Unwrap the results of type folders

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

compiler/rustc_trait_selection/src/lib.rs

@@ -22,6 +22,7 @@
 #![feature(never_type)]
 #![feature(crate_visibility_modifier)]
 #![feature(control_flow_enum)]
+#![feature(unwrap_infallible)]
 #![recursion_limit = "512"] // For rustdoc
 
 #[macro_use]

compiler/rustc_trait_selection/src/opaque_types.rs

@@ -65,14 +65,16 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
         // Convert the type from the function into a type valid outside
         // the function, by replacing invalid regions with 'static,
         // after producing an error for each of them.
-        let definition_ty = instantiated_ty.fold_with(&mut ReverseMapper::new(
-            self.tcx,
-            self.is_tainted_by_errors(),
-            def_id,
-            map,
-            instantiated_ty,
-            span,
-        ));
+        let definition_ty = instantiated_ty
+            .fold_with(&mut ReverseMapper::new(
+                self.tcx,
+                self.is_tainted_by_errors(),
+                def_id,
+                map,
+                instantiated_ty,
+                span,
+            ))
+            .into_ok();
         debug!(?definition_ty);
 
         definition_ty
@@ -123,14 +125,14 @@ impl ReverseMapper<'tcx> {
     ) -> GenericArg<'tcx> {
         assert!(!self.map_missing_regions_to_empty);
         self.map_missing_regions_to_empty = true;
-        let kind = kind.fold_with(self);
+        let kind = kind.fold_with(self).into_ok();
         self.map_missing_regions_to_empty = false;
         kind
     }
 
     fn fold_kind_normally(&mut self, kind: GenericArg<'tcx>) -> GenericArg<'tcx> {
         assert!(!self.map_missing_regions_to_empty);
-        kind.fold_with(self)
+        kind.fold_with(self).into_ok()
     }
 }
 

compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs

@@ -1916,8 +1916,9 @@ impl<'a, 'tcx> InferCtxtPrivExt<'tcx> for InferCtxt<'a, 'tcx> {
         self.probe(|_| {
             let mut selcx = SelectionContext::new(self);
 
-            let cleaned_pred =
-                pred.fold_with(&mut ParamToVarFolder { infcx: self, var_map: Default::default() });
+            let cleaned_pred = pred
+                .fold_with(&mut ParamToVarFolder { infcx: self, var_map: Default::default() })
+                .into_ok();
 
             let cleaned_pred = super::project::normalize(
                 &mut selcx,

compiler/rustc_trait_selection/src/traits/project.rs

@@ -339,7 +339,7 @@ impl<'a, 'b, 'tcx> AssocTypeNormalizer<'a, 'b, 'tcx> {
         if !needs_normalization(&value, self.param_env.reveal()) {
             value
         } else {
-            value.fold_with(self)
+            value.fold_with(self).into_ok()
         }
     }
 }
@@ -555,7 +555,7 @@ impl<'me, 'tcx> BoundVarReplacer<'me, 'tcx> {
             universe_indices,
         };
 
-        let value = value.super_fold_with(&mut replacer);
+        let value = value.super_fold_with(&mut replacer).into_ok();
 
         (value, replacer.mapped_regions, replacer.mapped_types, replacer.mapped_consts)
     }
@@ -681,7 +681,7 @@ impl<'me, 'tcx> PlaceholderReplacer<'me, 'tcx> {
             universe_indices,
             current_index: ty::INNERMOST,
         };
-        value.super_fold_with(&mut replacer)
+        value.super_fold_with(&mut replacer).into_ok()
     }
 }
 
@@ -1546,7 +1546,8 @@ fn confirm_candidate<'cx, 'tcx>(
     // when possible for this to work. See `auto-trait-projection-recursion.rs`
     // for a case where this matters.
     if progress.ty.has_infer_regions() {
-        progress.ty = OpportunisticRegionResolver::new(selcx.infcx()).fold_ty(progress.ty);
+        progress.ty =
+            OpportunisticRegionResolver::new(selcx.infcx()).fold_ty(progress.ty).into_ok();
     }
     progress
 }

compiler/rustc_trait_selection/src/traits/query/normalize.rs

@@ -88,7 +88,7 @@ impl<'cx, 'tcx> AtExt<'tcx> for At<'cx, 'tcx> {
                 normalizer.universes.extend((0..max_visitor.escaping).map(|_| None));
             }
         }
-        let result = value.fold_with(&mut normalizer);
+        let result = value.fold_with(&mut normalizer).into_ok();
         info!(
             "normalize::<{}>: result={:?} with {} obligations",
             std::any::type_name::<T>(),

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -2222,6 +2222,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             .predicate
             .to_poly_trait_ref()
             .fold_with(&mut self.freshener)
+            .into_ok()
             .with_constness(obligation.predicate.skip_binder().constness);
 
         let dfn = previous_stack.cache.next_dfn();