-Ztrait-solver=next: stop depending on old solver

compiler/rustc_infer/src/infer/projection.rs

@@ -21,29 +21,18 @@ impl<'tcx> InferCtxt<'tcx> {
         recursion_depth: usize,
         obligations: &mut Vec<PredicateObligation<'tcx>>,
     ) -> Ty<'tcx> {
-        if self.next_trait_solver() {
-            // FIXME(-Ztrait-solver=next): Instead of branching here,
-            // completely change the normalization routine with the new solver.
-            //
-            // The new solver correctly handles projection equality so this hack
-            // is not necessary. if re-enabled it should emit `PredicateKind::AliasRelate`
-            // not `PredicateKind::Clause(ClauseKind::Projection(..))` as in the new solver
-            // `Projection` is used as `normalizes-to` which will fail for `<T as Trait>::Assoc eq ?0`.
-            return projection_ty.to_ty(self.tcx);
-        } else {
-            let def_id = projection_ty.def_id;
-            let ty_var = self.next_ty_var(TypeVariableOrigin {
-                kind: TypeVariableOriginKind::NormalizeProjectionType,
-                span: self.tcx.def_span(def_id),
-            });
-            let projection =
-                ty::Binder::dummy(ty::PredicateKind::Clause(ty::ClauseKind::Projection(
-                    ty::ProjectionPredicate { projection_ty, term: ty_var.into() },
-                )));
-            let obligation =
-                Obligation::with_depth(self.tcx, cause, recursion_depth, param_env, projection);
-            obligations.push(obligation);
-            ty_var
-        }
+        debug_assert!(!self.next_trait_solver());
+        let def_id = projection_ty.def_id;
+        let ty_var = self.next_ty_var(TypeVariableOrigin {
+            kind: TypeVariableOriginKind::NormalizeProjectionType,
+            span: self.tcx.def_span(def_id),
+        });
+        let projection = ty::Binder::dummy(ty::PredicateKind::Clause(ty::ClauseKind::Projection(
+            ty::ProjectionPredicate { projection_ty, term: ty_var.into() },
+        )));
+        let obligation =
+            Obligation::with_depth(self.tcx, cause, recursion_depth, param_env, projection);
+        obligations.push(obligation);
+        ty_var
     }
 }

compiler/rustc_trait_selection/src/solve/normalize.rs

@@ -159,6 +159,7 @@ impl<'tcx> FallibleTypeFolder<TyCtxt<'tcx>> for NormalizationFolder<'_, 'tcx> {
     fn try_fold_ty(&mut self, ty: Ty<'tcx>) -> Result<Ty<'tcx>, Self::Error> {
         let reveal = self.at.param_env.reveal();
         let infcx = self.at.infcx;
+        debug_assert_eq!(ty, infcx.shallow_resolve(ty));
         if !needs_normalization(&ty, reveal) {
             return Ok(ty);
         }
@@ -192,6 +193,7 @@ impl<'tcx> FallibleTypeFolder<TyCtxt<'tcx>> for NormalizationFolder<'_, 'tcx> {
     fn try_fold_const(&mut self, ct: ty::Const<'tcx>) -> Result<ty::Const<'tcx>, Self::Error> {
         let reveal = self.at.param_env.reveal();
         let infcx = self.at.infcx;
+        debug_assert_eq!(ct, infcx.shallow_resolve(ct));
         if !needs_normalization(&ct, reveal) {
             return Ok(ct);
         }

compiler/rustc_trait_selection/src/traits/coherence.rs

@@ -30,6 +30,7 @@ use std::fmt::Debug;
 use std::iter;
 use std::ops::ControlFlow;
 
+use super::query::evaluate_obligation::InferCtxtExt;
 use super::NormalizeExt;
 
 /// Whether we do the orphan check relative to this crate or
@@ -290,19 +291,28 @@ fn impl_intersection_has_impossible_obligation<'cx, 'tcx>(
 ) -> bool {
     let infcx = selcx.infcx;
 
+    let obligation_guaranteed_to_fail = move |obligation: &PredicateObligation<'tcx>| {
+        if infcx.next_trait_solver() {
+            infcx.evaluate_obligation(obligation).map_or(false, |result| !result.may_apply())
+        } else {
+            // We use `evaluate_root_obligation` to correctly track
+            // intercrate ambiguity clauses. We do not need this in the
+            // new solver.
+            selcx.evaluate_root_obligation(obligation).map_or(
+                false, // Overflow has occurred, and treat the obligation as possibly holding.
+                |result| !result.may_apply(),
+            )
+        }
+    };
+
     let opt_failing_obligation = [&impl1_header.predicates, &impl2_header.predicates]
         .into_iter()
         .flatten()
         .map(|&predicate| {
             Obligation::new(infcx.tcx, ObligationCause::dummy(), param_env, predicate)
         })
         .chain(obligations)
-        .find(|o| {
-            selcx.evaluate_root_obligation(o).map_or(
-                false, // Overflow has occurred, and treat the obligation as possibly holding.
-                |result| !result.may_apply(),
-            )
-        });
+        .find(obligation_guaranteed_to_fail);
 
     if let Some(failing_obligation) = opt_failing_obligation {
         debug!("overlap: obligation unsatisfiable {:?}", failing_obligation);

compiler/rustc_trait_selection/src/traits/project.rs

@@ -447,6 +447,7 @@ impl<'a, 'b, 'tcx> AssocTypeNormalizer<'a, 'b, 'tcx> {
         depth: usize,
         obligations: &'a mut Vec<PredicateObligation<'tcx>>,
     ) -> AssocTypeNormalizer<'a, 'b, 'tcx> {
+        debug_assert!(!selcx.infcx.next_trait_solver());
         AssocTypeNormalizer {
             selcx,
             param_env,
@@ -1122,6 +1123,7 @@ fn opt_normalize_projection_type<'a, 'b, 'tcx>(
     obligations: &mut Vec<PredicateObligation<'tcx>>,
 ) -> Result<Option<Term<'tcx>>, InProgress> {
     let infcx = selcx.infcx;
+    debug_assert!(!selcx.infcx.next_trait_solver());
     // Don't use the projection cache in intercrate mode -
     // the `infcx` may be re-used between intercrate in non-intercrate
     // mode, which could lead to using incorrect cache results.

compiler/rustc_trait_selection/src/traits/query/evaluate_obligation.rs

@@ -97,6 +97,7 @@ impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
                 }
             })
         } else {
+            assert!(!self.intercrate);
             let c_pred = self.canonicalize_query_keep_static(
                 param_env.and(obligation.predicate),
                 &mut _orig_values,

compiler/rustc_trait_selection/src/traits/query/type_op/implied_outlives_bounds.rs

@@ -1,3 +1,4 @@
+use crate::solve;
 use crate::traits::query::NoSolution;
 use crate::traits::wf;
 use crate::traits::ObligationCtxt;
@@ -6,6 +7,7 @@ use rustc_infer::infer::canonical::Canonical;
 use rustc_infer::infer::outlives::components::{push_outlives_components, Component};
 use rustc_infer::traits::query::OutlivesBound;
 use rustc_middle::infer::canonical::CanonicalQueryResponse;
+use rustc_middle::traits::ObligationCause;
 use rustc_middle::ty::{self, ParamEnvAnd, Ty, TyCtxt, TypeVisitableExt};
 use rustc_span::def_id::CRATE_DEF_ID;
 use rustc_span::source_map::DUMMY_SP;
@@ -164,19 +166,29 @@ pub fn compute_implied_outlives_bounds_inner<'tcx>(
 
     // We lazily compute the outlives components as
     // `select_all_or_error` constrains inference variables.
-    let implied_bounds = outlives_bounds
-        .into_iter()
-        .flat_map(|ty::OutlivesPredicate(a, r_b)| match a.unpack() {
-            ty::GenericArgKind::Lifetime(r_a) => vec![OutlivesBound::RegionSubRegion(r_b, r_a)],
+    let mut implied_bounds = Vec::new();
+    for ty::OutlivesPredicate(a, r_b) in outlives_bounds {
+        match a.unpack() {
+            ty::GenericArgKind::Lifetime(r_a) => {
+                implied_bounds.push(OutlivesBound::RegionSubRegion(r_b, r_a))
+            }
             ty::GenericArgKind::Type(ty_a) => {
-                let ty_a = ocx.infcx.resolve_vars_if_possible(ty_a);
+                let mut ty_a = ocx.infcx.resolve_vars_if_possible(ty_a);
+                // Need to manually normalize in the new solver as `wf::obligations` does not.
+                if ocx.infcx.next_trait_solver() {
+                    ty_a = solve::deeply_normalize(
+                        ocx.infcx.at(&ObligationCause::dummy(), param_env),
+                        ty_a,
+                    )
+                    .map_err(|_errs| NoSolution)?;
+                }
                 let mut components = smallvec![];
                 push_outlives_components(tcx, ty_a, &mut components);
-                implied_bounds_from_components(r_b, components)
+                implied_bounds.extend(implied_bounds_from_components(r_b, components))
             }
             ty::GenericArgKind::Const(_) => unreachable!(),
-        })
-        .collect();
+        }
+    }
 
     Ok(implied_bounds)
 }

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

@@ -388,7 +388,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
     /// `FnPtr`, when we wanted to report that it doesn't implement `Trait`.
     #[instrument(level = "trace", skip(self), ret)]
     fn reject_fn_ptr_impls(
-        &self,
+        &mut self,
         impl_def_id: DefId,
         obligation: &TraitObligation<'tcx>,
         impl_self_ty: Ty<'tcx>,
@@ -464,7 +464,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred))
                 })),
             );
-            if let Ok(r) = self.infcx.evaluate_obligation(&obligation) {
+            if let Ok(r) = self.evaluate_root_obligation(&obligation) {
                 if !r.may_apply() {
                     return true;
                 }

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

@@ -34,8 +34,6 @@ use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_infer::infer::DefineOpaqueTypes;
 use rustc_infer::infer::LateBoundRegionConversionTime;
-use rustc_infer::traits::TraitEngine;
-use rustc_infer::traits::TraitEngineExt;
 use rustc_middle::dep_graph::{DepKind, DepNodeIndex};
 use rustc_middle::mir::interpret::ErrorHandled;
 use rustc_middle::ty::abstract_const::NotConstEvaluatable;
@@ -312,6 +310,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         &mut self,
         stack: &TraitObligationStack<'o, 'tcx>,
     ) -> SelectionResult<'tcx, SelectionCandidate<'tcx>> {
+        debug_assert!(!self.infcx.next_trait_solver());
         // Watch out for overflow. This intentionally bypasses (and does
         // not update) the cache.
         self.check_recursion_limit(&stack.obligation, &stack.obligation)?;
@@ -526,21 +525,20 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
     /// Evaluates whether the obligation `obligation` can be satisfied
     /// and returns an `EvaluationResult`. This is meant for the
     /// *initial* call.
+    ///
+    /// Do not use this directly, use `infcx.evaluate_obligation` instead.
     pub fn evaluate_root_obligation(
         &mut self,
         obligation: &PredicateObligation<'tcx>,
     ) -> Result<EvaluationResult, OverflowError> {
+        debug_assert!(!self.infcx.next_trait_solver());
         self.evaluation_probe(|this| {
             let goal =
                 this.infcx.resolve_vars_if_possible((obligation.predicate, obligation.param_env));
-            let mut result = if this.infcx.next_trait_solver() {
-                this.evaluate_predicates_recursively_in_new_solver([obligation.clone()])?
-            } else {
-                this.evaluate_predicate_recursively(
-                    TraitObligationStackList::empty(&ProvisionalEvaluationCache::default()),
-                    obligation.clone(),
-                )?
-            };
+            let mut result = this.evaluate_predicate_recursively(
+                TraitObligationStackList::empty(&ProvisionalEvaluationCache::default()),
+                obligation.clone(),
+            )?;
             // If the predicate has done any inference, then downgrade the
             // result to ambiguous.
             if this.infcx.shallow_resolve(goal) != goal {
@@ -587,42 +585,19 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
     where
         I: IntoIterator<Item = PredicateObligation<'tcx>> + std::fmt::Debug,
     {
-        if self.infcx.next_trait_solver() {
-            self.evaluate_predicates_recursively_in_new_solver(predicates)
-        } else {
-            let mut result = EvaluatedToOk;
-            for mut obligation in predicates {
-                obligation.set_depth_from_parent(stack.depth());
-                let eval = self.evaluate_predicate_recursively(stack, obligation.clone())?;
-                if let EvaluatedToErr = eval {
-                    // fast-path - EvaluatedToErr is the top of the lattice,
-                    // so we don't need to look on the other predicates.
-                    return Ok(EvaluatedToErr);
-                } else {
-                    result = cmp::max(result, eval);
-                }
+        let mut result = EvaluatedToOk;
+        for mut obligation in predicates {
+            obligation.set_depth_from_parent(stack.depth());
+            let eval = self.evaluate_predicate_recursively(stack, obligation.clone())?;
+            if let EvaluatedToErr = eval {
+                // fast-path - EvaluatedToErr is the top of the lattice,
+                // so we don't need to look on the other predicates.
+                return Ok(EvaluatedToErr);
+            } else {
+                result = cmp::max(result, eval);
             }
-            Ok(result)
-        }
-    }
-
-    /// Evaluates the predicates using the new solver when `-Ztrait-solver=next` is enabled
-    fn evaluate_predicates_recursively_in_new_solver(
-        &mut self,
-        predicates: impl IntoIterator<Item = PredicateObligation<'tcx>>,
-    ) -> Result<EvaluationResult, OverflowError> {
-        let mut fulfill_cx = crate::solve::FulfillmentCtxt::new(self.infcx);
-        fulfill_cx.register_predicate_obligations(self.infcx, predicates);
-        // True errors
-        // FIXME(-Ztrait-solver=next): Overflows are reported as ambig here, is that OK?
-        if !fulfill_cx.select_where_possible(self.infcx).is_empty() {
-            return Ok(EvaluatedToErr);
         }
-        if !fulfill_cx.select_all_or_error(self.infcx).is_empty() {
-            return Ok(EvaluatedToAmbig);
-        }
-        // Regions and opaques are handled in the `evaluation_probe` by looking at the snapshot
-        Ok(EvaluatedToOk)
+        Ok(result)
     }
 
     #[instrument(
@@ -636,6 +611,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         previous_stack: TraitObligationStackList<'o, 'tcx>,
         obligation: PredicateObligation<'tcx>,
     ) -> Result<EvaluationResult, OverflowError> {
+        debug_assert!(!self.infcx.next_trait_solver());
         // `previous_stack` stores a `TraitObligation`, while `obligation` is
         // a `PredicateObligation`. These are distinct types, so we can't
         // use any `Option` combinator method that would force them to be
@@ -1182,6 +1158,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         &mut self,
         stack: &TraitObligationStack<'o, 'tcx>,
     ) -> Result<EvaluationResult, OverflowError> {
+        debug_assert!(!self.infcx.next_trait_solver());
         // In intercrate mode, whenever any of the generics are unbound,
         // there can always be an impl. Even if there are no impls in
         // this crate, perhaps the type would be unified with

compiler/rustc_trait_selection/src/traits/wf.rs

@@ -303,6 +303,11 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> {
     }
 
     fn normalize(self, infcx: &InferCtxt<'tcx>) -> Vec<traits::PredicateObligation<'tcx>> {
+        // Do not normalize `wf` obligations with the new solver.
+        if infcx.next_trait_solver() {
+            return self.out;
+        }
+
         let cause = self.cause(traits::WellFormed(None));
         let param_env = self.param_env;
         let mut obligations = Vec::with_capacity(self.out.len());