categorical_logit_rng() doesn't accept negative_infinity() input

[mhollanders]

Hello everyone,

The following Stan program:

generated quantities {
  vector[3] theta = [0, 0.5, 0.5]';
  vector[3] log_theta = log(theta);
  int test = categorical_rng(theta);  // works
  int test2 = categorical_rng(exp(log_theta - log_sum_exp(log_theta)));  // works
  int test3 = categorical_logit_rng(log_theta);  // doesn't work
}

yields this error:

categorical_logit_rng: Log odds parameter[1] is -inf, but must be finite!

Given that exponentiating the normalised log probabilities works for categorical_rng, I think this is a bug. Please let me know if I'm wrong.

Thanks,

Matt