[libc++] Remove pair dependency (#85621)

This moves the definition of a `pair` constructor for `<tuple>` to
`<__utility/pair.h>` and uses the forward declaration of `pair` in
`<tuple>` instead of including the definition.

libcxx/include/__ranges/zip_view.h

@@ -36,6 +36,7 @@
 #include <__utility/forward.h>
 #include <__utility/integer_sequence.h>
 #include <__utility/move.h>
+#include <__utility/pair.h>
 #include <tuple>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)

libcxx/include/__utility/pair.h

@@ -431,7 +431,9 @@ private:
        tuple<_Args1...>& __first_args,
        tuple<_Args2...>& __second_args,
        __tuple_indices<_I1...>,
-       __tuple_indices<_I2...>);
+       __tuple_indices<_I2...>)
+      : first(std::forward<_Args1>(std::get<_I1>(__first_args))...),
+        second(std::forward<_Args2>(std::get<_I2>(__second_args))...) {}
 #endif
 };
 

libcxx/include/module.modulemap

@@ -1738,7 +1738,10 @@ module std_private_ranges_transform_view             [system] {
 }
 module std_private_ranges_view_interface             [system] { header "__ranges/view_interface.h" }
 module std_private_ranges_views                      [system] { header "__ranges/views.h" }
-module std_private_ranges_zip_view                   [system] { header "__ranges/zip_view.h" }
+module std_private_ranges_zip_view                   [system] {
+  header "__ranges/zip_view.h"
+  export std_private_utility_pair
+}
 
 module std_private_span_span_fwd [system] { header "__fwd/span.h" }
 

libcxx/include/tuple

@@ -210,6 +210,7 @@ template <class... Types>
 #include <__config>
 #include <__functional/invoke.h>
 #include <__fwd/array.h>
+#include <__fwd/pair.h>
 #include <__fwd/tuple.h>
 #include <__memory/allocator_arg_t.h>
 #include <__memory/uses_allocator.h>
@@ -250,7 +251,6 @@ template <class... Types>
 #include <__utility/forward.h>
 #include <__utility/integer_sequence.h>
 #include <__utility/move.h>
-#include <__utility/pair.h>
 #include <__utility/piecewise_construct.h>
 #include <__utility/swap.h>
 #include <cstddef>
@@ -1348,17 +1348,6 @@ tuple_cat(_Tuple0&& __t0, _Tuples&&... __tpls) {
 template <class... _Tp, class _Alloc>
 struct _LIBCPP_TEMPLATE_VIS uses_allocator<tuple<_Tp...>, _Alloc> : true_type {};
 
-template <class _T1, class _T2>
-template <class... _Args1, class... _Args2, size_t... _I1, size_t... _I2>
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_T1, _T2>::pair(
-    piecewise_construct_t,
-    tuple<_Args1...>& __first_args,
-    tuple<_Args2...>& __second_args,
-    __tuple_indices<_I1...>,
-    __tuple_indices<_I2...>)
-    : first(std::forward<_Args1>(std::get<_I1>(__first_args))...),
-      second(std::forward<_Args2>(std::get<_I2>(__second_args))...) {}
-
 #  if _LIBCPP_STD_VER >= 17
 #    define _LIBCPP_NOEXCEPT_RETURN(...)                                                                               \
       noexcept(noexcept(__VA_ARGS__)) { return __VA_ARGS__; }

libcxx/test/std/ranges/range.adaptors/range.zip/borrowing.compile.pass.cpp

@@ -13,7 +13,6 @@
 //      (enable_borrowed_range<Views> && ...);
 
 #include <ranges>
-#include <tuple>
 
 struct Borrowed : std::ranges::view_base {
   int* begin() const;

libcxx/test/std/ranges/range.utility/range.subrange/operator.pair_like.pass.cpp

@@ -17,6 +17,7 @@
 #include <cassert>
 #include <concepts>
 #include <ranges>
+#include <utility>
 
 #include "test_macros.h"
 

libcxx/test/std/utilities/tuple/tuple.tuple/tuple.helper/tuple_size_incomplete.pass.cpp

@@ -16,9 +16,10 @@
 
 // UNSUPPORTED: c++03
 
-#include <tuple>
 #include <array>
+#include <tuple>
 #include <type_traits>
+#include <utility>
 
 #include "test_macros.h"
 

libcxx/test/std/utilities/tuple/tuple.tuple/tuple.helper/tuple_size_structured_bindings.pass.cpp

@@ -16,10 +16,10 @@
 
 // UNSUPPORTED: c++03, c++11, c++14
 
-#include <tuple>
 #include <array>
-#include <type_traits>
 #include <cassert>
+#include <tuple>
+#include <utility>
 
 #include "test_macros.h"
 

libcxx/test/std/utilities/tuple/tuple.tuple/tuple.helper/tuple_size_value_sfinae.pass.cpp

@@ -17,7 +17,7 @@
 // UNSUPPORTED: c++03
 
 #include <tuple>
-#include <type_traits>
+#include <utility>
 
 #include "test_macros.h"