[gcc r14-8307] libstdc++: suppress -Wdangling-reference with operator| [PR111410]

[gcc r14-8307] libstdc++: suppress -Wdangling-reference with operator| [PR111410]

[Marek Polacek]

https://gcc.gnu.org/g:7db802d972e622242d015ecd5a8cecf63e69a45a

commit r14-8307-g7db802d972e622242d015ecd5a8cecf63e69a45a
Author: Marek Polacek <polacek@redhat.com>
Date:   Fri Jan 19 15:27:51 2024 -0500

    libstdc++: suppress -Wdangling-reference with operator| [PR111410]
    
    It seems to me that we should exclude std::ranges::views::__adaptor::operator|
    from the -Wdangling-reference warning.  It's commonly used when handling
    ranges.
    
            PR c++/111410
    
    libstdc++-v3/ChangeLog:
    
            * include/std/ranges: Add #pragma to disable -Wdangling-reference with
            std::ranges::views::__adaptor::operator|.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/warn/Wdangling-reference17.C: New test.

Diff:
---
 gcc/testsuite/g++.dg/warn/Wdangling-reference17.C | 15 +++++++++++++++
 libstdc++-v3/include/std/ranges                   |  3 +++
 2 files changed, 18 insertions(+)

diff --git a/gcc/testsuite/g++.dg/warn/Wdangling-reference17.C b/gcc/testsuite/g++.dg/warn/Wdangling-reference17.C
new file mode 100644
index 00000000000..223698422c2
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wdangling-reference17.C
@@ -0,0 +1,15 @@
+// PR c++/111410
+// { dg-do compile { target c++20 } }
+// { dg-options "-Wdangling-reference" }
+
+#include <vector>
+#include <ranges>
+
+int main()
+{
+  std::vector v{1, 2, 3, 4, 5};
+  for (auto i : std::span{v} | std::views::take(1))
+    {
+      (void) i;
+    }
+}
diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 7ef835f486a..f2413badd9c 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -942,6 +942,8 @@ namespace views::__adaptor
     concept __is_range_adaptor_closure
       = requires (_Tp __t) { __adaptor::__is_range_adaptor_closure_fn(__t, __t); };
 
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wdangling-reference"
   // range | adaptor is equivalent to adaptor(range).
   template<typename _Self, typename _Range>
     requires __is_range_adaptor_closure<_Self>
@@ -961,6 +963,7 @@ namespace views::__adaptor
       return _Pipe<decay_t<_Lhs>, decay_t<_Rhs>>{std::forward<_Lhs>(__lhs),
 						 std::forward<_Rhs>(__rhs)};
     }
+#pragma GCC diagnostic pop
 
   // The base class of every range adaptor non-closure.
   //