I need to expose a few function signatures.
Very straightforward. My intuition is to simply edit the function_signatures file in the stan repo. Or are we now doing everything in stanc3?
I agree with Steve and Sebastian that commented on the github issue. New language stuff goes to stanc3. That is what cmdstan 2.23 uses and so will rstan 2.23 when it comes out.
We already have a bunch of functions that are only in stanc3: reduce_sum, ordered logistic and categorical logit GLMs, vectorized dirichlet, std_normal_{cdf,lcdf,lccdf,rng}, etc.