 pub struct FulfillmentContext<'tcx> {
     obligations: FxIndexSet<PredicateObligation<'tcx>>,
 
     relationships: FxHashMap<ty::TyVid, ty::FoundRelationships>,
+
+    usable_in_snapshot: bool,
 }
 
 impl FulfillmentContext<'_> {
-    pub(crate) fn new() -> Self {
+    pub(super) fn new() -> Self {
         FulfillmentContext {
             obligations: FxIndexSet::default(),
             relationships: FxHashMap::default(),
+            usable_in_snapshot: false,
         }
     }
-}
 
-impl<'tcx> TraitEngine<'tcx> for FulfillmentContext<'tcx> {
-    fn normalize_projection_type(
-        &mut self,
-        infcx: &InferCtxt<'tcx>,
-        _param_env: ty::ParamEnv<'tcx>,
-        projection_ty: ty::ProjectionTy<'tcx>,
-        _cause: ObligationCause<'tcx>,
-    ) -> Ty<'tcx> {
-        infcx.tcx.mk_ty(ty::Projection(projection_ty))
+    pub(crate) fn new_in_snapshot() -> Self {
+        FulfillmentContext { usable_in_snapshot: true, ..Self::new() }
     }
+}
 
+impl<'tcx> TraitEngine<'tcx> for FulfillmentContext<'tcx> {
     fn register_predicate_obligation(
         &mut self,
         infcx: &InferCtxt<'tcx>,
         obligation: PredicateObligation<'tcx>,
     ) {
-        assert!(!infcx.is_in_snapshot());
+        if !self.usable_in_snapshot {
+            assert!(!infcx.is_in_snapshot());
+        }
         let obligation = infcx.resolve_vars_if_possible(obligation);
 
         super::relationships::update(self, infcx, &obligation);
@@ -72,7 +71,9 @@ impl<'tcx> TraitEngine<'tcx> for FulfillmentContext<'tcx> {
     }
 
     fn select_where_possible(&mut self, infcx: &InferCtxt<'tcx>) -> Vec<FulfillmentError<'tcx>> {
-        assert!(!infcx.is_in_snapshot());
+        if !self.usable_in_snapshot {
+            assert!(!infcx.is_in_snapshot());
+        }
 
         let mut errors = Vec::new();
         let mut next_round = FxIndexSet::default();
diff --git a/compiler/rustc_trait_selection/src/traits/coherence.rs b/compiler/rustc_trait_selection/src/traits/coherence.rs
index 8aab75490..899e30275 100644
--- a/compiler/rustc_trait_selection/src/traits/coherence.rs
+++ b/compiler/rustc_trait_selection/src/traits/coherence.rs
@@ -11,14 +11,14 @@ use crate::traits::select::IntercrateAmbiguityCause;
 use crate::traits::util::impl_subject_and_oblig;
 use crate::traits::SkipLeakCheck;
 use crate::traits::{
-    self, Normalized, Obligation, ObligationCause, ObligationCtxt, PredicateObligation,
-    PredicateObligations, SelectionContext,
+    self, Obligation, ObligationCause, ObligationCtxt, PredicateObligation, PredicateObligations,
+    SelectionContext,
 };
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_errors::Diagnostic;
 use rustc_hir::def_id::{DefId, CRATE_DEF_ID, LOCAL_CRATE};
 use rustc_hir::CRATE_HIR_ID;
-use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
+use rustc_infer::infer::{DefiningAnchor, InferCtxt, TyCtxtInferExt};
 use rustc_infer::traits::util;
 use rustc_middle::traits::specialization_graph::OverlapMode;
 use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams};
@@ -30,6 +30,8 @@ use std::fmt::Debug;
 use std::iter;
 use std::ops::ControlFlow;
 
+use super::NormalizeExt;
+
 /// Whether we do the orphan check relative to this crate or
 /// to some remote crate.
 #[derive(Copy, Clone, Debug)]
@@ -64,13 +66,13 @@ pub fn add_placeholder_note(err: &mut Diagnostic) {
 /// with a suitably-freshened `ImplHeader` with those types
 /// substituted. Otherwise, returns `None`.
 #[instrument(skip(tcx, skip_leak_check), level = "debug")]
-pub fn overlapping_impls(
-    tcx: TyCtxt<'_>,
+pub fn overlapping_impls<'tcx>(
+    tcx: TyCtxt<'tcx>,
     impl1_def_id: DefId,
     impl2_def_id: DefId,
     skip_leak_check: SkipLeakCheck,
     overlap_mode: OverlapMode,
-) -> Option<OverlapResult<'_>> {
+) -> Option<OverlapResult<'tcx>> {
     // Before doing expensive operations like entering an inference context, do
     // a quick check via fast_reject to tell if the impl headers could possibly
     // unify.
@@ -94,8 +96,9 @@ pub fn overlapping_impls(
         return None;
     }
 
-    let infcx = tcx.infer_ctxt().build();
-    let selcx = &mut SelectionContext::intercrate(&infcx);
+    let infcx =
+        tcx.infer_ctxt().with_opaque_type_inference(DefiningAnchor::Bubble).intercrate().build();
+    let selcx = &mut SelectionContext::new(&infcx);
     let overlaps =
         overlap(selcx, skip_leak_check, impl1_def_id, impl2_def_id, overlap_mode).is_some();
     if !overlaps {
@@ -105,8 +108,9 @@ pub fn overlapping_impls(
     // In the case where we detect an error, run the check again, but
     // this time tracking intercrate ambiguity causes for better
     // diagnostics. (These take time and can lead to false errors.)
-    let infcx = tcx.infer_ctxt().build();
-    let selcx = &mut SelectionContext::intercrate(&infcx);
+    let infcx =
+        tcx.infer_ctxt().with_opaque_type_inference(DefiningAnchor::Bubble).intercrate().build();
+    let selcx = &mut SelectionContext::new(&infcx);
     selcx.enable_tracking_intercrate_ambiguity_causes();
     Some(overlap(selcx, skip_leak_check, impl1_def_id, impl2_def_id, overlap_mode).unwrap())
 }
@@ -117,7 +121,7 @@ fn with_fresh_ty_vars<'cx, 'tcx>(
     impl_def_id: DefId,
 ) -> ty::ImplHeader<'tcx> {
     let tcx = selcx.tcx();
-    let impl_substs = selcx.infcx().fresh_substs_for_item(DUMMY_SP, impl_def_id);
+    let impl_substs = selcx.infcx.fresh_substs_for_item(DUMMY_SP, impl_def_id);
 
     let header = ty::ImplHeader {
         impl_def_id,
@@ -126,8 +130,8 @@ fn with_fresh_ty_vars<'cx, 'tcx>(
         predicates: tcx.predicates_of(impl_def_id).instantiate(tcx, impl_substs).predicates,
     };
 
-    let Normalized { value: mut header, obligations } =
-        traits::normalize(selcx, param_env, ObligationCause::dummy(), header);
+    let InferOk { value: mut header, obligations } =
+        selcx.infcx.at(&ObligationCause::dummy(), param_env).normalize(header);
 
     header.predicates.extend(obligations.into_iter().map(|o| o.predicate));
     header
@@ -147,7 +151,7 @@ fn overlap<'cx, 'tcx>(
         impl1_def_id, impl2_def_id, overlap_mode
     );
 
-    selcx.infcx().probe_maybe_skip_leak_check(skip_leak_check.is_yes(), |snapshot| {
+    selcx.infcx.probe_maybe_skip_leak_check(skip_leak_check.is_yes(), |snapshot| {
         overlap_within_probe(selcx, impl1_def_id, impl2_def_id, overlap_mode, snapshot)
     })
 }
@@ -159,11 +163,11 @@ fn overlap_within_probe<'cx, 'tcx>(
     overlap_mode: OverlapMode,
     snapshot: &CombinedSnapshot<'tcx>,
 ) -> Option<OverlapResult<'tcx>> {
-    let infcx = selcx.infcx();
+    let infcx = selcx.infcx;
 
     if overlap_mode.use_negative_impl() {
-        if negative_impl(selcx, impl1_def_id, impl2_def_id)
-            || negative_impl(selcx, impl2_def_id, impl1_def_id)
+        if negative_impl(infcx.tcx, impl1_def_id, impl2_def_id)
+            || negative_impl(infcx.tcx, impl2_def_id, impl1_def_id)
         {
             return None;
         }
@@ -198,9 +202,9 @@ fn overlap_within_probe<'cx, 'tcx>(
     debug!("overlap: intercrate_ambiguity_causes={:#?}", intercrate_ambiguity_causes);
 
     let involves_placeholder =
-        matches!(selcx.infcx().region_constraints_added_in_snapshot(snapshot), Some(true));
+        matches!(selcx.infcx.region_constraints_added_in_snapshot(snapshot), Some(true));
 
-    let impl_header = selcx.infcx().resolve_vars_if_possible(impl1_header);
+    let impl_header = selcx.infcx.resolve_vars_if_possible(impl1_header);
     Some(OverlapResult { impl_header, intercrate_ambiguity_causes, involves_placeholder })
 }
 
@@ -212,7 +216,7 @@ fn equate_impl_headers<'cx, 'tcx>(
     // Do `a` and `b` unify? If not, no overlap.
     debug!("equate_impl_headers(impl1_header={:?}, impl2_header={:?}", impl1_header, impl2_header);
     selcx
-        .infcx()
+        .infcx
         .at(&ObligationCause::dummy(), ty::ParamEnv::empty())
         .eq_impl_headers(impl1_header, impl2_header)
         .map(|infer_ok| infer_ok.obligations)
@@ -253,7 +257,7 @@ fn implicit_negative<'cx, 'tcx>(
         "implicit_negative(impl1_header={:?}, impl2_header={:?}, obligations={:?})",
         impl1_header, impl2_header, obligations
     );
-    let infcx = selcx.infcx();
+    let infcx = selcx.infcx;
     let opt_failing_obligation = impl1_header
         .predicates
         .iter()
@@ -279,13 +283,8 @@ fn implicit_negative<'cx, 'tcx>(
 
 /// Given impl1 and impl2 check if both impls are never satisfied by a common type (including
 /// where-clauses) If so, return true, they are disjoint and false otherwise.
-fn negative_impl<'cx, 'tcx>(
-    selcx: &mut SelectionContext<'cx, 'tcx>,
-    impl1_def_id: DefId,
-    impl2_def_id: DefId,
-) -> bool {
+fn negative_impl<'tcx>(tcx: TyCtxt<'tcx>, impl1_def_id: DefId, impl2_def_id: DefId) -> bool {
     debug!("negative_impl(impl1_def_id={:?}, impl2_def_id={:?})", impl1_def_id, impl2_def_id);
-    let tcx = selcx.infcx().tcx;
 
     // Create an infcx, taking the predicates of impl1 as assumptions:
     let infcx = tcx.infer_ctxt().build();
@@ -332,11 +331,10 @@ fn equate<'tcx>(
         return true;
     };
 
-    let selcx = &mut SelectionContext::new(&infcx);
     let opt_failing_obligation = obligations
         .into_iter()
         .chain(more_obligations)
-        .find(|o| negative_impl_exists(selcx, o, body_def_id));
+        .find(|o| negative_impl_exists(infcx, o, body_def_id));
 
     if let Some(failing_obligation) = opt_failing_obligation {
         debug!("overlap: obligation unsatisfiable {:?}", failing_obligation);
@@ -347,19 +345,19 @@ fn equate<'tcx>(
 }
 
 /// Try to prove that a negative impl exist for the given obligation and its super predicates.
-#[instrument(level = "debug", skip(selcx))]
-fn negative_impl_exists<'cx, 'tcx>(
-    selcx: &SelectionContext<'cx, 'tcx>,
+#[instrument(level = "debug", skip(infcx))]
+fn negative_impl_exists<'tcx>(
+    infcx: &InferCtxt<'tcx>,
     o: &PredicateObligation<'tcx>,
     body_def_id: DefId,
 ) -> bool {
-    if resolve_negative_obligation(selcx.infcx().fork(), o, body_def_id) {
+    if resolve_negative_obligation(infcx.fork(), o, body_def_id) {
         return true;
     }
 
     // Try to prove a negative obligation exists for super predicates
-    for o in util::elaborate_predicates(selcx.tcx(), iter::once(o.predicate)) {
-        if resolve_negative_obligation(selcx.infcx().fork(), &o, body_def_id) {
+    for o in util::elaborate_predicates(infcx.tcx, iter::once(o.predicate)) {
+        if resolve_negative_obligation(infcx.fork(), &o, body_def_id) {
             return true;
         }
     }
diff --git a/compiler/rustc_trait_selection/src/traits/const_evaluatable.rs b/compiler/rustc_trait_selection/src/traits/const_evaluatable.rs
index 84038625f..7c9fde274 100644
--- a/compiler/rustc_trait_selection/src/traits/const_evaluatable.rs
+++ b/compiler/rustc_trait_selection/src/traits/const_evaluatable.rs
@@ -8,164 +8,30 @@
 //! In this case we try to build an abstract representation of this constant using
 //! `thir_abstract_const` which can then be checked for structural equality with other
 //! generic constants mentioned in the `caller_bounds` of the current environment.
-use rustc_errors::ErrorGuaranteed;
+use rustc_hir::def::DefKind;
 use rustc_infer::infer::InferCtxt;
 use rustc_middle::mir::interpret::ErrorHandled;
-use rustc_middle::ty::abstract_const::{
-    walk_abstract_const, AbstractConst, FailureKind, Node, NotConstEvaluatable,
-};
-use rustc_middle::ty::{self, TyCtxt, TypeVisitable};
-use rustc_span::Span;
-
-use std::iter;
-use std::ops::ControlFlow;
-
-pub struct ConstUnifyCtxt<'tcx> {
-    pub tcx: TyCtxt<'tcx>,
-    pub param_env: ty::ParamEnv<'tcx>,
-}
-
-impl<'tcx> ConstUnifyCtxt<'tcx> {
-    // Substitutes generics repeatedly to allow AbstractConsts to unify where a
-    // ConstKind::Unevaluated could be turned into an AbstractConst that would unify e.g.
-    // Param(N) should unify with Param(T), substs: [Unevaluated("T2", [Unevaluated("T3", [Param(N)])])]
-    #[inline]
-    #[instrument(skip(self), level = "debug")]
-    fn try_replace_substs_in_root(
-        &self,
-        mut abstr_const: AbstractConst<'tcx>,
-    ) -> Option<AbstractConst<'tcx>> {
-        while let Node::Leaf(ct) = abstr_const.root(self.tcx) {
-            match AbstractConst::from_const(self.tcx, ct) {
-                Ok(Some(act)) => abstr_const = act,
-                Ok(None) => break,
-                Err(_) => return None,
-            }
-        }
-
-        Some(abstr_const)
-    }
 
-    /// Tries to unify two abstract constants using structural equality.
-    #[instrument(skip(self), level = "debug")]
-    pub fn try_unify(&self, a: AbstractConst<'tcx>, b: AbstractConst<'tcx>) -> bool {
-        let a = if let Some(a) = self.try_replace_substs_in_root(a) {
-            a
-        } else {
-            return true;
-        };
-
-        let b = if let Some(b) = self.try_replace_substs_in_root(b) {
-            b
-        } else {
-            return true;
-        };
-
-        let a_root = a.root(self.tcx);
-        let b_root = b.root(self.tcx);
-        debug!(?a_root, ?b_root);
-
-        match (a_root, b_root) {
-            (Node::Leaf(a_ct), Node::Leaf(b_ct)) => {
-                let a_ct = a_ct.eval(self.tcx, self.param_env);
-                debug!("a_ct evaluated: {:?}", a_ct);
-                let b_ct = b_ct.eval(self.tcx, self.param_env);
-                debug!("b_ct evaluated: {:?}", b_ct);
-
-                if a_ct.ty() != b_ct.ty() {
-                    return false;
-                }
+use rustc_middle::traits::ObligationCause;
+use rustc_middle::ty::abstract_const::NotConstEvaluatable;
+use rustc_middle::ty::{self, TyCtxt, TypeVisitable, TypeVisitor};
 
-                match (a_ct.kind(), b_ct.kind()) {
-                    // We can just unify errors with everything to reduce the amount of
-                    // emitted errors here.
-                    (ty::ConstKind::Error(_), _) | (_, ty::ConstKind::Error(_)) => true,
-                    (ty::ConstKind::Param(a_param), ty::ConstKind::Param(b_param)) => {
-                        a_param == b_param
-                    }
-                    (ty::ConstKind::Value(a_val), ty::ConstKind::Value(b_val)) => a_val == b_val,
-                    // If we have `fn a<const N: usize>() -> [u8; N + 1]` and `fn b<const M: usize>() -> [u8; 1 + M]`
-                    // we do not want to use `assert_eq!(a(), b())` to infer that `N` and `M` have to be `1`. This
-                    // means that we only allow inference variables if they are equal.
-                    (ty::ConstKind::Infer(a_val), ty::ConstKind::Infer(b_val)) => a_val == b_val,
-                    // We expand generic anonymous constants at the start of this function, so this
-                    // branch should only be taking when dealing with associated constants, at
-                    // which point directly comparing them seems like the desired behavior.
-                    //
-                    // FIXME(generic_const_exprs): This isn't actually the case.
-                    // We also take this branch for concrete anonymous constants and
-                    // expand generic anonymous constants with concrete substs.
-                    (ty::ConstKind::Unevaluated(a_uv), ty::ConstKind::Unevaluated(b_uv)) => {
-                        a_uv == b_uv
-                    }
-                    // FIXME(generic_const_exprs): We may want to either actually try
-                    // to evaluate `a_ct` and `b_ct` if they are fully concrete or something like
-                    // this, for now we just return false here.
-                    _ => false,
-                }
-            }
-            (Node::Binop(a_op, al, ar), Node::Binop(b_op, bl, br)) if a_op == b_op => {
-                self.try_unify(a.subtree(al), b.subtree(bl))
-                    && self.try_unify(a.subtree(ar), b.subtree(br))
-            }
-            (Node::UnaryOp(a_op, av), Node::UnaryOp(b_op, bv)) if a_op == b_op => {
-                self.try_unify(a.subtree(av), b.subtree(bv))
-            }
-            (Node::FunctionCall(a_f, a_args), Node::FunctionCall(b_f, b_args))
-                if a_args.len() == b_args.len() =>
-            {
-                self.try_unify(a.subtree(a_f), b.subtree(b_f))
-                    && iter::zip(a_args, b_args)
-                        .all(|(&an, &bn)| self.try_unify(a.subtree(an), b.subtree(bn)))
-            }
-            (Node::Cast(a_kind, a_operand, a_ty), Node::Cast(b_kind, b_operand, b_ty))
-                if (a_ty == b_ty) && (a_kind == b_kind) =>
-            {
-                self.try_unify(a.subtree(a_operand), b.subtree(b_operand))
-            }
-            // use this over `_ => false` to make adding variants to `Node` less error prone
-            (Node::Cast(..), _)
-            | (Node::FunctionCall(..), _)
-            | (Node::UnaryOp(..), _)
-            | (Node::Binop(..), _)
-            | (Node::Leaf(..), _) => false,
-        }
-    }
-}
-
-#[instrument(skip(tcx), level = "debug")]
-pub fn try_unify_abstract_consts<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    (a, b): (ty::UnevaluatedConst<'tcx>, ty::UnevaluatedConst<'tcx>),
-    param_env: ty::ParamEnv<'tcx>,
-) -> bool {
-    (|| {
-        if let Some(a) = AbstractConst::new(tcx, a)? {
-            if let Some(b) = AbstractConst::new(tcx, b)? {
-                let const_unify_ctxt = ConstUnifyCtxt { tcx, param_env };
-                return Ok(const_unify_ctxt.try_unify(a, b));
-            }
-        }
+use rustc_span::Span;
+use std::ops::ControlFlow;
 
-        Ok(false)
-    })()
-    .unwrap_or_else(|_: ErrorGuaranteed| true)
-    // FIXME(generic_const_exprs): We should instead have this
-    // method return the resulting `ty::Const` and return `ConstKind::Error`
-    // on `ErrorGuaranteed`.
-}
+use crate::traits::ObligationCtxt;
 
 /// Check if a given constant can be evaluated.
 #[instrument(skip(infcx), level = "debug")]
 pub fn is_const_evaluatable<'tcx>(
     infcx: &InferCtxt<'tcx>,
-    ct: ty::Const<'tcx>,
+    unexpanded_ct: ty::Const<'tcx>,
     param_env: ty::ParamEnv<'tcx>,
     span: Span,
 ) -> Result<(), NotConstEvaluatable> {
     let tcx = infcx.tcx;
-    let uv = match ct.kind() {
-        ty::ConstKind::Unevaluated(uv) => uv,
+    match tcx.expand_abstract_consts(unexpanded_ct).kind() {
+        ty::ConstKind::Unevaluated(_) | ty::ConstKind::Expr(_) => (),
         ty::ConstKind::Param(_)
         | ty::ConstKind::Bound(_, _)
         | ty::ConstKind::Placeholder(_)
@@ -175,40 +41,59 @@ pub fn is_const_evaluatable<'tcx>(
     };
 
     if tcx.features().generic_const_exprs {
-        if let Some(ct) = AbstractConst::new(tcx, uv)? {
-            if satisfied_from_param_env(tcx, ct, param_env)? {
+        let ct = tcx.expand_abstract_consts(unexpanded_ct);
+
+        let is_anon_ct = if let ty::ConstKind::Unevaluated(uv) = ct.kind() {
+            tcx.def_kind(uv.def.did) == DefKind::AnonConst
+        } else {
+            false
+        };
+
+        if !is_anon_ct {
+            if satisfied_from_param_env(tcx, infcx, ct, param_env) {
                 return Ok(());
             }
-            match ct.unify_failure_kind(tcx) {
-                FailureKind::MentionsInfer => {
-                    return Err(NotConstEvaluatable::MentionsInfer);
-                }
-                FailureKind::MentionsParam => {
-                    return Err(NotConstEvaluatable::MentionsParam);
-                }
-                // returned below
-                FailureKind::Concrete => {}
+            if ct.has_non_region_infer() {
+                return Err(NotConstEvaluatable::MentionsInfer);
+            } else if ct.has_non_region_param() {
+                return Err(NotConstEvaluatable::MentionsParam);
             }
         }
-        let concrete = infcx.const_eval_resolve(param_env, uv, Some(span));
-        match concrete {
-            Err(ErrorHandled::TooGeneric) => {
-                Err(NotConstEvaluatable::Error(infcx.tcx.sess.delay_span_bug(
+
+        match unexpanded_ct.kind() {
+            ty::ConstKind::Expr(_) => {
+                // FIXME(generic_const_exprs): we have a `ConstKind::Expr` which is fully concrete, but
+                // currently it is not possible to evaluate `ConstKind::Expr` so we are unable to tell if it
+                // is evaluatable or not. For now we just ICE until this is implemented.
+                Err(NotConstEvaluatable::Error(tcx.sess.delay_span_bug(
                     span,
-                    format!("Missing value for constant, but no error reported?"),
+                    "evaluating `ConstKind::Expr` is not currently supported",
                 )))
             }
-            Err(ErrorHandled::Linted) => {
-                let reported = infcx
-                    .tcx
-                    .sess
-                    .delay_span_bug(span, "constant in type had error reported as lint");
-                Err(NotConstEvaluatable::Error(reported))
+            ty::ConstKind::Unevaluated(uv) => {
+                let concrete = infcx.const_eval_resolve(param_env, uv, Some(span));
+                match concrete {
+                    Err(ErrorHandled::TooGeneric) => {
+                        Err(NotConstEvaluatable::Error(infcx.tcx.sess.delay_span_bug(
+                            span,
+                            "Missing value for constant, but no error reported?",
+                        )))
+                    }
+                    Err(ErrorHandled::Reported(e)) => Err(NotConstEvaluatable::Error(e)),
+                    Ok(_) => Ok(()),
+                }
             }
-            Err(ErrorHandled::Reported(e)) => Err(NotConstEvaluatable::Error(e)),
-            Ok(_) => Ok(()),
+            _ => bug!("unexpected constkind in `is_const_evalautable: {unexpanded_ct:?}`"),
         }
     } else {
+        let uv = match unexpanded_ct.kind() {
+            ty::ConstKind::Unevaluated(uv) => uv,
+            ty::ConstKind::Expr(_) => {
+                bug!("`ConstKind::Expr` without `feature(generic_const_exprs)` enabled")
+            }
+            _ => bug!("unexpected constkind in `is_const_evalautable: {unexpanded_ct:?}`"),
+        };
+
         // FIXME: We should only try to evaluate a given constant here if it is fully concrete
         // as we don't want to allow things like `[u8; std::mem::size_of::<*mut T>()]`.
         //
@@ -218,28 +103,33 @@ pub fn is_const_evaluatable<'tcx>(
         //
         // See #74595 for more details about this.
         let concrete = infcx.const_eval_resolve(param_env, uv, Some(span));
-
         match concrete {
-          // If we're evaluating a foreign constant, under a nightly compiler without generic
-          // const exprs, AND it would've passed if that expression had been evaluated with
-          // generic const exprs, then suggest using generic const exprs.
-          Err(_) if tcx.sess.is_nightly_build()
-            && let Ok(Some(ct)) = AbstractConst::new(tcx, uv)
-            && satisfied_from_param_env(tcx, ct, param_env) == Ok(true) => {
-              tcx.sess
-                  .struct_span_fatal(
-                      // Slightly better span than just using `span` alone
-                      if span == rustc_span::DUMMY_SP { tcx.def_span(uv.def.did) } else { span },
-                      "failed to evaluate generic const expression",
-                  )
-                  .note("the crate this constant originates from uses `#![feature(generic_const_exprs)]`")
-                  .span_suggestion_verbose(
-                      rustc_span::DUMMY_SP,
-                      "consider enabling this feature",
-                      "#![feature(generic_const_exprs)]\n",
-                      rustc_errors::Applicability::MaybeIncorrect,
-                  )
-                  .emit()
+            // If we're evaluating a generic foreign constant, under a nightly compiler while
+            // the current crate does not enable `feature(generic_const_exprs)`, abort
+            // compilation with a useful error.
+            Err(_)
+                if tcx.sess.is_nightly_build()
+                    && satisfied_from_param_env(
+                        tcx,
+                        infcx,
+                        tcx.expand_abstract_consts(unexpanded_ct),
+                        param_env,
+                    ) =>
+            {
+                tcx.sess
+                    .struct_span_fatal(
+                        // Slightly better span than just using `span` alone
+                        if span == rustc_span::DUMMY_SP { tcx.def_span(uv.def.did) } else { span },
+                        "failed to evaluate generic const expression",
+                    )
+                    .note("the crate this constant originates from uses `#![feature(generic_const_exprs)]`")
+                    .span_suggestion_verbose(
+                        rustc_span::DUMMY_SP,
+                        "consider enabling this feature",
+                        "#![feature(generic_const_exprs)]\n",
+                        rustc_errors::Applicability::MaybeIncorrect,
+                    )
+                    .emit()
             }
 
             Err(ErrorHandled::TooGeneric) => {
@@ -248,16 +138,14 @@ pub fn is_const_evaluatable<'tcx>(
                 } else if uv.has_non_region_param() {
                     NotConstEvaluatable::MentionsParam
                 } else {
-                    let guar = infcx.tcx.sess.delay_span_bug(span, format!("Missing value for constant, but no error reported?"));
+                    let guar = infcx.tcx.sess.delay_span_bug(
+                        span,
+                        format!("Missing value for constant, but no error reported?"),
+                    );
                     NotConstEvaluatable::Error(guar)
                 };
 
                 Err(err)
-            },
-            Err(ErrorHandled::Linted) => {
-                let reported =
-                    infcx.tcx.sess.delay_span_bug(span, "constant in type had error reported as lint");
-                Err(NotConstEvaluatable::Error(reported))
             }
             Err(ErrorHandled::Reported(e)) => Err(NotConstEvaluatable::Error(e)),
             Ok(_) => Ok(()),
@@ -265,37 +153,69 @@ pub fn is_const_evaluatable<'tcx>(
     }
 }
 
-#[instrument(skip(tcx), level = "debug")]
+#[instrument(skip(infcx, tcx), level = "debug")]
 fn satisfied_from_param_env<'tcx>(
     tcx: TyCtxt<'tcx>,
-    ct: AbstractConst<'tcx>,
+    infcx: &InferCtxt<'tcx>,
+    ct: ty::Const<'tcx>,
     param_env: ty::ParamEnv<'tcx>,
-) -> Result<bool, NotConstEvaluatable> {
+) -> bool {
+    // Try to unify with each subtree in the AbstractConst to allow for
+    // `N + 1` being const evaluatable even if theres only a `ConstEvaluatable`
+    // predicate for `(N + 1) * 2`
+    struct Visitor<'a, 'tcx> {
+        ct: ty::Const<'tcx>,
+        param_env: ty::ParamEnv<'tcx>,
+
+        infcx: &'a InferCtxt<'tcx>,
+    }
+    impl<'a, 'tcx> TypeVisitor<'tcx> for Visitor<'a, 'tcx> {
+        type BreakTy = ();
+        fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
+            debug!("is_const_evaluatable: candidate={:?}", c);
+            if let Ok(()) = self.infcx.commit_if_ok(|_| {
+                let ocx = ObligationCtxt::new_in_snapshot(self.infcx);
+                if let Ok(()) = ocx.eq(&ObligationCause::dummy(), self.param_env, c.ty(), self.ct.ty())
+                    && let Ok(()) = ocx.eq(&ObligationCause::dummy(), self.param_env, c, self.ct)
+                    && ocx.select_all_or_error().is_empty()
+                {
+                    Ok(())
+                } else {
+                    Err(())
+                }
+            }) {
+                ControlFlow::BREAK
+            } else if let ty::ConstKind::Expr(e) = c.kind() {
+                e.visit_with(self)
+            } else {
+                // FIXME(generic_const_exprs): This doesn't recurse into `<T as Trait<U>>::ASSOC`'s substs.
+                // This is currently unobservable as `<T as Trait<{ U + 1 }>>::ASSOC` creates an anon const
+                // with its own `ConstEvaluatable` bound in the param env which we will visit separately.
+                //
+                // If we start allowing directly writing `ConstKind::Expr` without an intermediate anon const
+                // this will be incorrect. It might be worth investigating making `predicates_of` elaborate
+                // all of the `ConstEvaluatable` bounds rather than having a visitor here.
+                ControlFlow::CONTINUE
+            }
+        }
+    }
+
     for pred in param_env.caller_bounds() {
         match pred.kind().skip_binder() {
-            ty::PredicateKind::ConstEvaluatable(uv) => {
-                if let Some(b_ct) = AbstractConst::from_const(tcx, uv)? {
-                    let const_unify_ctxt = ConstUnifyCtxt { tcx, param_env };
-
-                    // Try to unify with each subtree in the AbstractConst to allow for
-                    // `N + 1` being const evaluatable even if theres only a `ConstEvaluatable`
-                    // predicate for `(N + 1) * 2`
-                    let result = walk_abstract_const(tcx, b_ct, |b_ct| {
-                        match const_unify_ctxt.try_unify(ct, b_ct) {
-                            true => ControlFlow::BREAK,
-                            false => ControlFlow::CONTINUE,
-                        }
-                    });
-
-                    if let ControlFlow::Break(()) = result {
-                        debug!("is_const_evaluatable: abstract_const ~~> ok");
-                        return Ok(true);
-                    }
+            ty::PredicateKind::ConstEvaluatable(ce) => {
+                let b_ct = tcx.expand_abstract_consts(ce);
+                let mut v = Visitor { ct, infcx, param_env };
+                let result = b_ct.visit_with(&mut v);
+
+                if let ControlFlow::Break(()) = result {
+                    debug!("is_const_evaluatable: yes");
+                    return true;
                 }
             }
             _ => {} // don't care
         }
     }
 
-    Ok(false)
+    debug!("is_const_evaluatable: no");
+    false
 }
diff --git a/compiler/rustc_trait_selection/src/traits/engine.rs b/compiler/rustc_trait_selection/src/traits/engine.rs
index e0c8deec9..c028e89e4 100644
--- a/compiler/rustc_trait_selection/src/traits/engine.rs
+++ b/compiler/rustc_trait_selection/src/traits/engine.rs
@@ -1,14 +1,21 @@
 use std::cell::RefCell;
+use std::fmt::Debug;
 
 use super::TraitEngine;
 use super::{ChalkFulfillmentContext, FulfillmentContext};
-use crate::infer::InferCtxtExt;
-use rustc_data_structures::fx::FxHashSet;
+use crate::traits::NormalizeExt;
+use rustc_data_structures::fx::FxIndexSet;
 use rustc_hir::def_id::{DefId, LocalDefId};
+use rustc_infer::infer::at::ToTrace;
+use rustc_infer::infer::canonical::{
+    Canonical, CanonicalVarValues, CanonicalizedQueryResponse, QueryResponse,
+};
 use rustc_infer::infer::{InferCtxt, InferOk};
+use rustc_infer::traits::query::Fallible;
 use rustc_infer::traits::{
     FulfillmentError, Obligation, ObligationCause, PredicateObligation, TraitEngineExt as _,
 };
+use rustc_middle::arena::ArenaAllocatable;
 use rustc_middle::ty::error::TypeError;
 use rustc_middle::ty::ToPredicate;
 use rustc_middle::ty::TypeFoldable;
@@ -31,7 +38,7 @@ impl<'tcx> TraitEngineExt<'tcx> for dyn TraitEngine<'tcx> {
 
     fn new_in_snapshot(tcx: TyCtxt<'tcx>) -> Box<Self> {
         if tcx.sess.opts.unstable_opts.chalk {
-            Box::new(ChalkFulfillmentContext::new())
+            Box::new(ChalkFulfillmentContext::new_in_snapshot())
         } else {
             Box::new(FulfillmentContext::new_in_snapshot())
         }
@@ -86,7 +93,7 @@ impl<'a, 'tcx> ObligationCtxt<'a, 'tcx> {
         def_id: DefId,
     ) {
         let tcx = self.infcx.tcx;
-        let trait_ref = ty::TraitRef { def_id, substs: tcx.mk_substs_trait(ty, &[]) };
+        let trait_ref = tcx.mk_trait_ref(def_id, [ty]);
         self.register_obligation(Obligation {
             cause,
             recursion_depth: 0,
@@ -97,28 +104,75 @@ impl<'a, 'tcx> ObligationCtxt<'a, 'tcx> {
 
     pub fn normalize<T: TypeFoldable<'tcx>>(
         &self,
-        cause: ObligationCause<'tcx>,
+        cause: &ObligationCause<'tcx>,
         param_env: ty::ParamEnv<'tcx>,
         value: T,
     ) -> T {
-        let infer_ok = self.infcx.partially_normalize_associated_types_in(cause, param_env, value);
+        let infer_ok = self.infcx.at(&cause, param_env).normalize(value);
         self.register_infer_ok_obligations(infer_ok)
     }
 
-    pub fn equate_types(
+    /// Makes `expected <: actual`.
+    pub fn eq_exp<T>(
+        &self,
+        cause: &ObligationCause<'tcx>,
+        param_env: ty::ParamEnv<'tcx>,
+        a_is_expected: bool,
+        a: T,
+        b: T,
+    ) -> Result<(), TypeError<'tcx>>
+    where
+        T: ToTrace<'tcx>,
+    {
+        self.infcx
+            .at(cause, param_env)
+            .eq_exp(a_is_expected, a, b)
+            .map(|infer_ok| self.register_infer_ok_obligations(infer_ok))
+    }
+
+    pub fn eq<T: ToTrace<'tcx>>(
         &self,
         cause: &ObligationCause<'tcx>,
         param_env: ty::ParamEnv<'tcx>,
-        expected: Ty<'tcx>,
-        actual: Ty<'tcx>,
+        expected: T,
+        actual: T,
     ) -> Result<(), TypeError<'tcx>> {
-        match self.infcx.at(cause, param_env).eq(expected, actual) {
-            Ok(InferOk { obligations, value: () }) => {
-                self.register_obligations(obligations);
-                Ok(())
-            }
-            Err(e) => Err(e),
-        }
+        self.infcx
+            .at(cause, param_env)
+            .eq(expected, actual)
+            .map(|infer_ok| self.register_infer_ok_obligations(infer_ok))
+    }
+
+    /// Checks whether `expected` is a subtype of `actual`: `expected <: actual`.
+    pub fn sub<T: ToTrace<'tcx>>(
+        &self,
+        cause: &ObligationCause<'tcx>,
+        param_env: ty::ParamEnv<'tcx>,
+        expected: T,
+        actual: T,
+    ) -> Result<(), TypeError<'tcx>> {
+        self.infcx
+            .at(cause, param_env)
+            .sup(expected, actual)
+            .map(|infer_ok| self.register_infer_ok_obligations(infer_ok))
+    }
+
+    /// Checks whether `expected` is a supertype of `actual`: `expected :> actual`.
+    pub fn sup<T: ToTrace<'tcx>>(
+        &self,
+        cause: &ObligationCause<'tcx>,
+        param_env: ty::ParamEnv<'tcx>,
+        expected: T,
+        actual: T,
+    ) -> Result<(), TypeError<'tcx>> {
+        self.infcx
+            .at(cause, param_env)
+            .sup(expected, actual)
+            .map(|infer_ok| self.register_infer_ok_obligations(infer_ok))
+    }
+
+    pub fn select_where_possible(&self) -> Vec<FulfillmentError<'tcx>> {
+        self.engine.borrow_mut().select_where_possible(self.infcx)
     }
 
     pub fn select_all_or_error(&self) -> Vec<FulfillmentError<'tcx>> {
@@ -130,10 +184,10 @@ impl<'a, 'tcx> ObligationCtxt<'a, 'tcx> {
         param_env: ty::ParamEnv<'tcx>,
         span: Span,
         def_id: LocalDefId,
-    ) -> FxHashSet<Ty<'tcx>> {
+    ) -> FxIndexSet<Ty<'tcx>> {
         let tcx = self.infcx.tcx;
         let assumed_wf_types = tcx.assumed_wf_types(def_id);
-        let mut implied_bounds = FxHashSet::default();
+        let mut implied_bounds = FxIndexSet::default();
         let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
         let cause = ObligationCause::misc(span, hir_id);
         for ty in assumed_wf_types {
@@ -149,9 +203,25 @@ impl<'a, 'tcx> ObligationCtxt<'a, 'tcx> {
             // sound and then uncomment this line again.
 
             // implied_bounds.insert(ty);
-            let normalized = self.normalize(cause.clone(), param_env, ty);
+            let normalized = self.normalize(&cause, param_env, ty);
             implied_bounds.insert(normalized);
         }
         implied_bounds
     }
+
+    pub fn make_canonicalized_query_response<T>(
+        &self,
+        inference_vars: CanonicalVarValues<'tcx>,
+        answer: T,
+    ) -> Fallible<CanonicalizedQueryResponse<'tcx, T>>
+    where
+        T: Debug + TypeFoldable<'tcx>,
+        Canonical<'tcx, QueryResponse<'tcx, T>>: ArenaAllocatable<'tcx>,
+    {
+        self.infcx.make_canonicalized_query_response(
+            inference_vars,
+            answer,
+            &mut **self.engine.borrow_mut(),
+        )
+    }
 }
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/ambiguity.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/ambiguity.rs
new file mode 100644
index 000000000..752b53fbc
--- /dev/null
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/ambiguity.rs
@@ -0,0 +1,52 @@
+use rustc_hir::def_id::DefId;
+use rustc_infer::infer::InferCtxt;
+use rustc_infer::traits::{Obligation, ObligationCause, TraitObligation};
+use rustc_span::DUMMY_SP;
+
+use crate::traits::ObligationCtxt;
+
+pub fn recompute_applicable_impls<'tcx>(
+    infcx: &InferCtxt<'tcx>,
+    obligation: &TraitObligation<'tcx>,
+) -> Vec<DefId> {
+    let tcx = infcx.tcx;
+    let param_env = obligation.param_env;
+    let dummy_cause = ObligationCause::dummy();
+    let impl_may_apply = |impl_def_id| {
+        let ocx = ObligationCtxt::new_in_snapshot(infcx);
+        let placeholder_obligation =
+            infcx.replace_bound_vars_with_placeholders(obligation.predicate);
+        let obligation_trait_ref =
+            ocx.normalize(&dummy_cause, param_env, placeholder_obligation.trait_ref);
+
+        let impl_substs = infcx.fresh_substs_for_item(DUMMY_SP, impl_def_id);
+        let impl_trait_ref = tcx.bound_impl_trait_ref(impl_def_id).unwrap().subst(tcx, impl_substs);
+        let impl_trait_ref = ocx.normalize(&ObligationCause::dummy(), param_env, impl_trait_ref);
+
+        if let Err(_) = ocx.eq(&dummy_cause, param_env, obligation_trait_ref, impl_trait_ref) {
+            return false;
+        }
+
+        let impl_predicates = tcx.predicates_of(impl_def_id).instantiate(tcx, impl_substs);
+        ocx.register_obligations(
+            impl_predicates
+                .predicates
+                .iter()
+                .map(|&predicate| Obligation::new(tcx, dummy_cause.clone(), param_env, predicate)),
+        );
+
+        ocx.select_where_possible().is_empty()
+    };
+
+    let mut impls = Vec::new();
+    tcx.for_each_relevant_impl(
+        obligation.predicate.def_id(),
+        obligation.predicate.skip_binder().trait_ref.self_ty(),
+        |impl_def_id| {
+            if infcx.probe(move |_snapshot| impl_may_apply(impl_def_id)) {
+                impls.push(impl_def_id)
+            }
+        },
+    );
+    impls
+}
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
index 1217d264a..dda7b2b2f 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
@@ -1,34 +1,40 @@
+mod ambiguity;
 pub mod on_unimplemented;
 pub mod suggestions;
 
 use super::{
-    FulfillmentContext, FulfillmentError, FulfillmentErrorCode, MismatchedProjectionTypes,
-    Obligation, ObligationCause, ObligationCauseCode, OnUnimplementedDirective,
-    OnUnimplementedNote, OutputTypeParameterMismatch, Overflow, PredicateObligation,
-    SelectionContext, SelectionError, TraitNotObjectSafe,
+    FulfillmentError, FulfillmentErrorCode, MismatchedProjectionTypes, Obligation, ObligationCause,
+    ObligationCauseCode, ObligationCtxt, OutputTypeParameterMismatch, Overflow,
+    PredicateObligation, SelectionContext, SelectionError, TraitNotObjectSafe,
 };
-
 use crate::infer::error_reporting::{TyCategory, TypeAnnotationNeeded as ErrorCode};
 use crate::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
-use crate::infer::{self, InferCtxt, TyCtxtInferExt};
-use rustc_data_structures::fx::FxHashMap;
+use crate::infer::{self, InferCtxt};
+use crate::traits::query::evaluate_obligation::InferCtxtExt as _;
+use crate::traits::query::normalize::QueryNormalizeExt as _;
+use crate::traits::specialize::to_pretty_impl_header;
+use crate::traits::NormalizeExt;
+use on_unimplemented::OnUnimplementedNote;
+use on_unimplemented::TypeErrCtxtExt as _;
+use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
 use rustc_errors::{
     pluralize, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed,
     MultiSpan, Style,
 };
 use rustc_hir as hir;
+use rustc_hir::def::Namespace;
 use rustc_hir::def_id::DefId;
 use rustc_hir::intravisit::Visitor;
 use rustc_hir::GenericParam;
 use rustc_hir::Item;
 use rustc_hir::Node;
 use rustc_infer::infer::error_reporting::TypeErrCtxt;
-use rustc_infer::infer::TypeTrace;
-use rustc_infer::traits::TraitEngine;
+use rustc_infer::infer::{InferOk, TypeTrace};
 use rustc_middle::traits::select::OverflowError;
 use rustc_middle::ty::abstract_const::NotConstEvaluatable;
 use rustc_middle::ty::error::ExpectedFound;
 use rustc_middle::ty::fold::{TypeFolder, TypeSuperFoldable};
+use rustc_middle::ty::print::{FmtPrinter, Print};
 use rustc_middle::ty::{
     self, SubtypePredicate, ToPolyTraitRef, ToPredicate, TraitRef, Ty, TyCtxt, TypeFoldable,
     TypeVisitable,
@@ -40,11 +46,6 @@ use rustc_span::{ExpnKind, Span, DUMMY_SP};
 use std::fmt;
 use std::iter;
 use std::ops::ControlFlow;
-
-use crate::traits::query::evaluate_obligation::InferCtxtExt as _;
-use crate::traits::query::normalize::AtExt as _;
-use crate::traits::specialize::to_pretty_impl_header;
-use on_unimplemented::TypeErrCtxtExt as _;
 use suggestions::TypeErrCtxtExt as _;
 
 pub use rustc_infer::traits::error_reporting::*;
@@ -70,7 +71,7 @@ pub trait InferCtxtExt<'tcx> {
     /// returns a span and `ArgKind` information that describes the
     /// arguments it expects. This can be supplied to
     /// `report_arg_count_mismatch`.
-    fn get_fn_like_arguments(&self, node: Node<'_>) -> Option<(Span, Vec<ArgKind>)>;
+    fn get_fn_like_arguments(&self, node: Node<'_>) -> Option<(Span, Option<Span>, Vec<ArgKind>)>;
 
     /// Reports an error when the number of arguments needed by a
     /// trait match doesn't match the number that the expression
@@ -82,6 +83,7 @@ pub trait InferCtxtExt<'tcx> {
         expected_args: Vec<ArgKind>,
         found_args: Vec<ArgKind>,
         is_closure: bool,
+        closure_pipe_span: Option<Span>,
     ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>;
 
     /// Checks if the type implements one of `Fn`, `FnMut`, or `FnOnce`
@@ -97,24 +99,36 @@ pub trait InferCtxtExt<'tcx> {
 }
 
 pub trait TypeErrCtxtExt<'tcx> {
+    fn report_overflow_error<T>(
+        &self,
+        predicate: &T,
+        span: Span,
+        suggest_increasing_limit: bool,
+        mutate: impl FnOnce(&mut Diagnostic),
+    ) -> !
+    where
+        T: fmt::Display
+            + TypeFoldable<'tcx>
+            + Print<'tcx, FmtPrinter<'tcx, 'tcx>, Output = FmtPrinter<'tcx, 'tcx>>,
+        <T as Print<'tcx, FmtPrinter<'tcx, 'tcx>>>::Error: std::fmt::Debug;
+
     fn report_fulfillment_errors(
         &self,
         errors: &[FulfillmentError<'tcx>],
         body_id: Option<hir::BodyId>,
-        fallback_has_occurred: bool,
     ) -> ErrorGuaranteed;
 
-    fn report_overflow_error<T>(
+    fn report_overflow_obligation<T>(
         &self,
         obligation: &Obligation<'tcx, T>,
         suggest_increasing_limit: bool,
     ) -> !
     where
-        T: fmt::Display + TypeFoldable<'tcx>;
+        T: ToPredicate<'tcx> + Clone;
 
     fn suggest_new_overflow_limit(&self, err: &mut Diagnostic);
 
-    fn report_overflow_error_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> !;
+    fn report_overflow_obligation_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> !;
 
     /// The `root_obligation` parameter should be the `root_obligation` field
     /// from a `FulfillmentError`. If no `FulfillmentError` is available,
@@ -124,7 +138,6 @@ pub trait TypeErrCtxtExt<'tcx> {
         obligation: PredicateObligation<'tcx>,
         root_obligation: &PredicateObligation<'tcx>,
         error: &SelectionError<'tcx>,
-        fallback_has_occurred: bool,
     );
 }
 
@@ -133,15 +146,16 @@ impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
     /// returns a span and `ArgKind` information that describes the
     /// arguments it expects. This can be supplied to
     /// `report_arg_count_mismatch`.
-    fn get_fn_like_arguments(&self, node: Node<'_>) -> Option<(Span, Vec<ArgKind>)> {
+    fn get_fn_like_arguments(&self, node: Node<'_>) -> Option<(Span, Option<Span>, Vec<ArgKind>)> {
         let sm = self.tcx.sess.source_map();
         let hir = self.tcx.hir();
         Some(match node {
             Node::Expr(&hir::Expr {
-                kind: hir::ExprKind::Closure(&hir::Closure { body, fn_decl_span, .. }),
+                kind: hir::ExprKind::Closure(&hir::Closure { body, fn_decl_span, fn_arg_span, .. }),
                 ..
             }) => (
                 fn_decl_span,
+                fn_arg_span,
                 hir.body(body)
                     .params
                     .iter()
@@ -172,6 +186,7 @@ impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
                 kind: hir::TraitItemKind::Fn(ref sig, _), ..
             }) => (
                 sig.span,
+                None,
                 sig.decl
                     .inputs
                     .iter()
@@ -186,7 +201,7 @@ impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
             ),
             Node::Ctor(ref variant_data) => {
                 let span = variant_data.ctor_hir_id().map_or(DUMMY_SP, |id| hir.span(id));
-                (span, vec![ArgKind::empty(); variant_data.fields().len()])
+                (span, None, vec![ArgKind::empty(); variant_data.fields().len()])
             }
             _ => panic!("non-FnLike node found: {:?}", node),
         })
@@ -202,6 +217,7 @@ impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
         expected_args: Vec<ArgKind>,
         found_args: Vec<ArgKind>,
         is_closure: bool,
+        closure_arg_span: Option<Span>,
     ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
         let kind = if is_closure { "closure" } else { "function" };
 
@@ -239,24 +255,13 @@ impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
         if let Some(found_span) = found_span {
             err.span_label(found_span, format!("takes {}", found_str));
 
-            // move |_| { ... }
-            // ^^^^^^^^-- def_span
-            //
-            // move |_| { ... }
-            // ^^^^^-- prefix
-            let prefix_span = self.tcx.sess.source_map().span_until_non_whitespace(found_span);
-            // move |_| { ... }
-            //      ^^^-- pipe_span
-            let pipe_span =
-                if let Some(span) = found_span.trim_start(prefix_span) { span } else { found_span };
-
             // Suggest to take and ignore the arguments with expected_args_length `_`s if
             // found arguments is empty (assume the user just wants to ignore args in this case).
             // For example, if `expected_args_length` is 2, suggest `|_, _|`.
             if found_args.is_empty() && is_closure {
                 let underscores = vec!["_"; expected_args.len()].join(", ");
                 err.span_suggestion_verbose(
-                    pipe_span,
+                    closure_arg_span.unwrap_or(found_span),
                     &format!(
                         "consider changing the closure to take and ignore the expected argument{}",
                         pluralize!(expected_args.len())
@@ -344,22 +349,19 @@ impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
                     span: DUMMY_SP,
                     kind: TypeVariableOriginKind::MiscVariable,
                 });
-                let substs = self.tcx.mk_substs_trait(ty.skip_binder(), &[var.into()]);
+                let trait_ref = self.tcx.mk_trait_ref(trait_def_id, [ty.skip_binder(), var]);
                 let obligation = Obligation::new(
+                    self.tcx,
                     ObligationCause::dummy(),
                     param_env,
-                    ty.rebind(ty::TraitPredicate {
-                        trait_ref: ty::TraitRef::new(trait_def_id, substs),
-                        constness,
-                        polarity,
-                    })
-                    .to_predicate(self.tcx),
+                    ty.rebind(ty::TraitPredicate { trait_ref, constness, polarity }),
                 );
-                let mut fulfill_cx = FulfillmentContext::new_in_snapshot();
-                fulfill_cx.register_predicate_obligation(self, obligation);
-                if fulfill_cx.select_all_or_error(self).is_empty() {
+                let ocx = ObligationCtxt::new_in_snapshot(self);
+                ocx.register_obligation(obligation);
+                if ocx.select_all_or_error().is_empty() {
                     return Ok((
-                        ty::ClosureKind::from_def_id(self.tcx, trait_def_id)
+                        self.tcx
+                            .fn_trait_kind_from_def_id(trait_def_id)
                             .expect("expected to map DefId to ClosureKind"),
                         ty.rebind(self.resolve_vars_if_possible(var)),
                     ));
@@ -375,7 +377,6 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         &self,
         errors: &[FulfillmentError<'tcx>],
         body_id: Option<hir::BodyId>,
-        fallback_has_occurred: bool,
     ) -> ErrorGuaranteed {
         #[derive(Debug)]
         struct ErrorDescriptor<'tcx> {
@@ -383,7 +384,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             index: Option<usize>, // None if this is an old error
         }
 
-        let mut error_map: FxHashMap<_, Vec<_>> = self
+        let mut error_map: FxIndexMap<_, Vec<_>> = self
             .reported_trait_errors
             .borrow()
             .iter()
@@ -452,7 +453,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
 
         for (error, suppressed) in iter::zip(errors, is_suppressed) {
             if !suppressed {
-                self.report_fulfillment_error(error, body_id, fallback_has_occurred);
+                self.report_fulfillment_error(error, body_id);
             }
         }
 
@@ -467,39 +468,84 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
     /// occurrences in any case.
     fn report_overflow_error<T>(
         &self,
-        obligation: &Obligation<'tcx, T>,
+        predicate: &T,
+        span: Span,
         suggest_increasing_limit: bool,
+        mutate: impl FnOnce(&mut Diagnostic),
     ) -> !
     where
-        T: fmt::Display + TypeFoldable<'tcx>,
+        T: fmt::Display
+            + TypeFoldable<'tcx>
+            + Print<'tcx, FmtPrinter<'tcx, 'tcx>, Output = FmtPrinter<'tcx, 'tcx>>,
+        <T as Print<'tcx, FmtPrinter<'tcx, 'tcx>>>::Error: std::fmt::Debug,
     {
-        let predicate = self.resolve_vars_if_possible(obligation.predicate.clone());
+        let predicate = self.resolve_vars_if_possible(predicate.clone());
+        let mut pred_str = predicate.to_string();
+
+        if pred_str.len() > 50 {
+            // We don't need to save the type to a file, we will be talking about this type already
+            // in a separate note when we explain the obligation, so it will be available that way.
+            pred_str = predicate
+                .print(FmtPrinter::new_with_limit(
+                    self.tcx,
+                    Namespace::TypeNS,
+                    rustc_session::Limit(6),
+                ))
+                .unwrap()
+                .into_buffer();
+        }
         let mut err = struct_span_err!(
             self.tcx.sess,
-            obligation.cause.span,
+            span,
             E0275,
             "overflow evaluating the requirement `{}`",
-            predicate
+            pred_str,
         );
 
         if suggest_increasing_limit {
             self.suggest_new_overflow_limit(&mut err);
         }
 
-        self.note_obligation_cause_code(
-            &mut err,
-            &obligation.predicate,
-            obligation.param_env,
-            obligation.cause.code(),
-            &mut vec![],
-            &mut Default::default(),
-        );
+        mutate(&mut err);
 
         err.emit();
         self.tcx.sess.abort_if_errors();
         bug!();
     }
 
+    /// Reports that an overflow has occurred and halts compilation. We
+    /// halt compilation unconditionally because it is important that
+    /// overflows never be masked -- they basically represent computations
+    /// whose result could not be truly determined and thus we can't say
+    /// if the program type checks or not -- and they are unusual
+    /// occurrences in any case.
+    fn report_overflow_obligation<T>(
+        &self,
+        obligation: &Obligation<'tcx, T>,
+        suggest_increasing_limit: bool,
+    ) -> !
+    where
+        T: ToPredicate<'tcx> + Clone,
+    {
+        let predicate = obligation.predicate.clone().to_predicate(self.tcx);
+        let predicate = self.resolve_vars_if_possible(predicate);
+        self.report_overflow_error(
+            &predicate,
+            obligation.cause.span,
+            suggest_increasing_limit,
+            |err| {
+                self.note_obligation_cause_code(
+                    err,
+                    &predicate,
+                    obligation.param_env,
+                    obligation.cause.code(),
+                    &mut vec![],
+                    &mut Default::default(),
+                );
+            },
+        );
+    }
+
     fn suggest_new_overflow_limit(&self, err: &mut Diagnostic) {
         let suggested_limit = match self.tcx.recursion_limit() {
             Limit(0) => Limit(2),
@@ -514,11 +560,11 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
     }
 
     /// Reports that a cycle was detected which led to overflow and halts
-    /// compilation. This is equivalent to `report_overflow_error` except
+    /// compilation. This is equivalent to `report_overflow_obligation` except
     /// that we can give a more helpful error message (and, in particular,
     /// we do not suggest increasing the overflow limit, which is not
     /// going to help).
-    fn report_overflow_error_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> ! {
+    fn report_overflow_obligation_cycle(&self, cycle: &[PredicateObligation<'tcx>]) -> ! {
         let cycle = self.resolve_vars_if_possible(cycle.to_owned());
         assert!(!cycle.is_empty());
 
@@ -526,7 +572,10 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
 
         // The 'deepest' obligation is most likely to have a useful
         // cause 'backtrace'
-        self.report_overflow_error(cycle.iter().max_by_key(|p| p.recursion_depth).unwrap(), false);
+        self.report_overflow_obligation(
+            cycle.iter().max_by_key(|p| p.recursion_depth).unwrap(),
+            false,
+        );
     }
 
     fn report_selection_error(
@@ -534,22 +583,15 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         mut obligation: PredicateObligation<'tcx>,
         root_obligation: &PredicateObligation<'tcx>,
         error: &SelectionError<'tcx>,
-        fallback_has_occurred: bool,
     ) {
-        self.set_tainted_by_errors();
         let tcx = self.tcx;
         let mut span = obligation.cause.span;
+        // FIXME: statically guarantee this by tainting after the diagnostic is emitted
+        self.set_tainted_by_errors(
+            tcx.sess.delay_span_bug(span, "`report_selection_error` did not emit an error"),
+        );
 
         let mut err = match *error {
-            SelectionError::Ambiguous(ref impls) => {
-                let mut err = self.tcx.sess.struct_span_err(
-                    obligation.cause.span,
-                    &format!("multiple applicable `impl`s for `{}`", obligation.predicate),
-                );
-                self.annotate_source_of_ambiguity(&mut err, impls, obligation.predicate);
-                err.emit();
-                return;
-            }
             SelectionError::Unimplemented => {
                 // If this obligation was generated as a result of well-formedness checking, see if we
                 // can get a better error message by performing HIR-based well-formedness checking.
@@ -582,7 +624,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
 
                 let bound_predicate = obligation.predicate.kind();
                 match bound_predicate.skip_binder() {
-                    ty::PredicateKind::Trait(trait_predicate) => {
+                    ty::PredicateKind::Clause(ty::Clause::Trait(trait_predicate)) => {
                         let trait_predicate = bound_predicate.rebind(trait_predicate);
                         let mut trait_predicate = self.resolve_vars_if_possible(trait_predicate);
 
@@ -663,40 +705,32 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                                 ))
                         );
 
-                        if is_try_conversion {
-                            let none_error = self
-                                .tcx
-                                .get_diagnostic_item(sym::none_error)
-                                .map(|def_id| tcx.type_of(def_id));
-                            let should_convert_option_to_result =
-                                Some(trait_ref.skip_binder().substs.type_at(1)) == none_error;
-                            let should_convert_result_to_option =
-                                Some(trait_ref.self_ty().skip_binder()) == none_error;
-                            if should_convert_option_to_result {
-                                err.span_suggestion_verbose(
-                                    span.shrink_to_lo(),
-                                    "consider converting the `Option<T>` into a `Result<T, _>` \
-                                     using `Option::ok_or` or `Option::ok_or_else`",
-                                    ".ok_or_else(|| /* error value */)",
-                                    Applicability::HasPlaceholders,
-                                );
-                            } else if should_convert_result_to_option {
-                                err.span_suggestion_verbose(
-                                    span.shrink_to_lo(),
-                                    "consider converting the `Result<T, _>` into an `Option<T>` \
-                                     using `Result::ok`",
-                                    ".ok()",
-                                    Applicability::MachineApplicable,
-                                );
-                            }
-                            if let Some(ret_span) = self.return_type_span(&obligation) {
-                                err.span_label(
-                                    ret_span,
-                                    &format!(
-                                        "expected `{}` because of this",
-                                        trait_ref.skip_binder().self_ty()
-                                    ),
-                                );
+                        if is_try_conversion && let Some(ret_span) = self.return_type_span(&obligation) {
+                            err.span_label(
+                                ret_span,
+                                &format!(
+                                    "expected `{}` because of this",
+                                    trait_ref.skip_binder().self_ty()
+                                ),
+                            );
+                        }
+
+                        if Some(trait_ref.def_id()) == tcx.lang_items().tuple_trait() {
+                            match obligation.cause.code().peel_derives() {
+                                ObligationCauseCode::RustCall => {
+                                    err.set_primary_message("functions with the \"rust-call\" ABI must take a single non-self tuple argument");
+                                }
+                                ObligationCauseCode::BindingObligation(def_id, _)
+                                | ObligationCauseCode::ItemObligation(def_id)
+                                    if tcx.is_fn_trait(*def_id) =>
+                                {
+                                    err.code(rustc_errors::error_code!(E0059));
+                                    err.set_primary_message(format!(
+                                        "type parameter to bare `{}` trait must be a tuple",
+                                        tcx.def_path_str(*def_id)
+                                    ));
+                                }
+                                _ => {}
                             }
                         }
 
@@ -848,12 +882,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                             );
                         }
 
-                        let is_fn_trait = [
-                            self.tcx.lang_items().fn_trait(),
-                            self.tcx.lang_items().fn_mut_trait(),
-                            self.tcx.lang_items().fn_once_trait(),
-                        ]
-                        .contains(&Some(trait_ref.def_id()));
+                        let is_fn_trait = tcx.is_fn_trait(trait_ref.def_id());
                         let is_target_feature_fn = if let ty::FnDef(def_id, _) =
                             *trait_ref.skip_binder().self_ty().kind()
                         {
@@ -883,7 +912,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                             // Note if the `FnMut` or `FnOnce` is less general than the trait we're trying
                             // to implement.
                             let selected_kind =
-                                ty::ClosureKind::from_def_id(self.tcx, trait_ref.def_id())
+                                self.tcx.fn_trait_kind_from_def_id(trait_ref.def_id())
                                     .expect("expected to map DefId to ClosureKind");
                             if !implemented_kind.extends(selected_kind) {
                                 err.note(
@@ -974,7 +1003,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                                 // useful for less general traits.
                                 if peeled
                                     && !self.tcx.trait_is_auto(def_id)
-                                    && !self.tcx.lang_items().items().contains(&Some(def_id))
+                                    && !self.tcx.lang_items().iter().any(|(_, id)| id == def_id)
                                 {
                                     let trait_ref = trait_pred.to_poly_trait_ref();
                                     let impl_candidates =
@@ -1000,16 +1029,12 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                         // variable that used to fallback to `()` now falling back to `!`. Issue a
                         // note informing about the change in behaviour.
                         if trait_predicate.skip_binder().self_ty().is_never()
-                            && fallback_has_occurred
+                            && self.fallback_has_occurred
                         {
-                            let predicate = trait_predicate.map_bound(|mut trait_pred| {
-                                trait_pred.trait_ref.substs = self.tcx.mk_substs_trait(
-                                    self.tcx.mk_unit(),
-                                    &trait_pred.trait_ref.substs[1..],
-                                );
-                                trait_pred
+                            let predicate = trait_predicate.map_bound(|trait_pred| {
+                                trait_pred.with_self_type(self.tcx, self.tcx.mk_unit())
                             });
-                            let unit_obligation = obligation.with(predicate.to_predicate(tcx));
+                            let unit_obligation = obligation.with(tcx, predicate);
                             if self.predicate_may_hold(&unit_obligation) {
                                 err.note(
                                     "this error might have been caused by changes to \
@@ -1062,9 +1087,9 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                         span_bug!(span, "coerce requirement gave wrong error: `{:?}`", predicate)
                     }
 
-                    ty::PredicateKind::RegionOutlives(..)
-                    | ty::PredicateKind::Projection(..)
-                    | ty::PredicateKind::TypeOutlives(..) => {
+                    ty::PredicateKind::Clause(ty::Clause::RegionOutlives(..))
+                    | ty::PredicateKind::Clause(ty::Clause::Projection(..))
+                    | ty::PredicateKind::Clause(ty::Clause::TypeOutlives(..)) => {
                         let predicate = self.resolve_vars_if_possible(obligation.predicate);
                         struct_span_err!(
                             self.tcx.sess,
@@ -1177,6 +1202,8 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                         )
                     }
 
+                    ty::PredicateKind::Ambiguous => span_bug!(span, "ambiguous"),
+
                     ty::PredicateKind::TypeWellFormedFromEnv(..) => span_bug!(
                         span,
                         "TypeWellFormedFromEnv predicate should only exist in the environment"
@@ -1260,13 +1287,14 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                         obligation.cause.code(),
                     )
                 } else {
-                    let (closure_span, found) = found_did
+                    let (closure_span, closure_arg_span, found) = found_did
                         .and_then(|did| {
                             let node = self.tcx.hir().get_if_local(did)?;
-                            let (found_span, found) = self.get_fn_like_arguments(node)?;
-                            Some((Some(found_span), found))
+                            let (found_span, closure_arg_span, found) =
+                                self.get_fn_like_arguments(node)?;
+                            Some((Some(found_span), closure_arg_span, found))
                         })
-                        .unwrap_or((found_span, found));
+                        .unwrap_or((found_span, None, found));
 
                     self.report_arg_count_mismatch(
                         span,
@@ -1274,6 +1302,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                         expected,
                         found,
                         found_trait_ty.is_closure(),
+                        closure_arg_span,
                     )
                 }
             }
@@ -1366,7 +1395,6 @@ trait InferCtxtPrivExt<'tcx> {
         &self,
         error: &FulfillmentError<'tcx>,
         body_id: Option<hir::BodyId>,
-        fallback_has_occurred: bool,
     );
 
     fn report_projection_error(
@@ -1483,9 +1511,10 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         // FIXME: It should be possible to deal with `ForAll` in a cleaner way.
         let bound_error = error.kind();
         let (cond, error) = match (cond.kind().skip_binder(), bound_error.skip_binder()) {
-            (ty::PredicateKind::Trait(..), ty::PredicateKind::Trait(error)) => {
-                (cond, bound_error.rebind(error))
-            }
+            (
+                ty::PredicateKind::Clause(ty::Clause::Trait(..)),
+                ty::PredicateKind::Clause(ty::Clause::Trait(error)),
+            ) => (cond, bound_error.rebind(error)),
             _ => {
                 // FIXME: make this work in other cases too.
                 return false;
@@ -1494,7 +1523,9 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
 
         for obligation in super::elaborate_predicates(self.tcx, std::iter::once(cond)) {
             let bound_predicate = obligation.predicate.kind();
-            if let ty::PredicateKind::Trait(implication) = bound_predicate.skip_binder() {
+            if let ty::PredicateKind::Clause(ty::Clause::Trait(implication)) =
+                bound_predicate.skip_binder()
+            {
                 let error = error.to_poly_trait_ref();
                 let implication = bound_predicate.rebind(implication.trait_ref);
                 // FIXME: I'm just not taking associated types at all here.
@@ -1516,7 +1547,6 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         &self,
         error: &FulfillmentError<'tcx>,
         body_id: Option<hir::BodyId>,
-        fallback_has_occurred: bool,
     ) {
         match error.code {
             FulfillmentErrorCode::CodeSelectionError(ref selection_error) => {
@@ -1524,7 +1554,6 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                     error.obligation.clone(),
                     &error.root_obligation,
                     selection_error,
-                    fallback_has_occurred,
                 );
             }
             FulfillmentErrorCode::CodeProjectionError(ref e) => {
@@ -1567,7 +1596,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                 diag.emit();
             }
             FulfillmentErrorCode::CodeCycle(ref cycle) => {
-                self.report_overflow_error_cycle(cycle);
+                self.report_overflow_obligation_cycle(cycle);
             }
         }
     }
@@ -1585,29 +1614,26 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         }
 
         self.probe(|_| {
-            let mut err = error.err;
-            let mut values = None;
+            let ocx = ObligationCtxt::new_in_snapshot(self);
 
             // try to find the mismatched types to report the error with.
             //
             // this can fail if the problem was higher-ranked, in which
             // cause I have no idea for a good error message.
             let bound_predicate = predicate.kind();
-            if let ty::PredicateKind::Projection(data) = bound_predicate.skip_binder() {
-                let mut selcx = SelectionContext::new(self);
+            let (values, err) = if let ty::PredicateKind::Clause(ty::Clause::Projection(data)) =
+                bound_predicate.skip_binder()
+            {
                 let data = self.replace_bound_vars_with_fresh_vars(
                     obligation.cause.span,
                     infer::LateBoundRegionConversionTime::HigherRankedType,
                     bound_predicate.rebind(data),
                 );
-                let mut obligations = vec![];
-                let normalized_ty = super::normalize_projection_type(
-                    &mut selcx,
+                let normalized_ty = ocx.normalize(
+                    &obligation.cause,
                     obligation.param_env,
-                    data.projection_ty,
-                    obligation.cause.clone(),
-                    0,
-                    &mut obligations,
+                    self.tcx
+                        .mk_projection(data.projection_ty.item_def_id, data.projection_ty.substs),
                 );
 
                 debug!(?obligation.cause, ?obligation.param_env);
@@ -1623,25 +1649,40 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                         | ObligationCauseCode::ObjectCastObligation(..)
                         | ObligationCauseCode::OpaqueType
                 );
-                if let Err(new_err) = self.at(&obligation.cause, obligation.param_env).eq_exp(
+                let expected_ty = data.term.ty().unwrap_or_else(|| self.tcx.ty_error());
+
+                // constrain inference variables a bit more to nested obligations from normalize so
+                // we can have more helpful errors.
+                ocx.select_where_possible();
+
+                if let Err(new_err) = ocx.eq_exp(
+                    &obligation.cause,
+                    obligation.param_env,
                     is_normalized_ty_expected,
                     normalized_ty,
-                    data.term,
+                    expected_ty,
                 ) {
-                    values = Some((data, is_normalized_ty_expected, normalized_ty, data.term));
-                    err = new_err;
+                    (Some((data, is_normalized_ty_expected, normalized_ty, expected_ty)), new_err)
+                } else {
+                    (None, error.err)
                 }
-            }
+            } else {
+                (None, error.err)
+            };
 
             let msg = values
                 .and_then(|(predicate, _, normalized_ty, expected_ty)| {
-                    self.maybe_detailed_projection_msg(predicate, normalized_ty, expected_ty)
+                    self.maybe_detailed_projection_msg(
+                        predicate,
+                        normalized_ty.into(),
+                        expected_ty.into(),
+                    )
                 })
                 .unwrap_or_else(|| format!("type mismatch resolving `{}`", predicate));
             let mut diag = struct_span_err!(self.tcx.sess, obligation.cause.span, E0271, "{msg}");
 
             let secondary_span = match predicate.kind().skip_binder() {
-                ty::PredicateKind::Projection(proj) => self
+                ty::PredicateKind::Clause(ty::Clause::Projection(proj)) => self
                     .tcx
                     .opt_associated_item(proj.projection_ty.item_def_id)
                     .and_then(|trait_assoc_item| {
@@ -1677,11 +1718,11 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                 &mut diag,
                 &obligation.cause,
                 secondary_span,
-                values.map(|(_, is_normalized_ty_expected, normalized_ty, term)| {
+                values.map(|(_, is_normalized_ty_expected, normalized_ty, expected_ty)| {
                     infer::ValuePairs::Terms(ExpectedFound::new(
                         is_normalized_ty_expected,
-                        normalized_ty,
-                        term,
+                        normalized_ty.into(),
+                        expected_ty.into(),
                     ))
                 }),
                 err,
@@ -1733,7 +1774,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                 ty::Bool => Some(0),
                 ty::Char => Some(1),
                 ty::Str => Some(2),
-                ty::Adt(def, _) if tcx.is_diagnostic_item(sym::String, def.did()) => Some(2),
+                ty::Adt(def, _) if Some(def.did()) == tcx.lang_items().string() => Some(2),
                 ty::Int(..)
                 | ty::Uint(..)
                 | ty::Float(..)
@@ -1811,7 +1852,8 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         &self,
         trait_pred: ty::PolyTraitPredicate<'tcx>,
     ) -> Vec<ImplCandidate<'tcx>> {
-        self.tcx
+        let mut candidates: Vec<_> = self
+            .tcx
             .all_impls(trait_pred.def_id())
             .filter_map(|def_id| {
                 if self.tcx.impl_polarity(def_id) == ty::ImplPolarity::Negative
@@ -1827,7 +1869,14 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                 self.fuzzy_match_tys(trait_pred.skip_binder().self_ty(), imp.self_ty(), false)
                     .map(|similarity| ImplCandidate { trait_ref: imp, similarity })
             })
-            .collect()
+            .collect();
+        if candidates.iter().any(|c| matches!(c.similarity, CandidateSimilarity::Exact { .. })) {
+            // If any of the candidates is a perfect match, we don't want to show all of them.
+            // This is particularly relevant for the case of numeric types (as they all have the
+            // same cathegory).
+            candidates.retain(|c| matches!(c.similarity, CandidateSimilarity::Exact { .. }));
+        }
+        candidates
     }
 
     fn report_similar_impl_candidates(
@@ -1898,7 +1947,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         let def_id = trait_ref.def_id();
         if impl_candidates.is_empty() {
             if self.tcx.trait_is_auto(def_id)
-                || self.tcx.lang_items().items().contains(&Some(def_id))
+                || self.tcx.lang_items().iter().any(|(_, id)| id == def_id)
                 || self.tcx.get_diagnostic_name(def_id).is_some()
             {
                 // Mentioning implementers of `Copy`, `Debug` and friends is not useful.
@@ -1935,14 +1984,6 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             return report(normalized_impl_candidates, err);
         }
 
-        let normalize = |candidate| {
-            let infcx = self.tcx.infer_ctxt().build();
-            infcx
-                .at(&ObligationCause::dummy(), ty::ParamEnv::empty())
-                .normalize(candidate)
-                .map_or(candidate, |normalized| normalized.value)
-        };
-
         // Sort impl candidates so that ordering is consistent for UI tests.
         // because the ordering of `impl_candidates` may not be deterministic:
         // https://github.com/rust-lang/rust/pull/57475#issuecomment-455519507
@@ -1952,7 +1993,11 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         let mut normalized_impl_candidates_and_similarities = impl_candidates
             .into_iter()
             .map(|ImplCandidate { trait_ref, similarity }| {
-                let normalized = normalize(trait_ref);
+                // FIXME(compiler-errors): This should be using `NormalizeExt::normalize`
+                let normalized = self
+                    .at(&ObligationCause::dummy(), ty::ParamEnv::empty())
+                    .query_normalize(trait_ref)
+                    .map_or(trait_ref, |normalized| normalized.value);
                 (similarity, normalized)
             })
             .collect::<Vec<_>>();
@@ -2032,15 +2077,10 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         param_env: ty::ParamEnv<'tcx>,
         trait_ref_and_ty: ty::Binder<'tcx, (ty::TraitPredicate<'tcx>, Ty<'tcx>)>,
     ) -> PredicateObligation<'tcx> {
-        let trait_pred = trait_ref_and_ty.map_bound_ref(|(tr, new_self_ty)| ty::TraitPredicate {
-            trait_ref: ty::TraitRef {
-                substs: self.tcx.mk_substs_trait(*new_self_ty, &tr.trait_ref.substs[1..]),
-                ..tr.trait_ref
-            },
-            ..*tr
-        });
+        let trait_pred = trait_ref_and_ty
+            .map_bound(|(tr, new_self_ty)| tr.with_self_type(self.tcx, new_self_ty));
 
-        Obligation::new(ObligationCause::dummy(), param_env, trait_pred.to_predicate(self.tcx))
+        Obligation::new(self.tcx, ObligationCause::dummy(), param_env, trait_pred)
     }
 
     #[instrument(skip(self), level = "debug")]
@@ -2064,7 +2104,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
 
         let bound_predicate = predicate.kind();
         let mut err = match bound_predicate.skip_binder() {
-            ty::PredicateKind::Trait(data) => {
+            ty::PredicateKind::Clause(ty::Clause::Trait(data)) => {
                 let trait_ref = bound_predicate.rebind(data.trait_ref);
                 debug!(?trait_ref);
 
@@ -2088,7 +2128,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                 // check upstream for type errors and don't add the obligations to
                 // begin with in those cases.
                 if self.tcx.lang_items().sized_trait() == Some(trait_ref.def_id()) {
-                    if !self.is_tainted_by_errors() {
+                    if let None = self.tainted_by_errors() {
                         self.emit_inference_failure_err(
                             body_id,
                             span,
@@ -2128,21 +2168,27 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                     )
                 };
 
-                let obligation = Obligation::new(
-                    obligation.cause.clone(),
-                    obligation.param_env,
-                    trait_ref.to_poly_trait_predicate(),
-                );
-                let mut selcx = SelectionContext::with_query_mode(
-                    &self,
-                    crate::traits::TraitQueryMode::Standard,
-                );
+                let obligation = obligation.with(self.tcx, trait_ref);
+                let mut selcx = SelectionContext::new(&self);
                 match selcx.select_from_obligation(&obligation) {
-                    Err(SelectionError::Ambiguous(impls)) if impls.len() > 1 => {
-                        self.annotate_source_of_ambiguity(&mut err, &impls, predicate);
+                    Ok(None) => {
+                        let impls = ambiguity::recompute_applicable_impls(self.infcx, &obligation);
+                        let has_non_region_infer =
+                            trait_ref.skip_binder().substs.types().any(|t| !t.is_ty_infer());
+                        // It doesn't make sense to talk about applicable impls if there are more
+                        // than a handful of them.
+                        if impls.len() > 1 && impls.len() < 5 && has_non_region_infer {
+                            self.annotate_source_of_ambiguity(&mut err, &impls, predicate);
+                        } else {
+                            if self.tainted_by_errors().is_some() {
+                                err.cancel();
+                                return;
+                            }
+                            err.note(&format!("cannot satisfy `{}`", predicate));
+                        }
                     }
                     _ => {
-                        if self.is_tainted_by_errors() {
+                        if self.tainted_by_errors().is_some() {
                             err.cancel();
                             return;
                         }
@@ -2160,7 +2206,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                     if generics.params.iter().any(|p| p.name != kw::SelfUpper)
                         && !snippet.ends_with('>')
                         && !generics.has_impl_trait()
-                        && !self.tcx.fn_trait_kind_from_lang_item(def_id).is_some()
+                        && !self.tcx.is_fn_trait(def_id)
                     {
                         // FIXME: To avoid spurious suggestions in functions where type arguments
                         // where already supplied, we check the snippet to make sure it doesn't
@@ -2245,7 +2291,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                         ] = path.segments
                         && data.trait_ref.def_id == *trait_id
                         && self.tcx.trait_of_item(*item_id) == Some(*trait_id)
-                        && !self.is_tainted_by_errors()
+                        && let None = self.tainted_by_errors()
                     {
                         let (verb, noun) = match self.tcx.associated_item(item_id).kind {
                             ty::AssocKind::Const => ("refer to the", "constant"),
@@ -2314,7 +2360,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                 // with error messages.
                 if arg.references_error()
                     || self.tcx.sess.has_errors().is_some()
-                    || self.is_tainted_by_errors()
+                    || self.tainted_by_errors().is_some()
                 {
                     return;
                 }
@@ -2325,7 +2371,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             ty::PredicateKind::Subtype(data) => {
                 if data.references_error()
                     || self.tcx.sess.has_errors().is_some()
-                    || self.is_tainted_by_errors()
+                    || self.tainted_by_errors().is_some()
                 {
                     // no need to overload user in such cases
                     return;
@@ -2335,8 +2381,8 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                 assert!(a.is_ty_var() && b.is_ty_var());
                 self.emit_inference_failure_err(body_id, span, a.into(), ErrorCode::E0282, true)
             }
-            ty::PredicateKind::Projection(data) => {
-                if predicate.references_error() || self.is_tainted_by_errors() {
+            ty::PredicateKind::Clause(ty::Clause::Projection(data)) => {
+                if predicate.references_error() || self.tainted_by_errors().is_some() {
                     return;
                 }
                 let subst = data
@@ -2370,7 +2416,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             }
 
             ty::PredicateKind::ConstEvaluatable(data) => {
-                if predicate.references_error() || self.is_tainted_by_errors() {
+                if predicate.references_error() || self.tainted_by_errors().is_some() {
                     return;
                 }
                 let subst = data.walk().find(|g| g.is_non_region_infer());
@@ -2397,7 +2443,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                 }
             }
             _ => {
-                if self.tcx.sess.has_errors().is_some() || self.is_tainted_by_errors() {
+                if self.tcx.sess.has_errors().is_some() || self.tainted_by_errors().is_some() {
                     return;
                 }
                 let mut err = struct_span_err!(
@@ -2435,14 +2481,13 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                 }
             }
         }
-        let msg = format!("multiple `impl`s satisfying `{}` found", predicate);
         let mut crate_names: Vec<_> = crates.iter().map(|n| format!("`{}`", n)).collect();
         crate_names.sort();
         crate_names.dedup();
         post.sort();
         post.dedup();
 
-        if self.is_tainted_by_errors()
+        if self.tainted_by_errors().is_some()
             && (crate_names.len() == 1
                 && spans.len() == 0
                 && ["`core`", "`alloc`", "`std`"].contains(&crate_names[0].as_str())
@@ -2456,13 +2501,9 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             err.downgrade_to_delayed_bug();
             return;
         }
-        let post = if post.len() > 4 {
-            format!(
-                ":\n{}\nand {} more",
-                post.iter().map(|p| format!("- {}", p)).take(4).collect::<Vec<_>>().join("\n"),
-                post.len() - 4,
-            )
-        } else if post.len() > 1 || (post.len() == 1 && post[0].contains('\n')) {
+
+        let msg = format!("multiple `impl`s satisfying `{}` found", predicate);
+        let post = if post.len() > 1 || (post.len() == 1 && post[0].contains('\n')) {
             format!(":\n{}", post.iter().map(|p| format!("- {}", p)).collect::<Vec<_>>().join("\n"),)
         } else if post.len() == 1 {
             format!(": `{}`", post[0])
@@ -2541,24 +2582,14 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         }
 
         self.probe(|_| {
-            let mut selcx = SelectionContext::new(self);
-
             let cleaned_pred =
                 pred.fold_with(&mut ParamToVarFolder { infcx: self, var_map: Default::default() });
 
-            let cleaned_pred = super::project::normalize(
-                &mut selcx,
-                param_env,
-                ObligationCause::dummy(),
-                cleaned_pred,
-            )
-            .value;
-
-            let obligation = Obligation::new(
-                ObligationCause::dummy(),
-                param_env,
-                cleaned_pred.to_predicate(selcx.tcx()),
-            );
+            let InferOk { value: cleaned_pred, .. } =
+                self.infcx.at(&ObligationCause::dummy(), param_env).normalize(cleaned_pred);
+
+            let obligation =
+                Obligation::new(self.tcx, ObligationCause::dummy(), param_env, cleaned_pred);
 
             self.predicate_may_hold(&obligation)
         })
@@ -2586,7 +2617,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         err: &mut Diagnostic,
         obligation: &PredicateObligation<'tcx>,
     ) {
-        let ty::PredicateKind::Trait(pred) = obligation.predicate.kind().skip_binder() else { return; };
+        let ty::PredicateKind::Clause(ty::Clause::Trait(pred)) = obligation.predicate.kind().skip_binder() else { return; };
         let (ObligationCauseCode::BindingObligation(item_def_id, span)
         | ObligationCauseCode::ExprBindingObligation(item_def_id, span, ..))
             = *obligation.cause.code().peel_derives() else { return; };
@@ -2612,11 +2643,10 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         let Some(param) = generics.params.iter().find(|param| param.span == span) else {
             return;
         };
-        let param_def_id = self.tcx.hir().local_def_id(param.hir_id);
         // Check that none of the explicit trait bounds is `Sized`. Assume that an explicit
         // `Sized` bound is there intentionally and we don't need to suggest relaxing it.
         let explicitly_sized = generics
-            .bounds_for_param(param_def_id)
+            .bounds_for_param(param.def_id)
             .flat_map(|bp| bp.bounds)
             .any(|bound| bound.trait_ref().and_then(|tr| tr.trait_def_id()) == sized_trait);
         if explicitly_sized {
@@ -2639,7 +2669,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             _ => {}
         };
         // Didn't add an indirection suggestion, so add a general suggestion to relax `Sized`.
-        let (span, separator) = if let Some(s) = generics.bounds_span_for_suggestions(param_def_id)
+        let (span, separator) = if let Some(s) = generics.bounds_span_for_suggestions(param.def_id)
         {
             (s, " +")
         } else {
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs
index 5eef54c63..9bfe52764 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs
@@ -1,14 +1,22 @@
-use super::{
-    ObligationCauseCode, OnUnimplementedDirective, OnUnimplementedNote, PredicateObligation,
-};
+use super::{ObligationCauseCode, PredicateObligation};
 use crate::infer::error_reporting::TypeErrCtxt;
+use rustc_ast::{MetaItem, NestedMetaItem};
+use rustc_attr as attr;
+use rustc_data_structures::fx::FxHashMap;
+use rustc_errors::{struct_span_err, ErrorGuaranteed};
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_middle::ty::SubstsRef;
-use rustc_middle::ty::{self, GenericParamDefKind};
-use rustc_span::symbol::sym;
+use rustc_middle::ty::{self, GenericParamDefKind, TyCtxt};
+use rustc_parse_format::{ParseMode, Parser, Piece, Position};
+use rustc_span::symbol::{kw, sym, Symbol};
+use rustc_span::{Span, DUMMY_SP};
 use std::iter;
 
+use crate::errors::{
+    EmptyOnClauseInOnUnimplemented, InvalidOnClauseInOnUnimplemented, NoValueInOnUnimplemented,
+};
+
 use super::InferCtxtPrivExt;
 
 pub trait TypeErrCtxtExt<'tcx> {
@@ -276,3 +284,383 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         }
     }
 }
+
+#[derive(Clone, Debug)]
+pub struct OnUnimplementedFormatString(Symbol);
+
+#[derive(Debug)]
+pub struct OnUnimplementedDirective {
+    pub condition: Option<MetaItem>,
+    pub subcommands: Vec<OnUnimplementedDirective>,
+    pub message: Option<OnUnimplementedFormatString>,
+    pub label: Option<OnUnimplementedFormatString>,
+    pub note: Option<OnUnimplementedFormatString>,
+    pub parent_label: Option<OnUnimplementedFormatString>,
+    pub append_const_msg: Option<Option<Symbol>>,
+}
+
+/// For the `#[rustc_on_unimplemented]` attribute
+#[derive(Default)]
+pub struct OnUnimplementedNote {
+    pub message: Option<String>,
+    pub label: Option<String>,
+    pub note: Option<String>,
+    pub parent_label: Option<String>,
+    /// Append a message for `~const Trait` errors. `None` means not requested and
+    /// should fallback to a generic message, `Some(None)` suggests using the default
+    /// appended message, `Some(Some(s))` suggests use the `s` message instead of the
+    /// default one..
+    pub append_const_msg: Option<Option<Symbol>>,
+}
+
+impl<'tcx> OnUnimplementedDirective {
+    fn parse(
+        tcx: TyCtxt<'tcx>,
+        item_def_id: DefId,
+        items: &[NestedMetaItem],
+        span: Span,
+        is_root: bool,
+    ) -> Result<Self, ErrorGuaranteed> {
+        let mut errored = None;
+        let mut item_iter = items.iter();
+
+        let parse_value = |value_str| {
+            OnUnimplementedFormatString::try_parse(tcx, item_def_id, value_str, span).map(Some)
+        };
+
+        let condition = if is_root {
+            None
+        } else {
+            let cond = item_iter
+                .next()
+                .ok_or_else(|| tcx.sess.emit_err(EmptyOnClauseInOnUnimplemented { span }))?
+                .meta_item()
+                .ok_or_else(|| tcx.sess.emit_err(InvalidOnClauseInOnUnimplemented { span }))?;
+            attr::eval_condition(cond, &tcx.sess.parse_sess, Some(tcx.features()), &mut |cfg| {
+                if let Some(value) = cfg.value && let Err(guar) = parse_value(value) {
+                    errored = Some(guar);
+                }
+                true
+            });
+            Some(cond.clone())
+        };
+
+        let mut message = None;
+        let mut label = None;
+        let mut note = None;
+        let mut parent_label = None;
+        let mut subcommands = vec![];
+        let mut append_const_msg = None;
+
+        for item in item_iter {
+            if item.has_name(sym::message) && message.is_none() {
+                if let Some(message_) = item.value_str() {
+                    message = parse_value(message_)?;
+                    continue;
+                }
+            } else if item.has_name(sym::label) && label.is_none() {
+                if let Some(label_) = item.value_str() {
+                    label = parse_value(label_)?;
+                    continue;
+                }
+            } else if item.has_name(sym::note) && note.is_none() {
+                if let Some(note_) = item.value_str() {
+                    note = parse_value(note_)?;
+                    continue;
+                }
+            } else if item.has_name(sym::parent_label) && parent_label.is_none() {
+                if let Some(parent_label_) = item.value_str() {
+                    parent_label = parse_value(parent_label_)?;
+                    continue;
+                }
+            } else if item.has_name(sym::on)
+                && is_root
+                && message.is_none()
+                && label.is_none()
+                && note.is_none()
+            {
+                if let Some(items) = item.meta_item_list() {
+                    match Self::parse(tcx, item_def_id, &items, item.span(), false) {
+                        Ok(subcommand) => subcommands.push(subcommand),
+                        Err(reported) => errored = Some(reported),
+                    };
+                    continue;
+                }
+            } else if item.has_name(sym::append_const_msg) && append_const_msg.is_none() {
+                if let Some(msg) = item.value_str() {
+                    append_const_msg = Some(Some(msg));
+                    continue;
+                } else if item.is_word() {
+                    append_const_msg = Some(None);
+                    continue;
+                }
+            }
+
+            // nothing found
+            tcx.sess.emit_err(NoValueInOnUnimplemented { span: item.span() });
+        }
+
+        if let Some(reported) = errored {
+            Err(reported)
+        } else {
+            Ok(OnUnimplementedDirective {
+                condition,
+                subcommands,
+                message,
+                label,
+                note,
+                parent_label,
+                append_const_msg,
+            })
+        }
+    }
+
+    pub fn of_item(tcx: TyCtxt<'tcx>, item_def_id: DefId) -> Result<Option<Self>, ErrorGuaranteed> {
+        let Some(attr) = tcx.get_attr(item_def_id, sym::rustc_on_unimplemented) else {
+            return Ok(None);
+        };
+
+        let result = if let Some(items) = attr.meta_item_list() {
+            Self::parse(tcx, item_def_id, &items, attr.span, true).map(Some)
+        } else if let Some(value) = attr.value_str() {
+            Ok(Some(OnUnimplementedDirective {
+                condition: None,
+                message: None,
+                subcommands: vec![],
+                label: Some(OnUnimplementedFormatString::try_parse(
+                    tcx,
+                    item_def_id,
+                    value,
+                    attr.span,
+                )?),
+                note: None,
+                parent_label: None,
+                append_const_msg: None,
+            }))
+        } else {
+            let reported =
+                tcx.sess.delay_span_bug(DUMMY_SP, "of_item: neither meta_item_list nor value_str");
+            return Err(reported);
+        };
+        debug!("of_item({:?}) = {:?}", item_def_id, result);
+        result
+    }
+
+    pub fn evaluate(
+        &self,
+        tcx: TyCtxt<'tcx>,
+        trait_ref: ty::TraitRef<'tcx>,
+        options: &[(Symbol, Option<String>)],
+    ) -> OnUnimplementedNote {
+        let mut message = None;
+        let mut label = None;
+        let mut note = None;
+        let mut parent_label = None;
+        let mut append_const_msg = None;
+        info!("evaluate({:?}, trait_ref={:?}, options={:?})", self, trait_ref, options);
+
+        let options_map: FxHashMap<Symbol, String> =
+            options.iter().filter_map(|(k, v)| v.clone().map(|v| (*k, v))).collect();
+
+        for command in self.subcommands.iter().chain(Some(self)).rev() {
+            if let Some(ref condition) = command.condition && !attr::eval_condition(
+                condition,
+                &tcx.sess.parse_sess,
+                Some(tcx.features()),
+                &mut |cfg| {
+                    let value = cfg.value.map(|v| {
+                        OnUnimplementedFormatString(v).format(tcx, trait_ref, &options_map)
+                    });
+
+                    options.contains(&(cfg.name, value))
+                },
+            ) {
+                debug!("evaluate: skipping {:?} due to condition", command);
+                continue;
+            }
+            debug!("evaluate: {:?} succeeded", command);
+            if let Some(ref message_) = command.message {
+                message = Some(message_.clone());
+            }
+
+            if let Some(ref label_) = command.label {
+                label = Some(label_.clone());
+            }
+
+            if let Some(ref note_) = command.note {
+                note = Some(note_.clone());
+            }
+
+            if let Some(ref parent_label_) = command.parent_label {
+                parent_label = Some(parent_label_.clone());
+            }
+
+            append_const_msg = command.append_const_msg;
+        }
+
+        OnUnimplementedNote {
+            label: label.map(|l| l.format(tcx, trait_ref, &options_map)),
+            message: message.map(|m| m.format(tcx, trait_ref, &options_map)),
+            note: note.map(|n| n.format(tcx, trait_ref, &options_map)),
+            parent_label: parent_label.map(|e_s| e_s.format(tcx, trait_ref, &options_map)),
+            append_const_msg,
+        }
+    }
+}
+
+impl<'tcx> OnUnimplementedFormatString {
+    fn try_parse(
+        tcx: TyCtxt<'tcx>,
+        item_def_id: DefId,
+        from: Symbol,
+        err_sp: Span,
+    ) -> Result<Self, ErrorGuaranteed> {
+        let result = OnUnimplementedFormatString(from);
+        result.verify(tcx, item_def_id, err_sp)?;
+        Ok(result)
+    }
+
+    fn verify(
+        &self,
+        tcx: TyCtxt<'tcx>,
+        item_def_id: DefId,
+        span: Span,
+    ) -> Result<(), ErrorGuaranteed> {
+        let trait_def_id = if tcx.is_trait(item_def_id) {
+            item_def_id
+        } else {
+            tcx.trait_id_of_impl(item_def_id)
+                .expect("expected `on_unimplemented` to correspond to a trait")
+        };
+        let trait_name = tcx.item_name(trait_def_id);
+        let generics = tcx.generics_of(item_def_id);
+        let s = self.0.as_str();
+        let parser = Parser::new(s, None, None, false, ParseMode::Format);
+        let mut result = Ok(());
+        for token in parser {
+            match token {
+                Piece::String(_) => (), // Normal string, no need to check it
+                Piece::NextArgument(a) => match a.position {
+                    Position::ArgumentNamed(s) => {
+                        match Symbol::intern(s) {
+                            // `{Self}` is allowed
+                            kw::SelfUpper => (),
+                            // `{ThisTraitsName}` is allowed
+                            s if s == trait_name => (),
+                            // `{from_method}` is allowed
+                            sym::from_method => (),
+                            // `{from_desugaring}` is allowed
+                            sym::from_desugaring => (),
+                            // `{ItemContext}` is allowed
+                            sym::ItemContext => (),
+                            // `{integral}` and `{integer}` and `{float}` are allowed
+                            sym::integral | sym::integer_ | sym::float => (),
+                            // So is `{A}` if A is a type parameter
+                            s => match generics.params.iter().find(|param| param.name == s) {
+                                Some(_) => (),
+                                None => {
+                                    let reported = struct_span_err!(
+                                        tcx.sess,
+                                        span,
+                                        E0230,
+                                        "there is no parameter `{}` on {}",
+                                        s,
+                                        if trait_def_id == item_def_id {
+                                            format!("trait `{}`", trait_name)
+                                        } else {
+                                            "impl".to_string()
+                                        }
+                                    )
+                                    .emit();
+                                    result = Err(reported);
+                                }
+                            },
+                        }
+                    }
+                    // `{:1}` and `{}` are not to be used
+                    Position::ArgumentIs(..) | Position::ArgumentImplicitlyIs(_) => {
+                        let reported = struct_span_err!(
+                            tcx.sess,
+                            span,
+                            E0231,
+                            "only named substitution parameters are allowed"
+                        )
+                        .emit();
+                        result = Err(reported);
+                    }
+                },
+            }
+        }
+
+        result
+    }
+
+    pub fn format(
+        &self,
+        tcx: TyCtxt<'tcx>,
+        trait_ref: ty::TraitRef<'tcx>,
+        options: &FxHashMap<Symbol, String>,
+    ) -> String {
+        let name = tcx.item_name(trait_ref.def_id);
+        let trait_str = tcx.def_path_str(trait_ref.def_id);
+        let generics = tcx.generics_of(trait_ref.def_id);
+        let generic_map = generics
+            .params
+            .iter()
+            .filter_map(|param| {
+                let value = match param.kind {
+                    GenericParamDefKind::Type { .. } | GenericParamDefKind::Const { .. } => {
+                        trait_ref.substs[param.index as usize].to_string()
+                    }
+                    GenericParamDefKind::Lifetime => return None,
+                };
+                let name = param.name;
+                Some((name, value))
+            })
+            .collect::<FxHashMap<Symbol, String>>();
+        let empty_string = String::new();
+
+        let s = self.0.as_str();
+        let parser = Parser::new(s, None, None, false, ParseMode::Format);
+        let item_context = (options.get(&sym::ItemContext)).unwrap_or(&empty_string);
+        parser
+            .map(|p| match p {
+                Piece::String(s) => s,
+                Piece::NextArgument(a) => match a.position {
+                    Position::ArgumentNamed(s) => {
+                        let s = Symbol::intern(s);
+                        match generic_map.get(&s) {
+                            Some(val) => val,
+                            None if s == name => &trait_str,
+                            None => {
+                                if let Some(val) = options.get(&s) {
+                                    val
+                                } else if s == sym::from_desugaring || s == sym::from_method {
+                                    // don't break messages using these two arguments incorrectly
+                                    &empty_string
+                                } else if s == sym::ItemContext {
+                                    &item_context
+                                } else if s == sym::integral {
+                                    "{integral}"
+                                } else if s == sym::integer_ {
+                                    "{integer}"
+                                } else if s == sym::float {
+                                    "{float}"
+                                } else {
+                                    bug!(
+                                        "broken on_unimplemented {:?} for {:?}: \
+                                      no argument matching {:?}",
+                                        self.0,
+                                        trait_ref,
+                                        s
+                                    )
+                                }
+                            }
+                        }
+                    }
+                    _ => bug!("broken on_unimplemented {:?} - bad format arg", self.0),
+                },
+            })
+            .collect()
+    }
+}
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
index 8c41d9d24..6ea54b625 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
@@ -1,11 +1,8 @@
-use super::{
-    DefIdOrName, Obligation, ObligationCause, ObligationCauseCode, PredicateObligation,
-    SelectionContext,
-};
+use super::{DefIdOrName, Obligation, ObligationCause, ObligationCauseCode, PredicateObligation};
 
 use crate::autoderef::Autoderef;
 use crate::infer::InferCtxt;
-use crate::traits::normalize_to;
+use crate::traits::NormalizeExt;
 
 use hir::def::CtorOf;
 use hir::HirId;
@@ -23,7 +20,7 @@ use rustc_hir::lang_items::LangItem;
 use rustc_hir::{AsyncGeneratorKind, GeneratorKind, Node};
 use rustc_infer::infer::error_reporting::TypeErrCtxt;
 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
-use rustc_infer::infer::LateBoundRegionConversionTime;
+use rustc_infer::infer::{InferOk, LateBoundRegionConversionTime};
 use rustc_middle::hir::map;
 use rustc_middle::ty::{
     self, suggest_arbitrary_trait_bound, suggest_constraining_type_param, AdtKind, DefIdTree,
@@ -44,7 +41,7 @@ use rustc_middle::ty::print::with_no_trimmed_paths;
 #[derive(Debug)]
 pub enum GeneratorInteriorOrUpvar {
     // span of interior type
-    Interior(Span),
+    Interior(Span, Option<(Option<Span>, Span, Option<hir::HirId>, Option<Span>)>),
     // span of upvar
     Upvar(Span),
 }
@@ -283,7 +280,6 @@ pub trait TypeErrCtxtExt<'tcx> {
         &self,
         err: &mut Diagnostic,
         interior_or_upvar_span: GeneratorInteriorOrUpvar,
-        interior_extra_info: Option<(Option<Span>, Span, Option<hir::HirId>, Option<Span>)>,
         is_async: bool,
         outer_generator: Option<DefId>,
         trait_pred: ty::TraitPredicate<'tcx>,
@@ -302,7 +298,7 @@ pub trait TypeErrCtxtExt<'tcx> {
         obligated_types: &mut Vec<Ty<'tcx>>,
         seen_requirements: &mut FxHashSet<DefId>,
     ) where
-        T: fmt::Display;
+        T: fmt::Display + ToPredicate<'tcx>;
 
     /// Suggest to await before try: future? => future.await?
     fn suggest_await_before_try(
@@ -335,7 +331,7 @@ pub trait TypeErrCtxtExt<'tcx> {
     );
 }
 
-fn predicate_constraint(generics: &hir::Generics<'_>, pred: String) -> (Span, String) {
+fn predicate_constraint(generics: &hir::Generics<'_>, pred: ty::Predicate<'_>) -> (Span, String) {
     (
         generics.tail_span_for_predicate_suggestion(),
         format!("{} {}", generics.add_where_or_trailing_comma(), pred),
@@ -417,7 +413,7 @@ fn suggest_restriction<'tcx>(
             },
             // `fn foo(t: impl Trait)`
             //                       ^ suggest `where <T as Trait>::A: Bound`
-            predicate_constraint(hir_generics, trait_pred.to_predicate(tcx).to_string()),
+            predicate_constraint(hir_generics, trait_pred.to_predicate(tcx)),
         ];
         sugg.extend(ty_spans.into_iter().map(|s| (s, type_param_name.to_string())));
 
@@ -441,9 +437,7 @@ fn suggest_restriction<'tcx>(
                 .find(|p| !matches!(p.kind, hir::GenericParamKind::Type { synthetic: true, .. })),
             super_traits,
         ) {
-            (_, None) => {
-                predicate_constraint(hir_generics, trait_pred.to_predicate(tcx).to_string())
-            }
+            (_, None) => predicate_constraint(hir_generics, trait_pred.to_predicate(tcx)),
             (None, Some((ident, []))) => (
                 ident.span.shrink_to_hi(),
                 format!(": {}", trait_pred.print_modifiers_and_trait_path()),
@@ -714,7 +708,6 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                     obligation.cause.body_id,
                     span,
                     base_ty,
-                    span,
                 );
                 if let Some(steps) = autoderef.find_map(|(ty, steps)| {
                     // Re-add the `&`
@@ -814,7 +807,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         err: &mut Diagnostic,
         trait_pred: ty::PolyTraitPredicate<'tcx>,
     ) -> bool {
-        if let ty::PredicateKind::Trait(trait_pred) = obligation.predicate.kind().skip_binder()
+        if let ty::PredicateKind::Clause(ty::Clause::Trait(trait_pred)) = obligation.predicate.kind().skip_binder()
             && Some(trait_pred.def_id()) == self.tcx.lang_items().sized_trait()
         {
             // Don't suggest calling to turn an unsized type into a sized type
@@ -843,7 +836,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             }
             ty::Opaque(def_id, substs) => {
                 self.tcx.bound_item_bounds(def_id).subst(self.tcx, substs).iter().find_map(|pred| {
-                    if let ty::PredicateKind::Projection(proj) = pred.kind().skip_binder()
+                    if let ty::PredicateKind::Clause(ty::Clause::Projection(proj)) = pred.kind().skip_binder()
                     && Some(proj.projection_ty.item_def_id) == self.tcx.lang_items().fn_once_output()
                     // args tuple will always be substs[1]
                     && let ty::Tuple(args) = proj.projection_ty.substs.type_at(1).kind()
@@ -877,7 +870,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             }
             ty::Param(_) => {
                 obligation.param_env.caller_bounds().iter().find_map(|pred| {
-                    if let ty::PredicateKind::Projection(proj) = pred.kind().skip_binder()
+                    if let ty::PredicateKind::Clause(ty::Clause::Projection(proj)) = pred.kind().skip_binder()
                     && Some(proj.projection_ty.item_def_id) == self.tcx.lang_items().fn_once_output()
                     && proj.projection_ty.self_ty() == found
                     // args tuple will always be substs[1]
@@ -1019,7 +1012,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         let mut never_suggest_borrow: Vec<_> =
             [LangItem::Copy, LangItem::Clone, LangItem::Unpin, LangItem::Sized]
                 .iter()
-                .filter_map(|lang_item| self.tcx.lang_items().require(*lang_item).ok())
+                .filter_map(|lang_item| self.tcx.lang_items().get(*lang_item))
                 .collect();
 
         if let Some(def_id) = self.tcx.get_diagnostic_item(sym::Send) {
@@ -1063,7 +1056,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                 {
                     (
                         mk_result(old_pred.map_bound(|trait_pred| (trait_pred, *ty))),
-                        matches!(mutability, hir::Mutability::Mut),
+                        mutability.is_mut(),
                     )
                 } else {
                     (false, false)
@@ -1117,7 +1110,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                         err.span_suggestions(
                             span.shrink_to_lo(),
                             "consider borrowing here",
-                            ["&".to_string(), "&mut ".to_string()].into_iter(),
+                            ["&".to_string(), "&mut ".to_string()],
                             Applicability::MaybeIncorrect,
                         );
                     } else {
@@ -1164,7 +1157,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
 
         for predicate in predicates.iter() {
             if !self.predicate_must_hold_modulo_regions(
-                &obligation.with(predicate.with_self_ty(self.tcx, self_ref_ty)),
+                &obligation.with(self.tcx, predicate.with_self_ty(self.tcx, self_ref_ty)),
             ) {
                 return;
             }
@@ -1260,7 +1253,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                     );
                     // FIXME: account for associated `async fn`s.
                     if let hir::Expr { span, kind: hir::ExprKind::Call(base, _), .. } = expr {
-                        if let ty::PredicateKind::Trait(pred) =
+                        if let ty::PredicateKind::Clause(ty::Clause::Trait(pred)) =
                             obligation.predicate.kind().skip_binder()
                         {
                             err.span_label(
@@ -1353,7 +1346,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                         .sess
                         .source_map()
                         .span_take_while(span, |c| c.is_whitespace() || *c == '&');
-                    if points_at_arg && mutability == hir::Mutability::Not && refs_number > 0 {
+                    if points_at_arg && mutability.is_not() && refs_number > 0 {
                         err.span_suggestion_verbose(
                             sp,
                             "consider changing this borrow's mutability",
@@ -1525,7 +1518,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                         let self_ty_satisfies_dyn_predicates = |self_ty| {
                             predicates.iter().all(|predicate| {
                                 let pred = predicate.with_self_ty(self.tcx, self_ty);
-                                let obl = Obligation::new(cause.clone(), param_env, pred);
+                                let obl = Obligation::new(self.tcx, cause.clone(), param_env, pred);
                                 self.predicate_may_hold(&obl)
                             })
                         };
@@ -1688,9 +1681,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         ) -> Ty<'tcx> {
             let inputs = trait_ref.skip_binder().substs.type_at(1);
             let sig = match inputs.kind() {
-                ty::Tuple(inputs)
-                    if infcx.tcx.fn_trait_kind_from_lang_item(trait_ref.def_id()).is_some() =>
-                {
+                ty::Tuple(inputs) if infcx.tcx.is_fn_trait(trait_ref.def_id()) => {
                     infcx.tcx.mk_fn_sig(
                         inputs.iter(),
                         infcx.next_ty_var(TypeVariableOrigin {
@@ -1760,8 +1751,8 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         if let ObligationCauseCode::ExprBindingObligation(def_id, _, _, idx) = cause
             && let predicates = self.tcx.predicates_of(def_id).instantiate_identity(self.tcx)
             && let Some(pred) = predicates.predicates.get(*idx)
-            && let ty::PredicateKind::Trait(trait_pred) = pred.kind().skip_binder()
-            && ty::ClosureKind::from_def_id(self.tcx, trait_pred.def_id()).is_some()
+            && let ty::PredicateKind::Clause(ty::Clause::Trait(trait_pred)) = pred.kind().skip_binder()
+            && self.tcx.is_fn_trait(trait_pred.def_id())
         {
             let expected_self =
                 self.tcx.anonymize_late_bound_regions(pred.kind().rebind(trait_pred.self_ty()));
@@ -1774,9 +1765,8 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             let other_pred = std::iter::zip(&predicates.predicates, &predicates.spans)
                 .enumerate()
                 .find(|(other_idx, (pred, _))| match pred.kind().skip_binder() {
-                    ty::PredicateKind::Trait(trait_pred)
-                        if ty::ClosureKind::from_def_id(self.tcx, trait_pred.def_id())
-                            .is_some()
+                    ty::PredicateKind::Clause(ty::Clause::Trait(trait_pred))
+                        if self.tcx.is_fn_trait(trait_pred.def_id())
                             && other_idx != idx
                             // Make sure that the self type matches
                             // (i.e. constraining this closure)
@@ -1890,13 +1880,9 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         //
         // - `BuiltinDerivedObligation` with a generator witness (B)
         // - `BuiltinDerivedObligation` with a generator (B)
-        // - `BuiltinDerivedObligation` with `std::future::GenFuture` (B)
-        // - `BuiltinDerivedObligation` with `impl std::future::Future` (B)
         // - `BuiltinDerivedObligation` with `impl std::future::Future` (B)
         // - `BuiltinDerivedObligation` with a generator witness (A)
         // - `BuiltinDerivedObligation` with a generator (A)
-        // - `BuiltinDerivedObligation` with `std::future::GenFuture` (A)
-        // - `BuiltinDerivedObligation` with `impl std::future::Future` (A)
         // - `BuiltinDerivedObligation` with `impl std::future::Future` (A)
         // - `BindingObligation` with `impl_send (Send requirement)
         //
@@ -1905,7 +1891,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         // bound was introduced. At least one generator should be present for this diagnostic to be
         // modified.
         let (mut trait_ref, mut target_ty) = match obligation.predicate.kind().skip_binder() {
-            ty::PredicateKind::Trait(p) => (Some(p), Some(p.self_ty())),
+            ty::PredicateKind::Clause(ty::Clause::Trait(p)) => (Some(p), Some(p.self_ty())),
             _ => (None, None),
         };
         let mut generator = None;
@@ -2004,17 +1990,6 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             .as_local()
             .and_then(|def_id| hir.maybe_body_owned_by(def_id))
             .map(|body_id| hir.body(body_id));
-        let is_async = match generator_did.as_local() {
-            Some(_) => generator_body
-                .and_then(|body| body.generator_kind())
-                .map(|generator_kind| matches!(generator_kind, hir::GeneratorKind::Async(..)))
-                .unwrap_or(false),
-            None => self
-                .tcx
-                .generator_kind(generator_did)
-                .map(|generator_kind| matches!(generator_kind, hir::GeneratorKind::Async(..)))
-                .unwrap_or(false),
-        };
         let mut visitor = AwaitsVisitor::default();
         if let Some(body) = generator_body {
             visitor.visit_body(body);
@@ -2044,61 +2019,61 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             eq
         };
 
-        let mut interior_or_upvar_span = None;
-        let mut interior_extra_info = None;
-
         // Get the typeck results from the infcx if the generator is the function we are currently
         // type-checking; otherwise, get them by performing a query.  This is needed to avoid
         // cycles. If we can't use resolved types because the generator comes from another crate,
         // we still provide a targeted error but without all the relevant spans.
-        let generator_data: Option<GeneratorData<'tcx, '_>> = match &self.typeck_results {
-            Some(t) if t.hir_owner.to_def_id() == generator_did_root => {
-                Some(GeneratorData::Local(&t))
-            }
+        let generator_data = match &self.typeck_results {
+            Some(t) if t.hir_owner.to_def_id() == generator_did_root => GeneratorData::Local(&t),
             _ if generator_did.is_local() => {
-                Some(GeneratorData::Local(self.tcx.typeck(generator_did.expect_local())))
+                GeneratorData::Local(self.tcx.typeck(generator_did.expect_local()))
             }
-            _ => self
-                .tcx
-                .generator_diagnostic_data(generator_did)
-                .as_ref()
-                .map(|generator_diag_data| GeneratorData::Foreign(generator_diag_data)),
+            _ if let Some(generator_diag_data) = self.tcx.generator_diagnostic_data(generator_did) => {
+                GeneratorData::Foreign(generator_diag_data)
+            }
+            _ => return false,
         };
 
-        if let Some(generator_data) = generator_data.as_ref() {
-            interior_or_upvar_span =
-                generator_data.try_get_upvar_span(&self, generator_did, ty_matches);
+        let mut interior_or_upvar_span = None;
 
-            // The generator interior types share the same binders
-            if let Some(cause) =
-                generator_data.get_generator_interior_types().skip_binder().iter().find(
-                    |ty::GeneratorInteriorTypeCause { ty, .. }| {
-                        ty_matches(generator_data.get_generator_interior_types().rebind(*ty))
-                    },
-                )
-            {
-                let from_awaited_ty = generator_data.get_from_await_ty(visitor, hir, ty_matches);
-                let ty::GeneratorInteriorTypeCause { span, scope_span, yield_span, expr, .. } =
-                    cause;
+        let from_awaited_ty = generator_data.get_from_await_ty(visitor, hir, ty_matches);
+        debug!(?from_awaited_ty);
 
-                interior_or_upvar_span = Some(GeneratorInteriorOrUpvar::Interior(*span));
-                interior_extra_info = Some((*scope_span, *yield_span, *expr, from_awaited_ty));
-            }
+        // The generator interior types share the same binders
+        if let Some(cause) =
+            generator_data.get_generator_interior_types().skip_binder().iter().find(
+                |ty::GeneratorInteriorTypeCause { ty, .. }| {
+                    ty_matches(generator_data.get_generator_interior_types().rebind(*ty))
+                },
+            )
+        {
+            let ty::GeneratorInteriorTypeCause { span, scope_span, yield_span, expr, .. } = cause;
 
-            if interior_or_upvar_span.is_none() && generator_data.is_foreign() {
-                interior_or_upvar_span = Some(GeneratorInteriorOrUpvar::Interior(span));
-            }
+            interior_or_upvar_span = Some(GeneratorInteriorOrUpvar::Interior(
+                *span,
+                Some((*scope_span, *yield_span, *expr, from_awaited_ty)),
+            ));
         }
 
+        if interior_or_upvar_span.is_none() {
+            interior_or_upvar_span =
+                generator_data.try_get_upvar_span(&self, generator_did, ty_matches);
+        }
+
+        if interior_or_upvar_span.is_none() && generator_data.is_foreign() {
+            interior_or_upvar_span = Some(GeneratorInteriorOrUpvar::Interior(span, None));
+        }
+
+        debug!(?interior_or_upvar_span);
         if let Some(interior_or_upvar_span) = interior_or_upvar_span {
-            let typeck_results = generator_data.and_then(|generator_data| match generator_data {
+            let is_async = self.tcx.generator_is_async(generator_did);
+            let typeck_results = match generator_data {
                 GeneratorData::Local(typeck_results) => Some(typeck_results),
                 GeneratorData::Foreign(_) => None,
-            });
+            };
             self.note_obligation_cause_for_async_await(
                 err,
                 interior_or_upvar_span,
-                interior_extra_info,
                 is_async,
                 outer_generator,
                 trait_ref,
@@ -2120,7 +2095,6 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         &self,
         err: &mut Diagnostic,
         interior_or_upvar_span: GeneratorInteriorOrUpvar,
-        interior_extra_info: Option<(Option<Span>, Span, Option<hir::HirId>, Option<Span>)>,
         is_async: bool,
         outer_generator: Option<DefId>,
         trait_pred: ty::TraitPredicate<'tcx>,
@@ -2242,7 +2216,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             }
         };
         match interior_or_upvar_span {
-            GeneratorInteriorOrUpvar::Interior(interior_span) => {
+            GeneratorInteriorOrUpvar::Interior(interior_span, interior_extra_info) => {
                 if let Some((scope_span, yield_span, expr, from_awaited_ty)) = interior_extra_info {
                     if let Some(await_span) = from_awaited_ty {
                         // The type causing this obligation is one being awaited at await_span.
@@ -2379,7 +2353,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         obligated_types: &mut Vec<Ty<'tcx>>,
         seen_requirements: &mut FxHashSet<DefId>,
     ) where
-        T: fmt::Display,
+        T: fmt::Display + ToPredicate<'tcx>,
     {
         let tcx = self.tcx;
         match *cause_code {
@@ -2407,7 +2381,8 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             | ObligationCauseCode::CheckAssociatedTypeBounds { .. }
             | ObligationCauseCode::LetElse
             | ObligationCauseCode::BinOp { .. }
-            | ObligationCauseCode::AscribeUserTypeProvePredicate(..) => {}
+            | ObligationCauseCode::AscribeUserTypeProvePredicate(..)
+            | ObligationCauseCode::RustCall => {}
             ObligationCauseCode::SliceOrArrayElem => {
                 err.note("slice and array elements must have `Sized` type");
             }
@@ -2445,12 +2420,12 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                             (Ok(l), Ok(r)) => l.line == r.line,
                             _ => true,
                         };
-                    if !ident.span.overlaps(span) && !same_line {
+                    if !ident.span.is_dummy() && !ident.span.overlaps(span) && !same_line {
                         multispan.push_span_label(ident.span, "required by a bound in this");
                     }
                 }
                 let descr = format!("required by a bound in `{}`", item_name);
-                if span != DUMMY_SP {
+                if !span.is_dummy() {
                     let msg = format!("required by this bound in `{}`", item_name);
                     multispan.push_span_label(span, msg);
                     err.span_note(multispan, &descr);
@@ -2636,30 +2611,24 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                     }
                 };
 
-                let from_generator = tcx.lang_items().from_generator_fn().unwrap();
+                let identity_future = tcx.require_lang_item(LangItem::IdentityFuture, None);
 
                 // Don't print the tuple of capture types
                 'print: {
                     if !is_upvar_tys_infer_tuple {
                         let msg = format!("required because it appears within the type `{}`", ty);
                         match ty.kind() {
-                            ty::Adt(def, _) => {
-                                // `gen_future` is used in all async functions; it doesn't add any additional info.
-                                if self.tcx.is_diagnostic_item(sym::gen_future, def.did()) {
-                                    break 'print;
-                                }
-                                match self.tcx.opt_item_ident(def.did()) {
-                                    Some(ident) => err.span_note(ident.span, &msg),
-                                    None => err.note(&msg),
-                                }
-                            }
+                            ty::Adt(def, _) => match self.tcx.opt_item_ident(def.did()) {
+                                Some(ident) => err.span_note(ident.span, &msg),
+                                None => err.note(&msg),
+                            },
                             ty::Opaque(def_id, _) => {
-                                // Avoid printing the future from `core::future::from_generator`, it's not helpful
-                                if tcx.parent(*def_id) == from_generator {
+                                // Avoid printing the future from `core::future::identity_future`, it's not helpful
+                                if tcx.parent(*def_id) == identity_future {
                                     break 'print;
                                 }
 
-                                // If the previous type is `from_generator`, this is the future generated by the body of an async function.
+                                // If the previous type is `identity_future`, this is the future generated by the body of an async function.
                                 // Avoid printing it twice (it was already printed in the `ty::Generator` arm below).
                                 let is_future = tcx.ty_is_opaque_future(ty);
                                 debug!(
@@ -2669,8 +2638,8 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                                 );
                                 if is_future
                                     && obligated_types.last().map_or(false, |ty| match ty.kind() {
-                                        ty::Opaque(last_def_id, _) => {
-                                            tcx.parent(*last_def_id) == from_generator
+                                        ty::Generator(last_def_id, ..) => {
+                                            tcx.generator_is_async(*last_def_id)
                                         }
                                         _ => false,
                                     })
@@ -2696,7 +2665,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                                 let sp = self.tcx.def_span(def_id);
 
                                 // Special-case this to say "async block" instead of `[static generator]`.
-                                let kind = tcx.generator_kind(def_id).unwrap();
+                                let kind = tcx.generator_kind(def_id).unwrap().descr();
                                 err.span_note(
                                     sp,
                                     &format!("required because it's used within this {}", kind),
@@ -2713,7 +2682,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
 
                 obligated_types.push(ty);
 
-                let parent_predicate = parent_trait_ref.to_predicate(tcx);
+                let parent_predicate = parent_trait_ref;
                 if !self.is_recursive_obligation(obligated_types, &data.parent_code) {
                     // #74711: avoid a stack overflow
                     ensure_sufficient_stack(|| {
@@ -2744,9 +2713,10 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                     self.resolve_vars_if_possible(data.derived.parent_trait_pred);
                 parent_trait_pred.remap_constness_diag(param_env);
                 let parent_def_id = parent_trait_pred.def_id();
+                let (self_ty, file) =
+                    self.tcx.short_ty_string(parent_trait_pred.skip_binder().self_ty());
                 let msg = format!(
-                    "required for `{}` to implement `{}`",
-                    parent_trait_pred.skip_binder().self_ty(),
+                    "required for `{self_ty}` to implement `{}`",
                     parent_trait_pred.print_modifiers_and_trait_path()
                 );
                 let mut is_auto_trait = false;
@@ -2775,7 +2745,13 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                     _ => err.note(&msg),
                 };
 
-                let mut parent_predicate = parent_trait_pred.to_predicate(tcx);
+                if let Some(file) = file {
+                    err.note(&format!(
+                        "the full type name has been written to '{}'",
+                        file.display(),
+                    ));
+                }
+                let mut parent_predicate = parent_trait_pred;
                 let mut data = &data.derived;
                 let mut count = 0;
                 seen_requirements.insert(parent_def_id);
@@ -2815,11 +2791,18 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                         count,
                         pluralize!(count)
                     ));
+                    let (self_ty, file) =
+                        self.tcx.short_ty_string(parent_trait_pred.skip_binder().self_ty());
                     err.note(&format!(
-                        "required for `{}` to implement `{}`",
-                        parent_trait_pred.skip_binder().self_ty(),
+                        "required for `{self_ty}` to implement `{}`",
                         parent_trait_pred.print_modifiers_and_trait_path()
                     ));
+                    if let Some(file) = file {
+                        err.note(&format!(
+                            "the full type name has been written to '{}'",
+                            file.display(),
+                        ));
+                    }
                 }
                 // #74711: avoid a stack overflow
                 ensure_sufficient_stack(|| {
@@ -2835,7 +2818,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             }
             ObligationCauseCode::DerivedObligation(ref data) => {
                 let parent_trait_ref = self.resolve_vars_if_possible(data.parent_trait_pred);
-                let parent_predicate = parent_trait_ref.to_predicate(tcx);
+                let parent_predicate = parent_trait_ref;
                 // #74711: avoid a stack overflow
                 ensure_sufficient_stack(|| {
                     self.note_obligation_cause_code(
@@ -2968,8 +2951,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                 let self_ty = self.resolve_vars_if_possible(trait_pred.self_ty());
                 let impls_future = self.type_implements_trait(
                     future_trait,
-                    self.tcx.erase_late_bound_regions(self_ty),
-                    ty::List::empty(),
+                    [self.tcx.erase_late_bound_regions(self_ty)],
                     obligation.param_env,
                 );
                 if !impls_future.must_apply_modulo_regions() {
@@ -2982,16 +2964,11 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                     self.tcx.mk_projection(
                         item_def_id,
                         // Future::Output has no substs
-                        self.tcx.mk_substs_trait(trait_pred.self_ty(), &[]),
+                        self.tcx.mk_substs_trait(trait_pred.self_ty(), []),
                     )
                 });
-                let projection_ty = normalize_to(
-                    &mut SelectionContext::new(self),
-                    obligation.param_env,
-                    obligation.cause.clone(),
-                    projection_ty,
-                    &mut vec![],
-                );
+                let InferOk { value: projection_ty, .. } =
+                    self.at(&obligation.cause, obligation.param_env).normalize(projection_ty);
 
                 debug!(
                     normalized_projection_type = ?self.resolve_vars_if_possible(projection_ty)
@@ -3067,21 +3044,22 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                     let field_ty = field.ty(self.tcx, substs);
                     let trait_substs = match diagnostic_name {
                         sym::PartialEq | sym::PartialOrd => {
-                            self.tcx.mk_substs_trait(field_ty, &[field_ty.into()])
+                            Some(field_ty)
                         }
-                        _ => self.tcx.mk_substs_trait(field_ty, &[]),
+                        _ => None,
                     };
                     let trait_pred = trait_pred.map_bound_ref(|tr| ty::TraitPredicate {
-                        trait_ref: ty::TraitRef {
-                            substs: trait_substs,
-                            ..trait_pred.skip_binder().trait_ref
-                        },
+                        trait_ref: self.tcx.mk_trait_ref(
+                            trait_pred.def_id(),
+                            [field_ty].into_iter().chain(trait_substs),
+                        ),
                         ..*tr
                     });
                     let field_obl = Obligation::new(
+                        self.tcx,
                         obligation.cause.clone(),
                         obligation.param_env,
-                        trait_pred.to_predicate(self.tcx),
+                        trait_pred,
                     );
                     self.predicate_must_hold_modulo_regions(&field_obl)
                 })
diff --git a/compiler/rustc_trait_selection/src/traits/fulfill.rs b/compiler/rustc_trait_selection/src/traits/fulfill.rs
index a417e1440..76a755ed9 100644
--- a/compiler/rustc_trait_selection/src/traits/fulfill.rs
+++ b/compiler/rustc_trait_selection/src/traits/fulfill.rs
@@ -4,13 +4,12 @@ use rustc_data_structures::obligation_forest::ProcessResult;
 use rustc_data_structures::obligation_forest::{Error, ForestObligation, Outcome};
 use rustc_data_structures::obligation_forest::{ObligationForest, ObligationProcessor};
 use rustc_infer::traits::ProjectionCacheKey;
-use rustc_infer::traits::{SelectionError, TraitEngine, TraitEngineExt as _, TraitObligation};
+use rustc_infer::traits::{SelectionError, TraitEngine, TraitObligation};
 use rustc_middle::mir::interpret::ErrorHandled;
 use rustc_middle::ty::abstract_const::NotConstEvaluatable;
 use rustc_middle::ty::error::{ExpectedFound, TypeError};
 use rustc_middle::ty::subst::SubstsRef;
-use rustc_middle::ty::ToPredicate;
-use rustc_middle::ty::{self, Binder, Const, Ty, TypeVisitable};
+use rustc_middle::ty::{self, Binder, Const, TypeVisitable};
 use std::marker::PhantomData;
 
 use super::const_evaluatable;
@@ -21,9 +20,9 @@ use super::CodeAmbiguity;
 use super::CodeProjectionError;
 use super::CodeSelectionError;
 use super::EvaluationResult;
+use super::PredicateObligation;
 use super::Unimplemented;
 use super::{FulfillmentError, FulfillmentErrorCode};
-use super::{ObligationCause, PredicateObligation};
 
 use crate::traits::project::PolyProjectionObligation;
 use crate::traits::project::ProjectionCacheKeyExt as _;
@@ -85,7 +84,7 @@ static_assert_size!(PendingPredicateObligation<'_>, 72);
 
 impl<'a, 'tcx> FulfillmentContext<'tcx> {
     /// Creates a new fulfillment context.
-    pub fn new() -> FulfillmentContext<'tcx> {
+    pub(super) fn new() -> FulfillmentContext<'tcx> {
         FulfillmentContext {
             predicates: ObligationForest::new(),
             relationships: FxHashMap::default(),
@@ -93,7 +92,7 @@ impl<'a, 'tcx> FulfillmentContext<'tcx> {
         }
     }
 
-    pub fn new_in_snapshot() -> FulfillmentContext<'tcx> {
+    pub(super) fn new_in_snapshot() -> FulfillmentContext<'tcx> {
         FulfillmentContext {
             predicates: ObligationForest::new(),
             relationships: FxHashMap::default(),
@@ -127,42 +126,6 @@ impl<'a, 'tcx> FulfillmentContext<'tcx> {
 }
 
 impl<'tcx> TraitEngine<'tcx> for FulfillmentContext<'tcx> {
-    /// "Normalize" a projection type `<SomeType as SomeTrait>::X` by
-    /// creating a fresh type variable `$0` as well as a projection
-    /// predicate `<SomeType as SomeTrait>::X == $0`. When the
-    /// inference engine runs, it will attempt to find an impl of
-    /// `SomeTrait` or a where-clause that lets us unify `$0` with
-    /// something concrete. If this fails, we'll unify `$0` with
-    /// `projection_ty` again.
-    #[instrument(level = "debug", skip(self, infcx, param_env, cause))]
-    fn normalize_projection_type(
-        &mut self,
-        infcx: &InferCtxt<'tcx>,
-        param_env: ty::ParamEnv<'tcx>,
-        projection_ty: ty::ProjectionTy<'tcx>,
-        cause: ObligationCause<'tcx>,
-    ) -> Ty<'tcx> {
-        debug_assert!(!projection_ty.has_escaping_bound_vars());
-
-        // FIXME(#20304) -- cache
-
-        let mut selcx = SelectionContext::new(infcx);
-        let mut obligations = vec![];
-        let normalized_ty = project::normalize_projection_type(
-            &mut selcx,
-            param_env,
-            projection_ty,
-            cause,
-            0,
-            &mut obligations,
-        );
-        self.register_predicate_obligations(infcx, obligations);
-
-        debug!(?normalized_ty);
-
-        normalized_ty.ty().unwrap()
-    }
-
     fn register_predicate_obligation(
         &mut self,
         infcx: &InferCtxt<'tcx>,
@@ -236,7 +199,7 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
             // code is so hot. 1 and 0 dominate; 2+ is fairly rare.
             1 => {
                 let infer_var = pending_obligation.stalled_on[0];
-                self.selcx.infcx().ty_or_const_infer_var_changed(infer_var)
+                self.selcx.infcx.ty_or_const_infer_var_changed(infer_var)
             }
             0 => {
                 // In this case we haven't changed, but wish to make a change.
@@ -247,7 +210,7 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                 // form was a perf win. See #64545 for details.
                 (|| {
                     for &infer_var in &pending_obligation.stalled_on {
-                        if self.selcx.infcx().ty_or_const_infer_var_changed(infer_var) {
+                        if self.selcx.infcx.ty_or_const_infer_var_changed(infer_var) {
                             return true;
                         }
                     }
@@ -277,13 +240,12 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
         debug!(?obligation, "pre-resolve");
 
         if obligation.predicate.has_non_region_infer() {
-            obligation.predicate =
-                self.selcx.infcx().resolve_vars_if_possible(obligation.predicate);
+            obligation.predicate = self.selcx.infcx.resolve_vars_if_possible(obligation.predicate);
         }
 
         let obligation = &pending_obligation.obligation;
 
-        let infcx = self.selcx.infcx();
+        let infcx = self.selcx.infcx;
 
         if obligation.predicate.has_projections() {
             let mut obligations = Vec::new();
@@ -296,7 +258,7 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                 &mut obligations,
             );
             if predicate != obligation.predicate {
-                obligations.push(obligation.with(predicate));
+                obligations.push(obligation.with(infcx.tcx, predicate));
                 return ProcessResult::Changed(mk_pending(obligations));
             }
         }
@@ -306,8 +268,8 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                 // Evaluation will discard candidates using the leak check.
                 // This means we need to pass it the bound version of our
                 // predicate.
-                ty::PredicateKind::Trait(trait_ref) => {
-                    let trait_obligation = obligation.with(binder.rebind(trait_ref));
+                ty::PredicateKind::Clause(ty::Clause::Trait(trait_ref)) => {
+                    let trait_obligation = obligation.with(infcx.tcx, binder.rebind(trait_ref));
 
                     self.process_trait_obligation(
                         obligation,
@@ -315,8 +277,8 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                         &mut pending_obligation.stalled_on,
                     )
                 }
-                ty::PredicateKind::Projection(data) => {
-                    let project_obligation = obligation.with(binder.rebind(data));
+                ty::PredicateKind::Clause(ty::Clause::Projection(data)) => {
+                    let project_obligation = obligation.with(infcx.tcx, binder.rebind(data));
 
                     self.process_projection_obligation(
                         obligation,
@@ -324,8 +286,8 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                         &mut pending_obligation.stalled_on,
                     )
                 }
-                ty::PredicateKind::RegionOutlives(_)
-                | ty::PredicateKind::TypeOutlives(_)
+                ty::PredicateKind::Clause(ty::Clause::RegionOutlives(_))
+                | ty::PredicateKind::Clause(ty::Clause::TypeOutlives(_))
                 | ty::PredicateKind::WellFormed(_)
                 | ty::PredicateKind::ObjectSafe(_)
                 | ty::PredicateKind::ClosureKind(..)
@@ -335,17 +297,16 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                 | ty::PredicateKind::ConstEquate(..) => {
                     let pred =
                         ty::Binder::dummy(infcx.replace_bound_vars_with_placeholders(binder));
-                    ProcessResult::Changed(mk_pending(vec![
-                        obligation.with(pred.to_predicate(self.selcx.tcx())),
-                    ]))
+                    ProcessResult::Changed(mk_pending(vec![obligation.with(infcx.tcx, pred)]))
                 }
+                ty::PredicateKind::Ambiguous => ProcessResult::Unchanged,
                 ty::PredicateKind::TypeWellFormedFromEnv(..) => {
                     bug!("TypeWellFormedFromEnv is only used for Chalk")
                 }
             },
             Some(pred) => match pred {
-                ty::PredicateKind::Trait(data) => {
-                    let trait_obligation = obligation.with(Binder::dummy(data));
+                ty::PredicateKind::Clause(ty::Clause::Trait(data)) => {
+                    let trait_obligation = obligation.with(infcx.tcx, Binder::dummy(data));
 
                     self.process_trait_obligation(
                         obligation,
@@ -354,7 +315,7 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                     )
                 }
 
-                ty::PredicateKind::RegionOutlives(data) => {
+                ty::PredicateKind::Clause(ty::Clause::RegionOutlives(data)) => {
                     if infcx.considering_regions {
                         infcx.region_outlives_predicate(&obligation.cause, Binder::dummy(data));
                     }
@@ -362,15 +323,18 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                     ProcessResult::Changed(vec![])
                 }
 
-                ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(t_a, r_b)) => {
+                ty::PredicateKind::Clause(ty::Clause::TypeOutlives(ty::OutlivesPredicate(
+                    t_a,
+                    r_b,
+                ))) => {
                     if infcx.considering_regions {
                         infcx.register_region_obligation_with_cause(t_a, r_b, &obligation.cause);
                     }
                     ProcessResult::Changed(vec![])
                 }
 
-                ty::PredicateKind::Projection(ref data) => {
-                    let project_obligation = obligation.with(Binder::dummy(*data));
+                ty::PredicateKind::Clause(ty::Clause::Projection(ref data)) => {
+                    let project_obligation = obligation.with(infcx.tcx, Binder::dummy(*data));
 
                     self.process_projection_obligation(
                         obligation,
@@ -388,7 +352,7 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                 }
 
                 ty::PredicateKind::ClosureKind(_, closure_substs, kind) => {
-                    match self.selcx.infcx().closure_kind(closure_substs) {
+                    match self.selcx.infcx.closure_kind(closure_substs) {
                         Some(closure_kind) => {
                             if closure_kind.extends(kind) {
                                 ProcessResult::Changed(vec![])
@@ -402,7 +366,7 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
 
                 ty::PredicateKind::WellFormed(arg) => {
                     match wf::obligations(
-                        self.selcx.infcx(),
+                        self.selcx.infcx,
                         obligation.param_env,
                         obligation.cause.body_id,
                         obligation.recursion_depth + 1,
@@ -419,7 +383,7 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                 }
 
                 ty::PredicateKind::Subtype(subtype) => {
-                    match self.selcx.infcx().subtype_predicate(
+                    match self.selcx.infcx.subtype_predicate(
                         &obligation.cause,
                         obligation.param_env,
                         Binder::dummy(subtype),
@@ -443,7 +407,7 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                 }
 
                 ty::PredicateKind::Coerce(coerce) => {
-                    match self.selcx.infcx().coerce_predicate(
+                    match self.selcx.infcx.coerce_predicate(
                         &obligation.cause,
                         obligation.param_env,
                         Binder::dummy(coerce),
@@ -467,7 +431,7 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
 
                 ty::PredicateKind::ConstEvaluatable(uv) => {
                     match const_evaluatable::is_const_evaluatable(
-                        self.selcx.infcx(),
+                        self.selcx.infcx,
                         uv,
                         obligation.param_env,
                         obligation.cause.span,
@@ -490,20 +454,47 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                 }
 
                 ty::PredicateKind::ConstEquate(c1, c2) => {
+                    let tcx = self.selcx.tcx();
                     assert!(
-                        self.selcx.tcx().features().generic_const_exprs,
+                        tcx.features().generic_const_exprs,
                         "`ConstEquate` without a feature gate: {c1:?} {c2:?}",
                     );
-                    debug!(?c1, ?c2, "equating consts");
                     // FIXME: we probably should only try to unify abstract constants
                     // if the constants depend on generic parameters.
                     //
                     // Let's just see where this breaks :shrug:
-                    if let (ty::ConstKind::Unevaluated(a), ty::ConstKind::Unevaluated(b)) =
-                        (c1.kind(), c2.kind())
                     {
-                        if infcx.try_unify_abstract_consts(a, b, obligation.param_env) {
-                            return ProcessResult::Changed(vec![]);
+                        let c1 = tcx.expand_abstract_consts(c1);
+                        let c2 = tcx.expand_abstract_consts(c2);
+                        debug!("equating consts:\nc1= {:?}\nc2= {:?}", c1, c2);
+
+                        use rustc_hir::def::DefKind;
+                        use ty::ConstKind::Unevaluated;
+                        match (c1.kind(), c2.kind()) {
+                            (Unevaluated(a), Unevaluated(b))
+                                if a.def.did == b.def.did
+                                    && tcx.def_kind(a.def.did) == DefKind::AssocConst =>
+                            {
+                                if let Ok(new_obligations) = infcx
+                                    .at(&obligation.cause, obligation.param_env)
+                                    .trace(c1, c2)
+                                    .eq(a.substs, b.substs)
+                                {
+                                    return ProcessResult::Changed(mk_pending(
+                                        new_obligations.into_obligations(),
+                                    ));
+                                }
+                            }
+                            (_, Unevaluated(_)) | (Unevaluated(_), _) => (),
+                            (_, _) => {
+                                if let Ok(new_obligations) =
+                                    infcx.at(&obligation.cause, obligation.param_env).eq(c1, c2)
+                                {
+                                    return ProcessResult::Changed(mk_pending(
+                                        new_obligations.into_obligations(),
+                                    ));
+                                }
+                            }
                         }
                     }
 
@@ -511,7 +502,7 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
 
                     let mut evaluate = |c: Const<'tcx>| {
                         if let ty::ConstKind::Unevaluated(unevaluated) = c.kind() {
-                            match self.selcx.infcx().try_const_eval_resolve(
+                            match self.selcx.infcx.try_const_eval_resolve(
                                 obligation.param_env,
                                 unevaluated,
                                 c.ty(),
@@ -539,11 +530,13 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                         (Ok(c1), Ok(c2)) => {
                             match self
                                 .selcx
-                                .infcx()
+                                .infcx
                                 .at(&obligation.cause, obligation.param_env)
                                 .eq(c1, c2)
                             {
-                                Ok(_) => ProcessResult::Changed(vec![]),
+                                Ok(inf_ok) => {
+                                    ProcessResult::Changed(mk_pending(inf_ok.into_obligations()))
+                                }
                                 Err(err) => ProcessResult::Error(
                                     FulfillmentErrorCode::CodeConstEquateError(
                                         ExpectedFound::new(true, c1, c2),
@@ -558,12 +551,6 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                                 NotConstEvaluatable::Error(reported),
                             )),
                         ),
-                        (Err(ErrorHandled::Linted), _) | (_, Err(ErrorHandled::Linted)) => {
-                            span_bug!(
-                                obligation.cause.span(),
-                                "ConstEquate: const_eval_resolve returned an unexpected error"
-                            )
-                        }
                         (Err(ErrorHandled::TooGeneric), _) | (_, Err(ErrorHandled::TooGeneric)) => {
                             if c1.has_non_region_infer() || c2.has_non_region_infer() {
                                 ProcessResult::Unchanged
@@ -578,6 +565,7 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                         }
                     }
                 }
+                ty::PredicateKind::Ambiguous => ProcessResult::Unchanged,
                 ty::PredicateKind::TypeWellFormedFromEnv(..) => {
                     bug!("TypeWellFormedFromEnv is only used for Chalk")
                 }
@@ -612,7 +600,7 @@ impl<'a, 'tcx> FulfillProcessor<'a, 'tcx> {
         trait_obligation: TraitObligation<'tcx>,
         stalled_on: &mut Vec<TyOrConstInferVar<'tcx>>,
     ) -> ProcessResult<PendingPredicateObligation<'tcx>, FulfillmentErrorCode<'tcx>> {
-        let infcx = self.selcx.infcx();
+        let infcx = self.selcx.infcx;
         if obligation.predicate.is_global() {
             // no type variables present, can use evaluation for better caching.
             // FIXME: consider caching errors too.
@@ -670,7 +658,7 @@ impl<'a, 'tcx> FulfillProcessor<'a, 'tcx> {
         if obligation.predicate.is_global() {
             // no type variables present, can use evaluation for better caching.
             // FIXME: consider caching errors too.
-            if self.selcx.infcx().predicate_must_hold_considering_regions(obligation) {
+            if self.selcx.infcx.predicate_must_hold_considering_regions(obligation) {
                 if let Some(key) = ProjectionCacheKey::from_poly_projection_predicate(
                     &mut self.selcx,
                     project_obligation.predicate,
@@ -679,7 +667,7 @@ impl<'a, 'tcx> FulfillProcessor<'a, 'tcx> {
                     // evaluated all sub-obligations. We can therefore mark the 'root'
                     // obligation as complete, and skip evaluating sub-obligations.
                     self.selcx
-                        .infcx()
+                        .infcx
                         .inner
                         .borrow_mut()
                         .projection_cache()
@@ -703,7 +691,7 @@ impl<'a, 'tcx> FulfillProcessor<'a, 'tcx> {
             }
             // Let the caller handle the recursion
             ProjectAndUnifyResult::Recursive => ProcessResult::Changed(mk_pending(vec![
-                project_obligation.with(project_obligation.predicate.to_predicate(tcx)),
+                project_obligation.with(tcx, project_obligation.predicate),
             ])),
             ProjectAndUnifyResult::MismatchedProjectionTypes(e) => {
                 ProcessResult::Error(CodeProjectionError(e))
@@ -718,7 +706,7 @@ fn substs_infer_vars<'a, 'tcx>(
     substs: ty::Binder<'tcx, SubstsRef<'tcx>>,
 ) -> impl Iterator<Item = TyOrConstInferVar<'tcx>> {
     selcx
-        .infcx()
+        .infcx
         .resolve_vars_if_possible(substs)
         .skip_binder() // ok because this check doesn't care about regions
         .iter()
diff --git a/compiler/rustc_trait_selection/src/traits/misc.rs b/compiler/rustc_trait_selection/src/traits/misc.rs
index be603c609..b6ded4ce5 100644
--- a/compiler/rustc_trait_selection/src/traits/misc.rs
+++ b/compiler/rustc_trait_selection/src/traits/misc.rs
@@ -70,7 +70,7 @@ pub fn can_type_implement_copy<'tcx>(
                     }
                 }
                 Err(errors) => {
-                    infcx.err_ctxt().report_fulfillment_errors(&errors, None, false);
+                    infcx.err_ctxt().report_fulfillment_errors(&errors, None);
                 }
             };
         }
diff --git a/compiler/rustc_trait_selection/src/traits/mod.rs b/compiler/rustc_trait_selection/src/traits/mod.rs
index 0bf54c096..ea4bf42c5 100644
--- a/compiler/rustc_trait_selection/src/traits/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/mod.rs
@@ -4,7 +4,6 @@
 
 pub mod auto_trait;
 mod chalk_fulfill;
-pub mod codegen;
 mod coherence;
 pub mod const_evaluatable;
 mod engine;
@@ -12,7 +11,6 @@ pub mod error_reporting;
 mod fulfill;
 pub mod misc;
 mod object_safety;
-mod on_unimplemented;
 pub mod outlives_bounds;
 mod project;
 pub mod query;
@@ -21,9 +19,9 @@ mod select;
 mod specialize;
 mod structural_match;
 mod util;
+mod vtable;
 pub mod wf;
 
-use crate::errors::DumpVTableEntries;
 use crate::infer::outlives::env::OutlivesEnvironment;
 use crate::infer::{InferCtxt, TyCtxtInferExt};
 use crate::traits::error_reporting::TypeErrCtxtExt as _;
@@ -31,16 +29,11 @@ use crate::traits::query::evaluate_obligation::InferCtxtExt as _;
 use rustc_errors::ErrorGuaranteed;
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
-use rustc_hir::lang_items::LangItem;
-use rustc_infer::traits::TraitEngineExt as _;
 use rustc_middle::ty::fold::TypeFoldable;
 use rustc_middle::ty::visit::TypeVisitable;
-use rustc_middle::ty::{
-    self, DefIdTree, GenericParamDefKind, ToPredicate, Ty, TyCtxt, TypeSuperVisitable, VtblEntry,
-};
+use rustc_middle::ty::{self, DefIdTree, ToPredicate, Ty, TyCtxt, TypeSuperVisitable};
 use rustc_middle::ty::{InternalSubsts, SubstsRef};
-use rustc_span::{sym, Span};
-use smallvec::SmallVec;
+use rustc_span::Span;
 
 use std::fmt::Debug;
 use std::ops::ControlFlow;
@@ -58,8 +51,7 @@ pub use self::object_safety::astconv_object_safety_violations;
 pub use self::object_safety::is_vtable_safe_method;
 pub use self::object_safety::MethodViolationCode;
 pub use self::object_safety::ObjectSafetyViolation;
-pub use self::on_unimplemented::{OnUnimplementedDirective, OnUnimplementedNote};
-pub use self::project::{normalize, normalize_projection_type, normalize_to};
+pub use self::project::{normalize_projection_type, NormalizeExt};
 pub use self::select::{EvaluationCache, SelectionCache, SelectionContext};
 pub use self::select::{EvaluationResult, IntercrateAmbiguityCause, OverflowError};
 pub use self::specialize::specialization_graph::FutureCompatOverlapError;
@@ -117,14 +109,12 @@ pub enum TraitQueryMode {
 }
 
 /// Creates predicate obligations from the generic bounds.
+#[instrument(level = "debug", skip(cause, param_env))]
 pub fn predicates_for_generics<'tcx>(
     cause: impl Fn(usize, Span) -> ObligationCause<'tcx>,
     param_env: ty::ParamEnv<'tcx>,
     generic_bounds: ty::InstantiatedPredicates<'tcx>,
 ) -> impl Iterator<Item = PredicateObligation<'tcx>> {
-    let generic_bounds = generic_bounds;
-    debug!("predicates_for_generics(generic_bounds={:?})", generic_bounds);
-
     std::iter::zip(generic_bounds.predicates, generic_bounds.spans).enumerate().map(
         move |(idx, (predicate, span))| Obligation {
             cause: cause(idx, span),
@@ -147,64 +137,50 @@ pub fn type_known_to_meet_bound_modulo_regions<'tcx>(
     def_id: DefId,
     span: Span,
 ) -> bool {
-    debug!(
-        "type_known_to_meet_bound_modulo_regions(ty={:?}, bound={:?})",
-        ty,
-        infcx.tcx.def_path_str(def_id)
-    );
+    let trait_ref = ty::Binder::dummy(infcx.tcx.mk_trait_ref(def_id, [ty]));
+    pred_known_to_hold_modulo_regions(infcx, param_env, trait_ref.without_const(), span)
+}
 
-    let trait_ref =
-        ty::Binder::dummy(ty::TraitRef { def_id, substs: infcx.tcx.mk_substs_trait(ty, &[]) });
+#[instrument(level = "debug", skip(infcx, param_env, span, pred), ret)]
+fn pred_known_to_hold_modulo_regions<'tcx>(
+    infcx: &InferCtxt<'tcx>,
+    param_env: ty::ParamEnv<'tcx>,
+    pred: impl ToPredicate<'tcx> + TypeVisitable<'tcx>,
+    span: Span,
+) -> bool {
+    let has_non_region_infer = pred.has_non_region_infer();
     let obligation = Obligation {
         param_env,
+        // We can use a dummy node-id here because we won't pay any mind
+        // to region obligations that arise (there shouldn't really be any
+        // anyhow).
         cause: ObligationCause::misc(span, hir::CRATE_HIR_ID),
         recursion_depth: 0,
-        predicate: trait_ref.without_const().to_predicate(infcx.tcx),
+        predicate: pred.to_predicate(infcx.tcx),
     };
 
     let result = infcx.predicate_must_hold_modulo_regions(&obligation);
-    debug!(
-        "type_known_to_meet_ty={:?} bound={} => {:?}",
-        ty,
-        infcx.tcx.def_path_str(def_id),
-        result
-    );
+    debug!(?result);
 
-    if result && ty.has_non_region_infer() {
+    if result && has_non_region_infer {
         // Because of inference "guessing", selection can sometimes claim
         // to succeed while the success requires a guess. To ensure
         // this function's result remains infallible, we must confirm
         // that guess. While imperfect, I believe this is sound.
 
-        // We can use a dummy node-id here because we won't pay any mind
-        // to region obligations that arise (there shouldn't really be any
-        // anyhow).
-        let cause = ObligationCause::misc(span, hir::CRATE_HIR_ID);
-
+        // FIXME(@lcnr): this function doesn't seem right.
         // The handling of regions in this area of the code is terrible,
         // see issue #29149. We should be able to improve on this with
         // NLL.
-        let errors = fully_solve_bound(infcx, cause, param_env, ty, def_id);
+        let errors = fully_solve_obligation(infcx, obligation);
 
         // Note: we only assume something is `Copy` if we can
         // *definitively* show that it implements `Copy`. Otherwise,
         // assume it is move; linear is always ok.
         match &errors[..] {
-            [] => {
-                debug!(
-                    "type_known_to_meet_bound_modulo_regions: ty={:?} bound={} success",
-                    ty,
-                    infcx.tcx.def_path_str(def_id)
-                );
-                true
-            }
+            [] => true,
             errors => {
-                debug!(
-                    ?ty,
-                    bound = %infcx.tcx.def_path_str(def_id),
-                    ?errors,
-                    "type_known_to_meet_bound_modulo_regions"
-                );
+                debug!(?errors);
                 false
             }
         }
@@ -238,7 +214,7 @@ fn do_normalize_predicates<'tcx>(
     let predicates = match fully_normalize(&infcx, cause, elaborated_env, predicates) {
         Ok(predicates) => predicates,
         Err(errors) => {
-            let reported = infcx.err_ctxt().report_fulfillment_errors(&errors, None, false);
+            let reported = infcx.err_ctxt().report_fulfillment_errors(&errors, None);
             return Err(reported);
         }
     };
@@ -336,7 +312,10 @@ pub fn normalize_param_env_or_error<'tcx>(
     // TypeOutlives predicates - these are normally used by regionck.
     let outlives_predicates: Vec<_> = predicates
         .drain_filter(|predicate| {
-            matches!(predicate.kind().skip_binder(), ty::PredicateKind::TypeOutlives(..))
+            matches!(
+                predicate.kind().skip_binder(),
+                ty::PredicateKind::Clause(ty::Clause::TypeOutlives(..))
+            )
         })
         .collect();
 
@@ -390,6 +369,7 @@ pub fn normalize_param_env_or_error<'tcx>(
 }
 
 /// Normalize a type and process all resulting obligations, returning any errors
+#[instrument(skip_all)]
 pub fn fully_normalize<'tcx, T>(
     infcx: &InferCtxt<'tcx>,
     cause: ObligationCause<'tcx>,
@@ -399,28 +379,18 @@ pub fn fully_normalize<'tcx, T>(
 where
     T: TypeFoldable<'tcx>,
 {
-    debug!("fully_normalize_with_fulfillcx(value={:?})", value);
-    let selcx = &mut SelectionContext::new(infcx);
-    let Normalized { value: normalized_value, obligations } =
-        project::normalize(selcx, param_env, cause, value);
-    debug!(
-        "fully_normalize: normalized_value={:?} obligations={:?}",
-        normalized_value, obligations
-    );
-
-    let mut fulfill_cx = FulfillmentContext::new();
-    for obligation in obligations {
-        fulfill_cx.register_predicate_obligation(infcx, obligation);
-    }
-
-    debug!("fully_normalize: select_all_or_error start");
-    let errors = fulfill_cx.select_all_or_error(infcx);
+    let ocx = ObligationCtxt::new(infcx);
+    debug!(?value);
+    let normalized_value = ocx.normalize(&cause, param_env, value);
+    debug!(?normalized_value);
+    debug!("select_all_or_error start");
+    let errors = ocx.select_all_or_error();
     if !errors.is_empty() {
         return Err(errors);
     }
-    debug!("fully_normalize: select_all_or_error complete");
+    debug!("select_all_or_error complete");
     let resolved_value = infcx.resolve_vars_if_possible(normalized_value);
-    debug!("fully_normalize: resolved_value={:?}", resolved_value);
+    debug!(?resolved_value);
     Ok(resolved_value)
 }
 
@@ -430,9 +400,7 @@ pub fn fully_solve_obligation<'tcx>(
     infcx: &InferCtxt<'tcx>,
     obligation: PredicateObligation<'tcx>,
 ) -> Vec<FulfillmentError<'tcx>> {
-    let mut engine = <dyn TraitEngine<'tcx>>::new(infcx.tcx);
-    engine.register_predicate_obligation(infcx, obligation);
-    engine.select_all_or_error(infcx)
+    fully_solve_obligations(infcx, [obligation])
 }
 
 /// Process a set of obligations (and any nested obligations that come from them)
@@ -441,9 +409,9 @@ pub fn fully_solve_obligations<'tcx>(
     infcx: &InferCtxt<'tcx>,
     obligations: impl IntoIterator<Item = PredicateObligation<'tcx>>,
 ) -> Vec<FulfillmentError<'tcx>> {
-    let mut engine = <dyn TraitEngine<'tcx>>::new(infcx.tcx);
-    engine.register_predicate_obligations(infcx, obligations);
-    engine.select_all_or_error(infcx)
+    let ocx = ObligationCtxt::new(infcx);
+    ocx.register_obligations(obligations);
+    ocx.select_all_or_error()
 }
 
 /// Process a bound (and any nested obligations that come from it) to completion.
@@ -456,9 +424,16 @@ pub fn fully_solve_bound<'tcx>(
     ty: Ty<'tcx>,
     bound: DefId,
 ) -> Vec<FulfillmentError<'tcx>> {
-    let mut engine = <dyn TraitEngine<'tcx>>::new(infcx.tcx);
-    engine.register_bound(infcx, param_env, ty, bound, cause);
-    engine.select_all_or_error(infcx)
+    let tcx = infcx.tcx;
+    let trait_ref = ty::TraitRef { def_id: bound, substs: tcx.mk_substs_trait(ty, []) };
+    let obligation = Obligation {
+        cause,
+        recursion_depth: 0,
+        param_env,
+        predicate: ty::Binder::dummy(trait_ref).without_const().to_predicate(tcx),
+    };
+
+    fully_solve_obligation(infcx, obligation)
 }
 
 /// Normalizes the predicates and checks whether they hold in an empty environment. If this
@@ -473,9 +448,9 @@ pub fn impossible_predicates<'tcx>(
     let infcx = tcx.infer_ctxt().build();
     let param_env = ty::ParamEnv::reveal_all();
     let ocx = ObligationCtxt::new(&infcx);
-    let predicates = ocx.normalize(ObligationCause::dummy(), param_env, predicates);
+    let predicates = ocx.normalize(&ObligationCause::dummy(), param_env, predicates);
     for predicate in predicates {
-        let obligation = Obligation::new(ObligationCause::dummy(), param_env, predicate);
+        let obligation = Obligation::new(tcx, ObligationCause::dummy(), param_env, predicate);
         ocx.register_obligation(obligation);
     }
     let errors = ocx.select_all_or_error();
@@ -500,7 +475,7 @@ fn subst_and_check_impossible_predicates<'tcx>(
     // associated items.
     if let Some(trait_def_id) = tcx.trait_of_item(key.0) {
         let trait_ref = ty::TraitRef::from_method(tcx, trait_def_id, key.1);
-        predicates.push(ty::Binder::dummy(trait_ref).to_poly_trait_predicate().to_predicate(tcx));
+        predicates.push(ty::Binder::dummy(trait_ref).to_predicate(tcx));
     }
 
     predicates.retain(|predicate| !predicate.needs_subst());
@@ -565,6 +540,7 @@ fn is_impossible_method<'tcx>(
     let predicates_for_trait = predicates.predicates.iter().filter_map(|(pred, span)| {
         if pred.visit_with(&mut visitor).is_continue() {
             Some(Obligation::new(
+                tcx,
                 ObligationCause::dummy_with_span(*span),
                 param_env,
                 ty::EarlyBinder(*pred).subst(tcx, impl_trait_ref.substs),
@@ -586,390 +562,14 @@ fn is_impossible_method<'tcx>(
     false
 }
 
-#[derive(Clone, Debug)]
-enum VtblSegment<'tcx> {
-    MetadataDSA,
-    TraitOwnEntries { trait_ref: ty::PolyTraitRef<'tcx>, emit_vptr: bool },
-}
-
-/// Prepare the segments for a vtable
-fn prepare_vtable_segments<'tcx, T>(
-    tcx: TyCtxt<'tcx>,
-    trait_ref: ty::PolyTraitRef<'tcx>,
-    mut segment_visitor: impl FnMut(VtblSegment<'tcx>) -> ControlFlow<T>,
-) -> Option<T> {
-    // The following constraints holds for the final arrangement.
-    // 1. The whole virtual table of the first direct super trait is included as the
-    //    the prefix. If this trait doesn't have any super traits, then this step
-    //    consists of the dsa metadata.
-    // 2. Then comes the proper pointer metadata(vptr) and all own methods for all
-    //    other super traits except those already included as part of the first
-    //    direct super trait virtual table.
-    // 3. finally, the own methods of this trait.
-
-    // This has the advantage that trait upcasting to the first direct super trait on each level
-    // is zero cost, and to another trait includes only replacing the pointer with one level indirection,
-    // while not using too much extra memory.
-
-    // For a single inheritance relationship like this,
-    //   D --> C --> B --> A
-    // The resulting vtable will consists of these segments:
-    //  DSA, A, B, C, D
-
-    // For a multiple inheritance relationship like this,
-    //   D --> C --> A
-    //           \-> B
-    // The resulting vtable will consists of these segments:
-    //  DSA, A, B, B-vptr, C, D
-
-    // For a diamond inheritance relationship like this,
-    //   D --> B --> A
-    //     \-> C -/
-    // The resulting vtable will consists of these segments:
-    //  DSA, A, B, C, C-vptr, D
-
-    // For a more complex inheritance relationship like this:
-    //   O --> G --> C --> A
-    //     \     \     \-> B
-    //     |     |-> F --> D
-    //     |           \-> E
-    //     |-> N --> J --> H
-    //           \     \-> I
-    //           |-> M --> K
-    //                 \-> L
-    // The resulting vtable will consists of these segments:
-    //  DSA, A, B, B-vptr, C, D, D-vptr, E, E-vptr, F, F-vptr, G,
-    //  H, H-vptr, I, I-vptr, J, J-vptr, K, K-vptr, L, L-vptr, M, M-vptr,
-    //  N, N-vptr, O
-
-    // emit dsa segment first.
-    if let ControlFlow::Break(v) = (segment_visitor)(VtblSegment::MetadataDSA) {
-        return Some(v);
-    }
-
-    let mut emit_vptr_on_new_entry = false;
-    let mut visited = util::PredicateSet::new(tcx);
-    let predicate = trait_ref.without_const().to_predicate(tcx);
-    let mut stack: SmallVec<[(ty::PolyTraitRef<'tcx>, _, _); 5]> =
-        smallvec![(trait_ref, emit_vptr_on_new_entry, None)];
-    visited.insert(predicate);
-
-    // the main traversal loop:
-    // basically we want to cut the inheritance directed graph into a few non-overlapping slices of nodes
-    // that each node is emitted after all its descendents have been emitted.
-    // so we convert the directed graph into a tree by skipping all previously visited nodes using a visited set.
-    // this is done on the fly.
-    // Each loop run emits a slice - it starts by find a "childless" unvisited node, backtracking upwards, and it
-    // stops after it finds a node that has a next-sibling node.
-    // This next-sibling node will used as the starting point of next slice.
-
-    // Example:
-    // For a diamond inheritance relationship like this,
-    //   D#1 --> B#0 --> A#0
-    //     \-> C#1 -/
-
-    // Starting point 0 stack [D]
-    // Loop run #0: Stack after diving in is [D B A], A is "childless"
-    // after this point, all newly visited nodes won't have a vtable that equals to a prefix of this one.
-    // Loop run #0: Emitting the slice [B A] (in reverse order), B has a next-sibling node, so this slice stops here.
-    // Loop run #0: Stack after exiting out is [D C], C is the next starting point.
-    // Loop run #1: Stack after diving in is [D C], C is "childless", since its child A is skipped(already emitted).
-    // Loop run #1: Emitting the slice [D C] (in reverse order). No one has a next-sibling node.
-    // Loop run #1: Stack after exiting out is []. Now the function exits.
-
-    loop {
-        // dive deeper into the stack, recording the path
-        'diving_in: loop {
-            if let Some((inner_most_trait_ref, _, _)) = stack.last() {
-                let inner_most_trait_ref = *inner_most_trait_ref;
-                let mut direct_super_traits_iter = tcx
-                    .super_predicates_of(inner_most_trait_ref.def_id())
-                    .predicates
-                    .into_iter()
-                    .filter_map(move |(pred, _)| {
-                        pred.subst_supertrait(tcx, &inner_most_trait_ref).to_opt_poly_trait_pred()
-                    });
-
-                'diving_in_skip_visited_traits: loop {
-                    if let Some(next_super_trait) = direct_super_traits_iter.next() {
-                        if visited.insert(next_super_trait.to_predicate(tcx)) {
-                            // We're throwing away potential constness of super traits here.
-                            // FIXME: handle ~const super traits
-                            let next_super_trait = next_super_trait.map_bound(|t| t.trait_ref);
-                            stack.push((
-                                next_super_trait,
-                                emit_vptr_on_new_entry,
-                                Some(direct_super_traits_iter),
-                            ));
-                            break 'diving_in_skip_visited_traits;
-                        } else {
-                            continue 'diving_in_skip_visited_traits;
-                        }
-                    } else {
-                        break 'diving_in;
-                    }
-                }
-            }
-        }
-
-        // Other than the left-most path, vptr should be emitted for each trait.
-        emit_vptr_on_new_entry = true;
-
-        // emit innermost item, move to next sibling and stop there if possible, otherwise jump to outer level.
-        'exiting_out: loop {
-            if let Some((inner_most_trait_ref, emit_vptr, siblings_opt)) = stack.last_mut() {
-                if let ControlFlow::Break(v) = (segment_visitor)(VtblSegment::TraitOwnEntries {
-                    trait_ref: *inner_most_trait_ref,
-                    emit_vptr: *emit_vptr,
-                }) {
-                    return Some(v);
-                }
-
-                'exiting_out_skip_visited_traits: loop {
-                    if let Some(siblings) = siblings_opt {
-                        if let Some(next_inner_most_trait_ref) = siblings.next() {
-                            if visited.insert(next_inner_most_trait_ref.to_predicate(tcx)) {
-                                // We're throwing away potential constness of super traits here.
-                                // FIXME: handle ~const super traits
-                                let next_inner_most_trait_ref =
-                                    next_inner_most_trait_ref.map_bound(|t| t.trait_ref);
-                                *inner_most_trait_ref = next_inner_most_trait_ref;
-                                *emit_vptr = emit_vptr_on_new_entry;
-                                break 'exiting_out;
-                            } else {
-                                continue 'exiting_out_skip_visited_traits;
-                            }
-                        }
-                    }
-                    stack.pop();
-                    continue 'exiting_out;
-                }
-            }
-            // all done
-            return None;
-        }
-    }
-}
-
-fn dump_vtable_entries<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    sp: Span,
-    trait_ref: ty::PolyTraitRef<'tcx>,
-    entries: &[VtblEntry<'tcx>],
-) {
-    tcx.sess.emit_err(DumpVTableEntries {
-        span: sp,
-        trait_ref,
-        entries: format!("{:#?}", entries),
-    });
-}
-
-fn own_existential_vtable_entries<'tcx>(tcx: TyCtxt<'tcx>, trait_def_id: DefId) -> &'tcx [DefId] {
-    let trait_methods = tcx
-        .associated_items(trait_def_id)
-        .in_definition_order()
-        .filter(|item| item.kind == ty::AssocKind::Fn);
-    // Now list each method's DefId (for within its trait).
-    let own_entries = trait_methods.filter_map(move |trait_method| {
-        debug!("own_existential_vtable_entry: trait_method={:?}", trait_method);
-        let def_id = trait_method.def_id;
-
-        // Some methods cannot be called on an object; skip those.
-        if !is_vtable_safe_method(tcx, trait_def_id, &trait_method) {
-            debug!("own_existential_vtable_entry: not vtable safe");
-            return None;
-        }
-
-        Some(def_id)
-    });
-
-    tcx.arena.alloc_from_iter(own_entries.into_iter())
-}
-
-/// Given a trait `trait_ref`, iterates the vtable entries
-/// that come from `trait_ref`, including its supertraits.
-fn vtable_entries<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    trait_ref: ty::PolyTraitRef<'tcx>,
-) -> &'tcx [VtblEntry<'tcx>] {
-    debug!("vtable_entries({:?})", trait_ref);
-
-    let mut entries = vec![];
-
-    let vtable_segment_callback = |segment| -> ControlFlow<()> {
-        match segment {
-            VtblSegment::MetadataDSA => {
-                entries.extend(TyCtxt::COMMON_VTABLE_ENTRIES);
-            }
-            VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => {
-                let existential_trait_ref = trait_ref
-                    .map_bound(|trait_ref| ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref));
-
-                // Lookup the shape of vtable for the trait.
-                let own_existential_entries =
-                    tcx.own_existential_vtable_entries(existential_trait_ref.def_id());
-
-                let own_entries = own_existential_entries.iter().copied().map(|def_id| {
-                    debug!("vtable_entries: trait_method={:?}", def_id);
-
-                    // The method may have some early-bound lifetimes; add regions for those.
-                    let substs = trait_ref.map_bound(|trait_ref| {
-                        InternalSubsts::for_item(tcx, def_id, |param, _| match param.kind {
-                            GenericParamDefKind::Lifetime => tcx.lifetimes.re_erased.into(),
-                            GenericParamDefKind::Type { .. }
-                            | GenericParamDefKind::Const { .. } => {
-                                trait_ref.substs[param.index as usize]
-                            }
-                        })
-                    });
-
-                    // The trait type may have higher-ranked lifetimes in it;
-                    // erase them if they appear, so that we get the type
-                    // at some particular call site.
-                    let substs = tcx
-                        .normalize_erasing_late_bound_regions(ty::ParamEnv::reveal_all(), substs);
-
-                    // It's possible that the method relies on where-clauses that
-                    // do not hold for this particular set of type parameters.
-                    // Note that this method could then never be called, so we
-                    // do not want to try and codegen it, in that case (see #23435).
-                    let predicates = tcx.predicates_of(def_id).instantiate_own(tcx, substs);
-                    if impossible_predicates(tcx, predicates.predicates) {
-                        debug!("vtable_entries: predicates do not hold");
-                        return VtblEntry::Vacant;
-                    }
-
-                    let instance = ty::Instance::resolve_for_vtable(
-                        tcx,
-                        ty::ParamEnv::reveal_all(),
-                        def_id,
-                        substs,
-                    )
-                    .expect("resolution failed during building vtable representation");
-                    VtblEntry::Method(instance)
-                });
-
-                entries.extend(own_entries);
-
-                if emit_vptr {
-                    entries.push(VtblEntry::TraitVPtr(trait_ref));
-                }
-            }
-        }
-
-        ControlFlow::Continue(())
-    };
-
-    let _ = prepare_vtable_segments(tcx, trait_ref, vtable_segment_callback);
-
-    if tcx.has_attr(trait_ref.def_id(), sym::rustc_dump_vtable) {
-        let sp = tcx.def_span(trait_ref.def_id());
-        dump_vtable_entries(tcx, sp, trait_ref, &entries);
-    }
-
-    tcx.arena.alloc_from_iter(entries.into_iter())
-}
-
-/// Find slot base for trait methods within vtable entries of another trait
-fn vtable_trait_first_method_offset<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    key: (
-        ty::PolyTraitRef<'tcx>, // trait_to_be_found
-        ty::PolyTraitRef<'tcx>, // trait_owning_vtable
-    ),
-) -> usize {
-    let (trait_to_be_found, trait_owning_vtable) = key;
-
-    // #90177
-    let trait_to_be_found_erased = tcx.erase_regions(trait_to_be_found);
-
-    let vtable_segment_callback = {
-        let mut vtable_base = 0;
-
-        move |segment| {
-            match segment {
-                VtblSegment::MetadataDSA => {
-                    vtable_base += TyCtxt::COMMON_VTABLE_ENTRIES.len();
-                }
-                VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => {
-                    if tcx.erase_regions(trait_ref) == trait_to_be_found_erased {
-                        return ControlFlow::Break(vtable_base);
-                    }
-                    vtable_base += util::count_own_vtable_entries(tcx, trait_ref);
-                    if emit_vptr {
-                        vtable_base += 1;
-                    }
-                }
-            }
-            ControlFlow::Continue(())
-        }
-    };
-
-    if let Some(vtable_base) =
-        prepare_vtable_segments(tcx, trait_owning_vtable, vtable_segment_callback)
-    {
-        vtable_base
-    } else {
-        bug!("Failed to find info for expected trait in vtable");
-    }
-}
-
-/// Find slot offset for trait vptr within vtable entries of another trait
-pub fn vtable_trait_upcasting_coercion_new_vptr_slot<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    key: (
-        Ty<'tcx>, // trait object type whose trait owning vtable
-        Ty<'tcx>, // trait object for supertrait
-    ),
-) -> Option<usize> {
-    let (source, target) = key;
-    assert!(matches!(&source.kind(), &ty::Dynamic(..)) && !source.needs_infer());
-    assert!(matches!(&target.kind(), &ty::Dynamic(..)) && !target.needs_infer());
-
-    // this has been typecked-before, so diagnostics is not really needed.
-    let unsize_trait_did = tcx.require_lang_item(LangItem::Unsize, None);
-
-    let trait_ref = ty::TraitRef {
-        def_id: unsize_trait_did,
-        substs: tcx.mk_substs_trait(source, &[target.into()]),
-    };
-    let obligation = Obligation::new(
-        ObligationCause::dummy(),
-        ty::ParamEnv::reveal_all(),
-        ty::Binder::dummy(ty::TraitPredicate {
-            trait_ref,
-            constness: ty::BoundConstness::NotConst,
-            polarity: ty::ImplPolarity::Positive,
-        }),
-    );
-
-    let infcx = tcx.infer_ctxt().build();
-    let mut selcx = SelectionContext::new(&infcx);
-    let implsrc = selcx.select(&obligation).unwrap();
-
-    let Some(ImplSource::TraitUpcasting(implsrc_traitcasting)) = implsrc else {
-        bug!();
-    };
-
-    implsrc_traitcasting.vtable_vptr_slot
-}
-
 pub fn provide(providers: &mut ty::query::Providers) {
     object_safety::provide(providers);
-    structural_match::provide(providers);
+    vtable::provide(providers);
     *providers = ty::query::Providers {
         specialization_graph_of: specialize::specialization_graph_provider,
         specializes: specialize::specializes,
-        codegen_select_candidate: codegen::codegen_select_candidate,
-        own_existential_vtable_entries,
-        vtable_entries,
-        vtable_trait_upcasting_coercion_new_vptr_slot,
         subst_and_check_impossible_predicates,
         is_impossible_method,
-        try_unify_abstract_consts: |tcx, param_env_and| {
-            let (param_env, (a, b)) = param_env_and.into_parts();
-            const_evaluatable::try_unify_abstract_consts(tcx, (a, b), param_env)
-        },
         ..*providers
     };
 }
diff --git a/compiler/rustc_trait_selection/src/traits/object_safety.rs b/compiler/rustc_trait_selection/src/traits/object_safety.rs
index 0bb25a74d..a45749fe4 100644
--- a/compiler/rustc_trait_selection/src/traits/object_safety.rs
+++ b/compiler/rustc_trait_selection/src/traits/object_safety.rs
@@ -17,11 +17,10 @@ use hir::def::DefKind;
 use rustc_errors::{DelayDm, FatalError, MultiSpan};
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
-use rustc_middle::ty::abstract_const::{walk_abstract_const, AbstractConst};
+use rustc_middle::ty::subst::{GenericArg, InternalSubsts};
 use rustc_middle::ty::{
     self, EarlyBinder, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitor,
 };
-use rustc_middle::ty::{GenericArg, InternalSubsts};
 use rustc_middle::ty::{Predicate, ToPredicate};
 use rustc_session::lint::builtin::WHERE_CLAUSES_OBJECT_SAFETY;
 use rustc_span::symbol::Symbol;
@@ -288,11 +287,11 @@ fn predicate_references_self<'tcx>(
     let self_ty = tcx.types.self_param;
     let has_self_ty = |arg: &GenericArg<'tcx>| arg.walk().any(|arg| arg == self_ty.into());
     match predicate.kind().skip_binder() {
-        ty::PredicateKind::Trait(ref data) => {
+        ty::PredicateKind::Clause(ty::Clause::Trait(ref data)) => {
             // In the case of a trait predicate, we can skip the "self" type.
             if data.trait_ref.substs[1..].iter().any(has_self_ty) { Some(sp) } else { None }
         }
-        ty::PredicateKind::Projection(ref data) => {
+        ty::PredicateKind::Clause(ty::Clause::Projection(ref data)) => {
             // And similarly for projections. This should be redundant with
             // the previous check because any projection should have a
             // matching `Trait` predicate with the same inputs, but we do
@@ -312,13 +311,14 @@ fn predicate_references_self<'tcx>(
         }
         ty::PredicateKind::WellFormed(..)
         | ty::PredicateKind::ObjectSafe(..)
-        | ty::PredicateKind::TypeOutlives(..)
-        | ty::PredicateKind::RegionOutlives(..)
+        | ty::PredicateKind::Clause(ty::Clause::TypeOutlives(..))
+        | ty::PredicateKind::Clause(ty::Clause::RegionOutlives(..))
         | ty::PredicateKind::ClosureKind(..)
         | ty::PredicateKind::Subtype(..)
         | ty::PredicateKind::Coerce(..)
         | ty::PredicateKind::ConstEvaluatable(..)
         | ty::PredicateKind::ConstEquate(..)
+        | ty::PredicateKind::Ambiguous
         | ty::PredicateKind::TypeWellFormedFromEnv(..) => None,
     }
 }
@@ -337,19 +337,20 @@ fn generics_require_sized_self(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
     let predicates = predicates.instantiate_identity(tcx).predicates;
     elaborate_predicates(tcx, predicates.into_iter()).any(|obligation| {
         match obligation.predicate.kind().skip_binder() {
-            ty::PredicateKind::Trait(ref trait_pred) => {
+            ty::PredicateKind::Clause(ty::Clause::Trait(ref trait_pred)) => {
                 trait_pred.def_id() == sized_def_id && trait_pred.self_ty().is_param(0)
             }
-            ty::PredicateKind::Projection(..)
+            ty::PredicateKind::Clause(ty::Clause::Projection(..))
             | ty::PredicateKind::Subtype(..)
             | ty::PredicateKind::Coerce(..)
-            | ty::PredicateKind::RegionOutlives(..)
+            | ty::PredicateKind::Clause(ty::Clause::RegionOutlives(..))
             | ty::PredicateKind::WellFormed(..)
             | ty::PredicateKind::ObjectSafe(..)
             | ty::PredicateKind::ClosureKind(..)
-            | ty::PredicateKind::TypeOutlives(..)
+            | ty::PredicateKind::Clause(ty::Clause::TypeOutlives(..))
             | ty::PredicateKind::ConstEvaluatable(..)
             | ty::PredicateKind::ConstEquate(..)
+            | ty::PredicateKind::Ambiguous
             | ty::PredicateKind::TypeWellFormedFromEnv(..) => false,
         }
     })
@@ -375,6 +376,7 @@ fn object_safety_violation_for_method(
         let span = match (&v, node) {
             (MethodViolationCode::ReferencesSelfInput(Some(span)), _) => *span,
             (MethodViolationCode::UndispatchableReceiver(Some(span)), _) => *span,
+            (MethodViolationCode::ReferencesImplTraitInTrait(span), _) => *span,
             (MethodViolationCode::ReferencesSelfOutput, Some(node)) => {
                 node.fn_decl().map_or(method.ident(tcx).span, |decl| decl.output.span())
             }
@@ -437,8 +439,8 @@ fn virtual_call_violation_for_method<'tcx>(
     if contains_illegal_self_type_reference(tcx, trait_def_id, sig.output()) {
         return Some(MethodViolationCode::ReferencesSelfOutput);
     }
-    if contains_illegal_impl_trait_in_trait(tcx, sig.output()) {
-        return Some(MethodViolationCode::ReferencesImplTraitInTrait);
+    if let Some(code) = contains_illegal_impl_trait_in_trait(tcx, method.def_id, sig.output()) {
+        return Some(code);
     }
 
     // We can't monomorphize things like `fn foo<A>(...)`.
@@ -684,10 +686,9 @@ fn receiver_is_dispatchable<'tcx>(
         let param_env = tcx.param_env(method.def_id);
 
         // Self: Unsize<U>
-        let unsize_predicate = ty::Binder::dummy(ty::TraitRef {
-            def_id: unsize_did,
-            substs: tcx.mk_substs_trait(tcx.types.self_param, &[unsized_self_ty.into()]),
-        })
+        let unsize_predicate = ty::Binder::dummy(
+            tcx.mk_trait_ref(unsize_did, [tcx.types.self_param, unsized_self_ty]),
+        )
         .without_const()
         .to_predicate(tcx);
 
@@ -719,14 +720,11 @@ fn receiver_is_dispatchable<'tcx>(
 
     // Receiver: DispatchFromDyn<Receiver[Self => U]>
     let obligation = {
-        let predicate = ty::Binder::dummy(ty::TraitRef {
-            def_id: dispatch_from_dyn_did,
-            substs: tcx.mk_substs_trait(receiver_ty, &[unsized_receiver_ty.into()]),
-        })
-        .without_const()
-        .to_predicate(tcx);
+        let predicate = ty::Binder::dummy(
+            tcx.mk_trait_ref(dispatch_from_dyn_did, [receiver_ty, unsized_receiver_ty]),
+        );
 
-        Obligation::new(ObligationCause::dummy(), param_env, predicate)
+        Obligation::new(tcx, ObligationCause::dummy(), param_env, predicate)
     };
 
     let infcx = tcx.infer_ctxt().build();
@@ -838,23 +836,9 @@ fn contains_illegal_self_type_reference<'tcx, T: TypeVisitable<'tcx>>(
         }
 
         fn visit_const(&mut self, ct: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
-            // Constants can only influence object safety if they reference `Self`.
+            // Constants can only influence object safety if they are generic and reference `Self`.
             // This is only possible for unevaluated constants, so we walk these here.
-            //
-            // If `AbstractConst::from_const` returned an error we already failed compilation
-            // so we don't have to emit an additional error here.
-            use rustc_middle::ty::abstract_const::Node;
-            if let Ok(Some(ct)) = AbstractConst::from_const(self.tcx, ct) {
-                walk_abstract_const(self.tcx, ct, |node| match node.root(self.tcx) {
-                    Node::Leaf(leaf) => self.visit_const(leaf),
-                    Node::Cast(_, _, ty) => self.visit_ty(ty),
-                    Node::Binop(..) | Node::UnaryOp(..) | Node::FunctionCall(_, _) => {
-                        ControlFlow::CONTINUE
-                    }
-                })
-            } else {
-                ct.super_visit_with(self)
-            }
+            self.tcx.expand_abstract_consts(ct).super_visit_with(self)
         }
     }
 
@@ -865,16 +849,24 @@ fn contains_illegal_self_type_reference<'tcx, T: TypeVisitable<'tcx>>(
 
 pub fn contains_illegal_impl_trait_in_trait<'tcx>(
     tcx: TyCtxt<'tcx>,
+    fn_def_id: DefId,
     ty: ty::Binder<'tcx, Ty<'tcx>>,
-) -> bool {
+) -> Option<MethodViolationCode> {
+    // This would be caught below, but rendering the error as a separate
+    // `async-specific` message is better.
+    if tcx.asyncness(fn_def_id).is_async() {
+        return Some(MethodViolationCode::AsyncFn);
+    }
+
     // FIXME(RPITIT): Perhaps we should use a visitor here?
-    ty.skip_binder().walk().any(|arg| {
+    ty.skip_binder().walk().find_map(|arg| {
         if let ty::GenericArgKind::Type(ty) = arg.unpack()
             && let ty::Projection(proj) = ty.kind()
+            && tcx.def_kind(proj.item_def_id) == DefKind::ImplTraitPlaceholder
         {
-            tcx.def_kind(proj.item_def_id) == DefKind::ImplTraitPlaceholder
+            Some(MethodViolationCode::ReferencesImplTraitInTrait(tcx.def_span(proj.item_def_id)))
         } else {
-            false
+            None
         }
     })
 }
diff --git a/compiler/rustc_trait_selection/src/traits/on_unimplemented.rs b/compiler/rustc_trait_selection/src/traits/on_unimplemented.rs
deleted file mode 100644
index 4a4f34b76..000000000
--- a/compiler/rustc_trait_selection/src/traits/on_unimplemented.rs
+++ /dev/null
@@ -1,392 +0,0 @@
-use rustc_ast::{MetaItem, NestedMetaItem};
-use rustc_attr as attr;
-use rustc_data_structures::fx::FxHashMap;
-use rustc_errors::{struct_span_err, ErrorGuaranteed};
-use rustc_hir::def_id::DefId;
-use rustc_middle::ty::{self, GenericParamDefKind, TyCtxt};
-use rustc_parse_format::{ParseMode, Parser, Piece, Position};
-use rustc_span::symbol::{kw, sym, Symbol};
-use rustc_span::{Span, DUMMY_SP};
-
-use crate::errors::{
-    EmptyOnClauseInOnUnimplemented, InvalidOnClauseInOnUnimplemented, NoValueInOnUnimplemented,
-};
-
-#[derive(Clone, Debug)]
-pub struct OnUnimplementedFormatString(Symbol);
-
-#[derive(Debug)]
-pub struct OnUnimplementedDirective {
-    pub condition: Option<MetaItem>,
-    pub subcommands: Vec<OnUnimplementedDirective>,
-    pub message: Option<OnUnimplementedFormatString>,
-    pub label: Option<OnUnimplementedFormatString>,
-    pub note: Option<OnUnimplementedFormatString>,
-    pub parent_label: Option<OnUnimplementedFormatString>,
-    pub append_const_msg: Option<Option<Symbol>>,
-}
-
-#[derive(Default)]
-pub struct OnUnimplementedNote {
-    pub message: Option<String>,
-    pub label: Option<String>,
-    pub note: Option<String>,
-    pub parent_label: Option<String>,
-    /// Append a message for `~const Trait` errors. `None` means not requested and
-    /// should fallback to a generic message, `Some(None)` suggests using the default
-    /// appended message, `Some(Some(s))` suggests use the `s` message instead of the
-    /// default one..
-    pub append_const_msg: Option<Option<Symbol>>,
-}
-
-impl<'tcx> OnUnimplementedDirective {
-    fn parse(
-        tcx: TyCtxt<'tcx>,
-        item_def_id: DefId,
-        items: &[NestedMetaItem],
-        span: Span,
-        is_root: bool,
-    ) -> Result<Self, ErrorGuaranteed> {
-        let mut errored = None;
-        let mut item_iter = items.iter();
-
-        let parse_value = |value_str| {
-            OnUnimplementedFormatString::try_parse(tcx, item_def_id, value_str, span).map(Some)
-        };
-
-        let condition = if is_root {
-            None
-        } else {
-            let cond = item_iter
-                .next()
-                .ok_or_else(|| tcx.sess.emit_err(EmptyOnClauseInOnUnimplemented { span }))?
-                .meta_item()
-                .ok_or_else(|| tcx.sess.emit_err(InvalidOnClauseInOnUnimplemented { span }))?;
-            attr::eval_condition(cond, &tcx.sess.parse_sess, Some(tcx.features()), &mut |cfg| {
-                if let Some(value) = cfg.value && let Err(guar) = parse_value(value) {
-                    errored = Some(guar);
-                }
-                true
-            });
-            Some(cond.clone())
-        };
-
-        let mut message = None;
-        let mut label = None;
-        let mut note = None;
-        let mut parent_label = None;
-        let mut subcommands = vec![];
-        let mut append_const_msg = None;
-
-        for item in item_iter {
-            if item.has_name(sym::message) && message.is_none() {
-                if let Some(message_) = item.value_str() {
-                    message = parse_value(message_)?;
-                    continue;
-                }
-            } else if item.has_name(sym::label) && label.is_none() {
-                if let Some(label_) = item.value_str() {
-                    label = parse_value(label_)?;
-                    continue;
-                }
-            } else if item.has_name(sym::note) && note.is_none() {
-                if let Some(note_) = item.value_str() {
-                    note = parse_value(note_)?;
-                    continue;
-                }
-            } else if item.has_name(sym::parent_label) && parent_label.is_none() {
-                if let Some(parent_label_) = item.value_str() {
-                    parent_label = parse_value(parent_label_)?;
-                    continue;
-                }
-            } else if item.has_name(sym::on)
-                && is_root
-                && message.is_none()
-                && label.is_none()
-                && note.is_none()
-            {
-                if let Some(items) = item.meta_item_list() {
-                    match Self::parse(tcx, item_def_id, &items, item.span(), false) {
-                        Ok(subcommand) => subcommands.push(subcommand),
-                        Err(reported) => errored = Some(reported),
-                    };
-                    continue;
-                }
-            } else if item.has_name(sym::append_const_msg) && append_const_msg.is_none() {
-                if let Some(msg) = item.value_str() {
-                    append_const_msg = Some(Some(msg));
-                    continue;
-                } else if item.is_word() {
-                    append_const_msg = Some(None);
-                    continue;
-                }
-            }
-
-            // nothing found
-            tcx.sess.emit_err(NoValueInOnUnimplemented { span: item.span() });
-        }
-
-        if let Some(reported) = errored {
-            Err(reported)
-        } else {
-            Ok(OnUnimplementedDirective {
-                condition,
-                subcommands,
-                message,
-                label,
-                note,
-                parent_label,
-                append_const_msg,
-            })
-        }
-    }
-
-    pub fn of_item(tcx: TyCtxt<'tcx>, item_def_id: DefId) -> Result<Option<Self>, ErrorGuaranteed> {
-        let Some(attr) = tcx.get_attr(item_def_id, sym::rustc_on_unimplemented) else {
-            return Ok(None);
-        };
-
-        let result = if let Some(items) = attr.meta_item_list() {
-            Self::parse(tcx, item_def_id, &items, attr.span, true).map(Some)
-        } else if let Some(value) = attr.value_str() {
-            Ok(Some(OnUnimplementedDirective {
-                condition: None,
-                message: None,
-                subcommands: vec![],
-                label: Some(OnUnimplementedFormatString::try_parse(
-                    tcx,
-                    item_def_id,
-                    value,
-                    attr.span,
-                )?),
-                note: None,
-                parent_label: None,
-                append_const_msg: None,
-            }))
-        } else {
-            let reported =
-                tcx.sess.delay_span_bug(DUMMY_SP, "of_item: neither meta_item_list nor value_str");
-            return Err(reported);
-        };
-        debug!("of_item({:?}) = {:?}", item_def_id, result);
-        result
-    }
-
-    pub fn evaluate(
-        &self,
-        tcx: TyCtxt<'tcx>,
-        trait_ref: ty::TraitRef<'tcx>,
-        options: &[(Symbol, Option<String>)],
-    ) -> OnUnimplementedNote {
-        let mut message = None;
-        let mut label = None;
-        let mut note = None;
-        let mut parent_label = None;
-        let mut append_const_msg = None;
-        info!("evaluate({:?}, trait_ref={:?}, options={:?})", self, trait_ref, options);
-
-        let options_map: FxHashMap<Symbol, String> =
-            options.iter().filter_map(|(k, v)| v.as_ref().map(|v| (*k, v.to_owned()))).collect();
-
-        for command in self.subcommands.iter().chain(Some(self)).rev() {
-            if let Some(ref condition) = command.condition && !attr::eval_condition(
-                condition,
-                &tcx.sess.parse_sess,
-                Some(tcx.features()),
-                &mut |cfg| {
-                    let value = cfg.value.map(|v| {
-                        OnUnimplementedFormatString(v).format(tcx, trait_ref, &options_map)
-                    });
-
-                    options.contains(&(cfg.name, value))
-                },
-            ) {
-                debug!("evaluate: skipping {:?} due to condition", command);
-                continue;
-            }
-            debug!("evaluate: {:?} succeeded", command);
-            if let Some(ref message_) = command.message {
-                message = Some(message_.clone());
-            }
-
-            if let Some(ref label_) = command.label {
-                label = Some(label_.clone());
-            }
-
-            if let Some(ref note_) = command.note {
-                note = Some(note_.clone());
-            }
-
-            if let Some(ref parent_label_) = command.parent_label {
-                parent_label = Some(parent_label_.clone());
-            }
-
-            append_const_msg = command.append_const_msg;
-        }
-
-        OnUnimplementedNote {
-            label: label.map(|l| l.format(tcx, trait_ref, &options_map)),
-            message: message.map(|m| m.format(tcx, trait_ref, &options_map)),
-            note: note.map(|n| n.format(tcx, trait_ref, &options_map)),
-            parent_label: parent_label.map(|e_s| e_s.format(tcx, trait_ref, &options_map)),
-            append_const_msg,
-        }
-    }
-}
-
-impl<'tcx> OnUnimplementedFormatString {
-    fn try_parse(
-        tcx: TyCtxt<'tcx>,
-        item_def_id: DefId,
-        from: Symbol,
-        err_sp: Span,
-    ) -> Result<Self, ErrorGuaranteed> {
-        let result = OnUnimplementedFormatString(from);
-        result.verify(tcx, item_def_id, err_sp)?;
-        Ok(result)
-    }
-
-    fn verify(
-        &self,
-        tcx: TyCtxt<'tcx>,
-        item_def_id: DefId,
-        span: Span,
-    ) -> Result<(), ErrorGuaranteed> {
-        let trait_def_id = if tcx.is_trait(item_def_id) {
-            item_def_id
-        } else {
-            tcx.trait_id_of_impl(item_def_id)
-                .expect("expected `on_unimplemented` to correspond to a trait")
-        };
-        let trait_name = tcx.item_name(trait_def_id);
-        let generics = tcx.generics_of(item_def_id);
-        let s = self.0.as_str();
-        let parser = Parser::new(s, None, None, false, ParseMode::Format);
-        let mut result = Ok(());
-        for token in parser {
-            match token {
-                Piece::String(_) => (), // Normal string, no need to check it
-                Piece::NextArgument(a) => match a.position {
-                    Position::ArgumentNamed(s) => {
-                        match Symbol::intern(s) {
-                            // `{Self}` is allowed
-                            kw::SelfUpper => (),
-                            // `{ThisTraitsName}` is allowed
-                            s if s == trait_name => (),
-                            // `{from_method}` is allowed
-                            sym::from_method => (),
-                            // `{from_desugaring}` is allowed
-                            sym::from_desugaring => (),
-                            // `{ItemContext}` is allowed
-                            sym::ItemContext => (),
-                            // `{integral}` and `{integer}` and `{float}` are allowed
-                            sym::integral | sym::integer_ | sym::float => (),
-                            // So is `{A}` if A is a type parameter
-                            s => match generics.params.iter().find(|param| param.name == s) {
-                                Some(_) => (),
-                                None => {
-                                    let reported = struct_span_err!(
-                                        tcx.sess,
-                                        span,
-                                        E0230,
-                                        "there is no parameter `{}` on {}",
-                                        s,
-                                        if trait_def_id == item_def_id {
-                                            format!("trait `{}`", trait_name)
-                                        } else {
-                                            "impl".to_string()
-                                        }
-                                    )
-                                    .emit();
-                                    result = Err(reported);
-                                }
-                            },
-                        }
-                    }
-                    // `{:1}` and `{}` are not to be used
-                    Position::ArgumentIs(..) | Position::ArgumentImplicitlyIs(_) => {
-                        let reported = struct_span_err!(
-                            tcx.sess,
-                            span,
-                            E0231,
-                            "only named substitution parameters are allowed"
-                        )
-                        .emit();
-                        result = Err(reported);
-                    }
-                },
-            }
-        }
-
-        result
-    }
-
-    pub fn format(
-        &self,
-        tcx: TyCtxt<'tcx>,
-        trait_ref: ty::TraitRef<'tcx>,
-        options: &FxHashMap<Symbol, String>,
-    ) -> String {
-        let name = tcx.item_name(trait_ref.def_id);
-        let trait_str = tcx.def_path_str(trait_ref.def_id);
-        let generics = tcx.generics_of(trait_ref.def_id);
-        let generic_map = generics
-            .params
-            .iter()
-            .filter_map(|param| {
-                let value = match param.kind {
-                    GenericParamDefKind::Type { .. } | GenericParamDefKind::Const { .. } => {
-                        trait_ref.substs[param.index as usize].to_string()
-                    }
-                    GenericParamDefKind::Lifetime => return None,
-                };
-                let name = param.name;
-                Some((name, value))
-            })
-            .collect::<FxHashMap<Symbol, String>>();
-        let empty_string = String::new();
-
-        let s = self.0.as_str();
-        let parser = Parser::new(s, None, None, false, ParseMode::Format);
-        let item_context = (options.get(&sym::ItemContext)).unwrap_or(&empty_string);
-        parser
-            .map(|p| match p {
-                Piece::String(s) => s,
-                Piece::NextArgument(a) => match a.position {
-                    Position::ArgumentNamed(s) => {
-                        let s = Symbol::intern(s);
-                        match generic_map.get(&s) {
-                            Some(val) => val,
-                            None if s == name => &trait_str,
-                            None => {
-                                if let Some(val) = options.get(&s) {
-                                    val
-                                } else if s == sym::from_desugaring || s == sym::from_method {
-                                    // don't break messages using these two arguments incorrectly
-                                    &empty_string
-                                } else if s == sym::ItemContext {
-                                    &item_context
-                                } else if s == sym::integral {
-                                    "{integral}"
-                                } else if s == sym::integer_ {
-                                    "{integer}"
-                                } else if s == sym::float {
-                                    "{float}"
-                                } else {
-                                    bug!(
-                                        "broken on_unimplemented {:?} for {:?}: \
-                                      no argument matching {:?}",
-                                        self.0,
-                                        trait_ref,
-                                        s
-                                    )
-                                }
-                            }
-                        }
-                    }
-                    _ => bug!("broken on_unimplemented {:?} - bad format arg", self.0),
-                },
-            })
-            .collect()
-    }
-}
diff --git a/compiler/rustc_trait_selection/src/traits/outlives_bounds.rs b/compiler/rustc_trait_selection/src/traits/outlives_bounds.rs
index 108dae092..e1092a788 100644
--- a/compiler/rustc_trait_selection/src/traits/outlives_bounds.rs
+++ b/compiler/rustc_trait_selection/src/traits/outlives_bounds.rs
@@ -1,8 +1,8 @@
 use crate::infer::InferCtxt;
 use crate::traits::query::type_op::{self, TypeOp, TypeOpOutput};
 use crate::traits::query::NoSolution;
-use crate::traits::{ObligationCause, TraitEngine, TraitEngineExt};
-use rustc_data_structures::fx::FxHashSet;
+use crate::traits::ObligationCause;
+use rustc_data_structures::fx::FxIndexSet;
 use rustc_hir as hir;
 use rustc_hir::HirId;
 use rustc_middle::ty::{self, ParamEnv, Ty};
@@ -22,7 +22,7 @@ pub trait InferCtxtExt<'a, 'tcx> {
         &'a self,
         param_env: ty::ParamEnv<'tcx>,
         body_id: hir::HirId,
-        tys: FxHashSet<Ty<'tcx>>,
+        tys: FxIndexSet<Ty<'tcx>>,
     ) -> Bounds<'a, 'tcx>;
 }
 
@@ -74,20 +74,20 @@ impl<'a, 'tcx: 'a> InferCtxtExt<'a, 'tcx> for InferCtxt<'tcx> {
             debug!(?constraints);
             // Instantiation may have produced new inference variables and constraints on those
             // variables. Process these constraints.
-            let mut fulfill_cx = <dyn TraitEngine<'tcx>>::new(self.tcx);
             let cause = ObligationCause::misc(span, body_id);
-            for &constraint in &constraints.outlives {
-                let obligation = self.query_outlives_constraint_to_obligation(
-                    constraint,
-                    cause.clone(),
-                    param_env,
-                );
-                fulfill_cx.register_predicate_obligation(self, obligation);
-            }
+            let errors = super::fully_solve_obligations(
+                self,
+                constraints.outlives.iter().map(|constraint| {
+                    self.query_outlives_constraint_to_obligation(
+                        *constraint,
+                        cause.clone(),
+                        param_env,
+                    )
+                }),
+            );
             if !constraints.member_constraints.is_empty() {
                 span_bug!(span, "{:#?}", constraints.member_constraints);
             }
-            let errors = fulfill_cx.select_all_or_error(self);
             if !errors.is_empty() {
                 self.tcx.sess.delay_span_bug(
                     span,
@@ -103,7 +103,7 @@ impl<'a, 'tcx: 'a> InferCtxtExt<'a, 'tcx> for InferCtxt<'tcx> {
         &'a self,
         param_env: ParamEnv<'tcx>,
         body_id: HirId,
-        tys: FxHashSet<Ty<'tcx>>,
+        tys: FxIndexSet<Ty<'tcx>>,
     ) -> Bounds<'a, 'tcx> {
         tys.into_iter()
             .map(move |ty| {
diff --git a/compiler/rustc_trait_selection/src/traits/project.rs b/compiler/rustc_trait_selection/src/traits/project.rs
index e4284b9d3..5789754e4 100644
--- a/compiler/rustc_trait_selection/src/traits/project.rs
+++ b/compiler/rustc_trait_selection/src/traits/project.rs
@@ -11,8 +11,8 @@ use super::Selection;
 use super::SelectionContext;
 use super::SelectionError;
 use super::{
-    ImplSourceClosureData, ImplSourceDiscriminantKindData, ImplSourceFnPointerData,
-    ImplSourceGeneratorData, ImplSourcePointeeData, ImplSourceUserDefinedData,
+    ImplSourceClosureData, ImplSourceFnPointerData, ImplSourceFutureData, ImplSourceGeneratorData,
+    ImplSourceUserDefinedData,
 };
 use super::{Normalized, NormalizedTy, ProjectionCacheEntry, ProjectionCacheKey};
 
@@ -27,7 +27,9 @@ use rustc_errors::ErrorGuaranteed;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::DefId;
 use rustc_hir::lang_items::LangItem;
+use rustc_infer::infer::at::At;
 use rustc_infer::infer::resolve::OpportunisticRegionResolver;
+use rustc_infer::traits::ImplSourceBuiltinData;
 use rustc_middle::traits::select::OverflowError;
 use rustc_middle::ty::fold::{TypeFoldable, TypeFolder, TypeSuperFoldable};
 use rustc_middle::ty::visit::{MaxUniverse, TypeVisitable};
@@ -47,6 +49,23 @@ pub type ProjectionTyObligation<'tcx> = Obligation<'tcx, ty::ProjectionTy<'tcx>>
 
 pub(super) struct InProgress;
 
+pub trait NormalizeExt<'tcx> {
+    /// Normalize a value using the `AssocTypeNormalizer`.
+    ///
+    /// This normalization should be used when the type contains inference variables or the
+    /// projection may be fallible.
+    fn normalize<T: TypeFoldable<'tcx>>(&self, t: T) -> InferOk<'tcx, T>;
+}
+
+impl<'tcx> NormalizeExt<'tcx> for At<'_, 'tcx> {
+    fn normalize<T: TypeFoldable<'tcx>>(&self, value: T) -> InferOk<'tcx, T> {
+        let mut selcx = SelectionContext::new(self.infcx);
+        let Normalized { value, obligations } =
+            normalize_with_depth(&mut selcx, self.param_env, self.cause.clone(), 0, value);
+        InferOk { value, obligations }
+    }
+}
+
 /// When attempting to resolve `<T as TraitRef>::Name` ...
 #[derive(Debug)]
 pub enum ProjectionError<'tcx> {
@@ -193,14 +212,14 @@ pub(super) fn poly_project_and_unify_type<'cx, 'tcx>(
     selcx: &mut SelectionContext<'cx, 'tcx>,
     obligation: &PolyProjectionObligation<'tcx>,
 ) -> ProjectAndUnifyResult<'tcx> {
-    let infcx = selcx.infcx();
+    let infcx = selcx.infcx;
     let r = infcx.commit_if_ok(|_snapshot| {
         let old_universe = infcx.universe();
         let placeholder_predicate =
             infcx.replace_bound_vars_with_placeholders(obligation.predicate);
         let new_universe = infcx.universe();
 
-        let placeholder_obligation = obligation.with(placeholder_predicate);
+        let placeholder_obligation = obligation.with(infcx.tcx, placeholder_predicate);
         match project_and_unify_type(selcx, &placeholder_obligation) {
             ProjectAndUnifyResult::MismatchedProjectionTypes(e) => Err(e),
             ProjectAndUnifyResult::Holds(obligations)
@@ -249,7 +268,7 @@ fn project_and_unify_type<'cx, 'tcx>(
 ) -> ProjectAndUnifyResult<'tcx> {
     let mut obligations = vec![];
 
-    let infcx = selcx.infcx();
+    let infcx = selcx.infcx;
     let normalized = match opt_normalize_projection_type(
         selcx,
         obligation.param_env,
@@ -268,7 +287,7 @@ fn project_and_unify_type<'cx, 'tcx>(
     // This allows users to omit re-mentioning all bounds on an associated type and just use an
     // `impl Trait` for the assoc type to add more bounds.
     let InferOk { value: actual, obligations: new } =
-        selcx.infcx().replace_opaque_types_with_inference_vars(
+        selcx.infcx.replace_opaque_types_with_inference_vars(
             actual,
             obligation.cause.body_id,
             obligation.cause.span,
@@ -288,39 +307,8 @@ fn project_and_unify_type<'cx, 'tcx>(
     }
 }
 
-/// Normalizes any associated type projections in `value`, replacing
-/// them with a fully resolved type where possible. The return value
-/// combines the normalized result and any additional obligations that
-/// were incurred as result.
-pub fn normalize<'a, 'b, 'tcx, T>(
-    selcx: &'a mut SelectionContext<'b, 'tcx>,
-    param_env: ty::ParamEnv<'tcx>,
-    cause: ObligationCause<'tcx>,
-    value: T,
-) -> Normalized<'tcx, T>
-where
-    T: TypeFoldable<'tcx>,
-{
-    let mut obligations = Vec::new();
-    let value = normalize_to(selcx, param_env, cause, value, &mut obligations);
-    Normalized { value, obligations }
-}
-
-pub fn normalize_to<'a, 'b, 'tcx, T>(
-    selcx: &'a mut SelectionContext<'b, 'tcx>,
-    param_env: ty::ParamEnv<'tcx>,
-    cause: ObligationCause<'tcx>,
-    value: T,
-    obligations: &mut Vec<PredicateObligation<'tcx>>,
-) -> T
-where
-    T: TypeFoldable<'tcx>,
-{
-    normalize_with_depth_to(selcx, param_env, cause, 0, value, obligations)
-}
-
 /// As `normalize`, but with a custom depth.
-pub fn normalize_with_depth<'a, 'b, 'tcx, T>(
+pub(crate) fn normalize_with_depth<'a, 'b, 'tcx, T>(
     selcx: &'a mut SelectionContext<'b, 'tcx>,
     param_env: ty::ParamEnv<'tcx>,
     cause: ObligationCause<'tcx>,
@@ -336,7 +324,7 @@ where
 }
 
 #[instrument(level = "info", skip(selcx, param_env, cause, obligations))]
-pub fn normalize_with_depth_to<'a, 'b, 'tcx, T>(
+pub(crate) fn normalize_with_depth_to<'a, 'b, 'tcx, T>(
     selcx: &'a mut SelectionContext<'b, 'tcx>,
     param_env: ty::ParamEnv<'tcx>,
     cause: ObligationCause<'tcx>,
@@ -356,7 +344,7 @@ where
 }
 
 #[instrument(level = "info", skip(selcx, param_env, cause, obligations))]
-pub fn try_normalize_with_depth_to<'a, 'b, 'tcx, T>(
+pub(crate) fn try_normalize_with_depth_to<'a, 'b, 'tcx, T>(
     selcx: &'a mut SelectionContext<'b, 'tcx>,
     param_env: ty::ParamEnv<'tcx>,
     cause: ObligationCause<'tcx>,
@@ -444,7 +432,7 @@ impl<'a, 'b, 'tcx> AssocTypeNormalizer<'a, 'b, 'tcx> {
     }
 
     fn fold<T: TypeFoldable<'tcx>>(&mut self, value: T) -> T {
-        let value = self.selcx.infcx().resolve_vars_if_possible(value);
+        let value = self.selcx.infcx.resolve_vars_if_possible(value);
         debug!(?value);
 
         assert!(
@@ -516,13 +504,12 @@ impl<'a, 'b, 'tcx> TypeFolder<'tcx> for AssocTypeNormalizer<'a, 'b, 'tcx> {
                     Reveal::All => {
                         let recursion_limit = self.tcx().recursion_limit();
                         if !recursion_limit.value_within_limit(self.depth) {
-                            let obligation = Obligation::with_depth(
-                                self.cause.clone(),
-                                recursion_limit.0,
-                                self.param_env,
-                                ty,
+                            self.selcx.infcx.err_ctxt().report_overflow_error(
+                                &ty,
+                                self.cause.span,
+                                true,
+                                |_| {},
                             );
-                            self.selcx.infcx().err_ctxt().report_overflow_error(&obligation, true);
                         }
 
                         let substs = substs.fold_with(self);
@@ -588,7 +575,7 @@ impl<'a, 'b, 'tcx> TypeFolder<'tcx> for AssocTypeNormalizer<'a, 'b, 'tcx> {
                 // want to figure out how to register obligations with escaping vars
                 // or handle this some other way.
 
-                let infcx = self.selcx.infcx();
+                let infcx = self.selcx.infcx;
                 let (data, mapped_regions, mapped_types, mapped_consts) =
                     BoundVarReplacer::replace_bound_vars(infcx, &mut self.universes, data);
                 let data = data.fold_with(self);
@@ -632,13 +619,13 @@ impl<'a, 'b, 'tcx> TypeFolder<'tcx> for AssocTypeNormalizer<'a, 'b, 'tcx> {
     #[instrument(skip(self), level = "debug")]
     fn fold_const(&mut self, constant: ty::Const<'tcx>) -> ty::Const<'tcx> {
         let tcx = self.selcx.tcx();
-        if tcx.lazy_normalization() {
+        if tcx.lazy_normalization() || !needs_normalization(&constant, self.param_env.reveal()) {
             constant
         } else {
             let constant = constant.super_fold_with(self);
             debug!(?constant, ?self.param_env);
             with_replaced_escaping_bound_vars(
-                self.selcx.infcx(),
+                self.selcx.infcx,
                 &mut self.universes,
                 constant,
                 |constant| constant.eval(tcx, self.param_env),
@@ -816,9 +803,7 @@ impl<'tcx> TypeFolder<'tcx> for BoundVarReplacer<'_, 'tcx> {
                 let universe = self.universe_for(debruijn);
                 let p = ty::PlaceholderConst { universe, name: bound_const };
                 self.mapped_consts.insert(p, bound_const);
-                self.infcx
-                    .tcx
-                    .mk_const(ty::ConstS { kind: ty::ConstKind::Placeholder(p), ty: ct.ty() })
+                self.infcx.tcx.mk_const(p, ct.ty())
             }
             _ => ct.super_fold_with(self),
         }
@@ -829,7 +814,7 @@ impl<'tcx> TypeFolder<'tcx> for BoundVarReplacer<'_, 'tcx> {
     }
 }
 
-// The inverse of `BoundVarReplacer`: replaces placeholders with the bound vars from which they came.
+/// The inverse of [`BoundVarReplacer`]: replaces placeholders with the bound vars from which they came.
 pub struct PlaceholderReplacer<'me, 'tcx> {
     infcx: &'me InferCtxt<'tcx>,
     mapped_regions: BTreeMap<ty::PlaceholderRegion, ty::BoundRegion>,
@@ -953,10 +938,7 @@ impl<'tcx> TypeFolder<'tcx> for PlaceholderReplacer<'_, 'tcx> {
                     let db = ty::DebruijnIndex::from_usize(
                         self.universe_indices.len() - index + self.current_index.as_usize() - 1,
                     );
-                    self.tcx().mk_const(ty::ConstS {
-                        kind: ty::ConstKind::Bound(db, *replace_var),
-                        ty: ct.ty(),
-                    })
+                    self.tcx().mk_const(ty::ConstKind::Bound(db, *replace_var), ct.ty())
                 }
                 None => ct,
             }
@@ -995,10 +977,7 @@ pub fn normalize_projection_type<'a, 'b, 'tcx>(
         // and a deferred predicate to resolve this when more type
         // information is available.
 
-        selcx
-            .infcx()
-            .infer_projection(param_env, projection_ty, cause, depth + 1, obligations)
-            .into()
+        selcx.infcx.infer_projection(param_env, projection_ty, cause, depth + 1, obligations).into()
     })
 }
 
@@ -1021,7 +1000,7 @@ fn opt_normalize_projection_type<'a, 'b, 'tcx>(
     depth: usize,
     obligations: &mut Vec<PredicateObligation<'tcx>>,
 ) -> Result<Option<Term<'tcx>>, InProgress> {
-    let infcx = selcx.infcx();
+    let infcx = selcx.infcx;
     // Don't use the projection cache in intercrate mode -
     // the `infcx` may be re-used between intercrate in non-intercrate
     // mode, which could lead to using incorrect cache results.
@@ -1100,7 +1079,8 @@ fn opt_normalize_projection_type<'a, 'b, 'tcx>(
         }
     }
 
-    let obligation = Obligation::with_depth(cause.clone(), depth, param_env, projection_ty);
+    let obligation =
+        Obligation::with_depth(selcx.tcx(), cause.clone(), depth, param_env, projection_ty);
 
     match project(selcx, &obligation) {
         Ok(Projected::Progress(Progress {
@@ -1112,7 +1092,7 @@ fn opt_normalize_projection_type<'a, 'b, 'tcx>(
             // an impl, where-clause etc) and hence we must
             // re-normalize it
 
-            let projected_term = selcx.infcx().resolve_vars_if_possible(projected_term);
+            let projected_term = selcx.infcx.resolve_vars_if_possible(projected_term);
 
             let mut result = if projected_term.has_projections() {
                 let mut normalizer = AssocTypeNormalizer::new(
@@ -1208,9 +1188,9 @@ fn normalize_to_error<'a, 'tcx>(
         param_env,
         predicate: trait_ref.without_const().to_predicate(selcx.tcx()),
     };
-    let tcx = selcx.infcx().tcx;
+    let tcx = selcx.infcx.tcx;
     let def_id = projection_ty.item_def_id;
-    let new_value = selcx.infcx().next_ty_var(TypeVariableOrigin {
+    let new_value = selcx.infcx.next_ty_var(TypeVariableOrigin {
         kind: TypeVariableOriginKind::NormalizeProjectionType,
         span: tcx.def_span(def_id),
     });
@@ -1330,11 +1310,10 @@ fn assemble_candidate_for_impl_trait_in_trait<'cx, 'tcx>(
             obligation.predicate.substs.truncate_to(tcx, tcx.generics_of(trait_def_id));
         // FIXME(named-returns): Binders
         let trait_predicate =
-            ty::Binder::dummy(ty::TraitRef { def_id: trait_def_id, substs: trait_substs })
-                .to_poly_trait_predicate();
+            ty::Binder::dummy(ty::TraitRef { def_id: trait_def_id, substs: trait_substs });
 
-        let _ =
-            selcx.infcx().commit_if_ok(|_| match selcx.select(&obligation.with(trait_predicate)) {
+        let _ = selcx.infcx.commit_if_ok(|_| {
+            match selcx.select(&obligation.with(tcx, trait_predicate)) {
                 Ok(Some(super::ImplSource::UserDefined(data))) => {
                     candidate_set.push_candidate(ProjectionCandidate::ImplTraitInTrait(
                         ImplTraitInTraitCandidate::Impl(data),
@@ -1354,7 +1333,8 @@ fn assemble_candidate_for_impl_trait_in_trait<'cx, 'tcx>(
                     candidate_set.mark_error(e);
                     return Err(());
                 }
-            });
+            }
+        });
     }
 }
 
@@ -1437,7 +1417,7 @@ fn assemble_candidates_from_object_ty<'cx, 'tcx>(
     let tcx = selcx.tcx();
 
     let self_ty = obligation.predicate.self_ty();
-    let object_ty = selcx.infcx().shallow_resolve(self_ty);
+    let object_ty = selcx.infcx.shallow_resolve(self_ty);
     let data = match object_ty.kind() {
         ty::Dynamic(data, ..) => data,
         ty::Infer(ty::TyVar(_)) => {
@@ -1475,10 +1455,12 @@ fn assemble_candidates_from_predicates<'cx, 'tcx>(
     env_predicates: impl Iterator<Item = ty::Predicate<'tcx>>,
     potentially_unnormalized_candidates: bool,
 ) {
-    let infcx = selcx.infcx();
+    let infcx = selcx.infcx;
     for predicate in env_predicates {
         let bound_predicate = predicate.kind();
-        if let ty::PredicateKind::Projection(data) = predicate.kind().skip_binder() {
+        if let ty::PredicateKind::Clause(ty::Clause::Projection(data)) =
+            predicate.kind().skip_binder()
+        {
             let data = bound_predicate.rebind(data);
             if data.projection_def_id() != obligation.predicate.item_def_id {
                 continue;
@@ -1528,8 +1510,8 @@ fn assemble_candidates_from_impls<'cx, 'tcx>(
     // If we are resolving `<T as TraitRef<...>>::Item == Type`,
     // start out by selecting the predicate `T as TraitRef<...>`:
     let poly_trait_ref = ty::Binder::dummy(obligation.predicate.trait_ref(selcx.tcx()));
-    let trait_obligation = obligation.with(poly_trait_ref.to_poly_trait_predicate());
-    let _ = selcx.infcx().commit_if_ok(|_| {
+    let trait_obligation = obligation.with(selcx.tcx(), poly_trait_ref);
+    let _ = selcx.infcx.commit_if_ok(|_| {
         let impl_source = match selcx.select(&trait_obligation) {
             Ok(Some(impl_source)) => impl_source,
             Ok(None) => {
@@ -1546,6 +1528,7 @@ fn assemble_candidates_from_impls<'cx, 'tcx>(
         let eligible = match &impl_source {
             super::ImplSource::Closure(_)
             | super::ImplSource::Generator(_)
+            | super::ImplSource::Future(_)
             | super::ImplSource::FnPointer(_)
             | super::ImplSource::TraitAlias(_) => true,
             super::ImplSource::UserDefined(impl_data) => {
@@ -1586,7 +1569,7 @@ fn assemble_candidates_from_impls<'cx, 'tcx>(
                     if obligation.param_env.reveal() == Reveal::All {
                         // NOTE(eddyb) inference variables can resolve to parameters, so
                         // assume `poly_trait_ref` isn't monomorphic, if it contains any.
-                        let poly_trait_ref = selcx.infcx().resolve_vars_if_possible(poly_trait_ref);
+                        let poly_trait_ref = selcx.infcx.resolve_vars_if_possible(poly_trait_ref);
                         !poly_trait_ref.still_further_specializable()
                     } else {
                         debug!(
@@ -1598,128 +1581,126 @@ fn assemble_candidates_from_impls<'cx, 'tcx>(
                     }
                 }
             }
-            super::ImplSource::DiscriminantKind(..) => {
-                // While `DiscriminantKind` is automatically implemented for every type,
-                // the concrete discriminant may not be known yet.
-                //
-                // Any type with multiple potential discriminant types is therefore not eligible.
-                let self_ty = selcx.infcx().shallow_resolve(obligation.predicate.self_ty());
-
-                match self_ty.kind() {
-                    ty::Bool
-                    | ty::Char
-                    | ty::Int(_)
-                    | ty::Uint(_)
-                    | ty::Float(_)
-                    | ty::Adt(..)
-                    | ty::Foreign(_)
-                    | ty::Str
-                    | ty::Array(..)
-                    | ty::Slice(_)
-                    | ty::RawPtr(..)
-                    | ty::Ref(..)
-                    | ty::FnDef(..)
-                    | ty::FnPtr(..)
-                    | ty::Dynamic(..)
-                    | ty::Closure(..)
-                    | ty::Generator(..)
-                    | ty::GeneratorWitness(..)
-                    | ty::Never
-                    | ty::Tuple(..)
-                    // Integers and floats always have `u8` as their discriminant.
-                    | ty::Infer(ty::InferTy::IntVar(_) | ty::InferTy::FloatVar(..)) => true,
-
-                    ty::Projection(..)
-                    | ty::Opaque(..)
-                    | ty::Param(..)
-                    | ty::Bound(..)
-                    | ty::Placeholder(..)
-                    | ty::Infer(..)
-                    | ty::Error(_) => false,
-                }
-            }
-            super::ImplSource::Pointee(..) => {
-                // While `Pointee` is automatically implemented for every type,
-                // the concrete metadata type may not be known yet.
-                //
-                // Any type with multiple potential metadata types is therefore not eligible.
-                let self_ty = selcx.infcx().shallow_resolve(obligation.predicate.self_ty());
-
-                let tail = selcx.tcx().struct_tail_with_normalize(
-                    self_ty,
-                    |ty| {
-                        // We throw away any obligations we get from this, since we normalize
-                        // and confirm these obligations once again during confirmation
-                        normalize_with_depth(
-                            selcx,
-                            obligation.param_env,
-                            obligation.cause.clone(),
-                            obligation.recursion_depth + 1,
-                            ty,
-                        )
-                        .value
-                    },
-                    || {},
-                );
-
-                match tail.kind() {
-                    ty::Bool
-                    | ty::Char
-                    | ty::Int(_)
-                    | ty::Uint(_)
-                    | ty::Float(_)
-                    | ty::Str
-                    | ty::Array(..)
-                    | ty::Slice(_)
-                    | ty::RawPtr(..)
-                    | ty::Ref(..)
-                    | ty::FnDef(..)
-                    | ty::FnPtr(..)
-                    | ty::Dynamic(..)
-                    | ty::Closure(..)
-                    | ty::Generator(..)
-                    | ty::GeneratorWitness(..)
-                    | ty::Never
-                    // Extern types have unit metadata, according to RFC 2850
-                    | ty::Foreign(_)
-                    // If returned by `struct_tail_without_normalization` this is a unit struct
-                    // without any fields, or not a struct, and therefore is Sized.
-                    | ty::Adt(..)
-                    // If returned by `struct_tail_without_normalization` this is the empty tuple.
-                    | ty::Tuple(..)
-                    // Integers and floats are always Sized, and so have unit type metadata.
-                    | ty::Infer(ty::InferTy::IntVar(_) | ty::InferTy::FloatVar(..)) => true,
-
-                    // type parameters, opaques, and unnormalized projections have pointer
-                    // metadata if they're known (e.g. by the param_env) to be sized
-                    ty::Param(_) | ty::Projection(..) | ty::Opaque(..)
-                        if selcx.infcx().predicate_must_hold_modulo_regions(
-                            &obligation.with(
-                                ty::Binder::dummy(ty::TraitRef::new(
-                                    selcx.tcx().require_lang_item(LangItem::Sized, None),
-                                    selcx.tcx().mk_substs_trait(self_ty, &[]),
-                                ))
-                                .without_const()
-                                .to_predicate(selcx.tcx()),
-                            ),
-                        ) =>
-                    {
-                        true
+            super::ImplSource::Builtin(..) => {
+                // While a builtin impl may be known to exist, the associated type may not yet
+                // be known. Any type with multiple potential associated types is therefore
+                // not eligible.
+                let self_ty = selcx.infcx.shallow_resolve(obligation.predicate.self_ty());
+
+                let lang_items = selcx.tcx().lang_items();
+                if lang_items.discriminant_kind_trait() == Some(poly_trait_ref.def_id()) {
+                    match self_ty.kind() {
+                        ty::Bool
+                        | ty::Char
+                        | ty::Int(_)
+                        | ty::Uint(_)
+                        | ty::Float(_)
+                        | ty::Adt(..)
+                        | ty::Foreign(_)
+                        | ty::Str
+                        | ty::Array(..)
+                        | ty::Slice(_)
+                        | ty::RawPtr(..)
+                        | ty::Ref(..)
+                        | ty::FnDef(..)
+                        | ty::FnPtr(..)
+                        | ty::Dynamic(..)
+                        | ty::Closure(..)
+                        | ty::Generator(..)
+                        | ty::GeneratorWitness(..)
+                        | ty::Never
+                        | ty::Tuple(..)
+                        // Integers and floats always have `u8` as their discriminant.
+                        | ty::Infer(ty::InferTy::IntVar(_) | ty::InferTy::FloatVar(..)) => true,
+
+                         // type parameters, opaques, and unnormalized projections have pointer
+                        // metadata if they're known (e.g. by the param_env) to be sized
+                        ty::Param(_)
+                        | ty::Projection(..)
+                        | ty::Opaque(..)
+                        | ty::Bound(..)
+                        | ty::Placeholder(..)
+                        | ty::Infer(..)
+                        | ty::Error(_) => false,
                     }
+                } else if lang_items.pointee_trait() == Some(poly_trait_ref.def_id()) {
+                    let tail = selcx.tcx().struct_tail_with_normalize(
+                        self_ty,
+                        |ty| {
+                            // We throw away any obligations we get from this, since we normalize
+                            // and confirm these obligations once again during confirmation
+                            normalize_with_depth(
+                                selcx,
+                                obligation.param_env,
+                                obligation.cause.clone(),
+                                obligation.recursion_depth + 1,
+                                ty,
+                            )
+                            .value
+                        },
+                        || {},
+                    );
 
-                    // FIXME(compiler-errors): are Bound and Placeholder types ever known sized?
-                    ty::Param(_)
-                    | ty::Projection(..)
-                    | ty::Opaque(..)
-                    | ty::Bound(..)
-                    | ty::Placeholder(..)
-                    | ty::Infer(..)
-                    | ty::Error(_) => {
-                        if tail.has_infer_types() {
-                            candidate_set.mark_ambiguous();
+                    match tail.kind() {
+                        ty::Bool
+                        | ty::Char
+                        | ty::Int(_)
+                        | ty::Uint(_)
+                        | ty::Float(_)
+                        | ty::Str
+                        | ty::Array(..)
+                        | ty::Slice(_)
+                        | ty::RawPtr(..)
+                        | ty::Ref(..)
+                        | ty::FnDef(..)
+                        | ty::FnPtr(..)
+                        | ty::Dynamic(..)
+                        | ty::Closure(..)
+                        | ty::Generator(..)
+                        | ty::GeneratorWitness(..)
+                        | ty::Never
+                        // Extern types have unit metadata, according to RFC 2850
+                        | ty::Foreign(_)
+                        // If returned by `struct_tail_without_normalization` this is a unit struct
+                        // without any fields, or not a struct, and therefore is Sized.
+                        | ty::Adt(..)
+                        // If returned by `struct_tail_without_normalization` this is the empty tuple.
+                        | ty::Tuple(..)
+                        // Integers and floats are always Sized, and so have unit type metadata.
+                        | ty::Infer(ty::InferTy::IntVar(_) | ty::InferTy::FloatVar(..)) => true,
+
+                        // type parameters, opaques, and unnormalized projections have pointer
+                        // metadata if they're known (e.g. by the param_env) to be sized
+                        ty::Param(_) | ty::Projection(..) | ty::Opaque(..)
+                            if selcx.infcx.predicate_must_hold_modulo_regions(
+                                &obligation.with(
+                                    selcx.tcx(),
+                                    ty::Binder::dummy(
+                                        selcx.tcx().at(obligation.cause.span()).mk_trait_ref(LangItem::Sized, [self_ty]),
+                                    )
+                                    .without_const(),
+                                ),
+                            ) =>
+                        {
+                            true
+                        }
+
+                        // FIXME(compiler-errors): are Bound and Placeholder types ever known sized?
+                        ty::Param(_)
+                        | ty::Projection(..)
+                        | ty::Opaque(..)
+                        | ty::Bound(..)
+                        | ty::Placeholder(..)
+                        | ty::Infer(..)
+                        | ty::Error(_) => {
+                            if tail.has_infer_types() {
+                                candidate_set.mark_ambiguous();
+                            }
+                            false
                         }
-                        false
                     }
+                } else {
+                    bug!("unexpected builtin trait with associated type: {poly_trait_ref:?}")
                 }
             }
             super::ImplSource::Param(..) => {
@@ -1757,7 +1738,6 @@ fn assemble_candidates_from_impls<'cx, 'tcx>(
                 false
             }
             super::ImplSource::AutoImpl(..)
-            | super::ImplSource::Builtin(..)
             | super::ImplSource::TraitUpcasting(_)
             | super::ImplSource::ConstDestruct(_) => {
                 // These traits have no associated types.
@@ -1820,8 +1800,7 @@ fn confirm_candidate<'cx, 'tcx>(
     // when possible for this to work. See `auto-trait-projection-recursion.rs`
     // for a case where this matters.
     if progress.term.has_infer_regions() {
-        progress.term =
-            progress.term.fold_with(&mut OpportunisticRegionResolver::new(selcx.infcx()));
+        progress.term = progress.term.fold_with(&mut OpportunisticRegionResolver::new(selcx.infcx));
     }
     progress
 }
@@ -1834,16 +1813,13 @@ fn confirm_select_candidate<'cx, 'tcx>(
     match impl_source {
         super::ImplSource::UserDefined(data) => confirm_impl_candidate(selcx, obligation, data),
         super::ImplSource::Generator(data) => confirm_generator_candidate(selcx, obligation, data),
+        super::ImplSource::Future(data) => confirm_future_candidate(selcx, obligation, data),
         super::ImplSource::Closure(data) => confirm_closure_candidate(selcx, obligation, data),
         super::ImplSource::FnPointer(data) => confirm_fn_pointer_candidate(selcx, obligation, data),
-        super::ImplSource::DiscriminantKind(data) => {
-            confirm_discriminant_kind_candidate(selcx, obligation, data)
-        }
-        super::ImplSource::Pointee(data) => confirm_pointee_candidate(selcx, obligation, data),
+        super::ImplSource::Builtin(data) => confirm_builtin_candidate(selcx, obligation, data),
         super::ImplSource::Object(_)
         | super::ImplSource::AutoImpl(..)
         | super::ImplSource::Param(..)
-        | super::ImplSource::Builtin(..)
         | super::ImplSource::TraitUpcasting(_)
         | super::ImplSource::TraitAlias(..)
         | super::ImplSource::ConstDestruct(_) => {
@@ -1907,74 +1883,97 @@ fn confirm_generator_candidate<'cx, 'tcx>(
         .with_addl_obligations(obligations)
 }
 
-fn confirm_discriminant_kind_candidate<'cx, 'tcx>(
+fn confirm_future_candidate<'cx, 'tcx>(
     selcx: &mut SelectionContext<'cx, 'tcx>,
     obligation: &ProjectionTyObligation<'tcx>,
-    _: ImplSourceDiscriminantKindData,
+    impl_source: ImplSourceFutureData<'tcx, PredicateObligation<'tcx>>,
 ) -> Progress<'tcx> {
-    let tcx = selcx.tcx();
+    let gen_sig = impl_source.substs.as_generator().poly_sig();
+    let Normalized { value: gen_sig, obligations } = normalize_with_depth(
+        selcx,
+        obligation.param_env,
+        obligation.cause.clone(),
+        obligation.recursion_depth + 1,
+        gen_sig,
+    );
 
-    let self_ty = selcx.infcx().shallow_resolve(obligation.predicate.self_ty());
-    // We get here from `poly_project_and_unify_type` which replaces bound vars
-    // with placeholders
-    debug_assert!(!self_ty.has_escaping_bound_vars());
-    let substs = tcx.mk_substs([self_ty.into()].iter());
+    debug!(?obligation, ?gen_sig, ?obligations, "confirm_future_candidate");
 
-    let discriminant_def_id = tcx.require_lang_item(LangItem::Discriminant, None);
+    let tcx = selcx.tcx();
+    let fut_def_id = tcx.require_lang_item(LangItem::Future, None);
 
-    let predicate = ty::ProjectionPredicate {
-        projection_ty: ty::ProjectionTy { substs, item_def_id: discriminant_def_id },
-        term: self_ty.discriminant_ty(tcx).into(),
-    };
+    let predicate = super::util::future_trait_ref_and_outputs(
+        tcx,
+        fut_def_id,
+        obligation.predicate.self_ty(),
+        gen_sig,
+    )
+    .map_bound(|(trait_ref, return_ty)| {
+        debug_assert_eq!(tcx.associated_item(obligation.predicate.item_def_id).name, sym::Output);
 
-    // We get here from `poly_project_and_unify_type` which replaces bound vars
-    // with placeholders, so dummy is okay here.
-    confirm_param_env_candidate(selcx, obligation, ty::Binder::dummy(predicate), false)
+        ty::ProjectionPredicate {
+            projection_ty: ty::ProjectionTy {
+                substs: trait_ref.substs,
+                item_def_id: obligation.predicate.item_def_id,
+            },
+            term: return_ty.into(),
+        }
+    });
+
+    confirm_param_env_candidate(selcx, obligation, predicate, false)
+        .with_addl_obligations(impl_source.nested)
+        .with_addl_obligations(obligations)
 }
 
-fn confirm_pointee_candidate<'cx, 'tcx>(
+fn confirm_builtin_candidate<'cx, 'tcx>(
     selcx: &mut SelectionContext<'cx, 'tcx>,
     obligation: &ProjectionTyObligation<'tcx>,
-    _: ImplSourcePointeeData,
+    data: ImplSourceBuiltinData<PredicateObligation<'tcx>>,
 ) -> Progress<'tcx> {
     let tcx = selcx.tcx();
-    let self_ty = selcx.infcx().shallow_resolve(obligation.predicate.self_ty());
-
-    let mut obligations = vec![];
-    let (metadata_ty, check_is_sized) = self_ty.ptr_metadata_ty(tcx, |ty| {
-        normalize_with_depth_to(
-            selcx,
-            obligation.param_env,
-            obligation.cause.clone(),
-            obligation.recursion_depth + 1,
-            ty,
-            &mut obligations,
-        )
-    });
-    if check_is_sized {
-        let sized_predicate = ty::Binder::dummy(ty::TraitRef::new(
-            tcx.require_lang_item(LangItem::Sized, None),
-            tcx.mk_substs_trait(self_ty, &[]),
-        ))
-        .without_const()
-        .to_predicate(tcx);
-        obligations.push(Obligation::new(
-            obligation.cause.clone(),
-            obligation.param_env,
-            sized_predicate,
-        ));
-    }
-
+    let self_ty = obligation.predicate.self_ty();
     let substs = tcx.mk_substs([self_ty.into()].iter());
-    let metadata_def_id = tcx.require_lang_item(LangItem::Metadata, None);
-
-    let predicate = ty::ProjectionPredicate {
-        projection_ty: ty::ProjectionTy { substs, item_def_id: metadata_def_id },
-        term: metadata_ty.into(),
+    let lang_items = tcx.lang_items();
+    let item_def_id = obligation.predicate.item_def_id;
+    let trait_def_id = tcx.trait_of_item(item_def_id).unwrap();
+    let (term, obligations) = if lang_items.discriminant_kind_trait() == Some(trait_def_id) {
+        let discriminant_def_id = tcx.require_lang_item(LangItem::Discriminant, None);
+        assert_eq!(discriminant_def_id, item_def_id);
+
+        (self_ty.discriminant_ty(tcx).into(), Vec::new())
+    } else if lang_items.pointee_trait() == Some(trait_def_id) {
+        let metadata_def_id = tcx.require_lang_item(LangItem::Metadata, None);
+        assert_eq!(metadata_def_id, item_def_id);
+
+        let mut obligations = Vec::new();
+        let (metadata_ty, check_is_sized) = self_ty.ptr_metadata_ty(tcx, |ty| {
+            normalize_with_depth_to(
+                selcx,
+                obligation.param_env,
+                obligation.cause.clone(),
+                obligation.recursion_depth + 1,
+                ty,
+                &mut obligations,
+            )
+        });
+        if check_is_sized {
+            let sized_predicate = ty::Binder::dummy(
+                tcx.at(obligation.cause.span()).mk_trait_ref(LangItem::Sized, [self_ty]),
+            )
+            .without_const();
+            obligations.push(obligation.with(tcx, sized_predicate));
+        }
+        (metadata_ty.into(), obligations)
+    } else {
+        bug!("unexpected builtin trait with associated type: {:?}", obligation.predicate);
     };
 
+    let predicate =
+        ty::ProjectionPredicate { projection_ty: ty::ProjectionTy { substs, item_def_id }, term };
+
     confirm_param_env_candidate(selcx, obligation, ty::Binder::dummy(predicate), false)
         .with_addl_obligations(obligations)
+        .with_addl_obligations(data.nested)
 }
 
 fn confirm_fn_pointer_candidate<'cx, 'tcx>(
@@ -1982,7 +1981,7 @@ fn confirm_fn_pointer_candidate<'cx, 'tcx>(
     obligation: &ProjectionTyObligation<'tcx>,
     fn_pointer_impl_source: ImplSourceFnPointerData<'tcx, PredicateObligation<'tcx>>,
 ) -> Progress<'tcx> {
-    let fn_type = selcx.infcx().shallow_resolve(fn_pointer_impl_source.fn_ty);
+    let fn_type = selcx.infcx.shallow_resolve(fn_pointer_impl_source.fn_ty);
     let sig = fn_type.fn_sig(selcx.tcx());
     let Normalized { value: sig, obligations } = normalize_with_depth(
         selcx,
@@ -2055,7 +2054,7 @@ fn confirm_param_env_candidate<'cx, 'tcx>(
     poly_cache_entry: ty::PolyProjectionPredicate<'tcx>,
     potentially_unnormalized_candidate: bool,
 ) -> Progress<'tcx> {
-    let infcx = selcx.infcx();
+    let infcx = selcx.infcx;
     let cause = &obligation.cause;
     let param_env = obligation.param_env;
 
@@ -2150,7 +2149,7 @@ fn confirm_impl_candidate<'cx, 'tcx>(
     // * `substs` ends up as `[u32, S]`
     let substs = obligation.predicate.substs.rebase_onto(tcx, trait_def_id, substs);
     let substs =
-        translate_substs(selcx.infcx(), param_env, impl_def_id, substs, assoc_ty.defining_node);
+        translate_substs(selcx.infcx, param_env, impl_def_id, substs, assoc_ty.defining_node);
     let ty = tcx.bound_type_of(assoc_ty.item.def_id);
     let is_const = matches!(tcx.def_kind(assoc_ty.item.def_id), DefKind::AssocConst);
     let term: ty::EarlyBinder<ty::Term<'tcx>> = if is_const {
@@ -2158,7 +2157,7 @@ fn confirm_impl_candidate<'cx, 'tcx>(
             crate::traits::InternalSubsts::identity_for_item(tcx, assoc_ty.item.def_id);
         let did = ty::WithOptConstParam::unknown(assoc_ty.item.def_id);
         let kind = ty::ConstKind::Unevaluated(ty::UnevaluatedConst::new(did, identity_substs));
-        ty.map_bound(|ty| tcx.mk_const(ty::ConstS { ty, kind }).into())
+        ty.map_bound(|ty| tcx.mk_const(kind, ty).into())
     } else {
         ty.map_bound(|ty| ty.into())
     };
@@ -2177,7 +2176,7 @@ fn confirm_impl_candidate<'cx, 'tcx>(
 // Verify that the trait item and its implementation have compatible substs lists
 fn check_substs_compatible<'tcx>(
     tcx: TyCtxt<'tcx>,
-    assoc_ty: &ty::AssocItem,
+    assoc_item: &ty::AssocItem,
     substs: ty::SubstsRef<'tcx>,
 ) -> bool {
     fn check_substs_compatible_inner<'tcx>(
@@ -2209,7 +2208,10 @@ fn check_substs_compatible<'tcx>(
         true
     }
 
-    check_substs_compatible_inner(tcx, tcx.generics_of(assoc_ty.def_id), substs.as_slice())
+    let generics = tcx.generics_of(assoc_item.def_id);
+    // Chop off any additional substs (RPITIT) substs
+    let substs = &substs[0..generics.count().min(substs.len())];
+    check_substs_compatible_inner(tcx, generics, substs)
 }
 
 fn confirm_impl_trait_in_trait_candidate<'tcx>(
@@ -2238,11 +2240,27 @@ fn confirm_impl_trait_in_trait_candidate<'tcx>(
         };
     }
 
-    let impl_fn_def_id = leaf_def.item.def_id;
     // Rebase from {trait}::{fn}::{opaque} to {impl}::{fn}::{opaque},
     // since `data.substs` are the impl substs.
     let impl_fn_substs =
         obligation.predicate.substs.rebase_onto(tcx, tcx.parent(trait_fn_def_id), data.substs);
+    let impl_fn_substs = translate_substs(
+        selcx.infcx,
+        obligation.param_env,
+        data.impl_def_id,
+        impl_fn_substs,
+        leaf_def.defining_node,
+    );
+
+    if !check_substs_compatible(tcx, &leaf_def.item, impl_fn_substs) {
+        let err = tcx.ty_error_with_message(
+            obligation.cause.span,
+            "impl method and trait method have different parameters",
+        );
+        return Progress { term: err.into(), obligations };
+    }
+
+    let impl_fn_def_id = leaf_def.item.def_id;
 
     let cause = ObligationCause::new(
         obligation.cause.span,
@@ -2260,6 +2278,7 @@ fn confirm_impl_trait_in_trait_candidate<'tcx>(
     obligations.extend(std::iter::zip(predicates.predicates, predicates.spans).map(
         |(pred, span)| {
             Obligation::with_depth(
+                tcx,
                 ObligationCause::new(
                     obligation.cause.span,
                     obligation.cause.body_id,
@@ -2276,10 +2295,11 @@ fn confirm_impl_trait_in_trait_candidate<'tcx>(
         },
     ));
 
-    let ty = super::normalize_to(
+    let ty = normalize_with_depth_to(
         selcx,
         obligation.param_env,
         cause.clone(),
+        obligation.recursion_depth + 1,
         tcx.bound_trait_impl_trait_tys(impl_fn_def_id)
             .map_bound(|tys| {
                 tys.map_or_else(|_| tcx.ty_error(), |tys| tys[&obligation.predicate.item_def_id])
@@ -2299,11 +2319,10 @@ fn assoc_ty_own_obligations<'cx, 'tcx>(
     nested: &mut Vec<PredicateObligation<'tcx>>,
 ) {
     let tcx = selcx.tcx();
-    for predicate in tcx
+    let own = tcx
         .predicates_of(obligation.predicate.item_def_id)
-        .instantiate_own(tcx, obligation.predicate.substs)
-        .predicates
-    {
+        .instantiate_own(tcx, obligation.predicate.substs);
+    for (predicate, span) in std::iter::zip(own.predicates, own.spans) {
         let normalized = normalize_with_depth_to(
             selcx,
             obligation.param_env,
@@ -2312,8 +2331,30 @@ fn assoc_ty_own_obligations<'cx, 'tcx>(
             predicate,
             nested,
         );
+
+        let nested_cause = if matches!(
+            obligation.cause.code(),
+            super::CompareImplItemObligation { .. }
+                | super::CheckAssociatedTypeBounds { .. }
+                | super::AscribeUserTypeProvePredicate(..)
+        ) {
+            obligation.cause.clone()
+        } else if span.is_dummy() {
+            ObligationCause::new(
+                obligation.cause.span,
+                obligation.cause.body_id,
+                super::ItemObligation(obligation.predicate.item_def_id),
+            )
+        } else {
+            ObligationCause::new(
+                obligation.cause.span,
+                obligation.cause.body_id,
+                super::BindingObligation(obligation.predicate.item_def_id, span),
+            )
+        };
         nested.push(Obligation::with_depth(
-            obligation.cause.clone(),
+            tcx,
+            nested_cause,
             obligation.recursion_depth + 1,
             obligation.param_env,
             normalized,
@@ -2385,7 +2426,7 @@ impl<'cx, 'tcx> ProjectionCacheKeyExt<'cx, 'tcx> for ProjectionCacheKey<'tcx> {
         selcx: &mut SelectionContext<'cx, 'tcx>,
         predicate: ty::PolyProjectionPredicate<'tcx>,
     ) -> Option<Self> {
-        let infcx = selcx.infcx();
+        let infcx = selcx.infcx;
         // We don't do cross-snapshot caching of obligations with escaping regions,
         // so there's no cache key to use
         predicate.no_bound_vars().map(|predicate| {
diff --git a/compiler/rustc_trait_selection/src/traits/query/evaluate_obligation.rs b/compiler/rustc_trait_selection/src/traits/query/evaluate_obligation.rs
index c84f128dd..09b58894d 100644
--- a/compiler/rustc_trait_selection/src/traits/query/evaluate_obligation.rs
+++ b/compiler/rustc_trait_selection/src/traits/query/evaluate_obligation.rs
@@ -2,9 +2,7 @@ use rustc_middle::ty;
 
 use crate::infer::canonical::OriginalQueryValues;
 use crate::infer::InferCtxt;
-use crate::traits::{
-    EvaluationResult, OverflowError, PredicateObligation, SelectionContext, TraitQueryMode,
-};
+use crate::traits::{EvaluationResult, OverflowError, PredicateObligation, SelectionContext};
 
 pub trait InferCtxtExt<'tcx> {
     fn predicate_may_hold(&self, obligation: &PredicateObligation<'tcx>) -> bool;
@@ -68,7 +66,7 @@ impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
         let mut _orig_values = OriginalQueryValues::default();
 
         let param_env = match obligation.predicate.kind().skip_binder() {
-            ty::PredicateKind::Trait(pred) => {
+            ty::PredicateKind::Clause(ty::Clause::Trait(pred)) => {
                 // we ignore the value set to it.
                 let mut _constness = pred.constness;
                 obligation
@@ -97,7 +95,7 @@ impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
         match self.evaluate_obligation(obligation) {
             Ok(result) => result,
             Err(OverflowError::Canonical) => {
-                let mut selcx = SelectionContext::with_query_mode(&self, TraitQueryMode::Standard);
+                let mut selcx = SelectionContext::new(&self);
                 selcx.evaluate_root_obligation(obligation).unwrap_or_else(|r| match r {
                     OverflowError::Canonical => {
                         span_bug!(
diff --git a/compiler/rustc_trait_selection/src/traits/query/normalize.rs b/compiler/rustc_trait_selection/src/traits/query/normalize.rs
index 58e4597b7..7ad532d8a 100644
--- a/compiler/rustc_trait_selection/src/traits/query/normalize.rs
+++ b/compiler/rustc_trait_selection/src/traits/query/normalize.rs
@@ -7,7 +7,7 @@ use crate::infer::canonical::OriginalQueryValues;
 use crate::infer::{InferCtxt, InferOk};
 use crate::traits::error_reporting::TypeErrCtxtExt;
 use crate::traits::project::{needs_normalization, BoundVarReplacer, PlaceholderReplacer};
-use crate::traits::{Obligation, ObligationCause, PredicateObligation, Reveal};
+use crate::traits::{ObligationCause, PredicateObligation, Reveal};
 use rustc_data_structures::sso::SsoHashMap;
 use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_infer::traits::Normalized;
@@ -22,13 +22,20 @@ use super::NoSolution;
 
 pub use rustc_middle::traits::query::NormalizationResult;
 
-pub trait AtExt<'tcx> {
-    fn normalize<T>(&self, value: T) -> Result<Normalized<'tcx, T>, NoSolution>
+pub trait QueryNormalizeExt<'tcx> {
+    /// Normalize a value using the `QueryNormalizer`.
+    ///
+    /// This normalization should *only* be used when the projection does not
+    /// have possible ambiguity or may not be well-formed.
+    ///
+    /// After codegen, when lifetimes do not matter, it is preferable to instead
+    /// use [`TyCtxt::normalize_erasing_regions`], which wraps this procedure.
+    fn query_normalize<T>(&self, value: T) -> Result<Normalized<'tcx, T>, NoSolution>
     where
         T: TypeFoldable<'tcx>;
 }
 
-impl<'cx, 'tcx> AtExt<'tcx> for At<'cx, 'tcx> {
+impl<'cx, 'tcx> QueryNormalizeExt<'tcx> for At<'cx, 'tcx> {
     /// Normalize `value` in the context of the inference context,
     /// yielding a resulting type, or an error if `value` cannot be
     /// normalized. If you don't care about regions, you should prefer
@@ -42,7 +49,7 @@ impl<'cx, 'tcx> AtExt<'tcx> for At<'cx, 'tcx> {
     /// normalizing, but for now should be used only when we actually
     /// know that normalization will succeed, since error reporting
     /// and other details are still "under development".
-    fn normalize<T>(&self, value: T) -> Result<Normalized<'tcx, T>, NoSolution>
+    fn query_normalize<T>(&self, value: T) -> Result<Normalized<'tcx, T>, NoSolution>
     where
         T: TypeFoldable<'tcx>,
     {
@@ -207,13 +214,12 @@ impl<'cx, 'tcx> FallibleTypeFolder<'tcx> for QueryNormalizer<'cx, 'tcx> {
                         let substs = substs.try_fold_with(self)?;
                         let recursion_limit = self.tcx().recursion_limit();
                         if !recursion_limit.value_within_limit(self.anon_depth) {
-                            let obligation = Obligation::with_depth(
-                                self.cause.clone(),
-                                recursion_limit.0,
-                                self.param_env,
-                                ty,
+                            self.infcx.err_ctxt().report_overflow_error(
+                                &ty,
+                                self.cause.span,
+                                true,
+                                |_| {},
                             );
-                            self.infcx.err_ctxt().report_overflow_error(&obligation, true);
                         }
 
                         let generic_ty = self.tcx().bound_type_of(def_id);
@@ -353,6 +359,10 @@ impl<'cx, 'tcx> FallibleTypeFolder<'tcx> for QueryNormalizer<'cx, 'tcx> {
         &mut self,
         constant: ty::Const<'tcx>,
     ) -> Result<ty::Const<'tcx>, Self::Error> {
+        if !needs_normalization(&constant, self.param_env.reveal()) {
+            return Ok(constant);
+        }
+
         let constant = constant.try_super_fold_with(self)?;
         debug!(?constant, ?self.param_env);
         Ok(crate::traits::project::with_replaced_escaping_bound_vars(
diff --git a/compiler/rustc_trait_selection/src/traits/query/type_op/prove_predicate.rs b/compiler/rustc_trait_selection/src/traits/query/type_op/prove_predicate.rs
index 081308ac7..68434c2b6 100644
--- a/compiler/rustc_trait_selection/src/traits/query/type_op/prove_predicate.rs
+++ b/compiler/rustc_trait_selection/src/traits/query/type_op/prove_predicate.rs
@@ -15,7 +15,9 @@ impl<'tcx> super::QueryTypeOp<'tcx> for ProvePredicate<'tcx> {
         // `&T`, accounts for about 60% percentage of the predicates
         // we have to prove. No need to canonicalize and all that for
         // such cases.
-        if let ty::PredicateKind::Trait(trait_ref) = key.value.predicate.kind().skip_binder() {
+        if let ty::PredicateKind::Clause(ty::Clause::Trait(trait_ref)) =
+            key.value.predicate.kind().skip_binder()
+        {
             if let Some(sized_def_id) = tcx.lang_items().sized_trait() {
                 if trait_ref.def_id() == sized_def_id {
                     if trait_ref.self_ty().is_trivially_sized(tcx) {
@@ -33,7 +35,7 @@ impl<'tcx> super::QueryTypeOp<'tcx> for ProvePredicate<'tcx> {
         mut canonicalized: Canonicalized<'tcx, ParamEnvAnd<'tcx, Self>>,
     ) -> Fallible<CanonicalizedQueryResponse<'tcx, ()>> {
         match canonicalized.value.value.predicate.kind().skip_binder() {
-            ty::PredicateKind::Trait(pred) => {
+            ty::PredicateKind::Clause(ty::Clause::Trait(pred)) => {
                 canonicalized.value.param_env.remap_constness_with(pred.constness);
             }
             _ => canonicalized.value.param_env = canonicalized.value.param_env.without_const(),
diff --git a/compiler/rustc_trait_selection/src/traits/relationships.rs b/compiler/rustc_trait_selection/src/traits/relationships.rs
index 8cf500a46..bfa318787 100644
--- a/compiler/rustc_trait_selection/src/traits/relationships.rs
+++ b/compiler/rustc_trait_selection/src/traits/relationships.rs
@@ -1,8 +1,8 @@
 use crate::infer::InferCtxt;
 use crate::traits::query::evaluate_obligation::InferCtxtExt;
-use crate::traits::{ObligationCause, PredicateObligation};
+use crate::traits::PredicateObligation;
 use rustc_infer::traits::TraitEngine;
-use rustc_middle::ty::{self, ToPredicate};
+use rustc_middle::ty;
 
 pub(crate) fn update<'tcx, T>(
     engine: &mut T,
@@ -12,34 +12,22 @@ pub(crate) fn update<'tcx, T>(
     T: TraitEngine<'tcx>,
 {
     // (*) binder skipped
-    if let ty::PredicateKind::Trait(tpred) = obligation.predicate.kind().skip_binder()
+    if let ty::PredicateKind::Clause(ty::Clause::Trait(tpred)) = obligation.predicate.kind().skip_binder()
         && let Some(ty) = infcx.shallow_resolve(tpred.self_ty()).ty_vid().map(|t| infcx.root_var(t))
         && infcx.tcx.lang_items().sized_trait().map_or(false, |st| st != tpred.trait_ref.def_id)
     {
         let new_self_ty = infcx.tcx.types.unit;
 
-        let trait_ref = ty::TraitRef {
-            substs: infcx.tcx.mk_substs_trait(new_self_ty, &tpred.trait_ref.substs[1..]),
-            ..tpred.trait_ref
-        };
-
         // Then construct a new obligation with Self = () added
         // to the ParamEnv, and see if it holds.
-        let o = rustc_infer::traits::Obligation::new(
-            ObligationCause::dummy(),
-            obligation.param_env,
+        let o = obligation.with(infcx.tcx,
             obligation
                 .predicate
                 .kind()
                 .rebind(
                     // (*) binder moved here
-                    ty::PredicateKind::Trait(ty::TraitPredicate {
-                        trait_ref,
-                        constness: tpred.constness,
-                        polarity: tpred.polarity,
-                    })
-                )
-                .to_predicate(infcx.tcx),
+                    ty::PredicateKind::Clause(ty::Clause::Trait(tpred.with_self_type(infcx.tcx, new_self_ty)))
+                ),
         );
         // Don't report overflow errors. Otherwise equivalent to may_hold.
         if let Ok(result) = infcx.probe(|_| infcx.evaluate_obligation(&o)) && result.may_apply() {
@@ -47,7 +35,9 @@ pub(crate) fn update<'tcx, T>(
         }
     }
 
-    if let ty::PredicateKind::Projection(predicate) = obligation.predicate.kind().skip_binder() {
+    if let ty::PredicateKind::Clause(ty::Clause::Projection(predicate)) =
+        obligation.predicate.kind().skip_binder()
+    {
         // If the projection predicate (Foo::Bar == X) has X as a non-TyVid,
         // we need to make it into one.
         if let Some(vid) = predicate.term.ty().and_then(|ty| ty.ty_vid()) {
diff --git a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
index 4c5bc3339..e4b70f0d2 100644
--- a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
@@ -6,239 +6,21 @@
 //!
 //! [rustc dev guide]:https://rustc-dev-guide.rust-lang.org/traits/resolution.html#candidate-assembly
 use hir::LangItem;
-use rustc_errors::DelayDm;
 use rustc_hir as hir;
-use rustc_hir::def_id::DefId;
 use rustc_infer::traits::ObligationCause;
 use rustc_infer::traits::{Obligation, SelectionError, TraitObligation};
-use rustc_lint_defs::builtin::DEREF_INTO_DYN_SUPERTRAIT;
-use rustc_middle::ty::print::with_no_trimmed_paths;
-use rustc_middle::ty::{self, ToPredicate, Ty, TypeVisitable};
+use rustc_middle::ty::{self, Ty, TypeVisitable};
 use rustc_target::spec::abi::Abi;
 
 use crate::traits;
-use crate::traits::coherence::Conflict;
 use crate::traits::query::evaluate_obligation::InferCtxtExt;
-use crate::traits::{util, SelectionResult};
-use crate::traits::{Ambiguous, ErrorReporting, Overflow, Unimplemented};
+use crate::traits::util;
 
 use super::BuiltinImplConditions;
-use super::IntercrateAmbiguityCause;
-use super::OverflowError;
-use super::SelectionCandidate::{self, *};
-use super::{EvaluatedCandidate, SelectionCandidateSet, SelectionContext, TraitObligationStack};
+use super::SelectionCandidate::*;
+use super::{SelectionCandidateSet, SelectionContext, TraitObligationStack};
 
 impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
-    #[instrument(level = "debug", skip(self), ret)]
-    pub(super) fn candidate_from_obligation<'o>(
-        &mut self,
-        stack: &TraitObligationStack<'o, 'tcx>,
-    ) -> SelectionResult<'tcx, SelectionCandidate<'tcx>> {
-        // Watch out for overflow. This intentionally bypasses (and does
-        // not update) the cache.
-        self.check_recursion_limit(&stack.obligation, &stack.obligation)?;
-
-        // Check the cache. Note that we freshen the trait-ref
-        // separately rather than using `stack.fresh_trait_ref` --
-        // this is because we want the unbound variables to be
-        // replaced with fresh types starting from index 0.
-        let cache_fresh_trait_pred = self.infcx.freshen(stack.obligation.predicate);
-        debug!(?cache_fresh_trait_pred);
-        debug_assert!(!stack.obligation.predicate.has_escaping_bound_vars());
-
-        if let Some(c) =
-            self.check_candidate_cache(stack.obligation.param_env, cache_fresh_trait_pred)
-        {
-            debug!("CACHE HIT");
-            return c;
-        }
-
-        // If no match, compute result and insert into cache.
-        //
-        // FIXME(nikomatsakis) -- this cache is not taking into
-        // account cycles that may have occurred in forming the
-        // candidate. I don't know of any specific problems that
-        // result but it seems awfully suspicious.
-        let (candidate, dep_node) =
-            self.in_task(|this| this.candidate_from_obligation_no_cache(stack));
-
-        debug!("CACHE MISS");
-        self.insert_candidate_cache(
-            stack.obligation.param_env,
-            cache_fresh_trait_pred,
-            dep_node,
-            candidate.clone(),
-        );
-        candidate
-    }
-
-    fn candidate_from_obligation_no_cache<'o>(
-        &mut self,
-        stack: &TraitObligationStack<'o, 'tcx>,
-    ) -> SelectionResult<'tcx, SelectionCandidate<'tcx>> {
-        if let Err(conflict) = self.is_knowable(stack) {
-            debug!("coherence stage: not knowable");
-            if self.intercrate_ambiguity_causes.is_some() {
-                debug!("evaluate_stack: intercrate_ambiguity_causes is some");
-                // Heuristics: show the diagnostics when there are no candidates in crate.
-                if let Ok(candidate_set) = self.assemble_candidates(stack) {
-                    let mut no_candidates_apply = true;
-
-                    for c in candidate_set.vec.iter() {
-                        if self.evaluate_candidate(stack, &c)?.may_apply() {
-                            no_candidates_apply = false;
-                            break;
-                        }
-                    }
-
-                    if !candidate_set.ambiguous && no_candidates_apply {
-                        let trait_ref = stack.obligation.predicate.skip_binder().trait_ref;
-                        let self_ty = trait_ref.self_ty();
-                        let (trait_desc, self_desc) = with_no_trimmed_paths!({
-                            let trait_desc = trait_ref.print_only_trait_path().to_string();
-                            let self_desc = if self_ty.has_concrete_skeleton() {
-                                Some(self_ty.to_string())
-                            } else {
-                                None
-                            };
-                            (trait_desc, self_desc)
-                        });
-                        let cause = if let Conflict::Upstream = conflict {
-                            IntercrateAmbiguityCause::UpstreamCrateUpdate { trait_desc, self_desc }
-                        } else {
-                            IntercrateAmbiguityCause::DownstreamCrate { trait_desc, self_desc }
-                        };
-                        debug!(?cause, "evaluate_stack: pushing cause");
-                        self.intercrate_ambiguity_causes.as_mut().unwrap().insert(cause);
-                    }
-                }
-            }
-            return Ok(None);
-        }
-
-        let candidate_set = self.assemble_candidates(stack)?;
-
-        if candidate_set.ambiguous {
-            debug!("candidate set contains ambig");
-            return Ok(None);
-        }
-
-        let candidates = candidate_set.vec;
-
-        debug!(?stack, ?candidates, "assembled {} candidates", candidates.len());
-
-        // At this point, we know that each of the entries in the
-        // candidate set is *individually* applicable. Now we have to
-        // figure out if they contain mutual incompatibilities. This
-        // frequently arises if we have an unconstrained input type --
-        // for example, we are looking for `$0: Eq` where `$0` is some
-        // unconstrained type variable. In that case, we'll get a
-        // candidate which assumes $0 == int, one that assumes `$0 ==
-        // usize`, etc. This spells an ambiguity.
-
-        let mut candidates = self.filter_impls(candidates, stack.obligation);
-
-        // If there is more than one candidate, first winnow them down
-        // by considering extra conditions (nested obligations and so
-        // forth). We don't winnow if there is exactly one
-        // candidate. This is a relatively minor distinction but it
-        // can lead to better inference and error-reporting. An
-        // example would be if there was an impl:
-        //
-        //     impl<T:Clone> Vec<T> { fn push_clone(...) { ... } }
-        //
-        // and we were to see some code `foo.push_clone()` where `boo`
-        // is a `Vec<Bar>` and `Bar` does not implement `Clone`.  If
-        // we were to winnow, we'd wind up with zero candidates.
-        // Instead, we select the right impl now but report "`Bar` does
-        // not implement `Clone`".
-        if candidates.len() == 1 {
-            return self.filter_reservation_impls(candidates.pop().unwrap(), stack.obligation);
-        }
-
-        // Winnow, but record the exact outcome of evaluation, which
-        // is needed for specialization. Propagate overflow if it occurs.
-        let mut candidates = candidates
-            .into_iter()
-            .map(|c| match self.evaluate_candidate(stack, &c) {
-                Ok(eval) if eval.may_apply() => {
-                    Ok(Some(EvaluatedCandidate { candidate: c, evaluation: eval }))
-                }
-                Ok(_) => Ok(None),
-                Err(OverflowError::Canonical) => Err(Overflow(OverflowError::Canonical)),
-                Err(OverflowError::ErrorReporting) => Err(ErrorReporting),
-                Err(OverflowError::Error(e)) => Err(Overflow(OverflowError::Error(e))),
-            })
-            .flat_map(Result::transpose)
-            .collect::<Result<Vec<_>, _>>()?;
-
-        debug!(?stack, ?candidates, "winnowed to {} candidates", candidates.len());
-
-        let needs_infer = stack.obligation.predicate.has_non_region_infer();
-
-        // If there are STILL multiple candidates, we can further
-        // reduce the list by dropping duplicates -- including
-        // resolving specializations.
-        if candidates.len() > 1 {
-            let mut i = 0;
-            while i < candidates.len() {
-                let is_dup = (0..candidates.len()).filter(|&j| i != j).any(|j| {
-                    self.candidate_should_be_dropped_in_favor_of(
-                        &candidates[i],
-                        &candidates[j],
-                        needs_infer,
-                    )
-                });
-                if is_dup {
-                    debug!(candidate = ?candidates[i], "Dropping candidate #{}/{}", i, candidates.len());
-                    candidates.swap_remove(i);
-                } else {
-                    debug!(candidate = ?candidates[i], "Retaining candidate #{}/{}", i, candidates.len());
-                    i += 1;
-
-                    // If there are *STILL* multiple candidates, give up
-                    // and report ambiguity.
-                    if i > 1 {
-                        debug!("multiple matches, ambig");
-                        return Err(Ambiguous(
-                            candidates
-                                .into_iter()
-                                .filter_map(|c| match c.candidate {
-                                    SelectionCandidate::ImplCandidate(def_id) => Some(def_id),
-                                    _ => None,
-                                })
-                                .collect(),
-                        ));
-                    }
-                }
-            }
-        }
-
-        // If there are *NO* candidates, then there are no impls --
-        // that we know of, anyway. Note that in the case where there
-        // are unbound type variables within the obligation, it might
-        // be the case that you could still satisfy the obligation
-        // from another crate by instantiating the type variables with
-        // a type from another crate that does have an impl. This case
-        // is checked for in `evaluate_stack` (and hence users
-        // who might care about this case, like coherence, should use
-        // that function).
-        if candidates.is_empty() {
-            // If there's an error type, 'downgrade' our result from
-            // `Err(Unimplemented)` to `Ok(None)`. This helps us avoid
-            // emitting additional spurious errors, since we're guaranteed
-            // to have emitted at least one.
-            if stack.obligation.predicate.references_error() {
-                debug!(?stack.obligation.predicate, "found error type in predicate, treating as ambiguous");
-                return Ok(None);
-            }
-            return Err(Unimplemented);
-        }
-
-        // Just one candidate left.
-        self.filter_reservation_impls(candidates.pop().unwrap().candidate, stack.obligation)
-    }
-
     #[instrument(skip(self, stack), level = "debug")]
     pub(super) fn assemble_candidates<'o>(
         &mut self,
@@ -249,7 +31,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             param_env: obligation.param_env,
             cause: obligation.cause.clone(),
             recursion_depth: obligation.recursion_depth,
-            predicate: self.infcx().resolve_vars_if_possible(obligation.predicate),
+            predicate: self.infcx.resolve_vars_if_possible(obligation.predicate),
         };
 
         if obligation.predicate.skip_binder().self_ty().is_ty_var() {
@@ -293,10 +75,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 self.assemble_builtin_bound_candidates(copy_conditions, &mut candidates);
             } else if lang_items.discriminant_kind_trait() == Some(def_id) {
                 // `DiscriminantKind` is automatically implemented for every type.
-                candidates.vec.push(DiscriminantKindCandidate);
+                candidates.vec.push(BuiltinCandidate { has_nested: false });
             } else if lang_items.pointee_trait() == Some(def_id) {
                 // `Pointee` is automatically implemented for every type.
-                candidates.vec.push(PointeeCandidate);
+                candidates.vec.push(BuiltinCandidate { has_nested: false });
             } else if lang_items.sized_trait() == Some(def_id) {
                 // Sized is never implementable by end-users, it is
                 // always automatically computed.
@@ -312,6 +94,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 self.assemble_candidates_for_transmutability(obligation, &mut candidates);
             } else if lang_items.tuple_trait() == Some(def_id) {
                 self.assemble_candidate_for_tuple(obligation, &mut candidates);
+            } else if lang_items.pointer_sized() == Some(def_id) {
+                self.assemble_candidate_for_ptr_sized(obligation, &mut candidates);
             } else {
                 if lang_items.clone_trait() == Some(def_id) {
                     // Same builtin conditions as `Copy`, i.e., every type which has builtin support
@@ -321,7 +105,12 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     self.assemble_builtin_bound_candidates(clone_conditions, &mut candidates);
                 }
 
-                self.assemble_generator_candidates(obligation, &mut candidates);
+                if lang_items.gen_trait() == Some(def_id) {
+                    self.assemble_generator_candidates(obligation, &mut candidates);
+                } else if lang_items.future_trait() == Some(def_id) {
+                    self.assemble_future_candidates(obligation, &mut candidates);
+                }
+
                 self.assemble_closure_candidates(obligation, &mut candidates);
                 self.assemble_fn_pointer_candidates(obligation, &mut candidates);
                 self.assemble_candidates_from_impls(obligation, &mut candidates);
@@ -409,16 +198,14 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         obligation: &TraitObligation<'tcx>,
         candidates: &mut SelectionCandidateSet<'tcx>,
     ) {
-        if self.tcx().lang_items().gen_trait() != Some(obligation.predicate.def_id()) {
-            return;
-        }
-
         // Okay to skip binder because the substs on generator types never
         // touch bound regions, they just capture the in-scope
         // type/region parameters.
         let self_ty = obligation.self_ty().skip_binder();
         match self_ty.kind() {
-            ty::Generator(..) => {
+            // async constructs get lowered to a special kind of generator that
+            // should *not* `impl Generator`.
+            ty::Generator(did, ..) if !self.tcx().generator_is_async(*did) => {
                 debug!(?self_ty, ?obligation, "assemble_generator_candidates",);
 
                 candidates.vec.push(GeneratorCandidate);
@@ -431,6 +218,23 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         }
     }
 
+    fn assemble_future_candidates(
+        &mut self,
+        obligation: &TraitObligation<'tcx>,
+        candidates: &mut SelectionCandidateSet<'tcx>,
+    ) {
+        let self_ty = obligation.self_ty().skip_binder();
+        if let ty::Generator(did, ..) = self_ty.kind() {
+            // async constructs get lowered to a special kind of generator that
+            // should directly `impl Future`.
+            if self.tcx().generator_is_async(*did) {
+                debug!(?self_ty, ?obligation, "assemble_future_candidates",);
+
+                candidates.vec.push(FutureCandidate);
+            }
+        }
+    }
+
     /// Checks for the artificial impl that the compiler will create for an obligation like `X :
     /// FnMut<..>` where `X` is a closure type.
     ///
@@ -442,7 +246,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         obligation: &TraitObligation<'tcx>,
         candidates: &mut SelectionCandidateSet<'tcx>,
     ) {
-        let Some(kind) = self.tcx().fn_trait_kind_from_lang_item(obligation.predicate.def_id()) else {
+        let Some(kind) = self.tcx().fn_trait_kind_from_def_id(obligation.predicate.def_id()) else {
             return;
         };
 
@@ -480,7 +284,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         candidates: &mut SelectionCandidateSet<'tcx>,
     ) {
         // We provide impl of all fn traits for fn pointers.
-        if self.tcx().fn_trait_kind_from_lang_item(obligation.predicate.def_id()).is_none() {
+        if !self.tcx().is_fn_trait(obligation.predicate.def_id()) {
             return;
         }
 
@@ -680,9 +484,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
             debug!(?poly_trait_ref, "assemble_candidates_from_object_ty");
 
-            let poly_trait_predicate = self.infcx().resolve_vars_if_possible(obligation.predicate);
+            let poly_trait_predicate = self.infcx.resolve_vars_if_possible(obligation.predicate);
             let placeholder_trait_predicate =
-                self.infcx().replace_bound_vars_with_placeholders(poly_trait_predicate);
+                self.infcx.replace_bound_vars_with_placeholders(poly_trait_predicate);
 
             // Count only those upcast versions that match the trait-ref
             // we are looking for. Specifically, do not only check for the
@@ -713,48 +517,40 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         ty: Ty<'tcx>,
         param_env: ty::ParamEnv<'tcx>,
         cause: &ObligationCause<'tcx>,
-    ) -> Option<(Ty<'tcx>, DefId)> {
+    ) -> Option<ty::PolyExistentialTraitRef<'tcx>> {
         let tcx = self.tcx();
         if tcx.features().trait_upcasting {
             return None;
         }
 
         // <ty as Deref>
-        let trait_ref = ty::TraitRef {
-            def_id: tcx.lang_items().deref_trait()?,
-            substs: tcx.mk_substs_trait(ty, &[]),
-        };
+        let trait_ref = tcx.mk_trait_ref(tcx.lang_items().deref_trait()?, [ty]);
 
-        let obligation = traits::Obligation::new(
-            cause.clone(),
-            param_env,
-            ty::Binder::dummy(trait_ref).without_const().to_predicate(tcx),
-        );
+        let obligation =
+            traits::Obligation::new(tcx, cause.clone(), param_env, ty::Binder::dummy(trait_ref));
         if !self.infcx.predicate_may_hold(&obligation) {
             return None;
         }
 
-        let ty = traits::normalize_projection_type(
-            self,
-            param_env,
-            ty::ProjectionTy {
-                item_def_id: tcx.lang_items().deref_target()?,
-                substs: trait_ref.substs,
-            },
-            cause.clone(),
-            0,
-            // We're *intentionally* throwing these away,
-            // since we don't actually use them.
-            &mut vec![],
-        )
-        .ty()
-        .unwrap();
-
-        if let ty::Dynamic(data, ..) = ty.kind() {
-            Some((ty, data.principal_def_id()?))
-        } else {
-            None
-        }
+        self.infcx.probe(|_| {
+            let ty = traits::normalize_projection_type(
+                self,
+                param_env,
+                ty::ProjectionTy {
+                    item_def_id: tcx.lang_items().deref_target()?,
+                    substs: trait_ref.substs,
+                },
+                cause.clone(),
+                0,
+                // We're *intentionally* throwing these away,
+                // since we don't actually use them.
+                &mut vec![],
+            )
+            .ty()
+            .unwrap();
+
+            if let ty::Dynamic(data, ..) = ty.kind() { data.principal() } else { None }
+        })
     }
 
     /// Searches for unsizing that might apply to `obligation`.
@@ -787,7 +583,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
         match (source.kind(), target.kind()) {
             // Trait+Kx+'a -> Trait+Ky+'b (upcasts).
-            (&ty::Dynamic(ref data_a, ..), &ty::Dynamic(ref data_b, ..)) => {
+            (&ty::Dynamic(ref data_a, _, ty::Dyn), &ty::Dynamic(ref data_b, _, ty::Dyn)) => {
                 // Upcast coercions permit several things:
                 //
                 // 1. Dropping auto traits, e.g., `Foo + Send` to `Foo`
@@ -814,24 +610,12 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                         let principal_a = data_a.principal().unwrap();
                         let target_trait_did = principal_def_id_b.unwrap();
                         let source_trait_ref = principal_a.with_self_ty(self.tcx(), source);
-                        if let Some((deref_output_ty, deref_output_trait_did)) = self
-                            .need_migrate_deref_output_trait_object(
-                                source,
-                                obligation.param_env,
-                                &obligation.cause,
-                            )
-                        {
-                            if deref_output_trait_did == target_trait_did {
-                                self.tcx().struct_span_lint_hir(
-                                    DEREF_INTO_DYN_SUPERTRAIT,
-                                    obligation.cause.body_id,
-                                    obligation.cause.span,
-                                    DelayDm(|| format!(
-                                        "`{}` implements `Deref` with supertrait `{}` as output",
-                                        source, deref_output_ty
-                                    )),
-                                    |lint| lint,
-                                );
+                        if let Some(deref_trait_ref) = self.need_migrate_deref_output_trait_object(
+                            source,
+                            obligation.param_env,
+                            &obligation.cause,
+                        ) {
+                            if deref_trait_ref.def_id() == target_trait_did {
                                 return;
                             }
                         }
@@ -848,7 +632,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             }
 
             // `T` -> `Trait`
-            (_, &ty::Dynamic(..)) => {
+            (_, &ty::Dynamic(_, _, ty::Dyn)) => {
                 candidates.vec.push(BuiltinUnsizeCandidate);
             }
 
@@ -951,7 +735,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             return;
         }
 
-        let self_ty = self.infcx().shallow_resolve(obligation.self_ty());
+        let self_ty = self.infcx.shallow_resolve(obligation.self_ty());
         match self_ty.skip_binder().kind() {
             ty::Opaque(..)
             | ty::Dynamic(..)
@@ -1018,7 +802,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         obligation: &TraitObligation<'tcx>,
         candidates: &mut SelectionCandidateSet<'tcx>,
     ) {
-        let self_ty = self.infcx().shallow_resolve(obligation.self_ty().skip_binder());
+        let self_ty = self.infcx.shallow_resolve(obligation.self_ty().skip_binder());
         match self_ty.kind() {
             ty::Tuple(_) => {
                 candidates.vec.push(BuiltinCandidate { has_nested: false });
@@ -1054,4 +838,30 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             | ty::Placeholder(_) => {}
         }
     }
+
+    fn assemble_candidate_for_ptr_sized(
+        &mut self,
+        obligation: &TraitObligation<'tcx>,
+        candidates: &mut SelectionCandidateSet<'tcx>,
+    ) {
+        // The regions of a type don't affect the size of the type
+        let self_ty = self
+            .tcx()
+            .erase_regions(self.tcx().erase_late_bound_regions(obligation.predicate.self_ty()));
+
+        // But if there are inference variables, we have to wait until it's resolved.
+        if self_ty.has_non_region_infer() {
+            candidates.ambiguous = true;
+            return;
+        }
+
+        let usize_layout =
+            self.tcx().layout_of(ty::ParamEnv::empty().and(self.tcx().types.usize)).unwrap().layout;
+        if let Ok(layout) = self.tcx().layout_of(obligation.param_env.and(self_ty))
+            && layout.layout.size() == usize_layout.size()
+            && layout.layout.align().abi == usize_layout.align().abi
+        {
+            candidates.vec.push(BuiltinCandidate { has_nested: false });
+        }
+    }
 }
diff --git a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
index ed22058c6..fda415155 100644
--- a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
@@ -19,14 +19,18 @@ use rustc_span::def_id::DefId;
 
 use crate::traits::project::{normalize_with_depth, normalize_with_depth_to};
 use crate::traits::util::{self, closure_trait_ref_and_return_type, predicate_for_trait_def};
+use crate::traits::vtable::{
+    count_own_vtable_entries, prepare_vtable_segments, vtable_trait_first_method_offset,
+    VtblSegment,
+};
 use crate::traits::{
     BuiltinDerivedObligation, ImplDerivedObligation, ImplDerivedObligationCause, ImplSource,
     ImplSourceAutoImplData, ImplSourceBuiltinData, ImplSourceClosureData,
-    ImplSourceConstDestructData, ImplSourceDiscriminantKindData, ImplSourceFnPointerData,
-    ImplSourceGeneratorData, ImplSourceObjectData, ImplSourcePointeeData, ImplSourceTraitAliasData,
+    ImplSourceConstDestructData, ImplSourceFnPointerData, ImplSourceFutureData,
+    ImplSourceGeneratorData, ImplSourceObjectData, ImplSourceTraitAliasData,
     ImplSourceTraitUpcastingData, ImplSourceUserDefinedData, Normalized, ObjectCastObligation,
     Obligation, ObligationCause, OutputTypeParameterMismatch, PredicateObligation, Selection,
-    SelectionError, TraitNotObjectSafe, TraitObligation, Unimplemented, VtblSegment,
+    SelectionError, TraitNotObjectSafe, TraitObligation, Unimplemented,
 };
 
 use super::BuiltinImplConditions;
@@ -89,17 +93,16 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 ImplSource::Generator(vtable_generator)
             }
 
+            FutureCandidate => {
+                let vtable_future = self.confirm_future_candidate(obligation)?;
+                ImplSource::Future(vtable_future)
+            }
+
             FnPointerCandidate { .. } => {
                 let data = self.confirm_fn_pointer_candidate(obligation)?;
                 ImplSource::FnPointer(data)
             }
 
-            DiscriminantKindCandidate => {
-                ImplSource::DiscriminantKind(ImplSourceDiscriminantKindData)
-            }
-
-            PointeeCandidate => ImplSource::Pointee(ImplSourcePointeeData),
-
             TraitAliasCandidate => {
                 let data = self.confirm_trait_alias_candidate(obligation);
                 ImplSource::TraitAlias(data)
@@ -148,7 +151,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
         let trait_predicate = self.infcx.shallow_resolve(obligation.predicate);
         let placeholder_trait_predicate =
-            self.infcx().replace_bound_vars_with_placeholders(trait_predicate).trait_ref;
+            self.infcx.replace_bound_vars_with_placeholders(trait_predicate).trait_ref;
         let placeholder_self_ty = placeholder_trait_predicate.self_ty();
         let placeholder_trait_predicate = ty::Binder::dummy(placeholder_trait_predicate);
         let (def_id, substs) = match *placeholder_self_ty.kind() {
@@ -194,6 +197,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     &mut obligations,
                 );
                 obligations.push(Obligation::with_depth(
+                    self.tcx(),
                     obligation.cause.clone(),
                     obligation.recursion_depth + 1,
                     obligation.param_env,
@@ -482,11 +486,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 super_trait,
                 &mut nested,
             );
-            nested.push(Obligation::new(
-                obligation.cause.clone(),
-                obligation.param_env,
-                normalized_super_trait,
-            ));
+            nested.push(obligation.with(tcx, normalized_super_trait));
         }
 
         let assoc_types: Vec<_> = tcx
@@ -555,13 +555,13 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                             GenericParamDefKind::Const { .. } => {
                                 let bound_var = ty::BoundVariableKind::Const;
                                 bound_vars.push(bound_var);
-                                tcx.mk_const(ty::ConstS {
-                                    ty: tcx.type_of(param.def_id),
-                                    kind: ty::ConstKind::Bound(
+                                tcx.mk_const(
+                                    ty::ConstKind::Bound(
                                         ty::INNERMOST,
                                         ty::BoundVar::from_usize(bound_vars.len() - 1),
                                     ),
-                                })
+                                    tcx.type_of(param.def_id),
+                                )
                                 .into()
                             }
                         });
@@ -581,17 +581,13 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     subst_bound,
                     &mut nested,
                 );
-                nested.push(Obligation::new(
-                    obligation.cause.clone(),
-                    obligation.param_env,
-                    normalized_bound,
-                ));
+                nested.push(obligation.with(tcx, normalized_bound));
             }
         }
 
         debug!(?nested, "object nested obligations");
 
-        let vtable_base = super::super::vtable_trait_first_method_offset(
+        let vtable_base = vtable_trait_first_method_offset(
             tcx,
             (unnormalized_upcast_trait_ref, ty::Binder::dummy(object_trait_ref)),
         );
@@ -606,8 +602,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
     {
         debug!(?obligation, "confirm_fn_pointer_candidate");
 
-        // Okay to skip binder; it is reintroduced below.
-        let self_ty = self.infcx.shallow_resolve(obligation.self_ty().skip_binder());
+        let self_ty = self
+            .infcx
+            .shallow_resolve(obligation.self_ty().no_bound_vars())
+            .expect("fn pointer should not capture bound vars from predicate");
         let sig = self_ty.fn_sig(self.tcx());
         let trait_ref = closure_trait_ref_and_return_type(
             self.tcx(),
@@ -622,15 +620,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
         // Confirm the `type Output: Sized;` bound that is present on `FnOnce`
         let cause = obligation.derived_cause(BuiltinDerivedObligation);
-        // The binder on the Fn obligation is "less" important than the one on
-        // the signature, as evidenced by how we treat it during projection.
-        // The safe thing to do here is to liberate it, though, which should
-        // have no worse effect than skipping the binder here.
-        let liberated_fn_ty =
-            self.infcx.replace_bound_vars_with_placeholders(obligation.predicate.rebind(self_ty));
-        let output_ty = self
-            .infcx
-            .replace_bound_vars_with_placeholders(liberated_fn_ty.fn_sig(self.tcx()).output());
+        let output_ty = self.infcx.replace_bound_vars_with_placeholders(sig.output());
         let output_ty = normalize_with_depth_to(
             self,
             obligation.param_env,
@@ -639,15 +629,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             output_ty,
             &mut nested,
         );
-        let tr = ty::Binder::dummy(ty::TraitRef::new(
-            self.tcx().require_lang_item(LangItem::Sized, None),
-            self.tcx().mk_substs_trait(output_ty, &[]),
-        ));
-        nested.push(Obligation::new(
-            cause,
-            obligation.param_env,
-            tr.to_poly_trait_predicate().to_predicate(self.tcx()),
-        ));
+        let tr =
+            ty::Binder::dummy(self.tcx().at(cause.span).mk_trait_ref(LangItem::Sized, [output_ty]));
+        nested.push(Obligation::new(self.infcx.tcx, cause, obligation.param_env, tr));
 
         Ok(ImplSourceFnPointerData { fn_ty: self_ty, nested })
     }
@@ -659,7 +643,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         debug!(?obligation, "confirm_trait_alias_candidate");
 
         let alias_def_id = obligation.predicate.def_id();
-        let predicate = self.infcx().replace_bound_vars_with_placeholders(obligation.predicate);
+        let predicate = self.infcx.replace_bound_vars_with_placeholders(obligation.predicate);
         let trait_ref = predicate.trait_ref;
         let trait_def_id = trait_ref.def_id;
         let substs = trait_ref.substs;
@@ -693,7 +677,24 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
         debug!(?obligation, ?generator_def_id, ?substs, "confirm_generator_candidate");
 
-        let trait_ref = self.generator_trait_ref_unnormalized(obligation, substs);
+        let gen_sig = substs.as_generator().poly_sig();
+
+        // NOTE: The self-type is a generator type and hence is
+        // in fact unparameterized (or at least does not reference any
+        // regions bound in the obligation).
+        let self_ty = obligation
+            .predicate
+            .self_ty()
+            .no_bound_vars()
+            .expect("unboxed closure type should not capture bound vars from the predicate");
+
+        let trait_ref = super::util::generator_trait_ref_and_outputs(
+            self.tcx(),
+            obligation.predicate.def_id(),
+            self_ty,
+            gen_sig,
+        )
+        .map_bound(|(trait_ref, ..)| trait_ref);
 
         let nested = self.confirm_poly_trait_refs(obligation, trait_ref)?;
         debug!(?trait_ref, ?nested, "generator candidate obligations");
@@ -701,6 +702,36 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         Ok(ImplSourceGeneratorData { generator_def_id, substs, nested })
     }
 
+    fn confirm_future_candidate(
+        &mut self,
+        obligation: &TraitObligation<'tcx>,
+    ) -> Result<ImplSourceFutureData<'tcx, PredicateObligation<'tcx>>, SelectionError<'tcx>> {
+        // Okay to skip binder because the substs on generator types never
+        // touch bound regions, they just capture the in-scope
+        // type/region parameters.
+        let self_ty = self.infcx.shallow_resolve(obligation.self_ty().skip_binder());
+        let ty::Generator(generator_def_id, substs, _) = *self_ty.kind() else {
+            bug!("closure candidate for non-closure {:?}", obligation);
+        };
+
+        debug!(?obligation, ?generator_def_id, ?substs, "confirm_future_candidate");
+
+        let gen_sig = substs.as_generator().poly_sig();
+
+        let trait_ref = super::util::future_trait_ref_and_outputs(
+            self.tcx(),
+            obligation.predicate.def_id(),
+            obligation.predicate.no_bound_vars().expect("future has no bound vars").self_ty(),
+            gen_sig,
+        )
+        .map_bound(|(trait_ref, ..)| trait_ref);
+
+        let nested = self.confirm_poly_trait_refs(obligation, trait_ref)?;
+        debug!(?trait_ref, ?nested, "future candidate obligations");
+
+        Ok(ImplSourceFutureData { generator_def_id, substs, nested })
+    }
+
     #[instrument(skip(self), level = "debug")]
     fn confirm_closure_candidate(
         &mut self,
@@ -708,7 +739,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
     ) -> Result<ImplSourceClosureData<'tcx, PredicateObligation<'tcx>>, SelectionError<'tcx>> {
         let kind = self
             .tcx()
-            .fn_trait_kind_from_lang_item(obligation.predicate.def_id())
+            .fn_trait_kind_from_def_id(obligation.predicate.def_id())
             .unwrap_or_else(|| bug!("closure candidate for non-fn trait {:?}", obligation));
 
         // Okay to skip binder because the substs on closure types never
@@ -727,11 +758,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         // FIXME: Chalk
 
         if !self.tcx().sess.opts.unstable_opts.chalk {
-            nested.push(Obligation::new(
-                obligation.cause.clone(),
-                obligation.param_env,
-                ty::Binder::dummy(ty::PredicateKind::ClosureKind(closure_def_id, substs, kind))
-                    .to_predicate(self.tcx()),
+            nested.push(obligation.with(
+                self.tcx(),
+                ty::Binder::dummy(ty::PredicateKind::ClosureKind(closure_def_id, substs, kind)),
             ));
         }
 
@@ -813,9 +842,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         let upcast_trait_ref;
         match (source.kind(), target.kind()) {
             // TraitA+Kx+'a -> TraitB+Ky+'b (trait upcasting coercion).
-            (&ty::Dynamic(ref data_a, r_a, repr_a), &ty::Dynamic(ref data_b, r_b, repr_b))
-                if repr_a == repr_b =>
-            {
+            (
+                &ty::Dynamic(ref data_a, r_a, repr_a @ ty::Dyn),
+                &ty::Dynamic(ref data_b, r_b, ty::Dyn),
+            ) => {
                 // See `assemble_candidates_for_unsizing` for more info.
                 // We already checked the compatibility of auto traits within `assemble_candidates_for_unsizing`.
                 let principal_a = data_a.principal().unwrap();
@@ -841,7 +871,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                             .map(ty::Binder::dummy),
                     );
                 let existential_predicates = tcx.mk_poly_existential_predicates(iter);
-                let source_trait = tcx.mk_dynamic(existential_predicates, r_b, repr_b);
+                let source_trait = tcx.mk_dynamic(existential_predicates, r_b, repr_a);
 
                 // Require that the traits involved in this upcast are **equal**;
                 // only the **lifetime bound** is changed.
@@ -860,10 +890,11 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 );
                 let outlives = ty::OutlivesPredicate(r_a, r_b);
                 nested.push(Obligation::with_depth(
+                    tcx,
                     cause,
                     obligation.recursion_depth + 1,
                     obligation.param_env,
-                    obligation.predicate.rebind(outlives).to_predicate(tcx),
+                    obligation.predicate.rebind(outlives),
                 ));
             }
             _ => bug!(),
@@ -877,7 +908,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                         vptr_offset += TyCtxt::COMMON_VTABLE_ENTRIES.len();
                     }
                     VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => {
-                        vptr_offset += util::count_own_vtable_entries(tcx, trait_ref);
+                        vptr_offset += count_own_vtable_entries(tcx, trait_ref);
                         if trait_ref == upcast_trait_ref {
                             if emit_vptr {
                                 return ControlFlow::Break(Some(vptr_offset));
@@ -896,8 +927,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         };
 
         let vtable_vptr_slot =
-            super::super::prepare_vtable_segments(tcx, source_trait_ref, vtable_segment_callback)
-                .unwrap();
+            prepare_vtable_segments(tcx, source_trait_ref, vtable_segment_callback).unwrap();
 
         Ok(ImplSourceTraitUpcastingData { upcast_trait_ref, vtable_vptr_slot, nested })
     }
@@ -919,7 +949,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         let mut nested = vec![];
         match (source.kind(), target.kind()) {
             // Trait+Kx+'a -> Trait+Ky+'b (auto traits and lifetime subtyping).
-            (&ty::Dynamic(ref data_a, r_a, ty::Dyn), &ty::Dynamic(ref data_b, r_b, ty::Dyn)) => {
+            (&ty::Dynamic(ref data_a, r_a, dyn_a), &ty::Dynamic(ref data_b, r_b, dyn_b))
+                if dyn_a == dyn_b =>
+            {
                 // See `assemble_candidates_for_unsizing` for more info.
                 // We already checked the compatibility of auto traits within `assemble_candidates_for_unsizing`.
                 let iter = data_a
@@ -938,7 +970,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                             .map(ty::Binder::dummy),
                     );
                 let existential_predicates = tcx.mk_poly_existential_predicates(iter);
-                let source_trait = tcx.mk_dynamic(existential_predicates, r_b, ty::Dyn);
+                let source_trait = tcx.mk_dynamic(existential_predicates, r_b, dyn_a);
 
                 // Require that the traits involved in this upcast are **equal**;
                 // only the **lifetime bound** is changed.
@@ -957,10 +989,11 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 );
                 let outlives = ty::OutlivesPredicate(r_a, r_b);
                 nested.push(Obligation::with_depth(
+                    tcx,
                     cause,
                     obligation.recursion_depth + 1,
                     obligation.param_env,
-                    obligation.predicate.rebind(outlives).to_predicate(tcx),
+                    obligation.predicate.rebind(outlives),
                 ));
             }
 
@@ -979,6 +1012,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
                 let predicate_to_obligation = |predicate| {
                     Obligation::with_depth(
+                        tcx,
                         cause.clone(),
                         obligation.recursion_depth + 1,
                         obligation.param_env,
@@ -999,10 +1033,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 );
 
                 // We can only make objects from sized types.
-                let tr = ty::Binder::dummy(ty::TraitRef::new(
-                    tcx.require_lang_item(LangItem::Sized, None),
-                    tcx.mk_substs_trait(source, &[]),
-                ));
+                let tr =
+                    ty::Binder::dummy(tcx.at(cause.span).mk_trait_ref(LangItem::Sized, [source]));
                 nested.push(predicate_to_obligation(tr.without_const().to_predicate(tcx)));
 
                 // If the type is `Foo + 'a`, ensure that the type
@@ -1108,8 +1140,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     obligation.cause.clone(),
                     obligation.predicate.def_id(),
                     obligation.recursion_depth + 1,
-                    source_tail,
-                    &[target_tail.into()],
+                    [source_tail, target_tail],
                 ));
             }
 
@@ -1139,13 +1170,12 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                         obligation.cause.clone(),
                         obligation.predicate.def_id(),
                         obligation.recursion_depth + 1,
-                        a_last,
-                        &[b_last.into()],
+                        [a_last, b_last],
                     )
                 }));
             }
 
-            _ => bug!(),
+            _ => bug!("source: {source}, target: {target}"),
         };
 
         Ok(ImplSourceBuiltinData { nested })
@@ -1255,20 +1285,19 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                         obligation.param_env,
                         cause.clone(),
                         obligation.recursion_depth + 1,
-                        self_ty
-                            .rebind(ty::TraitPredicate {
-                                trait_ref: ty::TraitRef {
-                                    def_id: self.tcx().require_lang_item(LangItem::Destruct, None),
-                                    substs: self.tcx().mk_substs_trait(nested_ty, &[]),
-                                },
-                                constness: ty::BoundConstness::ConstIfConst,
-                                polarity: ty::ImplPolarity::Positive,
-                            })
-                            .to_predicate(tcx),
+                        self_ty.rebind(ty::TraitPredicate {
+                            trait_ref: self
+                                .tcx()
+                                .at(cause.span)
+                                .mk_trait_ref(LangItem::Destruct, [nested_ty]),
+                            constness: ty::BoundConstness::ConstIfConst,
+                            polarity: ty::ImplPolarity::Positive,
+                        }),
                         &mut nested,
                     );
 
                     nested.push(Obligation::with_depth(
+                        tcx,
                         cause.clone(),
                         obligation.recursion_depth + 1,
                         obligation.param_env,
@@ -1280,18 +1309,17 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 // since it's either not `const Drop` (and we raise an error during selection),
                 // or it's an ADT (and we need to check for a custom impl during selection)
                 _ => {
-                    let predicate = self_ty
-                        .rebind(ty::TraitPredicate {
-                            trait_ref: ty::TraitRef {
-                                def_id: self.tcx().require_lang_item(LangItem::Destruct, None),
-                                substs: self.tcx().mk_substs_trait(nested_ty, &[]),
-                            },
-                            constness: ty::BoundConstness::ConstIfConst,
-                            polarity: ty::ImplPolarity::Positive,
-                        })
-                        .to_predicate(tcx);
+                    let predicate = self_ty.rebind(ty::TraitPredicate {
+                        trait_ref: self
+                            .tcx()
+                            .at(cause.span)
+                            .mk_trait_ref(LangItem::Destruct, [nested_ty]),
+                        constness: ty::BoundConstness::ConstIfConst,
+                        polarity: ty::ImplPolarity::Positive,
+                    });
 
                     nested.push(Obligation::with_depth(
+                        tcx,
                         cause.clone(),
                         obligation.recursion_depth + 1,
                         obligation.param_env,
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index 9ebff4892..035deb616 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -2,6 +2,12 @@
 //!
 //! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/traits/resolution.html#selection
 
+// FIXME: The `map` field in ProvisionalEvaluationCache should be changed to
+// a `FxIndexMap` to avoid query instability, but right now it causes a perf regression. This would be
+// fixed or at least lightened by the addition of the `drain_filter` method to `FxIndexMap`
+// Relevant: https://github.com/rust-lang/rust/pull/103723 and https://github.com/bluss/indexmap/issues/242
+#![allow(rustc::potential_query_instability)]
+
 use self::EvaluationResult::*;
 use self::SelectionCandidate::*;
 
@@ -24,9 +30,11 @@ use crate::traits::error_reporting::TypeErrCtxtExt;
 use crate::traits::project::ProjectAndUnifyResult;
 use crate::traits::project::ProjectionCacheKeyExt;
 use crate::traits::ProjectionCacheKey;
-use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet};
+use crate::traits::Unimplemented;
+use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::fx::{FxHashSet, FxIndexSet};
 use rustc_data_structures::stack::ensure_sufficient_stack;
-use rustc_errors::{Diagnostic, ErrorGuaranteed};
+use rustc_errors::Diagnostic;
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_infer::infer::LateBoundRegionConversionTime;
@@ -47,6 +55,7 @@ use std::fmt::{self, Display};
 use std::iter;
 
 pub use rustc_middle::traits::select::*;
+use rustc_middle::ty::print::with_no_trimmed_paths;
 
 mod candidate_assembly;
 mod confirmation;
@@ -93,7 +102,7 @@ impl IntercrateAmbiguityCause {
 }
 
 pub struct SelectionContext<'cx, 'tcx> {
-    infcx: &'cx InferCtxt<'tcx>,
+    pub infcx: &'cx InferCtxt<'tcx>,
 
     /// Freshener used specifically for entries on the obligation
     /// stack. This ensures that all entries on the stack at one time
@@ -102,25 +111,6 @@ pub struct SelectionContext<'cx, 'tcx> {
     /// require themselves.
     freshener: TypeFreshener<'cx, 'tcx>,
 
-    /// During coherence we have to assume that other crates may add
-    /// additional impls which we currently don't know about.
-    ///
-    /// To deal with this evaluation should be conservative
-    /// and consider the possibility of impls from outside this crate.
-    /// This comes up primarily when resolving ambiguity. Imagine
-    /// there is some trait reference `$0: Bar` where `$0` is an
-    /// inference variable. If `intercrate` is true, then we can never
-    /// say for sure that this reference is not implemented, even if
-    /// there are *no impls at all for `Bar`*, because `$0` could be
-    /// bound to some type that in a downstream crate that implements
-    /// `Bar`.
-    ///
-    /// Outside of coherence we set this to false because we are only
-    /// interested in types that the user could actually have written.
-    /// In other words, we consider `$0: Bar` to be unimplemented if
-    /// there is no type that the user could *actually name* that
-    /// would satisfy it. This avoids crippling inference, basically.
-    intercrate: bool,
     /// If `intercrate` is set, we remember predicates which were
     /// considered ambiguous because of impls potentially added in other crates.
     /// This is used in coherence to give improved diagnostics.
@@ -218,16 +208,11 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         SelectionContext {
             infcx,
             freshener: infcx.freshener_keep_static(),
-            intercrate: false,
             intercrate_ambiguity_causes: None,
             query_mode: TraitQueryMode::Standard,
         }
     }
 
-    pub fn intercrate(infcx: &'cx InferCtxt<'tcx>) -> SelectionContext<'cx, 'tcx> {
-        SelectionContext { intercrate: true, ..SelectionContext::new(infcx) }
-    }
-
     pub fn with_query_mode(
         infcx: &'cx InferCtxt<'tcx>,
         query_mode: TraitQueryMode,
@@ -239,7 +224,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
     /// Enables tracking of intercrate ambiguity causes. See
     /// the documentation of [`Self::intercrate_ambiguity_causes`] for more.
     pub fn enable_tracking_intercrate_ambiguity_causes(&mut self) {
-        assert!(self.intercrate);
+        assert!(self.is_intercrate());
         assert!(self.intercrate_ambiguity_causes.is_none());
         self.intercrate_ambiguity_causes = Some(FxIndexSet::default());
         debug!("selcx: enable_tracking_intercrate_ambiguity_causes");
@@ -249,20 +234,16 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
     /// was enabled and disables tracking at the same time. If
     /// tracking is not enabled, just returns an empty vector.
     pub fn take_intercrate_ambiguity_causes(&mut self) -> FxIndexSet<IntercrateAmbiguityCause> {
-        assert!(self.intercrate);
+        assert!(self.is_intercrate());
         self.intercrate_ambiguity_causes.take().unwrap_or_default()
     }
 
-    pub fn infcx(&self) -> &'cx InferCtxt<'tcx> {
-        self.infcx
-    }
-
     pub fn tcx(&self) -> TyCtxt<'tcx> {
         self.infcx.tcx
     }
 
     pub fn is_intercrate(&self) -> bool {
-        self.intercrate
+        self.infcx.intercrate
     }
 
     ///////////////////////////////////////////////////////////////////////////
@@ -294,9 +275,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 assert!(self.query_mode == TraitQueryMode::Canonical);
                 return Err(SelectionError::Overflow(OverflowError::Canonical));
             }
-            Err(SelectionError::Ambiguous(_)) => {
-                return Ok(None);
-            }
             Err(e) => {
                 return Err(e);
             }
@@ -328,6 +306,213 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         self.candidate_from_obligation(&stack)
     }
 
+    #[instrument(level = "debug", skip(self), ret)]
+    fn candidate_from_obligation<'o>(
+        &mut self,
+        stack: &TraitObligationStack<'o, 'tcx>,
+    ) -> SelectionResult<'tcx, SelectionCandidate<'tcx>> {
+        // Watch out for overflow. This intentionally bypasses (and does
+        // not update) the cache.
+        self.check_recursion_limit(&stack.obligation, &stack.obligation)?;
+
+        // Check the cache. Note that we freshen the trait-ref
+        // separately rather than using `stack.fresh_trait_ref` --
+        // this is because we want the unbound variables to be
+        // replaced with fresh types starting from index 0.
+        let cache_fresh_trait_pred = self.infcx.freshen(stack.obligation.predicate);
+        debug!(?cache_fresh_trait_pred);
+        debug_assert!(!stack.obligation.predicate.has_escaping_bound_vars());
+
+        if let Some(c) =
+            self.check_candidate_cache(stack.obligation.param_env, cache_fresh_trait_pred)
+        {
+            debug!("CACHE HIT");
+            return c;
+        }
+
+        // If no match, compute result and insert into cache.
+        //
+        // FIXME(nikomatsakis) -- this cache is not taking into
+        // account cycles that may have occurred in forming the
+        // candidate. I don't know of any specific problems that
+        // result but it seems awfully suspicious.
+        let (candidate, dep_node) =
+            self.in_task(|this| this.candidate_from_obligation_no_cache(stack));
+
+        debug!("CACHE MISS");
+        self.insert_candidate_cache(
+            stack.obligation.param_env,
+            cache_fresh_trait_pred,
+            dep_node,
+            candidate.clone(),
+        );
+        candidate
+    }
+
+    fn candidate_from_obligation_no_cache<'o>(
+        &mut self,
+        stack: &TraitObligationStack<'o, 'tcx>,
+    ) -> SelectionResult<'tcx, SelectionCandidate<'tcx>> {
+        if let Err(conflict) = self.is_knowable(stack) {
+            debug!("coherence stage: not knowable");
+            if self.intercrate_ambiguity_causes.is_some() {
+                debug!("evaluate_stack: intercrate_ambiguity_causes is some");
+                // Heuristics: show the diagnostics when there are no candidates in crate.
+                if let Ok(candidate_set) = self.assemble_candidates(stack) {
+                    let mut no_candidates_apply = true;
+
+                    for c in candidate_set.vec.iter() {
+                        if self.evaluate_candidate(stack, &c)?.may_apply() {
+                            no_candidates_apply = false;
+                            break;
+                        }
+                    }
+
+                    if !candidate_set.ambiguous && no_candidates_apply {
+                        let trait_ref = stack.obligation.predicate.skip_binder().trait_ref;
+                        if !trait_ref.references_error() {
+                            let self_ty = trait_ref.self_ty();
+                            let (trait_desc, self_desc) = with_no_trimmed_paths!({
+                                let trait_desc = trait_ref.print_only_trait_path().to_string();
+                                let self_desc = if self_ty.has_concrete_skeleton() {
+                                    Some(self_ty.to_string())
+                                } else {
+                                    None
+                                };
+                                (trait_desc, self_desc)
+                            });
+                            let cause = if let Conflict::Upstream = conflict {
+                                IntercrateAmbiguityCause::UpstreamCrateUpdate {
+                                    trait_desc,
+                                    self_desc,
+                                }
+                            } else {
+                                IntercrateAmbiguityCause::DownstreamCrate { trait_desc, self_desc }
+                            };
+                            debug!(?cause, "evaluate_stack: pushing cause");
+                            self.intercrate_ambiguity_causes.as_mut().unwrap().insert(cause);
+                        }
+                    }
+                }
+            }
+            return Ok(None);
+        }
+
+        let candidate_set = self.assemble_candidates(stack)?;
+
+        if candidate_set.ambiguous {
+            debug!("candidate set contains ambig");
+            return Ok(None);
+        }
+
+        let candidates = candidate_set.vec;
+
+        debug!(?stack, ?candidates, "assembled {} candidates", candidates.len());
+
+        // At this point, we know that each of the entries in the
+        // candidate set is *individually* applicable. Now we have to
+        // figure out if they contain mutual incompatibilities. This
+        // frequently arises if we have an unconstrained input type --
+        // for example, we are looking for `$0: Eq` where `$0` is some
+        // unconstrained type variable. In that case, we'll get a
+        // candidate which assumes $0 == int, one that assumes `$0 ==
+        // usize`, etc. This spells an ambiguity.
+
+        let mut candidates = self.filter_impls(candidates, stack.obligation);
+
+        // If there is more than one candidate, first winnow them down
+        // by considering extra conditions (nested obligations and so
+        // forth). We don't winnow if there is exactly one
+        // candidate. This is a relatively minor distinction but it
+        // can lead to better inference and error-reporting. An
+        // example would be if there was an impl:
+        //
+        //     impl<T:Clone> Vec<T> { fn push_clone(...) { ... } }
+        //
+        // and we were to see some code `foo.push_clone()` where `boo`
+        // is a `Vec<Bar>` and `Bar` does not implement `Clone`.  If
+        // we were to winnow, we'd wind up with zero candidates.
+        // Instead, we select the right impl now but report "`Bar` does
+        // not implement `Clone`".
+        if candidates.len() == 1 {
+            return self.filter_reservation_impls(candidates.pop().unwrap(), stack.obligation);
+        }
+
+        // Winnow, but record the exact outcome of evaluation, which
+        // is needed for specialization. Propagate overflow if it occurs.
+        let mut candidates = candidates
+            .into_iter()
+            .map(|c| match self.evaluate_candidate(stack, &c) {
+                Ok(eval) if eval.may_apply() => {
+                    Ok(Some(EvaluatedCandidate { candidate: c, evaluation: eval }))
+                }
+                Ok(_) => Ok(None),
+                Err(OverflowError::Canonical) => Err(Overflow(OverflowError::Canonical)),
+                Err(OverflowError::ErrorReporting) => Err(ErrorReporting),
+                Err(OverflowError::Error(e)) => Err(Overflow(OverflowError::Error(e))),
+            })
+            .flat_map(Result::transpose)
+            .collect::<Result<Vec<_>, _>>()?;
+
+        debug!(?stack, ?candidates, "winnowed to {} candidates", candidates.len());
+
+        let needs_infer = stack.obligation.predicate.has_non_region_infer();
+
+        // If there are STILL multiple candidates, we can further
+        // reduce the list by dropping duplicates -- including
+        // resolving specializations.
+        if candidates.len() > 1 {
+            let mut i = 0;
+            while i < candidates.len() {
+                let is_dup = (0..candidates.len()).filter(|&j| i != j).any(|j| {
+                    self.candidate_should_be_dropped_in_favor_of(
+                        &candidates[i],
+                        &candidates[j],
+                        needs_infer,
+                    )
+                });
+                if is_dup {
+                    debug!(candidate = ?candidates[i], "Dropping candidate #{}/{}", i, candidates.len());
+                    candidates.swap_remove(i);
+                } else {
+                    debug!(candidate = ?candidates[i], "Retaining candidate #{}/{}", i, candidates.len());
+                    i += 1;
+
+                    // If there are *STILL* multiple candidates, give up
+                    // and report ambiguity.
+                    if i > 1 {
+                        debug!("multiple matches, ambig");
+                        return Ok(None);
+                    }
+                }
+            }
+        }
+
+        // If there are *NO* candidates, then there are no impls --
+        // that we know of, anyway. Note that in the case where there
+        // are unbound type variables within the obligation, it might
+        // be the case that you could still satisfy the obligation
+        // from another crate by instantiating the type variables with
+        // a type from another crate that does have an impl. This case
+        // is checked for in `evaluate_stack` (and hence users
+        // who might care about this case, like coherence, should use
+        // that function).
+        if candidates.is_empty() {
+            // If there's an error type, 'downgrade' our result from
+            // `Err(Unimplemented)` to `Ok(None)`. This helps us avoid
+            // emitting additional spurious errors, since we're guaranteed
+            // to have emitted at least one.
+            if stack.obligation.predicate.references_error() {
+                debug!(?stack.obligation.predicate, "found error type in predicate, treating as ambiguous");
+                return Ok(None);
+            }
+            return Err(Unimplemented);
+        }
+
+        // Just one candidate left.
+        self.filter_reservation_impls(candidates.pop().unwrap().candidate, stack.obligation)
+    }
+
     ///////////////////////////////////////////////////////////////////////////
     // EVALUATION
     //
@@ -438,10 +623,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         ensure_sufficient_stack(|| {
             let bound_predicate = obligation.predicate.kind();
             match bound_predicate.skip_binder() {
-                ty::PredicateKind::Trait(t) => {
+                ty::PredicateKind::Clause(ty::Clause::Trait(t)) => {
                     let t = bound_predicate.rebind(t);
                     debug_assert!(!t.has_escaping_bound_vars());
-                    let obligation = obligation.with(t);
+                    let obligation = obligation.with(self.tcx(), t);
                     self.evaluate_trait_predicate_recursively(previous_stack, obligation)
                 }
 
@@ -565,7 +750,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     }
                 }
 
-                ty::PredicateKind::TypeOutlives(pred) => {
+                ty::PredicateKind::Clause(ty::Clause::TypeOutlives(pred)) => {
                     // A global type with no late-bound regions can only
                     // contain the "'static" lifetime (any other lifetime
                     // would either be late-bound or local), so it is guaranteed
@@ -577,7 +762,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     }
                 }
 
-                ty::PredicateKind::RegionOutlives(..) => {
+                ty::PredicateKind::Clause(ty::Clause::RegionOutlives(..)) => {
                     // We do not consider region relationships when evaluating trait matches.
                     Ok(EvaluatedToOkModuloRegions)
                 }
@@ -590,9 +775,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     }
                 }
 
-                ty::PredicateKind::Projection(data) => {
+                ty::PredicateKind::Clause(ty::Clause::Projection(data)) => {
                     let data = bound_predicate.rebind(data);
-                    let project_obligation = obligation.with(data);
+                    let project_obligation = obligation.with(self.tcx(), data);
                     match project::poly_project_and_unify_type(self, &project_obligation) {
                         ProjectAndUnifyResult::Holds(mut subobligations) => {
                             'compute_res: {
@@ -676,21 +861,62 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 }
 
                 ty::PredicateKind::ConstEquate(c1, c2) => {
+                    let tcx = self.tcx();
                     assert!(
-                        self.tcx().features().generic_const_exprs,
+                        tcx.features().generic_const_exprs,
                         "`ConstEquate` without a feature gate: {c1:?} {c2:?}",
                     );
-                    debug!(?c1, ?c2, "evaluate_predicate_recursively: equating consts");
 
-                    // FIXME: we probably should only try to unify abstract constants
-                    // if the constants depend on generic parameters.
-                    //
-                    // Let's just see where this breaks :shrug:
-                    if let (ty::ConstKind::Unevaluated(a), ty::ConstKind::Unevaluated(b)) =
-                        (c1.kind(), c2.kind())
                     {
-                        if self.infcx.try_unify_abstract_consts(a, b, obligation.param_env) {
-                            return Ok(EvaluatedToOk);
+                        let c1 = tcx.expand_abstract_consts(c1);
+                        let c2 = tcx.expand_abstract_consts(c2);
+                        debug!(
+                            "evalaute_predicate_recursively: equating consts:\nc1= {:?}\nc2= {:?}",
+                            c1, c2
+                        );
+
+                        use rustc_hir::def::DefKind;
+                        use ty::ConstKind::Unevaluated;
+                        match (c1.kind(), c2.kind()) {
+                            (Unevaluated(a), Unevaluated(b))
+                                if a.def.did == b.def.did
+                                    && tcx.def_kind(a.def.did) == DefKind::AssocConst =>
+                            {
+                                if let Ok(new_obligations) = self
+                                    .infcx
+                                    .at(&obligation.cause, obligation.param_env)
+                                    .trace(c1, c2)
+                                    .eq(a.substs, b.substs)
+                                {
+                                    let mut obligations = new_obligations.obligations;
+                                    self.add_depth(
+                                        obligations.iter_mut(),
+                                        obligation.recursion_depth,
+                                    );
+                                    return self.evaluate_predicates_recursively(
+                                        previous_stack,
+                                        obligations.into_iter(),
+                                    );
+                                }
+                            }
+                            (_, Unevaluated(_)) | (Unevaluated(_), _) => (),
+                            (_, _) => {
+                                if let Ok(new_obligations) = self
+                                    .infcx
+                                    .at(&obligation.cause, obligation.param_env)
+                                    .eq(c1, c2)
+                                {
+                                    let mut obligations = new_obligations.obligations;
+                                    self.add_depth(
+                                        obligations.iter_mut(),
+                                        obligation.recursion_depth,
+                                    );
+                                    return self.evaluate_predicates_recursively(
+                                        previous_stack,
+                                        obligations.into_iter(),
+                                    );
+                                }
+                            }
                         }
                     }
 
@@ -712,23 +938,17 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
                     match (evaluate(c1), evaluate(c2)) {
                         (Ok(c1), Ok(c2)) => {
-                            match self
-                                .infcx()
-                                .at(&obligation.cause, obligation.param_env)
-                                .eq(c1, c2)
+                            match self.infcx.at(&obligation.cause, obligation.param_env).eq(c1, c2)
                             {
-                                Ok(_) => Ok(EvaluatedToOk),
+                                Ok(inf_ok) => self.evaluate_predicates_recursively(
+                                    previous_stack,
+                                    inf_ok.into_obligations(),
+                                ),
                                 Err(_) => Ok(EvaluatedToErr),
                             }
                         }
                         (Err(ErrorHandled::Reported(_)), _)
                         | (_, Err(ErrorHandled::Reported(_))) => Ok(EvaluatedToErr),
-                        (Err(ErrorHandled::Linted), _) | (_, Err(ErrorHandled::Linted)) => {
-                            span_bug!(
-                                obligation.cause.span(),
-                                "ConstEquate: const_eval_resolve returned an unexpected error"
-                            )
-                        }
                         (Err(ErrorHandled::TooGeneric), _) | (_, Err(ErrorHandled::TooGeneric)) => {
                             if c1.has_non_region_infer() || c2.has_non_region_infer() {
                                 Ok(EvaluatedToAmbig)
@@ -742,6 +962,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 ty::PredicateKind::TypeWellFormedFromEnv(..) => {
                     bug!("TypeWellFormedFromEnv is only used for chalk")
                 }
+                ty::PredicateKind::Ambiguous => Ok(EvaluatedToAmbig),
             }
         })
     }
@@ -752,7 +973,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         previous_stack: TraitObligationStackList<'o, 'tcx>,
         mut obligation: TraitObligation<'tcx>,
     ) -> Result<EvaluationResult, OverflowError> {
-        if !self.intercrate
+        if !self.is_intercrate()
             && obligation.is_global()
             && obligation.param_env.caller_bounds().iter().all(|bound| bound.needs_subst())
         {
@@ -931,7 +1152,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
         match self.candidate_from_obligation(stack) {
             Ok(Some(c)) => self.evaluate_candidate(stack, &c),
-            Err(SelectionError::Ambiguous(_)) => Ok(EvaluatedToAmbig),
             Ok(None) => Ok(EvaluatedToAmbig),
             Err(Overflow(OverflowError::Canonical)) => Err(OverflowError::Canonical),
             Err(ErrorReporting) => Err(OverflowError::ErrorReporting),
@@ -956,7 +1176,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
     fn coinductive_predicate(&self, predicate: ty::Predicate<'tcx>) -> bool {
         let result = match predicate.kind().skip_binder() {
-            ty::PredicateKind::Trait(ref data) => self.tcx().trait_is_auto(data.def_id()),
+            ty::PredicateKind::Clause(ty::Clause::Trait(ref data)) => {
+                self.tcx().trait_is_coinductive(data.def_id())
+            }
             ty::PredicateKind::WellFormed(_) => true,
             _ => false,
         };
@@ -1016,7 +1238,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         // mode, so don't do any caching. In particular, we might
         // re-use the same `InferCtxt` with both an intercrate
         // and non-intercrate `SelectionContext`
-        if self.intercrate {
+        if self.is_intercrate() {
             return None;
         }
 
@@ -1046,7 +1268,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         // mode, so don't do any caching. In particular, we might
         // re-use the same `InferCtxt` with both an intercrate
         // and non-intercrate `SelectionContext`
-        if self.intercrate {
+        if self.is_intercrate() {
             return;
         }
 
@@ -1084,20 +1306,21 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         it.for_each(|o| o.recursion_depth = cmp::max(min_depth, o.recursion_depth) + 1);
     }
 
-    fn check_recursion_depth<T: Display + TypeFoldable<'tcx>>(
+    fn check_recursion_depth<T>(
         &self,
         depth: usize,
         error_obligation: &Obligation<'tcx, T>,
-    ) -> Result<(), OverflowError> {
+    ) -> Result<(), OverflowError>
+    where
+        T: ToPredicate<'tcx> + Clone,
+    {
         if !self.infcx.tcx.recursion_limit().value_within_limit(depth) {
             match self.query_mode {
                 TraitQueryMode::Standard => {
-                    if self.infcx.is_tainted_by_errors() {
-                        return Err(OverflowError::Error(
-                            ErrorGuaranteed::unchecked_claim_error_was_emitted(),
-                        ));
+                    if let Some(e) = self.infcx.tainted_by_errors() {
+                        return Err(OverflowError::Error(e));
                     }
-                    self.infcx.err_ctxt().report_overflow_error(error_obligation, true);
+                    self.infcx.err_ctxt().report_overflow_obligation(error_obligation, true);
                 }
                 TraitQueryMode::Canonical => {
                     return Err(OverflowError::Canonical);
@@ -1112,11 +1335,14 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
     /// The weird return type of this function allows it to be used with the `try` (`?`)
     /// operator within certain functions.
     #[inline(always)]
-    fn check_recursion_limit<T: Display + TypeFoldable<'tcx>, V: Display + TypeFoldable<'tcx>>(
+    fn check_recursion_limit<T: Display + TypeFoldable<'tcx>, V>(
         &self,
         obligation: &Obligation<'tcx, T>,
         error_obligation: &Obligation<'tcx, V>,
-    ) -> Result<(), OverflowError> {
+    ) -> Result<(), OverflowError>
+    where
+        V: ToPredicate<'tcx> + Clone,
+    {
         self.check_recursion_depth(obligation.recursion_depth, error_obligation)
     }
 
@@ -1132,12 +1358,13 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
     /// filter_impls filters constant trait obligations and candidates that have a positive impl
     /// for a negative goal and a negative impl for a positive goal
-    #[instrument(level = "debug", skip(self))]
+    #[instrument(level = "debug", skip(self, candidates))]
     fn filter_impls(
         &mut self,
         candidates: Vec<SelectionCandidate<'tcx>>,
         obligation: &TraitObligation<'tcx>,
     ) -> Vec<SelectionCandidate<'tcx>> {
+        trace!("{candidates:#?}");
         let tcx = self.tcx();
         let mut result = Vec::with_capacity(candidates.len());
 
@@ -1153,9 +1380,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     ProjectionCandidate(_, ty::BoundConstness::ConstIfConst) => {}
                     // auto trait impl
                     AutoImplCandidate => {}
-                    // generator, this will raise error in other places
+                    // generator / future, this will raise error in other places
                     // or ignore error with const_async_blocks feature
                     GeneratorCandidate => {}
+                    FutureCandidate => {}
                     // FnDef where the function is const
                     FnPointerCandidate { is_const: true } => {}
                     ConstDestructCandidate(_) => {}
@@ -1177,6 +1405,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             }
         }
 
+        trace!("{result:#?}");
         result
     }
 
@@ -1215,14 +1444,14 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
     }
 
     fn is_knowable<'o>(&mut self, stack: &TraitObligationStack<'o, 'tcx>) -> Result<(), Conflict> {
-        debug!("is_knowable(intercrate={:?})", self.intercrate);
+        debug!("is_knowable(intercrate={:?})", self.is_intercrate());
 
-        if !self.intercrate || stack.obligation.polarity() == ty::ImplPolarity::Negative {
+        if !self.is_intercrate() || stack.obligation.polarity() == ty::ImplPolarity::Negative {
             return Ok(());
         }
 
         let obligation = &stack.obligation;
-        let predicate = self.infcx().resolve_vars_if_possible(obligation.predicate);
+        let predicate = self.infcx.resolve_vars_if_possible(obligation.predicate);
 
         // Okay to skip binder because of the nature of the
         // trait-ref-is-knowable check, which does not care about
@@ -1248,7 +1477,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         // the master cache. Since coherence executes pretty quickly,
         // it's not worth going to more trouble to increase the
         // hit-rate, I don't think.
-        if self.intercrate {
+        if self.is_intercrate() {
             return false;
         }
 
@@ -1265,7 +1494,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         // mode, so don't do any caching. In particular, we might
         // re-use the same `InferCtxt` with both an intercrate
         // and non-intercrate `SelectionContext`
-        if self.intercrate {
+        if self.is_intercrate() {
             return None;
         }
         let tcx = self.tcx();
@@ -1304,7 +1533,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         // mode, so don't do any caching. In particular, we might
         // re-use the same `InferCtxt` with both an intercrate
         // and non-intercrate `SelectionContext`
-        if self.intercrate {
+        if self.is_intercrate() {
             return false;
         }
         match result {
@@ -1359,9 +1588,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         &mut self,
         obligation: &TraitObligation<'tcx>,
     ) -> smallvec::SmallVec<[(usize, ty::BoundConstness); 2]> {
-        let poly_trait_predicate = self.infcx().resolve_vars_if_possible(obligation.predicate);
+        let poly_trait_predicate = self.infcx.resolve_vars_if_possible(obligation.predicate);
         let placeholder_trait_predicate =
-            self.infcx().replace_bound_vars_with_placeholders(poly_trait_predicate);
+            self.infcx.replace_bound_vars_with_placeholders(poly_trait_predicate);
         debug!(?placeholder_trait_predicate);
 
         let tcx = self.infcx.tcx;
@@ -1389,7 +1618,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             .enumerate()
             .filter_map(|(idx, bound)| {
                 let bound_predicate = bound.kind();
-                if let ty::PredicateKind::Trait(pred) = bound_predicate.skip_binder() {
+                if let ty::PredicateKind::Clause(ty::Clause::Trait(pred)) =
+                    bound_predicate.skip_binder()
+                {
                     let bound = bound_predicate.rebind(pred.trait_ref);
                     if self.infcx.probe(|_| {
                         match self.match_normalize_trait_ref(
@@ -1581,20 +1812,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             (TransmutabilityCandidate, _) | (_, TransmutabilityCandidate) => false,
 
             // (*)
-            (
-                BuiltinCandidate { has_nested: false }
-                | DiscriminantKindCandidate
-                | PointeeCandidate
-                | ConstDestructCandidate(_),
-                _,
-            ) => true,
-            (
-                _,
-                BuiltinCandidate { has_nested: false }
-                | DiscriminantKindCandidate
-                | PointeeCandidate
-                | ConstDestructCandidate(_),
-            ) => false,
+            (BuiltinCandidate { has_nested: false } | ConstDestructCandidate(_), _) => true,
+            (_, BuiltinCandidate { has_nested: false } | ConstDestructCandidate(_)) => false,
 
             (ParamCandidate(other), ParamCandidate(victim)) => {
                 let same_except_bound_vars = other.skip_binder().trait_ref
@@ -1633,6 +1852,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 ImplCandidate(..)
                 | ClosureCandidate
                 | GeneratorCandidate
+                | FutureCandidate
                 | FnPointerCandidate { .. }
                 | BuiltinObjectCandidate
                 | BuiltinUnsizeCandidate
@@ -1651,6 +1871,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 ImplCandidate(_)
                 | ClosureCandidate
                 | GeneratorCandidate
+                | FutureCandidate
                 | FnPointerCandidate { .. }
                 | BuiltinObjectCandidate
                 | BuiltinUnsizeCandidate
@@ -1681,6 +1902,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 ImplCandidate(..)
                 | ClosureCandidate
                 | GeneratorCandidate
+                | FutureCandidate
                 | FnPointerCandidate { .. }
                 | BuiltinObjectCandidate
                 | BuiltinUnsizeCandidate
@@ -1693,6 +1915,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 ImplCandidate(..)
                 | ClosureCandidate
                 | GeneratorCandidate
+                | FutureCandidate
                 | FnPointerCandidate { .. }
                 | BuiltinObjectCandidate
                 | BuiltinUnsizeCandidate
@@ -1774,6 +1997,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 ImplCandidate(_)
                 | ClosureCandidate
                 | GeneratorCandidate
+                | FutureCandidate
                 | FnPointerCandidate { .. }
                 | BuiltinObjectCandidate
                 | BuiltinUnsizeCandidate
@@ -1783,6 +2007,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 ImplCandidate(_)
                 | ClosureCandidate
                 | GeneratorCandidate
+                | FutureCandidate
                 | FnPointerCandidate { .. }
                 | BuiltinObjectCandidate
                 | BuiltinUnsizeCandidate
@@ -1973,6 +2198,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
     /// Bar<i32> where struct Bar<T> { x: T, y: u32 } -> [i32, u32]
     /// Zed<i32> where enum Zed { A(T), B(u32) } -> [i32, u32]
     /// ```
+    #[instrument(level = "debug", skip(self), ret)]
     fn constituent_types_for_ty(
         &self,
         t: ty::Binder<'tcx, Ty<'tcx>>,
@@ -2089,8 +2315,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     cause.clone(),
                     trait_def_id,
                     recursion_depth,
-                    normalized_ty,
-                    &[],
+                    [normalized_ty],
                 );
                 obligations.push(placeholder_obligation);
                 obligations
@@ -2117,6 +2342,13 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         match self.match_impl(impl_def_id, impl_trait_ref, obligation) {
             Ok(substs) => substs,
             Err(()) => {
+                // FIXME: A rematch may fail when a candidate cache hit occurs
+                // on thefreshened form of the trait predicate, but the match
+                // fails for some reason that is not captured in the freshened
+                // cache key. For example, equating an impl trait ref against
+                // the placeholder trait ref may fail due the Generalizer relation
+                // raising a CyclicalTy error due to a sub_root_var relation
+                // for a variable being generalized...
                 self.infcx.tcx.sess.delay_span_bug(
                     obligation.cause.span,
                     &format!(
@@ -2145,7 +2377,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         obligation: &TraitObligation<'tcx>,
     ) -> Result<Normalized<'tcx, SubstsRef<'tcx>>, ()> {
         let placeholder_obligation =
-            self.infcx().replace_bound_vars_with_placeholders(obligation.predicate);
+            self.infcx.replace_bound_vars_with_placeholders(obligation.predicate);
         let placeholder_obligation_trait_ref = placeholder_obligation.trait_ref;
 
         let impl_substs = self.infcx.fresh_substs_for_item(obligation.cause.span, impl_def_id);
@@ -2181,7 +2413,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             .map_err(|e| debug!("match_impl: failed eq_trait_refs due to `{e}`"))?;
         nested_obligations.extend(obligations);
 
-        if !self.intercrate
+        if !self.is_intercrate()
             && self.tcx().impl_polarity(impl_def_id) == ty::ImplPolarity::Reservation
         {
             debug!("reservation impls only apply in intercrate mode");
@@ -2277,43 +2509,25 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
         debug!(?closure_sig);
 
-        // (1) Feels icky to skip the binder here, but OTOH we know
-        // that the self-type is an unboxed closure type and hence is
+        // NOTE: The self-type is an unboxed closure type and hence is
         // in fact unparameterized (or at least does not reference any
-        // regions bound in the obligation). Still probably some
-        // refactoring could make this nicer.
+        // regions bound in the obligation).
+        let self_ty = obligation
+            .predicate
+            .self_ty()
+            .no_bound_vars()
+            .expect("unboxed closure type should not capture bound vars from the predicate");
+
         closure_trait_ref_and_return_type(
             self.tcx(),
             obligation.predicate.def_id(),
-            obligation.predicate.skip_binder().self_ty(), // (1)
+            self_ty,
             closure_sig,
             util::TupleArgumentsFlag::No,
         )
         .map_bound(|(trait_ref, _)| trait_ref)
     }
 
-    fn generator_trait_ref_unnormalized(
-        &mut self,
-        obligation: &TraitObligation<'tcx>,
-        substs: SubstsRef<'tcx>,
-    ) -> ty::PolyTraitRef<'tcx> {
-        let gen_sig = substs.as_generator().poly_sig();
-
-        // (1) Feels icky to skip the binder here, but OTOH we know
-        // that the self-type is an generator type and hence is
-        // in fact unparameterized (or at least does not reference any
-        // regions bound in the obligation). Still probably some
-        // refactoring could make this nicer.
-
-        super::util::generator_trait_ref_and_outputs(
-            self.tcx(),
-            obligation.predicate.def_id(),
-            obligation.predicate.skip_binder().self_ty(), // (1)
-            gen_sig,
-        )
-        .map_bound(|(trait_ref, ..)| trait_ref)
-    }
-
     /// Returns the obligations that are implied by instantiating an
     /// impl or trait. The obligations are substituted and fully
     /// normalized. This is used when confirming an impl or default
diff --git a/compiler/rustc_trait_selection/src/traits/specialize/mod.rs b/compiler/rustc_trait_selection/src/traits/specialize/mod.rs
index c89165858..a251a508b 100644
--- a/compiler/rustc_trait_selection/src/traits/specialize/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/specialize/mod.rs
@@ -15,11 +15,13 @@ use specialization_graph::GraphExt;
 use crate::errors::NegativePositiveConflict;
 use crate::infer::{InferCtxt, InferOk, TyCtxtInferExt};
 use crate::traits::select::IntercrateAmbiguityCause;
-use crate::traits::{self, coherence, FutureCompatOverlapErrorKind, ObligationCause};
-use rustc_data_structures::fx::{FxHashSet, FxIndexSet};
-use rustc_errors::{struct_span_err, DiagnosticBuilder, EmissionGuarantee};
+use crate::traits::{
+    self, coherence, FutureCompatOverlapErrorKind, ObligationCause, ObligationCtxt,
+};
+use rustc_data_structures::fx::FxIndexSet;
+use rustc_errors::{error_code, DelayDm, Diagnostic};
 use rustc_hir::def_id::{DefId, LocalDefId};
-use rustc_middle::ty::{self, ImplSubject, TyCtxt};
+use rustc_middle::ty::{self, ImplSubject, Ty, TyCtxt};
 use rustc_middle::ty::{InternalSubsts, SubstsRef};
 use rustc_session::lint::builtin::COHERENCE_LEAK_CHECK;
 use rustc_session::lint::builtin::ORDER_DEPENDENT_TRAIT_OBJECTS;
@@ -30,10 +32,10 @@ use super::SelectionContext;
 
 /// Information pertinent to an overlapping impl error.
 #[derive(Debug)]
-pub struct OverlapError {
+pub struct OverlapError<'tcx> {
     pub with_impl: DefId,
-    pub trait_desc: String,
-    pub self_desc: Option<String>,
+    pub trait_ref: ty::TraitRef<'tcx>,
+    pub self_ty: Option<Ty<'tcx>>,
     pub intercrate_ambiguity_causes: FxIndexSet<IntercrateAmbiguityCause>,
     pub involves_placeholder: bool,
 }
@@ -200,39 +202,35 @@ fn fulfill_implication<'tcx>(
         return Err(());
     };
 
+    // Needs to be `in_snapshot` because this function is used to rebase
+    // substitutions, which may happen inside of a select within a probe.
+    let ocx = ObligationCtxt::new_in_snapshot(infcx);
     // attempt to prove all of the predicates for impl2 given those for impl1
     // (which are packed up in penv)
+    ocx.register_obligations(obligations.chain(more_obligations));
 
-    infcx.save_and_restore_in_snapshot_flag(|infcx| {
-        let errors = traits::fully_solve_obligations(&infcx, obligations.chain(more_obligations));
-        match &errors[..] {
-            [] => {
-                debug!(
-                    "fulfill_implication: an impl for {:?} specializes {:?}",
-                    source_trait, target_trait
-                );
+    let errors = ocx.select_all_or_error();
+    if !errors.is_empty() {
+        // no dice!
+        debug!(
+            "fulfill_implication: for impls on {:?} and {:?}, \
+                 could not fulfill: {:?} given {:?}",
+            source_trait,
+            target_trait,
+            errors,
+            param_env.caller_bounds()
+        );
+        return Err(());
+    }
 
-                // Now resolve the *substitution* we built for the target earlier, replacing
-                // the inference variables inside with whatever we got from fulfillment.
-                Ok(infcx.resolve_vars_if_possible(target_substs))
-            }
-            errors => {
-                // no dice!
-                debug!(
-                    "fulfill_implication: for impls on {:?} and {:?}, \
-                     could not fulfill: {:?} given {:?}",
-                    source_trait,
-                    target_trait,
-                    errors,
-                    param_env.caller_bounds()
-                );
-                Err(())
-            }
-        }
-    })
+    debug!("fulfill_implication: an impl for {:?} specializes {:?}", source_trait, target_trait);
+
+    // Now resolve the *substitution* we built for the target earlier, replacing
+    // the inference variables inside with whatever we got from fulfillment.
+    Ok(infcx.resolve_vars_if_possible(target_substs))
 }
 
-// Query provider for `specialization_graph_of`.
+/// Query provider for `specialization_graph_of`.
 pub(super) fn specialization_graph_provider(
     tcx: TyCtxt<'_>,
     trait_id: DefId,
@@ -277,9 +275,9 @@ pub(super) fn specialization_graph_provider(
 // it negatively impacts perf.
 #[cold]
 #[inline(never)]
-fn report_overlap_conflict(
-    tcx: TyCtxt<'_>,
-    overlap: OverlapError,
+fn report_overlap_conflict<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    overlap: OverlapError<'tcx>,
     impl_def_id: LocalDefId,
     used_to_be_allowed: Option<FutureCompatOverlapErrorKind>,
     sg: &mut specialization_graph::Graph,
@@ -315,9 +313,9 @@ fn report_overlap_conflict(
     }
 }
 
-fn report_negative_positive_conflict(
-    tcx: TyCtxt<'_>,
-    overlap: &OverlapError,
+fn report_negative_positive_conflict<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    overlap: &OverlapError<'tcx>,
     local_impl_def_id: LocalDefId,
     negative_impl_def_id: DefId,
     positive_impl_def_id: DefId,
@@ -325,17 +323,17 @@ fn report_negative_positive_conflict(
 ) {
     let mut err = tcx.sess.create_err(NegativePositiveConflict {
         impl_span: tcx.def_span(local_impl_def_id),
-        trait_desc: &overlap.trait_desc,
-        self_desc: &overlap.self_desc,
+        trait_desc: overlap.trait_ref,
+        self_ty: overlap.self_ty,
         negative_impl_span: tcx.span_of_impl(negative_impl_def_id),
         positive_impl_span: tcx.span_of_impl(positive_impl_def_id),
     });
     sg.has_errored = Some(err.emit());
 }
 
-fn report_conflicting_impls(
-    tcx: TyCtxt<'_>,
-    overlap: OverlapError,
+fn report_conflicting_impls<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    overlap: OverlapError<'tcx>,
     impl_def_id: LocalDefId,
     used_to_be_allowed: Option<FutureCompatOverlapErrorKind>,
     sg: &mut specialization_graph::Graph,
@@ -345,12 +343,12 @@ fn report_conflicting_impls(
     // Work to be done after we've built the DiagnosticBuilder. We have to define it
     // now because the struct_lint methods don't return back the DiagnosticBuilder
     // that's passed in.
-    fn decorate<'a, 'b, G: EmissionGuarantee>(
-        tcx: TyCtxt<'_>,
-        overlap: OverlapError,
+    fn decorate<'tcx>(
+        tcx: TyCtxt<'tcx>,
+        overlap: &OverlapError<'tcx>,
         impl_span: Span,
-        err: &'b mut DiagnosticBuilder<'a, G>,
-    ) -> &'b mut DiagnosticBuilder<'a, G> {
+        err: &mut Diagnostic,
+    ) {
         match tcx.span_of_impl(overlap.with_impl) {
             Ok(span) => {
                 err.span_label(span, "first implementation here");
@@ -359,7 +357,7 @@ fn report_conflicting_impls(
                     impl_span,
                     format!(
                         "conflicting implementation{}",
-                        overlap.self_desc.map_or_else(String::new, |ty| format!(" for `{}`", ty))
+                        overlap.self_ty.map_or_else(String::new, |ty| format!(" for `{}`", ty))
                     ),
                 );
             }
@@ -381,26 +379,28 @@ fn report_conflicting_impls(
         if overlap.involves_placeholder {
             coherence::add_placeholder_note(err);
         }
-        err
     }
 
-    let msg = format!(
-        "conflicting implementations of trait `{}`{}{}",
-        overlap.trait_desc,
-        overlap.self_desc.as_deref().map_or_else(String::new, |ty| format!(" for type `{ty}`")),
-        match used_to_be_allowed {
-            Some(FutureCompatOverlapErrorKind::Issue33140) => ": (E0119)",
-            _ => "",
-        }
-    );
+    let msg = DelayDm(|| {
+        format!(
+            "conflicting implementations of trait `{}`{}{}",
+            overlap.trait_ref.print_only_trait_path(),
+            overlap.self_ty.map_or_else(String::new, |ty| format!(" for type `{ty}`")),
+            match used_to_be_allowed {
+                Some(FutureCompatOverlapErrorKind::Issue33140) => ": (E0119)",
+                _ => "",
+            }
+        )
+    });
 
     match used_to_be_allowed {
         None => {
             let reported = if overlap.with_impl.is_local()
                 || tcx.orphan_check_impl(impl_def_id).is_ok()
             {
-                let mut err = struct_span_err!(tcx.sess, impl_span, E0119, "{msg}",);
-                decorate(tcx, overlap, impl_span, &mut err);
+                let mut err = tcx.sess.struct_span_err(impl_span, msg);
+                err.code(error_code!(E0119));
+                decorate(tcx, &overlap, impl_span, &mut err);
                 Some(err.emit())
             } else {
                 Some(tcx.sess.delay_span_bug(impl_span, "impl should have failed the orphan check"))
@@ -417,7 +417,10 @@ fn report_conflicting_impls(
                 tcx.hir().local_def_id_to_hir_id(impl_def_id),
                 impl_span,
                 msg,
-                |err| decorate(tcx, overlap, impl_span, err),
+                |err| {
+                    decorate(tcx, &overlap, impl_span, err);
+                    err
+                },
             );
         }
     };
@@ -435,7 +438,7 @@ pub(crate) fn to_pretty_impl_header(tcx: TyCtxt<'_>, impl_def_id: DefId) -> Opti
 
     // FIXME: Currently only handles ?Sized.
     //        Needs to support ?Move and ?DynSized when they are implemented.
-    let mut types_without_default_bounds = FxHashSet::default();
+    let mut types_without_default_bounds = FxIndexSet::default();
     let sized_trait = tcx.lang_items().sized_trait();
 
     if !substs.is_empty() {
@@ -473,7 +476,9 @@ pub(crate) fn to_pretty_impl_header(tcx: TyCtxt<'_>, impl_def_id: DefId) -> Opti
                     trait_pred
                 });
 
-                p = tcx.mk_predicate(new_trait_pred.map_bound(ty::PredicateKind::Trait))
+                p = tcx.mk_predicate(
+                    new_trait_pred.map_bound(|p| ty::PredicateKind::Clause(ty::Clause::Trait(p))),
+                )
             }
         }
         pretty_predicates.push(p.to_string());
diff --git a/compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs b/compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs
index 63f89a33e..4546c9533 100644
--- a/compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs
+++ b/compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs
@@ -3,7 +3,6 @@ use super::OverlapError;
 use crate::traits;
 use rustc_hir::def_id::DefId;
 use rustc_middle::ty::fast_reject::{self, SimplifiedType, TreatParams};
-use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_middle::ty::{self, TyCtxt, TypeVisitable};
 
 pub use rustc_middle::traits::specialization_graph::*;
@@ -15,15 +14,15 @@ pub enum FutureCompatOverlapErrorKind {
 }
 
 #[derive(Debug)]
-pub struct FutureCompatOverlapError {
-    pub error: OverlapError,
+pub struct FutureCompatOverlapError<'tcx> {
+    pub error: OverlapError<'tcx>,
     pub kind: FutureCompatOverlapErrorKind,
 }
 
 /// The result of attempting to insert an impl into a group of children.
-enum Inserted {
+enum Inserted<'tcx> {
     /// The impl was inserted as a new child in this group of children.
-    BecameNewSibling(Option<FutureCompatOverlapError>),
+    BecameNewSibling(Option<FutureCompatOverlapError<'tcx>>),
 
     /// The impl should replace existing impls [X1, ..], because the impl specializes X1, X2, etc.
     ReplaceChildren(Vec<DefId>),
@@ -42,12 +41,12 @@ trait ChildrenExt<'tcx> {
         impl_def_id: DefId,
         simplified_self: Option<SimplifiedType>,
         overlap_mode: OverlapMode,
-    ) -> Result<Inserted, OverlapError>;
+    ) -> Result<Inserted<'tcx>, OverlapError<'tcx>>;
 }
 
-impl ChildrenExt<'_> for Children {
+impl<'tcx> ChildrenExt<'tcx> for Children {
     /// Insert an impl into this set of children without comparing to any existing impls.
-    fn insert_blindly(&mut self, tcx: TyCtxt<'_>, impl_def_id: DefId) {
+    fn insert_blindly(&mut self, tcx: TyCtxt<'tcx>, impl_def_id: DefId) {
         let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
         if let Some(st) = fast_reject::simplify_type(tcx, trait_ref.self_ty(), TreatParams::AsInfer)
         {
@@ -62,7 +61,7 @@ impl ChildrenExt<'_> for Children {
     /// Removes an impl from this set of children. Used when replacing
     /// an impl with a parent. The impl must be present in the list of
     /// children already.
-    fn remove_existing(&mut self, tcx: TyCtxt<'_>, impl_def_id: DefId) {
+    fn remove_existing(&mut self, tcx: TyCtxt<'tcx>, impl_def_id: DefId) {
         let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
         let vec: &mut Vec<DefId>;
         if let Some(st) = fast_reject::simplify_type(tcx, trait_ref.self_ty(), TreatParams::AsInfer)
@@ -82,11 +81,11 @@ impl ChildrenExt<'_> for Children {
     /// specialization relationships.
     fn insert(
         &mut self,
-        tcx: TyCtxt<'_>,
+        tcx: TyCtxt<'tcx>,
         impl_def_id: DefId,
         simplified_self: Option<SimplifiedType>,
         overlap_mode: OverlapMode,
-    ) -> Result<Inserted, OverlapError> {
+    ) -> Result<Inserted<'tcx>, OverlapError<'tcx>> {
         let mut last_lint = None;
         let mut replace_children = Vec::new();
 
@@ -103,30 +102,23 @@ impl ChildrenExt<'_> for Children {
                 impl_def_id, simplified_self, possible_sibling,
             );
 
-            let create_overlap_error = |overlap: traits::coherence::OverlapResult<'_>| {
+            let create_overlap_error = |overlap: traits::coherence::OverlapResult<'tcx>| {
                 let trait_ref = overlap.impl_header.trait_ref.unwrap();
                 let self_ty = trait_ref.self_ty();
 
-                // FIXME: should postpone string formatting until we decide to actually emit.
-                with_no_trimmed_paths!({
-                    OverlapError {
-                        with_impl: possible_sibling,
-                        trait_desc: trait_ref.print_only_trait_path().to_string(),
-                        // Only report the `Self` type if it has at least
-                        // some outer concrete shell; otherwise, it's
-                        // not adding much information.
-                        self_desc: if self_ty.has_concrete_skeleton() {
-                            Some(self_ty.to_string())
-                        } else {
-                            None
-                        },
-                        intercrate_ambiguity_causes: overlap.intercrate_ambiguity_causes,
-                        involves_placeholder: overlap.involves_placeholder,
-                    }
-                })
+                OverlapError {
+                    with_impl: possible_sibling,
+                    trait_ref,
+                    // Only report the `Self` type if it has at least
+                    // some outer concrete shell; otherwise, it's
+                    // not adding much information.
+                    self_ty: if self_ty.has_concrete_skeleton() { Some(self_ty) } else { None },
+                    intercrate_ambiguity_causes: overlap.intercrate_ambiguity_causes,
+                    involves_placeholder: overlap.involves_placeholder,
+                }
             };
 
-            let report_overlap_error = |overlap: traits::coherence::OverlapResult<'_>,
+            let report_overlap_error = |overlap: traits::coherence::OverlapResult<'tcx>,
                                         last_lint: &mut _| {
                 // Found overlap, but no specialization; error out or report future-compat warning.
 
@@ -255,31 +247,31 @@ where
     }
 }
 
-pub trait GraphExt {
+pub trait GraphExt<'tcx> {
     /// Insert a local impl into the specialization graph. If an existing impl
     /// conflicts with it (has overlap, but neither specializes the other),
     /// information about the area of overlap is returned in the `Err`.
     fn insert(
         &mut self,
-        tcx: TyCtxt<'_>,
+        tcx: TyCtxt<'tcx>,
         impl_def_id: DefId,
         overlap_mode: OverlapMode,
-    ) -> Result<Option<FutureCompatOverlapError>, OverlapError>;
+    ) -> Result<Option<FutureCompatOverlapError<'tcx>>, OverlapError<'tcx>>;
 
     /// Insert cached metadata mapping from a child impl back to its parent.
-    fn record_impl_from_cstore(&mut self, tcx: TyCtxt<'_>, parent: DefId, child: DefId);
+    fn record_impl_from_cstore(&mut self, tcx: TyCtxt<'tcx>, parent: DefId, child: DefId);
 }
 
-impl GraphExt for Graph {
+impl<'tcx> GraphExt<'tcx> for Graph {
     /// Insert a local impl into the specialization graph. If an existing impl
     /// conflicts with it (has overlap, but neither specializes the other),
     /// information about the area of overlap is returned in the `Err`.
     fn insert(
         &mut self,
-        tcx: TyCtxt<'_>,
+        tcx: TyCtxt<'tcx>,
         impl_def_id: DefId,
         overlap_mode: OverlapMode,
-    ) -> Result<Option<FutureCompatOverlapError>, OverlapError> {
+    ) -> Result<Option<FutureCompatOverlapError<'tcx>>, OverlapError<'tcx>> {
         assert!(impl_def_id.is_local());
 
         let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
@@ -376,7 +368,7 @@ impl GraphExt for Graph {
     }
 
     /// Insert cached metadata mapping from a child impl back to its parent.
-    fn record_impl_from_cstore(&mut self, tcx: TyCtxt<'_>, parent: DefId, child: DefId) {
+    fn record_impl_from_cstore(&mut self, tcx: TyCtxt<'tcx>, parent: DefId, child: DefId) {
         if self.parent.insert(child, parent).is_some() {
             bug!(
                 "When recording an impl from the crate store, information about its parent \
diff --git a/compiler/rustc_trait_selection/src/traits/structural_match.rs b/compiler/rustc_trait_selection/src/traits/structural_match.rs
index 932dbbb81..4dc08e0f9 100644
--- a/compiler/rustc_trait_selection/src/traits/structural_match.rs
+++ b/compiler/rustc_trait_selection/src/traits/structural_match.rs
@@ -1,11 +1,5 @@
-use crate::infer::{InferCtxt, TyCtxtInferExt};
-use crate::traits::ObligationCause;
-use crate::traits::{TraitEngine, TraitEngineExt};
-
 use rustc_data_structures::fx::FxHashSet;
 use rustc_hir as hir;
-use rustc_hir::lang_items::LangItem;
-use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitor};
 use rustc_span::Span;
 use std::ops::ControlFlow;
@@ -60,53 +54,6 @@ pub fn search_for_adt_const_param_violation<'tcx>(
         .break_value()
 }
 
-/// This method returns true if and only if `adt_ty` itself has been marked as
-/// eligible for structural-match: namely, if it implements both
-/// `StructuralPartialEq` and `StructuralEq` (which are respectively injected by
-/// `#[derive(PartialEq)]` and `#[derive(Eq)]`).
-///
-/// Note that this does *not* recursively check if the substructure of `adt_ty`
-/// implements the traits.
-fn type_marked_structural<'tcx>(
-    infcx: &InferCtxt<'tcx>,
-    adt_ty: Ty<'tcx>,
-    cause: ObligationCause<'tcx>,
-) -> bool {
-    let mut fulfillment_cx = <dyn TraitEngine<'tcx>>::new(infcx.tcx);
-    // require `#[derive(PartialEq)]`
-    let structural_peq_def_id =
-        infcx.tcx.require_lang_item(LangItem::StructuralPeq, Some(cause.span));
-    fulfillment_cx.register_bound(
-        infcx,
-        ty::ParamEnv::empty(),
-        adt_ty,
-        structural_peq_def_id,
-        cause.clone(),
-    );
-    // for now, require `#[derive(Eq)]`. (Doing so is a hack to work around
-    // the type `for<'a> fn(&'a ())` failing to implement `Eq` itself.)
-    let structural_teq_def_id =
-        infcx.tcx.require_lang_item(LangItem::StructuralTeq, Some(cause.span));
-    fulfillment_cx.register_bound(
-        infcx,
-        ty::ParamEnv::empty(),
-        adt_ty,
-        structural_teq_def_id,
-        cause,
-    );
-
-    // We deliberately skip *reporting* fulfillment errors (via
-    // `report_fulfillment_errors`), for two reasons:
-    //
-    // 1. The error messages would mention `std::marker::StructuralPartialEq`
-    //    (a trait which is solely meant as an implementation detail
-    //    for now), and
-    //
-    // 2. We are sometimes doing future-incompatibility lints for
-    //    now, so we do not want unconditional errors here.
-    fulfillment_cx.select_all_or_error(infcx).is_empty()
-}
-
 /// This implements the traversal over the structure of a given type to try to
 /// find instances of ADTs (specifically structs or enums) that do not implement
 /// the structural-match traits (`StructuralPartialEq` and `StructuralEq`).
@@ -262,11 +209,3 @@ impl<'tcx> TypeVisitor<'tcx> for Search<'tcx> {
         })
     }
 }
-
-pub fn provide(providers: &mut Providers) {
-    providers.has_structural_eq_impls = |tcx, ty| {
-        let infcx = tcx.infer_ctxt().build();
-        let cause = ObligationCause::dummy();
-        type_marked_structural(&infcx, ty, cause)
-    };
-}
diff --git a/compiler/rustc_trait_selection/src/traits/util.rs b/compiler/rustc_trait_selection/src/traits/util.rs
index ed47d2f83..f3ca6a6c7 100644
--- a/compiler/rustc_trait_selection/src/traits/util.rs
+++ b/compiler/rustc_trait_selection/src/traits/util.rs
@@ -8,7 +8,9 @@ use rustc_hir::def_id::DefId;
 use rustc_middle::ty::{self, ImplSubject, ToPredicate, Ty, TyCtxt, TypeVisitable};
 use rustc_middle::ty::{GenericArg, SubstsRef};
 
-use super::{Normalized, Obligation, ObligationCause, PredicateObligation, SelectionContext};
+use super::NormalizeExt;
+use super::{Obligation, ObligationCause, PredicateObligation, SelectionContext};
+use rustc_infer::infer::InferOk;
 pub use rustc_infer::traits::{self, util::*};
 
 ///////////////////////////////////////////////////////////////////////////
@@ -200,13 +202,13 @@ pub fn impl_subject_and_oblig<'a, 'tcx>(
 ) -> (ImplSubject<'tcx>, impl Iterator<Item = PredicateObligation<'tcx>>) {
     let subject = selcx.tcx().bound_impl_subject(impl_def_id);
     let subject = subject.subst(selcx.tcx(), impl_substs);
-    let Normalized { value: subject, obligations: normalization_obligations1 } =
-        super::normalize(selcx, param_env, ObligationCause::dummy(), subject);
+    let InferOk { value: subject, obligations: normalization_obligations1 } =
+        selcx.infcx.at(&ObligationCause::dummy(), param_env).normalize(subject);
 
     let predicates = selcx.tcx().predicates_of(impl_def_id);
     let predicates = predicates.instantiate(selcx.tcx(), impl_substs);
-    let Normalized { value: predicates, obligations: normalization_obligations2 } =
-        super::normalize(selcx, param_env, ObligationCause::dummy(), predicates);
+    let InferOk { value: predicates, obligations: normalization_obligations2 } =
+        selcx.infcx.at(&ObligationCause::dummy(), param_env).normalize(predicates);
     let impl_obligations =
         super::predicates_for_generics(|_, _| ObligationCause::dummy(), param_env, predicates);
 
@@ -238,11 +240,9 @@ pub fn predicate_for_trait_def<'tcx>(
     cause: ObligationCause<'tcx>,
     trait_def_id: DefId,
     recursion_depth: usize,
-    self_ty: Ty<'tcx>,
-    params: &[GenericArg<'tcx>],
+    params: impl IntoIterator<Item = impl Into<GenericArg<'tcx>>>,
 ) -> PredicateObligation<'tcx> {
-    let trait_ref =
-        ty::TraitRef { def_id: trait_def_id, substs: tcx.mk_substs_trait(self_ty, params) };
+    let trait_ref = tcx.mk_trait_ref(trait_def_id, params);
     predicate_for_trait_ref(tcx, cause, param_env, trait_ref, recursion_depth)
 }
 
@@ -261,16 +261,6 @@ pub fn upcast_choices<'tcx>(
     supertraits(tcx, source_trait_ref).filter(|r| r.def_id() == target_trait_def_id).collect()
 }
 
-/// Given a trait `trait_ref`, returns the number of vtable entries
-/// that come from `trait_ref`, excluding its supertraits. Used in
-/// computing the vtable base for an upcast trait of a trait object.
-pub fn count_own_vtable_entries<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    trait_ref: ty::PolyTraitRef<'tcx>,
-) -> usize {
-    tcx.own_existential_vtable_entries(trait_ref.def_id()).len()
-}
-
 /// Given an upcast trait object described by `object`, returns the
 /// index of the method `method_def_id` (which should be part of
 /// `object.upcast_trait_ref`) within the vtable for `object`.
@@ -300,15 +290,12 @@ pub fn closure_trait_ref_and_return_type<'tcx>(
     sig: ty::PolyFnSig<'tcx>,
     tuple_arguments: TupleArgumentsFlag,
 ) -> ty::Binder<'tcx, (ty::TraitRef<'tcx>, Ty<'tcx>)> {
+    assert!(!self_ty.has_escaping_bound_vars());
     let arguments_tuple = match tuple_arguments {
         TupleArgumentsFlag::No => sig.skip_binder().inputs()[0],
         TupleArgumentsFlag::Yes => tcx.intern_tup(sig.skip_binder().inputs()),
     };
-    debug_assert!(!self_ty.has_escaping_bound_vars());
-    let trait_ref = ty::TraitRef {
-        def_id: fn_trait_def_id,
-        substs: tcx.mk_substs_trait(self_ty, &[arguments_tuple.into()]),
-    };
+    let trait_ref = tcx.mk_trait_ref(fn_trait_def_id, [self_ty, arguments_tuple]);
     sig.map_bound(|sig| (trait_ref, sig.output()))
 }
 
@@ -318,14 +305,22 @@ pub fn generator_trait_ref_and_outputs<'tcx>(
     self_ty: Ty<'tcx>,
     sig: ty::PolyGenSig<'tcx>,
 ) -> ty::Binder<'tcx, (ty::TraitRef<'tcx>, Ty<'tcx>, Ty<'tcx>)> {
-    debug_assert!(!self_ty.has_escaping_bound_vars());
-    let trait_ref = ty::TraitRef {
-        def_id: fn_trait_def_id,
-        substs: tcx.mk_substs_trait(self_ty, &[sig.skip_binder().resume_ty.into()]),
-    };
+    assert!(!self_ty.has_escaping_bound_vars());
+    let trait_ref = tcx.mk_trait_ref(fn_trait_def_id, [self_ty, sig.skip_binder().resume_ty]);
     sig.map_bound(|sig| (trait_ref, sig.yield_ty, sig.return_ty))
 }
 
+pub fn future_trait_ref_and_outputs<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    fn_trait_def_id: DefId,
+    self_ty: Ty<'tcx>,
+    sig: ty::PolyGenSig<'tcx>,
+) -> ty::Binder<'tcx, (ty::TraitRef<'tcx>, Ty<'tcx>)> {
+    assert!(!self_ty.has_escaping_bound_vars());
+    let trait_ref = tcx.mk_trait_ref(fn_trait_def_id, [self_ty]);
+    sig.map_bound(|sig| (trait_ref, sig.return_ty))
+}
+
 pub fn impl_item_is_final(tcx: TyCtxt<'_>, assoc_item: &ty::AssocItem) -> bool {
     assoc_item.defaultness(tcx).is_final()
         && tcx.impl_defaultness(assoc_item.container_id(tcx)).is_final()
diff --git a/compiler/rustc_trait_selection/src/traits/vtable.rs b/compiler/rustc_trait_selection/src/traits/vtable.rs
new file mode 100644
index 000000000..41ce6cdf7
--- /dev/null
+++ b/compiler/rustc_trait_selection/src/traits/vtable.rs
@@ -0,0 +1,386 @@
+use crate::errors::DumpVTableEntries;
+use crate::traits::{impossible_predicates, is_vtable_safe_method};
+use rustc_hir::def_id::DefId;
+use rustc_hir::lang_items::LangItem;
+use rustc_infer::traits::util::PredicateSet;
+use rustc_infer::traits::ImplSource;
+use rustc_middle::ty::visit::TypeVisitable;
+use rustc_middle::ty::InternalSubsts;
+use rustc_middle::ty::{self, GenericParamDefKind, ToPredicate, Ty, TyCtxt, VtblEntry};
+use rustc_span::{sym, Span};
+use smallvec::SmallVec;
+
+use std::fmt::Debug;
+use std::ops::ControlFlow;
+
+#[derive(Clone, Debug)]
+pub(super) enum VtblSegment<'tcx> {
+    MetadataDSA,
+    TraitOwnEntries { trait_ref: ty::PolyTraitRef<'tcx>, emit_vptr: bool },
+}
+
+/// Prepare the segments for a vtable
+pub(super) fn prepare_vtable_segments<'tcx, T>(
+    tcx: TyCtxt<'tcx>,
+    trait_ref: ty::PolyTraitRef<'tcx>,
+    mut segment_visitor: impl FnMut(VtblSegment<'tcx>) -> ControlFlow<T>,
+) -> Option<T> {
+    // The following constraints holds for the final arrangement.
+    // 1. The whole virtual table of the first direct super trait is included as the
+    //    the prefix. If this trait doesn't have any super traits, then this step
+    //    consists of the dsa metadata.
+    // 2. Then comes the proper pointer metadata(vptr) and all own methods for all
+    //    other super traits except those already included as part of the first
+    //    direct super trait virtual table.
+    // 3. finally, the own methods of this trait.
+
+    // This has the advantage that trait upcasting to the first direct super trait on each level
+    // is zero cost, and to another trait includes only replacing the pointer with one level indirection,
+    // while not using too much extra memory.
+
+    // For a single inheritance relationship like this,
+    //   D --> C --> B --> A
+    // The resulting vtable will consists of these segments:
+    //  DSA, A, B, C, D
+
+    // For a multiple inheritance relationship like this,
+    //   D --> C --> A
+    //           \-> B
+    // The resulting vtable will consists of these segments:
+    //  DSA, A, B, B-vptr, C, D
+
+    // For a diamond inheritance relationship like this,
+    //   D --> B --> A
+    //     \-> C -/
+    // The resulting vtable will consists of these segments:
+    //  DSA, A, B, C, C-vptr, D
+
+    // For a more complex inheritance relationship like this:
+    //   O --> G --> C --> A
+    //     \     \     \-> B
+    //     |     |-> F --> D
+    //     |           \-> E
+    //     |-> N --> J --> H
+    //           \     \-> I
+    //           |-> M --> K
+    //                 \-> L
+    // The resulting vtable will consists of these segments:
+    //  DSA, A, B, B-vptr, C, D, D-vptr, E, E-vptr, F, F-vptr, G,
+    //  H, H-vptr, I, I-vptr, J, J-vptr, K, K-vptr, L, L-vptr, M, M-vptr,
+    //  N, N-vptr, O
+
+    // emit dsa segment first.
+    if let ControlFlow::Break(v) = (segment_visitor)(VtblSegment::MetadataDSA) {
+        return Some(v);
+    }
+
+    let mut emit_vptr_on_new_entry = false;
+    let mut visited = PredicateSet::new(tcx);
+    let predicate = trait_ref.without_const().to_predicate(tcx);
+    let mut stack: SmallVec<[(ty::PolyTraitRef<'tcx>, _, _); 5]> =
+        smallvec![(trait_ref, emit_vptr_on_new_entry, None)];
+    visited.insert(predicate);
+
+    // the main traversal loop:
+    // basically we want to cut the inheritance directed graph into a few non-overlapping slices of nodes
+    // that each node is emitted after all its descendents have been emitted.
+    // so we convert the directed graph into a tree by skipping all previously visited nodes using a visited set.
+    // this is done on the fly.
+    // Each loop run emits a slice - it starts by find a "childless" unvisited node, backtracking upwards, and it
+    // stops after it finds a node that has a next-sibling node.
+    // This next-sibling node will used as the starting point of next slice.
+
+    // Example:
+    // For a diamond inheritance relationship like this,
+    //   D#1 --> B#0 --> A#0
+    //     \-> C#1 -/
+
+    // Starting point 0 stack [D]
+    // Loop run #0: Stack after diving in is [D B A], A is "childless"
+    // after this point, all newly visited nodes won't have a vtable that equals to a prefix of this one.
+    // Loop run #0: Emitting the slice [B A] (in reverse order), B has a next-sibling node, so this slice stops here.
+    // Loop run #0: Stack after exiting out is [D C], C is the next starting point.
+    // Loop run #1: Stack after diving in is [D C], C is "childless", since its child A is skipped(already emitted).
+    // Loop run #1: Emitting the slice [D C] (in reverse order). No one has a next-sibling node.
+    // Loop run #1: Stack after exiting out is []. Now the function exits.
+
+    loop {
+        // dive deeper into the stack, recording the path
+        'diving_in: loop {
+            if let Some((inner_most_trait_ref, _, _)) = stack.last() {
+                let inner_most_trait_ref = *inner_most_trait_ref;
+                let mut direct_super_traits_iter = tcx
+                    .super_predicates_of(inner_most_trait_ref.def_id())
+                    .predicates
+                    .into_iter()
+                    .filter_map(move |(pred, _)| {
+                        pred.subst_supertrait(tcx, &inner_most_trait_ref).to_opt_poly_trait_pred()
+                    });
+
+                'diving_in_skip_visited_traits: loop {
+                    if let Some(next_super_trait) = direct_super_traits_iter.next() {
+                        if visited.insert(next_super_trait.to_predicate(tcx)) {
+                            // We're throwing away potential constness of super traits here.
+                            // FIXME: handle ~const super traits
+                            let next_super_trait = next_super_trait.map_bound(|t| t.trait_ref);
+                            stack.push((
+                                next_super_trait,
+                                emit_vptr_on_new_entry,
+                                Some(direct_super_traits_iter),
+                            ));
+                            break 'diving_in_skip_visited_traits;
+                        } else {
+                            continue 'diving_in_skip_visited_traits;
+                        }
+                    } else {
+                        break 'diving_in;
+                    }
+                }
+            }
+        }
+
+        // Other than the left-most path, vptr should be emitted for each trait.
+        emit_vptr_on_new_entry = true;
+
+        // emit innermost item, move to next sibling and stop there if possible, otherwise jump to outer level.
+        'exiting_out: loop {
+            if let Some((inner_most_trait_ref, emit_vptr, siblings_opt)) = stack.last_mut() {
+                if let ControlFlow::Break(v) = (segment_visitor)(VtblSegment::TraitOwnEntries {
+                    trait_ref: *inner_most_trait_ref,
+                    emit_vptr: *emit_vptr,
+                }) {
+                    return Some(v);
+                }
+
+                'exiting_out_skip_visited_traits: loop {
+                    if let Some(siblings) = siblings_opt {
+                        if let Some(next_inner_most_trait_ref) = siblings.next() {
+                            if visited.insert(next_inner_most_trait_ref.to_predicate(tcx)) {
+                                // We're throwing away potential constness of super traits here.
+                                // FIXME: handle ~const super traits
+                                let next_inner_most_trait_ref =
+                                    next_inner_most_trait_ref.map_bound(|t| t.trait_ref);
+                                *inner_most_trait_ref = next_inner_most_trait_ref;
+                                *emit_vptr = emit_vptr_on_new_entry;
+                                break 'exiting_out;
+                            } else {
+                                continue 'exiting_out_skip_visited_traits;
+                            }
+                        }
+                    }
+                    stack.pop();
+                    continue 'exiting_out;
+                }
+            }
+            // all done
+            return None;
+        }
+    }
+}
+
+fn dump_vtable_entries<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    sp: Span,
+    trait_ref: ty::PolyTraitRef<'tcx>,
+    entries: &[VtblEntry<'tcx>],
+) {
+    tcx.sess.emit_err(DumpVTableEntries {
+        span: sp,
+        trait_ref,
+        entries: format!("{:#?}", entries),
+    });
+}
+
+fn own_existential_vtable_entries<'tcx>(tcx: TyCtxt<'tcx>, trait_def_id: DefId) -> &'tcx [DefId] {
+    let trait_methods = tcx
+        .associated_items(trait_def_id)
+        .in_definition_order()
+        .filter(|item| item.kind == ty::AssocKind::Fn);
+    // Now list each method's DefId (for within its trait).
+    let own_entries = trait_methods.filter_map(move |trait_method| {
+        debug!("own_existential_vtable_entry: trait_method={:?}", trait_method);
+        let def_id = trait_method.def_id;
+
+        // Some methods cannot be called on an object; skip those.
+        if !is_vtable_safe_method(tcx, trait_def_id, &trait_method) {
+            debug!("own_existential_vtable_entry: not vtable safe");
+            return None;
+        }
+
+        Some(def_id)
+    });
+
+    tcx.arena.alloc_from_iter(own_entries.into_iter())
+}
+
+/// Given a trait `trait_ref`, iterates the vtable entries
+/// that come from `trait_ref`, including its supertraits.
+fn vtable_entries<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    trait_ref: ty::PolyTraitRef<'tcx>,
+) -> &'tcx [VtblEntry<'tcx>] {
+    debug!("vtable_entries({:?})", trait_ref);
+
+    let mut entries = vec![];
+
+    let vtable_segment_callback = |segment| -> ControlFlow<()> {
+        match segment {
+            VtblSegment::MetadataDSA => {
+                entries.extend(TyCtxt::COMMON_VTABLE_ENTRIES);
+            }
+            VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => {
+                let existential_trait_ref = trait_ref
+                    .map_bound(|trait_ref| ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref));
+
+                // Lookup the shape of vtable for the trait.
+                let own_existential_entries =
+                    tcx.own_existential_vtable_entries(existential_trait_ref.def_id());
+
+                let own_entries = own_existential_entries.iter().copied().map(|def_id| {
+                    debug!("vtable_entries: trait_method={:?}", def_id);
+
+                    // The method may have some early-bound lifetimes; add regions for those.
+                    let substs = trait_ref.map_bound(|trait_ref| {
+                        InternalSubsts::for_item(tcx, def_id, |param, _| match param.kind {
+                            GenericParamDefKind::Lifetime => tcx.lifetimes.re_erased.into(),
+                            GenericParamDefKind::Type { .. }
+                            | GenericParamDefKind::Const { .. } => {
+                                trait_ref.substs[param.index as usize]
+                            }
+                        })
+                    });
+
+                    // The trait type may have higher-ranked lifetimes in it;
+                    // erase them if they appear, so that we get the type
+                    // at some particular call site.
+                    let substs = tcx
+                        .normalize_erasing_late_bound_regions(ty::ParamEnv::reveal_all(), substs);
+
+                    // It's possible that the method relies on where-clauses that
+                    // do not hold for this particular set of type parameters.
+                    // Note that this method could then never be called, so we
+                    // do not want to try and codegen it, in that case (see #23435).
+                    let predicates = tcx.predicates_of(def_id).instantiate_own(tcx, substs);
+                    if impossible_predicates(tcx, predicates.predicates) {
+                        debug!("vtable_entries: predicates do not hold");
+                        return VtblEntry::Vacant;
+                    }
+
+                    let instance = ty::Instance::resolve_for_vtable(
+                        tcx,
+                        ty::ParamEnv::reveal_all(),
+                        def_id,
+                        substs,
+                    )
+                    .expect("resolution failed during building vtable representation");
+                    VtblEntry::Method(instance)
+                });
+
+                entries.extend(own_entries);
+
+                if emit_vptr {
+                    entries.push(VtblEntry::TraitVPtr(trait_ref));
+                }
+            }
+        }
+
+        ControlFlow::Continue(())
+    };
+
+    let _ = prepare_vtable_segments(tcx, trait_ref, vtable_segment_callback);
+
+    if tcx.has_attr(trait_ref.def_id(), sym::rustc_dump_vtable) {
+        let sp = tcx.def_span(trait_ref.def_id());
+        dump_vtable_entries(tcx, sp, trait_ref, &entries);
+    }
+
+    tcx.arena.alloc_from_iter(entries.into_iter())
+}
+
+/// Find slot base for trait methods within vtable entries of another trait
+pub(super) fn vtable_trait_first_method_offset<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    key: (
+        ty::PolyTraitRef<'tcx>, // trait_to_be_found
+        ty::PolyTraitRef<'tcx>, // trait_owning_vtable
+    ),
+) -> usize {
+    let (trait_to_be_found, trait_owning_vtable) = key;
+
+    // #90177
+    let trait_to_be_found_erased = tcx.erase_regions(trait_to_be_found);
+
+    let vtable_segment_callback = {
+        let mut vtable_base = 0;
+
+        move |segment| {
+            match segment {
+                VtblSegment::MetadataDSA => {
+                    vtable_base += TyCtxt::COMMON_VTABLE_ENTRIES.len();
+                }
+                VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => {
+                    if tcx.erase_regions(trait_ref) == trait_to_be_found_erased {
+                        return ControlFlow::Break(vtable_base);
+                    }
+                    vtable_base += count_own_vtable_entries(tcx, trait_ref);
+                    if emit_vptr {
+                        vtable_base += 1;
+                    }
+                }
+            }
+            ControlFlow::Continue(())
+        }
+    };
+
+    if let Some(vtable_base) =
+        prepare_vtable_segments(tcx, trait_owning_vtable, vtable_segment_callback)
+    {
+        vtable_base
+    } else {
+        bug!("Failed to find info for expected trait in vtable");
+    }
+}
+
+/// Find slot offset for trait vptr within vtable entries of another trait
+pub(crate) fn vtable_trait_upcasting_coercion_new_vptr_slot<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    key: (
+        Ty<'tcx>, // trait object type whose trait owning vtable
+        Ty<'tcx>, // trait object for supertrait
+    ),
+) -> Option<usize> {
+    let (source, target) = key;
+    assert!(matches!(&source.kind(), &ty::Dynamic(..)) && !source.needs_infer());
+    assert!(matches!(&target.kind(), &ty::Dynamic(..)) && !target.needs_infer());
+
+    // this has been typecked-before, so diagnostics is not really needed.
+    let unsize_trait_did = tcx.require_lang_item(LangItem::Unsize, None);
+
+    let trait_ref = tcx.mk_trait_ref(unsize_trait_did, [source, target]);
+
+    match tcx.codegen_select_candidate((ty::ParamEnv::reveal_all(), ty::Binder::dummy(trait_ref))) {
+        Ok(ImplSource::TraitUpcasting(implsrc_traitcasting)) => {
+            implsrc_traitcasting.vtable_vptr_slot
+        }
+        otherwise => bug!("expected TraitUpcasting candidate, got {otherwise:?}"),
+    }
+}
+
+/// Given a trait `trait_ref`, returns the number of vtable entries
+/// that come from `trait_ref`, excluding its supertraits. Used in
+/// computing the vtable base for an upcast trait of a trait object.
+pub(crate) fn count_own_vtable_entries<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    trait_ref: ty::PolyTraitRef<'tcx>,
+) -> usize {
+    tcx.own_existential_vtable_entries(trait_ref.def_id()).len()
+}
+
+pub(super) fn provide(providers: &mut ty::query::Providers) {
+    *providers = ty::query::Providers {
+        own_existential_vtable_entries,
+        vtable_entries,
+        vtable_trait_upcasting_coercion_new_vptr_slot,
+        ..*providers
+    };
+}
diff --git a/compiler/rustc_trait_selection/src/traits/wf.rs b/compiler/rustc_trait_selection/src/traits/wf.rs
index fc0a9f690..681fb753f 100644
--- a/compiler/rustc_trait_selection/src/traits/wf.rs
+++ b/compiler/rustc_trait_selection/src/traits/wf.rs
@@ -4,7 +4,7 @@ use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_hir::lang_items::LangItem;
 use rustc_middle::ty::subst::{GenericArg, GenericArgKind, SubstsRef};
-use rustc_middle::ty::{self, ToPredicate, Ty, TyCtxt, TypeVisitable};
+use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitable};
 use rustc_span::Span;
 
 use std::iter;
@@ -121,14 +121,14 @@ pub fn predicate_obligations<'tcx>(
 
     // It's ok to skip the binder here because wf code is prepared for it
     match predicate.kind().skip_binder() {
-        ty::PredicateKind::Trait(t) => {
+        ty::PredicateKind::Clause(ty::Clause::Trait(t)) => {
             wf.compute_trait_pred(&t, Elaborate::None);
         }
-        ty::PredicateKind::RegionOutlives(..) => {}
-        ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(ty, _reg)) => {
+        ty::PredicateKind::Clause(ty::Clause::RegionOutlives(..)) => {}
+        ty::PredicateKind::Clause(ty::Clause::TypeOutlives(ty::OutlivesPredicate(ty, _reg))) => {
             wf.compute(ty.into());
         }
-        ty::PredicateKind::Projection(t) => {
+        ty::PredicateKind::Clause(ty::Clause::Projection(t)) => {
             wf.compute_projection(t.projection_ty);
             wf.compute(match t.term.unpack() {
                 ty::TermKind::Ty(ty) => ty.into(),
@@ -155,6 +155,7 @@ pub fn predicate_obligations<'tcx>(
             wf.compute(c1.into());
             wf.compute(c2.into());
         }
+        ty::PredicateKind::Ambiguous => {}
         ty::PredicateKind::TypeWellFormedFromEnv(..) => {
             bug!("TypeWellFormedFromEnv is only used for Chalk")
         }
@@ -227,7 +228,7 @@ fn extend_cause_with_original_assoc_item_obligation<'tcx>(
 
     // It is fine to skip the binder as we don't care about regions here.
     match pred.kind().skip_binder() {
-        ty::PredicateKind::Projection(proj) => {
+        ty::PredicateKind::Clause(ty::Clause::Projection(proj)) => {
             // The obligation comes not from the current `impl` nor the `trait` being implemented,
             // but rather from a "second order" obligation, where an associated type has a
             // projection coming from another associated type. See
@@ -244,7 +245,7 @@ fn extend_cause_with_original_assoc_item_obligation<'tcx>(
                 cause.span = impl_item_span;
             }
         }
-        ty::PredicateKind::Trait(pred) => {
+        ty::PredicateKind::Clause(ty::Clause::Trait(pred)) => {
             // An associated item obligation born out of the `trait` failed to be met. An example
             // can be seen in `ui/associated-types/point-at-type-on-obligation-failure-2.rs`.
             debug!("extended_cause_with_original_assoc_item_obligation trait proj {:?}", pred);
@@ -324,7 +325,7 @@ impl<'tcx> WfPredicates<'tcx> {
             extend_cause_with_original_assoc_item_obligation(
                 tcx, trait_ref, item, &mut cause, predicate,
             );
-            traits::Obligation::with_depth(cause, depth, param_env, predicate)
+            traits::Obligation::with_depth(tcx, cause, depth, param_env, predicate)
         };
 
         if let Elaborate::All = elaborate {
@@ -356,10 +357,11 @@ impl<'tcx> WfPredicates<'tcx> {
                         }
                     }
                     traits::Obligation::with_depth(
+                        tcx,
                         cause,
                         depth,
                         param_env,
-                        ty::Binder::dummy(ty::PredicateKind::WellFormed(arg)).to_predicate(tcx),
+                        ty::Binder::dummy(ty::PredicateKind::WellFormed(arg)),
                     )
                 }),
         );
@@ -407,10 +409,11 @@ impl<'tcx> WfPredicates<'tcx> {
                 .filter(|arg| !arg.has_escaping_bound_vars())
                 .map(|arg| {
                     traits::Obligation::with_depth(
+                        tcx,
                         cause.clone(),
                         depth,
                         param_env,
-                        ty::Binder::dummy(ty::PredicateKind::WellFormed(arg)).to_predicate(tcx),
+                        ty::Binder::dummy(ty::PredicateKind::WellFormed(arg)),
                     )
                 }),
         );
@@ -419,15 +422,13 @@ impl<'tcx> WfPredicates<'tcx> {
     fn require_sized(&mut self, subty: Ty<'tcx>, cause: traits::ObligationCauseCode<'tcx>) {
         if !subty.has_escaping_bound_vars() {
             let cause = self.cause(cause);
-            let trait_ref = ty::TraitRef {
-                def_id: self.tcx.require_lang_item(LangItem::Sized, None),
-                substs: self.tcx.mk_substs_trait(subty, &[]),
-            };
+            let trait_ref = self.tcx.at(cause.span).mk_trait_ref(LangItem::Sized, [subty]);
             self.out.push(traits::Obligation::with_depth(
+                self.tcx,
                 cause,
                 self.recursion_depth,
                 self.param_env,
-                ty::Binder::dummy(trait_ref).without_const().to_predicate(self.tcx),
+                ty::Binder::dummy(trait_ref).without_const(),
             ));
         }
     }
@@ -454,10 +455,10 @@ impl<'tcx> WfPredicates<'tcx> {
                             self.out.extend(obligations);
 
                             let predicate =
-                                ty::Binder::dummy(ty::PredicateKind::ConstEvaluatable(ct))
-                                    .to_predicate(self.tcx());
+                                ty::Binder::dummy(ty::PredicateKind::ConstEvaluatable(ct));
                             let cause = self.cause(traits::WellFormed(None));
                             self.out.push(traits::Obligation::with_depth(
+                                self.tcx(),
                                 cause,
                                 self.recursion_depth,
                                 self.param_env,
@@ -468,13 +469,33 @@ impl<'tcx> WfPredicates<'tcx> {
                             let cause = self.cause(traits::WellFormed(None));
 
                             self.out.push(traits::Obligation::with_depth(
+                                self.tcx(),
                                 cause,
                                 self.recursion_depth,
                                 self.param_env,
-                                ty::Binder::dummy(ty::PredicateKind::WellFormed(ct.into()))
-                                    .to_predicate(self.tcx()),
+                                ty::Binder::dummy(ty::PredicateKind::WellFormed(ct.into())),
                             ));
                         }
+                        ty::ConstKind::Expr(_) => {
+                            // FIXME(generic_const_exprs): this doesnt verify that given `Expr(N + 1)` the
+                            // trait bound `typeof(N): Add<typeof(1)>` holds. This is currently unnecessary
+                            // as `ConstKind::Expr` is only produced via normalization of `ConstKind::Unevaluated`
+                            // which means that the `DefId` would have been typeck'd elsewhere. However in
+                            // the future we may allow directly lowering to `ConstKind::Expr` in which case
+                            // we would not be proving bounds we should.
+
+                            let predicate =
+                                ty::Binder::dummy(ty::PredicateKind::ConstEvaluatable(ct));
+                            let cause = self.cause(traits::WellFormed(None));
+                            self.out.push(traits::Obligation::with_depth(
+                                self.tcx(),
+                                cause,
+                                self.recursion_depth,
+                                self.param_env,
+                                predicate,
+                            ));
+                        }
+
                         ty::ConstKind::Error(_)
                         | ty::ConstKind::Param(_)
                         | ty::ConstKind::Bound(..)
@@ -556,13 +577,13 @@ impl<'tcx> WfPredicates<'tcx> {
                     if !r.has_escaping_bound_vars() && !rty.has_escaping_bound_vars() {
                         let cause = self.cause(traits::ReferenceOutlivesReferent(ty));
                         self.out.push(traits::Obligation::with_depth(
+                            self.tcx(),
                             cause,
                             depth,
                             param_env,
-                            ty::Binder::dummy(ty::PredicateKind::TypeOutlives(
+                            ty::Binder::dummy(ty::PredicateKind::Clause(ty::Clause::TypeOutlives(
                                 ty::OutlivesPredicate(rty, r),
-                            ))
-                            .to_predicate(self.tcx()),
+                            ))),
                         ));
                     }
                 }
@@ -631,7 +652,7 @@ impl<'tcx> WfPredicates<'tcx> {
                     // All of the requirements on type parameters
                     // have already been checked for `impl Trait` in
                     // return position. We do need to check type-alias-impl-trait though.
-                    if ty::is_impl_trait_defn(self.tcx, did).is_none() {
+                    if self.tcx.is_type_alias_impl_trait(did) {
                         let obligations = self.nominal_obligations(did, substs);
                         self.out.extend(obligations);
                     }
@@ -656,11 +677,11 @@ impl<'tcx> WfPredicates<'tcx> {
                         let tcx = self.tcx();
                         self.out.extend(component_traits.map(|did| {
                             traits::Obligation::with_depth(
+                                tcx,
                                 cause.clone(),
                                 depth,
                                 param_env,
-                                ty::Binder::dummy(ty::PredicateKind::ObjectSafe(did))
-                                    .to_predicate(tcx),
+                                ty::Binder::dummy(ty::PredicateKind::ObjectSafe(did)),
                             )
                         }));
                     }
@@ -681,11 +702,11 @@ impl<'tcx> WfPredicates<'tcx> {
                 ty::Infer(_) => {
                     let cause = self.cause(traits::WellFormed(None));
                     self.out.push(traits::Obligation::with_depth(
+                        self.tcx(),
                         cause,
                         self.recursion_depth,
                         param_env,
-                        ty::Binder::dummy(ty::PredicateKind::WellFormed(ty.into()))
-                            .to_predicate(self.tcx()),
+                        ty::Binder::dummy(ty::PredicateKind::WellFormed(ty.into())),
                     ));
                 }
             }
@@ -724,7 +745,13 @@ impl<'tcx> WfPredicates<'tcx> {
                 if remap_constness {
                     pred = pred.without_const(self.tcx);
                 }
-                traits::Obligation::with_depth(cause, self.recursion_depth, self.param_env, pred)
+                traits::Obligation::with_depth(
+                    self.tcx,
+                    cause,
+                    self.recursion_depth,
+                    self.param_env,
+                    pred,
+                )
             })
             .filter(|pred| !pred.has_escaping_bound_vars())
             .collect()
@@ -749,7 +776,7 @@ impl<'tcx> WfPredicates<'tcx> {
     fn from_object_ty(
         &mut self,
         ty: Ty<'tcx>,
-        data: &'tcx ty::List<ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>>,
+        data: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>,
         region: ty::Region<'tcx>,
     ) {
         // Imagine a type like this:
@@ -794,10 +821,11 @@ impl<'tcx> WfPredicates<'tcx> {
                 let outlives =
                     ty::Binder::dummy(ty::OutlivesPredicate(explicit_bound, implicit_bound));
                 self.out.push(traits::Obligation::with_depth(
+                    self.tcx,
                     cause,
                     self.recursion_depth,
                     self.param_env,
-                    outlives.to_predicate(self.tcx),
+                    outlives,
                 ));
             }
         }
@@ -812,7 +840,7 @@ impl<'tcx> WfPredicates<'tcx> {
 /// `infer::required_region_bounds`, see that for more information.
 pub fn object_region_bounds<'tcx>(
     tcx: TyCtxt<'tcx>,
-    existential_predicates: &'tcx ty::List<ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>>,
+    existential_predicates: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>,
 ) -> Vec<ty::Region<'tcx>> {
     // Since we don't actually *know* the self type for an object,
     // this "open(err)" serves as a kind of dummy standin -- basically
@@ -858,18 +886,22 @@ pub(crate) fn required_region_bounds<'tcx>(
         .filter_map(|obligation| {
             debug!(?obligation);
             match obligation.predicate.kind().skip_binder() {
-                ty::PredicateKind::Projection(..)
-                | ty::PredicateKind::Trait(..)
+                ty::PredicateKind::Clause(ty::Clause::Projection(..))
+                | ty::PredicateKind::Clause(ty::Clause::Trait(..))
                 | ty::PredicateKind::Subtype(..)
                 | ty::PredicateKind::Coerce(..)
                 | ty::PredicateKind::WellFormed(..)
                 | ty::PredicateKind::ObjectSafe(..)
                 | ty::PredicateKind::ClosureKind(..)
-                | ty::PredicateKind::RegionOutlives(..)
+                | ty::PredicateKind::Clause(ty::Clause::RegionOutlives(..))
                 | ty::PredicateKind::ConstEvaluatable(..)
                 | ty::PredicateKind::ConstEquate(..)
+                | ty::PredicateKind::Ambiguous
                 | ty::PredicateKind::TypeWellFormedFromEnv(..) => None,
-                ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(ref t, ref r)) => {
+                ty::PredicateKind::Clause(ty::Clause::TypeOutlives(ty::OutlivesPredicate(
+                    ref t,
+                    ref r,
+                ))) => {
                     // Search for a bound of the form `erased_self_ty
                     // : 'a`, but be wary of something like `for<'a>
                     // erased_self_ty : 'a` (we interpret a
diff --git a/compiler/rustc_trait_selection/src/traits/codegen.rs b/compiler/rustc_traits/src/codegen.rs
index 8a62bf015..f8f74b732 100644
--- a/compiler/rustc_trait_selection/src/traits/codegen.rs
+++ b/compiler/rustc_traits/src/codegen.rs
@@ -3,15 +3,15 @@
 // seems likely that they should eventually be merged into more
 // general routines.
 
-use crate::infer::{DefiningAnchor, TyCtxtInferExt};
-use crate::traits::error_reporting::TypeErrCtxtExt;
-use crate::traits::{
-    ImplSource, Obligation, ObligationCause, SelectionContext, TraitEngine, TraitEngineExt,
-    Unimplemented,
-};
+use rustc_infer::infer::{DefiningAnchor, TyCtxtInferExt};
 use rustc_infer::traits::FulfillmentErrorCode;
 use rustc_middle::traits::CodegenObligationError;
 use rustc_middle::ty::{self, TyCtxt};
+use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt;
+use rustc_trait_selection::traits::{
+    ImplSource, Obligation, ObligationCause, SelectionContext, TraitEngine, TraitEngineExt,
+    Unimplemented,
+};
 
 /// Attempts to resolve an obligation to an `ImplSource`. The result is
 /// a shallow `ImplSource` resolution, meaning that we do not
@@ -39,8 +39,7 @@ pub fn codegen_select_candidate<'tcx>(
     let mut selcx = SelectionContext::new(&infcx);
 
     let obligation_cause = ObligationCause::dummy();
-    let obligation =
-        Obligation::new(obligation_cause, param_env, trait_ref.to_poly_trait_predicate());
+    let obligation = Obligation::new(tcx, obligation_cause, param_env, trait_ref);
 
     let selection = match selcx.select(&obligation) {
         Ok(Some(selection)) => selection,
@@ -71,7 +70,7 @@ pub fn codegen_select_candidate<'tcx>(
         // `rustc_ty_utils::resolve_associated_item` doesn't return `None` post-monomorphization.
         for err in errors {
             if let FulfillmentErrorCode::CodeCycle(cycle) = err.code {
-                infcx.err_ctxt().report_overflow_error_cycle(&cycle);
+                infcx.err_ctxt().report_overflow_obligation_cycle(&cycle);
             }
         }
         return Err(CodegenObligationError::FulfillmentError);