Merging upstream version 1.67.1+dfsg1.

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

11 files changed, 398 insertions, 382 deletions

diff --git a/compiler/rustc_traits/Cargo.toml b/compiler/rustc_traits/Cargo.toml
index 951554c77..a432498ab 100644
--- a/compiler/rustc_traits/Cargo.toml
+++ b/compiler/rustc_traits/Cargo.toml
@@ -12,9 +12,10 @@ rustc_hir = { path = "../rustc_hir" }
 rustc_index = { path = "../rustc_index" }
 rustc_ast = { path = "../rustc_ast" }
 rustc_span = { path = "../rustc_span" }
-chalk-ir = "0.80.0"
-chalk-engine = "0.80.0"
-chalk-solve = "0.80.0"
+rustc_target = { path = "../rustc_target" }
+chalk-ir = "0.87.0"
+chalk-engine = "0.87.0"
+chalk-solve = "0.87.0"
 smallvec = { version = "1.8.1", features = ["union", "may_dangle"] }
 rustc_infer = { path = "../rustc_infer" }
 rustc_trait_selection = { path = "../rustc_trait_selection" }
diff --git a/compiler/rustc_traits/src/chalk/db.rs b/compiler/rustc_traits/src/chalk/db.rs
index 0de28b826..344c8b93c 100644
--- a/compiler/rustc_traits/src/chalk/db.rs
+++ b/compiler/rustc_traits/src/chalk/db.rs
@@ -9,9 +9,9 @@
 use rustc_middle::traits::ChalkRustInterner as RustInterner;
 use rustc_middle::ty::{self, AssocKind, EarlyBinder, Ty, TyCtxt, TypeFoldable, TypeSuperFoldable};
 use rustc_middle::ty::{InternalSubsts, SubstsRef};
+use rustc_target::abi::{Integer, IntegerType};
 
 use rustc_ast::ast;
-use rustc_attr as attr;
 
 use rustc_hir::def_id::DefId;
 
@@ -142,6 +142,8 @@ impl<'tcx> chalk_solve::RustIrDatabase<RustInterner<'tcx>> for RustIrDatabase<'t
             Some(CoerceUnsized)
         } else if lang_items.dispatch_from_dyn_trait() == Some(def_id) {
             Some(DispatchFromDyn)
+        } else if lang_items.tuple_trait() == Some(def_id) {
+            Some(Tuple)
         } else {
             None
         };
@@ -216,21 +218,21 @@ impl<'tcx> chalk_solve::RustIrDatabase<RustInterner<'tcx>> for RustIrDatabase<'t
             c: adt_def.repr().c(),
             packed: adt_def.repr().packed(),
             int: adt_def.repr().int.map(|i| match i {
-                attr::IntType::SignedInt(ty) => match ty {
-                    ast::IntTy::Isize => int(chalk_ir::IntTy::Isize),
-                    ast::IntTy::I8 => int(chalk_ir::IntTy::I8),
-                    ast::IntTy::I16 => int(chalk_ir::IntTy::I16),
-                    ast::IntTy::I32 => int(chalk_ir::IntTy::I32),
-                    ast::IntTy::I64 => int(chalk_ir::IntTy::I64),
-                    ast::IntTy::I128 => int(chalk_ir::IntTy::I128),
+                IntegerType::Pointer(true) => int(chalk_ir::IntTy::Isize),
+                IntegerType::Pointer(false) => uint(chalk_ir::UintTy::Usize),
+                IntegerType::Fixed(i, true) => match i {
+                    Integer::I8 => int(chalk_ir::IntTy::I8),
+                    Integer::I16 => int(chalk_ir::IntTy::I16),
+                    Integer::I32 => int(chalk_ir::IntTy::I32),
+                    Integer::I64 => int(chalk_ir::IntTy::I64),
+                    Integer::I128 => int(chalk_ir::IntTy::I128),
                 },
-                attr::IntType::UnsignedInt(ty) => match ty {
-                    ast::UintTy::Usize => uint(chalk_ir::UintTy::Usize),
-                    ast::UintTy::U8 => uint(chalk_ir::UintTy::U8),
-                    ast::UintTy::U16 => uint(chalk_ir::UintTy::U16),
-                    ast::UintTy::U32 => uint(chalk_ir::UintTy::U32),
-                    ast::UintTy::U64 => uint(chalk_ir::UintTy::U64),
-                    ast::UintTy::U128 => uint(chalk_ir::UintTy::U128),
+                IntegerType::Fixed(i, false) => match i {
+                    Integer::I8 => uint(chalk_ir::UintTy::U8),
+                    Integer::I16 => uint(chalk_ir::UintTy::U16),
+                    Integer::I32 => uint(chalk_ir::UintTy::U32),
+                    Integer::I64 => uint(chalk_ir::UintTy::U64),
+                    Integer::I128 => uint(chalk_ir::UintTy::U128),
                 },
             }),
         })
@@ -570,6 +572,7 @@ impl<'tcx> chalk_solve::RustIrDatabase<RustInterner<'tcx>> for RustIrDatabase<'t
             CoerceUnsized => lang_items.coerce_unsized_trait(),
             DiscriminantKind => lang_items.discriminant_kind_trait(),
             DispatchFromDyn => lang_items.dispatch_from_dyn_trait(),
+            Tuple => lang_items.tuple_trait(),
         };
         def_id.map(chalk_ir::TraitId)
     }
@@ -728,16 +731,16 @@ fn bound_vars_for_item<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> SubstsRef<'tcx
         ty::GenericParamDefKind::Lifetime => {
             let br = ty::BoundRegion {
                 var: ty::BoundVar::from_usize(substs.len()),
-                kind: ty::BrAnon(substs.len() as u32),
+                kind: ty::BrAnon(substs.len() as u32, None),
             };
             tcx.mk_region(ty::ReLateBound(ty::INNERMOST, br)).into()
         }
 
         ty::GenericParamDefKind::Const { .. } => tcx
-            .mk_const(ty::ConstS {
-                kind: ty::ConstKind::Bound(ty::INNERMOST, ty::BoundVar::from(param.index)),
-                ty: tcx.type_of(param.def_id),
-            })
+            .mk_const(
+                ty::ConstKind::Bound(ty::INNERMOST, ty::BoundVar::from(param.index)),
+                tcx.type_of(param.def_id),
+            )
             .into(),
     })
 }
diff --git a/compiler/rustc_traits/src/chalk/lowering.rs b/compiler/rustc_traits/src/chalk/lowering.rs
index 45d5ea93d..c4ab86e9e 100644
--- a/compiler/rustc_traits/src/chalk/lowering.rs
+++ b/compiler/rustc_traits/src/chalk/lowering.rs
@@ -89,24 +89,32 @@ impl<'tcx> LowerInto<'tcx, chalk_ir::InEnvironment<chalk_ir::Goal<RustInterner<'
                 ty::PredicateKind::TypeWellFormedFromEnv(ty) => {
                     chalk_ir::DomainGoal::FromEnv(chalk_ir::FromEnv::Ty(ty.lower_into(interner)))
                 }
-                ty::PredicateKind::Trait(predicate) => chalk_ir::DomainGoal::FromEnv(
-                    chalk_ir::FromEnv::Trait(predicate.trait_ref.lower_into(interner)),
-                ),
-                ty::PredicateKind::RegionOutlives(predicate) => chalk_ir::DomainGoal::Holds(
-                    chalk_ir::WhereClause::LifetimeOutlives(chalk_ir::LifetimeOutlives {
-                        a: predicate.0.lower_into(interner),
-                        b: predicate.1.lower_into(interner),
-                    }),
-                ),
-                ty::PredicateKind::TypeOutlives(predicate) => chalk_ir::DomainGoal::Holds(
-                    chalk_ir::WhereClause::TypeOutlives(chalk_ir::TypeOutlives {
-                        ty: predicate.0.lower_into(interner),
-                        lifetime: predicate.1.lower_into(interner),
-                    }),
-                ),
-                ty::PredicateKind::Projection(predicate) => chalk_ir::DomainGoal::Holds(
-                    chalk_ir::WhereClause::AliasEq(predicate.lower_into(interner)),
-                ),
+                ty::PredicateKind::Clause(ty::Clause::Trait(predicate)) => {
+                    chalk_ir::DomainGoal::FromEnv(chalk_ir::FromEnv::Trait(
+                        predicate.trait_ref.lower_into(interner),
+                    ))
+                }
+                ty::PredicateKind::Clause(ty::Clause::RegionOutlives(predicate)) => {
+                    chalk_ir::DomainGoal::Holds(chalk_ir::WhereClause::LifetimeOutlives(
+                        chalk_ir::LifetimeOutlives {
+                            a: predicate.0.lower_into(interner),
+                            b: predicate.1.lower_into(interner),
+                        },
+                    ))
+                }
+                ty::PredicateKind::Clause(ty::Clause::TypeOutlives(predicate)) => {
+                    chalk_ir::DomainGoal::Holds(chalk_ir::WhereClause::TypeOutlives(
+                        chalk_ir::TypeOutlives {
+                            ty: predicate.0.lower_into(interner),
+                            lifetime: predicate.1.lower_into(interner),
+                        },
+                    ))
+                }
+                ty::PredicateKind::Clause(ty::Clause::Projection(predicate)) => {
+                    chalk_ir::DomainGoal::Holds(chalk_ir::WhereClause::AliasEq(
+                        predicate.lower_into(interner),
+                    ))
+                }
                 ty::PredicateKind::WellFormed(arg) => match arg.unpack() {
                     ty::GenericArgKind::Type(ty) => chalk_ir::DomainGoal::WellFormed(
                         chalk_ir::WellFormed::Ty(ty.lower_into(interner)),
@@ -121,6 +129,7 @@ impl<'tcx> LowerInto<'tcx, chalk_ir::InEnvironment<chalk_ir::Goal<RustInterner<'
                 | ty::PredicateKind::Subtype(..)
                 | ty::PredicateKind::Coerce(..)
                 | ty::PredicateKind::ConstEvaluatable(..)
+                | ty::PredicateKind::Ambiguous
                 | ty::PredicateKind::ConstEquate(..) => bug!("unexpected predicate {}", predicate),
             };
             let value = chalk_ir::ProgramClauseImplication {
@@ -148,12 +157,12 @@ impl<'tcx> LowerInto<'tcx, chalk_ir::GoalData<RustInterner<'tcx>>> for ty::Predi
             collect_bound_vars(interner, interner.tcx, self.kind());
 
         let value = match predicate {
-            ty::PredicateKind::Trait(predicate) => {
+            ty::PredicateKind::Clause(ty::Clause::Trait(predicate)) => {
                 chalk_ir::GoalData::DomainGoal(chalk_ir::DomainGoal::Holds(
                     chalk_ir::WhereClause::Implemented(predicate.trait_ref.lower_into(interner)),
                 ))
             }
-            ty::PredicateKind::RegionOutlives(predicate) => {
+            ty::PredicateKind::Clause(ty::Clause::RegionOutlives(predicate)) => {
                 chalk_ir::GoalData::DomainGoal(chalk_ir::DomainGoal::Holds(
                     chalk_ir::WhereClause::LifetimeOutlives(chalk_ir::LifetimeOutlives {
                         a: predicate.0.lower_into(interner),
@@ -161,7 +170,7 @@ impl<'tcx> LowerInto<'tcx, chalk_ir::GoalData<RustInterner<'tcx>>> for ty::Predi
                     }),
                 ))
             }
-            ty::PredicateKind::TypeOutlives(predicate) => {
+            ty::PredicateKind::Clause(ty::Clause::TypeOutlives(predicate)) => {
                 chalk_ir::GoalData::DomainGoal(chalk_ir::DomainGoal::Holds(
                     chalk_ir::WhereClause::TypeOutlives(chalk_ir::TypeOutlives {
                         ty: predicate.0.lower_into(interner),
@@ -169,7 +178,7 @@ impl<'tcx> LowerInto<'tcx, chalk_ir::GoalData<RustInterner<'tcx>>> for ty::Predi
                     }),
                 ))
             }
-            ty::PredicateKind::Projection(predicate) => {
+            ty::PredicateKind::Clause(ty::Clause::Projection(predicate)) => {
                 chalk_ir::GoalData::DomainGoal(chalk_ir::DomainGoal::Holds(
                     chalk_ir::WhereClause::AliasEq(predicate.lower_into(interner)),
                 ))
@@ -212,6 +221,7 @@ impl<'tcx> LowerInto<'tcx, chalk_ir::GoalData<RustInterner<'tcx>>> for ty::Predi
             ty::PredicateKind::ClosureKind(..)
             | ty::PredicateKind::Coerce(..)
             | ty::PredicateKind::ConstEvaluatable(..)
+            | ty::PredicateKind::Ambiguous
             | ty::PredicateKind::ConstEquate(..) => {
                 chalk_ir::GoalData::All(chalk_ir::Goals::empty(interner))
             }
@@ -411,7 +421,11 @@ impl<'tcx> LowerInto<'tcx, Ty<'tcx>> for &chalk_ir::Ty<RustInterner<'tcx>> {
             TyKind::Closure(closure, substitution) => {
                 ty::Closure(closure.0, substitution.lower_into(interner))
             }
-            TyKind::Generator(..) => unimplemented!(),
+            TyKind::Generator(generator, substitution) => ty::Generator(
+                generator.0,
+                substitution.lower_into(interner),
+                ast::Movability::Static,
+            ),
             TyKind::GeneratorWitness(..) => unimplemented!(),
             TyKind::Never => ty::Never,
             TyKind::Tuple(_len, substitution) => {
@@ -498,18 +512,15 @@ impl<'tcx> LowerInto<'tcx, Region<'tcx>> for &chalk_ir::Lifetime<RustInterner<'t
                 ty::DebruijnIndex::from_u32(var.debruijn.depth()),
                 ty::BoundRegion {
                     var: ty::BoundVar::from_usize(var.index),
-                    kind: ty::BrAnon(var.index as u32),
+                    kind: ty::BrAnon(var.index as u32, None),
                 },
             ),
             chalk_ir::LifetimeData::InferenceVar(_var) => unimplemented!(),
             chalk_ir::LifetimeData::Placeholder(p) => ty::RePlaceholder(ty::Placeholder {
                 universe: ty::UniverseIndex::from_usize(p.ui.counter),
-                name: ty::BoundRegionKind::BrAnon(p.idx as u32),
+                name: ty::BoundRegionKind::BrAnon(p.idx as u32, None),
             }),
             chalk_ir::LifetimeData::Static => return interner.tcx.lifetimes.re_static,
-            chalk_ir::LifetimeData::Empty(_) => {
-                bug!("Chalk should not have been passed an empty lifetime.")
-            }
             chalk_ir::LifetimeData::Erased => return interner.tcx.lifetimes.re_erased,
             chalk_ir::LifetimeData::Phantom(void, _) => match *void {},
         };
@@ -546,7 +557,7 @@ impl<'tcx> LowerInto<'tcx, ty::Const<'tcx>> for &chalk_ir::Const<RustInterner<'t
             chalk_ir::ConstValue::Placeholder(_p) => unimplemented!(),
             chalk_ir::ConstValue::Concrete(c) => ty::ConstKind::Value(c.interned),
         };
-        interner.tcx.mk_const(ty::ConstS { ty, kind })
+        interner.tcx.mk_const(kind, ty)
     }
 }
 
@@ -602,22 +613,22 @@ impl<'tcx> LowerInto<'tcx, Option<chalk_ir::QuantifiedWhereClause<RustInterner<'
         let (predicate, binders, _named_regions) =
             collect_bound_vars(interner, interner.tcx, self.kind());
         let value = match predicate {
-            ty::PredicateKind::Trait(predicate) => {
+            ty::PredicateKind::Clause(ty::Clause::Trait(predicate)) => {
                 Some(chalk_ir::WhereClause::Implemented(predicate.trait_ref.lower_into(interner)))
             }
-            ty::PredicateKind::RegionOutlives(predicate) => {
+            ty::PredicateKind::Clause(ty::Clause::RegionOutlives(predicate)) => {
                 Some(chalk_ir::WhereClause::LifetimeOutlives(chalk_ir::LifetimeOutlives {
                     a: predicate.0.lower_into(interner),
                     b: predicate.1.lower_into(interner),
                 }))
             }
-            ty::PredicateKind::TypeOutlives(predicate) => {
+            ty::PredicateKind::Clause(ty::Clause::TypeOutlives(predicate)) => {
                 Some(chalk_ir::WhereClause::TypeOutlives(chalk_ir::TypeOutlives {
                     ty: predicate.0.lower_into(interner),
                     lifetime: predicate.1.lower_into(interner),
                 }))
             }
-            ty::PredicateKind::Projection(predicate) => {
+            ty::PredicateKind::Clause(ty::Clause::Projection(predicate)) => {
                 Some(chalk_ir::WhereClause::AliasEq(predicate.lower_into(interner)))
             }
             ty::PredicateKind::WellFormed(_ty) => None,
@@ -628,6 +639,7 @@ impl<'tcx> LowerInto<'tcx, Option<chalk_ir::QuantifiedWhereClause<RustInterner<'
             | ty::PredicateKind::Coerce(..)
             | ty::PredicateKind::ConstEvaluatable(..)
             | ty::PredicateKind::ConstEquate(..)
+            | ty::PredicateKind::Ambiguous
             | ty::PredicateKind::TypeWellFormedFromEnv(..) => {
                 bug!("unexpected predicate {}", &self)
             }
@@ -637,7 +649,7 @@ impl<'tcx> LowerInto<'tcx, Option<chalk_ir::QuantifiedWhereClause<RustInterner<'
 }
 
 impl<'tcx> LowerInto<'tcx, chalk_ir::Binders<chalk_ir::QuantifiedWhereClauses<RustInterner<'tcx>>>>
-    for &'tcx ty::List<ty::Binder<'tcx, ty::ExistentialPredicate<'tcx>>>
+    for &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>
 {
     fn lower_into(
         self,
@@ -692,7 +704,7 @@ impl<'tcx> LowerInto<'tcx, chalk_ir::Binders<chalk_ir::QuantifiedWhereClauses<Ru
                         trait_id: chalk_ir::TraitId(def_id),
                         substitution: interner
                             .tcx
-                            .mk_substs_trait(self_ty, &[])
+                            .mk_substs_trait(self_ty, [])
                             .lower_into(interner),
                     }),
                 ),
@@ -737,26 +749,31 @@ impl<'tcx> LowerInto<'tcx, Option<chalk_solve::rust_ir::QuantifiedInlineBound<Ru
         let (predicate, binders, _named_regions) =
             collect_bound_vars(interner, interner.tcx, self.kind());
         match predicate {
-            ty::PredicateKind::Trait(predicate) => Some(chalk_ir::Binders::new(
-                binders,
-                chalk_solve::rust_ir::InlineBound::TraitBound(
-                    predicate.trait_ref.lower_into(interner),
-                ),
-            )),
-            ty::PredicateKind::Projection(predicate) => Some(chalk_ir::Binders::new(
-                binders,
-                chalk_solve::rust_ir::InlineBound::AliasEqBound(predicate.lower_into(interner)),
-            )),
-            ty::PredicateKind::TypeOutlives(_predicate) => None,
+            ty::PredicateKind::Clause(ty::Clause::Trait(predicate)) => {
+                Some(chalk_ir::Binders::new(
+                    binders,
+                    chalk_solve::rust_ir::InlineBound::TraitBound(
+                        predicate.trait_ref.lower_into(interner),
+                    ),
+                ))
+            }
+            ty::PredicateKind::Clause(ty::Clause::Projection(predicate)) => {
+                Some(chalk_ir::Binders::new(
+                    binders,
+                    chalk_solve::rust_ir::InlineBound::AliasEqBound(predicate.lower_into(interner)),
+                ))
+            }
+            ty::PredicateKind::Clause(ty::Clause::TypeOutlives(_predicate)) => None,
             ty::PredicateKind::WellFormed(_ty) => None,
 
-            ty::PredicateKind::RegionOutlives(..)
+            ty::PredicateKind::Clause(ty::Clause::RegionOutlives(..))
             | ty::PredicateKind::ObjectSafe(..)
             | ty::PredicateKind::ClosureKind(..)
             | ty::PredicateKind::Subtype(..)
             | ty::PredicateKind::Coerce(..)
             | ty::PredicateKind::ConstEvaluatable(..)
             | ty::PredicateKind::ConstEquate(..)
+            | ty::PredicateKind::Ambiguous
             | ty::PredicateKind::TypeWellFormedFromEnv(..) => {
                 bug!("unexpected predicate {}", &self)
             }
@@ -933,7 +950,7 @@ impl<'tcx> TypeVisitor<'tcx> for BoundVarsCollector<'tcx> {
                     }
                 }
 
-                ty::BoundRegionKind::BrAnon(var) => match self.parameters.entry(var) {
+                ty::BoundRegionKind::BrAnon(var, _) => match self.parameters.entry(var) {
                     Entry::Vacant(entry) => {
                         entry.insert(chalk_ir::VariableKind::Lifetime);
                     }
@@ -991,13 +1008,13 @@ impl<'a, 'tcx> TypeFolder<'tcx> for NamedBoundVarSubstitutor<'a, 'tcx> {
             ty::ReLateBound(index, br) if index == self.binder_index => match br.kind {
                 ty::BrNamed(def_id, _name) => match self.named_parameters.get(&def_id) {
                     Some(idx) => {
-                        let new_br = ty::BoundRegion { var: br.var, kind: ty::BrAnon(*idx) };
+                        let new_br = ty::BoundRegion { var: br.var, kind: ty::BrAnon(*idx, None) };
                         return self.tcx.mk_region(ty::ReLateBound(index, new_br));
                     }
                     None => panic!("Missing `BrNamed`."),
                 },
                 ty::BrEnv => unimplemented!(),
-                ty::BrAnon(_) => {}
+                ty::BrAnon(..) => {}
             },
             _ => (),
         };
@@ -1072,14 +1089,16 @@ impl<'tcx> TypeFolder<'tcx> for ParamsSubstitutor<'tcx> {
                 Some(idx) => {
                     let br = ty::BoundRegion {
                         var: ty::BoundVar::from_u32(*idx),
-                        kind: ty::BrAnon(*idx),
+                        kind: ty::BrAnon(*idx, None),
                     };
                     self.tcx.mk_region(ty::ReLateBound(self.binder_index, br))
                 }
                 None => {
                     let idx = self.named_regions.len() as u32;
-                    let br =
-                        ty::BoundRegion { var: ty::BoundVar::from_u32(idx), kind: ty::BrAnon(idx) };
+                    let br = ty::BoundRegion {
+                        var: ty::BoundVar::from_u32(idx),
+                        kind: ty::BrAnon(idx, None),
+                    };
                     self.named_regions.insert(_re.def_id, idx);
                     self.tcx.mk_region(ty::ReLateBound(self.binder_index, br))
                 }
@@ -1156,7 +1175,7 @@ impl<'tcx> TypeVisitor<'tcx> for PlaceholdersCollector {
     fn visit_region(&mut self, r: Region<'tcx>) -> ControlFlow<Self::BreakTy> {
         match *r {
             ty::RePlaceholder(p) if p.universe == self.universe_index => {
-                if let ty::BoundRegionKind::BrAnon(anon) = p.name {
+                if let ty::BoundRegionKind::BrAnon(anon, _) = p.name {
                     self.next_anon_region_placeholder = self.next_anon_region_placeholder.max(anon);
                 }
             }
diff --git a/compiler/rustc_traits/src/codegen.rs b/compiler/rustc_traits/src/codegen.rs
new file mode 100644
index 000000000..f8f74b732
--- /dev/null
+++ b/compiler/rustc_traits/src/codegen.rs
@@ -0,0 +1,88 @@
+// This file contains various trait resolution methods used by codegen.
+// They all assume regions can be erased and monomorphic types.  It
+// seems likely that they should eventually be merged into more
+// general routines.
+
+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
+/// (necessarily) resolve all nested obligations on the impl. Note
+/// that type check should guarantee to us that all nested
+/// obligations *could be* resolved if we wanted to.
+///
+/// This also expects that `trait_ref` is fully normalized.
+pub fn codegen_select_candidate<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    (param_env, trait_ref): (ty::ParamEnv<'tcx>, ty::PolyTraitRef<'tcx>),
+) -> Result<&'tcx ImplSource<'tcx, ()>, CodegenObligationError> {
+    // We expect the input to be fully normalized.
+    debug_assert_eq!(trait_ref, tcx.normalize_erasing_regions(param_env, trait_ref));
+
+    // Do the initial selection for the obligation. This yields the
+    // shallow result we are looking for -- that is, what specific impl.
+    let infcx = tcx
+        .infer_ctxt()
+        .ignoring_regions()
+        .with_opaque_type_inference(DefiningAnchor::Bubble)
+        .build();
+    //~^ HACK `Bubble` is required for
+    // this test to pass: type-alias-impl-trait/assoc-projection-ice.rs
+    let mut selcx = SelectionContext::new(&infcx);
+
+    let obligation_cause = ObligationCause::dummy();
+    let obligation = Obligation::new(tcx, obligation_cause, param_env, trait_ref);
+
+    let selection = match selcx.select(&obligation) {
+        Ok(Some(selection)) => selection,
+        Ok(None) => return Err(CodegenObligationError::Ambiguity),
+        Err(Unimplemented) => return Err(CodegenObligationError::Unimplemented),
+        Err(e) => {
+            bug!("Encountered error `{:?}` selecting `{:?}` during codegen", e, trait_ref)
+        }
+    };
+
+    debug!(?selection);
+
+    // Currently, we use a fulfillment context to completely resolve
+    // all nested obligations. This is because they can inform the
+    // inference of the impl's type parameters.
+    let mut fulfill_cx = <dyn TraitEngine<'tcx>>::new(tcx);
+    let impl_source = selection.map(|predicate| {
+        fulfill_cx.register_predicate_obligation(&infcx, predicate);
+    });
+
+    // In principle, we only need to do this so long as `impl_source`
+    // contains unbound type parameters. It could be a slight
+    // optimization to stop iterating early.
+    let errors = fulfill_cx.select_all_or_error(&infcx);
+    if !errors.is_empty() {
+        // `rustc_monomorphize::collector` assumes there are no type errors.
+        // Cycle errors are the only post-monomorphization errors possible; emit them now so
+        // `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_obligation_cycle(&cycle);
+            }
+        }
+        return Err(CodegenObligationError::FulfillmentError);
+    }
+
+    let impl_source = infcx.resolve_vars_if_possible(impl_source);
+    let impl_source = infcx.tcx.erase_regions(impl_source);
+
+    // Opaque types may have gotten their hidden types constrained, but we can ignore them safely
+    // as they will get constrained elsewhere, too.
+    // (ouz-a) This is required for `type-alias-impl-trait/assoc-projection-ice.rs` to pass
+    let _ = infcx.inner.borrow_mut().opaque_type_storage.take_opaque_types();
+
+    Ok(&*tcx.arena.alloc(impl_source))
+}
diff --git a/compiler/rustc_traits/src/dropck_outlives.rs b/compiler/rustc_traits/src/dropck_outlives.rs
index d5a8ca5ea..66ab742f1 100644
--- a/compiler/rustc_traits/src/dropck_outlives.rs
+++ b/compiler/rustc_traits/src/dropck_outlives.rs
@@ -2,20 +2,18 @@ use rustc_data_structures::fx::FxHashSet;
 use rustc_hir::def_id::DefId;
 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::InternalSubsts;
 use rustc_middle::ty::{self, EarlyBinder, ParamEnvAnd, Ty, TyCtxt};
 use rustc_span::source_map::{Span, DUMMY_SP};
+use rustc_trait_selection::infer::InferCtxtBuilderExt;
 use rustc_trait_selection::traits::query::dropck_outlives::trivial_dropck_outlives;
 use rustc_trait_selection::traits::query::dropck_outlives::{
     DropckConstraint, DropckOutlivesResult,
 };
-use rustc_trait_selection::traits::query::normalize::AtExt;
+use rustc_trait_selection::traits::query::normalize::QueryNormalizeExt;
 use rustc_trait_selection::traits::query::{CanonicalTyGoal, NoSolution};
-use rustc_trait_selection::traits::{
-    Normalized, ObligationCause, TraitEngine, TraitEngineExt as _,
-};
+use rustc_trait_selection::traits::{Normalized, ObligationCause};
 
 pub(crate) fn provide(p: &mut Providers) {
     *p = Providers { dropck_outlives, adt_dtorck_constraint, ..*p };
@@ -27,120 +25,109 @@ fn dropck_outlives<'tcx>(
 ) -> Result<&'tcx Canonical<'tcx, QueryResponse<'tcx, DropckOutlivesResult<'tcx>>>, NoSolution> {
     debug!("dropck_outlives(goal={:#?})", canonical_goal);
 
-    let (ref infcx, goal, canonical_inference_vars) =
-        tcx.infer_ctxt().build_with_canonical(DUMMY_SP, &canonical_goal);
-    let tcx = infcx.tcx;
-    let ParamEnvAnd { param_env, value: for_ty } = goal;
-
-    let mut result = DropckOutlivesResult { kinds: vec![], overflows: vec![] };
-
-    // A stack of types left to process. Each round, we pop
-    // something from the stack and invoke
-    // `dtorck_constraint_for_ty`. This may produce new types that
-    // have to be pushed on the stack. This continues until we have explored
-    // all the reachable types from the type `for_ty`.
-    //
-    // Example: Imagine that we have the following code:
-    //
-    // ```rust
-    // struct A {
-    //     value: B,
-    //     children: Vec<A>,
-    // }
-    //
-    // struct B {
-    //     value: u32
-    // }
-    //
-    // fn f() {
-    //   let a: A = ...;
-    //   ..
-    // } // here, `a` is dropped
-    // ```
-    //
-    // at the point where `a` is dropped, we need to figure out
-    // which types inside of `a` contain region data that may be
-    // accessed by any destructors in `a`. We begin by pushing `A`
-    // onto the stack, as that is the type of `a`. We will then
-    // invoke `dtorck_constraint_for_ty` which will expand `A`
-    // into the types of its fields `(B, Vec<A>)`. These will get
-    // pushed onto the stack. Eventually, expanding `Vec<A>` will
-    // lead to us trying to push `A` a second time -- to prevent
-    // infinite recursion, we notice that `A` was already pushed
-    // once and stop.
-    let mut ty_stack = vec![(for_ty, 0)];
-
-    // Set used to detect infinite recursion.
-    let mut ty_set = FxHashSet::default();
-
-    let mut fulfill_cx = <dyn TraitEngine<'_>>::new(infcx.tcx);
-
-    let cause = ObligationCause::dummy();
-    let mut constraints = DropckConstraint::empty();
-    while let Some((ty, depth)) = ty_stack.pop() {
-        debug!(
-            "{} kinds, {} overflows, {} ty_stack",
-            result.kinds.len(),
-            result.overflows.len(),
-            ty_stack.len()
-        );
-        dtorck_constraint_for_ty(tcx, DUMMY_SP, for_ty, depth, ty, &mut constraints)?;
-
-        // "outlives" represent types/regions that may be touched
-        // by a destructor.
-        result.kinds.append(&mut constraints.outlives);
-        result.overflows.append(&mut constraints.overflows);
-
-        // If we have even one overflow, we should stop trying to evaluate further --
-        // chances are, the subsequent overflows for this evaluation won't provide useful
-        // information and will just decrease the speed at which we can emit these errors
-        // (since we'll be printing for just that much longer for the often enormous types
-        // that result here).
-        if !result.overflows.is_empty() {
-            break;
-        }
+    tcx.infer_ctxt().enter_canonical_trait_query(&canonical_goal, |ocx, goal| {
+        let tcx = ocx.infcx.tcx;
+        let ParamEnvAnd { param_env, value: for_ty } = goal;
+
+        let mut result = DropckOutlivesResult { kinds: vec![], overflows: vec![] };
+
+        // A stack of types left to process. Each round, we pop
+        // something from the stack and invoke
+        // `dtorck_constraint_for_ty`. This may produce new types that
+        // have to be pushed on the stack. This continues until we have explored
+        // all the reachable types from the type `for_ty`.
+        //
+        // Example: Imagine that we have the following code:
+        //
+        // ```rust
+        // struct A {
+        //     value: B,
+        //     children: Vec<A>,
+        // }
+        //
+        // struct B {
+        //     value: u32
+        // }
+        //
+        // fn f() {
+        //   let a: A = ...;
+        //   ..
+        // } // here, `a` is dropped
+        // ```
+        //
+        // at the point where `a` is dropped, we need to figure out
+        // which types inside of `a` contain region data that may be
+        // accessed by any destructors in `a`. We begin by pushing `A`
+        // onto the stack, as that is the type of `a`. We will then
+        // invoke `dtorck_constraint_for_ty` which will expand `A`
+        // into the types of its fields `(B, Vec<A>)`. These will get
+        // pushed onto the stack. Eventually, expanding `Vec<A>` will
+        // lead to us trying to push `A` a second time -- to prevent
+        // infinite recursion, we notice that `A` was already pushed
+        // once and stop.
+        let mut ty_stack = vec![(for_ty, 0)];
+
+        // Set used to detect infinite recursion.
+        let mut ty_set = FxHashSet::default();
+
+        let cause = ObligationCause::dummy();
+        let mut constraints = DropckConstraint::empty();
+        while let Some((ty, depth)) = ty_stack.pop() {
+            debug!(
+                "{} kinds, {} overflows, {} ty_stack",
+                result.kinds.len(),
+                result.overflows.len(),
+                ty_stack.len()
+            );
+            dtorck_constraint_for_ty(tcx, DUMMY_SP, for_ty, depth, ty, &mut constraints)?;
+
+            // "outlives" represent types/regions that may be touched
+            // by a destructor.
+            result.kinds.append(&mut constraints.outlives);
+            result.overflows.append(&mut constraints.overflows);
+
+            // If we have even one overflow, we should stop trying to evaluate further --
+            // chances are, the subsequent overflows for this evaluation won't provide useful
+            // information and will just decrease the speed at which we can emit these errors
+            // (since we'll be printing for just that much longer for the often enormous types
+            // that result here).
+            if !result.overflows.is_empty() {
+                break;
+            }
 
-        // dtorck types are "types that will get dropped but which
-        // do not themselves define a destructor", more or less. We have
-        // to push them onto the stack to be expanded.
-        for ty in constraints.dtorck_types.drain(..) {
-            match infcx.at(&cause, param_env).normalize(ty) {
-                Ok(Normalized { value: ty, obligations }) => {
-                    fulfill_cx.register_predicate_obligations(infcx, obligations);
-
-                    debug!("dropck_outlives: ty from dtorck_types = {:?}", ty);
-
-                    match ty.kind() {
-                        // All parameters live for the duration of the
-                        // function.
-                        ty::Param(..) => {}
-
-                        // A projection that we couldn't resolve - it
-                        // might have a destructor.
-                        ty::Projection(..) | ty::Opaque(..) => {
-                            result.kinds.push(ty.into());
-                        }
+            // dtorck types are "types that will get dropped but which
+            // do not themselves define a destructor", more or less. We have
+            // to push them onto the stack to be expanded.
+            for ty in constraints.dtorck_types.drain(..) {
+                let Normalized { value: ty, obligations } =
+                    ocx.infcx.at(&cause, param_env).query_normalize(ty)?;
+                ocx.register_obligations(obligations);
+
+                debug!("dropck_outlives: ty from dtorck_types = {:?}", ty);
+
+                match ty.kind() {
+                    // All parameters live for the duration of the
+                    // function.
+                    ty::Param(..) => {}
+
+                    // A projection that we couldn't resolve - it
+                    // might have a destructor.
+                    ty::Projection(..) | ty::Opaque(..) => {
+                        result.kinds.push(ty.into());
+                    }
 
-                        _ => {
-                            if ty_set.insert(ty) {
-                                ty_stack.push((ty, depth + 1));
-                            }
+                    _ => {
+                        if ty_set.insert(ty) {
+                            ty_stack.push((ty, depth + 1));
                         }
                     }
                 }
-
-                // We don't actually expect to fail to normalize.
-                // That implies a WF error somewhere else.
-                Err(NoSolution) => {
-                    return Err(NoSolution);
-                }
             }
         }
-    }
-
-    debug!("dropck_outlives: result = {:#?}", result);
 
-    infcx.make_canonicalized_query_response(canonical_inference_vars, result, &mut *fulfill_cx)
+        debug!("dropck_outlives: result = {:#?}", result);
+        Ok(result)
+    })
 }
 
 /// Returns a set of constraints that needs to be satisfied in
diff --git a/compiler/rustc_traits/src/evaluate_obligation.rs b/compiler/rustc_traits/src/evaluate_obligation.rs
index 493d5de08..e94c8efe6 100644
--- a/compiler/rustc_traits/src/evaluate_obligation.rs
+++ b/compiler/rustc_traits/src/evaluate_obligation.rs
@@ -26,7 +26,7 @@ fn evaluate_obligation<'tcx>(
     let ParamEnvAnd { param_env, value: predicate } = goal;
 
     let mut selcx = SelectionContext::with_query_mode(&infcx, TraitQueryMode::Canonical);
-    let obligation = Obligation::new(ObligationCause::dummy(), param_env, predicate);
+    let obligation = Obligation::new(tcx, ObligationCause::dummy(), param_env, predicate);
 
     selcx.evaluate_root_obligation(&obligation)
 }
diff --git a/compiler/rustc_traits/src/implied_outlives_bounds.rs b/compiler/rustc_traits/src/implied_outlives_bounds.rs
index 7d36b9558..010233d77 100644
--- a/compiler/rustc_traits/src/implied_outlives_bounds.rs
+++ b/compiler/rustc_traits/src/implied_outlives_bounds.rs
@@ -5,16 +5,15 @@
 use rustc_hir as hir;
 use rustc_infer::infer::canonical::{self, Canonical};
 use rustc_infer::infer::outlives::components::{push_outlives_components, Component};
-use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
+use rustc_infer::infer::TyCtxtInferExt;
 use rustc_infer::traits::query::OutlivesBound;
-use rustc_infer::traits::TraitEngineExt as _;
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitable};
 use rustc_span::source_map::DUMMY_SP;
 use rustc_trait_selection::infer::InferCtxtBuilderExt;
 use rustc_trait_selection::traits::query::{CanonicalTyGoal, Fallible, NoSolution};
 use rustc_trait_selection::traits::wf;
-use rustc_trait_selection::traits::{TraitEngine, TraitEngineExt};
+use rustc_trait_selection::traits::ObligationCtxt;
 use smallvec::{smallvec, SmallVec};
 
 pub(crate) fn provide(p: &mut Providers) {
@@ -28,18 +27,18 @@ 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, param_env, ty)
     })
 }
 
 fn compute_implied_outlives_bounds<'tcx>(
-    infcx: &InferCtxt<'tcx>,
+    ocx: &ObligationCtxt<'_, 'tcx>,
     param_env: ty::ParamEnv<'tcx>,
     ty: Ty<'tcx>,
 ) -> Fallible<Vec<OutlivesBound<'tcx>>> {
-    let tcx = infcx.tcx;
+    let tcx = ocx.infcx.tcx;
 
     // Sometimes when we ask what it takes for T: WF, we get back that
     // U: WF is required; in that case, we push U onto this stack and
@@ -52,8 +51,6 @@ fn compute_implied_outlives_bounds<'tcx>(
     let mut outlives_bounds: Vec<ty::OutlivesPredicate<ty::GenericArg<'tcx>, ty::Region<'tcx>>> =
         vec![];
 
-    let mut fulfill_cx = <dyn TraitEngine<'tcx>>::new(tcx);
-
     while let Some(arg) = wf_args.pop() {
         if !checked_wf_args.insert(arg) {
             continue;
@@ -70,15 +67,15 @@ fn compute_implied_outlives_bounds<'tcx>(
         // FIXME(@lcnr): It's not really "always fine", having fewer implied
         // bounds can be backward incompatible, e.g. #101951 was caused by
         // us not dealing with inference vars in `TypeOutlives` predicates.
-        let obligations = wf::obligations(infcx, param_env, hir::CRATE_HIR_ID, 0, arg, DUMMY_SP)
-            .unwrap_or_default();
+        let obligations =
+            wf::obligations(ocx.infcx, param_env, hir::CRATE_HIR_ID, 0, arg, DUMMY_SP)
+                .unwrap_or_default();
 
         // While these predicates should all be implied by other parts of
         // the program, they are still relevant as they may constrain
         // inference variables, which is necessary to add the correct
         // implied bounds in some cases, mostly when dealing with projections.
-        fulfill_cx.register_predicate_obligations(
-            infcx,
+        ocx.register_obligations(
             obligations.iter().filter(|o| o.predicate.has_non_region_infer()).cloned(),
         );
 
@@ -89,35 +86,37 @@ fn compute_implied_outlives_bounds<'tcx>(
             match obligation.predicate.kind().no_bound_vars() {
                 None => None,
                 Some(pred) => match pred {
-                    ty::PredicateKind::Trait(..)
+                    ty::PredicateKind::Clause(ty::Clause::Trait(..))
                     | ty::PredicateKind::Subtype(..)
                     | ty::PredicateKind::Coerce(..)
-                    | ty::PredicateKind::Projection(..)
+                    | ty::PredicateKind::Clause(ty::Clause::Projection(..))
                     | ty::PredicateKind::ClosureKind(..)
                     | ty::PredicateKind::ObjectSafe(..)
                     | ty::PredicateKind::ConstEvaluatable(..)
                     | ty::PredicateKind::ConstEquate(..)
+                    | ty::PredicateKind::Ambiguous
                     | ty::PredicateKind::TypeWellFormedFromEnv(..) => None,
                     ty::PredicateKind::WellFormed(arg) => {
                         wf_args.push(arg);
                         None
                     }
 
-                    ty::PredicateKind::RegionOutlives(ty::OutlivesPredicate(r_a, r_b)) => {
-                        Some(ty::OutlivesPredicate(r_a.into(), r_b))
-                    }
+                    ty::PredicateKind::Clause(ty::Clause::RegionOutlives(
+                        ty::OutlivesPredicate(r_a, r_b),
+                    )) => Some(ty::OutlivesPredicate(r_a.into(), r_b)),
 
-                    ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(ty_a, r_b)) => {
-                        Some(ty::OutlivesPredicate(ty_a.into(), r_b))
-                    }
+                    ty::PredicateKind::Clause(ty::Clause::TypeOutlives(ty::OutlivesPredicate(
+                        ty_a,
+                        r_b,
+                    ))) => Some(ty::OutlivesPredicate(ty_a.into(), r_b)),
                 },
             }
         }));
     }
 
-    // Ensure that those obligations that we had to solve
-    // get solved *here*.
-    match fulfill_cx.select_all_or_error(infcx).as_slice() {
+    // This call to `select_all_or_error` is necessary to constrain inference variables, which we
+    // use further down when computing the implied bounds.
+    match ocx.select_all_or_error().as_slice() {
         [] => (),
         _ => return Err(NoSolution),
     }
@@ -129,7 +128,7 @@ fn compute_implied_outlives_bounds<'tcx>(
         .flat_map(|ty::OutlivesPredicate(a, r_b)| match a.unpack() {
             ty::GenericArgKind::Lifetime(r_a) => vec![OutlivesBound::RegionSubRegion(r_b, r_a)],
             ty::GenericArgKind::Type(ty_a) => {
-                let ty_a = infcx.resolve_vars_if_possible(ty_a);
+                let ty_a = ocx.infcx.resolve_vars_if_possible(ty_a);
                 let mut components = smallvec![];
                 push_outlives_components(tcx, ty_a, &mut components);
                 implied_bounds_from_components(r_b, components)
diff --git a/compiler/rustc_traits/src/lib.rs b/compiler/rustc_traits/src/lib.rs
index 0da28737f..9aa26667e 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]
@@ -11,6 +12,7 @@ extern crate tracing;
 extern crate rustc_middle;
 
 mod chalk;
+mod codegen;
 mod dropck_outlives;
 mod evaluate_obligation;
 mod implied_outlives_bounds;
@@ -30,4 +32,5 @@ pub fn provide(p: &mut Providers) {
     normalize_projection_ty::provide(p);
     normalize_erasing_regions::provide(p);
     type_op::provide(p);
+    p.codegen_select_candidate = codegen::codegen_select_candidate;
 }
diff --git a/compiler/rustc_traits/src/normalize_erasing_regions.rs b/compiler/rustc_traits/src/normalize_erasing_regions.rs
index 2da64d73d..44fd8bfb3 100644
--- a/compiler/rustc_traits/src/normalize_erasing_regions.rs
+++ b/compiler/rustc_traits/src/normalize_erasing_regions.rs
@@ -2,7 +2,7 @@ use rustc_infer::infer::TyCtxtInferExt;
 use rustc_middle::traits::query::NoSolution;
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::{self, ParamEnvAnd, TyCtxt, TypeFoldable};
-use rustc_trait_selection::traits::query::normalize::AtExt;
+use rustc_trait_selection::traits::query::normalize::QueryNormalizeExt;
 use rustc_trait_selection::traits::{Normalized, ObligationCause};
 use std::sync::atomic::Ordering;
 
@@ -29,12 +29,14 @@ fn try_normalize_after_erasing_regions<'tcx, T: TypeFoldable<'tcx> + PartialEq +
     let ParamEnvAnd { param_env, value } = goal;
     let infcx = tcx.infer_ctxt().build();
     let cause = ObligationCause::dummy();
-    match infcx.at(&cause, param_env).normalize(value) {
+    match infcx.at(&cause, param_env).query_normalize(value) {
         Ok(Normalized { value: normalized_value, obligations: normalized_obligations }) => {
             // We don't care about the `obligations`; they are
             // always only region relations, and we are about to
             // erase those anyway:
-            debug_assert_eq!(
+            // This has been seen to fail in RL, so making it a non-debug assertion to better catch
+            // those cases.
+            assert_eq!(
                 normalized_obligations.iter().find(|p| not_outlives_predicate(p.predicate)),
                 None,
             );
@@ -54,9 +56,10 @@ fn try_normalize_after_erasing_regions<'tcx, T: TypeFoldable<'tcx> + PartialEq +
 
 fn not_outlives_predicate<'tcx>(p: ty::Predicate<'tcx>) -> bool {
     match p.kind().skip_binder() {
-        ty::PredicateKind::RegionOutlives(..) | ty::PredicateKind::TypeOutlives(..) => false,
-        ty::PredicateKind::Trait(..)
-        | ty::PredicateKind::Projection(..)
+        ty::PredicateKind::Clause(ty::Clause::RegionOutlives(..))
+        | ty::PredicateKind::Clause(ty::Clause::TypeOutlives(..)) => false,
+        ty::PredicateKind::Clause(ty::Clause::Trait(..))
+        | ty::PredicateKind::Clause(ty::Clause::Projection(..))
         | ty::PredicateKind::WellFormed(..)
         | ty::PredicateKind::ObjectSafe(..)
         | ty::PredicateKind::ClosureKind(..)
@@ -64,6 +67,7 @@ fn not_outlives_predicate<'tcx>(p: ty::Predicate<'tcx>) -> bool {
         | ty::PredicateKind::Coerce(..)
         | ty::PredicateKind::ConstEvaluatable(..)
         | ty::PredicateKind::ConstEquate(..)
+        | ty::PredicateKind::Ambiguous
         | ty::PredicateKind::TypeWellFormedFromEnv(..) => true,
     }
 }
diff --git a/compiler/rustc_traits/src/normalize_projection_ty.rs b/compiler/rustc_traits/src/normalize_projection_ty.rs
index 98bb42c9a..e805eb428 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 bca7458ed..7f964afde 100644
--- a/compiler/rustc_traits/src/type_op.rs
+++ b/compiler/rustc_traits/src/type_op.rs
@@ -1,26 +1,21 @@
 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::normalize::QueryNormalizeExt;
 use rustc_trait_selection::traits::query::type_op::ascribe_user_type::AscribeUserType;
 use rustc_trait_selection::traits::query::type_op::eq::Eq;
 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 +37,16 @@ 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> {
@@ -61,157 +55,81 @@ 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 span = span.unwrap_or(DUMMY_SP);
 
-    let mut cx = AscribeUserTypeCx { infcx, param_env, span: span.unwrap_or(DUMMY_SP), fulfill_cx };
-    cx.relate_mir_and_user_ty(mir_ty, def_id, user_substs)?;
-    Ok(())
-}
+    let UserSubsts { user_self_ty, substs } = user_substs;
+    let tcx = ocx.infcx.tcx;
+    let cause = ObligationCause::dummy_with_span(span);
 
-struct AscribeUserTypeCx<'me, 'tcx> {
-    infcx: &'me InferCtxt<'tcx>,
-    param_env: ParamEnv<'tcx>,
-    span: Span,
-    fulfill_cx: &'me mut dyn TraitEngine<'tcx>,
-}
+    let ty = tcx.bound_type_of(def_id).subst(tcx, substs);
+    let ty = ocx.normalize(&cause, param_env, ty);
+    debug!("relate_type_and_user_type: ty of def-id is {:?}", ty);
 
-impl<'me, 'tcx> AscribeUserTypeCx<'me, 'tcx> {
-    fn normalize<T>(&mut self, value: T) -> T
-    where
-        T: TypeFoldable<'tcx>,
-    {
-        self.normalize_with_cause(value, ObligationCause::misc(self.span, hir::CRATE_HIR_ID))
-    }
+    ocx.eq(&cause, param_env, mir_ty, ty)?;
 
-    fn normalize_with_cause<T>(&mut 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)
-    }
+    // 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 = tcx.predicates_of(def_id).instantiate(tcx, substs);
 
-    fn relate<T>(&mut self, a: T, variance: Variance, b: T) -> Result<(), NoSolution>
-    where
-        T: ToTrace<'tcx>,
+    debug!(?instantiated_predicates);
+    for (instantiated_predicate, predicate_span) in
+        zip(instantiated_predicates.predicates, instantiated_predicates.spans)
     {
-        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(())
-    }
-
-    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),
+        let span = if span == DUMMY_SP { predicate_span } else { span };
+        let cause = ObligationCause::new(
+            span,
+            hir::CRATE_HIR_ID,
+            ObligationCauseCode::AscribeUserTypeProvePredicate(predicate_span),
         );
-    }
+        let instantiated_predicate =
+            ocx.normalize(&cause.clone(), param_env, instantiated_predicate);
 
-    fn tcx(&self) -> TyCtxt<'tcx> {
-        self.infcx.tcx
+        ocx.register_obligation(Obligation::new(tcx, cause, param_env, instantiated_predicate));
     }
 
-    fn subst<T>(&self, value: T, substs: &[GenericArg<'tcx>]) -> T
-    where
-        T: TypeFoldable<'tcx>,
-    {
-        EarlyBinder(value).subst(self.tcx(), substs)
-    }
+    if let Some(UserSelfTy { impl_def_id, self_ty }) = user_self_ty {
+        let impl_self_ty = tcx.bound_type_of(impl_def_id).subst(tcx, substs);
+        let impl_self_ty = ocx.normalize(&cause, param_env, impl_self_ty);
 
-    #[instrument(level = "debug", skip(self))]
-    fn relate_mir_and_user_ty(
-        &mut self,
-        mir_ty: Ty<'tcx>,
-        def_id: DefId,
-        user_substs: UserSubsts<'tcx>,
-    ) -> Result<(), NoSolution> {
-        let UserSubsts { user_self_ty, substs } = user_substs;
-        let tcx = self.tcx();
+        ocx.eq(&cause, param_env, self_ty, impl_self_ty)?;
 
-        let ty = tcx.type_of(def_id);
-        let ty = self.subst(ty, 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)?;
-
-        // 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 cause = ObligationCause::dummy_with_span(self.span);
-
-        debug!(?instantiated_predicates);
-        for (instantiated_predicate, predicate_span) in
-            zip(instantiated_predicates.predicates, instantiated_predicates.spans)
-        {
-            let span = if self.span == DUMMY_SP { predicate_span } else { self.span };
-            let cause = ObligationCause::new(
-                span,
-                hir::CRATE_HIR_ID,
-                ObligationCauseCode::AscribeUserTypeProvePredicate(predicate_span),
-            );
-            let instantiated_predicate =
-                self.normalize_with_cause(instantiated_predicate, cause.clone());
-            self.prove_predicate(instantiated_predicate, cause);
-        }
-
-        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 = self.normalize(impl_self_ty);
-
-            self.relate(self_ty, Variance::Invariant, impl_self_ty)?;
-
-            self.prove_predicate(
-                ty::Binder::dummy(ty::PredicateKind::WellFormed(impl_self_ty.into()))
-                    .to_predicate(self.tcx()),
-                cause.clone(),
-            );
-        }
-
-        // In addition to proving the predicates, we have to
-        // prove that `ty` is well-formed -- this is because
-        // the WF of `ty` is predicated on the substs being
-        // well-formed, and we haven't proven *that*. We don't
-        // want to prove the WF of types from  `substs` directly because they
-        // haven't been normalized.
-        //
-        // FIXME(nmatsakis): Well, perhaps we should normalize
-        // them?  This would only be relevant if some input
-        // 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()),
-            cause,
-        );
-        Ok(())
+        let predicate: Predicate<'tcx> =
+            ty::Binder::dummy(ty::PredicateKind::WellFormed(impl_self_ty.into())).to_predicate(tcx);
+        ocx.register_obligation(Obligation::new(tcx, cause.clone(), param_env, predicate));
     }
+
+    // In addition to proving the predicates, we have to
+    // prove that `ty` is well-formed -- this is because
+    // the WF of `ty` is predicated on the substs being
+    // well-formed, and we haven't proven *that*. We don't
+    // want to prove the WF of types from  `substs` directly because they
+    // haven't been normalized.
+    //
+    // FIXME(nmatsakis): Well, perhaps we should normalize
+    // them?  This would only be relevant if some input
+    // type were ill-formed but did not appear in `ty`,
+    // which...could happen with normalization...
+    let predicate: Predicate<'tcx> =
+        ty::Binder::dummy(ty::PredicateKind::WellFormed(ty.into())).to_predicate(tcx);
+    ocx.register_obligation(Obligation::new(tcx, cause, param_env, predicate));
+    Ok(())
 }
 
 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 +137,8 @@ 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).query_normalize(value)?;
+    ocx.register_obligations(obligations);
     Ok(value)
 }
 
@@ -256,13 +174,9 @@ 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 +188,8 @@ 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 +198,11 @@ 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(ocx.infcx.tcx, cause, param_env, predicate));
 }