In Priestly v. Superior Court (1958) 50 Cal.2d 812, the prosecution attempted to show reasonable cause for a warrantless search by testimony as to communications from a confidential informant. The defendant sought either to exclude the testimony or to compel disclosure of the informant's identity. On review our Supreme Court stated the following: "If testimony of communications from a confidential informer is necessary to establish the legality of a search, the defendant must be given a fair opportunity to rebut that testimony. He must therefore be permitted to ascertain the identity of the informer, since the legality of the officer's action depends upon the credibility of the information, not upon facts that he directly witnessed and upon which he could be cross-examined. If an officer were allowed to establish unimpeachably the lawfulness of a search merely by testifying that he received justifying information from a reliable person whose identity cannot be revealed, he would become the sole judge of what is probable cause to make the search. Such a holding would destroy the exclusionary rule. Only by requiring disclosure and giving the defendant an opportunity to present contrary or impeaching evidence as to the truth of the officer's testimony and the reasonableness of his reliance on the informer can the court make a fair determination of the issue." (P. 818.) The Priestly rule was modified by the enactment of Evidence Code section 1042, subdivision (c). ( Parsley v. Superior Court (1973) 9 Cal.3d 934.) Subdivision (c) provides that ". . . in any preliminary hearing, criminal trial, or other criminal proceeding, any otherwise admissible evidence of information communicated to a peace officer by a confidential informant, who is not a material witness to the guilt or innocence of the accused of the offense charged, is admissible on the issue of reasonable cause to make an arrest or search without requiring that the name or identity of the informant be disclosed if the judge or magistrate is satisfied, based upon evidence produced in open court, out of the presence of the jury, that such information was received from a reliable informant and in his discretion does not require such disclosure." (Italics supplied.) The Parsley court construed subdivision (c) in light of the Priestly rule: " In order to admit at a preliminary hearing evidence relevant to the reasonableness of an arrest or search that is based on communications of a confidential informant, the judge or magistrate must either (1) compel disclosure of the informant's identity as required by Priestly, or (2) exercise his discretion based on evidence produced in open court that the informant is reliable and that disclosure is not required." (9 Cal.3d at p. 942.) The court reasoned that, "full cross-examination of prosecution witnesses concerning informant reliability is not only necessary for proper exercise of the court's discretion on this issue under section 1042, subdivision (c), it appears to be a constitutional prerequisite to invoking the informant privilege." (Ibid.)