Auto merge of #107507 - BoxyUwU:deferred_projection_equality, r=lcnr

Implement `deferred_projection_equality` for erica solver

Somewhat of a revival of #96912. When relating projections now emit an `AliasEq` obligation instead of attempting to determine equality of projections that may not be as normalized as possible (i.e. because of lazy norm, or just containing inference variables that prevent us from resolving an impl). Only do this when the new solver is enabled

Author: bors

compiler/rustc_borrowck/src/type_check/relate_tys.rs

@@ -1,4 +1,4 @@
-use rustc_infer::infer::nll_relate::{NormalizationStrategy, TypeRelating, TypeRelatingDelegate};
+use rustc_infer::infer::nll_relate::{TypeRelating, TypeRelatingDelegate};
 use rustc_infer::infer::NllRegionVariableOrigin;
 use rustc_infer::traits::PredicateObligations;
 use rustc_middle::mir::ConstraintCategory;
@@ -140,10 +140,6 @@ impl<'tcx> TypeRelatingDelegate<'tcx> for NllTypeRelatingDelegate<'_, '_, 'tcx>
         );
     }
 
-    fn normalization() -> NormalizationStrategy {
-        NormalizationStrategy::Eager
-    }
-
     fn forbid_inference_vars() -> bool {
         true
     }

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -1320,6 +1320,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     ty::Clause::RegionOutlives(_) => bug!(),
                 },
                 ty::PredicateKind::WellFormed(_)
+                | ty::PredicateKind::AliasEq(..)
                 | ty::PredicateKind::ObjectSafe(_)
                 | ty::PredicateKind::ClosureKind(_, _, _)
                 | ty::PredicateKind::Subtype(_)

compiler/rustc_hir_analysis/src/impl_wf_check/min_specialization.rs

@@ -517,6 +517,7 @@ fn trait_predicate_kind<'tcx>(
         ty::PredicateKind::Clause(ty::Clause::RegionOutlives(_))
         | ty::PredicateKind::Clause(ty::Clause::TypeOutlives(_))
         | ty::PredicateKind::Clause(ty::Clause::Projection(_))
+        | ty::PredicateKind::AliasEq(..)
         | ty::PredicateKind::WellFormed(_)
         | ty::PredicateKind::Subtype(_)
         | ty::PredicateKind::Coerce(_)

compiler/rustc_hir_analysis/src/outlives/explicit.rs

@@ -55,6 +55,7 @@ impl<'tcx> ExplicitPredicatesMap<'tcx> {
                     ty::PredicateKind::Clause(ty::Clause::Trait(..))
                     | ty::PredicateKind::Clause(ty::Clause::Projection(..))
                     | ty::PredicateKind::WellFormed(..)
+                    | ty::PredicateKind::AliasEq(..)
                     | ty::PredicateKind::ObjectSafe(..)
                     | ty::PredicateKind::ClosureKind(..)
                     | ty::PredicateKind::Subtype(..)

compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

@@ -669,6 +669,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 | ty::PredicateKind::Clause(ty::Clause::TypeOutlives(..))
                 | ty::PredicateKind::WellFormed(..)
                 | ty::PredicateKind::ObjectSafe(..)
+                | ty::PredicateKind::AliasEq(..)
                 | ty::PredicateKind::ConstEvaluatable(..)
                 | ty::PredicateKind::ConstEquate(..)
                 // N.B., this predicate is created by breaking down a

compiler/rustc_hir_typeck/src/method/probe.rs

@@ -837,6 +837,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                 | ty::PredicateKind::ConstEvaluatable(..)
                 | ty::PredicateKind::ConstEquate(..)
                 | ty::PredicateKind::Ambiguous
+                | ty::PredicateKind::AliasEq(..)
                 | ty::PredicateKind::TypeWellFormedFromEnv(..) => None,
             }
         });

compiler/rustc_infer/src/infer/canonical/query_response.rs

@@ -12,7 +12,7 @@ use crate::infer::canonical::{
     Canonical, CanonicalQueryResponse, CanonicalVarValues, Certainty, OriginalQueryValues,
     QueryOutlivesConstraint, QueryRegionConstraints, QueryResponse,
 };
-use crate::infer::nll_relate::{NormalizationStrategy, TypeRelating, TypeRelatingDelegate};
+use crate::infer::nll_relate::{TypeRelating, TypeRelatingDelegate};
 use crate::infer::region_constraints::{Constraint, RegionConstraintData};
 use crate::infer::{InferCtxt, InferOk, InferResult, NllRegionVariableOrigin};
 use crate::traits::query::{Fallible, NoSolution};
@@ -717,10 +717,6 @@ impl<'tcx> TypeRelatingDelegate<'tcx> for QueryTypeRelatingDelegate<'_, 'tcx> {
         });
     }
 
-    fn normalization() -> NormalizationStrategy {
-        NormalizationStrategy::Eager
-    }
-
     fn forbid_inference_vars() -> bool {
         true
     }

compiler/rustc_infer/src/infer/combine.rs

@@ -38,8 +38,8 @@ use rustc_middle::ty::error::{ExpectedFound, TypeError};
 use rustc_middle::ty::relate::{self, Relate, RelateResult, TypeRelation};
 use rustc_middle::ty::subst::SubstsRef;
 use rustc_middle::ty::{
-    self, FallibleTypeFolder, InferConst, Ty, TyCtxt, TypeFoldable, TypeSuperFoldable,
-    TypeVisitable,
+    self, AliasKind, FallibleTypeFolder, InferConst, ToPredicate, Ty, TyCtxt, TypeFoldable,
+    TypeSuperFoldable, TypeVisitable,
 };
 use rustc_middle::ty::{IntType, UintType};
 use rustc_span::{Span, DUMMY_SP};
@@ -74,7 +74,7 @@ impl<'tcx> InferCtxt<'tcx> {
         b: Ty<'tcx>,
     ) -> RelateResult<'tcx, Ty<'tcx>>
     where
-        R: TypeRelation<'tcx>,
+        R: ObligationEmittingRelation<'tcx>,
     {
         let a_is_expected = relation.a_is_expected();
 
@@ -122,6 +122,15 @@ impl<'tcx> InferCtxt<'tcx> {
                 Err(TypeError::Sorts(ty::relate::expected_found(relation, a, b)))
             }
 
+            (ty::Alias(AliasKind::Projection, _), _) if self.tcx.trait_solver_next() => {
+                relation.register_type_equate_obligation(a.into(), b.into());
+                Ok(b)
+            }
+            (_, ty::Alias(AliasKind::Projection, _)) if self.tcx.trait_solver_next() => {
+                relation.register_type_equate_obligation(b.into(), a.into());
+                Ok(a)
+            }
+
             _ => ty::relate::super_relate_tys(relation, a, b),
         }
     }
@@ -133,7 +142,7 @@ impl<'tcx> InferCtxt<'tcx> {
         b: ty::Const<'tcx>,
     ) -> RelateResult<'tcx, ty::Const<'tcx>>
     where
-        R: ConstEquateRelation<'tcx>,
+        R: ObligationEmittingRelation<'tcx>,
     {
         debug!("{}.consts({:?}, {:?})", relation.tag(), a, b);
         if a == b {
@@ -169,15 +178,15 @@ impl<'tcx> InferCtxt<'tcx> {
                 // FIXME(#59490): Need to remove the leak check to accommodate
                 // escaping bound variables here.
                 if !a.has_escaping_bound_vars() && !b.has_escaping_bound_vars() {
-                    relation.const_equate_obligation(a, b);
+                    relation.register_const_equate_obligation(a, b);
                 }
                 return Ok(b);
             }
             (_, ty::ConstKind::Unevaluated(..)) if self.tcx.lazy_normalization() => {
                 // FIXME(#59490): Need to remove the leak check to accommodate
                 // escaping bound variables here.
                 if !a.has_escaping_bound_vars() && !b.has_escaping_bound_vars() {
-                    relation.const_equate_obligation(a, b);
+                    relation.register_const_equate_obligation(a, b);
                 }
                 return Ok(a);
             }
@@ -435,32 +444,21 @@ impl<'infcx, 'tcx> CombineFields<'infcx, 'tcx> {
         Ok(Generalization { ty, needs_wf })
     }
 
-    pub fn add_const_equate_obligation(
+    pub fn register_obligations(&mut self, obligations: PredicateObligations<'tcx>) {
+        self.obligations.extend(obligations.into_iter());
+    }
+
+    pub fn register_predicates(
         &mut self,
-        a_is_expected: bool,
-        a: ty::Const<'tcx>,
-        b: ty::Const<'tcx>,
+        obligations: impl IntoIterator<Item = impl ToPredicate<'tcx>>,
     ) {
-        let predicate = if a_is_expected {
-            ty::PredicateKind::ConstEquate(a, b)
-        } else {
-            ty::PredicateKind::ConstEquate(b, a)
-        };
-        self.obligations.push(Obligation::new(
-            self.tcx(),
-            self.trace.cause.clone(),
-            self.param_env,
-            ty::Binder::dummy(predicate),
-        ));
+        self.obligations.extend(obligations.into_iter().map(|to_pred| {
+            Obligation::new(self.infcx.tcx, self.trace.cause.clone(), self.param_env, to_pred)
+        }))
     }
 
     pub fn mark_ambiguous(&mut self) {
-        self.obligations.push(Obligation::new(
-            self.tcx(),
-            self.trace.cause.clone(),
-            self.param_env,
-            ty::Binder::dummy(ty::PredicateKind::Ambiguous),
-        ));
+        self.register_predicates([ty::Binder::dummy(ty::PredicateKind::Ambiguous)]);
     }
 }
 
@@ -779,11 +777,42 @@ impl<'tcx> TypeRelation<'tcx> for Generalizer<'_, 'tcx> {
     }
 }
 
-pub trait ConstEquateRelation<'tcx>: TypeRelation<'tcx> {
+pub trait ObligationEmittingRelation<'tcx>: TypeRelation<'tcx> {
+    /// Register obligations that must hold in order for this relation to hold
+    fn register_obligations(&mut self, obligations: PredicateObligations<'tcx>);
+
+    /// Register predicates that must hold in order for this relation to hold. Uses
+    /// a default obligation cause, [`ObligationEmittingRelation::register_obligations`] should
+    /// be used if control over the obligaton causes is required.
+    fn register_predicates(
+        &mut self,
+        obligations: impl IntoIterator<Item = impl ToPredicate<'tcx>>,
+    );
+
     /// Register an obligation that both constants must be equal to each other.
     ///
     /// If they aren't equal then the relation doesn't hold.
-    fn const_equate_obligation(&mut self, a: ty::Const<'tcx>, b: ty::Const<'tcx>);
+    fn register_const_equate_obligation(&mut self, a: ty::Const<'tcx>, b: ty::Const<'tcx>) {
+        let (a, b) = if self.a_is_expected() { (a, b) } else { (b, a) };
+
+        self.register_predicates([ty::Binder::dummy(if self.tcx().trait_solver_next() {
+            ty::PredicateKind::AliasEq(a.into(), b.into())
+        } else {
+            ty::PredicateKind::ConstEquate(a, b)
+        })]);
+    }
+
+    /// Register an obligation that both types must be equal to each other.
+    ///
+    /// If they aren't equal then the relation doesn't hold.
+    fn register_type_equate_obligation(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) {
+        let (a, b) = if self.a_is_expected() { (a, b) } else { (b, a) };
+
+        self.register_predicates([ty::Binder::dummy(ty::PredicateKind::AliasEq(
+            a.into(),
+            b.into(),
+        ))]);
+    }
 }
 
 fn int_unification_error<'tcx>(

compiler/rustc_infer/src/infer/equate.rs

@@ -1,4 +1,6 @@
-use super::combine::{CombineFields, ConstEquateRelation, RelationDir};
+use crate::traits::PredicateObligations;
+
+use super::combine::{CombineFields, ObligationEmittingRelation, RelationDir};
 use super::Subtype;
 
 use rustc_middle::ty::relate::{self, Relate, RelateResult, TypeRelation};
@@ -198,8 +200,15 @@ impl<'tcx> TypeRelation<'tcx> for Equate<'_, '_, 'tcx> {
     }
 }
 
-impl<'tcx> ConstEquateRelation<'tcx> for Equate<'_, '_, 'tcx> {
-    fn const_equate_obligation(&mut self, a: ty::Const<'tcx>, b: ty::Const<'tcx>) {
-        self.fields.add_const_equate_obligation(self.a_is_expected, a, b);
+impl<'tcx> ObligationEmittingRelation<'tcx> for Equate<'_, '_, 'tcx> {
+    fn register_predicates(
+        &mut self,
+        obligations: impl IntoIterator<Item = impl ty::ToPredicate<'tcx>>,
+    ) {
+        self.fields.register_predicates(obligations);
+    }
+
+    fn register_obligations(&mut self, obligations: PredicateObligations<'tcx>) {
+        self.fields.register_obligations(obligations);
     }
 }

compiler/rustc_infer/src/infer/glb.rs

@@ -1,12 +1,11 @@
 //! Greatest lower bound. See [`lattice`].
 
-use super::combine::CombineFields;
+use super::combine::{CombineFields, ObligationEmittingRelation};
 use super::lattice::{self, LatticeDir};
 use super::InferCtxt;
 use super::Subtype;
 
-use crate::infer::combine::ConstEquateRelation;
-use crate::traits::{ObligationCause, PredicateObligation};
+use crate::traits::{ObligationCause, PredicateObligations};
 use rustc_middle::ty::relate::{Relate, RelateResult, TypeRelation};
 use rustc_middle::ty::{self, Ty, TyCtxt};
 
@@ -136,10 +135,6 @@ impl<'combine, 'infcx, 'tcx> LatticeDir<'infcx, 'tcx> for Glb<'combine, 'infcx,
         &self.fields.trace.cause
     }
 
-    fn add_obligations(&mut self, obligations: Vec<PredicateObligation<'tcx>>) {
-        self.fields.obligations.extend(obligations)
-    }
-
     fn relate_bound(&mut self, v: Ty<'tcx>, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, ()> {
         let mut sub = self.fields.sub(self.a_is_expected);
         sub.relate(v, a)?;
@@ -152,8 +147,15 @@ impl<'combine, 'infcx, 'tcx> LatticeDir<'infcx, 'tcx> for Glb<'combine, 'infcx,
     }
 }
 
-impl<'tcx> ConstEquateRelation<'tcx> for Glb<'_, '_, 'tcx> {
-    fn const_equate_obligation(&mut self, a: ty::Const<'tcx>, b: ty::Const<'tcx>) {
-        self.fields.add_const_equate_obligation(self.a_is_expected, a, b);
+impl<'tcx> ObligationEmittingRelation<'tcx> for Glb<'_, '_, 'tcx> {
+    fn register_predicates(
+        &mut self,
+        obligations: impl IntoIterator<Item = impl ty::ToPredicate<'tcx>>,
+    ) {
+        self.fields.register_predicates(obligations);
+    }
+
+    fn register_obligations(&mut self, obligations: PredicateObligations<'tcx>) {
+        self.fields.register_obligations(obligations);
     }
 }