Fix one layer of closures not being able to constrain opaque types

compiler/rustc_ty_utils/src/opaque_types.rs

@@ -322,7 +322,10 @@ fn opaque_types_defined_by<'tcx>(tcx: TyCtxt<'tcx>, item: LocalDefId) -> &'tcx [
         | DefKind::GlobalAsm
         | DefKind::Impl { .. } => {}
         DefKind::Closure | DefKind::Generator => {
-            return tcx.opaque_types_defined_by(tcx.local_parent(item));
+            // 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();
         }
     }
     tcx.arena.alloc_from_iter(collector.opaques)

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

@@ -5,6 +5,5 @@ fn main() {
         type Tait = impl Sized;
         let y: Tait = ();
         //~^ ERROR: item constrains opaque type that is not in its signature
-        //~| ERROR: item constrains opaque type that is not in its signature
     };
 }

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

@@ -11,18 +11,5 @@ note: this item must have the opaque type in its signature in order to be able t
 LL | fn main() {
    |    ^^^^
 
-error: item constrains opaque type that is not in its signature
+error: aborting due to previous error
-  --> $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:4:13
-   |
-LL |     let x = || {
-   |             ^^
-
-error: aborting due to 2 previous errors