code: @CheckReturnValue
    private FlowScope traverseReturn(Node n, FlowScope scope) {
      scope = traverseChildren(n, scope);
  
      Node retValue = n.getFirstChild();
      if (retValue != null) {
        JSType type = functionScope.getRootNode().getJSType();
        if (type != null) {
          FunctionType fnType = type.toMaybeFunctionType();
          if (fnType != null) {
            inferPropertyTypesToMatchConstraint(
                retValue.getJSType(), fnType.getReturnType());
          }
        }
      }
      return scope;
    }
docs: Traverse a return value.