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libstdc++: Add static assertions to futures and promises [LWG 3458]

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LWG recently decided it should be ill-formed to instantiate std::future
and std::shared_future for types that can't be returned from a function.
This adds static assertions to enforce it (std::future already failed,
but this makes the error more understandable).

LWG 3466 extends that to std::promise. The actual constraint is that
t.~T() is well-formed for the primary template, but rejecting arrays and
functions as done for futures matches that condition.

libstdc++-v3/ChangeLog:

	* include/std/future (future, shared_future, promise): Add
	static assertions to the primary template to reject array and
	function types.
	* testsuite/30_threads/future/requirements/lwg3458.cc: New test.
	* testsuite/30_threads/promise/requirements/lwg3466.cc: New test.
	* testsuite/30_threads/shared_future/requirements/lwg3458.cc: New test.
This commit is contained in:
Jonathan Wakely 2020-07-22 20:10:38 +01:00
parent e55ba804d3
commit 1f53367fb5
4 changed files with 115 additions and 0 deletions
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15
libstdc++-v3/include/std/future
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@ -763,6 +763,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
template<typename _Res>
class future : public __basic_future<_Res>
{
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 3458. Is shared_future intended to work with arrays or function types?
static_assert(!is_array<_Res>{}, "result type is not an array");
static_assert(!is_function<_Res>{}, "result type is not a function");
friend class promise<_Res>;
template<typename> friend class packaged_task;
template<typename _Fn, typename... _Args>
@ -893,6 +898,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
template<typename _Res>
class shared_future : public __basic_future<_Res>
{
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 3458. Is shared_future intended to work with arrays or function types?
static_assert(!is_array<_Res>{}, "result type is not an array");
static_assert(!is_function<_Res>{}, "result type is not a function");
typedef __basic_future<_Res> _Base_type;
public:
@ -1045,6 +1055,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
template<typename _Res>
class promise
{
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 3466: Specify the requirements for promise/future/[...] consistently
static_assert(!is_array<_Res>{}, "result type is not an array");
static_assert(!is_function<_Res>{}, "result type is not a function");
typedef __future_base::_State_base _State;
typedef __future_base::_Result<_Res> _Res_type;
typedef __future_base::_Ptr<_Res_type> _Ptr_type;

34
libstdc++-v3/testsuite/30_threads/future/requirements/lwg3458.cc Normal file
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@ -0,0 +1,34 @@
// 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 } }
// LWG 3458
// Is shared_future intended to work with arrays or function types?
#include <future>
std::future<int(&)[1]> good;
std::future<int(&)()> good2;
std::future<int[1]> bad; // { dg-error "here" }
// { dg-error "result type is not an array" "" { target *-*-* } 0 }
// { dg-prune-output "function returning an array" }
std::future<int()> bad2; // { dg-error "here" }
// { dg-error "result type is not a function" "" { target *-*-* } 0 }
// { dg-prune-output "function returning a function" }

34
libstdc++-v3/testsuite/30_threads/promise/requirements/lwg3466.cc Normal file
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@ -0,0 +1,34 @@
// 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 } }
// LWG 3466
// Specify the requirements for promise/future/shared_future consistently
#include <future>
std::promise<int(&)[1]> good;
std::promise<int(&)()> good2;
std::promise<int[1]> bad; // { dg-error "here" }
// { dg-error "result type is not an array" "" { target *-*-* } 0 }
// { dg-prune-output {request for member '~int \[1\]'} }
std::promise<int()> bad2; // { dg-error "here" }
// { dg-error "result type is not a function" "" { target *-*-* } 0 }
// { dg-prune-output {'sizeof \(int\(\)\)'} }

32
libstdc++-v3/testsuite/30_threads/shared_future/requirements/lwg3458.cc Normal file
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@ -0,0 +1,32 @@
// 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 } }
// LWG 3458
// Is shared_future intended to work with arrays or function types?
#include <future>
std::shared_future<int(&)[1]> good;
std::shared_future<int(&)()> good2;
std::shared_future<int[1]> bad; // { dg-error "here" }
// { dg-error "result type is not an array" "" { target *-*-* } 0 }
std::shared_future<int()> bad2; // { dg-error "here" }
// { dg-error "result type is not a function" "" { target *-*-* } 0 }