add back accidentally deleted accumulate and count vars

Author: SteveBronder

stan/math/prim/functor/iter_tuple_nested.hpp

@@ -20,7 +20,7 @@ namespace stan::math {
  * only create side effects.
  */
 template <typename F, typename... Types>
-inline auto iter_tuple_nested(F&& f, Types&&... args) {
+inline void iter_tuple_nested(F&& f, Types&&... args) {
   constexpr bool is_vec_container
       = (is_std_vector_v<Types> && ...)
         && (!is_stan_scalar<value_type_t<Types>>::value && ...);

stan/math/rev/core/accumulate_adjoints.hpp

@@ -140,6 +140,13 @@ inline double* accumulate_adjoints(double* dest, Arith&& x, Pargs&&... args) {
   return accumulate_adjoints(dest, std::forward<Pargs>(args)...);
 }
 
+/**
+ * End accumulate_adjoints recursion and return pointer
+ *
+ * @param dest Pointer
+ */
+inline double* accumulate_adjoints(double* dest) { return dest; }
+
 }  // namespace math
 }  // namespace stan
 

stan/math/rev/core/count_vars.hpp

@@ -33,6 +33,7 @@ template <typename Arith, require_arithmetic_t<scalar_type_t<Arith>>* = nullptr,
           typename... Pargs>
 inline size_t count_vars_impl(size_t count, Arith& x, Pargs&&... args);
 
+inline size_t count_vars_impl(size_t count);
 /**
  * Count the number of vars in x (a std::vector of vars),
  *  add it to the running total,