Introduce `TypeVisitor::BreakTy`

30 files changed, 156 insertions, 127 deletions

diff --git a/compiler/rustc_infer/src/infer/error_reporting/mod.rs b/compiler/rustc_infer/src/infer/error_reporting/mod.rs
index 524efd04cfc..b0d9daf3927 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/mod.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/mod.rs
@@ -1498,7 +1498,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         }
 
         impl<'tcx> ty::fold::TypeVisitor<'tcx> for OpaqueTypesVisitor<'tcx> {
-            fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<()> {
+            fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
                 if let Some((kind, def_id)) = TyCategory::from_ty(t) {
                     let span = self.tcx.def_span(def_id);
                     // Avoid cluttering the output when the "found" and error span overlap:
diff --git a/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/static_impl_trait.rs b/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/static_impl_trait.rs
index df3dbfca01d..7b0deb45f86 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/static_impl_trait.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/nice_region_error/static_impl_trait.rs
@@ -474,7 +474,7 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
 struct TraitObjectVisitor(Vec<DefId>);
 
 impl TypeVisitor<'_> for TraitObjectVisitor {
-    fn visit_ty(&mut self, t: Ty<'_>) -> ControlFlow<()> {
+    fn visit_ty(&mut self, t: Ty<'_>) -> ControlFlow<Self::BreakTy> {
         match t.kind() {
             ty::Dynamic(preds, RegionKind::ReStatic) => {
                 if let Some(def_id) = preds.principal_def_id() {
diff --git a/compiler/rustc_infer/src/infer/nll_relate/mod.rs b/compiler/rustc_infer/src/infer/nll_relate/mod.rs
index 9b2ffc7a920..0b2847658f7 100644
--- a/compiler/rustc_infer/src/infer/nll_relate/mod.rs
+++ b/compiler/rustc_infer/src/infer/nll_relate/mod.rs
@@ -741,7 +741,10 @@ struct ScopeInstantiator<'me, 'tcx> {
 }
 
 impl<'me, 'tcx> TypeVisitor<'tcx> for ScopeInstantiator<'me, 'tcx> {
-    fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ControlFlow<()> {
+    fn visit_binder<T: TypeFoldable<'tcx>>(
+        &mut self,
+        t: &ty::Binder<T>,
+    ) -> ControlFlow<Self::BreakTy> {
         self.target_index.shift_in(1);
         t.super_visit_with(self);
         self.target_index.shift_out(1);
@@ -749,7 +752,7 @@ impl<'me, 'tcx> TypeVisitor<'tcx> for ScopeInstantiator<'me, 'tcx> {
         ControlFlow::CONTINUE
     }
 
-    fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<()> {
+    fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
         let ScopeInstantiator { bound_region_scope, next_region, .. } = self;
 
         match r {
diff --git a/compiler/rustc_infer/src/infer/resolve.rs b/compiler/rustc_infer/src/infer/resolve.rs
index fe4ba5aa4e8..e2531dc7ad9 100644
--- a/compiler/rustc_infer/src/infer/resolve.rs
+++ b/compiler/rustc_infer/src/infer/resolve.rs
@@ -123,7 +123,7 @@ impl<'a, 'tcx> UnresolvedTypeFinder<'a, 'tcx> {
 }
 
 impl<'a, 'tcx> TypeVisitor<'tcx> for UnresolvedTypeFinder<'a, 'tcx> {
-    fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<()> {
+    fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
         let t = self.infcx.shallow_resolve(t);
         if t.has_infer_types() {
             if let ty::Infer(infer_ty) = *t.kind() {
diff --git a/compiler/rustc_infer/src/traits/structural_impls.rs b/compiler/rustc_infer/src/traits/structural_impls.rs
index 1a1c2637a6f..d6500f62e78 100644
--- a/compiler/rustc_infer/src/traits/structural_impls.rs
+++ b/compiler/rustc_infer/src/traits/structural_impls.rs
@@ -69,7 +69,7 @@ impl<'tcx, O: TypeFoldable<'tcx>> TypeFoldable<'tcx> for traits::Obligation<'tcx
         }
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         self.predicate.visit_with(visitor)
     }
 }
diff --git a/compiler/rustc_lint/src/types.rs b/compiler/rustc_lint/src/types.rs
index 467a3a42590..802fb1970cd 100644
--- a/compiler/rustc_lint/src/types.rs
+++ b/compiler/rustc_lint/src/types.rs
@@ -1135,7 +1135,7 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
         };
 
         impl<'a, 'tcx> ty::fold::TypeVisitor<'tcx> for ProhibitOpaqueTypes<'a, 'tcx> {
-            fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<()> {
+            fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
                 match ty.kind() {
                     ty::Opaque(..) => {
                         self.ty = Some(ty);
diff --git a/compiler/rustc_macros/src/type_foldable.rs b/compiler/rustc_macros/src/type_foldable.rs
index 8fa6e6a7101..18d7affa75d 100644
--- a/compiler/rustc_macros/src/type_foldable.rs
+++ b/compiler/rustc_macros/src/type_foldable.rs
@@ -35,7 +35,7 @@ pub fn type_foldable_derive(mut s: synstructure::Structure<'_>) -> proc_macro2::
             fn super_visit_with<__F: ::rustc_middle::ty::fold::TypeVisitor<'tcx>>(
                 &self,
                 __folder: &mut __F
-            ) -> ::std::ops::ControlFlow<()> {
+            ) -> ::std::ops::ControlFlow<__F::BreakTy> {
                 match *self { #body_visit }
                 ::std::ops::ControlFlow::CONTINUE
             }
diff --git a/compiler/rustc_middle/src/lib.rs b/compiler/rustc_middle/src/lib.rs
index 4a1d5459d1e..cdc5940d9ba 100644
--- a/compiler/rustc_middle/src/lib.rs
+++ b/compiler/rustc_middle/src/lib.rs
@@ -51,6 +51,7 @@
 #![feature(half_open_range_patterns)]
 #![feature(exclusive_range_pattern)]
 #![feature(control_flow_enum)]
+#![feature(associated_type_defaults)]
 #![recursion_limit = "512"]
 
 #[macro_use]
diff --git a/compiler/rustc_middle/src/macros.rs b/compiler/rustc_middle/src/macros.rs
index 921086366be..057f2615a44 100644
--- a/compiler/rustc_middle/src/macros.rs
+++ b/compiler/rustc_middle/src/macros.rs
@@ -62,7 +62,7 @@ macro_rules! CloneTypeFoldableImpls {
                 fn super_visit_with<F: $crate::ty::fold::TypeVisitor<$tcx>>(
                     &self,
                     _: &mut F)
-                    -> ::std::ops::ControlFlow<()>
+                    -> ::std::ops::ControlFlow<F::BreakTy>
                 {
                     ::std::ops::ControlFlow::CONTINUE
                 }
@@ -105,7 +105,7 @@ macro_rules! EnumTypeFoldableImpl {
             fn super_visit_with<V: $crate::ty::fold::TypeVisitor<$tcx>>(
                 &self,
                 visitor: &mut V,
-            ) -> ::std::ops::ControlFlow<()> {
+            ) -> ::std::ops::ControlFlow<V::BreakTy> {
                 EnumTypeFoldableImpl!(@VisitVariants(self, visitor) input($($variants)*) output())
             }
         }
diff --git a/compiler/rustc_middle/src/mir/mod.rs b/compiler/rustc_middle/src/mir/mod.rs
index 5fe7b0f647d..15783cfd00c 100644
--- a/compiler/rustc_middle/src/mir/mod.rs
+++ b/compiler/rustc_middle/src/mir/mod.rs
@@ -2477,7 +2477,10 @@ impl<'tcx> TypeFoldable<'tcx> for UserTypeProjection {
         UserTypeProjection { base, projs }
     }
 
-    fn super_visit_with<Vs: TypeVisitor<'tcx>>(&self, visitor: &mut Vs) -> ControlFlow<()> {
+    fn super_visit_with<Vs: TypeVisitor<'tcx>>(
+        &self,
+        visitor: &mut Vs,
+    ) -> ControlFlow<Vs::BreakTy> {
         self.base.visit_with(visitor)
         // Note: there's nothing in `self.proj` to visit.
     }
diff --git a/compiler/rustc_middle/src/mir/type_foldable.rs b/compiler/rustc_middle/src/mir/type_foldable.rs
index 0801188b278..0e6bf0fd029 100644
--- a/compiler/rustc_middle/src/mir/type_foldable.rs
+++ b/compiler/rustc_middle/src/mir/type_foldable.rs
@@ -87,7 +87,7 @@ impl<'tcx> TypeFoldable<'tcx> for Terminator<'tcx> {
         Terminator { source_info: self.source_info, kind }
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         use crate::mir::TerminatorKind::*;
 
         match self.kind {
@@ -144,7 +144,7 @@ impl<'tcx> TypeFoldable<'tcx> for GeneratorKind {
         *self
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, _: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, _: &mut V) -> ControlFlow<V::BreakTy> {
         ControlFlow::CONTINUE
     }
 }
@@ -154,7 +154,7 @@ impl<'tcx> TypeFoldable<'tcx> for Place<'tcx> {
         Place { local: self.local.fold_with(folder), projection: self.projection.fold_with(folder) }
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         self.local.visit_with(visitor)?;
         self.projection.visit_with(visitor)
     }
@@ -166,7 +166,7 @@ impl<'tcx> TypeFoldable<'tcx> for &'tcx ty::List<PlaceElem<'tcx>> {
         folder.tcx().intern_place_elems(&v)
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         self.iter().try_for_each(|t| t.visit_with(visitor))
     }
 }
@@ -216,7 +216,7 @@ impl<'tcx> TypeFoldable<'tcx> for Rvalue<'tcx> {
         }
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         use crate::mir::Rvalue::*;
         match *self {
             Use(ref op) => op.visit_with(visitor),
@@ -271,7 +271,7 @@ impl<'tcx> TypeFoldable<'tcx> for Operand<'tcx> {
         }
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         match *self {
             Operand::Copy(ref place) | Operand::Move(ref place) => place.visit_with(visitor),
             Operand::Constant(ref c) => c.visit_with(visitor),
@@ -295,7 +295,10 @@ impl<'tcx> TypeFoldable<'tcx> for PlaceElem<'tcx> {
         }
     }
 
-    fn super_visit_with<Vs: TypeVisitor<'tcx>>(&self, visitor: &mut Vs) -> ControlFlow<()> {
+    fn super_visit_with<Vs: TypeVisitor<'tcx>>(
+        &self,
+        visitor: &mut Vs,
+    ) -> ControlFlow<Vs::BreakTy> {
         use crate::mir::ProjectionElem::*;
 
         match self {
@@ -310,7 +313,7 @@ impl<'tcx> TypeFoldable<'tcx> for Field {
     fn super_fold_with<F: TypeFolder<'tcx>>(&self, _: &mut F) -> Self {
         *self
     }
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, _: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, _: &mut V) -> ControlFlow<V::BreakTy> {
         ControlFlow::CONTINUE
     }
 }
@@ -319,7 +322,7 @@ impl<'tcx> TypeFoldable<'tcx> for GeneratorSavedLocal {
     fn super_fold_with<F: TypeFolder<'tcx>>(&self, _: &mut F) -> Self {
         *self
     }
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, _: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, _: &mut V) -> ControlFlow<V::BreakTy> {
         ControlFlow::CONTINUE
     }
 }
@@ -328,7 +331,7 @@ impl<'tcx, R: Idx, C: Idx> TypeFoldable<'tcx> for BitMatrix<R, C> {
     fn super_fold_with<F: TypeFolder<'tcx>>(&self, _: &mut F) -> Self {
         self.clone()
     }
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, _: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, _: &mut V) -> ControlFlow<V::BreakTy> {
         ControlFlow::CONTINUE
     }
 }
@@ -341,7 +344,7 @@ impl<'tcx> TypeFoldable<'tcx> for Constant<'tcx> {
             literal: self.literal.fold_with(folder),
         }
     }
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         self.literal.visit_with(visitor)
     }
 }
diff --git a/compiler/rustc_middle/src/ty/fold.rs b/compiler/rustc_middle/src/ty/fold.rs
index 70a8157c04a..c24cb9b4c0f 100644
--- a/compiler/rustc_middle/src/ty/fold.rs
+++ b/compiler/rustc_middle/src/ty/fold.rs
@@ -49,8 +49,8 @@ pub trait TypeFoldable<'tcx>: fmt::Debug + Clone {
         self.super_fold_with(folder)
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()>;
-    fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy>;
+    fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         self.super_visit_with(visitor)
     }
 
@@ -161,7 +161,7 @@ impl TypeFoldable<'tcx> for hir::Constness {
     fn super_fold_with<F: TypeFolder<'tcx>>(&self, _: &mut F) -> Self {
         *self
     }
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, _: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, _: &mut V) -> ControlFlow<V::BreakTy> {
         ControlFlow::CONTINUE
     }
 }
@@ -195,23 +195,25 @@ pub trait TypeFolder<'tcx>: Sized {
 }
 
 pub trait TypeVisitor<'tcx>: Sized {
-    fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> ControlFlow<()> {
+    type BreakTy = ();
+
+    fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> ControlFlow<Self::BreakTy> {
         t.super_visit_with(self)
     }
 
-    fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<()> {
+    fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
         t.super_visit_with(self)
     }
 
-    fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<()> {
+    fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
         r.super_visit_with(self)
     }
 
-    fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> ControlFlow<()> {
+    fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
         c.super_visit_with(self)
     }
 
-    fn visit_predicate(&mut self, p: ty::Predicate<'tcx>) -> ControlFlow<()> {
+    fn visit_predicate(&mut self, p: ty::Predicate<'tcx>) -> ControlFlow<Self::BreakTy> {
         p.super_visit_with(self)
     }
 }
@@ -329,14 +331,17 @@ impl<'tcx> TyCtxt<'tcx> {
         where
             F: FnMut(ty::Region<'tcx>) -> bool,
         {
-            fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> ControlFlow<()> {
+            fn visit_binder<T: TypeFoldable<'tcx>>(
+                &mut self,
+                t: &Binder<T>,
+            ) -> ControlFlow<Self::BreakTy> {
                 self.outer_index.shift_in(1);
                 let result = t.as_ref().skip_binder().visit_with(self);
                 self.outer_index.shift_out(1);
                 result
             }
 
-            fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<()> {
+            fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
                 match *r {
                     ty::ReLateBound(debruijn, _) if debruijn < self.outer_index => {
                         ControlFlow::CONTINUE
@@ -351,7 +356,7 @@ impl<'tcx> TyCtxt<'tcx> {
                 }
             }
 
-            fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<()> {
+            fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
                 // We're only interested in types involving regions
                 if ty.flags().intersects(TypeFlags::HAS_FREE_REGIONS) {
                     ty.super_visit_with(self)
@@ -844,14 +849,14 @@ struct HasEscapingVarsVisitor {
 }
 
 impl<'tcx> TypeVisitor<'tcx> for HasEscapingVarsVisitor {
-    fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> ControlFlow<()> {
+    fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> ControlFlow<Self::BreakTy> {
         self.outer_index.shift_in(1);
         let result = t.super_visit_with(self);
         self.outer_index.shift_out(1);
         result
     }
 
-    fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<()> {
+    fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
         // If the outer-exclusive-binder is *strictly greater* than
         // `outer_index`, that means that `t` contains some content
         // bound at `outer_index` or above (because
@@ -864,7 +869,7 @@ impl<'tcx> TypeVisitor<'tcx> for HasEscapingVarsVisitor {
         }
     }
 
-    fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<()> {
+    fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
         // If the region is bound by `outer_index` or anything outside
         // of outer index, then it escapes the binders we have
         // visited.
@@ -875,7 +880,7 @@ impl<'tcx> TypeVisitor<'tcx> for HasEscapingVarsVisitor {
         }
     }
 
-    fn visit_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> ControlFlow<()> {
+    fn visit_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
         // we don't have a `visit_infer_const` callback, so we have to
         // hook in here to catch this case (annoying...), but
         // otherwise we do want to remember to visit the rest of the
@@ -887,7 +892,7 @@ impl<'tcx> TypeVisitor<'tcx> for HasEscapingVarsVisitor {
         }
     }
 
-    fn visit_predicate(&mut self, predicate: ty::Predicate<'tcx>) -> ControlFlow<()> {
+    fn visit_predicate(&mut self, predicate: ty::Predicate<'tcx>) -> ControlFlow<Self::BreakTy> {
         if predicate.inner.outer_exclusive_binder > self.outer_index {
             ControlFlow::BREAK
         } else {
@@ -902,7 +907,7 @@ struct HasTypeFlagsVisitor {
 }
 
 impl<'tcx> TypeVisitor<'tcx> for HasTypeFlagsVisitor {
-    fn visit_ty(&mut self, t: Ty<'_>) -> ControlFlow<()> {
+    fn visit_ty(&mut self, t: Ty<'_>) -> ControlFlow<Self::BreakTy> {
         debug!(
             "HasTypeFlagsVisitor: t={:?} t.flags={:?} self.flags={:?}",
             t,
@@ -912,19 +917,19 @@ impl<'tcx> TypeVisitor<'tcx> for HasTypeFlagsVisitor {
         if t.flags().intersects(self.flags) { ControlFlow::BREAK } else { ControlFlow::CONTINUE }
     }
 
-    fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<()> {
+    fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
         let flags = r.type_flags();
         debug!("HasTypeFlagsVisitor: r={:?} r.flags={:?} self.flags={:?}", r, flags, self.flags);
         if flags.intersects(self.flags) { ControlFlow::BREAK } else { ControlFlow::CONTINUE }
     }
 
-    fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> ControlFlow<()> {
+    fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
         let flags = FlagComputation::for_const(c);
         debug!("HasTypeFlagsVisitor: c={:?} c.flags={:?} self.flags={:?}", c, flags, self.flags);
         if flags.intersects(self.flags) { ControlFlow::BREAK } else { ControlFlow::CONTINUE }
     }
 
-    fn visit_predicate(&mut self, predicate: ty::Predicate<'tcx>) -> ControlFlow<()> {
+    fn visit_predicate(&mut self, predicate: ty::Predicate<'tcx>) -> ControlFlow<Self::BreakTy> {
         debug!(
             "HasTypeFlagsVisitor: predicate={:?} predicate.flags={:?} self.flags={:?}",
             predicate, predicate.inner.flags, self.flags
@@ -964,14 +969,14 @@ impl LateBoundRegionsCollector {
 }
 
 impl<'tcx> TypeVisitor<'tcx> for LateBoundRegionsCollector {
-    fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> ControlFlow<()> {
+    fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> ControlFlow<Self::BreakTy> {
         self.current_index.shift_in(1);
         let result = t.super_visit_with(self);
         self.current_index.shift_out(1);
         result
     }
 
-    fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<()> {
+    fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
         // if we are only looking for "constrained" region, we have to
         // ignore the inputs to a projection, as they may not appear
         // in the normalized form
@@ -984,7 +989,7 @@ impl<'tcx> TypeVisitor<'tcx> for LateBoundRegionsCollector {
         t.super_visit_with(self)
     }
 
-    fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> ControlFlow<()> {
+    fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
         // if we are only looking for "constrained" region, we have to
         // ignore the inputs of an unevaluated const, as they may not appear
         // in the normalized form
@@ -997,7 +1002,7 @@ impl<'tcx> TypeVisitor<'tcx> for LateBoundRegionsCollector {
         c.super_visit_with(self)
     }
 
-    fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<()> {
+    fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
         if let ty::ReLateBound(debruijn, br) = *r {
             if debruijn == self.current_index {
                 self.regions.insert(br);
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index 06e69a0009b..dee0abb868e 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -1781,7 +1781,7 @@ impl<'tcx> TypeFoldable<'tcx> for ParamEnv<'tcx> {
         ParamEnv::new(self.caller_bounds().fold_with(folder), self.reveal().fold_with(folder))
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         self.caller_bounds().visit_with(visitor)?;
         self.reveal().visit_with(visitor)
     }
diff --git a/compiler/rustc_middle/src/ty/print/pretty.rs b/compiler/rustc_middle/src/ty/print/pretty.rs
index 1e4fd0921ee..d4fad188e21 100644
--- a/compiler/rustc_middle/src/ty/print/pretty.rs
+++ b/compiler/rustc_middle/src/ty/print/pretty.rs
@@ -1796,7 +1796,7 @@ impl<F: fmt::Write> FmtPrinter<'_, 'tcx, F> {
     {
         struct LateBoundRegionNameCollector<'a>(&'a mut FxHashSet<Symbol>);
         impl<'tcx> ty::fold::TypeVisitor<'tcx> for LateBoundRegionNameCollector<'_> {
-            fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<()> {
+            fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
                 if let ty::ReLateBound(_, ty::BrNamed(_, name)) = *r {
                     self.0.insert(name);
                 }
diff --git a/compiler/rustc_middle/src/ty/structural_impls.rs b/compiler/rustc_middle/src/ty/structural_impls.rs
index 89fd803fe51..d42a1b772a0 100644
--- a/compiler/rustc_middle/src/ty/structural_impls.rs
+++ b/compiler/rustc_middle/src/ty/structural_impls.rs
@@ -729,7 +729,7 @@ impl<'tcx> TypeFoldable<'tcx> for &'tcx ty::AdtDef {
         *self
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, _visitor: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, _visitor: &mut V) -> ControlFlow<V::BreakTy> {
         ControlFlow::CONTINUE
     }
 }
@@ -739,7 +739,7 @@ impl<'tcx, T: TypeFoldable<'tcx>, U: TypeFoldable<'tcx>> TypeFoldable<'tcx> for
         (self.0.fold_with(folder), self.1.fold_with(folder))
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         self.0.visit_with(visitor)?;
         self.1.visit_with(visitor)
     }
@@ -752,7 +752,7 @@ impl<'tcx, A: TypeFoldable<'tcx>, B: TypeFoldable<'tcx>, C: TypeFoldable<'tcx>>
         (self.0.fold_with(folder), self.1.fold_with(folder), self.2.fold_with(folder))
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         self.0.visit_with(visitor)?;
         self.1.visit_with(visitor)?;
         self.2.visit_with(visitor)
@@ -778,7 +778,7 @@ impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for Rc<T> {
         Rc::new((**self).fold_with(folder))
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         (**self).visit_with(visitor)
     }
 }
@@ -788,7 +788,7 @@ impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for Arc<T> {
         Arc::new((**self).fold_with(folder))
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         (**self).visit_with(visitor)
     }
 }
@@ -799,7 +799,7 @@ impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for Box<T> {
         box content
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         (**self).visit_with(visitor)
     }
 }
@@ -809,7 +809,7 @@ impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for Vec<T> {
         self.iter().map(|t| t.fold_with(folder)).collect()
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         self.iter().try_for_each(|t| t.visit_with(visitor))
     }
 }
@@ -819,7 +819,7 @@ impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for Box<[T]> {
         self.iter().map(|t| t.fold_with(folder)).collect::<Vec<_>>().into_boxed_slice()
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         self.iter().try_for_each(|t| t.visit_with(visitor))
     }
 }
@@ -833,11 +833,11 @@ impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for ty::Binder<T> {
         folder.fold_binder(self)
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         self.as_ref().skip_binder().visit_with(visitor)
     }
 
-    fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         visitor.visit_binder(self)
     }
 }
@@ -847,7 +847,7 @@ impl<'tcx> TypeFoldable<'tcx> for &'tcx ty::List<ty::ExistentialPredicate<'tcx>>
         fold_list(*self, folder, |tcx, v| tcx.intern_existential_predicates(v))
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         self.iter().try_for_each(|p| p.visit_with(visitor))
     }
 }
@@ -857,7 +857,7 @@ impl<'tcx> TypeFoldable<'tcx> for &'tcx ty::List<Ty<'tcx>> {
         fold_list(*self, folder, |tcx, v| tcx.intern_type_list(v))
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         self.iter().try_for_each(|t| t.visit_with(visitor))
     }
 }
@@ -867,7 +867,7 @@ impl<'tcx> TypeFoldable<'tcx> for &'tcx ty::List<ProjectionKind> {
         fold_list(*self, folder, |tcx, v| tcx.intern_projs(v))
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         self.iter().try_for_each(|t| t.visit_with(visitor))
     }
 }
@@ -893,7 +893,7 @@ impl<'tcx> TypeFoldable<'tcx> for ty::instance::Instance<'tcx> {
         }
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         use crate::ty::InstanceDef::*;
         self.substs.visit_with(visitor)?;
         match self.def {
@@ -919,7 +919,7 @@ impl<'tcx> TypeFoldable<'tcx> for interpret::GlobalId<'tcx> {
         Self { instance: self.instance.fold_with(folder), promoted: self.promoted }
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         self.instance.visit_with(visitor)
     }
 }
@@ -968,7 +968,7 @@ impl<'tcx> TypeFoldable<'tcx> for Ty<'tcx> {
         folder.fold_ty(*self)
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         match self.kind() {
             ty::RawPtr(ref tm) => tm.visit_with(visitor),
             ty::Array(typ, sz) => {
@@ -1010,7 +1010,7 @@ impl<'tcx> TypeFoldable<'tcx> for Ty<'tcx> {
         }
     }
 
-    fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         visitor.visit_ty(self)
     }
 }
@@ -1024,11 +1024,11 @@ impl<'tcx> TypeFoldable<'tcx> for ty::Region<'tcx> {
         folder.fold_region(*self)
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, _visitor: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, _visitor: &mut V) -> ControlFlow<V::BreakTy> {
         ControlFlow::CONTINUE
     }
 
-    fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         visitor.visit_region(*self)
     }
 }
@@ -1039,11 +1039,11 @@ impl<'tcx> TypeFoldable<'tcx> for ty::Predicate<'tcx> {
         folder.tcx().reuse_or_mk_predicate(*self, new)
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         ty::PredicateKind::super_visit_with(&self.inner.kind, visitor)
     }
 
-    fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         visitor.visit_predicate(*self)
     }
 
@@ -1061,7 +1061,7 @@ impl<'tcx> TypeFoldable<'tcx> for &'tcx ty::List<ty::Predicate<'tcx>> {
         fold_list(*self, folder, |tcx, v| tcx.intern_predicates(v))
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         self.iter().try_for_each(|p| p.visit_with(visitor))
     }
 }
@@ -1071,7 +1071,7 @@ impl<'tcx, T: TypeFoldable<'tcx>, I: Idx> TypeFoldable<'tcx> for IndexVec<I, T>
         self.iter().map(|x| x.fold_with(folder)).collect()
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         self.iter().try_for_each(|t| t.visit_with(visitor))
     }
 }
@@ -1091,12 +1091,12 @@ impl<'tcx> TypeFoldable<'tcx> for &'tcx ty::Const<'tcx> {
         folder.fold_const(*self)
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         self.ty.visit_with(visitor)?;
         self.val.visit_with(visitor)
     }
 
-    fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         visitor.visit_const(self)
     }
 }
@@ -1116,7 +1116,7 @@ impl<'tcx> TypeFoldable<'tcx> for ty::ConstKind<'tcx> {
         }
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         match *self {
             ty::ConstKind::Infer(ic) => ic.visit_with(visitor),
             ty::ConstKind::Param(p) => p.visit_with(visitor),
@@ -1134,7 +1134,7 @@ impl<'tcx> TypeFoldable<'tcx> for InferConst<'tcx> {
         *self
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, _visitor: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, _visitor: &mut V) -> ControlFlow<V::BreakTy> {
         ControlFlow::CONTINUE
     }
 }
diff --git a/compiler/rustc_middle/src/ty/subst.rs b/compiler/rustc_middle/src/ty/subst.rs
index 07f775cf8b1..343322cfe58 100644
--- a/compiler/rustc_middle/src/ty/subst.rs
+++ b/compiler/rustc_middle/src/ty/subst.rs
@@ -160,7 +160,7 @@ impl<'tcx> TypeFoldable<'tcx> for GenericArg<'tcx> {
         }
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         match self.unpack() {
             GenericArgKind::Lifetime(lt) => lt.visit_with(visitor),
             GenericArgKind::Type(ty) => ty.visit_with(visitor),
@@ -392,7 +392,7 @@ impl<'tcx> TypeFoldable<'tcx> for SubstsRef<'tcx> {
         }
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<()> {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         self.iter().try_for_each(|t| t.visit_with(visitor))
     }
 }
diff --git a/compiler/rustc_mir/src/interpret/util.rs b/compiler/rustc_mir/src/interpret/util.rs
index fce5553c993..f7fca4822ef 100644
--- a/compiler/rustc_mir/src/interpret/util.rs
+++ b/compiler/rustc_mir/src/interpret/util.rs
@@ -18,7 +18,7 @@ where
     };
 
     impl<'tcx> TypeVisitor<'tcx> for UsedParamsNeedSubstVisitor<'tcx> {
-        fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> ControlFlow<()> {
+        fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
             if !c.needs_subst() {
                 return ControlFlow::CONTINUE;
             }
@@ -29,7 +29,7 @@ where
             }
         }
 
-        fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<()> {
+        fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
             if !ty.needs_subst() {
                 return ControlFlow::CONTINUE;
             }
diff --git a/compiler/rustc_mir/src/monomorphize/polymorphize.rs b/compiler/rustc_mir/src/monomorphize/polymorphize.rs
index c2ebc954a22..6a50a924378 100644
--- a/compiler/rustc_mir/src/monomorphize/polymorphize.rs
+++ b/compiler/rustc_mir/src/monomorphize/polymorphize.rs
@@ -250,7 +250,7 @@ impl<'a, 'tcx> Visitor<'tcx> for MarkUsedGenericParams<'a, 'tcx> {
 }
 
 impl<'a, 'tcx> TypeVisitor<'tcx> for MarkUsedGenericParams<'a, 'tcx> {
-    fn visit_const(&mut self, c: &'tcx Const<'tcx>) -> ControlFlow<()> {
+    fn visit_const(&mut self, c: &'tcx Const<'tcx>) -> ControlFlow<Self::BreakTy> {
         debug!("visit_const: c={:?}", c);
         if !c.has_param_types_or_consts() {
             return ControlFlow::CONTINUE;
@@ -283,7 +283,7 @@ impl<'a, 'tcx> TypeVisitor<'tcx> for MarkUsedGenericParams<'a, 'tcx> {
         }
     }
 
-    fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<()> {
+    fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
         debug!("visit_ty: ty={:?}", ty);
         if !ty.has_param_types_or_consts() {
             return ControlFlow::CONTINUE;
@@ -318,7 +318,7 @@ struct HasUsedGenericParams<'a> {
 }
 
 impl<'a, 'tcx> TypeVisitor<'tcx> for HasUsedGenericParams<'a> {
-    fn visit_const(&mut self, c: &'tcx Const<'tcx>) -> ControlFlow<()> {
+    fn visit_const(&mut self, c: &'tcx Const<'tcx>) -> ControlFlow<Self::BreakTy> {
         debug!("visit_const: c={:?}", c);
         if !c.has_param_types_or_consts() {
             return ControlFlow::CONTINUE;
@@ -336,7 +336,7 @@ impl<'a, 'tcx> TypeVisitor<'tcx> for HasUsedGenericParams<'a> {
         }
     }
 
-    fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<()> {
+    fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
         debug!("visit_ty: ty={:?}", ty);
         if !ty.has_param_types_or_consts() {
             return ControlFlow::CONTINUE;
diff --git a/compiler/rustc_mir/src/util/pretty.rs b/compiler/rustc_mir/src/util/pretty.rs
index 8bee8417c51..cd60602b088 100644
--- a/compiler/rustc_mir/src/util/pretty.rs
+++ b/compiler/rustc_mir/src/util/pretty.rs
@@ -640,7 +640,7 @@ pub fn write_allocations<'tcx>(
     }
     struct CollectAllocIds(BTreeSet<AllocId>);
     impl<'tcx> TypeVisitor<'tcx> for CollectAllocIds {
-        fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> ControlFlow<()> {
+        fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
             if let ty::ConstKind::Value(val) = c.val {
                 self.0.extend(alloc_ids_from_const(val));
             }
diff --git a/compiler/rustc_privacy/src/lib.rs b/compiler/rustc_privacy/src/lib.rs
index 75d75433f1b..4a0d356d337 100644
--- a/compiler/rustc_privacy/src/lib.rs
+++ b/compiler/rustc_privacy/src/lib.rs
@@ -4,6 +4,7 @@
 #![feature(or_patterns)]
 #![feature(control_flow_enum)]
 #![feature(try_blocks)]
+#![feature(associated_type_defaults)]
 #![recursion_limit = "256"]
 
 use rustc_attr as attr;
@@ -44,6 +45,8 @@ use std::{cmp, fmt, mem};
 /// manually. Second, it doesn't visit some type components like signatures of fn types, or traits
 /// in `impl Trait`, see individual comments in `DefIdVisitorSkeleton::visit_ty`.
 trait DefIdVisitor<'tcx> {
+    type BreakTy = ();
+
     fn tcx(&self) -> TyCtxt<'tcx>;
     fn shallow(&self) -> bool {
         false
@@ -56,7 +59,7 @@ trait DefIdVisitor<'tcx> {
         def_id: DefId,
         kind: &str,
         descr: &dyn fmt::Display,
-    ) -> ControlFlow<()>;
+    ) -> ControlFlow<Self::BreakTy>;
 
     /// Not overridden, but used to actually visit types and traits.
     fn skeleton(&mut self) -> DefIdVisitorSkeleton<'_, 'tcx, Self> {
@@ -66,13 +69,16 @@ trait DefIdVisitor<'tcx> {
             dummy: Default::default(),
         }
     }
-    fn visit(&mut self, ty_fragment: impl TypeFoldable<'tcx>) -> ControlFlow<()> {
+    fn visit(&mut self, ty_fragment: impl TypeFoldable<'tcx>) -> ControlFlow<Self::BreakTy> {
         ty_fragment.visit_with(&mut self.skeleton())
     }
-    fn visit_trait(&mut self, trait_ref: TraitRef<'tcx>) -> ControlFlow<()> {
+    fn visit_trait(&mut self, trait_ref: TraitRef<'tcx>) -> ControlFlow<Self::BreakTy> {
         self.skeleton().visit_trait(trait_ref)
     }
-    fn visit_predicates(&mut self, predicates: ty::GenericPredicates<'tcx>) -> ControlFlow<()> {
+    fn visit_predicates(
+        &mut self,
+        predicates: ty::GenericPredicates<'tcx>,
+    ) -> ControlFlow<Self::BreakTy> {
         self.skeleton().visit_predicates(predicates)
     }
 }
@@ -87,13 +93,13 @@ impl<'tcx, V> DefIdVisitorSkeleton<'_, 'tcx, V>
 where
     V: DefIdVisitor<'tcx> + ?Sized,
 {
-    fn visit_trait(&mut self, trait_ref: TraitRef<'tcx>) -> ControlFlow<()> {
+    fn visit_trait(&mut self, trait_ref: TraitRef<'tcx>) -> ControlFlow<V::BreakTy> {
         let TraitRef { def_id, substs } = trait_ref;
         self.def_id_visitor.visit_def_id(def_id, "trait", &trait_ref.print_only_trait_path())?;
         if self.def_id_visitor.shallow() { ControlFlow::CONTINUE } else { substs.visit_with(self) }
     }
 
-    fn visit_predicate(&mut self, predicate: ty::Predicate<'tcx>) -> ControlFlow<()> {
+    fn visit_predicate(&mut self, predicate: ty::Predicate<'tcx>) -> ControlFlow<V::BreakTy> {
         match predicate.skip_binders() {
             ty::PredicateAtom::Trait(ty::TraitPredicate { trait_ref }, _) => {
                 self.visit_trait(trait_ref)
@@ -119,7 +125,10 @@ where
         }
     }
 
-    fn visit_predicates(&mut self, predicates: ty::GenericPredicates<'tcx>) -> ControlFlow<()> {
+    fn visit_predicates(
+        &mut self,
+        predicates: ty::GenericPredicates<'tcx>,
+    ) -> ControlFlow<V::BreakTy> {
         let ty::GenericPredicates { parent: _, predicates } = predicates;
         predicates.iter().try_for_each(|&(predicate, _span)| self.visit_predicate(predicate))
     }
@@ -129,7 +138,9 @@ impl<'tcx, V> TypeVisitor<'tcx> for DefIdVisitorSkeleton<'_, 'tcx, V>
 where
     V: DefIdVisitor<'tcx> + ?Sized,
 {
-    fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<()> {
+    type BreakTy = V::BreakTy;
+
+    fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<V::BreakTy> {
         let tcx = self.def_id_visitor.tcx();
         // InternalSubsts are not visited here because they are visited below in `super_visit_with`.
         match *ty.kind() {
@@ -283,7 +294,7 @@ impl<'a, 'tcx, VL: VisibilityLike> DefIdVisitor<'tcx> for FindMin<'a, 'tcx, VL>
         def_id: DefId,
         _kind: &str,
         _descr: &dyn fmt::Display,
-    ) -> ControlFlow<()> {
+    ) -> ControlFlow<Self::BreakTy> {
         self.min = VL::new_min(self, def_id);
         ControlFlow::CONTINUE
     }
@@ -902,7 +913,7 @@ impl DefIdVisitor<'tcx> for ReachEverythingInTheInterfaceVisitor<'_, 'tcx> {
         def_id: DefId,
         _kind: &str,
         _descr: &dyn fmt::Display,
-    ) -> ControlFlow<()> {
+    ) -> ControlFlow<Self::BreakTy> {
         if let Some(def_id) = def_id.as_local() {
             if let (ty::Visibility::Public, _) | (_, Some(AccessLevel::ReachableFromImplTrait)) =
                 (self.tcx().visibility(def_id.to_def_id()), self.access_level)
@@ -1299,7 +1310,7 @@ impl DefIdVisitor<'tcx> for TypePrivacyVisitor<'tcx> {
         def_id: DefId,
         kind: &str,
         descr: &dyn fmt::Display,
-    ) -> ControlFlow<()> {
+    ) -> ControlFlow<Self::BreakTy> {
         if self.check_def_id(def_id, kind, descr) {
             ControlFlow::BREAK
         } else {
@@ -1799,7 +1810,7 @@ impl DefIdVisitor<'tcx> for SearchInterfaceForPrivateItemsVisitor<'tcx> {
         def_id: DefId,
         kind: &str,
         descr: &dyn fmt::Display,
-    ) -> ControlFlow<()> {
+    ) -> ControlFlow<Self::BreakTy> {
         if self.check_def_id(def_id, kind, descr) {
             ControlFlow::BREAK
         } else {
diff --git a/compiler/rustc_trait_selection/src/opaque_types.rs b/compiler/rustc_trait_selection/src/opaque_types.rs
index 914fa1e52c2..c3b2d72fb73 100644
--- a/compiler/rustc_trait_selection/src/opaque_types.rs
+++ b/compiler/rustc_trait_selection/src/opaque_types.rs
@@ -693,12 +693,15 @@ impl<'tcx, OP> TypeVisitor<'tcx> for ConstrainOpaqueTypeRegionVisitor<OP>
 where
     OP: FnMut(ty::Region<'tcx>),
 {
-    fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ControlFlow<()> {
+    fn visit_binder<T: TypeFoldable<'tcx>>(
+        &mut self,
+        t: &ty::Binder<T>,
+    ) -> ControlFlow<Self::BreakTy> {
         t.as_ref().skip_binder().visit_with(self);
         ControlFlow::CONTINUE
     }
 
-    fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<()> {
+    fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
         match *r {
             // ignore bound regions, keep visiting
             ty::ReLateBound(_, _) => ControlFlow::CONTINUE,
@@ -709,7 +712,7 @@ where
         }
     }
 
-    fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<()> {
+    fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
         // We're only interested in types involving regions
         if !ty.flags().intersects(ty::TypeFlags::HAS_FREE_REGIONS) {
             return ControlFlow::CONTINUE;
diff --git a/compiler/rustc_trait_selection/src/traits/const_evaluatable.rs b/compiler/rustc_trait_selection/src/traits/const_evaluatable.rs
index e1721a5a88a..fdb2361ba03 100644
--- a/compiler/rustc_trait_selection/src/traits/const_evaluatable.rs
+++ b/compiler/rustc_trait_selection/src/traits/const_evaluatable.rs
@@ -78,7 +78,7 @@ pub fn is_const_evaluatable<'cx, 'tcx>(
                     Concrete,
                 }
                 let mut failure_kind = FailureKind::Concrete;
-                walk_abstract_const(tcx, ct, |node| match node {
+                walk_abstract_const::<!, _>(tcx, ct, |node| match node {
                     Node::Leaf(leaf) => {
                         let leaf = leaf.subst(tcx, ct.substs);
                         if leaf.has_infer_types_or_consts() {
@@ -574,19 +574,19 @@ pub(super) fn try_unify_abstract_consts<'tcx>(
     // on `ErrorReported`.
 }
 
-pub fn walk_abstract_const<'tcx, F>(
+pub fn walk_abstract_const<'tcx, R, F>(
     tcx: TyCtxt<'tcx>,
     ct: AbstractConst<'tcx>,
     mut f: F,
-) -> ControlFlow<()>
+) -> ControlFlow<R>
 where
-    F: FnMut(Node<'tcx>) -> ControlFlow<()>,
+    F: FnMut(Node<'tcx>) -> ControlFlow<R>,
 {
-    fn recurse<'tcx>(
+    fn recurse<'tcx, R>(
         tcx: TyCtxt<'tcx>,
         ct: AbstractConst<'tcx>,
-        f: &mut dyn FnMut(Node<'tcx>) -> ControlFlow<()>,
-    ) -> ControlFlow<()> {
+        f: &mut dyn FnMut(Node<'tcx>) -> ControlFlow<R>,
+    ) -> ControlFlow<R> {
         let root = ct.root();
         f(root)?;
         match root {
diff --git a/compiler/rustc_trait_selection/src/traits/object_safety.rs b/compiler/rustc_trait_selection/src/traits/object_safety.rs
index 32e0991733b..7da5ec051cb 100644
--- a/compiler/rustc_trait_selection/src/traits/object_safety.rs
+++ b/compiler/rustc_trait_selection/src/traits/object_safety.rs
@@ -771,7 +771,7 @@ fn contains_illegal_self_type_reference<'tcx, T: TypeFoldable<'tcx>>(
     }
 
     impl<'tcx> TypeVisitor<'tcx> for IllegalSelfTypeVisitor<'tcx> {
-        fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<()> {
+        fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
             match t.kind() {
                 ty::Param(_) => {
                     if t == self.tcx.types.self_param {
@@ -812,7 +812,7 @@ fn contains_illegal_self_type_reference<'tcx, T: TypeFoldable<'tcx>>(
             }
         }
 
-        fn visit_const(&mut self, ct: &ty::Const<'tcx>) -> ControlFlow<()> {
+        fn visit_const(&mut self, ct: &ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
             // First check if the type of this constant references `Self`.
             self.visit_ty(ct.ty)?;
 
@@ -844,7 +844,7 @@ fn contains_illegal_self_type_reference<'tcx, T: TypeFoldable<'tcx>>(
             }
         }
 
-        fn visit_predicate(&mut self, pred: ty::Predicate<'tcx>) -> ControlFlow<()> {
+        fn visit_predicate(&mut self, pred: ty::Predicate<'tcx>) -> ControlFlow<Self::BreakTy> {
             if let ty::PredicateAtom::ConstEvaluatable(def, substs) = pred.skip_binders() {
                 // FIXME(const_evaluatable_checked): We should probably deduplicate the logic for
                 // `AbstractConst`s here, it might make sense to change `ConstEvaluatable` to
diff --git a/compiler/rustc_trait_selection/src/traits/structural_match.rs b/compiler/rustc_trait_selection/src/traits/structural_match.rs
index ce0d3ef8a6a..edab1e031cc 100644
--- a/compiler/rustc_trait_selection/src/traits/structural_match.rs
+++ b/compiler/rustc_trait_selection/src/traits/structural_match.rs
@@ -135,7 +135,7 @@ impl Search<'a, 'tcx> {
 }
 
 impl<'a, 'tcx> TypeVisitor<'tcx> for Search<'a, 'tcx> {
-    fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<()> {
+    fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
         debug!("Search visiting ty: {:?}", ty);
 
         let (adt_def, substs) = match *ty.kind() {
diff --git a/compiler/rustc_traits/src/chalk/lowering.rs b/compiler/rustc_traits/src/chalk/lowering.rs
index c4e2c7f839d..4c616ccc086 100644
--- a/compiler/rustc_traits/src/chalk/lowering.rs
+++ b/compiler/rustc_traits/src/chalk/lowering.rs
@@ -859,14 +859,14 @@ impl<'tcx> BoundVarsCollector<'tcx> {
 }
 
 impl<'tcx> TypeVisitor<'tcx> for BoundVarsCollector<'tcx> {
-    fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> ControlFlow<()> {
+    fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> ControlFlow<Self::BreakTy> {
         self.binder_index.shift_in(1);
         let result = t.super_visit_with(self);
         self.binder_index.shift_out(1);
         result
     }
 
-    fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<()> {
+    fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
         match *t.kind() {
             ty::Bound(debruijn, bound_ty) if debruijn == self.binder_index => {
                 match self.parameters.entry(bound_ty.var.as_u32()) {
@@ -886,7 +886,7 @@ impl<'tcx> TypeVisitor<'tcx> for BoundVarsCollector<'tcx> {
         t.super_visit_with(self)
     }
 
-    fn visit_region(&mut self, r: Region<'tcx>) -> ControlFlow<()> {
+    fn visit_region(&mut self, r: Region<'tcx>) -> ControlFlow<Self::BreakTy> {
         match r {
             ty::ReLateBound(index, br) if *index == self.binder_index => match br {
                 ty::BoundRegion::BrNamed(def_id, _name) => {
@@ -1076,7 +1076,7 @@ impl PlaceholdersCollector {
 }
 
 impl<'tcx> TypeVisitor<'tcx> for PlaceholdersCollector {
-    fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<()> {
+    fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
         match t.kind() {
             ty::Placeholder(p) if p.universe == self.universe_index => {
                 self.next_ty_placeholder = self.next_ty_placeholder.max(p.name.as_usize() + 1);
@@ -1088,7 +1088,7 @@ impl<'tcx> TypeVisitor<'tcx> for PlaceholdersCollector {
         t.super_visit_with(self)
     }
 
-    fn visit_region(&mut self, r: Region<'tcx>) -> ControlFlow<()> {
+    fn visit_region(&mut self, r: Region<'tcx>) -> ControlFlow<Self::BreakTy> {
         match r {
             ty::RePlaceholder(p) if p.universe == self.universe_index => {
                 if let ty::BoundRegion::BrAnon(anon) = p.name {
diff --git a/compiler/rustc_typeck/src/check/check.rs b/compiler/rustc_typeck/src/check/check.rs
index 70d94ef869d..0e6e289c9fb 100644
--- a/compiler/rustc_typeck/src/check/check.rs
+++ b/compiler/rustc_typeck/src/check/check.rs
@@ -450,7 +450,7 @@ pub(super) fn check_opaque_for_inheriting_lifetimes(
     };
 
     impl<'tcx> ty::fold::TypeVisitor<'tcx> for ProhibitOpaqueVisitor<'tcx> {
-        fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<()> {
+        fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
             debug!("check_opaque_for_inheriting_lifetimes: (visit_ty) t={:?}", t);
             if t != self.opaque_identity_ty && t.super_visit_with(self).is_break() {
                 self.ty = Some(t);
@@ -459,7 +459,7 @@ pub(super) fn check_opaque_for_inheriting_lifetimes(
             ControlFlow::CONTINUE
         }
 
-        fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<()> {
+        fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
             debug!("check_opaque_for_inheriting_lifetimes: (visit_region) r={:?}", r);
             if let RegionKind::ReEarlyBound(ty::EarlyBoundRegion { index, .. }) = r {
                 if *index < self.generics.parent_count as u32 {
@@ -472,7 +472,7 @@ pub(super) fn check_opaque_for_inheriting_lifetimes(
             r.super_visit_with(self)
         }
 
-        fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> ControlFlow<()> {
+        fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
             if let ty::ConstKind::Unevaluated(..) = c.val {
                 // FIXME(#72219) We currenctly don't detect lifetimes within substs
                 // which would violate this check. Even though the particular substitution is not used
@@ -1455,7 +1455,7 @@ fn opaque_type_cycle_error(tcx: TyCtxt<'tcx>, def_id: LocalDefId, span: Span) {
             {
                 struct VisitTypes(Vec<DefId>);
                 impl<'tcx> ty::fold::TypeVisitor<'tcx> for VisitTypes {
-                    fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<()> {
+                    fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
                         match *t.kind() {
                             ty::Opaque(def, _) => {
                                 self.0.push(def);
diff --git a/compiler/rustc_typeck/src/check/op.rs b/compiler/rustc_typeck/src/check/op.rs
index 247b5256726..8e69df734e6 100644
--- a/compiler/rustc_typeck/src/check/op.rs
+++ b/compiler/rustc_typeck/src/check/op.rs
@@ -983,7 +983,7 @@ fn suggest_constraining_param(
 struct TypeParamVisitor<'tcx>(Vec<Ty<'tcx>>);
 
 impl<'tcx> TypeVisitor<'tcx> for TypeParamVisitor<'tcx> {
-    fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<()> {
+    fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
         if let ty::Param(_) = ty.kind() {
             self.0.push(ty);
         }
diff --git a/compiler/rustc_typeck/src/check/wfcheck.rs b/compiler/rustc_typeck/src/check/wfcheck.rs
index 1e27357ce44..95ad977abd1 100644
--- a/compiler/rustc_typeck/src/check/wfcheck.rs
+++ b/compiler/rustc_typeck/src/check/wfcheck.rs
@@ -800,18 +800,18 @@ fn check_where_clauses<'tcx, 'fcx>(
                 params: FxHashSet<u32>,
             }
             impl<'tcx> ty::fold::TypeVisitor<'tcx> for CountParams {
-                fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<()> {
+                fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
                     if let ty::Param(param) = t.kind() {
                         self.params.insert(param.index);
                     }
                     t.super_visit_with(self)
                 }
 
-                fn visit_region(&mut self, _: ty::Region<'tcx>) -> ControlFlow<()> {
+                fn visit_region(&mut self, _: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
                     ControlFlow::BREAK
                 }
 
-                fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> ControlFlow<()> {
+                fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
                     if let ty::ConstKind::Param(param) = c.val {
                         self.params.insert(param.index);
                     }
diff --git a/compiler/rustc_typeck/src/collect.rs b/compiler/rustc_typeck/src/collect.rs
index b431de90369..7779794b9db 100644
--- a/compiler/rustc_typeck/src/collect.rs
+++ b/compiler/rustc_typeck/src/collect.rs
@@ -2062,7 +2062,7 @@ fn const_evaluatable_predicates_of<'tcx>(
             }
 
             impl<'a, 'tcx> TypeVisitor<'tcx> for TyAliasVisitor<'a, 'tcx> {
-                fn visit_const(&mut self, ct: &'tcx Const<'tcx>) -> ControlFlow<()> {
+                fn visit_const(&mut self, ct: &'tcx Const<'tcx>) -> ControlFlow<Self::BreakTy> {
                     if let ty::ConstKind::Unevaluated(def, substs, None) = ct.val {
                         self.preds.insert((
                             ty::PredicateAtom::ConstEvaluatable(def, substs).to_predicate(self.tcx),
diff --git a/compiler/rustc_typeck/src/constrained_generic_params.rs b/compiler/rustc_typeck/src/constrained_generic_params.rs
index bae5bde7002..e389fd4d9f0 100644
--- a/compiler/rustc_typeck/src/constrained_generic_params.rs
+++ b/compiler/rustc_typeck/src/constrained_generic_params.rs
@@ -57,7 +57,7 @@ struct ParameterCollector {
 }
 
 impl<'tcx> TypeVisitor<'tcx> for ParameterCollector {
-    fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<()> {
+    fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
         match *t.kind() {
             ty::Projection(..) | ty::Opaque(..) if !self.include_nonconstraining => {
                 // projections are not injective
@@ -72,14 +72,14 @@ impl<'tcx> TypeVisitor<'tcx> for ParameterCollector {
         t.super_visit_with(self)
     }
 
-    fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<()> {
+    fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
         if let ty::ReEarlyBound(data) = *r {
             self.parameters.push(Parameter::from(data));
         }
         ControlFlow::CONTINUE
     }
 
-    fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> ControlFlow<()> {
+    fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
         match c.val {
             ty::ConstKind::Unevaluated(..) if !self.include_nonconstraining => {
                 // Constant expressions are not injective