Treat closures as part of their parent

compiler/rustc_ty_utils/src/opaque_types.rs

@@ -121,6 +121,12 @@ fn visit_nested_item(&mut self, id: rustc_hir::ItemId) {
                     self.collector.opaques.extend(items);
                 }
             }
+            #[instrument(level = "trace", skip(self))]
+            // Recurse into these, as they are type checked with their parent
+            fn visit_nested_body(&mut self, id: rustc_hir::BodyId) {
+                let body = self.collector.tcx.hir().body(id);
+                self.visit_body(body);
+            }
         }
         TaitInBodyFinder { collector: self }.visit_expr(body);
     }
@@ -280,11 +286,7 @@ fn opaque_types_defined_by<'tcx>(tcx: TyCtxt<'tcx>, item: LocalDefId) -> &'tcx [
             collector.collect_body_and_predicate_taits();
         }
         // Walk over the type of the item to find opaques.
-        DefKind::Static(_)
-        | DefKind::Const
-        | DefKind::AssocConst
-        | DefKind::AnonConst
-        | DefKind::InlineConst => {
+        DefKind::Static(_) | DefKind::Const | DefKind::AssocConst | DefKind::AnonConst => {
             let span = match tcx.hir().get_by_def_id(item).ty() {
                 Some(ty) => ty.span,
                 _ => tcx.def_span(item),
@@ -321,11 +323,9 @@ fn opaque_types_defined_by<'tcx>(tcx: TyCtxt<'tcx>, item: LocalDefId) -> &'tcx [
         | DefKind::LifetimeParam
         | DefKind::GlobalAsm
         | DefKind::Impl { .. } => {}
-        DefKind::Closure | DefKind::Generator => {
-            // All items in the signature of the parent are ok
-            collector.opaques.extend(tcx.opaque_types_defined_by(tcx.local_parent(item)));
-            // And items in the body of the closure itself
-            collector.collect_taits_declared_in_body();
+        // Closures and generators are type checked with their parent, so there is no difference here.
+        DefKind::Closure | DefKind::Generator | DefKind::InlineConst => {
+            return tcx.opaque_types_defined_by(tcx.local_parent(item));
         }
     }
     tcx.arena.alloc_from_iter(collector.opaques)

tests/ui/type-alias-impl-trait/nested_in_closure.rs

@@ -1,9 +1,17 @@
 #![feature(type_alias_impl_trait)]
+// check-pass
 
 fn main() {
     let x = || {
         type Tait = impl Sized;
         let y: Tait = ();
-        //~^ ERROR: item constrains opaque type that is not in its signature
     };
+
+    let y = || {
+        type Tait = impl std::fmt::Debug;
+        let y: Tait = ();
+        y
+    };
+    let mut z = y();
+    z = ();
 }

tests/ui/type-alias-impl-trait/nested_in_closure.stderr

@@ -1,15 +0,0 @@
-error: item constrains opaque type that is not in its signature
-  --> $DIR/nested_in_closure.rs:6:23
-   |
-LL |         let y: Tait = ();
-   |                       ^^
-   |
-   = note: this item must have the opaque type in its signature in order to be able to register hidden types
-note: this item must have the opaque type in its signature in order to be able to register hidden types
-  --> $DIR/nested_in_closure.rs:3:4
-   |
-LL | fn main() {
-   |    ^^^^
-
-error: aborting due to previous error
-