Instantiate predicate binder without recanonicalizing goal in new solver

compiler/rustc_hir_typeck/src/fn_ctxt/inspect_obligations.rs

@@ -1,7 +1,6 @@
 //! A utility module to inspect currently ambiguous obligations in the current context.
 
 use rustc_infer::traits::{self, ObligationCause, PredicateObligations};
-use rustc_middle::traits::solve::GoalSource;
 use rustc_middle::ty::{self, Ty, TypeVisitableExt};
 use rustc_span::Span;
 use rustc_trait_selection::solve::inspect::{
@@ -119,21 +118,7 @@ impl<'a, 'tcx> ProofTreeVisitor<'tcx> for NestedObligationsForSelfTy<'a, 'tcx> {
     fn visit_goal(&mut self, inspect_goal: &InspectGoal<'_, 'tcx>) {
         let tcx = self.fcx.tcx;
         let goal = inspect_goal.goal();
-        if self.fcx.predicate_has_self_ty(goal.predicate, self.self_ty)
-            // We do not push the instantiated forms of goals as it would cause any
-            // aliases referencing bound vars to go from having escaping bound vars to
-            // being able to be normalized to an inference variable.
-            //
-            // This is mostly just a hack as arbitrary nested goals could still contain
-            // such aliases while having a different `GoalSource`. Closure signature inference
-            // however can't really handle *every* higher ranked `Fn` goal also being present
-            // in the form of `?c: Fn<(<?x as Trait<'!a>>::Assoc)`.
-            //
-            // This also just better matches the behaviour of the old solver where we do not
-            // encounter instantiated forms of goals, only nested goals that referred to bound
-            // vars from instantiated goals.
-            && !matches!(inspect_goal.source(), GoalSource::InstantiateHigherRanked)
-        {
+        if self.fcx.predicate_has_self_ty(goal.predicate, self.self_ty) {
             self.obligations_for_self_ty.push(traits::Obligation::new(
                 tcx,
                 self.root_cause.clone(),

compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs

@@ -275,9 +275,6 @@ where
             // corecursive functions as explained in #136824, relating types never
             // introduces a constructor which could cause the recursion to be guarded.
             GoalSource::TypeRelating => PathKind::Inductive,
-            // Instantiating a higher ranked goal can never cause the recursion to be
-            // guarded and is therefore unproductive.
-            GoalSource::InstantiateHigherRanked => PathKind::Inductive,
             // These goal sources are likely unproductive and can be changed to
             // `PathKind::Inductive`. Keeping them as unknown until we're confident
             // about this and have an example where it is necessary.
@@ -500,63 +497,53 @@ where
     fn compute_goal(&mut self, goal: Goal<I, I::Predicate>) -> QueryResult<I> {
         let Goal { param_env, predicate } = goal;
         let kind = predicate.kind();
-        if let Some(kind) = kind.no_bound_vars() {
-            match kind {
-                ty::PredicateKind::Clause(ty::ClauseKind::Trait(predicate)) => {
-                    self.compute_trait_goal(Goal { param_env, predicate }).map(|(r, _via)| r)
-                }
-                ty::PredicateKind::Clause(ty::ClauseKind::HostEffect(predicate)) => {
-                    self.compute_host_effect_goal(Goal { param_env, predicate })
-                }
-                ty::PredicateKind::Clause(ty::ClauseKind::Projection(predicate)) => {
-                    self.compute_projection_goal(Goal { param_env, predicate })
-                }
-                ty::PredicateKind::Clause(ty::ClauseKind::TypeOutlives(predicate)) => {
-                    self.compute_type_outlives_goal(Goal { param_env, predicate })
-                }
-                ty::PredicateKind::Clause(ty::ClauseKind::RegionOutlives(predicate)) => {
-                    self.compute_region_outlives_goal(Goal { param_env, predicate })
-                }
-                ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType(ct, ty)) => {
-                    self.compute_const_arg_has_type_goal(Goal { param_env, predicate: (ct, ty) })
-                }
-                ty::PredicateKind::Subtype(predicate) => {
-                    self.compute_subtype_goal(Goal { param_env, predicate })
-                }
-                ty::PredicateKind::Coerce(predicate) => {
-                    self.compute_coerce_goal(Goal { param_env, predicate })
-                }
-                ty::PredicateKind::DynCompatible(trait_def_id) => {
-                    self.compute_dyn_compatible_goal(trait_def_id)
-                }
-                ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(term)) => {
-                    self.compute_well_formed_goal(Goal { param_env, predicate: term })
-                }
-                ty::PredicateKind::Clause(ty::ClauseKind::ConstEvaluatable(ct)) => {
-                    self.compute_const_evaluatable_goal(Goal { param_env, predicate: ct })
-                }
-                ty::PredicateKind::ConstEquate(_, _) => {
-                    panic!("ConstEquate should not be emitted when `-Znext-solver` is active")
-                }
-                ty::PredicateKind::NormalizesTo(predicate) => {
-                    self.compute_normalizes_to_goal(Goal { param_env, predicate })
-                }
-                ty::PredicateKind::AliasRelate(lhs, rhs, direction) => self
-                    .compute_alias_relate_goal(Goal {
-                        param_env,
-                        predicate: (lhs, rhs, direction),
-                    }),
-                ty::PredicateKind::Ambiguous => {
-                    self.evaluate_added_goals_and_make_canonical_response(Certainty::AMBIGUOUS)
-                }
+        self.enter_forall(kind, |ecx, kind| match kind {
+            ty::PredicateKind::Clause(ty::ClauseKind::Trait(predicate)) => {
+                ecx.compute_trait_goal(Goal { param_env, predicate }).map(|(r, _via)| r)
             }
-        } else {
-            self.enter_forall(kind, |ecx, kind| {
-                let goal = goal.with(ecx.cx(), ty::Binder::dummy(kind));
-                ecx.add_goal(GoalSource::InstantiateHigherRanked, goal);
-                ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
-            })
-        }
+            ty::PredicateKind::Clause(ty::ClauseKind::HostEffect(predicate)) => {
+                ecx.compute_host_effect_goal(Goal { param_env, predicate })
+            }
+            ty::PredicateKind::Clause(ty::ClauseKind::Projection(predicate)) => {
+                ecx.compute_projection_goal(Goal { param_env, predicate })
+            }
+            ty::PredicateKind::Clause(ty::ClauseKind::TypeOutlives(predicate)) => {
+                ecx.compute_type_outlives_goal(Goal { param_env, predicate })
+            }
+            ty::PredicateKind::Clause(ty::ClauseKind::RegionOutlives(predicate)) => {
+                ecx.compute_region_outlives_goal(Goal { param_env, predicate })
+            }
+            ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType(ct, ty)) => {
+                ecx.compute_const_arg_has_type_goal(Goal { param_env, predicate: (ct, ty) })
+            }
+            ty::PredicateKind::Subtype(predicate) => {
+                ecx.compute_subtype_goal(Goal { param_env, predicate })
+            }
+            ty::PredicateKind::Coerce(predicate) => {
+                ecx.compute_coerce_goal(Goal { param_env, predicate })
+            }
+            ty::PredicateKind::DynCompatible(trait_def_id) => {
+                ecx.compute_dyn_compatible_goal(trait_def_id)
+            }
+            ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(arg)) => {
+                ecx.compute_well_formed_goal(Goal { param_env, predicate: arg })
+            }
+            ty::PredicateKind::Clause(ty::ClauseKind::ConstEvaluatable(ct)) => {
+                ecx.compute_const_evaluatable_goal(Goal { param_env, predicate: ct })
+            }
+            ty::PredicateKind::ConstEquate(_, _) => {
+                panic!("ConstEquate should not be emitted when `-Znext-solver` is active")
+            }
+            ty::PredicateKind::NormalizesTo(predicate) => {
+                ecx.compute_normalizes_to_goal(Goal { param_env, predicate })
+            }
+            ty::PredicateKind::AliasRelate(lhs, rhs, direction) => {
+                ecx.compute_alias_relate_goal(Goal { param_env, predicate: (lhs, rhs, direction) })
+            }
+            ty::PredicateKind::Ambiguous => {
+                ecx.evaluate_added_goals_and_make_canonical_response(Certainty::AMBIGUOUS)
+            }
+        })
     }
 
     // Recursively evaluates all the goals added to this `EvalCtxt` to completion, returning

compiler/rustc_trait_selection/src/solve/fulfill/derive_errors.rs

@@ -221,7 +221,6 @@ impl<'tcx> BestObligation<'tcx> {
                                         nested_goal.source(),
                                         GoalSource::ImplWhereBound
                                             | GoalSource::AliasBoundConstCondition
-                                            | GoalSource::InstantiateHigherRanked
                                             | GoalSource::AliasWellFormed
                                     ) && nested_goal.result().is_err()
                                 },
@@ -511,10 +510,6 @@ impl<'tcx> ProofTreeVisitor<'tcx> for BestObligation<'tcx> {
                     ));
                     impl_where_bound_count += 1;
                 }
-                // Skip over a higher-ranked predicate.
-                (_, GoalSource::InstantiateHigherRanked) => {
-                    obligation = self.obligation.clone();
-                }
                 (ChildMode::PassThrough, _)
                 | (_, GoalSource::AliasWellFormed | GoalSource::AliasBoundConstCondition) => {
                     obligation = make_obligation(self.obligation.cause.clone());

compiler/rustc_trait_selection/src/traits/coherence.rs

@@ -661,9 +661,10 @@ impl<'a, 'tcx> ProofTreeVisitor<'tcx> for AmbiguityCausesVisitor<'a, 'tcx> {
         // For bound predicates we simply call `infcx.enter_forall`
         // and then prove the resulting predicate as a nested goal.
         let Goal { param_env, predicate } = goal.goal();
-        let trait_ref = match predicate.kind().no_bound_vars() {
-            Some(ty::PredicateKind::Clause(ty::ClauseKind::Trait(tr))) => tr.trait_ref,
-            Some(ty::PredicateKind::Clause(ty::ClauseKind::Projection(proj)))
+        let predicate_kind = goal.infcx().enter_forall_and_leak_universe(predicate.kind());
+        let trait_ref = match predicate_kind {
+            ty::PredicateKind::Clause(ty::ClauseKind::Trait(tr)) => tr.trait_ref,
+            ty::PredicateKind::Clause(ty::ClauseKind::Projection(proj))
                 if matches!(
                     infcx.tcx.def_kind(proj.projection_term.def_id),
                     DefKind::AssocTy | DefKind::AssocConst

compiler/rustc_type_ir/src/solve/mod.rs

@@ -80,8 +80,6 @@ pub enum GoalSource {
     ImplWhereBound,
     /// Const conditions that need to hold for `~const` alias bounds to hold.
     AliasBoundConstCondition,
-    /// Instantiating a higher-ranked goal and re-proving it.
-    InstantiateHigherRanked,
     /// Predicate required for an alias projection to be well-formed.
     /// This is used in three places:
     /// 1. projecting to an opaque whose hidden type is already registered in

tests/ui/coherence/coherence-overlap-unnormalizable-projection-1.stderr

@@ -12,7 +12,7 @@ LL |   impl<T> Trait for Box<T> {}
    |   ^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `Box<_>`
    |
    = note: downstream crates may implement trait `WithAssoc<'a>` for type `std::boxed::Box<_>`
-   = note: downstream crates may implement trait `WhereBound` for type `std::boxed::Box<_>`
+   = note: downstream crates may implement trait `WhereBound` for type `std::boxed::Box<<std::boxed::Box<_> as WithAssoc<'a>>::Assoc>`
 
 error: aborting due to 1 previous error
 

tests/ui/higher-ranked/leak-check/candidate-from-env-universe-err-1.rs

@@ -1,6 +1,6 @@
 //@ revisions: old next
 //@[next] compile-flags: -Znext-solver
-//@[old] check-pass
+//@ check-pass
 
 // cc #119820
 
@@ -25,7 +25,6 @@ where
     // the leak check both candidates may apply and we prefer the
     // `param_env` candidate in winnowing.
     hr_bound::<&T>();
-    //[next]~^ ERROR the trait bound `for<'a> &'a &T: Trait` is not satisfied
 }
 
 fn main() {}

tests/ui/higher-ranked/leak-check/candidate-from-env-universe-err-2.rs

@@ -1,6 +1,6 @@
 //@ revisions: current next
 //@[next] compile-flags: -Znext-solver
-//@[current] check-pass
+//@ check-pass
 
 // cc #119820
 
@@ -13,7 +13,6 @@ fn impl_hr<'b, T: for<'a> Trait<'a, 'b>>() {}
 
 fn not_hr<'a, T: for<'b> Trait<'a, 'b> + OtherTrait<'static>>() {
     impl_hr::<T>();
-    //[next]~^ ERROR the trait bound `for<'a> T: Trait<'a, '_>` is not satisfied
 }
 
 fn main() {}

tests/ui/higher-ranked/leak-check/candidate-from-env-universe-err-project.current.stderr

@@ -1,5 +1,5 @@
 error[E0308]: mismatched types
-  --> $DIR/candidate-from-env-universe-err-project.rs:38:5
+  --> $DIR/candidate-from-env-universe-err-project.rs:37:5
    |
 LL |     projection_bound::<T>();
    |     ^^^^^^^^^^^^^^^^^^^^^^^ one type is more general than the other
@@ -13,7 +13,7 @@ LL | fn projection_bound<T: for<'a> Trait<'a, Assoc = usize>>() {}
    |                                          ^^^^^^^^^^^^^
 
 error[E0308]: mismatched types
-  --> $DIR/candidate-from-env-universe-err-project.rs:52:30
+  --> $DIR/candidate-from-env-universe-err-project.rs:51:30
    |
 LL |     let _higher_ranked_norm: for<'a> fn(<T as Trait<'a>>::Assoc) = |_| ();
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ one type is more general than the other
@@ -22,7 +22,7 @@ LL |     let _higher_ranked_norm: for<'a> fn(<T as Trait<'a>>::Assoc) = |_| ();
               found associated type `<T as Trait<'a>>::Assoc`
 
 error[E0308]: mismatched types
-  --> $DIR/candidate-from-env-universe-err-project.rs:52:30
+  --> $DIR/candidate-from-env-universe-err-project.rs:51:30
    |
 LL |     let _higher_ranked_norm: for<'a> fn(<T as Trait<'a>>::Assoc) = |_| ();
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ one type is more general than the other

tests/ui/higher-ranked/leak-check/candidate-from-env-universe-err-project.next.stderr

@@ -1,41 +1,34 @@
-error[E0277]: the trait bound `for<'a> T: Trait<'a>` is not satisfied
-  --> $DIR/candidate-from-env-universe-err-project.rs:28:19
-   |
-LL |     trait_bound::<T>();
-   |                   ^ the trait `for<'a> Trait<'a>` is not implemented for `T`
-   |
-note: required by a bound in `trait_bound`
-  --> $DIR/candidate-from-env-universe-err-project.rs:17:19
-   |
-LL | fn trait_bound<T: for<'a> Trait<'a>>() {}
-   |                   ^^^^^^^^^^^^^^^^^ required by this bound in `trait_bound`
-
-error[E0277]: the trait bound `for<'a> T: Trait<'a>` is not satisfied
-  --> $DIR/candidate-from-env-universe-err-project.rs:38:24
+error[E0271]: type mismatch resolving `<T as Trait<'a>>::Assoc == usize`
+  --> $DIR/candidate-from-env-universe-err-project.rs:37:24
    |
 LL |     projection_bound::<T>();
-   |                        ^ the trait `for<'a> Trait<'a>` is not implemented for `T`
+   |                        ^ type mismatch resolving `<T as Trait<'a>>::Assoc == usize`
+   |
+note: types differ
+  --> $DIR/candidate-from-env-universe-err-project.rs:14:18
    |
+LL |     type Assoc = usize;
+   |                  ^^^^^
 note: required by a bound in `projection_bound`
-  --> $DIR/candidate-from-env-universe-err-project.rs:18:24
+  --> $DIR/candidate-from-env-universe-err-project.rs:18:42
    |
 LL | fn projection_bound<T: for<'a> Trait<'a, Assoc = usize>>() {}
-   |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `projection_bound`
+   |                                          ^^^^^^^^^^^^^ required by this bound in `projection_bound`
 
 error: higher-ranked subtype error
-  --> $DIR/candidate-from-env-universe-err-project.rs:52:30
+  --> $DIR/candidate-from-env-universe-err-project.rs:51:30
    |
 LL |     let _higher_ranked_norm: for<'a> fn(<T as Trait<'a>>::Assoc) = |_| ();
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: higher-ranked subtype error
-  --> $DIR/candidate-from-env-universe-err-project.rs:52:30
+  --> $DIR/candidate-from-env-universe-err-project.rs:51:30
    |
 LL |     let _higher_ranked_norm: for<'a> fn(<T as Trait<'a>>::Assoc) = |_| ();
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
-error: aborting due to 4 previous errors
+error: aborting due to 3 previous errors
 
-For more information about this error, try `rustc --explain E0277`.
+For more information about this error, try `rustc --explain E0271`.

tests/ui/higher-ranked/leak-check/candidate-from-env-universe-err-project.rs

@@ -20,13 +20,12 @@ fn projection_bound<T: for<'a> Trait<'a, Assoc = usize>>() {}
 // We use a function with a trivial where-bound which is more
 // restrictive than the impl.
 fn function1<T: Trait<'static>>() {
-    // err
+    // ok
     //
     // Proving `for<'a> T: Trait<'a>` using the where-bound does not
     // result in a leak check failure even though it does not apply.
     // We prefer env candidates over impl candidatescausing this to succeed.
     trait_bound::<T>();
-    //[next]~^ ERROR the trait bound `for<'a> T: Trait<'a>` is not satisfied
 }
 
 fn function2<T: Trait<'static, Assoc = usize>>() {
@@ -36,7 +35,7 @@ fn function2<T: Trait<'static, Assoc = usize>>() {
     // does not use the leak check when trying the where-bound, causing us
     // to prefer it over the impl, resulting in a placeholder error.
     projection_bound::<T>();
-    //[next]~^ ERROR the trait bound `for<'a> T: Trait<'a>` is not satisfied
+    //[next]~^ ERROR type mismatch resolving `<T as Trait<'a>>::Assoc == usize`
     //[current]~^^ ERROR mismatched types
 }