Does the waiver rule apply in cases where a guilty plea was not voluntary?

The rule should be stated as follows: Where a petition for habeas corpus raises a claim that a guilty plea was not voluntary, the standards of Townsend v. Sain are applicable in determining whether to hold a hearing; and although the waiver rule means that an allegation that the petitioner's constitutional rights were violated before the plea was taken is not, standing alone, sufficient to call the validity of the plea into question, nonetheless if it is alleged that the plea was coerced in a manner spelled out in the petition, the alleged violations are not irrelevant to the issue of the voluntariness of the plea. An alleged violation of constitutional rights is simply another factor to be taken into account in determining the voluntariness of the plea.