[gcc r12-10221] libstdc++: Add missing std::tuple constructor [PR114147]

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

https://gcc.gnu.org/g:fbdeeb1604d52a8ece8631f70ecd64d925d31741

commit r12-10221-gfbdeeb1604d52a8ece8631f70ecd64d925d31741
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Mar 1 11:16:58 2024 +0000

    libstdc++: Add missing std::tuple constructor [PR114147]
    
    I caused a regression with commit r10-908 by adding a constraint to the
    non-explicit allocator-extended default constructor, but seemingly
    forgot to add an explicit overload with the corresponding constraint.
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/114147
            * include/std/tuple (tuple::tuple(allocator_arg_t, const Alloc&)):
            Add missing overload of allocator-extended default constructor.
            (tuple<T1,T2>::tuple(allocator_arg_t, const Alloc&)): Likewise.
            * testsuite/20_util/tuple/cons/114147.cc: New test.
    
    (cherry picked from commit 0a545ac7000501844670add0b3560ebdbcb123c6)

Diff:
---
 libstdc++-v3/include/std/tuple                      | 14 ++++++++++++++
 libstdc++-v3/testsuite/20_util/tuple/cons/114147.cc | 15 +++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/libstdc++-v3/include/std/tuple b/libstdc++-v3/include/std/tuple
index 6d0060a191c..04b77113a84 100644
--- a/libstdc++-v3/include/std/tuple
+++ b/libstdc++-v3/include/std/tuple
@@ -801,6 +801,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	tuple(allocator_arg_t __tag, const _Alloc& __a)
 	: _Inherited(__tag, __a) { }
 
+      template<typename _Alloc,
+	       _ExplicitDefaultCtor<is_object<_Alloc>::value> = false>
+	_GLIBCXX20_CONSTEXPR
+	explicit
+	tuple(allocator_arg_t __tag, const _Alloc& __a)
+	: _Inherited(__tag, __a) { }
+
       template<typename _Alloc, bool _NotEmpty = (sizeof...(_Elements) >= 1),
 	       _ImplicitCtor<_NotEmpty, const _Elements&...> = true>
 	_GLIBCXX20_CONSTEXPR
@@ -1155,6 +1162,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	tuple(allocator_arg_t __tag, const _Alloc& __a)
 	: _Inherited(__tag, __a) { }
 
+      template<typename _Alloc,
+	       _ExplicitDefaultCtor<is_object<_Alloc>::value, _T1, _T2> = false>
+	_GLIBCXX20_CONSTEXPR
+	explicit
+	tuple(allocator_arg_t __tag, const _Alloc& __a)
+	: _Inherited(__tag, __a) { }
+
       template<typename _Alloc, bool _Dummy = true,
 	       _ImplicitCtor<_Dummy, const _T1&, const _T2&> = true>
 	_GLIBCXX20_CONSTEXPR
diff --git a/libstdc++-v3/testsuite/20_util/tuple/cons/114147.cc b/libstdc++-v3/testsuite/20_util/tuple/cons/114147.cc
new file mode 100644
index 00000000000..916e7204964
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/tuple/cons/114147.cc
@@ -0,0 +1,15 @@
+// { dg-do compile { target c++11 } }
+
+// PR libstdc++/114147
+// tuple allocator-extended ctor requires non-explicit default ctor
+
+#include <tuple>
+#include <memory>
+
+struct X { explicit X(); };
+
+std::allocator<int> a;
+std::tuple<X> t0(std::allocator_arg, a);
+std::tuple<int, X> t1(std::allocator_arg, a);
+std::tuple<X, int> t2(std::allocator_arg, a);
+std::tuple<int, X, int> t3(std::allocator_arg, a);