[gtest] Use `std::index_sequence` and friends instead of rolling our own

* Applies for `std::index_sequence`, `std::make_index_sequence`, and `std::index_sequence_for` replacing `IndexSequence`, `MakeIndexSequence` and IndexSequenceFor`
* Also deleted implementation helper `DoubleSequence`
* The standard interfaces [have been in the standard library since C++14](https://en.cppreference.com/w/cpp/utility/integer_sequence), which [is the minimum supported C++ version by Google Test](https://github.com/google/oss-policies-info/blob/main/foundational-cxx-support-matrix.md)

PiperOrigin-RevId: 621939977
Change-Id: Id264266f08da66c0fa2a6e6fbb8f86fd3cb3a421

7 files changed, 56 insertions, 103 deletions

diff --git a/googlemock/include/gmock/gmock-actions.h b/googlemock/include/gmock/gmock-actions.h
index fab9993..7e17b30 100644
--- a/googlemock/include/gmock/gmock-actions.h
+++ b/googlemock/include/gmock/gmock-actions.h
@@ -2135,13 +2135,13 @@ struct ActionImpl<R(Args...), Impl> : ImplBase<Impl>::type {
   R operator()(Args&&... arg) const {
     static constexpr size_t kMaxArgs =
         sizeof...(Args) <= 10 ? sizeof...(Args) : 10;
-    return Apply(MakeIndexSequence<kMaxArgs>{},
-                 MakeIndexSequence<10 - kMaxArgs>{},
+    return Apply(std::make_index_sequence<kMaxArgs>{},
+                 std::make_index_sequence<10 - kMaxArgs>{},
                  args_type{std::forward<Args>(arg)...});
   }
 
   template <std::size_t... arg_id, std::size_t... excess_id>
-  R Apply(IndexSequence<arg_id...>, IndexSequence<excess_id...>,
+  R Apply(std::index_sequence<arg_id...>, std::index_sequence<excess_id...>,
           const args_type& args) const {
     // Impl need not be specific to the signature of action being implemented;
     // only the implementing function body needs to have all of the specific
diff --git a/googlemock/include/gmock/gmock-matchers.h b/googlemock/include/gmock/gmock-matchers.h
index c4149f2..6b6b437 100644
--- a/googlemock/include/gmock/gmock-matchers.h
+++ b/googlemock/include/gmock/gmock-matchers.h
@@ -490,12 +490,12 @@ class MatcherBaseImpl<Derived<Ts...>> {
 
   template <typename F>
   operator ::testing::Matcher<F>() const {  // NOLINT(runtime/explicit)
-    return Apply<F>(MakeIndexSequence<sizeof...(Ts)>{});
+    return Apply<F>(std::make_index_sequence<sizeof...(Ts)>{});
   }
 
  private:
   template <typename F, std::size_t... tuple_ids>
-  ::testing::Matcher<F> Apply(IndexSequence<tuple_ids...>) const {
+  ::testing::Matcher<F> Apply(std::index_sequence<tuple_ids...>) const {
     return ::testing::Matcher<F>(
         new typename Derived<Ts...>::template gmock_Impl<F>(
             std::get<tuple_ids>(params_)...));
@@ -3152,8 +3152,8 @@ class PairMatcher {
 };
 
 template <typename T, size_t... I>
-auto UnpackStructImpl(const T& t, IndexSequence<I...>, int)
-    -> decltype(std::tie(get<I>(t)...)) {
+auto UnpackStructImpl(const T& t, std::index_sequence<I...>,
+                      int) -> decltype(std::tie(get<I>(t)...)) {
   static_assert(std::tuple_size<T>::value == sizeof...(I),
                 "Number of arguments doesn't match the number of fields.");
   return std::tie(get<I>(t)...);
@@ -3161,97 +3161,97 @@ auto UnpackStructImpl(const T& t, IndexSequence<I...>, int)
 
 #if defined(__cpp_structured_bindings) && __cpp_structured_bindings >= 201606
 template <typename T>
-auto UnpackStructImpl(const T& t, MakeIndexSequence<1>, char) {
+auto UnpackStructImpl(const T& t, std::make_index_sequence<1>, char) {
   const auto& [a] = t;
   return std::tie(a);
 }
 template <typename T>
-auto UnpackStructImpl(const T& t, MakeIndexSequence<2>, char) {
+auto UnpackStructImpl(const T& t, std::make_index_sequence<2>, char) {
   const auto& [a, b] = t;
   return std::tie(a, b);
 }
 template <typename T>
-auto UnpackStructImpl(const T& t, MakeIndexSequence<3>, char) {
+auto UnpackStructImpl(const T& t, std::make_index_sequence<3>, char) {
   const auto& [a, b, c] = t;
   return std::tie(a, b, c);
 }
 template <typename T>
-auto UnpackStructImpl(const T& t, MakeIndexSequence<4>, char) {
+auto UnpackStructImpl(const T& t, std::make_index_sequence<4>, char) {
   const auto& [a, b, c, d] = t;
   return std::tie(a, b, c, d);
 }
 template <typename T>
-auto UnpackStructImpl(const T& t, MakeIndexSequence<5>, char) {
+auto UnpackStructImpl(const T& t, std::make_index_sequence<5>, char) {
   const auto& [a, b, c, d, e] = t;
   return std::tie(a, b, c, d, e);
 }
 template <typename T>
-auto UnpackStructImpl(const T& t, MakeIndexSequence<6>, char) {
+auto UnpackStructImpl(const T& t, std::make_index_sequence<6>, char) {
   const auto& [a, b, c, d, e, f] = t;
   return std::tie(a, b, c, d, e, f);
 }
 template <typename T>
-auto UnpackStructImpl(const T& t, MakeIndexSequence<7>, char) {
+auto UnpackStructImpl(const T& t, std::make_index_sequence<7>, char) {
   const auto& [a, b, c, d, e, f, g] = t;
   return std::tie(a, b, c, d, e, f, g);
 }
 template <typename T>
-auto UnpackStructImpl(const T& t, MakeIndexSequence<8>, char) {
+auto UnpackStructImpl(const T& t, std::make_index_sequence<8>, char) {
   const auto& [a, b, c, d, e, f, g, h] = t;
   return std::tie(a, b, c, d, e, f, g, h);
 }
 template <typename T>
-auto UnpackStructImpl(const T& t, MakeIndexSequence<9>, char) {
+auto UnpackStructImpl(const T& t, std::make_index_sequence<9>, char) {
   const auto& [a, b, c, d, e, f, g, h, i] = t;
   return std::tie(a, b, c, d, e, f, g, h, i);
 }
 template <typename T>
-auto UnpackStructImpl(const T& t, MakeIndexSequence<10>, char) {
+auto UnpackStructImpl(const T& t, std::make_index_sequence<10>, char) {
   const auto& [a, b, c, d, e, f, g, h, i, j] = t;
   return std::tie(a, b, c, d, e, f, g, h, i, j);
 }
 template <typename T>
-auto UnpackStructImpl(const T& t, MakeIndexSequence<11>, char) {
+auto UnpackStructImpl(const T& t, std::make_index_sequence<11>, char) {
   const auto& [a, b, c, d, e, f, g, h, i, j, k] = t;
   return std::tie(a, b, c, d, e, f, g, h, i, j, k);
 }
 template <typename T>
-auto UnpackStructImpl(const T& t, MakeIndexSequence<12>, char) {
+auto UnpackStructImpl(const T& t, std::make_index_sequence<12>, char) {
   const auto& [a, b, c, d, e, f, g, h, i, j, k, l] = t;
   return std::tie(a, b, c, d, e, f, g, h, i, j, k, l);
 }
 template <typename T>
-auto UnpackStructImpl(const T& t, MakeIndexSequence<13>, char) {
+auto UnpackStructImpl(const T& t, std::make_index_sequence<13>, char) {
   const auto& [a, b, c, d, e, f, g, h, i, j, k, l, m] = t;
   return std::tie(a, b, c, d, e, f, g, h, i, j, k, l, m);
 }
 template <typename T>
-auto UnpackStructImpl(const T& t, MakeIndexSequence<14>, char) {
+auto UnpackStructImpl(const T& t, std::make_index_sequence<14>, char) {
   const auto& [a, b, c, d, e, f, g, h, i, j, k, l, m, n] = t;
   return std::tie(a, b, c, d, e, f, g, h, i, j, k, l, m, n);
 }
 template <typename T>
-auto UnpackStructImpl(const T& t, MakeIndexSequence<15>, char) {
+auto UnpackStructImpl(const T& t, std::make_index_sequence<15>, char) {
   const auto& [a, b, c, d, e, f, g, h, i, j, k, l, m, n, o] = t;
   return std::tie(a, b, c, d, e, f, g, h, i, j, k, l, m, n, o);
 }
 template <typename T>
-auto UnpackStructImpl(const T& t, MakeIndexSequence<16>, char) {
+auto UnpackStructImpl(const T& t, std::make_index_sequence<16>, char) {
   const auto& [a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p] = t;
   return std::tie(a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p);
 }
 template <typename T>
-auto UnpackStructImpl(const T& t, MakeIndexSequence<17>, char) {
+auto UnpackStructImpl(const T& t, std::make_index_sequence<17>, char) {
   const auto& [a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q] = t;
   return std::tie(a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q);
 }
 template <typename T>
-auto UnpackStructImpl(const T& t, MakeIndexSequence<18>, char) {
+auto UnpackStructImpl(const T& t, std::make_index_sequence<18>, char) {
   const auto& [a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r] = t;
   return std::tie(a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r);
 }
 template <typename T>
-auto UnpackStructImpl(const T& t, MakeIndexSequence<19>, char) {
+auto UnpackStructImpl(const T& t, std::make_index_sequence<19>, char) {
   const auto& [a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s] = t;
   return std::tie(a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s);
 }
@@ -3259,8 +3259,8 @@ auto UnpackStructImpl(const T& t, MakeIndexSequence<19>, char) {
 
 template <size_t I, typename T>
 auto UnpackStruct(const T& t)
-    -> decltype((UnpackStructImpl)(t, MakeIndexSequence<I>{}, 0)) {
-  return (UnpackStructImpl)(t, MakeIndexSequence<I>{}, 0);
+    -> decltype((UnpackStructImpl)(t, std::make_index_sequence<I>{}, 0)) {
+  return (UnpackStructImpl)(t, std::make_index_sequence<I>{}, 0);
 }
 
 // Helper function to do comma folding in C++11.
@@ -3273,7 +3273,7 @@ template <typename Struct, typename StructSize>
 class FieldsAreMatcherImpl;
 
 template <typename Struct, size_t... I>
-class FieldsAreMatcherImpl<Struct, IndexSequence<I...>>
+class FieldsAreMatcherImpl<Struct, std::index_sequence<I...>>
     : public MatcherInterface<Struct> {
   using UnpackedType =
       decltype(UnpackStruct<sizeof...(I)>(std::declval<const Struct&>()));
@@ -3355,8 +3355,8 @@ class FieldsAreMatcher {
   template <typename Struct>
   operator Matcher<Struct>() const {  // NOLINT
     return Matcher<Struct>(
-        new FieldsAreMatcherImpl<const Struct&, IndexSequenceFor<Inner...>>(
-            matchers_));
+        new FieldsAreMatcherImpl<const Struct&,
+                                 std::index_sequence_for<Inner...>>(matchers_));
   }
 
  private:
diff --git a/googlemock/include/gmock/internal/gmock-internal-utils.h b/googlemock/include/gmock/internal/gmock-internal-utils.h
index ead6d7c..b7685f5 100644
--- a/googlemock/include/gmock/internal/gmock-internal-utils.h
+++ b/googlemock/include/gmock/internal/gmock-internal-utils.h
@@ -44,6 +44,7 @@
 #include <ostream>  // NOLINT
 #include <string>
 #include <type_traits>
+#include <utility>
 #include <vector>
 
 #include "gmock/internal/gmock-port.h"
@@ -420,7 +421,7 @@ struct RemoveConstFromKey<std::pair<const K, V> > {
 GTEST_API_ void IllegalDoDefault(const char* file, int line);
 
 template <typename F, typename Tuple, size_t... Idx>
-auto ApplyImpl(F&& f, Tuple&& args, IndexSequence<Idx...>)
+auto ApplyImpl(F&& f, Tuple&& args, std::index_sequence<Idx...>)
     -> decltype(std::forward<F>(f)(
         std::get<Idx>(std::forward<Tuple>(args))...)) {
   return std::forward<F>(f)(std::get<Idx>(std::forward<Tuple>(args))...);
@@ -428,12 +429,13 @@ auto ApplyImpl(F&& f, Tuple&& args, IndexSequence<Idx...>)
 
 // Apply the function to a tuple of arguments.
 template <typename F, typename Tuple>
-auto Apply(F&& f, Tuple&& args) -> decltype(ApplyImpl(
-    std::forward<F>(f), std::forward<Tuple>(args),
-    MakeIndexSequence<std::tuple_size<
-        typename std::remove_reference<Tuple>::type>::value>())) {
+auto Apply(F&& f, Tuple&& args)
+    -> decltype(ApplyImpl(
+        std::forward<F>(f), std::forward<Tuple>(args),
+        std::make_index_sequence<std::tuple_size<
+            typename std::remove_reference<Tuple>::type>::value>())) {
   return ApplyImpl(std::forward<F>(f), std::forward<Tuple>(args),
-                   MakeIndexSequence<std::tuple_size<
+                   std::make_index_sequence<std::tuple_size<
                        typename std::remove_reference<Tuple>::type>::value>());
 }
 
diff --git a/googlemock/src/gmock-internal-utils.cc b/googlemock/src/gmock-internal-utils.cc
index 5c2ce0d..96c7e30 100644
--- a/googlemock/src/gmock-internal-utils.cc
+++ b/googlemock/src/gmock-internal-utils.cc
@@ -44,6 +44,7 @@
 #include <iostream>
 #include <ostream>  // NOLINT
 #include <string>
+#include <utility>
 #include <vector>
 
 #include "gmock/gmock.h"
@@ -211,14 +212,14 @@ constexpr char UnBase64Impl(char c, const char* const base64, char carry) {
 }
 
 template <size_t... I>
-constexpr std::array<char, 256> UnBase64Impl(IndexSequence<I...>,
+constexpr std::array<char, 256> UnBase64Impl(std::index_sequence<I...>,
                                              const char* const base64) {
   return {
       {UnBase64Impl(UndoWebSafeEncoding(static_cast<char>(I)), base64, 0)...}};
 }
 
 constexpr std::array<char, 256> UnBase64(const char* const base64) {
-  return UnBase64Impl(MakeIndexSequence<256>{}, base64);
+  return UnBase64Impl(std::make_index_sequence<256>{}, base64);
 }
 
 static constexpr char kBase64[] =
diff --git a/googletest/include/gtest/internal/gtest-internal.h b/googletest/include/gtest/internal/gtest-internal.h
index 4661248..cffb8e1 100644
--- a/googletest/include/gtest/internal/gtest-internal.h
+++ b/googletest/include/gtest/internal/gtest-internal.h
@@ -1137,40 +1137,6 @@ class NativeArray {
   void (NativeArray::*clone_)(const Element*, size_t);
 };
 
-// Backport of std::index_sequence.
-template <size_t... Is>
-struct IndexSequence {
-  using type = IndexSequence;
-};
-
-// Double the IndexSequence, and one if plus_one is true.
-template <bool plus_one, typename T, size_t sizeofT>
-struct DoubleSequence;
-template <size_t... I, size_t sizeofT>
-struct DoubleSequence<true, IndexSequence<I...>, sizeofT> {
-  using type = IndexSequence<I..., (sizeofT + I)..., 2 * sizeofT>;
-};
-template <size_t... I, size_t sizeofT>
-struct DoubleSequence<false, IndexSequence<I...>, sizeofT> {
-  using type = IndexSequence<I..., (sizeofT + I)...>;
-};
-
-// Backport of std::make_index_sequence.
-// It uses O(ln(N)) instantiation depth.
-template <size_t N>
-struct MakeIndexSequenceImpl
-    : DoubleSequence<N % 2 == 1, typename MakeIndexSequenceImpl<N / 2>::type,
-                     N / 2>::type {};
-
-template <>
-struct MakeIndexSequenceImpl<0> : IndexSequence<> {};
-
-template <size_t N>
-using MakeIndexSequence = typename MakeIndexSequenceImpl<N>::type;
-
-template <typename... T>
-using IndexSequenceFor = typename MakeIndexSequence<sizeof...(T)>::type;
-
 template <size_t>
 struct Ignore {
   Ignore(...);  // NOLINT
@@ -1179,7 +1145,7 @@ struct Ignore {
 template <typename>
 struct ElemFromListImpl;
 template <size_t... I>
-struct ElemFromListImpl<IndexSequence<I...>> {
+struct ElemFromListImpl<std::index_sequence<I...>> {
   // We make Ignore a template to solve a problem with MSVC.
   // A non-template Ignore would work fine with `decltype(Ignore(I))...`, but
   // MSVC doesn't understand how to deal with that pack expansion.
@@ -1190,9 +1156,8 @@ struct ElemFromListImpl<IndexSequence<I...>> {
 
 template <size_t N, typename... T>
 struct ElemFromList {
-  using type =
-      decltype(ElemFromListImpl<typename MakeIndexSequence<N>::type>::Apply(
-          static_cast<T (*)()>(nullptr)...));
+  using type = decltype(ElemFromListImpl<std::make_index_sequence<N>>::Apply(
+      static_cast<T (*)()>(nullptr)...));
 };
 
 struct FlatTupleConstructTag {};
@@ -1217,9 +1182,9 @@ template <typename Derived, typename Idx>
 struct FlatTupleBase;
 
 template <size_t... Idx, typename... T>
-struct FlatTupleBase<FlatTuple<T...>, IndexSequence<Idx...>>
+struct FlatTupleBase<FlatTuple<T...>, std::index_sequence<Idx...>>
     : FlatTupleElemBase<FlatTuple<T...>, Idx>... {
-  using Indices = IndexSequence<Idx...>;
+  using Indices = std::index_sequence<Idx...>;
   FlatTupleBase() = default;
   template <typename... Args>
   explicit FlatTupleBase(FlatTupleConstructTag, Args&&... args)
@@ -1254,14 +1219,15 @@ struct FlatTupleBase<FlatTuple<T...>, IndexSequence<Idx...>>
 // implementations.
 // FlatTuple and ElemFromList are not recursive and have a fixed depth
 // regardless of T...
-// MakeIndexSequence, on the other hand, it is recursive but with an
+// std::make_index_sequence, on the other hand, it is recursive but with an
 // instantiation depth of O(ln(N)).
 template <typename... T>
 class FlatTuple
     : private FlatTupleBase<FlatTuple<T...>,
-                            typename MakeIndexSequence<sizeof...(T)>::type> {
-  using Indices = typename FlatTupleBase<
-      FlatTuple<T...>, typename MakeIndexSequence<sizeof...(T)>::type>::Indices;
+                            std::make_index_sequence<sizeof...(T)>> {
+  using Indices =
+      typename FlatTupleBase<FlatTuple<T...>,
+                             std::make_index_sequence<sizeof...(T)>>::Indices;
 
  public:
   FlatTuple() = default;
diff --git a/googletest/include/gtest/internal/gtest-param-util.h b/googletest/include/gtest/internal/gtest-param-util.h
index 1fc500f..cc7ea53 100644
--- a/googletest/include/gtest/internal/gtest-param-util.h
+++ b/googletest/include/gtest/internal/gtest-param-util.h
@@ -807,12 +807,12 @@ class ValueArray {
 
   template <typename T>
   operator ParamGenerator<T>() const {  // NOLINT
-    return ValuesIn(MakeVector<T>(MakeIndexSequence<sizeof...(Ts)>()));
+    return ValuesIn(MakeVector<T>(std::make_index_sequence<sizeof...(Ts)>()));
   }
 
  private:
   template <typename T, size_t... I>
-  std::vector<T> MakeVector(IndexSequence<I...>) const {
+  std::vector<T> MakeVector(std::index_sequence<I...>) const {
     return std::vector<T>{static_cast<T>(v_.template Get<I>())...};
   }
 
@@ -842,7 +842,7 @@ class CartesianProductGenerator
   template <class I>
   class IteratorImpl;
   template <size_t... I>
-  class IteratorImpl<IndexSequence<I...>>
+  class IteratorImpl<std::index_sequence<I...>>
       : public ParamIteratorInterface<ParamType> {
    public:
     IteratorImpl(const ParamGeneratorInterface<ParamType>* base,
@@ -933,7 +933,7 @@ class CartesianProductGenerator
     std::shared_ptr<ParamType> current_value_;
   };
 
-  using Iterator = IteratorImpl<typename MakeIndexSequence<sizeof...(T)>::type>;
+  using Iterator = IteratorImpl<std::make_index_sequence<sizeof...(T)>>;
 
   std::tuple<ParamGenerator<T>...> generators_;
 };
diff --git a/googletest/test/gtest_unittest.cc b/googletest/test/gtest_unittest.cc
index 5d7cfb0..edbe2ea 100644
--- a/googletest/test/gtest_unittest.cc
+++ b/googletest/test/gtest_unittest.cc
@@ -7482,22 +7482,6 @@ TEST(NativeArrayTest, WorksForTwoDimensionalArray) {
   EXPECT_EQ(a, na.begin());
 }
 
-// IndexSequence
-TEST(IndexSequence, MakeIndexSequence) {
-  using testing::internal::IndexSequence;
-  using testing::internal::MakeIndexSequence;
-  EXPECT_TRUE(
-      (std::is_same<IndexSequence<>, MakeIndexSequence<0>::type>::value));
-  EXPECT_TRUE(
-      (std::is_same<IndexSequence<0>, MakeIndexSequence<1>::type>::value));
-  EXPECT_TRUE(
-      (std::is_same<IndexSequence<0, 1>, MakeIndexSequence<2>::type>::value));
-  EXPECT_TRUE((
-      std::is_same<IndexSequence<0, 1, 2>, MakeIndexSequence<3>::type>::value));
-  EXPECT_TRUE(
-      (std::is_base_of<IndexSequence<0, 1, 2>, MakeIndexSequence<3>>::value));
-}
-
 // ElemFromList
 TEST(ElemFromList, Basic) {
   using testing::internal::ElemFromList;