[PATCH] PR libstdc++/90700 Fix constructor constraint for std::tuple

[Jonathan Wakely]

        * include/std/tuple
        (tuple(allocator_arg_t, const A&, const tuple<UTypes...>&)): Fix
        value category of template argument to _TC::_NonNestedTuple.
        * testsuite/20_util/tuple/cons/90700.cc: New test.

This fixes the bug on gcc-9-branch, I plan to fix it differently on
trunk. Tested x86_64-lixnu, committed to gcc-9-branch.



commit 8d30f3df2677e249b50070312ca2b41a927ed10a
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Mon Jun 3 15:38:00 2019 +0100

    PR libstdc++/90700 Fix constructor constraint for std::tuple
    
            * include/std/tuple
            (tuple(allocator_arg_t, const A&, const tuple<UTypes...>&)): Fix
            value category of template argument to _TC::_NonNestedTuple.
            * testsuite/20_util/tuple/cons/90700.cc: New test.

diff --git a/libstdc++-v3/include/std/tuple b/libstdc++-v3/include/std/tuple
index bc0b1add764..f942109ed01 100644
--- a/libstdc++-v3/include/std/tuple
+++ b/libstdc++-v3/include/std/tuple
@@ -758,7 +758,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
                   && _TMCT<_UElements...>::template
                     _ImplicitlyConvertibleTuple<_UElements...>()
                   && _TNTC<_Dummy>::template
-                    _NonNestedTuple<tuple<_UElements...>&&>(),
+                    _NonNestedTuple<const tuple<_UElements...>&>(),
         bool>::type=true>
        tuple(allocator_arg_t __tag, const _Alloc& __a,
              const tuple<_UElements...>& __in)
@@ -773,7 +773,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
                   && !_TMCT<_UElements...>::template
                     _ImplicitlyConvertibleTuple<_UElements...>()
                   && _TNTC<_Dummy>::template
-                    _NonNestedTuple<tuple<_UElements...>&&>(),
+                    _NonNestedTuple<const tuple<_UElements...>&>(),
         bool>::type=false>
        explicit tuple(allocator_arg_t __tag, const _Alloc& __a,
              const tuple<_UElements...>& __in)
diff --git a/libstdc++-v3/testsuite/20_util/tuple/cons/90700.cc 
b/libstdc++-v3/testsuite/20_util/tuple/cons/90700.cc
new file mode 100644
index 00000000000..08e7787bf4f
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/tuple/cons/90700.cc
@@ -0,0 +1,66 @@
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-do compile { target c++11 } }
+
+#include <tuple>
+#include <memory>
+
+struct X { };
+
+struct Y
+{
+  Y(const std::tuple<X>&) = delete;
+  Y(std::tuple<X>&&) { throw 1; }
+  Y(const X&) { }
+};
+
+struct Z
+{
+  Z(X&&) { }
+  Z(const std::tuple<X>&) { throw 1; }
+  Z(std::tuple<X>&&) = delete;
+};
+
+void
+test01()
+{
+  // PR libstdc++/90700 wrong constraints on constructor
+  const std::allocator<int> a;
+  const std::tuple<X> x;
+
+  static_assert(!std::is_convertible<const std::tuple<X>&, Y>::value, "");
+  static_assert(!std::is_constructible<Y, const std::tuple<X>&>::value, "");
+  static_assert(!std::is_same<Y, X>::value, "");
+  // should use tuple<Y>::tuple<X>(allocator_arg_t, const A&, const tuple<X>&)
+  // and construct Y from X:
+  std::tuple<Y> y(std::allocator_arg, a, x);
+}
+
+void
+test02()
+{
+  const std::allocator<int> a;
+  std::tuple<X> x;
+
+  static_assert(!std::is_convertible<std::tuple<X>, Z>::value, "");
+  static_assert(!std::is_constructible<Z, std::tuple<X>>::value, "");
+  static_assert(!std::is_same<Z, X>::value, "");
+  // should use tuple<Z>::tuple<X>(allocator_arg_t, const A&, tuple<X>&&)
+  // and construct Z from X:
+  std::tuple<Z> z(std::allocator_arg, a, std::move(x));
+}