Normalize region obligation in lexical region resolution with next-gen solver

compiler/rustc_borrowck/src/type_check/constraint_conversion.rs

@@ -33,7 +33,7 @@ pub(crate) struct ConstraintConversion<'a, 'tcx> {
     /// our special inference variable there, we would mess that up.
     region_bound_pairs: &'a RegionBoundPairs<'tcx>,
     implicit_region_bound: ty::Region<'tcx>,
-    param_env: ty::ParamEnv<'tcx>,
+    known_type_outlives_obligations: &'tcx [ty::PolyTypeOutlivesPredicate<'tcx>],
     locations: Locations,
     span: Span,
     category: ConstraintCategory<'tcx>,
@@ -47,7 +47,7 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
         universal_regions: &'a UniversalRegions<'tcx>,
         region_bound_pairs: &'a RegionBoundPairs<'tcx>,
         implicit_region_bound: ty::Region<'tcx>,
-        param_env: ty::ParamEnv<'tcx>,
+        known_type_outlives_obligations: &'tcx [ty::PolyTypeOutlivesPredicate<'tcx>],
         locations: Locations,
         span: Span,
         category: ConstraintCategory<'tcx>,
@@ -59,7 +59,7 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
             universal_regions,
             region_bound_pairs,
             implicit_region_bound,
-            param_env,
+            known_type_outlives_obligations,
             locations,
             span,
             category,
@@ -136,7 +136,11 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
 
         // Extract out various useful fields we'll need below.
         let ConstraintConversion {
-            tcx, region_bound_pairs, implicit_region_bound, param_env, ..
+            tcx,
+            region_bound_pairs,
+            implicit_region_bound,
+            known_type_outlives_obligations,
+            ..
         } = *self;
 
         let ty::OutlivesPredicate(k1, r2) = predicate;
@@ -157,7 +161,7 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
                     tcx,
                     region_bound_pairs,
                     Some(implicit_region_bound),
-                    param_env,
+                    known_type_outlives_obligations,
                 )
                 .type_must_outlive(origin, t1, r2, constraint_category);
             }

compiler/rustc_borrowck/src/type_check/free_region_relations.rs

@@ -45,19 +45,22 @@ type NormalizedInputsAndOutput<'tcx> = Vec<Ty<'tcx>>;
 pub(crate) struct CreateResult<'tcx> {
     pub(crate) universal_region_relations: Frozen<UniversalRegionRelations<'tcx>>,
     pub(crate) region_bound_pairs: RegionBoundPairs<'tcx>,
+    pub(crate) known_type_outlives_obligations: &'tcx [ty::PolyTypeOutlivesPredicate<'tcx>],
     pub(crate) normalized_inputs_and_output: NormalizedInputsAndOutput<'tcx>,
 }
 
 pub(crate) fn create<'tcx>(
     infcx: &InferCtxt<'tcx>,
     param_env: ty::ParamEnv<'tcx>,
+    known_type_outlives_obligations: &'tcx [ty::PolyTypeOutlivesPredicate<'tcx>],
     implicit_region_bound: ty::Region<'tcx>,
     universal_regions: &Rc<UniversalRegions<'tcx>>,
     constraints: &mut MirTypeckRegionConstraints<'tcx>,
 ) -> CreateResult<'tcx> {
     UniversalRegionRelationsBuilder {
         infcx,
         param_env,
+        known_type_outlives_obligations,
         implicit_region_bound,
         constraints,
         universal_regions: universal_regions.clone(),
@@ -175,6 +178,7 @@ impl UniversalRegionRelations<'_> {
 struct UniversalRegionRelationsBuilder<'this, 'tcx> {
     infcx: &'this InferCtxt<'tcx>,
     param_env: ty::ParamEnv<'tcx>,
+    known_type_outlives_obligations: &'tcx [ty::PolyTypeOutlivesPredicate<'tcx>],
     universal_regions: Rc<UniversalRegions<'tcx>>,
     implicit_region_bound: ty::Region<'tcx>,
     constraints: &'this mut MirTypeckRegionConstraints<'tcx>,
@@ -200,7 +204,8 @@ impl<'tcx> UniversalRegionRelationsBuilder<'_, 'tcx> {
         let defining_ty_def_id = self.universal_regions.defining_ty.def_id().expect_local();
         let span = tcx.def_span(defining_ty_def_id);
 
-        // Insert the facts we know from the predicates. Why? Why not.
+        // Insert the `'a: 'b` we know from the predicates.
+        // This does not consider the type-outlives.
         let param_env = self.param_env;
         self.add_outlives_bounds(outlives::explicit_outlives_bounds(param_env));
 
@@ -308,6 +313,7 @@ impl<'tcx> UniversalRegionRelationsBuilder<'_, 'tcx> {
                 outlives: self.outlives.freeze(),
                 inverse_outlives: self.inverse_outlives.freeze(),
             }),
+            known_type_outlives_obligations: self.known_type_outlives_obligations,
             region_bound_pairs: self.region_bound_pairs,
             normalized_inputs_and_output,
         }
@@ -322,7 +328,7 @@ impl<'tcx> UniversalRegionRelationsBuilder<'_, 'tcx> {
             &self.universal_regions,
             &self.region_bound_pairs,
             self.implicit_region_bound,
-            self.param_env,
+            self.known_type_outlives_obligations,
             Locations::All(span),
             span,
             ConstraintCategory::Internal,

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -152,9 +152,14 @@ pub(crate) fn type_check<'mir, 'tcx>(
         universal_region_relations,
         region_bound_pairs,
         normalized_inputs_and_output,
+        known_type_outlives_obligations,
     } = free_region_relations::create(
         infcx,
         param_env,
+        // FIXME(-Znext-solver): These are unnormalized. Normalize them.
+        infcx.tcx.arena.alloc_from_iter(
+            param_env.caller_bounds().iter().filter_map(|clause| clause.as_type_outlives_clause()),
+        ),
         implicit_region_bound,
         universal_regions,
         &mut constraints,
@@ -176,6 +181,7 @@ pub(crate) fn type_check<'mir, 'tcx>(
         body,
         param_env,
         &region_bound_pairs,
+        known_type_outlives_obligations,
         implicit_region_bound,
         &mut borrowck_context,
     );
@@ -850,6 +856,7 @@ struct TypeChecker<'a, 'tcx> {
     /// all of the promoted items.
     user_type_annotations: &'a CanonicalUserTypeAnnotations<'tcx>,
     region_bound_pairs: &'a RegionBoundPairs<'tcx>,
+    known_type_outlives_obligations: &'tcx [ty::PolyTypeOutlivesPredicate<'tcx>],
     implicit_region_bound: ty::Region<'tcx>,
     reported_errors: FxIndexSet<(Ty<'tcx>, Span)>,
     borrowck_context: &'a mut BorrowCheckContext<'a, 'tcx>,
@@ -1000,6 +1007,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
         body: &'a Body<'tcx>,
         param_env: ty::ParamEnv<'tcx>,
         region_bound_pairs: &'a RegionBoundPairs<'tcx>,
+        known_type_outlives_obligations: &'tcx [ty::PolyTypeOutlivesPredicate<'tcx>],
         implicit_region_bound: ty::Region<'tcx>,
         borrowck_context: &'a mut BorrowCheckContext<'a, 'tcx>,
     ) -> Self {
@@ -1010,6 +1018,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
             user_type_annotations: &body.user_type_annotations,
             param_env,
             region_bound_pairs,
+            known_type_outlives_obligations,
             implicit_region_bound,
             borrowck_context,
             reported_errors: Default::default(),
@@ -1127,7 +1136,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
             self.borrowck_context.universal_regions,
             self.region_bound_pairs,
             self.implicit_region_bound,
-            self.param_env,
+            self.known_type_outlives_obligations,
             locations,
             locations.span(self.body),
             category,
@@ -2731,7 +2740,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                 self.borrowck_context.universal_regions,
                 self.region_bound_pairs,
                 self.implicit_region_bound,
-                self.param_env,
+                self.known_type_outlives_obligations,
                 locations,
                 DUMMY_SP,                   // irrelevant; will be overridden.
                 ConstraintCategory::Boring, // same as above.

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -20,6 +20,7 @@ use rustc_middle::ty::{
 };
 use rustc_middle::ty::{GenericParamDefKind, TyCtxt};
 use rustc_span::Span;
+use rustc_trait_selection::regions::InferCtxtRegionExt;
 use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt;
 use rustc_trait_selection::traits::outlives_bounds::InferCtxtExt as _;
 use rustc_trait_selection::traits::{

compiler/rustc_hir_analysis/src/check/compare_impl_item/refine.rs

@@ -8,6 +8,7 @@ use rustc_middle::ty::{
     self, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperVisitable, TypeVisitable, TypeVisitor,
 };
 use rustc_span::Span;
+use rustc_trait_selection::regions::InferCtxtRegionExt;
 use rustc_trait_selection::traits::{
     elaborate, normalize_param_env_or_error, outlives_bounds::InferCtxtExt, ObligationCtxt,
 };

compiler/rustc_hir_analysis/src/check/dropck.rs

@@ -8,6 +8,7 @@ use rustc_infer::infer::{RegionResolutionError, TyCtxtInferExt};
 use rustc_middle::ty::util::CheckRegions;
 use rustc_middle::ty::GenericArgsRef;
 use rustc_middle::ty::{self, TyCtxt};
+use rustc_trait_selection::regions::InferCtxtRegionExt;
 use rustc_trait_selection::traits::{self, ObligationCtxt};
 
 use crate::errors;
@@ -188,6 +189,7 @@ fn ensure_drop_predicates_are_implied_by_item_defn<'tcx>(
                 RegionResolutionError::UpperBoundUniverseConflict(a, _, _, _, b) => {
                     format!("{b}: {a}", a = ty::Region::new_var(tcx, a))
                 }
+                RegionResolutionError::CannotNormalize(..) => unreachable!(),
             };
             guar = Some(
                 struct_span_code_err!(

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -10,10 +10,8 @@ use rustc_hir as hir;
 use rustc_hir::def_id::{DefId, LocalDefId, LocalModDefId};
 use rustc_hir::lang_items::LangItem;
 use rustc_hir::ItemKind;
-use rustc_infer::infer::outlives::env::{OutlivesEnvironment, RegionBoundPairs};
-use rustc_infer::infer::outlives::obligations::TypeOutlives;
+use rustc_infer::infer::outlives::env::OutlivesEnvironment;
 use rustc_infer::infer::{self, InferCtxt, TyCtxtInferExt};
-use rustc_middle::mir::ConstraintCategory;
 use rustc_middle::query::Providers;
 use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_middle::ty::trait_def::TraitSpecializationKind;
@@ -26,6 +24,7 @@ use rustc_session::parse::feature_err;
 use rustc_span::symbol::{sym, Ident, Symbol};
 use rustc_span::{Span, DUMMY_SP};
 use rustc_target::spec::abi::Abi;
+use rustc_trait_selection::regions::InferCtxtRegionExt;
 use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt;
 use rustc_trait_selection::traits::misc::{
     type_allowed_to_implement_const_param_ty, ConstParamTyImplementationError,
@@ -731,10 +730,12 @@ fn ty_known_to_outlive<'tcx>(
     ty: Ty<'tcx>,
     region: ty::Region<'tcx>,
 ) -> bool {
-    resolve_regions_with_wf_tys(tcx, id, param_env, wf_tys, |infcx, region_bound_pairs| {
-        let origin = infer::RelateParamBound(DUMMY_SP, ty, None);
-        let outlives = &mut TypeOutlives::new(infcx, tcx, region_bound_pairs, None, param_env);
-        outlives.type_must_outlive(origin, ty, region, ConstraintCategory::BoringNoLocation);
+    test_region_obligations(tcx, id, param_env, wf_tys, |infcx| {
+        infcx.register_region_obligation(infer::RegionObligation {
+            sub_region: region,
+            sup_type: ty,
+            origin: infer::RelateParamBound(DUMMY_SP, ty, None),
+        });
     })
 }
 
@@ -748,40 +749,32 @@ fn region_known_to_outlive<'tcx>(
     region_a: ty::Region<'tcx>,
     region_b: ty::Region<'tcx>,
 ) -> bool {
-    resolve_regions_with_wf_tys(tcx, id, param_env, wf_tys, |mut infcx, _| {
-        use rustc_infer::infer::outlives::obligations::TypeOutlivesDelegate;
-        let origin = infer::RelateRegionParamBound(DUMMY_SP);
-        // `region_a: region_b` -> `region_b <= region_a`
-        infcx.push_sub_region_constraint(
-            origin,
-            region_b,
-            region_a,
-            ConstraintCategory::BoringNoLocation,
-        );
+    test_region_obligations(tcx, id, param_env, wf_tys, |infcx| {
+        infcx.sub_regions(infer::RelateRegionParamBound(DUMMY_SP), region_b, region_a);
     })
 }
 
 /// Given a known `param_env` and a set of well formed types, set up an
 /// `InferCtxt`, call the passed function (to e.g. set up region constraints
 /// to be tested), then resolve region and return errors
-fn resolve_regions_with_wf_tys<'tcx>(
+fn test_region_obligations<'tcx>(
     tcx: TyCtxt<'tcx>,
     id: LocalDefId,
     param_env: ty::ParamEnv<'tcx>,
     wf_tys: &FxIndexSet<Ty<'tcx>>,
-    add_constraints: impl for<'a> FnOnce(&'a InferCtxt<'tcx>, &'a RegionBoundPairs<'tcx>),
+    add_constraints: impl FnOnce(&InferCtxt<'tcx>),
 ) -> bool {
     // Unfortunately, we have to use a new `InferCtxt` each call, because
     // region constraints get added and solved there and we need to test each
     // call individually.
     let infcx = tcx.infer_ctxt().build();
+
+    add_constraints(&infcx);
+
     let outlives_environment = OutlivesEnvironment::with_bounds(
         param_env,
         infcx.implied_bounds_tys(param_env, id, wf_tys),
     );
-    let region_bound_pairs = outlives_environment.region_bound_pairs();
-
-    add_constraints(&infcx, region_bound_pairs);
 
     let errors = infcx.resolve_regions(&outlives_environment);
     debug!(?errors, "errors");

compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -518,6 +518,13 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
 
                         self.report_placeholder_failure(sup_origin, sub_r, sup_r).emit();
                     }
+
+                    RegionResolutionError::CannotNormalize(ty, origin) => {
+                        self.tcx
+                            .dcx()
+                            .struct_span_err(origin.span(), format!("cannot normalize `{ty}`"))
+                            .emit();
+                    }
                 }
             }
         }
@@ -559,7 +566,8 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
             RegionResolutionError::GenericBoundFailure(..) => true,
             RegionResolutionError::ConcreteFailure(..)
             | RegionResolutionError::SubSupConflict(..)
-            | RegionResolutionError::UpperBoundUniverseConflict(..) => false,
+            | RegionResolutionError::UpperBoundUniverseConflict(..)
+            | RegionResolutionError::CannotNormalize(..) => false,
         };
 
         let mut errors = if errors.iter().all(|e| is_bound_failure(e)) {
@@ -574,6 +582,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
             RegionResolutionError::GenericBoundFailure(ref sro, _, _) => sro.span(),
             RegionResolutionError::SubSupConflict(_, ref rvo, _, _, _, _, _) => rvo.span(),
             RegionResolutionError::UpperBoundUniverseConflict(_, ref rvo, _, _, _) => rvo.span(),
+            RegionResolutionError::CannotNormalize(_, ref sro) => sro.span(),
         });
         errors
     }

compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs

@@ -98,6 +98,8 @@ pub enum RegionResolutionError<'tcx> {
         SubregionOrigin<'tcx>, // cause of the constraint
         Region<'tcx>,          // the placeholder `'b`
     ),
+
+    CannotNormalize(Ty<'tcx>, SubregionOrigin<'tcx>),
 }
 
 impl<'tcx> RegionResolutionError<'tcx> {
@@ -106,7 +108,8 @@ impl<'tcx> RegionResolutionError<'tcx> {
             RegionResolutionError::ConcreteFailure(origin, _, _)
             | RegionResolutionError::GenericBoundFailure(origin, _, _)
             | RegionResolutionError::SubSupConflict(_, _, origin, _, _, _, _)
-            | RegionResolutionError::UpperBoundUniverseConflict(_, _, _, origin, _) => origin,
+            | RegionResolutionError::UpperBoundUniverseConflict(_, _, _, origin, _)
+            | RegionResolutionError::CannotNormalize(_, origin) => origin,
         }
     }
 }

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

@@ -1,11 +1,11 @@
 //! Various code related to computing outlives relations.
 use self::env::OutlivesEnvironment;
 use super::region_constraints::RegionConstraintData;
-use super::{InferCtxt, RegionResolutionError};
+use super::{InferCtxt, RegionResolutionError, SubregionOrigin};
 use crate::infer::free_regions::RegionRelations;
 use crate::infer::lexical_region_resolve;
 use rustc_middle::traits::query::OutlivesBound;
-use rustc_middle::ty;
+use rustc_middle::ty::{self, Ty};
 
 pub mod components;
 pub mod env;
@@ -41,12 +41,22 @@ impl<'tcx> InferCtxt<'tcx> {
     /// result. After this, no more unification operations should be
     /// done -- or the compiler will panic -- but it is legal to use
     /// `resolve_vars_if_possible` as well as `fully_resolve`.
+    ///
+    /// If you are in a crate that has access to `rustc_trait_selection`,
+    /// then it's probably better to use `resolve_regions`,
+    /// which knows how to normalize registered region obligations.
     #[must_use]
-    pub fn resolve_regions(
+    pub fn resolve_regions_with_normalize(
         &self,
         outlives_env: &OutlivesEnvironment<'tcx>,
+        deeply_normalize_ty: impl Fn(Ty<'tcx>, SubregionOrigin<'tcx>) -> Result<Ty<'tcx>, Ty<'tcx>>,
     ) -> Vec<RegionResolutionError<'tcx>> {
-        self.process_registered_region_obligations(outlives_env);
+        match self.process_registered_region_obligations(outlives_env, deeply_normalize_ty) {
+            Ok(()) => {}
+            Err((ty, origin)) => {
+                return vec![RegionResolutionError::CannotNormalize(ty, origin)];
+            }
+        };
 
         let (var_infos, data) = {
             let mut inner = self.inner.borrow_mut();

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

@@ -70,6 +70,7 @@ use rustc_data_structures::undo_log::UndoLogs;
 use rustc_middle::mir::ConstraintCategory;
 use rustc_middle::ty::GenericArgKind;
 use rustc_middle::ty::{self, GenericArgsRef, Region, Ty, TyCtxt, TypeVisitableExt};
+use rustc_span::DUMMY_SP;
 use smallvec::smallvec;
 
 use super::env::OutlivesEnvironment;
@@ -123,26 +124,54 @@ impl<'tcx> InferCtxt<'tcx> {
     /// flow of the inferencer. The key point is that it is
     /// invoked after all type-inference variables have been bound --
     /// right before lexical region resolution.
-    #[instrument(level = "debug", skip(self, outlives_env))]
-    pub fn process_registered_region_obligations(&self, outlives_env: &OutlivesEnvironment<'tcx>) {
+    #[instrument(level = "debug", skip(self, outlives_env, deeply_normalize_ty))]
+    pub fn process_registered_region_obligations<E>(
+        &self,
+        outlives_env: &OutlivesEnvironment<'tcx>,
+        mut deeply_normalize_ty: impl FnMut(Ty<'tcx>, SubregionOrigin<'tcx>) -> Result<Ty<'tcx>, E>,
+    ) -> Result<(), (E, SubregionOrigin<'tcx>)> {
         assert!(!self.in_snapshot(), "cannot process registered region obligations in a snapshot");
 
+        let normalized_caller_bounds: Vec<_> = outlives_env
+            .param_env
+            .caller_bounds()
+            .iter()
+            .filter_map(|clause| {
+                let bound_clause = clause.kind();
+                let ty::ClauseKind::TypeOutlives(outlives) = bound_clause.skip_binder() else {
+                    return None;
+                };
+                Some(
+                    deeply_normalize_ty(
+                        outlives.0,
+                        SubregionOrigin::AscribeUserTypeProvePredicate(DUMMY_SP),
+                    )
+                    .map(|ty| bound_clause.rebind(ty::OutlivesPredicate(ty, outlives.1))),
+                )
+            })
+            // FIXME(-Znext-solver): How do we accurately report an error here :(
+            .try_collect()
+            .map_err(|e| (e, SubregionOrigin::AscribeUserTypeProvePredicate(DUMMY_SP)))?;
+
         let my_region_obligations = self.take_registered_region_obligations();
 
         for RegionObligation { sup_type, sub_region, origin } in my_region_obligations {
+            let sup_type =
+                deeply_normalize_ty(sup_type, origin.clone()).map_err(|e| (e, origin.clone()))?;
             debug!(?sup_type, ?sub_region, ?origin);
-            let sup_type = self.resolve_vars_if_possible(sup_type);
 
             let outlives = &mut TypeOutlives::new(
                 self,
                 self.tcx,
                 outlives_env.region_bound_pairs(),
                 None,
-                outlives_env.param_env,
+                &normalized_caller_bounds,
             );
             let category = origin.to_constraint_category();
             outlives.type_must_outlive(origin, sup_type, sub_region, category);
         }
+
+        Ok(())
     }
 }
 
@@ -190,7 +219,7 @@ where
         tcx: TyCtxt<'tcx>,
         region_bound_pairs: &'cx RegionBoundPairs<'tcx>,
         implicit_region_bound: Option<ty::Region<'tcx>>,
-        param_env: ty::ParamEnv<'tcx>,
+        caller_bounds: &'cx [ty::PolyTypeOutlivesPredicate<'tcx>],
     ) -> Self {
         Self {
             delegate,
@@ -199,7 +228,7 @@ where
                 tcx,
                 region_bound_pairs,
                 implicit_region_bound,
-                param_env,
+                caller_bounds,
             ),
         }
     }

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

@@ -23,17 +23,17 @@ pub struct VerifyBoundCx<'cx, 'tcx> {
     /// Outside of borrowck the only way to prove `T: '?0` is by
     /// setting  `'?0` to `'empty`.
     implicit_region_bound: Option<ty::Region<'tcx>>,
-    param_env: ty::ParamEnv<'tcx>,
+    caller_bounds: &'cx [ty::PolyTypeOutlivesPredicate<'tcx>],
 }
 
 impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
     pub fn new(
         tcx: TyCtxt<'tcx>,
         region_bound_pairs: &'cx RegionBoundPairs<'tcx>,
         implicit_region_bound: Option<ty::Region<'tcx>>,
-        param_env: ty::ParamEnv<'tcx>,
+        caller_bounds: &'cx [ty::PolyTypeOutlivesPredicate<'tcx>],
     ) -> Self {
-        Self { tcx, region_bound_pairs, implicit_region_bound, param_env }
+        Self { tcx, region_bound_pairs, implicit_region_bound, caller_bounds }
     }
 
     #[instrument(level = "debug", skip(self))]
@@ -219,8 +219,9 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
         // To start, collect bounds from user environment. Note that
         // parameter environments are already elaborated, so we don't
         // have to worry about that.
-        let c_b = self.param_env.caller_bounds();
-        let param_bounds = self.collect_outlives_from_clause_list(erased_ty, c_b.into_iter());
+        let param_bounds = self.caller_bounds.iter().copied().filter(move |outlives_predicate| {
+            super::test_type_match::can_match_erased_ty(tcx, *outlives_predicate, erased_ty)
+        });
 
         // Next, collect regions we scraped from the well-formedness
         // constraints in the fn signature. To do that, we walk the list
@@ -307,22 +308,4 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
             .filter_map(|p| p.no_bound_vars())
             .map(|OutlivesPredicate(_, r)| r)
     }
-
-    /// Searches through a predicate list for a predicate `T: 'a`.
-    ///
-    /// Careful: does not elaborate predicates, and just uses `==`
-    /// when comparing `ty` for equality, so `ty` must be something
-    /// that does not involve inference variables and where you
-    /// otherwise want a precise match.
-    fn collect_outlives_from_clause_list(
-        &self,
-        erased_ty: Ty<'tcx>,
-        clauses: impl Iterator<Item = ty::Clause<'tcx>>,
-    ) -> impl Iterator<Item = ty::Binder<'tcx, ty::OutlivesPredicate<Ty<'tcx>, ty::Region<'tcx>>>>
-    {
-        let tcx = self.tcx;
-        clauses.filter_map(|p| p.as_type_outlives_clause()).filter(move |outlives_predicate| {
-            super::test_type_match::can_match_erased_ty(tcx, *outlives_predicate, erased_ty)
-        })
-    }
 }

compiler/rustc_infer/src/lib.rs

@@ -21,6 +21,7 @@
 #![feature(extend_one)]
 #![feature(let_chains)]
 #![feature(if_let_guard)]
+#![feature(iterator_try_collect)]
 #![feature(min_specialization)]
 #![feature(try_blocks)]
 #![recursion_limit = "512"] // For rustdoc

compiler/rustc_trait_selection/src/lib.rs

@@ -39,6 +39,7 @@ extern crate smallvec;
 
 pub mod errors;
 pub mod infer;
+pub mod regions;
 pub mod solve;
 pub mod traits;
 

compiler/rustc_trait_selection/src/regions.rs

@@ -0,0 +1,40 @@
+use rustc_infer::infer::outlives::env::OutlivesEnvironment;
+use rustc_infer::infer::{InferCtxt, RegionResolutionError};
+use rustc_middle::traits::ObligationCause;
+
+pub trait InferCtxtRegionExt<'tcx> {
+    /// Resolve regions, using the deep normalizer to normalize any type-outlives
+    /// obligations in the process. This is in `rustc_trait_selection` because
+    /// we need to normalize.
+    ///
+    /// Prefer this method over `resolve_regions_with_normalize`, unless you are
+    /// doing something specific for normalization.
+    fn resolve_regions(
+        &self,
+        outlives_env: &OutlivesEnvironment<'tcx>,
+    ) -> Vec<RegionResolutionError<'tcx>>;
+}
+
+impl<'tcx> InferCtxtRegionExt<'tcx> for InferCtxt<'tcx> {
+    fn resolve_regions(
+        &self,
+        outlives_env: &OutlivesEnvironment<'tcx>,
+    ) -> Vec<RegionResolutionError<'tcx>> {
+        self.resolve_regions_with_normalize(outlives_env, |ty, origin| {
+            let ty = self.resolve_vars_if_possible(ty);
+
+            if self.next_trait_solver() {
+                crate::solve::deeply_normalize(
+                    self.at(
+                        &ObligationCause::dummy_with_span(origin.span()),
+                        outlives_env.param_env,
+                    ),
+                    ty,
+                )
+                .map_err(|_| ty)
+            } else {
+                Ok(ty)
+            }
+        })
+    }
+}

compiler/rustc_trait_selection/src/traits/auto_trait.rs

@@ -179,7 +179,7 @@ impl<'tcx> AutoTraitFinder<'tcx> {
         }
 
         let outlives_env = OutlivesEnvironment::new(full_env);
-        infcx.process_registered_region_obligations(&outlives_env);
+        let _ = infcx.process_registered_region_obligations::<!>(&outlives_env, |ty, _| Ok(ty));
 
         let region_data =
             infcx.inner.borrow_mut().unwrap_region_constraints().region_constraint_data().clone();

compiler/rustc_trait_selection/src/traits/coherence.rs

@@ -6,6 +6,7 @@
 
 use crate::infer::outlives::env::OutlivesEnvironment;
 use crate::infer::InferOk;
+use crate::regions::InferCtxtRegionExt;
 use crate::solve::inspect::{InspectGoal, ProofTreeInferCtxtExt, ProofTreeVisitor};
 use crate::solve::{deeply_normalize_for_diagnostics, inspect};
 use crate::traits::engine::TraitEngineExt;

compiler/rustc_trait_selection/src/traits/engine.rs

@@ -3,6 +3,7 @@ use std::fmt::Debug;
 
 use super::FulfillmentContext;
 use super::TraitEngine;
+use crate::regions::InferCtxtRegionExt;
 use crate::solve::FulfillmentCtxt as NextFulfillmentCtxt;
 use crate::traits::error_reporting::TypeErrCtxtExt;
 use crate::traits::NormalizeExt;

compiler/rustc_trait_selection/src/traits/misc.rs

@@ -1,5 +1,6 @@
 //! Miscellaneous type-system utilities that are too small to deserve their own modules.
 
+use crate::regions::InferCtxtRegionExt;
 use crate::traits::{self, ObligationCause, ObligationCtxt};
 
 use hir::LangItem;

compiler/rustc_trait_selection/src/traits/mod.rs

@@ -25,6 +25,7 @@ pub mod wf;
 
 use crate::infer::outlives::env::OutlivesEnvironment;
 use crate::infer::{InferCtxt, TyCtxtInferExt};
+use crate::regions::InferCtxtRegionExt;
 use crate::traits::error_reporting::TypeErrCtxtExt as _;
 use crate::traits::query::evaluate_obligation::InferCtxtExt as _;
 use rustc_errors::ErrorGuaranteed;

tests/ui/traits/next-solver/normalize-region-obligations.rs

@@ -0,0 +1,22 @@
+// revisions: normalize_param_env normalize_obligation
+// check-pass
+// compile-flags: -Znext-solver
+
+trait Foo {
+    #[cfg(normalize_param_env)]
+    type Gat<'a> where <Self as Mirror>::Assoc: 'a;
+    #[cfg(normalize_obligation)]
+    type Gat<'a> where Self: 'a;
+}
+
+trait Mirror { type Assoc: ?Sized; }
+impl<T: ?Sized> Mirror for T { type Assoc = T; }
+
+impl<T> Foo for T {
+    #[cfg(normalize_param_env)]
+    type Gat<'a> = i32 where T: 'a;
+    #[cfg(normalize_obligation)]
+    type Gat<'a> = i32 where <T as Mirror>::Assoc: 'a;
+}
+
+fn main() {}

tests/ui/traits/next-solver/specialization-transmute.rs

@@ -1,4 +1,5 @@
 // compile-flags: -Znext-solver
+//~^ ERROR cannot normalize `<T as Default>::Id`
 
 #![feature(specialization)]
 //~^ WARN the feature `specialization` is incomplete

tests/ui/traits/next-solver/specialization-transmute.stderr

@@ -1,5 +1,5 @@
 warning: the feature `specialization` is incomplete and may not be safe to use and/or cause compiler crashes
-  --> $DIR/specialization-transmute.rs:3:12
+  --> $DIR/specialization-transmute.rs:4:12
    |
 LL | #![feature(specialization)]
    |            ^^^^^^^^^^^^^^
@@ -8,12 +8,14 @@ LL | #![feature(specialization)]
    = help: consider using `min_specialization` instead, which is more stable and complete
    = note: `#[warn(incomplete_features)]` on by default
 
+error: cannot normalize `<T as Default>::Id`
+
 error[E0282]: type annotations needed
-  --> $DIR/specialization-transmute.rs:13:23
+  --> $DIR/specialization-transmute.rs:14:23
    |
 LL |     default type Id = T;
    |                       ^ cannot infer type for associated type `<T as Default>::Id`
 
-error: aborting due to 1 previous error; 1 warning emitted
+error: aborting due to 2 previous errors; 1 warning emitted
 
 For more information about this error, try `rustc --explain E0282`.

tests/ui/traits/next-solver/unsound-region-obligation.rs

@@ -0,0 +1,13 @@
+//~ ERROR the type `<() as StaticTy>::Item<'a>` does not fulfill the required lifetime
+// compile-flags: -Znext-solver
+// Regression test for rust-lang/trait-system-refactor-initiative#59
+
+trait StaticTy {
+    type Item<'a>: 'static;
+}
+
+impl StaticTy for () {
+    type Item<'a> = &'a ();
+}
+
+fn main() {}

tests/ui/traits/next-solver/unsound-region-obligation.stderr

@@ -0,0 +1,7 @@
+error[E0477]: the type `<() as StaticTy>::Item<'a>` does not fulfill the required lifetime
+   |
+   = note: type must satisfy the static lifetime
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0477`.