TypeVisitor: use `ControlFlow` in rustc_{infer,lint,trait_selection}

compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -71,6 +71,7 @@
 };
 use rustc_span::{BytePos, DesugaringKind, Pos, Span};
 use rustc_target::spec::abi;
+use std::ops::ControlFlow;
 use std::{cmp, fmt};
 
 mod note;
@@ -1497,7 +1498,7 @@ fn add_labels_for_types(
         }
 
         impl<'tcx> ty::fold::TypeVisitor<'tcx> for OpaqueTypesVisitor<'tcx> {
-            fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
+            fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<(), ()> {
                 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:

compiler/rustc_infer/src/infer/error_reporting/nice_region_error/static_impl_trait.rs

@@ -15,6 +15,8 @@
 use rustc_span::symbol::Ident;
 use rustc_span::{MultiSpan, Span};
 
+use std::ops::ControlFlow;
+
 impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
     /// Print the error message for lifetime errors when the return type is a static `impl Trait`,
     /// `dyn Trait` or if a method call on a trait object introduces a static requirement.
@@ -472,13 +474,13 @@ fn suggest_constrain_dyn_trait_in_impl(
 struct TraitObjectVisitor(Vec<DefId>);
 
 impl TypeVisitor<'_> for TraitObjectVisitor {
-    fn visit_ty(&mut self, t: Ty<'_>) -> bool {
+    fn visit_ty(&mut self, t: Ty<'_>) -> ControlFlow<(), ()> {
         match t.kind() {
             ty::Dynamic(preds, RegionKind::ReStatic) => {
                 if let Some(def_id) = preds.principal_def_id() {
                     self.0.push(def_id);
                 }
-                false
+                ControlFlow::CONTINUE
             }
             _ => t.super_visit_with(self),
         }

compiler/rustc_infer/src/infer/nll_relate/mod.rs

@@ -30,6 +30,7 @@
 use rustc_middle::ty::relate::{self, Relate, RelateResult, TypeRelation};
 use rustc_middle::ty::{self, InferConst, Ty, TyCtxt};
 use std::fmt::Debug;
+use std::ops::ControlFlow;
 
 #[derive(PartialEq)]
 pub enum NormalizationStrategy {
@@ -740,15 +741,15 @@ 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>) -> bool {
+    fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ControlFlow<(), ()> {
         self.target_index.shift_in(1);
         t.super_visit_with(self);
         self.target_index.shift_out(1);
 
-        false
+        ControlFlow::CONTINUE
     }
 
-    fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
+    fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<(), ()> {
         let ScopeInstantiator { bound_region_scope, next_region, .. } = self;
 
         match r {
@@ -759,7 +760,7 @@ fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
             _ => {}
         }
 
-        false
+        ControlFlow::CONTINUE
     }
 }
 

compiler/rustc_infer/src/infer/resolve.rs

@@ -3,6 +3,8 @@
 use rustc_middle::ty::fold::{TypeFolder, TypeVisitor};
 use rustc_middle::ty::{self, Const, InferConst, Ty, TyCtxt, TypeFoldable};
 
+use std::ops::ControlFlow;
+
 ///////////////////////////////////////////////////////////////////////////
 // OPPORTUNISTIC VAR RESOLVER
 
@@ -121,7 +123,7 @@ pub fn new(infcx: &'a InferCtxt<'a, 'tcx>) -> Self {
 }
 
 impl<'a, 'tcx> TypeVisitor<'tcx> for UnresolvedTypeFinder<'a, 'tcx> {
-    fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
+    fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<(), ()> {
         let t = self.infcx.shallow_resolve(t);
         if t.has_infer_types() {
             if let ty::Infer(infer_ty) = *t.kind() {
@@ -143,7 +145,7 @@ fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
                     None
                 };
                 self.first_unresolved = Some((t, ty_var_span));
-                true // Halt visiting.
+                ControlFlow::BREAK
             } else {
                 // Otherwise, visit its contents.
                 t.super_visit_with(self)
@@ -151,7 +153,7 @@ fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
         } else {
             // All type variables in inference types must already be resolved,
             // - no need to visit the contents, continue visiting.
-            false
+            ControlFlow::CONTINUE
         }
     }
 }

compiler/rustc_infer/src/lib.rs

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

compiler/rustc_infer/src/traits/structural_impls.rs

@@ -4,6 +4,7 @@
 use rustc_middle::ty::fold::{TypeFoldable, TypeFolder, TypeVisitor};
 
 use std::fmt;
+use std::ops::ControlFlow;
 
 // Structural impls for the structs in `traits`.
 
@@ -68,7 +69,7 @@ fn super_fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Self {
         }
     }
 
-    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
+    fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<(), ()> {
         self.predicate.visit_with(visitor)
     }
 }

compiler/rustc_lint/src/lib.rs

@@ -37,6 +37,7 @@
 #![feature(or_patterns)]
 #![feature(half_open_range_patterns)]
 #![feature(exclusive_range_pattern)]
+#![feature(control_flow_enum)]
 #![recursion_limit = "256"]
 
 #[macro_use]

compiler/rustc_lint/src/types.rs

@@ -18,6 +18,7 @@
 use rustc_target::spec::abi::Abi as SpecAbi;
 
 use std::cmp;
+use std::ops::ControlFlow;
 use tracing::debug;
 
 declare_lint! {
@@ -1135,11 +1136,11 @@ struct ProhibitOpaqueTypes<'a, 'tcx> {
         };
 
         impl<'a, 'tcx> ty::fold::TypeVisitor<'tcx> for ProhibitOpaqueTypes<'a, 'tcx> {
-            fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
+            fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<(), ()> {
                 match ty.kind() {
                     ty::Opaque(..) => {
                         self.ty = Some(ty);
-                        true
+                        ControlFlow::BREAK
                     }
                     // Consider opaque types within projections FFI-safe if they do not normalize
                     // to more opaque types.
@@ -1148,7 +1149,11 @@ fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
 
                         // If `ty` is a opaque type directly then `super_visit_with` won't invoke
                         // this function again.
-                        if ty.has_opaque_types() { self.visit_ty(ty) } else { false }
+                        if ty.has_opaque_types() {
+                            self.visit_ty(ty)
+                        } else {
+                            ControlFlow::CONTINUE
+                        }
                     }
                     _ => ty.super_visit_with(self),
                 }

compiler/rustc_trait_selection/src/lib.rs

@@ -19,6 +19,7 @@
 #![feature(never_type)]
 #![feature(crate_visibility_modifier)]
 #![feature(or_patterns)]
+#![feature(control_flow_enum)]
 #![recursion_limit = "512"] // For rustdoc
 
 #[macro_use]

compiler/rustc_trait_selection/src/opaque_types.rs

@@ -15,6 +15,8 @@
 use rustc_session::config::nightly_options;
 use rustc_span::Span;
 
+use std::ops::ControlFlow;
+
 pub type OpaqueTypeMap<'tcx> = DefIdMap<OpaqueTypeDecl<'tcx>>;
 
 /// Information about the opaque types whose values we
@@ -691,26 +693,26 @@ 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>) -> bool {
+    fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ControlFlow<(), ()> {
         t.as_ref().skip_binder().visit_with(self);
-        false // keep visiting
+        ControlFlow::CONTINUE
     }
 
-    fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool {
+    fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<(), ()> {
         match *r {
             // ignore bound regions, keep visiting
-            ty::ReLateBound(_, _) => false,
+            ty::ReLateBound(_, _) => ControlFlow::CONTINUE,
             _ => {
                 (self.op)(r);
-                false
+                ControlFlow::CONTINUE
             }
         }
     }
 
-    fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
+    fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<(), ()> {
         // We're only interested in types involving regions
         if !ty.flags().intersects(ty::TypeFlags::HAS_FREE_REGIONS) {
-            return false; // keep visiting
+            return ControlFlow::CONTINUE;
         }
 
         match ty.kind() {
@@ -745,7 +747,7 @@ fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
             }
         }
 
-        false
+        ControlFlow::CONTINUE
     }
 }
 

compiler/rustc_trait_selection/src/traits/const_evaluatable.rs

@@ -24,6 +24,7 @@
 use rustc_span::Span;
 
 use std::cmp;
+use std::ops::ControlFlow;
 
 /// Check if a given constant can be evaluated.
 pub fn is_const_evaluatable<'cx, 'tcx>(
@@ -86,9 +87,11 @@ enum FailureKind {
                             failure_kind = cmp::min(failure_kind, FailureKind::MentionsParam);
                         }
 
-                        false
+                        ControlFlow::CONTINUE
+                    }
+                    Node::Binop(_, _, _) | Node::UnaryOp(_, _) | Node::FunctionCall(_, _) => {
+                        ControlFlow::CONTINUE
                     }
-                    Node::Binop(_, _, _) | Node::UnaryOp(_, _) | Node::FunctionCall(_, _) => false,
                 });
 
                 match failure_kind {
@@ -564,29 +567,33 @@ pub(super) fn try_unify_abstract_consts<'tcx>(
     // on `ErrorReported`.
 }
 
-// FIXME: Use `std::ops::ControlFlow` instead of `bool` here.
-pub fn walk_abstract_const<'tcx, F>(tcx: TyCtxt<'tcx>, ct: AbstractConst<'tcx>, mut f: F) -> bool
+pub fn walk_abstract_const<'tcx, F>(
+    tcx: TyCtxt<'tcx>,
+    ct: AbstractConst<'tcx>,
+    mut f: F,
+) -> ControlFlow<(), ()>
 where
-    F: FnMut(Node<'tcx>) -> bool,
+    F: FnMut(Node<'tcx>) -> ControlFlow<(), ()>,
 {
     fn recurse<'tcx>(
         tcx: TyCtxt<'tcx>,
         ct: AbstractConst<'tcx>,
-        f: &mut dyn FnMut(Node<'tcx>) -> bool,
-    ) -> bool {
+        f: &mut dyn FnMut(Node<'tcx>) -> ControlFlow<(), ()>,
+    ) -> ControlFlow<(), ()> {
         let root = ct.root();
-        f(root)
-            || match root {
-                Node::Leaf(_) => false,
-                Node::Binop(_, l, r) => {
-                    recurse(tcx, ct.subtree(l), f) || recurse(tcx, ct.subtree(r), f)
-                }
-                Node::UnaryOp(_, v) => recurse(tcx, ct.subtree(v), f),
-                Node::FunctionCall(func, args) => {
-                    recurse(tcx, ct.subtree(func), f)
-                        || args.iter().any(|&arg| recurse(tcx, ct.subtree(arg), f))
-                }
+        f(root)?;
+        match root {
+            Node::Leaf(_) => ControlFlow::CONTINUE,
+            Node::Binop(_, l, r) => {
+                recurse(tcx, ct.subtree(l), f)?;
+                recurse(tcx, ct.subtree(r), f)
+            }
+            Node::UnaryOp(_, v) => recurse(tcx, ct.subtree(v), f),
+            Node::FunctionCall(func, args) => {
+                recurse(tcx, ct.subtree(func), f)?;
+                args.iter().try_for_each(|&arg| recurse(tcx, ct.subtree(arg), f))
             }
+        }
     }
 
     recurse(tcx, ct, &mut f)

compiler/rustc_trait_selection/src/traits/object_safety.rs

@@ -27,6 +27,7 @@
 
 use std::array;
 use std::iter;
+use std::ops::ControlFlow;
 
 pub use crate::traits::{MethodViolationCode, ObjectSafetyViolation};
 
@@ -770,9 +771,15 @@ struct IllegalSelfTypeVisitor<'tcx> {
     }
 
     impl<'tcx> TypeVisitor<'tcx> for IllegalSelfTypeVisitor<'tcx> {
-        fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
+        fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<(), ()> {
             match t.kind() {
-                ty::Param(_) => t == self.tcx.types.self_param,
+                ty::Param(_) => {
+                    if t == self.tcx.types.self_param {
+                        ControlFlow::BREAK
+                    } else {
+                        ControlFlow::CONTINUE
+                    }
+                }
                 ty::Projection(ref data) => {
                     // This is a projected type `<Foo as SomeTrait>::X`.
 
@@ -796,7 +803,7 @@ fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
                         self.supertraits.as_ref().unwrap().contains(&projection_trait_ref);
 
                     if is_supertrait_of_current_trait {
-                        false // do not walk contained types, do not report error, do collect $200
+                        ControlFlow::CONTINUE // do not walk contained types, do not report error, do collect $200
                     } else {
                         t.super_visit_with(self) // DO walk contained types, POSSIBLY reporting an error
                     }
@@ -805,11 +812,9 @@ fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
             }
         }
 
-        fn visit_const(&mut self, ct: &ty::Const<'tcx>) -> bool {
+        fn visit_const(&mut self, ct: &ty::Const<'tcx>) -> ControlFlow<(), ()> {
             // First check if the type of this constant references `Self`.
-            if self.visit_ty(ct.ty) {
-                return true;
-            }
+            self.visit_ty(ct.ty)?;
 
             // Constants can only influence object safety if they reference `Self`.
             // This is only possible for unevaluated constants, so we walk these here.
@@ -830,14 +835,16 @@ fn visit_const(&mut self, ct: &ty::Const<'tcx>) -> bool {
                         let leaf = leaf.subst(self.tcx, ct.substs);
                         self.visit_const(leaf)
                     }
-                    Node::Binop(..) | Node::UnaryOp(..) | Node::FunctionCall(_, _) => false,
+                    Node::Binop(..) | Node::UnaryOp(..) | Node::FunctionCall(_, _) => {
+                        ControlFlow::CONTINUE
+                    }
                 })
             } else {
-                false
+                ControlFlow::CONTINUE
             }
         }
 
-        fn visit_predicate(&mut self, pred: ty::Predicate<'tcx>) -> bool {
+        fn visit_predicate(&mut self, pred: ty::Predicate<'tcx>) -> ControlFlow<(), ()> {
             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
@@ -849,10 +856,12 @@ fn visit_predicate(&mut self, pred: ty::Predicate<'tcx>) -> bool {
                             let leaf = leaf.subst(self.tcx, ct.substs);
                             self.visit_const(leaf)
                         }
-                        Node::Binop(..) | Node::UnaryOp(..) | Node::FunctionCall(_, _) => false,
+                        Node::Binop(..) | Node::UnaryOp(..) | Node::FunctionCall(_, _) => {
+                            ControlFlow::CONTINUE
+                        }
                     })
                 } else {
-                    false
+                    ControlFlow::CONTINUE
                 }
             } else {
                 pred.super_visit_with(self)
@@ -861,6 +870,7 @@ fn visit_predicate(&mut self, pred: ty::Predicate<'tcx>) -> bool {
     }
 
     value.visit_with(&mut IllegalSelfTypeVisitor { tcx, trait_def_id, supertraits: None })
+        == ControlFlow::BREAK
 }
 
 pub fn provide(providers: &mut ty::query::Providers) {

compiler/rustc_trait_selection/src/traits/structural_match.rs

@@ -8,6 +8,7 @@
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::{self, AdtDef, Ty, TyCtxt, TypeFoldable, TypeVisitor};
 use rustc_span::Span;
+use std::ops::ControlFlow;
 
 #[derive(Debug)]
 pub enum NonStructuralMatchTy<'tcx> {
@@ -134,38 +135,38 @@ fn type_marked_structural(&self, adt_ty: Ty<'tcx>) -> bool {
 }
 
 impl<'a, 'tcx> TypeVisitor<'tcx> for Search<'a, 'tcx> {
-    fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
+    fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<(), ()> {
         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 true; // Stop visiting.
+                return ControlFlow::BREAK;
             }
             ty::Dynamic(..) => {
                 self.found = Some(NonStructuralMatchTy::Dynamic);
-                return true; // Stop visiting.
+                return ControlFlow::BREAK;
             }
             ty::Foreign(_) => {
                 self.found = Some(NonStructuralMatchTy::Foreign);
-                return true; // Stop visiting.
+                return ControlFlow::BREAK;
             }
             ty::Opaque(..) => {
                 self.found = Some(NonStructuralMatchTy::Opaque);
-                return true; // Stop visiting.
+                return ControlFlow::BREAK;
             }
             ty::Projection(..) => {
                 self.found = Some(NonStructuralMatchTy::Projection);
-                return true; // Stop visiting.
+                return ControlFlow::BREAK;
             }
             ty::Generator(..) | ty::GeneratorWitness(..) => {
                 self.found = Some(NonStructuralMatchTy::Generator);
-                return true; // Stop visiting.
+                return ControlFlow::BREAK;
             }
             ty::Closure(..) => {
                 self.found = Some(NonStructuralMatchTy::Closure);
-                return true; // Stop visiting.
+                return ControlFlow::BREAK;
             }
             ty::RawPtr(..) => {
                 // structural-match ignores substructure of
@@ -182,39 +183,31 @@ fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
                 // Even though `NonStructural` does not implement `PartialEq`,
                 // structural equality on `T` does not recur into the raw
                 // pointer. Therefore, one can still use `C` in a pattern.
-
-                // (But still tell the caller to continue search.)
-                return false;
+                return ControlFlow::CONTINUE;
             }
             ty::FnDef(..) | ty::FnPtr(..) => {
                 // Types of formals and return in `fn(_) -> _` are also irrelevant;
                 // so we do not recur into them via `super_visit_with`
-                //
-                // (But still tell the caller to continue search.)
-                return false;
+                return ControlFlow::CONTINUE;
             }
             ty::Array(_, n)
                 if { n.try_eval_usize(self.tcx(), ty::ParamEnv::reveal_all()) == Some(0) } =>
             {
                 // rust-lang/rust#62336: ignore type of contents
                 // for empty array.
-                //
-                // (But still tell the caller to continue search.)
-                return false;
+                return ControlFlow::CONTINUE;
             }
             ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Str | ty::Never => {
                 // These primitive types are always structural match.
                 //
                 // `Never` is kind of special here, but as it is not inhabitable, this should be fine.
-                //
-                // (But still tell the caller to continue search.)
-                return false;
+                return ControlFlow::CONTINUE;
             }
 
             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 false;
+                return ControlFlow::CONTINUE;
             }
             ty::Infer(_) | ty::Placeholder(_) | ty::Bound(..) => {
                 bug!("unexpected type during structural-match checking: {:?}", ty);
@@ -223,22 +216,19 @@ fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
                 self.tcx().sess.delay_span_bug(self.span, "ty::Error in structural-match check");
                 // We still want to check other types after encountering an error,
                 // as this may still emit relevant errors.
-                //
-                // So we continue searching here.
-                return false;
+                return ControlFlow::CONTINUE;
             }
         };
 
         if !self.seen.insert(adt_def.did) {
             debug!("Search already seen adt_def: {:?}", adt_def);
-            // Let caller continue its search.
-            return false;
+            return ControlFlow::CONTINUE;
         }
 
         if !self.type_marked_structural(ty) {
             debug!("Search found ty: {:?}", ty);
             self.found = Some(NonStructuralMatchTy::Adt(&adt_def));
-            return true; // Halt visiting!
+            return ControlFlow::BREAK;
         }
 
         // structural-match does not care about the
@@ -258,16 +248,16 @@ fn visit_ty(&mut self, ty: Ty<'tcx>) -> bool {
             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) {
+            if ty.visit_with(self) == ControlFlow::BREAK {
                 // found an ADT without structural-match; halt visiting!
                 assert!(self.found.is_some());
-                return true;
+                return ControlFlow::BREAK;
             }
         }
 
         // Even though we do not want to recur on substs, we do
         // want our caller to continue its own search.
-        false
+        ControlFlow::CONTINUE
     }
 }