From 987e70f4290451abd98eda8b82e97b4ad25ee3c2 Mon Sep 17 00:00:00 2001
From: Jonathan Wakely <[email protected]>
Date: Sun, 7 Jul 2024 12:22:42 +0100
Subject: [PATCH] libstdc++: Fix _Atomic(T) macro in <stdatomic.h> [PR115807]

The definition of the _Atomic(T) macro needs to refer to ::std::atomic,
not some other std::atomic relative to the current namespace.

libstdc++-v3/ChangeLog:

	PR libstdc++/115807
	* include/c_compatibility/stdatomic.h (_Atomic): Ensure it
	refers to std::atomic in the global namespace.
	* testsuite/29_atomics/headers/stdatomic.h/115807.cc: New test.

(cherry picked from commit 40d234dd6439e8c8cfbf3f375a61906aed35c80d)
---
 libstdc++-v3/include/c_compatibility/stdatomic.h   |  2 +-
 .../29_atomics/headers/stdatomic.h/115807.cc       | 14 ++++++++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)
 create mode 100644 libstdc++-v3/testsuite/29_atomics/headers/stdatomic.h/115807.cc

diff --git a/libstdc++-v3/include/c_compatibility/stdatomic.h b/libstdc++-v3/include/c_compatibility/stdatomic.h
index b565a1c1ab187..2bb23decf8d1e 100644
--- a/libstdc++-v3/include/c_compatibility/stdatomic.h
+++ b/libstdc++-v3/include/c_compatibility/stdatomic.h
@@ -34,7 +34,7 @@
 
 #define __cpp_lib_stdatomic_h 202011L
 
-#define _Atomic(_Tp) std::atomic<_Tp>
+#define _Atomic(_Tp) ::std::atomic<_Tp>
 
 using std::memory_order;
 using std::memory_order_relaxed;
diff --git a/libstdc++-v3/testsuite/29_atomics/headers/stdatomic.h/115807.cc b/libstdc++-v3/testsuite/29_atomics/headers/stdatomic.h/115807.cc
new file mode 100644
index 0000000000000..14f320fe83575
--- /dev/null
+++ b/libstdc++-v3/testsuite/29_atomics/headers/stdatomic.h/115807.cc
@@ -0,0 +1,14 @@
+// { dg-do compile { target c++23 } }
+#include <stdatomic.h>
+namespace other {
+  namespace std {
+    int atomic = 0;
+  }
+  _Atomic(long) a{};
+}
+
+#include <type_traits>
+
+namespace non::std {
+  static_assert( ::std::is_same_v<_Atomic(int), ::std::atomic<int>> );
+}