[gcc r11-11021] libstdc++: Prevent unwanted ADL in std::to_array [PR111512]

[Jonathan Wakely <redi@gcc.gnu.org>]

https://gcc.gnu.org/g:97a33ab114187e7c6cd6c6c0f06cd8225e8aeef5

commit r11-11021-g97a33ab114187e7c6cd6c6c0f06cd8225e8aeef5
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Sep 21 09:14:57 2023 +0100

    libstdc++: Prevent unwanted ADL in std::to_array [PR111512]
    
    Qualify the calls to the __to_array helper to prevent ADL, so we don't
    try to complete associated classes.
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/111511
            PR c++/111512
            * include/std/array (to_array): Qualify calls to __to_array.
            * testsuite/23_containers/array/creation/111512.cc: New test.
    
    (cherry picked from commit 77cf3773021b0a20d89623e09d620747a05588ec)

Diff:
---
 libstdc++-v3/include/std/array                     |  4 ++--
 .../23_containers/array/creation/111512.cc         | 25 ++++++++++++++++++++++
 2 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/include/std/array b/libstdc++-v3/include/std/array
index 0c6f33e3276..95c9b688cdc 100644
--- a/libstdc++-v3/include/std/array
+++ b/libstdc++-v3/include/std/array
@@ -409,7 +409,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       static_assert(!is_array_v<_Tp>);
       static_assert(is_constructible_v<_Tp, _Tp&>);
       if constexpr (is_constructible_v<_Tp, _Tp&>)
-	return __to_array(__a, make_index_sequence<_Nm>{});
+	return std::__to_array(__a, make_index_sequence<_Nm>{});
       __builtin_unreachable(); // FIXME: see PR c++/91388
     }
 
@@ -421,7 +421,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       static_assert(!is_array_v<_Tp>);
       static_assert(is_move_constructible_v<_Tp>);
       if constexpr (is_move_constructible_v<_Tp>)
-	return __to_array<1>(__a, make_index_sequence<_Nm>{});
+	return std::__to_array<1>(__a, make_index_sequence<_Nm>{});
       __builtin_unreachable(); // FIXME: see PR c++/91388
     }
 #endif // C++20
diff --git a/libstdc++-v3/testsuite/23_containers/array/creation/111512.cc b/libstdc++-v3/testsuite/23_containers/array/creation/111512.cc
new file mode 100644
index 00000000000..f510480ae4b
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/array/creation/111512.cc
@@ -0,0 +1,25 @@
+// { dg-options "-std=gnu++20" }
+// { dg-do compile { target c++20 } }
+
+// Bug libstdc++/111511 - Incorrect ADL in std::to_array in GCC 11/12/13
+// Bug c++/111512 - GCC's __builtin_memcpy can trigger ADL
+
+#include <array>
+#include <utility>
+
+struct incomplete;
+
+template<class T>
+struct holder {
+    T t; // { dg-bogus "'holder<T>::t' has incomplete type" }
+};
+
+// A complete type that cannot be used as an associated type for ADL.
+using adl_bomb = holder<incomplete>*;
+
+int main()
+{
+    adl_bomb a[1]{};
+    (void) std::to_array(a);
+    (void) std::to_array(std::move(a));
+}