Avoid obligation construction dance with query region constraints

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -742,7 +742,7 @@ fn ty_known_to_outlive<'tcx>(
     region: ty::Region<'tcx>,
 ) -> bool {
     test_region_obligations(tcx, id, param_env, wf_tys, |infcx| {
-        infcx.register_region_obligation(infer::RegionObligation {
+        infcx.register_type_outlives_constraint_inner(infer::TypeOutlivesConstraint {
             sub_region: region,
             sup_type: ty,
             origin: infer::RelateParamBound(DUMMY_SP, ty, None),

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

@@ -12,23 +12,20 @@ use std::iter;
 
 use rustc_index::{Idx, IndexVec};
 use rustc_middle::arena::ArenaAllocatable;
+use rustc_middle::bug;
 use rustc_middle::mir::ConstraintCategory;
 use rustc_middle::ty::{self, BoundVar, GenericArg, GenericArgKind, Ty, TyCtxt, TypeFoldable};
-use rustc_middle::{bug, span_bug};
 use tracing::{debug, instrument};
 
 use crate::infer::canonical::instantiate::{CanonicalExt, instantiate_value};
 use crate::infer::canonical::{
     Canonical, CanonicalQueryResponse, CanonicalVarValues, Certainty, OriginalQueryValues,
-    QueryOutlivesConstraint, QueryRegionConstraints, QueryResponse,
+    QueryRegionConstraints, QueryResponse,
 };
 use crate::infer::region_constraints::{Constraint, RegionConstraintData};
 use crate::infer::{DefineOpaqueTypes, InferCtxt, InferOk, InferResult, SubregionOrigin};
 use crate::traits::query::NoSolution;
-use crate::traits::{
-    Obligation, ObligationCause, PredicateObligation, PredicateObligations, ScrubbedTraitError,
-    TraitEngine,
-};
+use crate::traits::{ObligationCause, PredicateObligations, ScrubbedTraitError, TraitEngine};
 
 impl<'tcx> InferCtxt<'tcx> {
     /// This method is meant to be invoked as the final step of a canonical query
@@ -169,15 +166,13 @@ impl<'tcx> InferCtxt<'tcx> {
     where
         R: Debug + TypeFoldable<TyCtxt<'tcx>>,
     {
-        let InferOk { value: result_args, mut obligations } =
+        let InferOk { value: result_args, obligations } =
             self.query_response_instantiation(cause, param_env, original_values, query_response)?;
 
-        obligations.extend(self.query_outlives_constraints_into_obligations(
-            cause,
-            param_env,
-            &query_response.value.region_constraints.outlives,
-            &result_args,
-        ));
+        for (predicate, _category) in &query_response.value.region_constraints.outlives {
+            let predicate = instantiate_value(self.tcx, &result_args, *predicate);
+            self.register_outlives_constraint(predicate, cause);
+        }
 
         let user_result: R =
             query_response.instantiate_projected(self.tcx, &result_args, |q_r| q_r.value.clone());
@@ -525,47 +520,6 @@ impl<'tcx> InferCtxt<'tcx> {
         self.unify_canonical_vars(cause, param_env, original_values, instantiated_query_response)
     }
 
-    /// Converts the region constraints resulting from a query into an
-    /// iterator of obligations.
-    fn query_outlives_constraints_into_obligations(
-        &self,
-        cause: &ObligationCause<'tcx>,
-        param_env: ty::ParamEnv<'tcx>,
-        uninstantiated_region_constraints: &[QueryOutlivesConstraint<'tcx>],
-        result_args: &CanonicalVarValues<'tcx>,
-    ) -> impl Iterator<Item = PredicateObligation<'tcx>> {
-        uninstantiated_region_constraints.iter().map(move |&constraint| {
-            let predicate = instantiate_value(self.tcx, result_args, constraint);
-            self.query_outlives_constraint_to_obligation(predicate, cause.clone(), param_env)
-        })
-    }
-
-    pub fn query_outlives_constraint_to_obligation(
-        &self,
-        (predicate, _): QueryOutlivesConstraint<'tcx>,
-        cause: ObligationCause<'tcx>,
-        param_env: ty::ParamEnv<'tcx>,
-    ) -> Obligation<'tcx, ty::Predicate<'tcx>> {
-        let ty::OutlivesPredicate(k1, r2) = predicate;
-
-        let atom = match k1.unpack() {
-            GenericArgKind::Lifetime(r1) => ty::PredicateKind::Clause(
-                ty::ClauseKind::RegionOutlives(ty::OutlivesPredicate(r1, r2)),
-            ),
-            GenericArgKind::Type(t1) => ty::PredicateKind::Clause(ty::ClauseKind::TypeOutlives(
-                ty::OutlivesPredicate(t1, r2),
-            )),
-            GenericArgKind::Const(..) => {
-                // Consts cannot outlive one another, so we don't expect to
-                // encounter this branch.
-                span_bug!(cause.span, "unexpected const outlives {:?}", predicate);
-            }
-        };
-        let predicate = ty::Binder::dummy(atom);
-
-        Obligation::new(self.tcx, cause, param_env, predicate)
-    }
-
     /// Given two sets of values for the same set of canonical variables, unify them.
     /// The second set is produced lazily by supplying indices from the first set.
     fn unify_canonical_vars(

compiler/rustc_infer/src/infer/context.rs

@@ -214,7 +214,7 @@ impl<'tcx> rustc_type_ir::InferCtxtLike for InferCtxt<'tcx> {
     }
 
     fn register_ty_outlives(&self, ty: Ty<'tcx>, r: ty::Region<'tcx>, span: Span) {
-        self.register_region_obligation_with_cause(ty, r, &ObligationCause::dummy_with_span(span));
+        self.register_type_outlives_constraint(ty, r, &ObligationCause::dummy_with_span(span));
     }
 
     type OpaqueTypeStorageEntries = OpaqueTypeStorageEntries;

compiler/rustc_infer/src/infer/mod.rs

@@ -150,7 +150,7 @@ pub struct InferCtxtInner<'tcx> {
     /// for each body-id in this map, which will process the
     /// obligations within. This is expected to be done 'late enough'
     /// that all type inference variables have been bound and so forth.
-    region_obligations: Vec<RegionObligation<'tcx>>,
+    region_obligations: Vec<TypeOutlivesConstraint<'tcx>>,
 
     /// Caches for opaque type inference.
     opaque_type_storage: OpaqueTypeStorage<'tcx>,
@@ -173,7 +173,7 @@ impl<'tcx> InferCtxtInner<'tcx> {
     }
 
     #[inline]
-    pub fn region_obligations(&self) -> &[RegionObligation<'tcx>] {
+    pub fn region_obligations(&self) -> &[TypeOutlivesConstraint<'tcx>] {
         &self.region_obligations
     }
 
@@ -488,7 +488,7 @@ impl fmt::Display for FixupError {
 
 /// See the `region_obligations` field for more information.
 #[derive(Clone, Debug)]
-pub struct RegionObligation<'tcx> {
+pub struct TypeOutlivesConstraint<'tcx> {
     pub sub_region: ty::Region<'tcx>,
     pub sup_type: Ty<'tcx>,
     pub origin: SubregionOrigin<'tcx>,
@@ -738,19 +738,6 @@ impl<'tcx> InferCtxt<'tcx> {
         })
     }
 
-    pub fn region_outlives_predicate(
-        &self,
-        cause: &traits::ObligationCause<'tcx>,
-        predicate: ty::PolyRegionOutlivesPredicate<'tcx>,
-    ) {
-        self.enter_forall(predicate, |ty::OutlivesPredicate(r_a, r_b)| {
-            let origin = SubregionOrigin::from_obligation_cause(cause, || {
-                RelateRegionParamBound(cause.span, None)
-            });
-            self.sub_regions(origin, r_b, r_a); // `b : a` ==> `a <= b`
-        })
-    }
-
     /// Number of type variables created so far.
     pub fn num_ty_vars(&self) -> usize {
         self.inner.borrow_mut().type_variables().num_vars()

compiler/rustc_infer/src/infer/outlives/obligations.rs

@@ -76,23 +76,56 @@ use crate::infer::outlives::env::RegionBoundPairs;
 use crate::infer::outlives::verify::VerifyBoundCx;
 use crate::infer::resolve::OpportunisticRegionResolver;
 use crate::infer::snapshot::undo_log::UndoLog;
-use crate::infer::{self, GenericKind, InferCtxt, RegionObligation, SubregionOrigin, VerifyBound};
+use crate::infer::{
+    self, GenericKind, InferCtxt, SubregionOrigin, TypeOutlivesConstraint, VerifyBound,
+};
 use crate::traits::{ObligationCause, ObligationCauseCode};
 
 impl<'tcx> InferCtxt<'tcx> {
+    pub fn register_outlives_constraint(
+        &self,
+        ty::OutlivesPredicate(arg, r2): ty::OutlivesPredicate<'tcx, ty::GenericArg<'tcx>>,
+        cause: &ObligationCause<'tcx>,
+    ) {
+        match arg.unpack() {
+            ty::GenericArgKind::Lifetime(r1) => {
+                self.register_region_outlives_constraint(ty::OutlivesPredicate(r1, r2), cause);
+            }
+            ty::GenericArgKind::Type(ty1) => {
+                self.register_type_outlives_constraint(ty1, r2, cause);
+            }
+            ty::GenericArgKind::Const(_) => unreachable!(),
+        }
+    }
+
+    pub fn register_region_outlives_constraint(
+        &self,
+        ty::OutlivesPredicate(r_a, r_b): ty::RegionOutlivesPredicate<'tcx>,
+        cause: &ObligationCause<'tcx>,
+    ) {
+        let origin = SubregionOrigin::from_obligation_cause(cause, || {
+            SubregionOrigin::RelateRegionParamBound(cause.span, None)
+        });
+        // `'a: 'b` ==> `'b <= 'a`
+        self.sub_regions(origin, r_b, r_a);
+    }
+
     /// Registers that the given region obligation must be resolved
     /// from within the scope of `body_id`. These regions are enqueued
     /// and later processed by regionck, when full type information is
     /// available (see `region_obligations` field for more
     /// information).
     #[instrument(level = "debug", skip(self))]
-    pub fn register_region_obligation(&self, obligation: RegionObligation<'tcx>) {
+    pub fn register_type_outlives_constraint_inner(
+        &self,
+        obligation: TypeOutlivesConstraint<'tcx>,
+    ) {
         let mut inner = self.inner.borrow_mut();
-        inner.undo_log.push(UndoLog::PushRegionObligation);
+        inner.undo_log.push(UndoLog::PushTypeOutlivesConstraint);
         inner.region_obligations.push(obligation);
     }
 
-    pub fn register_region_obligation_with_cause(
+    pub fn register_type_outlives_constraint(
         &self,
         sup_type: Ty<'tcx>,
         sub_region: Region<'tcx>,
@@ -124,11 +157,15 @@ impl<'tcx> InferCtxt<'tcx> {
             )
         });
 
-        self.register_region_obligation(RegionObligation { sup_type, sub_region, origin });
+        self.register_type_outlives_constraint_inner(TypeOutlivesConstraint {
+            sup_type,
+            sub_region,
+            origin,
+        });
     }
 
     /// Trait queries just want to pass back type obligations "as is"
-    pub fn take_registered_region_obligations(&self) -> Vec<RegionObligation<'tcx>> {
+    pub fn take_registered_region_obligations(&self) -> Vec<TypeOutlivesConstraint<'tcx>> {
         std::mem::take(&mut self.inner.borrow_mut().region_obligations)
     }
 
@@ -166,7 +203,7 @@ impl<'tcx> InferCtxt<'tcx> {
                 );
             }
 
-            for RegionObligation { sup_type, sub_region, origin } in my_region_obligations {
+            for TypeOutlivesConstraint { sup_type, sub_region, origin } in my_region_obligations {
                 let outlives = ty::Binder::dummy(ty::OutlivesPredicate(sup_type, sub_region));
                 let ty::OutlivesPredicate(sup_type, sub_region) =
                     deeply_normalize_ty(outlives, origin.clone())

compiler/rustc_infer/src/infer/snapshot/undo_log.rs

@@ -26,7 +26,7 @@ pub(crate) enum UndoLog<'tcx> {
     RegionConstraintCollector(region_constraints::UndoLog<'tcx>),
     RegionUnificationTable(sv::UndoLog<ut::Delegate<RegionVidKey<'tcx>>>),
     ProjectionCache(traits::UndoLog<'tcx>),
-    PushRegionObligation,
+    PushTypeOutlivesConstraint,
 }
 
 macro_rules! impl_from {
@@ -72,7 +72,7 @@ impl<'tcx> Rollback<UndoLog<'tcx>> for InferCtxtInner<'tcx> {
                 self.region_constraint_storage.as_mut().unwrap().unification_table.reverse(undo)
             }
             UndoLog::ProjectionCache(undo) => self.projection_cache.reverse(undo),
-            UndoLog::PushRegionObligation => {
+            UndoLog::PushTypeOutlivesConstraint => {
                 self.region_obligations.pop();
             }
         }

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

@@ -1024,7 +1024,7 @@ where
     }
 
     pub(super) fn register_region_outlives(&self, a: I::Region, b: I::Region) {
-        // `b : a` ==> `a <= b`
+        // `'a: 'b` ==> `'b <= 'a`
         self.delegate.sub_regions(b, a, self.origin_span);
     }
 

compiler/rustc_trait_selection/src/solve/delegate.rs

@@ -76,7 +76,7 @@ impl<'tcx> rustc_next_trait_solver::delegate::SolverDelegate for SolverDelegate<
                 Some(HasChanged::No)
             }
             ty::PredicateKind::Clause(ty::ClauseKind::TypeOutlives(outlives)) => {
-                self.0.register_region_obligation_with_cause(
+                self.0.register_type_outlives_constraint(
                     outlives.0,
                     outlives.1,
                     &ObligationCause::dummy_with_span(span),

compiler/rustc_trait_selection/src/traits/auto_trait.rs

@@ -726,7 +726,9 @@ impl<'tcx> AutoTraitFinder<'tcx> {
                 }
                 ty::PredicateKind::Clause(ty::ClauseKind::RegionOutlives(binder)) => {
                     let binder = bound_predicate.rebind(binder);
-                    selcx.infcx.region_outlives_predicate(&dummy_cause, binder)
+                    selcx.infcx.enter_forall(binder, |pred| {
+                        selcx.infcx.register_region_outlives_constraint(pred, &dummy_cause);
+                    });
                 }
                 ty::PredicateKind::Clause(ty::ClauseKind::TypeOutlives(binder)) => {
                     let binder = bound_predicate.rebind(binder);
@@ -735,14 +737,14 @@ impl<'tcx> AutoTraitFinder<'tcx> {
                         binder.map_bound_ref(|pred| pred.0).no_bound_vars(),
                     ) {
                         (None, Some(t_a)) => {
-                            selcx.infcx.register_region_obligation_with_cause(
+                            selcx.infcx.register_type_outlives_constraint(
                                 t_a,
                                 selcx.infcx.tcx.lifetimes.re_static,
                                 &dummy_cause,
                             );
                         }
                         (Some(ty::OutlivesPredicate(t_a, r_b)), _) => {
-                            selcx.infcx.register_region_obligation_with_cause(
+                            selcx.infcx.register_type_outlives_constraint(
                                 t_a,
                                 r_b,
                                 &dummy_cause,

compiler/rustc_trait_selection/src/traits/fulfill.rs

@@ -428,7 +428,7 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
 
                 ty::PredicateKind::Clause(ty::ClauseKind::RegionOutlives(data)) => {
                     if infcx.considering_regions {
-                        infcx.region_outlives_predicate(&obligation.cause, Binder::dummy(data));
+                        infcx.register_region_outlives_constraint(data, &obligation.cause);
                     }
 
                     ProcessResult::Changed(Default::default())
@@ -439,7 +439,7 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                     r_b,
                 ))) => {
                     if infcx.considering_regions {
-                        infcx.register_region_obligation_with_cause(t_a, r_b, &obligation.cause);
+                        infcx.register_type_outlives_constraint(t_a, r_b, &obligation.cause);
                     }
                     ProcessResult::Changed(Default::default())
                 }

compiler/rustc_trait_selection/src/traits/outlives_bounds.rs

@@ -9,7 +9,7 @@ use rustc_span::def_id::LocalDefId;
 use tracing::instrument;
 
 use crate::infer::InferCtxt;
-use crate::traits::{ObligationCause, ObligationCtxt};
+use crate::traits::ObligationCause;
 
 /// Implied bounds are region relationships that we deduce
 /// automatically. The idea is that (e.g.) a caller must check that a
@@ -79,24 +79,9 @@ fn implied_outlives_bounds<'a, 'tcx>(
 
     if !constraints.is_empty() {
         let QueryRegionConstraints { outlives } = constraints;
-        // Instantiation may have produced new inference variables and constraints on those
-        // variables. Process these constraints.
-        let ocx = ObligationCtxt::new(infcx);
         let cause = ObligationCause::misc(span, body_id);
-        for &constraint in &outlives {
-            ocx.register_obligation(infcx.query_outlives_constraint_to_obligation(
-                constraint,
-                cause.clone(),
-                param_env,
-            ));
-        }
-
-        let errors = ocx.select_all_or_error();
-        if !errors.is_empty() {
-            infcx.dcx().span_bug(
-                span,
-                "implied_outlives_bounds failed to solve obligations from instantiation",
-            );
+        for &(predicate, _) in &outlives {
+            infcx.register_outlives_constraint(predicate, &cause);
         }
     };
 

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

@@ -1,6 +1,6 @@
 use std::ops::ControlFlow;
 
-use rustc_infer::infer::RegionObligation;
+use rustc_infer::infer::TypeOutlivesConstraint;
 use rustc_infer::infer::canonical::CanonicalQueryInput;
 use rustc_infer::traits::query::OutlivesBound;
 use rustc_infer::traits::query::type_op::ImpliedOutlivesBounds;
@@ -141,7 +141,7 @@ pub fn compute_implied_outlives_bounds_inner<'tcx>(
         && !ocx.infcx.tcx.sess.opts.unstable_opts.no_implied_bounds_compat
         && ty.visit_with(&mut ContainsBevyParamSet { tcx: ocx.infcx.tcx }).is_break()
     {
-        for RegionObligation { sup_type, sub_region, .. } in
+        for TypeOutlivesConstraint { sup_type, sub_region, .. } in
             ocx.infcx.take_registered_region_obligations()
         {
             let mut components = smallvec![];