Unwrap the results of type folders

Co-authored-by: Alan Egerton <eggyal@gmail.com>

compiler/rustc_traits/src/chalk/db.rs

@@ -45,7 +45,7 @@ impl<'tcx> RustIrDatabase<'tcx> {
         predicates
             .iter()
             .map(|(wc, _)| wc.subst(self.interner.tcx, bound_vars))
-            .map(|wc| wc.fold_with(&mut regions_substitutor))
+            .map(|wc| wc.fold_with(&mut regions_substitutor).into_ok())
             .filter_map(|wc| LowerInto::<Option<chalk_ir::QuantifiedWhereClause<RustInterner<'tcx>>>>::lower_into(wc, &self.interner)).collect()
     }
 
@@ -287,7 +287,7 @@ impl<'tcx> chalk_solve::RustIrDatabase<RustInterner<'tcx>> for RustIrDatabase<'t
         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 trait_ref = trait_ref.fold_with(&mut regions_substitutor).into_ok();
 
         let where_clauses = self.where_clauses_for(def_id, bound_vars);
 
@@ -335,7 +335,7 @@ impl<'tcx> chalk_solve::RustIrDatabase<RustInterner<'tcx>> for RustIrDatabase<'t
             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 self_ty = self_ty.fold_with(&mut regions_substitutor).into_ok();
             let lowered_ty = self_ty.lower_into(&self.interner);
 
             parameters[0].assert_ty_ref(&self.interner).could_match(
@@ -501,22 +501,24 @@ impl<'tcx> chalk_solve::RustIrDatabase<RustInterner<'tcx>> for RustIrDatabase<'t
                 .iter()
                 .map(|(bound, _)| bound.subst(self.interner.tcx, &bound_vars))
                 .map(|bound| {
-                    bound.fold_with(&mut ty::fold::BottomUpFolder {
-                        tcx: self.interner.tcx,
-                        ty_op: |ty| {
-                            if let ty::Opaque(def_id, substs) = *ty.kind() {
-                                if def_id == opaque_ty_id.0 && substs == identity_substs {
-                                    return self.interner.tcx.mk_ty(ty::Bound(
-                                        ty::INNERMOST,
-                                        ty::BoundTy::from(ty::BoundVar::from_u32(0)),
-                                    ));
+                    bound
+                        .fold_with(&mut ty::fold::BottomUpFolder {
+                            tcx: self.interner.tcx,
+                            ty_op: |ty| {
+                                if let ty::Opaque(def_id, substs) = *ty.kind() {
+                                    if def_id == opaque_ty_id.0 && substs == identity_substs {
+                                        return self.interner.tcx.mk_ty(ty::Bound(
+                                            ty::INNERMOST,
+                                            ty::BoundTy::from(ty::BoundVar::from_u32(0)),
+                                        ));
+                                    }
                                 }
-                            }
-                            ty
-                        },
-                        lt_op: |lt| lt,
-                        ct_op: |ct| ct,
-                    })
+                                ty
+                            },
+                            lt_op: |lt| lt,
+                            ct_op: |ct| ct,
+                        })
+                        .into_ok()
                 })
                 .filter_map(|bound| {
                     LowerInto::<

compiler/rustc_traits/src/chalk/lowering.rs

@@ -817,7 +817,7 @@ crate fn collect_bound_vars<'tcx, T: TypeFoldable<'tcx>>(
         .collect();
 
     let mut bound_var_substitutor = NamedBoundVarSubstitutor::new(tcx, &named_parameters);
-    let new_ty = ty.skip_binder().fold_with(&mut bound_var_substitutor);
+    let new_ty = ty.skip_binder().fold_with(&mut bound_var_substitutor).into_ok();
 
     for var in named_parameters.values() {
         parameters.insert(*var, chalk_ir::VariableKind::Lifetime);

compiler/rustc_traits/src/chalk/mod.rs

@@ -49,12 +49,12 @@ crate fn evaluate_goal<'tcx>(
 
     let mut params_substitutor =
         ParamsSubstitutor::new(tcx, placeholders_collector.next_ty_placeholder);
-    let obligation = obligation.fold_with(&mut params_substitutor);
+    let obligation = obligation.fold_with(&mut params_substitutor).into_ok();
     // 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 obligation = obligation.fold_with(&mut regions_substitutor).into_ok();
 
     let max_universe = obligation.max_universe.index();
 

compiler/rustc_traits/src/lib.rs

@@ -4,6 +4,7 @@
 #![feature(crate_visibility_modifier)]
 #![feature(in_band_lifetimes)]
 #![feature(nll)]
+#![feature(unwrap_infallible)]
 #![recursion_limit = "256"]
 
 #[macro_use]