Use `ControlFlow` results for visitors that are only looking for a single value

6 files changed, 59 insertions, 87 deletions

diff --git a/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs b/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
index e291ebd9bb8..c2c3f5bc79e 100644
--- a/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs
@@ -39,6 +39,7 @@ use rustc_trait_selection::traits::error_reporting::suggestions::TypeErrCtxtExt;
 use rustc_trait_selection::traits::error_reporting::FindExprBySpan;
 use rustc_trait_selection::traits::{Obligation, ObligationCause, ObligationCtxt};
 use std::iter;
+use std::ops::ControlFlow;
 
 use crate::borrow_set::TwoPhaseActivation;
 use crate::borrowck_errors;
@@ -784,20 +785,20 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
         /// binding declaration within every scope we inspect.
         struct Finder {
             hir_id: hir::HirId,
-            found: bool,
         }
         impl<'hir> Visitor<'hir> for Finder {
-            fn visit_pat(&mut self, pat: &'hir hir::Pat<'hir>) {
+            type Result = ControlFlow<()>;
+            fn visit_pat(&mut self, pat: &'hir hir::Pat<'hir>) -> Self::Result {
                 if pat.hir_id == self.hir_id {
-                    self.found = true;
+                    return ControlFlow::Break(());
                 }
-                hir::intravisit::walk_pat(self, pat);
+                hir::intravisit::walk_pat(self, pat)
             }
-            fn visit_expr(&mut self, ex: &'hir hir::Expr<'hir>) {
+            fn visit_expr(&mut self, ex: &'hir hir::Expr<'hir>) -> Self::Result {
                 if ex.hir_id == self.hir_id {
-                    self.found = true;
+                    return ControlFlow::Break(());
                 }
-                hir::intravisit::walk_expr(self, ex);
+                hir::intravisit::walk_expr(self, ex)
             }
         }
         // The immediate HIR parent of the moved expression. We'll look for it to be a call.
@@ -822,9 +823,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
                 _ => continue,
             };
             if let Some(&hir_id) = local_hir_id {
-                let mut finder = Finder { hir_id, found: false };
-                finder.visit_expr(e);
-                if finder.found {
+                if (Finder { hir_id }).visit_expr(e).is_break() {
                     // The current scope includes the declaration of the binding we're accessing, we
                     // can't look up any further for loops.
                     break;
@@ -839,9 +838,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
                         hir::Node::Expr(hir::Expr {
                             kind: hir::ExprKind::If(cond, ..), ..
                         }) => {
-                            let mut finder = Finder { hir_id: expr.hir_id, found: false };
-                            finder.visit_expr(cond);
-                            if finder.found {
+                            if (Finder { hir_id: expr.hir_id }).visit_expr(cond).is_break() {
                                 // The expression where the move error happened is in a `while let`
                                 // condition Don't suggest clone as it will likely end in an
                                 // infinite loop.
@@ -1837,7 +1834,6 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
 
         pub struct Holds<'tcx> {
             ty: Ty<'tcx>,
-            holds: bool,
         }
 
         impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for Holds<'tcx> {
@@ -1845,7 +1841,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
 
             fn visit_ty(&mut self, t: Ty<'tcx>) -> Self::Result {
                 if t == self.ty {
-                    self.holds = true;
+                    return ControlFlow::Break(());
                 }
                 t.super_visit_with(self)
             }
@@ -1863,9 +1859,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
                 && rcvr_ty == ty
                 && let ty::Ref(_, inner, _) = rcvr_ty.kind()
                 && let inner = inner.peel_refs()
-                && let mut v = (Holds { ty: inner, holds: false })
-                && let _ = v.visit_ty(local_ty)
-                && v.holds
+                && (Holds { ty: inner }).visit_ty(local_ty).is_break()
                 && let None = self.infcx.type_implements_trait_shallow(clone, inner, self.param_env)
             {
                 err.span_label(
@@ -4325,15 +4319,14 @@ impl<'tcx> AnnotatedBorrowFnSignature<'tcx> {
 }
 
 /// Detect whether one of the provided spans is a statement nested within the top-most visited expr
-struct ReferencedStatementsVisitor<'a>(&'a [Span], bool);
+struct ReferencedStatementsVisitor<'a>(&'a [Span]);
 
-impl<'a, 'v> Visitor<'v> for ReferencedStatementsVisitor<'a> {
-    fn visit_stmt(&mut self, s: &'v hir::Stmt<'v>) {
+impl<'v> Visitor<'v> for ReferencedStatementsVisitor<'_> {
+    type Result = ControlFlow<()>;
+    fn visit_stmt(&mut self, s: &'v hir::Stmt<'v>) -> Self::Result {
         match s.kind {
-            hir::StmtKind::Semi(expr) if self.0.contains(&expr.span) => {
-                self.1 = true;
-            }
-            _ => {}
+            hir::StmtKind::Semi(expr) if self.0.contains(&expr.span) => ControlFlow::Break(()),
+            _ => ControlFlow::Continue(()),
         }
     }
 }
@@ -4375,9 +4368,7 @@ impl<'b, 'v, 'tcx> Visitor<'v> for ConditionVisitor<'b, 'tcx> {
             hir::ExprKind::If(cond, body, None) => {
                 // `if` expressions with no `else` that initialize the binding might be missing an
                 // `else` arm.
-                let mut v = ReferencedStatementsVisitor(self.spans, false);
-                v.visit_expr(body);
-                if v.1 {
+                if ReferencedStatementsVisitor(self.spans).visit_expr(body).is_break() {
                     self.errors.push((
                         cond.span,
                         format!(
@@ -4394,11 +4385,9 @@ impl<'b, 'v, 'tcx> Visitor<'v> for ConditionVisitor<'b, 'tcx> {
             hir::ExprKind::If(cond, body, Some(other)) => {
                 // `if` expressions where the binding is only initialized in one of the two arms
                 // might be missing a binding initialization.
-                let mut a = ReferencedStatementsVisitor(self.spans, false);
-                a.visit_expr(body);
-                let mut b = ReferencedStatementsVisitor(self.spans, false);
-                b.visit_expr(other);
-                match (a.1, b.1) {
+                let a = ReferencedStatementsVisitor(self.spans).visit_expr(body).is_break();
+                let b = ReferencedStatementsVisitor(self.spans).visit_expr(other).is_break();
+                match (a, b) {
                     (true, true) | (false, false) => {}
                     (true, false) => {
                         if other.span.is_desugaring(DesugaringKind::WhileLoop) {
@@ -4437,11 +4426,7 @@ impl<'b, 'v, 'tcx> Visitor<'v> for ConditionVisitor<'b, 'tcx> {
                 // arms might be missing an initialization.
                 let results: Vec<bool> = arms
                     .iter()
-                    .map(|arm| {
-                        let mut v = ReferencedStatementsVisitor(self.spans, false);
-                        v.visit_arm(arm);
-                        v.1
-                    })
+                    .map(|arm| ReferencedStatementsVisitor(self.spans).visit_arm(arm).is_break())
                     .collect();
                 if results.iter().any(|x| *x) && !results.iter().all(|x| *x) {
                     for (arm, seen) in arms.iter().zip(results) {
diff --git a/compiler/rustc_builtin_macros/src/deriving/default.rs b/compiler/rustc_builtin_macros/src/deriving/default.rs
index 577523a1d5a..7a65ed97f00 100644
--- a/compiler/rustc_builtin_macros/src/deriving/default.rs
+++ b/compiler/rustc_builtin_macros/src/deriving/default.rs
@@ -240,7 +240,7 @@ fn has_a_default_variant(item: &Annotatable) -> bool {
             if v.attrs.iter().any(|attr| attr.has_name(kw::Default)) {
                 ControlFlow::Break(())
             } else {
-                // no need to subrecurse.
+                // no need to walk the variant, we are only looking for top level variants
                 ControlFlow::Continue(())
             }
         }
diff --git a/compiler/rustc_hir_analysis/src/collect/generics_of.rs b/compiler/rustc_hir_analysis/src/collect/generics_of.rs
index 9b02c1a61fa..22d465c8e62 100644
--- a/compiler/rustc_hir_analysis/src/collect/generics_of.rs
+++ b/compiler/rustc_hir_analysis/src/collect/generics_of.rs
@@ -1,3 +1,5 @@
+use std::ops::ControlFlow;
+
 use crate::middle::resolve_bound_vars as rbv;
 use hir::{
     intravisit::{self, Visitor},
@@ -87,14 +89,9 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
             let mut in_param_ty = false;
             for (_parent, node) in tcx.hir().parent_iter(hir_id) {
                 if let Some(generics) = node.generics() {
-                    let mut visitor = AnonConstInParamTyDetector {
-                        in_param_ty: false,
-                        found_anon_const_in_param_ty: false,
-                        ct: hir_id,
-                    };
+                    let mut visitor = AnonConstInParamTyDetector { in_param_ty: false, ct: hir_id };
 
-                    visitor.visit_generics(generics);
-                    in_param_ty = visitor.found_anon_const_in_param_ty;
+                    in_param_ty = visitor.visit_generics(generics).is_break();
                     break;
                 }
             }
@@ -460,50 +457,45 @@ fn has_late_bound_regions<'tcx>(tcx: TyCtxt<'tcx>, node: Node<'tcx>) -> Option<S
     struct LateBoundRegionsDetector<'tcx> {
         tcx: TyCtxt<'tcx>,
         outer_index: ty::DebruijnIndex,
-        has_late_bound_regions: Option<Span>,
     }
 
     impl<'tcx> Visitor<'tcx> for LateBoundRegionsDetector<'tcx> {
-        fn visit_ty(&mut self, ty: &'tcx hir::Ty<'tcx>) {
-            if self.has_late_bound_regions.is_some() {
-                return;
-            }
+        type Result = ControlFlow<Span>;
+        fn visit_ty(&mut self, ty: &'tcx hir::Ty<'tcx>) -> ControlFlow<Span> {
             match ty.kind {
                 hir::TyKind::BareFn(..) => {
                     self.outer_index.shift_in(1);
-                    intravisit::walk_ty(self, ty);
+                    let res = intravisit::walk_ty(self, ty);
                     self.outer_index.shift_out(1);
+                    res
                 }
                 _ => intravisit::walk_ty(self, ty),
             }
         }
 
-        fn visit_poly_trait_ref(&mut self, tr: &'tcx hir::PolyTraitRef<'tcx>) {
-            if self.has_late_bound_regions.is_some() {
-                return;
-            }
+        fn visit_poly_trait_ref(&mut self, tr: &'tcx hir::PolyTraitRef<'tcx>) -> ControlFlow<Span> {
             self.outer_index.shift_in(1);
-            intravisit::walk_poly_trait_ref(self, tr);
+            let res = intravisit::walk_poly_trait_ref(self, tr);
             self.outer_index.shift_out(1);
+            res
         }
 
-        fn visit_lifetime(&mut self, lt: &'tcx hir::Lifetime) {
-            if self.has_late_bound_regions.is_some() {
-                return;
-            }
-
+        fn visit_lifetime(&mut self, lt: &'tcx hir::Lifetime) -> ControlFlow<Span> {
             match self.tcx.named_bound_var(lt.hir_id) {
-                Some(rbv::ResolvedArg::StaticLifetime | rbv::ResolvedArg::EarlyBound(..)) => {}
+                Some(rbv::ResolvedArg::StaticLifetime | rbv::ResolvedArg::EarlyBound(..)) => {
+                    ControlFlow::Continue(())
+                }
                 Some(rbv::ResolvedArg::LateBound(debruijn, _, _))
-                    if debruijn < self.outer_index => {}
+                    if debruijn < self.outer_index =>
+                {
+                    ControlFlow::Continue(())
+                }
                 Some(
                     rbv::ResolvedArg::LateBound(..)
                     | rbv::ResolvedArg::Free(..)
                     | rbv::ResolvedArg::Error(_),
                 )
-                | None => {
-                    self.has_late_bound_regions = Some(lt.ident.span);
-                }
+                | None => ControlFlow::Break(lt.ident.span),
             }
         }
     }
@@ -513,11 +505,7 @@ fn has_late_bound_regions<'tcx>(tcx: TyCtxt<'tcx>, node: Node<'tcx>) -> Option<S
         generics: &'tcx hir::Generics<'tcx>,
         decl: &'tcx hir::FnDecl<'tcx>,
     ) -> Option<Span> {
-        let mut visitor = LateBoundRegionsDetector {
-            tcx,
-            outer_index: ty::INNERMOST,
-            has_late_bound_regions: None,
-        };
+        let mut visitor = LateBoundRegionsDetector { tcx, outer_index: ty::INNERMOST };
         for param in generics.params {
             if let GenericParamKind::Lifetime { .. } = param.kind {
                 if tcx.is_late_bound(param.hir_id) {
@@ -525,8 +513,7 @@ fn has_late_bound_regions<'tcx>(tcx: TyCtxt<'tcx>, node: Node<'tcx>) -> Option<S
                 }
             }
         }
-        visitor.visit_fn_decl(decl);
-        visitor.has_late_bound_regions
+        visitor.visit_fn_decl(decl).break_value()
     }
 
     let decl = node.fn_decl()?;
@@ -536,26 +523,29 @@ fn has_late_bound_regions<'tcx>(tcx: TyCtxt<'tcx>, node: Node<'tcx>) -> Option<S
 
 struct AnonConstInParamTyDetector {
     in_param_ty: bool,
-    found_anon_const_in_param_ty: bool,
     ct: HirId,
 }
 
 impl<'v> Visitor<'v> for AnonConstInParamTyDetector {
-    fn visit_generic_param(&mut self, p: &'v hir::GenericParam<'v>) {
+    type Result = ControlFlow<()>;
+
+    fn visit_generic_param(&mut self, p: &'v hir::GenericParam<'v>) -> Self::Result {
         if let GenericParamKind::Const { ty, default: _, is_host_effect: _, synthetic: _ } = p.kind
         {
             let prev = self.in_param_ty;
             self.in_param_ty = true;
-            self.visit_ty(ty);
+            let res = self.visit_ty(ty);
             self.in_param_ty = prev;
+            res
+        } else {
+            ControlFlow::Continue(())
         }
     }
 
-    fn visit_anon_const(&mut self, c: &'v hir::AnonConst) {
+    fn visit_anon_const(&mut self, c: &'v hir::AnonConst) -> Self::Result {
         if self.in_param_ty && self.ct == c.hir_id {
-            self.found_anon_const_in_param_ty = true;
-        } else {
-            intravisit::walk_anon_const(self, c)
+            return ControlFlow::Break(());
         }
+        intravisit::walk_anon_const(self, c)
     }
 }
diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/inspect_obligations.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/inspect_obligations.rs
index fab7eb7495c..90dd5f73586 100644
--- a/compiler/rustc_hir_typeck/src/fn_ctxt/inspect_obligations.rs
+++ b/compiler/rustc_hir_typeck/src/fn_ctxt/inspect_obligations.rs
@@ -104,8 +104,6 @@ struct NestedObligationsForSelfTy<'a, 'tcx> {
 }
 
 impl<'a, 'tcx> ProofTreeVisitor<'tcx> for NestedObligationsForSelfTy<'a, 'tcx> {
-    type Result = ();
-
     fn span(&self) -> Span {
         self.root_cause.span
     }
diff --git a/compiler/rustc_trait_selection/src/traits/object_safety.rs b/compiler/rustc_trait_selection/src/traits/object_safety.rs
index f1611bd049d..5b2c8fb1950 100644
--- a/compiler/rustc_trait_selection/src/traits/object_safety.rs
+++ b/compiler/rustc_trait_selection/src/traits/object_safety.rs
@@ -805,10 +805,11 @@ fn contains_illegal_self_type_reference<'tcx, T: TypeVisitable<TyCtxt<'tcx>>>(
                         .unwrap()
                         .contains(&data.trait_ref(self.tcx).def_id);
 
+                    // only walk contained types if it's not a super trait
                     if is_supertrait_of_current_trait {
-                        ControlFlow::Continue(()) // do not walk contained types, do not report error, do collect $200
+                        ControlFlow::Continue(())
                     } else {
-                        t.super_visit_with(self) // DO walk contained types, POSSIBLY reporting an error
+                        t.super_visit_with(self) // POSSIBLY reporting an error
                     }
                 }
                 _ => t.super_visit_with(self), // walk contained types, if any
diff --git a/compiler/rustc_trait_selection/src/traits/wf.rs b/compiler/rustc_trait_selection/src/traits/wf.rs
index e3952679f96..f071dc6c784 100644
--- a/compiler/rustc_trait_selection/src/traits/wf.rs
+++ b/compiler/rustc_trait_selection/src/traits/wf.rs
@@ -640,8 +640,6 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> {
 }
 
 impl<'a, 'tcx> TypeVisitor<TyCtxt<'tcx>> for WfPredicates<'a, 'tcx> {
-    type Result = ();
-
     fn visit_ty(&mut self, t: Ty<'tcx>) -> Self::Result {
         debug!("wf bounds for t={:?} t.kind={:#?}", t, t.kind());