From 1fa5dd8f9862c3314b4499c944906424d7a5a8e7 Mon Sep 17 00:00:00 2001
From: =?utf8?q?Tomasz=20Kami=C5=84ski?= <tkaminsk@redhat.com>
Date: Thu, 6 Nov 2025 16:02:42 +0100
Subject: [PATCH] libstdc++: Add ranges::borrowed_range specialization for
 optional<T&> [PR122425]
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	PR libstdc++/122425

libstdc++-v3/ChangeLog:

	* include/std/optional
	(ranges::enable_borrowed_range<optional<_Tp&>>): Define.
	* testsuite/20_util/optional/range.cc: Update tests.

Reviewed-by: Jonathan Wakely <jwakely@redhat.com>
Signed-off-by: Tomasz Kamiński <tkaminsk@redhat.com>
---
 libstdc++-v3/include/std/optional                | 6 ++++++
 libstdc++-v3/testsuite/20_util/optional/range.cc | 6 +++++-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/std/optional b/libstdc++-v3/include/std/optional
index d191e51ed79..75a9531ccd5 100644
--- a/libstdc++-v3/include/std/optional
+++ b/libstdc++-v3/include/std/optional
@@ -2182,6 +2182,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     inline constexpr bool
       ranges::enable_view<optional<_Tp>> = true;
 
+#if __cpp_lib_optional >= 202506L // C++26
+  template<typename _Tp>
+    constexpr bool
+    ranges::enable_borrowed_range<optional<_Tp&>> = true;
+#endif
+ 
   template<typename _Tp>
     inline constexpr range_format
       format_kind<optional<_Tp>> = range_format::disabled;
diff --git a/libstdc++-v3/testsuite/20_util/optional/range.cc b/libstdc++-v3/testsuite/20_util/optional/range.cc
index 1cb3eb6ceff..981969cb614 100644
--- a/libstdc++-v3/testsuite/20_util/optional/range.cc
+++ b/libstdc++-v3/testsuite/20_util/optional/range.cc
@@ -19,12 +19,16 @@ test_range_concepts()
   static_assert(std::ranges::contiguous_range<O>);
   static_assert(std::ranges::sized_range<O>);
   static_assert(std::ranges::common_range<O>);
-  static_assert(!std::ranges::borrowed_range<O>);
+
+  // an optional<T&> is borrowed range
+  constexpr bool is_ref_opt = std::is_reference_v<T>;
+  static_assert(std::ranges::borrowed_range<O> == is_ref_opt);
 
   // an optional<const T> is not assignable, and therefore does not satisfy ranges::view
   constexpr bool is_const_opt = std::is_const_v<T>;
   static_assert(std::ranges::view<O> == !is_const_opt);
   static_assert(std::ranges::viewable_range<O> == !is_const_opt);
+
 }
 
 template<typename O>
-- 
2.47.3