Auto merge of #78779 - LeSeulArtichaut:ty-visitor-return, r=oli-obk

Introduce `TypeVisitor::BreakTy`

Implements MCP rust-lang/compiler-team#383.
r? `@ghost`
cc `@lcnr` `@oli-obk`

~~Blocked on FCP in rust-lang/compiler-team#383.~~

6 files changed, 13 insertions, 17 deletions

diff --git a/compiler/rustc_infer/src/infer/error_reporting/mod.rs b/compiler/rustc_infer/src/infer/error_reporting/mod.rs
index 5a164635f4f..183fb314a00 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 ede94c3d9f6..5264854d8eb 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/mod.rs b/compiler/rustc_infer/src/infer/mod.rs
index a045378f502..6affe0e5463 100644
--- a/compiler/rustc_infer/src/infer/mod.rs
+++ b/compiler/rustc_infer/src/infer/mod.rs
@@ -1,5 +1,3 @@
-//! See the Book for more information.
-
 pub use self::freshen::TypeFreshener;
 pub use self::LateBoundRegionConversionTime::*;
 pub use self::RegionVariableOrigin::*;
@@ -1334,9 +1332,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     where
         T: TypeFoldable<'tcx>,
     {
-        let mut r = resolve::UnresolvedTypeFinder::new(self);
-        value.visit_with(&mut r);
-        r.first_unresolved
+        value.visit_with(&mut resolve::UnresolvedTypeFinder::new(self)).break_value()
     }
 
     pub fn probe_const_var(
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 d05c90606cc..d72be0134fb 100644
--- a/compiler/rustc_infer/src/infer/resolve.rs
+++ b/compiler/rustc_infer/src/infer/resolve.rs
@@ -111,19 +111,17 @@ impl<'a, 'tcx> TypeFolder<'tcx> for OpportunisticRegionResolver<'a, 'tcx> {
 /// involve some hashing and so forth).
 pub struct UnresolvedTypeFinder<'a, 'tcx> {
     infcx: &'a InferCtxt<'a, 'tcx>,
-
-    /// Used to find the type parameter name and location for error reporting.
-    pub first_unresolved: Option<(Ty<'tcx>, Option<Span>)>,
 }
 
 impl<'a, 'tcx> UnresolvedTypeFinder<'a, 'tcx> {
     pub fn new(infcx: &'a InferCtxt<'a, 'tcx>) -> Self {
-        UnresolvedTypeFinder { infcx, first_unresolved: None }
+        UnresolvedTypeFinder { infcx }
     }
 }
 
 impl<'a, 'tcx> TypeVisitor<'tcx> for UnresolvedTypeFinder<'a, 'tcx> {
-    fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<()> {
+    type BreakTy = (Ty<'tcx>, Option<Span>);
+    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() {
@@ -144,8 +142,7 @@ impl<'a, 'tcx> TypeVisitor<'tcx> for UnresolvedTypeFinder<'a, 'tcx> {
                 } else {
                     None
                 };
-                self.first_unresolved = Some((t, ty_var_span));
-                ControlFlow::BREAK
+                ControlFlow::Break((t, ty_var_span))
             } else {
                 // Otherwise, visit its contents.
                 t.super_visit_with(self)
diff --git a/compiler/rustc_infer/src/traits/structural_impls.rs b/compiler/rustc_infer/src/traits/structural_impls.rs
index d8a1993b6cb..c4a2ecee096 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)
     }
 }