Merge branch 'develop' of github.com:stan-dev/math into develop

Author: SteveBronder

stan/math/prim/fun/promote_scalar.hpp

@@ -20,7 +20,8 @@ namespace math {
  */
 template <typename PromotionScalar, typename UnPromotedType,
           require_constructible_t<PromotionScalar, UnPromotedType>* = nullptr,
-          require_not_same_t<PromotionScalar, UnPromotedType>* = nullptr>
+          require_not_same_t<PromotionScalar, UnPromotedType>* = nullptr,
+          require_all_not_tuple_t<PromotionScalar, UnPromotedType>* = nullptr>
 inline constexpr auto promote_scalar(UnPromotedType&& x) {
   return PromotionScalar(std::forward<UnPromotedType>(x));
 }

test/unit/math/mix/fun/promote_scalar_test.cpp

@@ -65,6 +65,7 @@ void test_promote_scalar() {
                  inner_promo_type>>(tester);
   stan::math::test::expect_same_value_of_rec(tester, result);
 }
+
 TEST(mixFun, promote_scalar_tuple) {
   using stan::math::fvar;
   using stan::math::var;
@@ -83,3 +84,22 @@ TEST(mixFun, promote_scalar_tuple) {
   test_promote_scalar<std::complex<var>, double>();
   test_promote_scalar<std::complex<fvar<var>>, double>();
 }
+
+template <typename UnPromotedType>
+void test_promote_scalar_basic() {
+  std::tuple<UnPromotedType, UnPromotedType> x{UnPromotedType(3.5),
+                                               UnPromotedType(4.5)};
+  std::tuple<std::complex<UnPromotedType>, UnPromotedType> z
+      = stan::math::promote_scalar<
+          std::tuple<std::complex<UnPromotedType>, UnPromotedType>>(x);
+  stan::math::test::expect_same_value_of_rec(x, z);
+}
+
+TEST(mixFun, promote_scalar_tuple_basic) {
+  using stan::math::fvar;
+  using stan::math::var;
+  test_promote_scalar_basic<double>();
+  test_promote_scalar_basic<var>();
+  test_promote_scalar_basic<fvar<double>>();
+  test_promote_scalar_basic<fvar<var>>();
+}