[libcxx-commits] [libcxx] [libc++] Remove <array> include from <span> (PR #83742)

[Nikolas Klauser via libcxx-commits]

https://github.com/philnik777 created https://github.com/llvm/llvm-project/pull/83742

This reduces the include time of `<span>` from 122ms to 78ms.


>From f06058abe90aafb73b1e671b2d2da01801797fa2 Mon Sep 17 00:00:00 2001
From: Nikolas Klauser <nikolasklauser at berlin.de>
Date: Mon, 30 Oct 2023 16:57:51 +0100
Subject: [PATCH] [libc++] Remove <array> include from <span>

---
 libcxx/include/__fwd/array.h                     |  6 ++++++
 libcxx/include/span                              | 14 ++++++--------
 libcxx/test/libcxx/transitive_includes/cxx26.csv |  1 -
 3 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/libcxx/include/__fwd/array.h b/libcxx/include/__fwd/array.h
index ff3a3eeeefc71f..a2cb2efa6e4870 100644
--- a/libcxx/include/__fwd/array.h
+++ b/libcxx/include/__fwd/array.h
@@ -35,6 +35,12 @@ template <size_t _Ip, class _Tp, size_t _Size>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 const _Tp&& get(const array<_Tp, _Size>&&) _NOEXCEPT;
 #endif
 
+template <class>
+struct __is_std_array : false_type {};
+
+template <class _Tp, size_t _Size>
+struct __is_std_array<array<_Tp, _Size>> : true_type {};
+
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___FWD_ARRAY_H
diff --git a/libcxx/include/span b/libcxx/include/span
index 9efaac517fc8f6..77d2de14159dd0 100644
--- a/libcxx/include/span
+++ b/libcxx/include/span
@@ -130,10 +130,12 @@ template<class R>
 
 #include <__assert>
 #include <__config>
+#include <__fwd/array.h>
 #include <__fwd/span.h>
 #include <__iterator/bounded_iter.h>
 #include <__iterator/concepts.h>
 #include <__iterator/iterator_traits.h>
+#include <__iterator/reverse_iterator.h>
 #include <__iterator/wrap_iter.h>
 #include <__memory/pointer_traits.h>
 #include <__ranges/concepts.h>
@@ -141,13 +143,14 @@ template<class R>
 #include <__ranges/enable_borrowed_range.h>
 #include <__ranges/enable_view.h>
 #include <__ranges/size.h>
+#include <__type_traits/is_const.h>
 #include <__type_traits/is_convertible.h>
+#include <__type_traits/remove_cv.h>
 #include <__type_traits/remove_cvref.h>
 #include <__type_traits/remove_reference.h>
 #include <__type_traits/type_identity.h>
 #include <__utility/forward.h>
-#include <array>   // for array
-#include <cstddef> // for byte
+#include <cstddef>      // for byte
 #include <stdexcept>
 #include <version>
 
@@ -171,12 +174,6 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 
 #if _LIBCPP_STD_VER >= 20
 
-template <class _Tp>
-struct __is_std_array : false_type {};
-
-template <class _Tp, size_t _Sz>
-struct __is_std_array<array<_Tp, _Sz>> : true_type {};
-
 template <class _Tp>
 struct __is_std_span : false_type {};
 
@@ -588,6 +585,7 @@ _LIBCPP_END_NAMESPACE_STD
 _LIBCPP_POP_MACROS
 
 #if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 20
+#  include <array>
 #  include <concepts>
 #  include <functional>
 #  include <iterator>
diff --git a/libcxx/test/libcxx/transitive_includes/cxx26.csv b/libcxx/test/libcxx/transitive_includes/cxx26.csv
index 49b3ac265487d7..3896b826803c0a 100644
--- a/libcxx/test/libcxx/transitive_includes/cxx26.csv
+++ b/libcxx/test/libcxx/transitive_includes/cxx26.csv
@@ -510,7 +510,6 @@ shared_mutex string
 shared_mutex version
 source_location cstdint
 source_location version
-span array
 span cstddef
 span initializer_list
 span limits