What is the test for reversing a judgment of dismissal for a trial on the merits of a claim?

The trial court did not reach the merits of plaintiff's claim; however, because plaintiff's claims are pure questions of law, "it would be an idle act to reverse the judgment of dismissal for a trial on the merits." (Herzberg v. County of Plumas (2005) 133 Cal.App.4th 1, 24.) Under these circumstances, the reviewing court may consider the merits of the legal controversy, and "the opinion of the reviewing court will constitute the declaration of the legal rights and duties of the parties concerning the matter in controversy." (Ibid.)