Update comments

compiler/rustc_query_system/src/query/plumbing.rs

@@ -251,7 +251,10 @@ where
     Qcx: QueryContext,
 {
     let (query_map, complete) = qcx.collect_active_jobs();
+    // Ensure there was no errors collecting all active jobs.
+    // We need the complete map to ensure we find a cycle to break.
     assert!(complete, "failed to collect active queries");
+
     let error = try_execute.find_cycle_in_stack(query_map, &qcx.current_query_job(), span);
     (mk_cycle(query, qcx, error), None)
 }