[libcxx-commits] [libcxx] [libc++] Include range access headers in `<optional>` only since C++26 (PR #214688)

[A. Jiang via libcxx-commits]

https://github.com/frederick-vs-ja updated https://github.com/llvm/llvm-project/pull/214688

>From f5620f924c700a14574af1394496033484853f3c Mon Sep 17 00:00:00 2001
From: "A. Jiang" <de34 at live.cn>
Date: Fri, 7 Aug 2026 17:59:43 +0800
Subject: [PATCH 1/2] [libc++] Include range access headers in `<optional>`
 only since C++26

Inclusions of internal range access headers address LWG4131 which
patches P3168R2 "Give `std::optional` Range Support". As P3168R2 is
certainly a new feature in C++26, these includes are unnecessary in old
modes.

It was reported that these increase the size of `<optional>` by ~8%, so
probably it is better to avoid such overhead in old modes.
---
 libcxx/include/optional | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/libcxx/include/optional b/libcxx/include/optional
index bb12247b69083..0d0409ee8e2b3 100644
--- a/libcxx/include/optional
+++ b/libcxx/include/optional
@@ -275,12 +275,14 @@ namespace std {
 // [optional.syn]
 #  include <compare>
 
+#  if _LIBCPP_STD_VER >= 26
 // [iterator.range]
-#  include <__iterator/access.h>
-#  include <__iterator/data.h>
-#  include <__iterator/empty.h>
-#  include <__iterator/reverse_access.h>
-#  include <__iterator/size.h>
+#    include <__iterator/access.h>
+#    include <__iterator/data.h>
+#    include <__iterator/empty.h>
+#    include <__iterator/reverse_access.h>
+#    include <__iterator/size.h>
+#  endif // _LIBCPP_STD_VER >= 26
 
 #  if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #    pragma GCC system_header

>From 54a902a9353a47d5e35124bdd9b16dc3f3e1732e Mon Sep 17 00:00:00 2001
From: "A. Jiang" <de34 at live.cn>
Date: Fri, 7 Aug 2026 18:55:11 +0800
Subject: [PATCH 2/2] Quick fix for `mandatory_inclusions.gen.py`

---
 .../iterators/iterator.range/mandatory_inclusions.gen.py  | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/libcxx/test/std/iterators/iterator.range/mandatory_inclusions.gen.py b/libcxx/test/std/iterators/iterator.range/mandatory_inclusions.gen.py
index 5d960b3bfb851..e14f8f6676800 100644
--- a/libcxx/test/std/iterators/iterator.range/mandatory_inclusions.gen.py
+++ b/libcxx/test/std/iterators/iterator.range/mandatory_inclusions.gen.py
@@ -51,6 +51,12 @@
     )
 )
 
+def get_standard_mode_threshold(header):
+    if header == "optional":
+        return "26" # `optional` is a range only since C++26 via P3168R2.
+    else:
+        return "0" # Other related components are ranges at first.
+
 for header in headers:
     print(
         f"""\
@@ -81,6 +87,7 @@
 }};
 
 int main(int, char**)  {{
+#if TEST_STD_VER >= {get_standard_mode_threshold(header)}
   {{
     Container c;
     const auto& cc = c;
@@ -174,6 +181,7 @@
     assert(std::ssize(cil) == 3);
 #endif
   }}
+#endif
 
   return 0;
 }}