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PR libstdc++/91456 make INVOKE<R> work with uncopyable prvalues

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In C++17 a function can return a prvalue of a type that cannot be moved
or copied. The current implementation of std::is_invocable_r uses
std::is_convertible to test the conversion to R required by INVOKE<R>.
That fails for non-copyable prvalues, because std::is_convertible is
defined in terms of std::declval which uses std::add_rvalue_reference.
In C++17 conversion from R to R involves no copies and so is not the
same as conversion from R&& to R.

This commit changes std::is_invocable_r to check the conversion without
using std::is_convertible.

std::function also contains a similar check using std::is_convertible,
which can be fixed by simply reusing std::is_invocable_r (but because
std::is_invocable_r is not defined for C++11 it uses the underlying
std::__is_invocable_impl trait directly).

	PR libstdc++/91456
	* include/bits/std_function.h (__check_func_return_type): Remove.
	(function::_Callable): Use std::__is_invocable_impl instead of
	__check_func_return_type.
	* include/std/type_traits (__is_invocable_impl): Add another defaulted
	template parameter. Define a separate partial specialization for
	INVOKE and INVOKE<void>. For INVOKE<R> replace is_convertible check
	with a check that models delayed temporary materialization.
	* testsuite/20_util/function/91456.cc: New test.
	* testsuite/20_util/is_invocable/91456.cc: New test.

From-SVN: r274542
This commit is contained in:
Jonathan Wakely 2019-08-15 17:07:27 +01:00 committed by Jonathan Wakely
parent b3595983e3
commit d91f618d15
5 changed files with 126 additions and 9 deletions
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13
libstdc++-v3/ChangeLog
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@ -1,3 +1,16 @@
2019-08-15 Jonathan Wakely <jwakely@redhat.com>
PR libstdc++/91456
* include/bits/std_function.h (__check_func_return_type): Remove.
(function::_Callable): Use std::__is_invocable_impl instead of
__check_func_return_type.
* include/std/type_traits (__is_invocable_impl): Add another defaulted
template parameter. Define a separate partial specialization for
INVOKE and INVOKE<void>. For INVOKE<R> replace is_convertible check
with a check that models delayed temporary materialization.
* testsuite/20_util/function/91456.cc: New test.
* testsuite/20_util/is_invocable/91456.cc: New test.
2019-08-14 Jonathan Wakely <jwakely@redhat.com>
* include/std/type_traits (__is_nullptr_t): Add deprecated attribute.

10
libstdc++-v3/include/bits/std_function.h
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@ -293,10 +293,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
}
};
template<typename _From, typename _To>
using __check_func_return_type
= __or_<is_void<_To>, is_same<_From, _To>, is_convertible<_From, _To>>;
/**
* @brief Primary class template for std::function.
* @ingroup functors
@ -309,8 +305,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
private _Function_base
{
template<typename _Func,
typename _Res2 = typename result_of<_Func&(_ArgTypes...)>::type>
struct _Callable : __check_func_return_type<_Res2, _Res> { };
typename _Res2 = __invoke_result<_Func&, _ArgTypes...>>
struct _Callable
: __is_invocable_impl<_Res2, _Res>::type
{ };
// Used so the return type convertibility checks aren't done when
// performing overload resolution for copy construction/assignment.

41
libstdc++-v3/include/std/type_traits
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@ -2883,14 +2883,49 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
// __is_invocable (std::is_invocable for C++11)
template<typename _Result, typename _Ret, typename = void>
// The primary template is used for invalid INVOKE expressions.
template<typename _Result, typename _Ret,
bool = is_void<_Ret>::value, typename = void>
struct __is_invocable_impl : false_type { };
// Used for valid INVOKE and INVOKE<void> expressions.
template<typename _Result, typename _Ret>
struct __is_invocable_impl<_Result, _Ret, __void_t<typename _Result::type>>
: __or_<is_void<_Ret>, is_convertible<typename _Result::type, _Ret>>::type
struct __is_invocable_impl<_Result, _Ret,
/* is_void<_Ret> = */ true,
__void_t<typename _Result::type>>
: true_type
{ };
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wctor-dtor-privacy"
// Used for INVOKE<R> expressions to check the implicit conversion to R.
template<typename _Result, typename _Ret>
struct __is_invocable_impl<_Result, _Ret,
/* is_void<_Ret> = */ false,
__void_t<typename _Result::type>>
{
private:
// The type of the INVOKE expression.
// Unlike declval, this doesn't add_rvalue_reference.
static typename _Result::type _S_get();
template<typename _Tp>
static void _S_conv(_Tp);
// This overload is viable if INVOKE(f, args...) can convert to _Tp.
template<typename _Tp, typename = decltype(_S_conv<_Tp>(_S_get()))>
static true_type
_S_test(int);
template<typename _Tp>
static false_type
_S_test(...);
public:
using type = decltype(_S_test<_Ret>(1));
};
#pragma GCC diagnostic pop
template<typename _Fn, typename... _ArgTypes>
struct __is_invocable
: __is_invocable_impl<__invoke_result<_Fn, _ArgTypes...>, void>::type

37
libstdc++-v3/testsuite/20_util/function/91456.cc Normal file
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@ -0,0 +1,37 @@
// 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-options "-std=gnu++17" }
// { dg-do compile { target c++17 } }
#include <functional>
struct Immovable {
Immovable() = default;
Immovable(const Immovable&) = delete;
Immovable& operator=(const Immovable&) = delete;
};
Immovable get() { return {}; }
const Immovable i = get(); // OK
std::function<const Immovable()> f{&get}; // fails
const Immovable i2 = f();
const Immovable cget() { return {}; }
Immovable ci = cget(); // OK
std::function<Immovable()> cf{&cget}; // fails
Immovable ci2 = cf();

34
libstdc++-v3/testsuite/20_util/is_invocable/91456.cc Normal file
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@ -0,0 +1,34 @@
// 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-options "-std=gnu++17" }
// { dg-do compile { target c++17 } }
#include <type_traits>
#include <functional>
struct Immovable {
Immovable() = default;
Immovable(const Immovable&) = delete;
Immovable& operator=(const Immovable&) = delete;
};
Immovable get() { return {}; }
const Immovable i = get(); // OK
std::function<const Immovable()> f{&get}; // fails
const Immovable i2 = f();