Auto merge of #119101 - compiler-errors:outlives, r=lcnr

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

This normalizes region obligations when we `resolve_regions`, since they may be unnormalized with deferred projection equality.

It's pretty hard to add tests that exercise this without also triggering MIR borrowck errors (because we don't normalize there yet). I've added one test with two revisions that should test that we both 1. normalize region obligations in the param env, and 2. normalize registered region obligations during lexical region resolution.

Author: bors

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();