Uplift Goal to rustc_type_ir

compiler/rustc_borrowck/src/type_check/canonical.rs

@@ -115,7 +115,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
 
     pub(super) fn prove_predicates(
         &mut self,
-        predicates: impl IntoIterator<Item: Upcast<'tcx, ty::Predicate<'tcx>> + std::fmt::Debug>,
+        predicates: impl IntoIterator<Item: Upcast<TyCtxt<'tcx>, ty::Predicate<'tcx>> + std::fmt::Debug>,
         locations: Locations,
         category: ConstraintCategory<'tcx>,
     ) {
@@ -127,7 +127,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
     #[instrument(skip(self), level = "debug")]
     pub(super) fn prove_predicate(
         &mut self,
-        predicate: impl Upcast<'tcx, ty::Predicate<'tcx>> + std::fmt::Debug,
+        predicate: impl Upcast<TyCtxt<'tcx>, ty::Predicate<'tcx>> + std::fmt::Debug,
         locations: Locations,
         category: ConstraintCategory<'tcx>,
     ) {

compiler/rustc_borrowck/src/type_check/relate_tys.rs

@@ -548,7 +548,7 @@ impl<'bccx, 'tcx> ObligationEmittingRelation<'tcx> for NllTypeRelating<'_, 'bccx
 
     fn register_predicates(
         &mut self,
-        obligations: impl IntoIterator<Item: ty::Upcast<'tcx, ty::Predicate<'tcx>>>,
+        obligations: impl IntoIterator<Item: ty::Upcast<TyCtxt<'tcx>, ty::Predicate<'tcx>>>,
     ) {
         self.register_obligations(
             obligations

compiler/rustc_hir_typeck/src/fn_ctxt/inspect_obligations.rs

@@ -1,7 +1,7 @@
 //! A utility module to inspect currently ambiguous obligations in the current context.
 use crate::FnCtxt;
-use rustc_infer::traits::solve::Goal;
 use rustc_infer::traits::{self, ObligationCause};
+use rustc_middle::traits::solve::Goal;
 use rustc_middle::ty::{self, Ty, TypeVisitableExt};
 use rustc_span::Span;
 use rustc_trait_selection::solve::inspect::ProofTreeInferCtxtExt;

compiler/rustc_infer/src/infer/relate/combine.rs

@@ -339,7 +339,7 @@ impl<'infcx, 'tcx> CombineFields<'infcx, 'tcx> {
 
     pub fn register_predicates(
         &mut self,
-        obligations: impl IntoIterator<Item: Upcast<'tcx, ty::Predicate<'tcx>>>,
+        obligations: impl IntoIterator<Item: Upcast<TyCtxt<'tcx>, ty::Predicate<'tcx>>>,
     ) {
         self.obligations.extend(obligations.into_iter().map(|to_pred| {
             Obligation::new(self.infcx.tcx, self.trace.cause.clone(), self.param_env, to_pred)
@@ -365,7 +365,7 @@ pub trait ObligationEmittingRelation<'tcx>: TypeRelation<'tcx> {
     /// be used if control over the obligation causes is required.
     fn register_predicates(
         &mut self,
-        obligations: impl IntoIterator<Item: Upcast<'tcx, ty::Predicate<'tcx>>>,
+        obligations: impl IntoIterator<Item: Upcast<TyCtxt<'tcx>, ty::Predicate<'tcx>>>,
     );
 
     /// Register `AliasRelate` obligation(s) that both types must be related to each other.

compiler/rustc_infer/src/infer/relate/glb.rs

@@ -142,7 +142,7 @@ impl<'tcx> ObligationEmittingRelation<'tcx> for Glb<'_, '_, 'tcx> {
 
     fn register_predicates(
         &mut self,
-        obligations: impl IntoIterator<Item: ty::Upcast<'tcx, ty::Predicate<'tcx>>>,
+        obligations: impl IntoIterator<Item: ty::Upcast<TyCtxt<'tcx>, ty::Predicate<'tcx>>>,
     ) {
         self.fields.register_predicates(obligations);
     }

compiler/rustc_infer/src/infer/relate/lub.rs

@@ -142,7 +142,7 @@ impl<'tcx> ObligationEmittingRelation<'tcx> for Lub<'_, '_, 'tcx> {
 
     fn register_predicates(
         &mut self,
-        obligations: impl IntoIterator<Item: ty::Upcast<'tcx, ty::Predicate<'tcx>>>,
+        obligations: impl IntoIterator<Item: ty::Upcast<TyCtxt<'tcx>, ty::Predicate<'tcx>>>,
     ) {
         self.fields.register_predicates(obligations);
     }

compiler/rustc_infer/src/infer/relate/type_relating.rs

@@ -314,7 +314,7 @@ impl<'tcx> ObligationEmittingRelation<'tcx> for TypeRelating<'_, '_, 'tcx> {
 
     fn register_predicates(
         &mut self,
-        obligations: impl IntoIterator<Item: ty::Upcast<'tcx, ty::Predicate<'tcx>>>,
+        obligations: impl IntoIterator<Item: ty::Upcast<TyCtxt<'tcx>, ty::Predicate<'tcx>>>,
     ) {
         self.fields.register_predicates(obligations);
     }

compiler/rustc_infer/src/traits/mod.rs

@@ -78,9 +78,9 @@ impl<T: Hash> Hash for Obligation<'_, T> {
     }
 }
 
-impl<'tcx, P> From<Obligation<'tcx, P>> for solve::Goal<'tcx, P> {
+impl<'tcx, P> From<Obligation<'tcx, P>> for ty::Goal<'tcx, P> {
     fn from(value: Obligation<'tcx, P>) -> Self {
-        solve::Goal { param_env: value.param_env, predicate: value.predicate }
+        ty::Goal { param_env: value.param_env, predicate: value.predicate }
     }
 }
 
@@ -155,7 +155,7 @@ impl<'tcx, O> Obligation<'tcx, O> {
         tcx: TyCtxt<'tcx>,
         cause: ObligationCause<'tcx>,
         param_env: ty::ParamEnv<'tcx>,
-        predicate: impl Upcast<'tcx, O>,
+        predicate: impl Upcast<TyCtxt<'tcx>, O>,
     ) -> Obligation<'tcx, O> {
         Self::with_depth(tcx, cause, 0, param_env, predicate)
     }
@@ -173,7 +173,7 @@ impl<'tcx, O> Obligation<'tcx, O> {
         cause: ObligationCause<'tcx>,
         recursion_depth: usize,
         param_env: ty::ParamEnv<'tcx>,
-        predicate: impl Upcast<'tcx, O>,
+        predicate: impl Upcast<TyCtxt<'tcx>, O>,
     ) -> Obligation<'tcx, O> {
         let predicate = predicate.upcast(tcx);
         Obligation { cause, param_env, recursion_depth, predicate }
@@ -184,12 +184,16 @@ impl<'tcx, O> Obligation<'tcx, O> {
         span: Span,
         body_id: LocalDefId,
         param_env: ty::ParamEnv<'tcx>,
-        trait_ref: impl Upcast<'tcx, O>,
+        trait_ref: impl Upcast<TyCtxt<'tcx>, O>,
     ) -> Obligation<'tcx, O> {
         Obligation::new(tcx, ObligationCause::misc(span, body_id), param_env, trait_ref)
     }
 
-    pub fn with<P>(&self, tcx: TyCtxt<'tcx>, value: impl Upcast<'tcx, P>) -> Obligation<'tcx, P> {
+    pub fn with<P>(
+        &self,
+        tcx: TyCtxt<'tcx>,
+        value: impl Upcast<TyCtxt<'tcx>, P>,
+    ) -> Obligation<'tcx, P> {
         Obligation::with_depth(tcx, self.cause.clone(), self.recursion_depth, self.param_env, value)
     }
 }

compiler/rustc_middle/src/traits/solve.rs

@@ -8,8 +8,9 @@ use crate::traits::query::NoSolution;
 use crate::traits::Canonical;
 use crate::ty::{
     self, FallibleTypeFolder, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeVisitable, TypeVisitor,
-    Upcast,
 };
+// FIXME(compiler-errors): remove this import in favor of `use rustc_middle::ty::Goal`.
+pub use crate::ty::Goal;
 
 use super::BuiltinImplSource;
 
@@ -18,32 +19,6 @@ pub mod inspect;
 
 pub use cache::{CacheData, EvaluationCache};
 
-/// A goal is a statement, i.e. `predicate`, we want to prove
-/// given some assumptions, i.e. `param_env`.
-///
-/// Most of the time the `param_env` contains the `where`-bounds of the function
-/// we're currently typechecking while the `predicate` is some trait bound.
-#[derive(Debug, PartialEq, Eq, Clone, Copy, Hash, HashStable, TypeFoldable, TypeVisitable)]
-pub struct Goal<'tcx, P> {
-    pub predicate: P,
-    pub param_env: ty::ParamEnv<'tcx>,
-}
-
-impl<'tcx, P> Goal<'tcx, P> {
-    pub fn new(
-        tcx: TyCtxt<'tcx>,
-        param_env: ty::ParamEnv<'tcx>,
-        predicate: impl Upcast<'tcx, P>,
-    ) -> Goal<'tcx, P> {
-        Goal { param_env, predicate: predicate.upcast(tcx) }
-    }
-
-    /// Updates the goal to one with a different `predicate` but the same `param_env`.
-    pub fn with<Q>(self, tcx: TyCtxt<'tcx>, predicate: impl Upcast<'tcx, Q>) -> Goal<'tcx, Q> {
-        Goal { param_env: self.param_env, predicate: predicate.upcast(tcx) }
-    }
-}
-
 #[derive(Debug, PartialEq, Eq, Clone, Copy, Hash, HashStable, TypeFoldable, TypeVisitable)]
 pub struct Response<'tcx> {
     pub certainty: Certainty,

compiler/rustc_middle/src/ty/context.rs

@@ -132,6 +132,7 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
     type InferRegion = ty::RegionVid;
     type PlaceholderRegion = ty::PlaceholderRegion;
 
+    type ParamEnv = ty::ParamEnv<'tcx>;
     type Predicate = Predicate<'tcx>;
     type TraitPredicate = ty::TraitPredicate<'tcx>;
     type RegionOutlivesPredicate = ty::RegionOutlivesPredicate<'tcx>;

compiler/rustc_middle/src/ty/mod.rs

@@ -97,12 +97,13 @@ pub use self::parameterized::ParameterizedOverTcx;
 pub use self::pattern::{Pattern, PatternKind};
 pub use self::predicate::{
     AliasTerm, Clause, ClauseKind, CoercePredicate, ExistentialPredicate,
-    ExistentialPredicateStableCmpExt, ExistentialProjection, ExistentialTraitRef, NormalizesTo,
-    OutlivesPredicate, PolyCoercePredicate, PolyExistentialPredicate, PolyExistentialProjection,
-    PolyExistentialTraitRef, PolyProjectionPredicate, PolyRegionOutlivesPredicate,
-    PolySubtypePredicate, PolyTraitPredicate, PolyTraitRef, PolyTypeOutlivesPredicate, Predicate,
-    PredicateKind, ProjectionPredicate, RegionOutlivesPredicate, SubtypePredicate, ToPolyTraitRef,
-    TraitPredicate, TraitRef, TypeOutlivesPredicate, Upcast,
+    ExistentialPredicateStableCmpExt, ExistentialProjection, ExistentialTraitRef, Goal,
+    NormalizesTo, OutlivesPredicate, PolyCoercePredicate, PolyExistentialPredicate,
+    PolyExistentialProjection, PolyExistentialTraitRef, PolyProjectionPredicate,
+    PolyRegionOutlivesPredicate, PolySubtypePredicate, PolyTraitPredicate, PolyTraitRef,
+    PolyTypeOutlivesPredicate, Predicate, PredicateKind, ProjectionPredicate,
+    RegionOutlivesPredicate, SubtypePredicate, ToPolyTraitRef, TraitPredicate, TraitRef,
+    TypeOutlivesPredicate,
 };
 pub use self::region::{
     BoundRegion, BoundRegionKind, BoundRegionKind::*, EarlyParamRegion, LateParamRegion, Region,

compiler/rustc_middle/src/ty/predicate.rs

@@ -9,9 +9,10 @@ use std::cmp::Ordering;
 
 use crate::ty::{
     self, Binder, DebruijnIndex, EarlyBinder, PredicatePolarity, Term, Ty, TyCtxt, TypeFlags,
-    WithCachedTypeInfo,
+    Upcast, UpcastFrom, WithCachedTypeInfo,
 };
 
+pub type Goal<'tcx, P> = ir::Goal<TyCtxt<'tcx>, P>;
 pub type TraitRef<'tcx> = ir::TraitRef<TyCtxt<'tcx>>;
 pub type AliasTerm<'tcx> = ir::AliasTerm<TyCtxt<'tcx>>;
 pub type ProjectionPredicate<'tcx> = ir::ProjectionPredicate<TyCtxt<'tcx>>;
@@ -544,107 +545,82 @@ impl<'tcx> ToPolyTraitRef<'tcx> for PolyTraitPredicate<'tcx> {
     }
 }
 
-/// An `Into`-like trait that takes `TyCtxt` to perform interner-specific transformations.
-pub trait Upcast<'tcx, T> {
-    fn upcast(self, tcx: TyCtxt<'tcx>) -> T;
-}
-
-impl<'tcx, T, U> Upcast<'tcx, U> for T
-where
-    U: UpcastFrom<'tcx, T>,
-{
-    fn upcast(self, tcx: TyCtxt<'tcx>) -> U {
-        U::upcast_from(self, tcx)
-    }
-}
-
-/// A `From`-like trait that takes `TyCtxt` to perform interner-specific transformations.
-pub trait UpcastFrom<'tcx, T> {
-    fn upcast_from(from: T, tcx: TyCtxt<'tcx>) -> Self;
-}
-
-impl<'tcx, T> UpcastFrom<'tcx, T> for T {
-    fn upcast_from(from: T, _tcx: TyCtxt<'tcx>) -> Self {
-        from
-    }
-}
-
-impl<'tcx> UpcastFrom<'tcx, PredicateKind<'tcx>> for Predicate<'tcx> {
+impl<'tcx> UpcastFrom<TyCtxt<'tcx>, PredicateKind<'tcx>> for Predicate<'tcx> {
     fn upcast_from(from: PredicateKind<'tcx>, tcx: TyCtxt<'tcx>) -> Self {
         ty::Binder::dummy(from).upcast(tcx)
     }
 }
 
-impl<'tcx> UpcastFrom<'tcx, Binder<'tcx, PredicateKind<'tcx>>> for Predicate<'tcx> {
+impl<'tcx> UpcastFrom<TyCtxt<'tcx>, Binder<'tcx, PredicateKind<'tcx>>> for Predicate<'tcx> {
     fn upcast_from(from: Binder<'tcx, PredicateKind<'tcx>>, tcx: TyCtxt<'tcx>) -> Self {
         tcx.mk_predicate(from)
     }
 }
 
-impl<'tcx> UpcastFrom<'tcx, ClauseKind<'tcx>> for Predicate<'tcx> {
+impl<'tcx> UpcastFrom<TyCtxt<'tcx>, ClauseKind<'tcx>> for Predicate<'tcx> {
     fn upcast_from(from: ClauseKind<'tcx>, tcx: TyCtxt<'tcx>) -> Self {
         tcx.mk_predicate(ty::Binder::dummy(PredicateKind::Clause(from)))
     }
 }
 
-impl<'tcx> UpcastFrom<'tcx, Binder<'tcx, ClauseKind<'tcx>>> for Predicate<'tcx> {
+impl<'tcx> UpcastFrom<TyCtxt<'tcx>, Binder<'tcx, ClauseKind<'tcx>>> for Predicate<'tcx> {
     fn upcast_from(from: Binder<'tcx, ClauseKind<'tcx>>, tcx: TyCtxt<'tcx>) -> Self {
         tcx.mk_predicate(from.map_bound(PredicateKind::Clause))
     }
 }
 
-impl<'tcx> UpcastFrom<'tcx, Clause<'tcx>> for Predicate<'tcx> {
+impl<'tcx> UpcastFrom<TyCtxt<'tcx>, Clause<'tcx>> for Predicate<'tcx> {
     fn upcast_from(from: Clause<'tcx>, _tcx: TyCtxt<'tcx>) -> Self {
         from.as_predicate()
     }
 }
 
-impl<'tcx> UpcastFrom<'tcx, ClauseKind<'tcx>> for Clause<'tcx> {
+impl<'tcx> UpcastFrom<TyCtxt<'tcx>, ClauseKind<'tcx>> for Clause<'tcx> {
     fn upcast_from(from: ClauseKind<'tcx>, tcx: TyCtxt<'tcx>) -> Self {
         tcx.mk_predicate(Binder::dummy(PredicateKind::Clause(from))).expect_clause()
     }
 }
 
-impl<'tcx> UpcastFrom<'tcx, Binder<'tcx, ClauseKind<'tcx>>> for Clause<'tcx> {
+impl<'tcx> UpcastFrom<TyCtxt<'tcx>, Binder<'tcx, ClauseKind<'tcx>>> for Clause<'tcx> {
     fn upcast_from(from: Binder<'tcx, ClauseKind<'tcx>>, tcx: TyCtxt<'tcx>) -> Self {
         tcx.mk_predicate(from.map_bound(|clause| PredicateKind::Clause(clause))).expect_clause()
     }
 }
 
-impl<'tcx> UpcastFrom<'tcx, TraitRef<'tcx>> for Predicate<'tcx> {
+impl<'tcx> UpcastFrom<TyCtxt<'tcx>, TraitRef<'tcx>> for Predicate<'tcx> {
     fn upcast_from(from: TraitRef<'tcx>, tcx: TyCtxt<'tcx>) -> Self {
         ty::Binder::dummy(from).upcast(tcx)
     }
 }
 
-impl<'tcx> UpcastFrom<'tcx, TraitRef<'tcx>> for TraitPredicate<'tcx> {
+impl<'tcx> UpcastFrom<TyCtxt<'tcx>, TraitRef<'tcx>> for TraitPredicate<'tcx> {
     fn upcast_from(from: TraitRef<'tcx>, _tcx: TyCtxt<'tcx>) -> Self {
         TraitPredicate { trait_ref: from, polarity: PredicatePolarity::Positive }
     }
 }
 
-impl<'tcx> UpcastFrom<'tcx, TraitRef<'tcx>> for Clause<'tcx> {
+impl<'tcx> UpcastFrom<TyCtxt<'tcx>, TraitRef<'tcx>> for Clause<'tcx> {
     fn upcast_from(from: TraitRef<'tcx>, tcx: TyCtxt<'tcx>) -> Self {
         let p: Predicate<'tcx> = from.upcast(tcx);
         p.expect_clause()
     }
 }
 
-impl<'tcx> UpcastFrom<'tcx, Binder<'tcx, TraitRef<'tcx>>> for Predicate<'tcx> {
+impl<'tcx> UpcastFrom<TyCtxt<'tcx>, Binder<'tcx, TraitRef<'tcx>>> for Predicate<'tcx> {
     fn upcast_from(from: Binder<'tcx, TraitRef<'tcx>>, tcx: TyCtxt<'tcx>) -> Self {
         let pred: PolyTraitPredicate<'tcx> = from.upcast(tcx);
         pred.upcast(tcx)
     }
 }
 
-impl<'tcx> UpcastFrom<'tcx, Binder<'tcx, TraitRef<'tcx>>> for Clause<'tcx> {
+impl<'tcx> UpcastFrom<TyCtxt<'tcx>, Binder<'tcx, TraitRef<'tcx>>> for Clause<'tcx> {
     fn upcast_from(from: Binder<'tcx, TraitRef<'tcx>>, tcx: TyCtxt<'tcx>) -> Self {
         let pred: PolyTraitPredicate<'tcx> = from.upcast(tcx);
         pred.upcast(tcx)
     }
 }
 
-impl<'tcx> UpcastFrom<'tcx, Binder<'tcx, TraitRef<'tcx>>> for PolyTraitPredicate<'tcx> {
+impl<'tcx> UpcastFrom<TyCtxt<'tcx>, Binder<'tcx, TraitRef<'tcx>>> for PolyTraitPredicate<'tcx> {
     fn upcast_from(from: Binder<'tcx, TraitRef<'tcx>>, _tcx: TyCtxt<'tcx>) -> Self {
         from.map_bound(|trait_ref| TraitPredicate {
             trait_ref,
@@ -653,71 +629,73 @@ impl<'tcx> UpcastFrom<'tcx, Binder<'tcx, TraitRef<'tcx>>> for PolyTraitPredicate
     }
 }
 
-impl<'tcx> UpcastFrom<'tcx, TraitPredicate<'tcx>> for Predicate<'tcx> {
+impl<'tcx> UpcastFrom<TyCtxt<'tcx>, TraitPredicate<'tcx>> for Predicate<'tcx> {
     fn upcast_from(from: TraitPredicate<'tcx>, tcx: TyCtxt<'tcx>) -> Self {
         PredicateKind::Clause(ClauseKind::Trait(from)).upcast(tcx)
     }
 }
 
-impl<'tcx> UpcastFrom<'tcx, PolyTraitPredicate<'tcx>> for Predicate<'tcx> {
+impl<'tcx> UpcastFrom<TyCtxt<'tcx>, PolyTraitPredicate<'tcx>> for Predicate<'tcx> {
     fn upcast_from(from: PolyTraitPredicate<'tcx>, tcx: TyCtxt<'tcx>) -> Self {
         from.map_bound(|p| PredicateKind::Clause(ClauseKind::Trait(p))).upcast(tcx)
     }
 }
 
-impl<'tcx> UpcastFrom<'tcx, TraitPredicate<'tcx>> for Clause<'tcx> {
+impl<'tcx> UpcastFrom<TyCtxt<'tcx>, TraitPredicate<'tcx>> for Clause<'tcx> {
     fn upcast_from(from: TraitPredicate<'tcx>, tcx: TyCtxt<'tcx>) -> Self {
         let p: Predicate<'tcx> = from.upcast(tcx);
         p.expect_clause()
     }
 }
 
-impl<'tcx> UpcastFrom<'tcx, PolyTraitPredicate<'tcx>> for Clause<'tcx> {
+impl<'tcx> UpcastFrom<TyCtxt<'tcx>, PolyTraitPredicate<'tcx>> for Clause<'tcx> {
     fn upcast_from(from: PolyTraitPredicate<'tcx>, tcx: TyCtxt<'tcx>) -> Self {
         let p: Predicate<'tcx> = from.upcast(tcx);
         p.expect_clause()
     }
 }
 
-impl<'tcx> UpcastFrom<'tcx, PolyRegionOutlivesPredicate<'tcx>> for Predicate<'tcx> {
+impl<'tcx> UpcastFrom<TyCtxt<'tcx>, PolyRegionOutlivesPredicate<'tcx>> for Predicate<'tcx> {
     fn upcast_from(from: PolyRegionOutlivesPredicate<'tcx>, tcx: TyCtxt<'tcx>) -> Self {
         from.map_bound(|p| PredicateKind::Clause(ClauseKind::RegionOutlives(p))).upcast(tcx)
     }
 }
 
-impl<'tcx> UpcastFrom<'tcx, OutlivesPredicate<Ty<'tcx>, ty::Region<'tcx>>> for Predicate<'tcx> {
+impl<'tcx> UpcastFrom<TyCtxt<'tcx>, OutlivesPredicate<Ty<'tcx>, ty::Region<'tcx>>>
+    for Predicate<'tcx>
+{
     fn upcast_from(from: OutlivesPredicate<Ty<'tcx>, ty::Region<'tcx>>, tcx: TyCtxt<'tcx>) -> Self {
         ty::Binder::dummy(PredicateKind::Clause(ClauseKind::TypeOutlives(from))).upcast(tcx)
     }
 }
 
-impl<'tcx> UpcastFrom<'tcx, ProjectionPredicate<'tcx>> for Predicate<'tcx> {
+impl<'tcx> UpcastFrom<TyCtxt<'tcx>, ProjectionPredicate<'tcx>> for Predicate<'tcx> {
     fn upcast_from(from: ProjectionPredicate<'tcx>, tcx: TyCtxt<'tcx>) -> Self {
         ty::Binder::dummy(PredicateKind::Clause(ClauseKind::Projection(from))).upcast(tcx)
     }
 }
 
-impl<'tcx> UpcastFrom<'tcx, PolyProjectionPredicate<'tcx>> for Predicate<'tcx> {
+impl<'tcx> UpcastFrom<TyCtxt<'tcx>, PolyProjectionPredicate<'tcx>> for Predicate<'tcx> {
     fn upcast_from(from: PolyProjectionPredicate<'tcx>, tcx: TyCtxt<'tcx>) -> Self {
         from.map_bound(|p| PredicateKind::Clause(ClauseKind::Projection(p))).upcast(tcx)
     }
 }
 
-impl<'tcx> UpcastFrom<'tcx, ProjectionPredicate<'tcx>> for Clause<'tcx> {
+impl<'tcx> UpcastFrom<TyCtxt<'tcx>, ProjectionPredicate<'tcx>> for Clause<'tcx> {
     fn upcast_from(from: ProjectionPredicate<'tcx>, tcx: TyCtxt<'tcx>) -> Self {
         let p: Predicate<'tcx> = from.upcast(tcx);
         p.expect_clause()
     }
 }
 
-impl<'tcx> UpcastFrom<'tcx, PolyProjectionPredicate<'tcx>> for Clause<'tcx> {
+impl<'tcx> UpcastFrom<TyCtxt<'tcx>, PolyProjectionPredicate<'tcx>> for Clause<'tcx> {
     fn upcast_from(from: PolyProjectionPredicate<'tcx>, tcx: TyCtxt<'tcx>) -> Self {
         let p: Predicate<'tcx> = from.upcast(tcx);
         p.expect_clause()
     }
 }
 
-impl<'tcx> UpcastFrom<'tcx, NormalizesTo<'tcx>> for Predicate<'tcx> {
+impl<'tcx> UpcastFrom<TyCtxt<'tcx>, NormalizesTo<'tcx>> for Predicate<'tcx> {
     fn upcast_from(from: NormalizesTo<'tcx>, tcx: TyCtxt<'tcx>) -> Self {
         PredicateKind::NormalizesTo(from).upcast(tcx)
     }

compiler/rustc_trait_selection/src/solve/assembly/structural_traits.rs

@@ -6,8 +6,9 @@ use rustc_hir::{def_id::DefId, Movability, Mutability};
 use rustc_infer::traits::query::NoSolution;
 use rustc_macros::{TypeFoldable, TypeVisitable};
 use rustc_middle::bug;
-use rustc_middle::traits::solve::Goal;
-use rustc_middle::ty::{self, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable, Upcast};
+use rustc_middle::ty::{
+    self, Goal, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable, Upcast,
+};
 use rustc_span::sym;
 
 use crate::solve::EvalCtxt;

compiler/rustc_trait_selection/src/solve/mod.rs

@@ -20,11 +20,11 @@ use rustc_macros::extension;
 use rustc_middle::bug;
 use rustc_middle::infer::canonical::CanonicalVarInfos;
 use rustc_middle::traits::solve::{
-    CanonicalResponse, Certainty, ExternalConstraintsData, Goal, GoalSource, QueryResult, Response,
+    CanonicalResponse, Certainty, ExternalConstraintsData, GoalSource, QueryResult, Response,
 };
-use rustc_middle::ty::{self, AliasRelationDirection, Ty, TyCtxt, UniverseIndex};
 use rustc_middle::ty::{
-    CoercePredicate, RegionOutlivesPredicate, SubtypePredicate, TypeOutlivesPredicate,
+    self, AliasRelationDirection, CoercePredicate, Goal, RegionOutlivesPredicate, SubtypePredicate,
+    Ty, TyCtxt, TypeOutlivesPredicate, UniverseIndex,
 };
 
 mod alias_relate;

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -2703,7 +2703,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
         obligated_types: &mut Vec<Ty<'tcx>>,
         seen_requirements: &mut FxHashSet<DefId>,
     ) where
-        T: Upcast<'tcx, ty::Predicate<'tcx>>,
+        T: Upcast<TyCtxt<'tcx>, ty::Predicate<'tcx>>,
     {
         let mut long_ty_file = None;
 

compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs

@@ -302,7 +302,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
         suggest_increasing_limit: bool,
     ) -> !
     where
-        T: Upcast<'tcx, ty::Predicate<'tcx>> + Clone,
+        T: Upcast<TyCtxt<'tcx>, ty::Predicate<'tcx>> + Clone,
     {
         let predicate = obligation.predicate.clone().upcast(self.tcx);
         let predicate = self.resolve_vars_if_possible(predicate);

compiler/rustc_trait_selection/src/traits/mod.rs

@@ -142,7 +142,7 @@ pub fn type_known_to_meet_bound_modulo_regions<'tcx>(
 fn pred_known_to_hold_modulo_regions<'tcx>(
     infcx: &InferCtxt<'tcx>,
     param_env: ty::ParamEnv<'tcx>,
-    pred: impl Upcast<'tcx, ty::Predicate<'tcx>>,
+    pred: impl Upcast<TyCtxt<'tcx>, ty::Predicate<'tcx>>,
 ) -> bool {
     let obligation = Obligation::new(infcx.tcx, ObligationCause::dummy(), param_env, pred);
 

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -1378,7 +1378,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         error_obligation: &Obligation<'tcx, T>,
     ) -> Result<(), OverflowError>
     where
-        T: Upcast<'tcx, ty::Predicate<'tcx>> + Clone,
+        T: Upcast<TyCtxt<'tcx>, ty::Predicate<'tcx>> + Clone,
     {
         if !self.infcx.tcx.recursion_limit().value_within_limit(depth) {
             match self.query_mode {
@@ -1407,7 +1407,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         error_obligation: &Obligation<'tcx, V>,
     ) -> Result<(), OverflowError>
     where
-        V: Upcast<'tcx, ty::Predicate<'tcx>> + Clone,
+        V: Upcast<TyCtxt<'tcx>, ty::Predicate<'tcx>> + Clone,
     {
         self.check_recursion_depth(obligation.recursion_depth, error_obligation)
     }

compiler/rustc_type_ir/src/interner.rs

@@ -79,6 +79,7 @@ pub trait Interner:
     type PlaceholderRegion: PlaceholderLike;
 
     // Predicates
+    type ParamEnv: Copy + Debug + Hash + Eq;
     type Predicate: Predicate<Self>;
     type TraitPredicate: Copy + Debug + Hash + Eq;
     type RegionOutlivesPredicate: Copy + Debug + Hash + Eq;

compiler/rustc_type_ir/src/lib.rs

@@ -40,6 +40,7 @@ mod interner;
 mod predicate;
 mod predicate_kind;
 mod region_kind;
+mod upcast;
 
 pub use canonical::*;
 #[cfg(feature = "nightly")]
@@ -54,6 +55,7 @@ pub use predicate_kind::*;
 pub use region_kind::*;
 pub use ty_info::*;
 pub use ty_kind::*;
+pub use upcast::*;
 pub use AliasTyKind::*;
 pub use DynKind::*;
 pub use InferTy::*;

compiler/rustc_type_ir/src/predicate.rs

@@ -1,4 +1,5 @@
 use std::fmt;
+use std::hash::Hash;
 
 #[cfg(feature = "nightly")]
 use rustc_macros::{Decodable, Encodable, HashStable_NoContext, TyDecodable, TyEncodable};
@@ -7,9 +8,42 @@ use rustc_type_ir_macros::{Lift_Generic, TypeFoldable_Generic, TypeVisitable_Gen
 use crate::inherent::*;
 use crate::visit::TypeVisitableExt as _;
 use crate::{
-    AliasTy, AliasTyKind, DebugWithInfcx, InferCtxtLike, Interner, UnevaluatedConst, WithInfcx,
+    AliasTy, AliasTyKind, DebugWithInfcx, InferCtxtLike, Interner, UnevaluatedConst, Upcast,
+    WithInfcx,
 };
 
+/// A goal is a statement, i.e. `predicate`, we want to prove
+/// given some assumptions, i.e. `param_env`.
+///
+/// Most of the time the `param_env` contains the `where`-bounds of the function
+/// we're currently typechecking while the `predicate` is some trait bound.
+#[derive(derivative::Derivative)]
+#[derivative(
+    Clone(bound = "P: Clone"),
+    Copy(bound = "P: Copy"),
+    Hash(bound = "P: Hash"),
+    PartialEq(bound = "P: PartialEq"),
+    Eq(bound = "P: Eq"),
+    Debug(bound = "P: fmt::Debug")
+)]
+#[derive(TypeVisitable_Generic, TypeFoldable_Generic, Lift_Generic)]
+#[cfg_attr(feature = "nightly", derive(TyDecodable, TyEncodable, HashStable_NoContext))]
+pub struct Goal<I: Interner, P> {
+    pub param_env: I::ParamEnv,
+    pub predicate: P,
+}
+
+impl<I: Interner, P> Goal<I, P> {
+    pub fn new(tcx: I, param_env: I::ParamEnv, predicate: impl Upcast<I, P>) -> Goal<I, P> {
+        Goal { param_env, predicate: predicate.upcast(tcx) }
+    }
+
+    /// Updates the goal to one with a different `predicate` but the same `param_env`.
+    pub fn with<Q>(self, tcx: I, predicate: impl Upcast<I, Q>) -> Goal<I, Q> {
+        Goal { param_env: self.param_env, predicate: predicate.upcast(tcx) }
+    }
+}
+
 /// A complete reference to a trait. These take numerous guises in syntax,
 /// but perhaps the most recognizable form is in a where-clause:
 /// ```ignore (illustrative)

compiler/rustc_type_ir/src/upcast.rs

@@ -0,0 +1,24 @@
+/// An `Into`-like trait that takes `TyCtxt` to perform interner-specific transformations.
+pub trait Upcast<I, T> {
+    fn upcast(self, interner: I) -> T;
+}
+
+impl<I, T, U> Upcast<I, U> for T
+where
+    U: UpcastFrom<I, T>,
+{
+    fn upcast(self, interner: I) -> U {
+        U::upcast_from(self, interner)
+    }
+}
+
+/// A `From`-like trait that takes `TyCtxt` to perform interner-specific transformations.
+pub trait UpcastFrom<I, T> {
+    fn upcast_from(from: T, interner: I) -> Self;
+}
+
+impl<I, T> UpcastFrom<I, T> for T {
+    fn upcast_from(from: T, _tcx: I) -> Self {
+        from
+    }
+}