What is the current state of the law on disclosing the name of an informer?

Apparently the majority has adopted the reasoning in Roviaro v. United States, 353 U.S. 53, 77 S.Ct. 623, 1 L.Ed. 639, which dealt with the necessity of disclosing the name of the informer-participant (a much stronger situation requiring disclosure than in the case of a mere informer) where the court said: 'A further limitation on the applicability of the privilege [not to disclose] arises from the fundamental requirements of fairness.' 353 U.S. at page 60, 77 S.Ct. at page 628. But apparently the following from the same case was overlooked: