Stop using a placeholder for empty regions in Chalk

Author: matthewjasper

compiler/rustc_traits/src/chalk/db.rs

@@ -20,11 +20,10 @@ use rustc_span::symbol::sym;
 use std::fmt;
 use std::sync::Arc;
 
-use crate::chalk::lowering::{self, LowerInto};
+use crate::chalk::lowering::LowerInto;
 
 pub struct RustIrDatabase<'tcx> {
     pub(crate) interner: RustInterner<'tcx>,
-    pub(crate) reempty_placeholder: ty::Region<'tcx>,
 }
 
 impl fmt::Debug for RustIrDatabase<'_> {
@@ -40,12 +39,9 @@ impl<'tcx> RustIrDatabase<'tcx> {
         bound_vars: SubstsRef<'tcx>,
     ) -> Vec<chalk_ir::QuantifiedWhereClause<RustInterner<'tcx>>> {
         let predicates = self.interner.tcx.predicates_defined_on(def_id).predicates;
-        let mut regions_substitutor =
-            lowering::RegionsSubstitutor::new(self.interner.tcx, self.reempty_placeholder);
         predicates
             .iter()
             .map(|(wc, _)| wc.subst(self.interner.tcx, bound_vars))
-            .map(|wc| wc.fold_with(&mut regions_substitutor))
             .filter_map(|wc| LowerInto::<
                     Option<chalk_ir::QuantifiedWhereClause<RustInterner<'tcx>>>
                     >::lower_into(wc, self.interner)).collect()
@@ -287,9 +283,6 @@ impl<'tcx> chalk_solve::RustIrDatabase<RustInterner<'tcx>> for RustIrDatabase<'t
 
         let trait_ref = self.interner.tcx.impl_trait_ref(def_id).expect("not an impl");
         let trait_ref = trait_ref.subst(self.interner.tcx, bound_vars);
-        let mut regions_substitutor =
-            lowering::RegionsSubstitutor::new(self.interner.tcx, self.reempty_placeholder);
-        let trait_ref = trait_ref.fold_with(&mut regions_substitutor);
 
         let where_clauses = self.where_clauses_for(def_id, bound_vars);
 
@@ -335,9 +328,6 @@ impl<'tcx> chalk_solve::RustIrDatabase<RustInterner<'tcx>> for RustIrDatabase<'t
 
             let self_ty = trait_ref.self_ty();
             let self_ty = self_ty.subst(self.interner.tcx, bound_vars);
-            let mut regions_substitutor =
-                lowering::RegionsSubstitutor::new(self.interner.tcx, self.reempty_placeholder);
-            let self_ty = self_ty.fold_with(&mut regions_substitutor);
             let lowered_ty = self_ty.lower_into(self.interner);
 
             parameters[0].assert_ty_ref(self.interner).could_match(

compiler/rustc_traits/src/chalk/lowering.rs

@@ -464,9 +464,11 @@ impl<'tcx> LowerInto<'tcx, chalk_ir::Lifetime<RustInterner<'tcx>>> for Region<'t
                 })
                 .intern(interner)
             }
-            ReEmpty(_) => unimplemented!(),
-            // FIXME(chalk): need to handle ReErased
-            ReErased => unimplemented!(),
+            ReEmpty(ui) => {
+                chalk_ir::LifetimeData::Empty(chalk_ir::UniverseIndex { counter: ui.index() })
+                    .intern(interner)
+            }
+            ReErased => chalk_ir::LifetimeData::Erased.intern(interner),
         }
     }
 }
@@ -488,12 +490,12 @@ impl<'tcx> LowerInto<'tcx, Region<'tcx>> for &chalk_ir::Lifetime<RustInterner<'t
                     name: ty::BoundRegionKind::BrAnon(p.idx as u32),
                 })
             }
-            chalk_ir::LifetimeData::Static => ty::RegionKind::ReStatic,
-            chalk_ir::LifetimeData::Phantom(_, _) => unimplemented!(),
+            chalk_ir::LifetimeData::Static => return interner.tcx.lifetimes.re_static,
             chalk_ir::LifetimeData::Empty(ui) => {
-                ty::RegionKind::ReEmpty(ty::UniverseIndex::from_usize(ui.counter))
+                ty::ReEmpty(ty::UniverseIndex::from_usize(ui.counter))
             }
-            chalk_ir::LifetimeData::Erased => ty::RegionKind::ReErased,
+            chalk_ir::LifetimeData::Erased => return interner.tcx.lifetimes.re_erased,
+            chalk_ir::LifetimeData::Phantom(void, _) => match *void {},
         };
         interner.tcx.mk_region(kind)
     }
@@ -1110,32 +1112,3 @@ impl<'tcx> TypeVisitor<'tcx> for PlaceholdersCollector {
         r.super_visit_with(self)
     }
 }
-
-/// Used to substitute specific `Regions`s with placeholders.
-crate struct RegionsSubstitutor<'tcx> {
-    tcx: TyCtxt<'tcx>,
-    reempty_placeholder: ty::Region<'tcx>,
-}
-
-impl<'tcx> RegionsSubstitutor<'tcx> {
-    crate fn new(tcx: TyCtxt<'tcx>, reempty_placeholder: ty::Region<'tcx>) -> Self {
-        RegionsSubstitutor { tcx, reempty_placeholder }
-    }
-}
-
-impl<'tcx> TypeFolder<'tcx> for RegionsSubstitutor<'tcx> {
-    fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
-        self.tcx
-    }
-
-    fn fold_region(&mut self, r: Region<'tcx>) -> Region<'tcx> {
-        match r {
-            ty::ReEmpty(ui) => {
-                assert_eq!(ui.as_usize(), 0);
-                self.reempty_placeholder
-            }
-
-            _ => r.super_fold_with(self),
-        }
-    }
-}

compiler/rustc_traits/src/chalk/mod.rs

@@ -22,9 +22,8 @@ use rustc_infer::infer::canonical::{
 use rustc_infer::traits::{self, CanonicalChalkEnvironmentAndGoal};
 
 use crate::chalk::db::RustIrDatabase as ChalkRustIrDatabase;
-use crate::chalk::lowering::{
-    LowerInto, ParamsSubstitutor, PlaceholdersCollector, RegionsSubstitutor,
-};
+use crate::chalk::lowering::LowerInto;
+use crate::chalk::lowering::{ParamsSubstitutor, PlaceholdersCollector};
 
 use chalk_solve::Solution;
 
@@ -42,20 +41,11 @@ crate fn evaluate_goal<'tcx>(
     let mut placeholders_collector = PlaceholdersCollector::new();
     obligation.visit_with(&mut placeholders_collector);
 
-    let reempty_placeholder = tcx.mk_region(ty::RegionKind::RePlaceholder(ty::Placeholder {
-        universe: ty::UniverseIndex::ROOT,
-        name: ty::BoundRegionKind::BrAnon(placeholders_collector.next_anon_region_placeholder + 1),
-    }));
-
     let mut params_substitutor =
         ParamsSubstitutor::new(tcx, placeholders_collector.next_ty_placeholder);
     let obligation = obligation.fold_with(&mut params_substitutor);
-    // FIXME(chalk): we really should be substituting these back in the solution
     let _params: FxHashMap<usize, ParamTy> = params_substitutor.params;
 
-    let mut regions_substitutor = RegionsSubstitutor::new(tcx, reempty_placeholder);
-    let obligation = obligation.fold_with(&mut regions_substitutor);
-
     let max_universe = obligation.max_universe.index();
 
     let lowered_goal: chalk_ir::UCanonical<
@@ -96,7 +86,8 @@ crate fn evaluate_goal<'tcx>(
 
     use chalk_solve::Solver;
     let mut solver = chalk_engine::solve::SLGSolver::new(32, None);
-    let db = ChalkRustIrDatabase { interner, reempty_placeholder };
+    let db = ChalkRustIrDatabase { interner };
+    debug!(?lowered_goal);
     let solution = solver.solve(&db, &lowered_goal);
     debug!(?obligation, ?solution, "evaluate goal");