Missed header

andrjohns · andrjohns · commit d5eedf3959e8 · 2023-10-05T16:16:35.000+03:00
diff --git a/stan/math/prim/meta/ref_type.hpp b/stan/math/prim/meta/ref_type.hpp
@@ -2,6 +2,7 @@
 #define STAN_MATH_PRIM_META_REF_TYPE_HPP
 
 #include <stan/math/prim/fun/Eigen.hpp>
+#include <stan/math/prim/meta/is_constant.hpp>
 #include <stan/math/prim/meta/is_eigen.hpp>
 #include <stan/math/prim/meta/is_arena_matrix.hpp>
 #include <stan/math/prim/meta/is_vector.hpp>
