fix expression test failure

stan/math/rev/core/operator_addition.hpp

@@ -164,8 +164,8 @@ inline auto add(const VarMat& a, const Arith& b) {
   using op_ret_type
       = decltype((a.val().array() + as_array_or_scalar(b)).matrix());
   using ret_type = promote_var_matrix_t<op_ret_type, VarMat>;
-  arena_t<VarMat> arena_a = a;
-  arena_t<ret_type> ret(a.val().array() + as_array_or_scalar(b));
+  arena_t<VarMat> arena_a(a);
+  arena_t<ret_type> ret(arena_a.val().array() + as_array_or_scalar(b));
   reverse_pass_callback(
       [ret, arena_a]() mutable { arena_a.adj() += ret.adj_op(); });
   return ret_type(ret);
@@ -197,8 +197,8 @@ inline auto add(const Arith& a, const VarMat& b) {
  * @return Variable result of adding two variables.
  */
 template <typename Var, typename EigMat,
-          require_eigen_vt<std::is_arithmetic, EigMat>* = nullptr,
-          require_var_vt<std::is_arithmetic, Var>* = nullptr>
+          require_var_vt<std::is_arithmetic, Var>* = nullptr,
+          require_eigen_vt<std::is_arithmetic, EigMat>* = nullptr>
 inline auto add(const Var& a, const EigMat& b) {
   using ret_type = promote_scalar_t<var, EigMat>;
   arena_t<ret_type> ret(a.val() + b.array());
@@ -216,28 +216,28 @@ inline auto add(const Var& a, const EigMat& b) {
  * @return Variable result of adding two variables.
  */
 template <typename EigMat, typename Var,
-          require_var_vt<std::is_arithmetic, Var>* = nullptr,
-          require_eigen_vt<std::is_arithmetic, EigMat>* = nullptr>
+          require_eigen_vt<std::is_arithmetic, EigMat>* = nullptr,
+          require_var_vt<std::is_arithmetic, Var>* = nullptr>
 inline auto add(const EigMat& a, const Var& b) {
   return add(b, a);
 }
 
 /**
  * Addition operator for a variable and variable matrix (C++).
  *
+ * @tparam Var A `var_value` with an underlying arithmetic type.
  * @tparam VarMat An Eigen Matrix type with a variable Scalar type or a
  * `var_value` with an underlying matrix type.
- * @tparam Var A `var_value` with an underlying arithmetic type.
  * @param a First variable operand.
  * @param b Second variable operand.
  * @return Variable result of adding two variables.
  */
 template <typename Var, typename VarMat,
-          require_rev_matrix_t<VarMat>* = nullptr,
-          require_var_vt<std::is_arithmetic, Var>* = nullptr>
+          require_var_vt<std::is_arithmetic, Var>* = nullptr,
+          require_rev_matrix_t<VarMat>* = nullptr>
 inline auto add(const Var& a, const VarMat& b) {
   arena_t<VarMat> arena_b(b);
-  arena_t<VarMat> ret(a.val() + b.val().array());
+  arena_t<VarMat> ret(a.val() + arena_b.val().array());
   reverse_pass_callback([ret, a, arena_b]() mutable {
     for (Eigen::Index i = 0; i < arena_b.size(); ++i) {
       const auto ret_adj = ret.adj().coeffRef(i);
@@ -259,8 +259,8 @@ inline auto add(const Var& a, const VarMat& b) {
  * @return Variable result of adding two variables.
  */
 template <typename Var, typename VarMat,
-          require_rev_matrix_t<VarMat>* = nullptr,
-          require_var_vt<std::is_arithmetic, Var>* = nullptr>
+          require_var_vt<std::is_arithmetic, Var>* = nullptr,
+          require_rev_matrix_t<VarMat>* = nullptr>
 inline auto add(const VarMat& a, const Var& b) {
   return add(b, a);
 }