code: private void validateNoSideEffects(Node n, JSDocInfo info) {
      // Cannot have @modifies or @nosideeffects in regular (non externs) js. Report errors.
      if (info == null) {
        return;
      }
  
      if (n.isFromExterns()) {
        return;
      }
  
      if (info.hasSideEffectsArgumentsAnnotation() || info.modifiesThis()) {
        report(n, INVALID_MODIFIES_ANNOTATION);
      }
      if (info.isNoSideEffects()) {
        report(n, INVALID_NO_SIDE_EFFECT_ANNOTATION);
      }
    }
docs: Check that @nosideeeffects annotations are only present in externs.