Allow compilation with any GTest version 1.11+ (#13153)

GTest max support for `Types` was removed in 1.11, so we remove the workarounds in cudf_gtest.

Since we need to support our custom `Types` and the GTest 1.11+ version rework the type_list_utilities to be generic and not depend on specific traits.

Also corrected the `<<` overloads for GTest printing so that they work with GTest 1.11.

Authors:
  - Robert Maynard (https://github.com/robertmaynard)
  - Vukasin Milovanovic (https://github.com/vuule)

Approvers:
  - Bradley Dice (https://github.com/bdice)
  - Nghia Truong (https://github.com/ttnghia)

URL: #13153

cpp/include/cudf_test/cudf_gtest.hpp

@@ -22,7 +22,7 @@
 
 /**
  * @file cudf_gtest.hpp
- * @brief Work around for GTests emulation of variadic templates in
+ * @brief Work around for GTests( <=v1.10 ) emulation of variadic templates in
  * @verbatim ::Testing::Types @endverbatim
  *
  * @note Instead of including `gtest/gtest.h`, all libcudf test files should
@@ -35,6 +35,10 @@
  */
 
 // @cond
+#if __has_include(<gtest/internal/gtest-type-util.h.pump>)
+// gtest doesn't provide a version header so we need to
+// use a file existence trick.
+// gtest-type-util.h.pump only exists in versions < 1.11
 #define Types      Types_NOT_USED
 #define Types0     Types0_NOT_USED
 #define TypeList   TypeList_NOT_USED
@@ -89,6 +93,7 @@ struct TypeList<Types<TYPES...>> {
 
 }  // namespace internal
 }  // namespace testing
+#endif  // gtest < 1.11
 // @endcond
 
 #include <gmock/gmock.h>

cpp/include/cudf_test/type_list_utilities.hpp

@@ -90,14 +90,12 @@ template <class... T, int D>
 struct GetTypeImpl<Types<T...>, D> {
   static_assert(D < sizeof...(T), "Out of bounds");
 
-  using type = typename GetTypeImpl<typename Types<T...>::Tail, D - 1>::type;
+  using raw_type = decltype(std::get<D>(std::declval<std::tuple<T...>>()));
+  using type     = std::decay_t<raw_type>;
 };
-
-template <class... ARGS>
-struct GetTypeImpl<Types<ARGS...>, 0> {
-  static_assert(sizeof...(ARGS) > 0, "Out of bounds");
-
-  using type = typename Types<ARGS...>::Head;
+template <class T, class... ARGS>
+struct GetTypeImpl<Types<T, ARGS...>, 0> {
+  using type = T;
 };
 // @endcond
 

cpp/tests/iterator/optional_iterator_test_numeric.cu

@@ -24,6 +24,16 @@
 
 using TestingTypes = cudf::test::NumericTypes;
 
+namespace cudf {
+// To print meanvar for debug.
+// Needs to be in the cudf namespace for ADL
+template <typename T>
+std::ostream& operator<<(std::ostream& os, cudf::meanvar<T> const& rhs)
+{
+  return os << "[" << rhs.value << ", " << rhs.value_squared << ", " << rhs.count << "] ";
+};
+}  // namespace cudf
+
 template <typename T>
 struct NumericOptionalIteratorTest : public IteratorTest<T> {};
 
@@ -34,13 +44,6 @@ TYPED_TEST(NumericOptionalIteratorTest, nonull_optional_iterator)
 }
 TYPED_TEST(NumericOptionalIteratorTest, null_optional_iterator) { null_optional_iterator(*this); }
 
-// to print meanvar for debug.
-template <typename T>
-std::ostream& operator<<(std::ostream& os, cudf::meanvar<T> const& rhs)
-{
-  return os << "[" << rhs.value << ", " << rhs.value_squared << ", " << rhs.count << "] ";
-};
-
 // Transformers and Operators for optional_iterator test
 template <typename ElementType>
 struct transformer_optional_meanvar {

cpp/tests/iterator/pair_iterator_test_numeric.cu

@@ -22,20 +22,23 @@
 
 using TestingTypes = cudf::test::NumericTypes;
 
+namespace cudf {
+// To print meanvar for debug.
+// Needs to be in the cudf namespace for ADL
+template <typename T>
+std::ostream& operator<<(std::ostream& os, cudf::meanvar<T> const& rhs)
+{
+  return os << "[" << rhs.value << ", " << rhs.value_squared << ", " << rhs.count << "] ";
+};
+}  // namespace cudf
+
 template <typename T>
 struct NumericPairIteratorTest : public IteratorTest<T> {};
 
 TYPED_TEST_SUITE(NumericPairIteratorTest, TestingTypes);
 TYPED_TEST(NumericPairIteratorTest, nonull_pair_iterator) { nonull_pair_iterator(*this); }
 TYPED_TEST(NumericPairIteratorTest, null_pair_iterator) { null_pair_iterator(*this); }
 
-// to print meanvar for debug.
-template <typename T>
-std::ostream& operator<<(std::ostream& os, cudf::meanvar<T> const& rhs)
-{
-  return os << "[" << rhs.value << ", " << rhs.value_squared << ", " << rhs.count << "] ";
-};
-
 // Transformers and Operators for pair_iterator test
 template <typename ElementType>
 struct transformer_pair_meanvar {