Use TypeVisitor::BreakTy in structural_match::Search

compiler/rustc_trait_selection/src/traits/structural_match.rs

@@ -55,9 +55,7 @@ pub fn search_for_structural_match_violation<'tcx>(
 ) -> Option<NonStructuralMatchTy<'tcx>> {
     // FIXME: we should instead pass in an `infcx` from the outside.
     tcx.infer_ctxt().enter(|infcx| {
-        let mut search = Search { infcx, span, found: None, seen: FxHashSet::default() };
-        ty.visit_with(&mut search);
-        search.found
+        ty.visit_with(&mut Search { infcx, span, seen: FxHashSet::default() }).break_value()
     })
 }
 
@@ -116,9 +114,6 @@ struct Search<'a, 'tcx> {
 
     infcx: InferCtxt<'a, 'tcx>,
 
-    /// Records first ADT that does not implement a structural-match trait.
-    found: Option<NonStructuralMatchTy<'tcx>>,
-
     /// Tracks ADTs previously encountered during search, so that
     /// we will not recur on them again.
     seen: FxHashSet<hir::def_id::DefId>,
@@ -135,38 +130,33 @@ impl Search<'a, 'tcx> {
 }
 
 impl<'a, 'tcx> TypeVisitor<'tcx> for Search<'a, 'tcx> {
+    type BreakTy = NonStructuralMatchTy<'tcx>;
+
     fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
         debug!("Search visiting ty: {:?}", ty);
 
         let (adt_def, substs) = match *ty.kind() {
             ty::Adt(adt_def, substs) => (adt_def, substs),
             ty::Param(_) => {
-                self.found = Some(NonStructuralMatchTy::Param);
-                return ControlFlow::BREAK;
+                return ControlFlow::Break(NonStructuralMatchTy::Param);
             }
             ty::Dynamic(..) => {
-                self.found = Some(NonStructuralMatchTy::Dynamic);
-                return ControlFlow::BREAK;
+                return ControlFlow::Break(NonStructuralMatchTy::Dynamic);
             }
             ty::Foreign(_) => {
-                self.found = Some(NonStructuralMatchTy::Foreign);
-                return ControlFlow::BREAK;
+                return ControlFlow::Break(NonStructuralMatchTy::Foreign);
             }
             ty::Opaque(..) => {
-                self.found = Some(NonStructuralMatchTy::Opaque);
-                return ControlFlow::BREAK;
+                return ControlFlow::Break(NonStructuralMatchTy::Opaque);
             }
             ty::Projection(..) => {
-                self.found = Some(NonStructuralMatchTy::Projection);
-                return ControlFlow::BREAK;
+                return ControlFlow::Break(NonStructuralMatchTy::Projection);
             }
             ty::Generator(..) | ty::GeneratorWitness(..) => {
-                self.found = Some(NonStructuralMatchTy::Generator);
-                return ControlFlow::BREAK;
+                return ControlFlow::Break(NonStructuralMatchTy::Generator);
             }
             ty::Closure(..) => {
-                self.found = Some(NonStructuralMatchTy::Closure);
-                return ControlFlow::BREAK;
+                return ControlFlow::Break(NonStructuralMatchTy::Closure);
             }
             ty::RawPtr(..) => {
                 // structural-match ignores substructure of
@@ -206,8 +196,7 @@ impl<'a, 'tcx> TypeVisitor<'tcx> for Search<'a, 'tcx> {
 
             ty::Array(..) | ty::Slice(_) | ty::Ref(..) | ty::Tuple(..) => {
                 // First check all contained types and then tell the caller to continue searching.
-                ty.super_visit_with(self);
-                return ControlFlow::CONTINUE;
+                return ty.super_visit_with(self);
             }
             ty::Infer(_) | ty::Placeholder(_) | ty::Bound(..) => {
                 bug!("unexpected type during structural-match checking: {:?}", ty);
@@ -227,8 +216,7 @@ impl<'a, 'tcx> TypeVisitor<'tcx> for Search<'a, 'tcx> {
 
         if !self.type_marked_structural(ty) {
             debug!("Search found ty: {:?}", ty);
-            self.found = Some(NonStructuralMatchTy::Adt(&adt_def));
-            return ControlFlow::BREAK;
+            return ControlFlow::Break(NonStructuralMatchTy::Adt(&adt_def));
         }
 
         // structural-match does not care about the
@@ -244,20 +232,11 @@ impl<'a, 'tcx> TypeVisitor<'tcx> for Search<'a, 'tcx> {
         // even though we skip super_visit_with, we must recur on
         // fields of ADT.
         let tcx = self.tcx();
-        for field_ty in adt_def.all_fields().map(|field| field.ty(tcx, substs)) {
+        adt_def.all_fields().map(|field| field.ty(tcx, substs)).try_for_each(|field_ty| {
             let ty = self.tcx().normalize_erasing_regions(ty::ParamEnv::empty(), field_ty);
             debug!("structural-match ADT: field_ty={:?}, ty={:?}", field_ty, ty);
-
-            if ty.visit_with(self).is_break() {
-                // found an ADT without structural-match; halt visiting!
-                assert!(self.found.is_some());
-                return ControlFlow::BREAK;
-            }
-        }
-
-        // Even though we do not want to recur on substs, we do
-        // want our caller to continue its own search.
-        ControlFlow::CONTINUE
+            ty.visit_with(self)
+        })
     }
 }