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libstdc++: Add workaround for weird std::tuple error [PR 96592]

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This "fix" makes no sense, but it avoids an error from G++ about
std::is_constructible being incomplete. The real problem is elsewhere,
but this "fixes" the regression for now.

libstdc++-v3/ChangeLog:

	PR libstdc++/96592
	* include/std/tuple (_TupleConstraints<true, T...>): Use
	alternative is_constructible instead of std::is_constructible.
	* testsuite/20_util/tuple/cons/96592.cc: New test.
This commit is contained in:
Jonathan Wakely 2020-09-03 16:26:16 +01:00
parent 3c21913415
commit 032a4b42cc
2 changed files with 62 additions and 0 deletions
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4
libstdc++-v3/include/std/tuple
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@ -539,6 +539,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
template<bool, typename... _Types>
struct _TupleConstraints
{
template<typename _Tp, typename _Up> // Workaround for PR 96592
using is_constructible
= __bool_constant<__is_constructible(_Tp, _Up)>;
// Constraint for a non-explicit constructor.
// True iff each Ti in _Types... can be constructed from Ui in _UTypes...
// and every Ui is implicitly convertible to Ti.

58
libstdc++-v3/testsuite/20_util/tuple/cons/96592.cc Normal file
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@ -0,0 +1,58 @@
// Copyright (C) 2020 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>
// PR 96592 comment 0
template <typename SessionT>
struct SomeQuery {
SessionT& session_;
SomeQuery(SessionT& session) : session_(session) {}
};
template <typename SessionT>
struct Handler {
std::tuple<SomeQuery<SessionT>> queries_;
Handler(SessionT& session) : queries_(session) {}
};
struct Session {
Handler<Session> handler_;
Session() : handler_{*this} {}
};
Session session;
// PR 96592 comment 1
template <typename T>
class DependsOnT
{
public:
DependsOnT(T&) {}
};
class Test
{
public:
Test() : test_{*this} {}
private:
std::tuple<DependsOnT<Test>> test_;
};