make it recursive

compiler/rustc_trait_selection/src/traits/project.rs

@@ -1645,11 +1645,9 @@ fn assemble_candidates_from_trait_def<'cx, 'tcx>(
 
             ControlFlow::Continue(())
         },
-        || {
-            // `ProjectionCandidateSet` is borrowed in the above closure,
-            // so just mark ambiguous outside of the closure.
-            ambiguous = true;
-        },
+        // `ProjectionCandidateSet` is borrowed in the above closure,
+        // so just mark ambiguous outside of the closure.
+        || ambiguous = true,
     );
 
     if ambiguous {

compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs

@@ -201,10 +201,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
                     ControlFlow::Continue(())
                 },
-                || {
-                    // On ambiguity.
-                    candidates.ambiguous = true;
-                },
+                // On ambiguity.
+                || candidates.ambiguous = true,
             );
         });
     }