diff --git a/compiler/rustc_borrowck/src/diagnostics/bound_region_errors.rs b/compiler/rustc_borrowck/src/diagnostics/bound_region_errors.rs
index 02071ed6b3666..dac6abe37f589 100644
--- a/compiler/rustc_borrowck/src/diagnostics/bound_region_errors.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/bound_region_errors.rs
@@ -5,14 +5,14 @@ use rustc_infer::infer::region_constraints::Constraint;
 use rustc_infer::infer::region_constraints::RegionConstraintData;
 use rustc_infer::infer::RegionVariableOrigin;
 use rustc_infer::infer::{InferCtxt, RegionResolutionError, SubregionOrigin, TyCtxtInferExt as _};
-use rustc_infer::traits::{Normalized, ObligationCause, TraitEngine, TraitEngineExt};
+use rustc_infer::traits::ObligationCause;
 use rustc_middle::ty::error::TypeError;
 use rustc_middle::ty::RegionVid;
 use rustc_middle::ty::UniverseIndex;
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeFoldable};
 use rustc_span::Span;
 use rustc_trait_selection::traits::query::type_op;
-use rustc_trait_selection::traits::{SelectionContext, TraitEngineExt as _};
+use rustc_trait_selection::traits::ObligationCtxt;
 use rustc_traits::{type_op_ascribe_user_type_with_span, type_op_prove_predicate_with_cause};
 
 use std::fmt;
@@ -240,9 +240,9 @@ impl<'tcx> TypeOpInfo<'tcx> for PredicateQuery<'tcx> {
     ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
         let (ref infcx, key, _) =
             mbcx.infcx.tcx.infer_ctxt().build_with_canonical(cause.span, &self.canonical_query);
-        let mut fulfill_cx = <dyn TraitEngine<'_>>::new(infcx.tcx);
-        type_op_prove_predicate_with_cause(infcx, &mut *fulfill_cx, key, cause);
-        try_extract_error_from_fulfill_cx(fulfill_cx, infcx, placeholder_region, error_region)
+        let ocx = ObligationCtxt::new(infcx);
+        type_op_prove_predicate_with_cause(&ocx, key, cause);
+        try_extract_error_from_fulfill_cx(&ocx, placeholder_region, error_region)
     }
 }
 
@@ -281,9 +281,7 @@ where
     ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
         let (ref infcx, key, _) =
             mbcx.infcx.tcx.infer_ctxt().build_with_canonical(cause.span, &self.canonical_query);
-        let mut fulfill_cx = <dyn TraitEngine<'_>>::new(infcx.tcx);
-
-        let mut selcx = SelectionContext::new(infcx);
+        let ocx = ObligationCtxt::new(infcx);
 
         // FIXME(lqd): Unify and de-duplicate the following with the actual
         // `rustc_traits::type_op::type_op_normalize` query to allow the span we need in the
@@ -292,11 +290,9 @@ where
         // to normalize the `nll/relate_tys/impl-fn-ignore-binder-via-bottom.rs` test. Check
         // after #85499 lands to see if its fixes have erased this difference.
         let (param_env, value) = key.into_parts();
-        let Normalized { value: _, obligations } =
-            rustc_trait_selection::traits::normalize(&mut selcx, param_env, cause, value.value);
-        fulfill_cx.register_predicate_obligations(infcx, obligations);
+        let _ = ocx.normalize(cause, param_env, value.value);
 
-        try_extract_error_from_fulfill_cx(fulfill_cx, infcx, placeholder_region, error_region)
+        try_extract_error_from_fulfill_cx(&ocx, placeholder_region, error_region)
     }
 }
 
@@ -329,9 +325,9 @@ impl<'tcx> TypeOpInfo<'tcx> for AscribeUserTypeQuery<'tcx> {
     ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
         let (ref infcx, key, _) =
             mbcx.infcx.tcx.infer_ctxt().build_with_canonical(cause.span, &self.canonical_query);
-        let mut fulfill_cx = <dyn TraitEngine<'_>>::new(infcx.tcx);
-        type_op_ascribe_user_type_with_span(infcx, &mut *fulfill_cx, key, Some(cause.span)).ok()?;
-        try_extract_error_from_fulfill_cx(fulfill_cx, infcx, placeholder_region, error_region)
+        let ocx = ObligationCtxt::new(infcx);
+        type_op_ascribe_user_type_with_span(&ocx, key, Some(cause.span)).ok()?;
+        try_extract_error_from_fulfill_cx(&ocx, placeholder_region, error_region)
     }
 }
 
@@ -372,25 +368,24 @@ impl<'tcx> TypeOpInfo<'tcx> for crate::type_check::InstantiateOpaqueType<'tcx> {
     }
 }
 
-#[instrument(skip(fulfill_cx, infcx), level = "debug")]
+#[instrument(skip(ocx), level = "debug")]
 fn try_extract_error_from_fulfill_cx<'tcx>(
-    mut fulfill_cx: Box<dyn TraitEngine<'tcx> + 'tcx>,
-    infcx: &InferCtxt<'tcx>,
+    ocx: &ObligationCtxt<'_, 'tcx>,
     placeholder_region: ty::Region<'tcx>,
     error_region: Option<ty::Region<'tcx>>,
 ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
     // We generally shouldn't have errors here because the query was
     // already run, but there's no point using `delay_span_bug`
     // when we're going to emit an error here anyway.
-    let _errors = fulfill_cx.select_all_or_error(infcx);
-    let region_constraints = infcx.with_region_constraints(|r| r.clone());
+    let _errors = ocx.select_all_or_error();
+    let region_constraints = ocx.infcx.with_region_constraints(|r| r.clone());
     try_extract_error_from_region_constraints(
-        infcx,
+        ocx.infcx,
         placeholder_region,
         error_region,
         &region_constraints,
-        |vid| infcx.region_var_origin(vid),
-        |vid| infcx.universe_of_region(infcx.tcx.mk_region(ty::ReVar(vid))),
+        |vid| ocx.infcx.region_var_origin(vid),
+        |vid| ocx.infcx.universe_of_region(ocx.infcx.tcx.mk_region(ty::ReVar(vid))),
     )
 }
 
diff --git a/compiler/rustc_hir_analysis/src/check/compare_method.rs b/compiler/rustc_hir_analysis/src/check/compare_method.rs
index 32f66b06f8358..aeaf7a6cfe1f1 100644
--- a/compiler/rustc_hir_analysis/src/check/compare_method.rs
+++ b/compiler/rustc_hir_analysis/src/check/compare_method.rs
@@ -290,10 +290,7 @@ fn compare_predicate_entailment<'tcx>(
     // type would be more appropriate. In other places we have a `Vec<Span>`
     // corresponding to their `Vec<Predicate>`, but we don't have that here.
     // Fixing this would improve the output of test `issue-83765.rs`.
-    let mut result = infcx
-        .at(&cause, param_env)
-        .sup(trait_fty, impl_fty)
-        .map(|infer_ok| ocx.register_infer_ok_obligations(infer_ok));
+    let mut result = ocx.sup(&cause, param_env, trait_fty, impl_fty);
 
     // HACK(RPITIT): #101614. When we are trying to infer the hidden types for
     // RPITITs, we need to equate the output tys instead of just subtyping. If
@@ -301,12 +298,8 @@ fn compare_predicate_entailment<'tcx>(
     // us to infer `_#1t = #'_#2r str`, where `'_#2r` is unconstrained, which gets
     // fixed up to `ReEmpty`, and which is certainly not what we want.
     if trait_fty.has_infer_types() {
-        result = result.and_then(|()| {
-            infcx
-                .at(&cause, param_env)
-                .eq(trait_sig.output(), impl_sig.output())
-                .map(|infer_ok| ocx.register_infer_ok_obligations(infer_ok))
-        });
+        result =
+            result.and_then(|()| ocx.eq(&cause, param_env, trait_sig.output(), impl_sig.output()));
     }
 
     if let Err(terr) = result {
@@ -1389,10 +1382,7 @@ pub(crate) fn raw_compare_const_impl<'tcx>(
 
     debug!("compare_const_impl: trait_ty={:?}", trait_ty);
 
-    let err = infcx
-        .at(&cause, param_env)
-        .sup(trait_ty, impl_ty)
-        .map(|ok| ocx.register_infer_ok_obligations(ok));
+    let err = ocx.sup(&cause, param_env, trait_ty, impl_ty);
 
     if let Err(terr) = err {
         debug!(
diff --git a/compiler/rustc_hir_analysis/src/check/wfcheck.rs b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
index 99d0beacfa0a1..0117bdd0ba81c 100644
--- a/compiler/rustc_hir_analysis/src/check/wfcheck.rs
+++ b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
@@ -1674,7 +1674,7 @@ fn receiver_is_valid<'tcx>(
 
     // `self: Self` is always valid.
     if can_eq_self(receiver_ty) {
-        if let Err(err) = wfcx.equate_types(&cause, wfcx.param_env, self_ty, receiver_ty) {
+        if let Err(err) = wfcx.eq(&cause, wfcx.param_env, self_ty, receiver_ty) {
             infcx.err_ctxt().report_mismatched_types(&cause, self_ty, receiver_ty, err).emit();
         }
         return true;
@@ -1704,9 +1704,7 @@ fn receiver_is_valid<'tcx>(
             if can_eq_self(potential_self_ty) {
                 wfcx.register_obligations(autoderef.into_obligations());
 
-                if let Err(err) =
-                    wfcx.equate_types(&cause, wfcx.param_env, self_ty, potential_self_ty)
-                {
+                if let Err(err) = wfcx.eq(&cause, wfcx.param_env, self_ty, potential_self_ty) {
                     infcx
                         .err_ctxt()
                         .report_mismatched_types(&cause, self_ty, potential_self_ty, err)
diff --git a/compiler/rustc_infer/src/infer/canonical/mod.rs b/compiler/rustc_infer/src/infer/canonical/mod.rs
index 06ca2534d5c3f..cbd6481f9cb81 100644
--- a/compiler/rustc_infer/src/infer/canonical/mod.rs
+++ b/compiler/rustc_infer/src/infer/canonical/mod.rs
@@ -43,7 +43,7 @@ impl<'tcx> InferCtxt<'tcx> {
     ///
     /// This is only meant to be invoked as part of constructing an
     /// inference context at the start of a query (see
-    /// `InferCtxtBuilder::enter_with_canonical`). It basically
+    /// `InferCtxtBuilder::build_with_canonical`). It basically
     /// brings the canonical value "into scope" within your new infcx.
     ///
     /// At the end of processing, the substitution S (once
diff --git a/compiler/rustc_trait_selection/src/infer.rs b/compiler/rustc_trait_selection/src/infer.rs
index a335f8e06bc94..96ac4e9c1292a 100644
--- a/compiler/rustc_trait_selection/src/infer.rs
+++ b/compiler/rustc_trait_selection/src/infer.rs
@@ -1,5 +1,5 @@
 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;
@@ -142,7 +142,7 @@ 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 +170,17 @@ 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/traits/engine.rs b/compiler/rustc_trait_selection/src/traits/engine.rs
index e0c8deec91aff..21516c93efb53 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 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;
@@ -105,12 +112,12 @@ impl<'a, 'tcx> ObligationCtxt<'a, 'tcx> {
         self.register_infer_ok_obligations(infer_ok)
     }
 
-    pub fn equate_types(
+    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: () }) => {
@@ -121,6 +128,22 @@ impl<'a, 'tcx> ObligationCtxt<'a, 'tcx> {
         }
     }
 
+    pub fn sup<T: ToTrace<'tcx>>(
+        &self,
+        cause: &ObligationCause<'tcx>,
+        param_env: ty::ParamEnv<'tcx>,
+        expected: T,
+        actual: T,
+    ) -> Result<(), TypeError<'tcx>> {
+        match self.infcx.at(cause, param_env).sup(expected, actual) {
+            Ok(InferOk { obligations, value: () }) => {
+                self.register_obligations(obligations);
+                Ok(())
+            }
+            Err(e) => Err(e),
+        }
+    }
+
     pub fn select_all_or_error(&self) -> Vec<FulfillmentError<'tcx>> {
         self.engine.borrow_mut().select_all_or_error(self.infcx)
     }
@@ -154,4 +177,20 @@ impl<'a, 'tcx> ObligationCtxt<'a, 'tcx> {
         }
         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_traits/src/implied_outlives_bounds.rs b/compiler/rustc_traits/src/implied_outlives_bounds.rs
index 7d36b9558d50b..82f6111f6f92e 100644
--- a/compiler/rustc_traits/src/implied_outlives_bounds.rs
+++ b/compiler/rustc_traits/src/implied_outlives_bounds.rs
@@ -28,9 +28,9 @@ fn implied_outlives_bounds<'tcx>(
     &'tcx Canonical<'tcx, canonical::QueryResponse<'tcx, Vec<OutlivesBound<'tcx>>>>,
     NoSolution,
 > {
-    tcx.infer_ctxt().enter_canonical_trait_query(&goal, |infcx, _fulfill_cx, key| {
+    tcx.infer_ctxt().enter_canonical_trait_query(&goal, |ocx, key| {
         let (param_env, ty) = key.into_parts();
-        compute_implied_outlives_bounds(&infcx, param_env, ty)
+        compute_implied_outlives_bounds(&ocx.infcx, param_env, ty)
     })
 }
 
diff --git a/compiler/rustc_traits/src/lib.rs b/compiler/rustc_traits/src/lib.rs
index 0da28737f69bc..0ffa92f1ad55d 100644
--- a/compiler/rustc_traits/src/lib.rs
+++ b/compiler/rustc_traits/src/lib.rs
@@ -3,6 +3,7 @@
 
 #![deny(rustc::untranslatable_diagnostic)]
 #![deny(rustc::diagnostic_outside_of_impl)]
+#![feature(let_chains)]
 #![recursion_limit = "256"]
 
 #[macro_use]
diff --git a/compiler/rustc_traits/src/normalize_projection_ty.rs b/compiler/rustc_traits/src/normalize_projection_ty.rs
index 98bb42c9afda1..e805eb4282119 100644
--- a/compiler/rustc_traits/src/normalize_projection_ty.rs
+++ b/compiler/rustc_traits/src/normalize_projection_ty.rs
@@ -1,6 +1,5 @@
 use rustc_infer::infer::canonical::{Canonical, QueryResponse};
 use rustc_infer::infer::TyCtxtInferExt;
-use rustc_infer::traits::TraitEngineExt as _;
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::{ParamEnvAnd, TyCtxt};
 use rustc_trait_selection::infer::InferCtxtBuilderExt;
@@ -23,8 +22,8 @@ fn normalize_projection_ty<'tcx>(
     tcx.sess.perf_stats.normalize_projection_ty.fetch_add(1, Ordering::Relaxed);
     tcx.infer_ctxt().enter_canonical_trait_query(
         &goal,
-        |infcx, fulfill_cx, ParamEnvAnd { param_env, value: goal }| {
-            let selcx = &mut SelectionContext::new(infcx);
+        |ocx, ParamEnvAnd { param_env, value: goal }| {
+            let selcx = &mut SelectionContext::new(ocx.infcx);
             let cause = ObligationCause::dummy();
             let mut obligations = vec![];
             let answer = traits::normalize_projection_type(
@@ -35,7 +34,7 @@ fn normalize_projection_ty<'tcx>(
                 0,
                 &mut obligations,
             );
-            fulfill_cx.register_predicate_obligations(infcx, obligations);
+            ocx.register_obligations(obligations);
             // FIXME(associated_const_equality): All users of normalize_projection_ty expected
             // a type, but there is the possibility it could've been a const now. Maybe change
             // it to a Term later?
diff --git a/compiler/rustc_traits/src/type_op.rs b/compiler/rustc_traits/src/type_op.rs
index bca7458ed332b..98cb3f21555ac 100644
--- a/compiler/rustc_traits/src/type_op.rs
+++ b/compiler/rustc_traits/src/type_op.rs
@@ -2,17 +2,14 @@ use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_infer::infer::at::ToTrace;
 use rustc_infer::infer::canonical::{Canonical, QueryResponse};
-use rustc_infer::infer::{DefiningAnchor, InferCtxt, TyCtxtInferExt};
-use rustc_infer::traits::{ObligationCauseCode, TraitEngineExt as _};
+use rustc_infer::infer::{DefiningAnchor, TyCtxtInferExt};
+use rustc_infer::traits::ObligationCauseCode;
 use rustc_middle::ty::query::Providers;
-use rustc_middle::ty::{
-    self, EarlyBinder, FnSig, Lift, PolyFnSig, Ty, TyCtxt, TypeFoldable, Variance,
-};
-use rustc_middle::ty::{GenericArg, UserSelfTy, UserSubsts};
-use rustc_middle::ty::{ParamEnv, ParamEnvAnd, Predicate, ToPredicate};
+use rustc_middle::ty::{self, FnSig, Lift, PolyFnSig, Ty, TyCtxt, TypeFoldable};
+use rustc_middle::ty::{ParamEnvAnd, Predicate, ToPredicate};
+use rustc_middle::ty::{UserSelfTy, UserSubsts};
 use rustc_span::{Span, DUMMY_SP};
 use rustc_trait_selection::infer::InferCtxtBuilderExt;
-use rustc_trait_selection::infer::InferCtxtExt;
 use rustc_trait_selection::traits::query::normalize::AtExt;
 use rustc_trait_selection::traits::query::type_op::ascribe_user_type::AscribeUserType;
 use rustc_trait_selection::traits::query::type_op::eq::Eq;
@@ -20,7 +17,7 @@ use rustc_trait_selection::traits::query::type_op::normalize::Normalize;
 use rustc_trait_selection::traits::query::type_op::prove_predicate::ProvePredicate;
 use rustc_trait_selection::traits::query::type_op::subtype::Subtype;
 use rustc_trait_selection::traits::query::{Fallible, NoSolution};
-use rustc_trait_selection::traits::{Normalized, Obligation, ObligationCause, TraitEngine};
+use rustc_trait_selection::traits::{Normalized, Obligation, ObligationCause, ObligationCtxt};
 use std::fmt;
 use std::iter::zip;
 
@@ -42,17 +39,16 @@ fn type_op_ascribe_user_type<'tcx>(
     tcx: TyCtxt<'tcx>,
     canonicalized: Canonical<'tcx, ParamEnvAnd<'tcx, AscribeUserType<'tcx>>>,
 ) -> Result<&'tcx Canonical<'tcx, QueryResponse<'tcx, ()>>, NoSolution> {
-    tcx.infer_ctxt().enter_canonical_trait_query(&canonicalized, |infcx, fulfill_cx, key| {
-        type_op_ascribe_user_type_with_span(infcx, fulfill_cx, key, None)
+    tcx.infer_ctxt().enter_canonical_trait_query(&canonicalized, |ocx, key| {
+        type_op_ascribe_user_type_with_span(ocx, key, None)
     })
 }
 
 /// The core of the `type_op_ascribe_user_type` query: for diagnostics purposes in NLL HRTB errors,
 /// this query can be re-run to better track the span of the obligation cause, and improve the error
 /// message. Do not call directly unless you're in that very specific context.
-pub fn type_op_ascribe_user_type_with_span<'a, 'tcx: 'a>(
-    infcx: &'a InferCtxt<'tcx>,
-    fulfill_cx: &'a mut dyn TraitEngine<'tcx>,
+pub fn type_op_ascribe_user_type_with_span<'tcx>(
+    ocx: &ObligationCtxt<'_, 'tcx>,
     key: ParamEnvAnd<'tcx, AscribeUserType<'tcx>>,
     span: Option<Span>,
 ) -> Result<(), NoSolution> {
@@ -61,68 +57,50 @@ pub fn type_op_ascribe_user_type_with_span<'a, 'tcx: 'a>(
         "type_op_ascribe_user_type: mir_ty={:?} def_id={:?} user_substs={:?}",
         mir_ty, def_id, user_substs
     );
-
-    let mut cx = AscribeUserTypeCx { infcx, param_env, span: span.unwrap_or(DUMMY_SP), fulfill_cx };
+    let cx = AscribeUserTypeCx { ocx, param_env, span: span.unwrap_or(DUMMY_SP) };
     cx.relate_mir_and_user_ty(mir_ty, def_id, user_substs)?;
     Ok(())
 }
 
 struct AscribeUserTypeCx<'me, 'tcx> {
-    infcx: &'me InferCtxt<'tcx>,
-    param_env: ParamEnv<'tcx>,
+    ocx: &'me ObligationCtxt<'me, 'tcx>,
+    param_env: ty::ParamEnv<'tcx>,
     span: Span,
-    fulfill_cx: &'me mut dyn TraitEngine<'tcx>,
 }
 
 impl<'me, 'tcx> AscribeUserTypeCx<'me, 'tcx> {
-    fn normalize<T>(&mut self, value: T) -> T
+    fn normalize<T>(&self, value: T) -> T
     where
         T: TypeFoldable<'tcx>,
     {
         self.normalize_with_cause(value, ObligationCause::misc(self.span, hir::CRATE_HIR_ID))
     }
 
-    fn normalize_with_cause<T>(&mut self, value: T, cause: ObligationCause<'tcx>) -> T
+    fn normalize_with_cause<T>(&self, value: T, cause: ObligationCause<'tcx>) -> T
     where
         T: TypeFoldable<'tcx>,
     {
-        self.infcx
-            .partially_normalize_associated_types_in(cause, self.param_env, value)
-            .into_value_registering_obligations(self.infcx, self.fulfill_cx)
+        self.ocx.normalize(cause, self.param_env, value)
     }
 
-    fn relate<T>(&mut self, a: T, variance: Variance, b: T) -> Result<(), NoSolution>
+    fn eq<T>(&self, a: T, b: T) -> Result<(), NoSolution>
     where
         T: ToTrace<'tcx>,
     {
-        self.infcx
-            .at(&ObligationCause::dummy_with_span(self.span), self.param_env)
-            .relate(a, variance, b)?
-            .into_value_registering_obligations(self.infcx, self.fulfill_cx);
-        Ok(())
+        Ok(self.ocx.eq(&ObligationCause::dummy_with_span(self.span), self.param_env, a, b)?)
     }
 
-    fn prove_predicate(&mut self, predicate: Predicate<'tcx>, cause: ObligationCause<'tcx>) {
-        self.fulfill_cx.register_predicate_obligation(
-            self.infcx,
-            Obligation::new(cause, self.param_env, predicate),
-        );
+    fn prove_predicate(&self, predicate: Predicate<'tcx>, cause: ObligationCause<'tcx>) {
+        self.ocx.register_obligation(Obligation::new(cause, self.param_env, predicate));
     }
 
     fn tcx(&self) -> TyCtxt<'tcx> {
-        self.infcx.tcx
-    }
-
-    fn subst<T>(&self, value: T, substs: &[GenericArg<'tcx>]) -> T
-    where
-        T: TypeFoldable<'tcx>,
-    {
-        EarlyBinder(value).subst(self.tcx(), substs)
+        self.ocx.infcx.tcx
     }
 
     #[instrument(level = "debug", skip(self))]
     fn relate_mir_and_user_ty(
-        &mut self,
+        &self,
         mir_ty: Ty<'tcx>,
         def_id: DefId,
         user_substs: UserSubsts<'tcx>,
@@ -130,20 +108,18 @@ impl<'me, 'tcx> AscribeUserTypeCx<'me, 'tcx> {
         let UserSubsts { user_self_ty, substs } = user_substs;
         let tcx = self.tcx();
 
-        let ty = tcx.type_of(def_id);
-        let ty = self.subst(ty, substs);
+        let ty = tcx.bound_type_of(def_id).subst(tcx, substs);
         let ty = self.normalize(ty);
         debug!("relate_type_and_user_type: ty of def-id is {:?}", ty);
 
-        self.relate(mir_ty, Variance::Invariant, ty)?;
+        self.eq(mir_ty, ty)?;
 
         // Prove the predicates coming along with `def_id`.
         //
         // Also, normalize the `instantiated_predicates`
         // because otherwise we wind up with duplicate "type
         // outlives" error messages.
-        let instantiated_predicates =
-            self.tcx().predicates_of(def_id).instantiate(self.tcx(), substs);
+        let instantiated_predicates = tcx.predicates_of(def_id).instantiate(tcx, substs);
 
         let cause = ObligationCause::dummy_with_span(self.span);
 
@@ -163,15 +139,14 @@ impl<'me, 'tcx> AscribeUserTypeCx<'me, 'tcx> {
         }
 
         if let Some(UserSelfTy { impl_def_id, self_ty }) = user_self_ty {
-            let impl_self_ty = self.tcx().type_of(impl_def_id);
-            let impl_self_ty = self.subst(impl_self_ty, &substs);
+            let impl_self_ty = tcx.bound_type_of(impl_def_id).subst(tcx, substs);
             let impl_self_ty = self.normalize(impl_self_ty);
 
-            self.relate(self_ty, Variance::Invariant, impl_self_ty)?;
+            self.eq(self_ty, impl_self_ty)?;
 
             self.prove_predicate(
                 ty::Binder::dummy(ty::PredicateKind::WellFormed(impl_self_ty.into()))
-                    .to_predicate(self.tcx()),
+                    .to_predicate(tcx),
                 cause.clone(),
             );
         }
@@ -188,7 +163,7 @@ impl<'me, 'tcx> AscribeUserTypeCx<'me, 'tcx> {
         // type were ill-formed but did not appear in `ty`,
         // which...could happen with normalization...
         self.prove_predicate(
-            ty::Binder::dummy(ty::PredicateKind::WellFormed(ty.into())).to_predicate(self.tcx()),
+            ty::Binder::dummy(ty::PredicateKind::WellFormed(ty.into())).to_predicate(tcx),
             cause,
         );
         Ok(())
@@ -199,19 +174,14 @@ fn type_op_eq<'tcx>(
     tcx: TyCtxt<'tcx>,
     canonicalized: Canonical<'tcx, ParamEnvAnd<'tcx, Eq<'tcx>>>,
 ) -> Result<&'tcx Canonical<'tcx, QueryResponse<'tcx, ()>>, NoSolution> {
-    tcx.infer_ctxt().enter_canonical_trait_query(&canonicalized, |infcx, fulfill_cx, key| {
+    tcx.infer_ctxt().enter_canonical_trait_query(&canonicalized, |ocx, key| {
         let (param_env, Eq { a, b }) = key.into_parts();
-        infcx
-            .at(&ObligationCause::dummy(), param_env)
-            .eq(a, b)?
-            .into_value_registering_obligations(infcx, fulfill_cx);
-        Ok(())
+        Ok(ocx.eq(&ObligationCause::dummy(), param_env, a, b)?)
     })
 }
 
 fn type_op_normalize<'tcx, T>(
-    infcx: &InferCtxt<'tcx>,
-    fulfill_cx: &mut dyn TraitEngine<'tcx>,
+    ocx: &ObligationCtxt<'_, 'tcx>,
     key: ParamEnvAnd<'tcx, Normalize<T>>,
 ) -> Fallible<T>
 where
@@ -219,8 +189,8 @@ where
 {
     let (param_env, Normalize { value }) = key.into_parts();
     let Normalized { value, obligations } =
-        infcx.at(&ObligationCause::dummy(), param_env).normalize(value)?;
-    fulfill_cx.register_predicate_obligations(infcx, obligations);
+        ocx.infcx.at(&ObligationCause::dummy(), param_env).normalize(value)?;
+    ocx.register_obligations(obligations);
     Ok(value)
 }
 
@@ -256,13 +226,9 @@ fn type_op_subtype<'tcx>(
     tcx: TyCtxt<'tcx>,
     canonicalized: Canonical<'tcx, ParamEnvAnd<'tcx, Subtype<'tcx>>>,
 ) -> Result<&'tcx Canonical<'tcx, QueryResponse<'tcx, ()>>, NoSolution> {
-    tcx.infer_ctxt().enter_canonical_trait_query(&canonicalized, |infcx, fulfill_cx, key| {
+    tcx.infer_ctxt().enter_canonical_trait_query(&canonicalized, |ocx, key| {
         let (param_env, Subtype { sub, sup }) = key.into_parts();
-        infcx
-            .at(&ObligationCause::dummy(), param_env)
-            .sup(sup, sub)?
-            .into_value_registering_obligations(infcx, fulfill_cx);
-        Ok(())
+        Ok(ocx.sup(&ObligationCause::dummy(), param_env, sup, sub)?)
     })
 }
 
@@ -274,8 +240,8 @@ fn type_op_prove_predicate<'tcx>(
     // impl-trait/issue-99642.rs
     tcx.infer_ctxt().with_opaque_type_inference(DefiningAnchor::Bubble).enter_canonical_trait_query(
         &canonicalized,
-        |infcx, fulfill_cx, key| {
-            type_op_prove_predicate_with_cause(infcx, fulfill_cx, key, ObligationCause::dummy());
+        |ocx, key| {
+            type_op_prove_predicate_with_cause(ocx, key, ObligationCause::dummy());
             Ok(())
         },
     )
@@ -284,12 +250,11 @@ fn type_op_prove_predicate<'tcx>(
 /// The core of the `type_op_prove_predicate` query: for diagnostics purposes in NLL HRTB errors,
 /// this query can be re-run to better track the span of the obligation cause, and improve the error
 /// message. Do not call directly unless you're in that very specific context.
-pub fn type_op_prove_predicate_with_cause<'a, 'tcx: 'a>(
-    infcx: &'a InferCtxt<'tcx>,
-    fulfill_cx: &'a mut dyn TraitEngine<'tcx>,
+pub fn type_op_prove_predicate_with_cause<'tcx>(
+    ocx: &ObligationCtxt<'_, 'tcx>,
     key: ParamEnvAnd<'tcx, ProvePredicate<'tcx>>,
     cause: ObligationCause<'tcx>,
 ) {
     let (param_env, ProvePredicate { predicate }) = key.into_parts();
-    fulfill_cx.register_predicate_obligation(infcx, Obligation::new(cause, param_env, predicate));
+    ocx.register_obligation(Obligation::new(cause, param_env, predicate));
 }