diff --git a/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs b/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
index 2f632f750b761..16c75b781dbec 100644
--- a/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
+++ b/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
@@ -23,8 +23,10 @@ use rustc_span::{BytePos, DUMMY_SP, Span};
 use rustc_trait_selection::error_reporting::InferCtxtErrorExt;
 use rustc_trait_selection::infer::InferCtxtExt;
 use rustc_trait_selection::regions::InferCtxtRegionExt;
+use rustc_trait_selection::solve::NextSolverError;
 use rustc_trait_selection::traits::{
-    self, FulfillmentError, ObligationCause, ObligationCauseCode, ObligationCtxt,
+    self, FromSolverError, FulfillmentError, ObligationCause, ObligationCauseCode, ObligationCtxt,
+    OldSolverError,
 };
 use tracing::{debug, instrument};
 
@@ -801,10 +803,7 @@ struct ImplTraitInTraitCollector<'a, 'tcx, E> {
     impl_m_id: LocalDefId,
 }
 
-impl<'a, 'tcx, E> ImplTraitInTraitCollector<'a, 'tcx, E>
-where
-    E: 'tcx,
-{
+impl<'a, 'tcx, E> ImplTraitInTraitCollector<'a, 'tcx, E> {
     fn new(
         ocx: &'a ObligationCtxt<'a, 'tcx, E>,
         span: Span,
@@ -817,7 +816,7 @@ where
 
 impl<'tcx, E> TypeFolder<TyCtxt<'tcx>> for ImplTraitInTraitCollector<'_, 'tcx, E>
 where
-    E: 'tcx,
+    E: FromSolverError<'tcx, NextSolverError<'tcx>> + FromSolverError<'tcx, OldSolverError<'tcx>>,
 {
     fn cx(&self) -> TyCtxt<'tcx> {
         self.ocx.infcx.tcx
diff --git a/compiler/rustc_hir_typeck/src/fallback.rs b/compiler/rustc_hir_typeck/src/fallback.rs
index 0e34a6120b609..e753100a5e1a9 100644
--- a/compiler/rustc_hir_typeck/src/fallback.rs
+++ b/compiler/rustc_hir_typeck/src/fallback.rs
@@ -15,7 +15,7 @@ use rustc_middle::ty::{self, FloatVid, Ty, TyCtxt, TypeSuperVisitable, TypeVisit
 use rustc_session::lint;
 use rustc_span::def_id::LocalDefId;
 use rustc_span::{DUMMY_SP, Span};
-use rustc_trait_selection::traits::{ObligationCause, ObligationCtxt};
+use rustc_trait_selection::traits::{ObligationCause, ObligationCtxt, TraitEngine};
 use tracing::debug;
 
 use crate::{FnCtxt, diagnostics};
diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs
index 9a1b1f8300957..7d11beb7722b0 100644
--- a/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs
+++ b/compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs
@@ -37,7 +37,7 @@ use rustc_span::def_id::LocalDefId;
 use rustc_span::hygiene::DesugaringKind;
 use rustc_trait_selection::error_reporting::infer::need_type_info::TypeAnnotationNeeded;
 use rustc_trait_selection::traits::{
-    self, NormalizeExt, ObligationCauseCode, StructurallyNormalizeExt,
+    self, NormalizeExt, ObligationCauseCode, StructurallyNormalizeExt, TraitEngine,
 };
 use tracing::{debug, instrument};
 
@@ -1499,7 +1499,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             // in a reentrant borrow, causing an ICE.
             let result = self.at(&self.misc(sp), self.param_env).structurally_normalize_const(
                 Unnormalized::new_wip(ct),
-                &mut **self.fulfillment_cx.borrow_mut(),
+                &mut *self.fulfillment_cx.borrow_mut(),
             );
             match result {
                 Ok(normalized_ct) => normalized_ct,
diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/inspect_obligations.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/inspect_obligations.rs
index cfaa60231379e..b7fac3e2b993c 100644
--- a/compiler/rustc_hir_typeck/src/fn_ctxt/inspect_obligations.rs
+++ b/compiler/rustc_hir_typeck/src/fn_ctxt/inspect_obligations.rs
@@ -9,6 +9,7 @@ use rustc_trait_selection::solve::Certainty;
 use rustc_trait_selection::solve::inspect::{
     InferCtxtProofTreeExt, InspectConfig, InspectGoal, ProofTreeVisitor,
 };
+use rustc_trait_selection::traits::TraitEngine;
 use tracing::{debug, instrument, trace};
 
 use crate::FnCtxt;
diff --git a/compiler/rustc_hir_typeck/src/lib.rs b/compiler/rustc_hir_typeck/src/lib.rs
index dce7f0bd67794..73f4daeaa869b 100644
--- a/compiler/rustc_hir_typeck/src/lib.rs
+++ b/compiler/rustc_hir_typeck/src/lib.rs
@@ -57,6 +57,7 @@ use rustc_middle::{bug, span_bug};
 use rustc_session::config;
 use rustc_span::Span;
 use rustc_span::def_id::LocalDefId;
+use rustc_trait_selection::traits::TraitEngine;
 use tracing::{debug, instrument};
 use typeck_root_ctxt::TypeckRootCtxt;
 
diff --git a/compiler/rustc_hir_typeck/src/typeck_root_ctxt.rs b/compiler/rustc_hir_typeck/src/typeck_root_ctxt.rs
index e4dcead1f7954..30e796b133f25 100644
--- a/compiler/rustc_hir_typeck/src/typeck_root_ctxt.rs
+++ b/compiler/rustc_hir_typeck/src/typeck_root_ctxt.rs
@@ -8,7 +8,7 @@ use rustc_middle::span_bug;
 use rustc_middle::ty::{self, Ty, TyCtxt, TyVid, TypeVisitableExt, TypingMode};
 use rustc_span::Span;
 use rustc_span::def_id::LocalDefIdMap;
-use rustc_trait_selection::traits::{self, FulfillmentError, TraitEngine, TraitEngineExt as _};
+use rustc_trait_selection::traits::{self, DualFulfillmentCtxt, FulfillmentError, TraitEngine};
 use tracing::instrument;
 
 use super::callee::DeferredCallResolution;
@@ -31,7 +31,7 @@ pub(crate) struct TypeckRootCtxt<'tcx> {
 
     pub(super) locals: RefCell<HirIdMap<Ty<'tcx>>>,
 
-    pub(super) fulfillment_cx: RefCell<Box<dyn TraitEngine<'tcx, FulfillmentError<'tcx>>>>,
+    pub(super) fulfillment_cx: RefCell<DualFulfillmentCtxt<'tcx, FulfillmentError<'tcx>>>,
 
     // Used to detect opaque types uses added after we've already checked them.
     //
@@ -85,7 +85,7 @@ impl<'tcx> TypeckRootCtxt<'tcx> {
             .in_hir_typeck()
             .build(TypingMode::typeck_for_body(tcx, def_id));
         let typeck_results = RefCell::new(ty::TypeckResults::new(hir_owner));
-        let fulfillment_cx = RefCell::new(<dyn TraitEngine<'_, _>>::new(&infcx));
+        let fulfillment_cx = RefCell::new(DualFulfillmentCtxt::new(&infcx));
 
         TypeckRootCtxt {
             infcx,
diff --git a/compiler/rustc_infer/src/traits/engine.rs b/compiler/rustc_infer/src/traits/engine.rs
index 38fc991fcfeb6..be93d7cc58877 100644
--- a/compiler/rustc_infer/src/traits/engine.rs
+++ b/compiler/rustc_infer/src/traits/engine.rs
@@ -33,7 +33,7 @@ impl<'tcx> ScrubbedTraitError<'tcx> {
     }
 }
 
-pub trait TraitEngine<'tcx, E: 'tcx>: 'tcx {
+pub trait TraitEngine<'tcx, E>: 'tcx {
     /// Requires that `ty` must implement the trait with `def_id` in
     /// the given environment. This trait must not have any type
     /// parameters (except for `Self`).
diff --git a/compiler/rustc_middle/src/ty/context/impl_interner.rs b/compiler/rustc_middle/src/ty/context/impl_interner.rs
index 3b1a64a7e80bb..609cbca4ba7ee 100644
--- a/compiler/rustc_middle/src/ty/context/impl_interner.rs
+++ b/compiler/rustc_middle/src/ty/context/impl_interner.rs
@@ -690,14 +690,17 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
         self.specializes((impl_def_id, victim_def_id))
     }
 
+    #[inline]
     fn impl_is_default(self, impl_def_id: DefId) -> bool {
         self.defaultness(impl_def_id).is_default()
     }
 
+    #[inline]
     fn impl_trait_ref(self, impl_def_id: DefId) -> ty::EarlyBinder<'tcx, ty::TraitRef<'tcx>> {
         self.impl_trait_ref(impl_def_id)
     }
 
+    #[inline]
     fn impl_polarity(self, impl_def_id: DefId) -> ty::ImplPolarity {
         self.impl_polarity(impl_def_id)
     }
diff --git a/compiler/rustc_trait_selection/src/solve/fulfill.rs b/compiler/rustc_trait_selection/src/solve/fulfill.rs
index 4c2c92ebc5072..6c3214fcc0bc0 100644
--- a/compiler/rustc_trait_selection/src/solve/fulfill.rs
+++ b/compiler/rustc_trait_selection/src/solve/fulfill.rs
@@ -37,7 +37,7 @@ type PendingObligations<'tcx> =
 ///
 /// It is also likely that we want to use slightly different datastructures
 /// here as this will have to deal with far more root goals than `evaluate_all`.
-pub struct FulfillmentCtxt<'tcx, E: 'tcx> {
+pub struct FulfillmentCtxt<'tcx, E> {
     obligations: ObligationStorage<'tcx>,
 
     /// The snapshot in which this context was created. Using the context
diff --git a/compiler/rustc_trait_selection/src/traits/engine.rs b/compiler/rustc_trait_selection/src/traits/engine.rs
index 1990ebd913eca..327576bfcae4a 100644
--- a/compiler/rustc_trait_selection/src/traits/engine.rs
+++ b/compiler/rustc_trait_selection/src/traits/engine.rs
@@ -10,12 +10,11 @@ use rustc_infer::infer::canonical::{
 };
 use rustc_infer::infer::{DefineOpaqueTypes, InferCtxt, InferOk, RegionResolutionError, TypeTrace};
 use rustc_infer::traits::PredicateObligations;
-use rustc_macros::extension;
 use rustc_middle::arena::ArenaAllocatable;
 use rustc_middle::traits::query::NoSolution;
 use rustc_middle::ty::error::TypeError;
 use rustc_middle::ty::relate::Relate;
-use rustc_middle::ty::{self, Ty, TyCtxt, TypeFoldable, Unnormalized, Upcast, Variance};
+use rustc_middle::ty::{self, Ty, TyCtxt, TyVid, TypeFoldable, Unnormalized, Upcast, Variance};
 
 use super::{FromSolverError, FulfillmentContext, ScrubbedTraitError, TraitEngine};
 use crate::error_reporting::InferCtxtErrorExt;
@@ -27,20 +26,95 @@ use crate::traits::{
     StructurallyNormalizeExt,
 };
 
-#[extension(pub trait TraitEngineExt<'tcx, E>)]
-impl<'tcx, E> dyn TraitEngine<'tcx, E>
+/// An enum that lets us switch between the old and new solvers.
+pub enum DualFulfillmentCtxt<'tcx, E> {
+    Old(FulfillmentContext<'tcx, E>),
+    Next(NextFulfillmentCtxt<'tcx, E>),
+}
+
+impl<'tcx, E> DualFulfillmentCtxt<'tcx, E>
 where
-    E: FromSolverError<'tcx, NextSolverError<'tcx>> + FromSolverError<'tcx, OldSolverError<'tcx>>,
+    E: FromSolverError<'tcx, OldSolverError<'tcx>>,
 {
-    fn new(infcx: &InferCtxt<'tcx>) -> Box<Self> {
+    #[inline]
+    pub fn new(infcx: &InferCtxt<'tcx>) -> Self {
         if infcx.next_trait_solver() {
-            Box::new(NextFulfillmentCtxt::new(infcx))
+            DualFulfillmentCtxt::Next(NextFulfillmentCtxt::new(infcx))
         } else {
             assert!(
                 !infcx.tcx.next_trait_solver_globally(),
                 "using old solver even though new solver is enabled globally"
             );
-            Box::new(FulfillmentContext::new(infcx))
+            DualFulfillmentCtxt::Old(FulfillmentContext::new(infcx))
+        }
+    }
+}
+
+impl<'tcx, E> TraitEngine<'tcx, E> for DualFulfillmentCtxt<'tcx, E>
+where
+    E: FromSolverError<'tcx, NextSolverError<'tcx>> + FromSolverError<'tcx, OldSolverError<'tcx>>,
+{
+    fn register_predicate_obligation(
+        &mut self,
+        infcx: &InferCtxt<'tcx>,
+        obligation: PredicateObligation<'tcx>,
+    ) {
+        match self {
+            DualFulfillmentCtxt::Old(cx) => cx.register_predicate_obligation(infcx, obligation),
+            DualFulfillmentCtxt::Next(cx) => cx.register_predicate_obligation(infcx, obligation),
+        }
+    }
+
+    fn try_evaluate_obligations(&mut self, infcx: &InferCtxt<'tcx>) -> Vec<E> {
+        match self {
+            DualFulfillmentCtxt::Old(cx) => cx.try_evaluate_obligations(infcx),
+            DualFulfillmentCtxt::Next(cx) => cx.try_evaluate_obligations(infcx),
+        }
+    }
+
+    fn collect_remaining_errors(&mut self, infcx: &InferCtxt<'tcx>) -> Vec<E> {
+        match self {
+            DualFulfillmentCtxt::Old(cx) => cx.collect_remaining_errors(infcx),
+            DualFulfillmentCtxt::Next(cx) => cx.collect_remaining_errors(infcx),
+        }
+    }
+
+    fn has_pending_obligations(&self) -> bool {
+        match self {
+            DualFulfillmentCtxt::Old(cx) => cx.has_pending_obligations(),
+            DualFulfillmentCtxt::Next(cx) => cx.has_pending_obligations(),
+        }
+    }
+
+    fn pending_obligations(&self) -> PredicateObligations<'tcx> {
+        match self {
+            DualFulfillmentCtxt::Old(cx) => cx.pending_obligations(),
+            DualFulfillmentCtxt::Next(cx) => cx.pending_obligations(),
+        }
+    }
+
+    fn pending_obligations_potentially_referencing_sub_root(
+        &self,
+        infcx: &InferCtxt<'tcx>,
+        sub_root: TyVid,
+    ) -> PredicateObligations<'tcx> {
+        match self {
+            DualFulfillmentCtxt::Old(cx) => {
+                cx.pending_obligations_potentially_referencing_sub_root(infcx, sub_root)
+            }
+            DualFulfillmentCtxt::Next(cx) => {
+                cx.pending_obligations_potentially_referencing_sub_root(infcx, sub_root)
+            }
+        }
+    }
+
+    fn drain_stalled_obligations_for_coroutines(
+        &mut self,
+        infcx: &InferCtxt<'tcx>,
+    ) -> PredicateObligations<'tcx> {
+        match self {
+            DualFulfillmentCtxt::Old(cx) => cx.drain_stalled_obligations_for_coroutines(infcx),
+            DualFulfillmentCtxt::Next(cx) => cx.drain_stalled_obligations_for_coroutines(infcx),
         }
     }
 }
@@ -49,24 +123,26 @@ where
 /// with obligations outside of hir or mir typeck.
 pub struct ObligationCtxt<'a, 'tcx, E = ScrubbedTraitError<'tcx>> {
     pub infcx: &'a InferCtxt<'tcx>,
-    engine: RefCell<Box<dyn TraitEngine<'tcx, E>>>,
+    engine: RefCell<DualFulfillmentCtxt<'tcx, E>>,
 }
 
 impl<'a, 'tcx> ObligationCtxt<'a, 'tcx, FulfillmentError<'tcx>> {
+    #[inline]
     pub fn new_with_diagnostics(infcx: &'a InferCtxt<'tcx>) -> Self {
-        Self { infcx, engine: RefCell::new(<dyn TraitEngine<'tcx, _>>::new(infcx)) }
+        Self { infcx, engine: RefCell::new(DualFulfillmentCtxt::new(infcx)) }
     }
 }
 
 impl<'a, 'tcx> ObligationCtxt<'a, 'tcx, ScrubbedTraitError<'tcx>> {
+    #[inline]
     pub fn new(infcx: &'a InferCtxt<'tcx>) -> Self {
-        Self { infcx, engine: RefCell::new(<dyn TraitEngine<'tcx, _>>::new(infcx)) }
+        Self { infcx, engine: RefCell::new(DualFulfillmentCtxt::new(infcx)) }
     }
 }
 
 impl<'a, 'tcx, E> ObligationCtxt<'a, 'tcx, E>
 where
-    E: 'tcx,
+    E: FromSolverError<'tcx, NextSolverError<'tcx>> + FromSolverError<'tcx, OldSolverError<'tcx>>,
 {
     pub fn register_obligation(&self, obligation: PredicateObligation<'tcx>) {
         self.engine.borrow_mut().register_predicate_obligation(self.infcx, obligation);
@@ -297,14 +373,14 @@ impl<'tcx> ObligationCtxt<'_, 'tcx, ScrubbedTraitError<'tcx>> {
         self.infcx.make_canonicalized_query_response(
             inference_vars,
             answer,
-            &mut **self.engine.borrow_mut(),
+            &mut *self.engine.borrow_mut(),
         )
     }
 }
 
 impl<'tcx, E> ObligationCtxt<'_, 'tcx, E>
 where
-    E: FromSolverError<'tcx, NextSolverError<'tcx>>,
+    E: FromSolverError<'tcx, NextSolverError<'tcx>> + FromSolverError<'tcx, OldSolverError<'tcx>>,
 {
     pub fn assumed_wf_types(
         &self,
@@ -331,7 +407,7 @@ where
             match self
                 .infcx
                 .at(&cause, param_env)
-                .deeply_normalize(Unnormalized::new_wip(ty), &mut **self.engine.borrow_mut())
+                .deeply_normalize(Unnormalized::new_wip(ty), &mut *self.engine.borrow_mut())
             {
                 // Insert well-formed types, ignoring duplicates.
                 Ok(normalized) => drop(implied_bounds.insert(normalized)),
@@ -348,7 +424,7 @@ where
         param_env: ty::ParamEnv<'tcx>,
         value: Unnormalized<'tcx, T>,
     ) -> Result<T, Vec<E>> {
-        self.infcx.at(cause, param_env).deeply_normalize(value, &mut **self.engine.borrow_mut())
+        self.infcx.at(cause, param_env).deeply_normalize(value, &mut *self.engine.borrow_mut())
     }
 
     pub fn structurally_normalize_ty(
@@ -359,7 +435,7 @@ where
     ) -> Result<Ty<'tcx>, Vec<E>> {
         self.infcx
             .at(cause, param_env)
-            .structurally_normalize_ty(value, &mut **self.engine.borrow_mut())
+            .structurally_normalize_ty(value, &mut *self.engine.borrow_mut())
     }
 
     pub fn structurally_normalize_const(
@@ -370,7 +446,7 @@ where
     ) -> Result<ty::Const<'tcx>, Vec<E>> {
         self.infcx
             .at(cause, param_env)
-            .structurally_normalize_const(value, &mut **self.engine.borrow_mut())
+            .structurally_normalize_const(value, &mut *self.engine.borrow_mut())
     }
 
     pub fn structurally_normalize_term(
@@ -381,6 +457,6 @@ where
     ) -> Result<ty::Term<'tcx>, Vec<E>> {
         self.infcx
             .at(cause, param_env)
-            .structurally_normalize_term(value, &mut **self.engine.borrow_mut())
+            .structurally_normalize_term(value, &mut *self.engine.borrow_mut())
     }
 }
diff --git a/compiler/rustc_trait_selection/src/traits/fulfill.rs b/compiler/rustc_trait_selection/src/traits/fulfill.rs
index 95f0c3dc9881d..3a14dc0aa4040 100644
--- a/compiler/rustc_trait_selection/src/traits/fulfill.rs
+++ b/compiler/rustc_trait_selection/src/traits/fulfill.rs
@@ -57,7 +57,7 @@ impl<'tcx> ForestObligation for PendingPredicateObligation<'tcx> {
 /// along. Once all type inference constraints have been generated, the
 /// method `evaluate_obligations_error_on_ambiguity` can be used to report any remaining
 /// ambiguous cases as errors.
-pub struct FulfillmentContext<'tcx, E: 'tcx> {
+pub struct FulfillmentContext<'tcx, E> {
     /// A list of all obligations that have been registered with this
     /// fulfillment context.
     predicates: ObligationForest<PendingPredicateObligation<'tcx>>,
diff --git a/compiler/rustc_trait_selection/src/traits/mod.rs b/compiler/rustc_trait_selection/src/traits/mod.rs
index d3262bd6a6f96..f1e2d031bc040 100644
--- a/compiler/rustc_trait_selection/src/traits/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/mod.rs
@@ -50,7 +50,7 @@ pub use self::dyn_compatibility::{
     DynCompatibilityViolation, dyn_compatibility_violations_for_assoc_item,
     hir_ty_lowering_dyn_compatibility_violations, is_vtable_safe_method,
 };
-pub use self::engine::{ObligationCtxt, TraitEngineExt};
+pub use self::engine::{DualFulfillmentCtxt, ObligationCtxt};
 pub use self::fulfill::{FulfillmentContext, OldSolverError, PendingPredicateObligation};
 pub use self::normalize::NormalizeExt;
 pub use self::project::{normalize_inherent_projection, normalize_projection_term};
diff --git a/compiler/rustc_trait_selection/src/traits/query/dropck_outlives.rs b/compiler/rustc_trait_selection/src/traits/query/dropck_outlives.rs
index a9ed6126ea752..dee141e283a08 100644
--- a/compiler/rustc_trait_selection/src/traits/query/dropck_outlives.rs
+++ b/compiler/rustc_trait_selection/src/traits/query/dropck_outlives.rs
@@ -6,6 +6,7 @@ use rustc_span::Span;
 use tracing::{debug, instrument};
 
 use crate::solve::NextSolverError;
+use crate::traits::fulfill::OldSolverError;
 use crate::traits::query::NoSolution;
 use crate::traits::query::normalize::QueryNormalizeExt;
 use crate::traits::{FromSolverError, Normalized, ObligationCause, ObligationCtxt};
@@ -106,7 +107,7 @@ pub fn compute_dropck_outlives_with_errors<'tcx, E>(
     span: Span,
 ) -> Result<DropckOutlivesResult<'tcx>, Vec<E>>
 where
-    E: FromSolverError<'tcx, NextSolverError<'tcx>>,
+    E: FromSolverError<'tcx, NextSolverError<'tcx>> + FromSolverError<'tcx, OldSolverError<'tcx>>,
 {
     let tcx = ocx.infcx.tcx;
     let ParamEnvAnd { param_env, value: DropckOutlives { dropped_ty } } = goal;
diff --git a/compiler/rustc_type_ir/src/fast_reject.rs b/compiler/rustc_type_ir/src/fast_reject.rs
index 9b50657b6b8b1..e91ef8333d99e 100644
--- a/compiler/rustc_type_ir/src/fast_reject.rs
+++ b/compiler/rustc_type_ir/src/fast_reject.rs
@@ -208,6 +208,7 @@ impl<I: Interner, const INSTANTIATE_LHS_WITH_INFER: bool, const INSTANTIATE_RHS_
     // and small enough to prevent hangs.
     const STARTING_DEPTH: usize = 8;
 
+    #[inline]
     pub fn args_may_unify(
         self,
         obligation_args: I::GenericArgs,
@@ -224,6 +225,7 @@ impl<I: Interner, const INSTANTIATE_LHS_WITH_INFER: bool, const INSTANTIATE_RHS_
         self.types_may_unify_inner(lhs, rhs, depth_limit)
     }
 
+    #[inline]
     fn args_may_unify_inner(
         self,
         obligation_args: I::GenericArgs,