From d91f618d155a418acd7a7c9188af4c15d2583541 Mon Sep 17 00:00:00 2001 From: Jonathan Wakely Date: Thu, 15 Aug 2019 17:07:27 +0100 Subject: [PATCH] PR libstdc++/91456 make INVOKE work with uncopyable prvalues 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. 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. For INVOKE 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 --- libstdc++-v3/ChangeLog | 13 ++++++ libstdc++-v3/include/bits/std_function.h | 10 ++--- libstdc++-v3/include/std/type_traits | 41 +++++++++++++++++-- .../testsuite/20_util/function/91456.cc | 37 +++++++++++++++++ .../testsuite/20_util/is_invocable/91456.cc | 34 +++++++++++++++ 5 files changed, 126 insertions(+), 9 deletions(-) create mode 100644 libstdc++-v3/testsuite/20_util/function/91456.cc create mode 100644 libstdc++-v3/testsuite/20_util/is_invocable/91456.cc diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog index 2aaf4a5d8cc..144f8e63fa5 100644 --- a/libstdc++-v3/ChangeLog +++ b/libstdc++-v3/ChangeLog @@ -1,3 +1,16 @@ +2019-08-15 Jonathan Wakely + + 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. For INVOKE 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 * include/std/type_traits (__is_nullptr_t): Add deprecated attribute. diff --git a/libstdc++-v3/include/bits/std_function.h b/libstdc++-v3/include/bits/std_function.h index 5733bf5f3f9..42f87873d55 100644 --- a/libstdc++-v3/include/bits/std_function.h +++ b/libstdc++-v3/include/bits/std_function.h @@ -293,10 +293,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION } }; - template - using __check_func_return_type - = __or_, 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::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. diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits index d3f853d4ce2..44db2cade5d 100644 --- a/libstdc++-v3/include/std/type_traits +++ b/libstdc++-v3/include/std/type_traits @@ -2883,14 +2883,49 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION // __is_invocable (std::is_invocable for C++11) - template + // The primary template is used for invalid INVOKE expressions. + template::value, typename = void> struct __is_invocable_impl : false_type { }; + // Used for valid INVOKE and INVOKE expressions. template - struct __is_invocable_impl<_Result, _Ret, __void_t> - : __or_, is_convertible>::type + struct __is_invocable_impl<_Result, _Ret, + /* is_void<_Ret> = */ true, + __void_t> + : true_type { }; +#pragma GCC diagnostic push +#pragma GCC diagnostic ignored "-Wctor-dtor-privacy" + // Used for INVOKE expressions to check the implicit conversion to R. + template + struct __is_invocable_impl<_Result, _Ret, + /* is_void<_Ret> = */ false, + __void_t> + { + private: + // The type of the INVOKE expression. + // Unlike declval, this doesn't add_rvalue_reference. + static typename _Result::type _S_get(); + + template + static void _S_conv(_Tp); + + // This overload is viable if INVOKE(f, args...) can convert to _Tp. + template(_S_get()))> + static true_type + _S_test(int); + + template + static false_type + _S_test(...); + + public: + using type = decltype(_S_test<_Ret>(1)); + }; +#pragma GCC diagnostic pop + template struct __is_invocable : __is_invocable_impl<__invoke_result<_Fn, _ArgTypes...>, void>::type diff --git a/libstdc++-v3/testsuite/20_util/function/91456.cc b/libstdc++-v3/testsuite/20_util/function/91456.cc new file mode 100644 index 00000000000..a2d412d7bec --- /dev/null +++ b/libstdc++-v3/testsuite/20_util/function/91456.cc @@ -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 +// . + +// { dg-options "-std=gnu++17" } +// { dg-do compile { target c++17 } } + +#include + +struct Immovable { + Immovable() = default; + Immovable(const Immovable&) = delete; + Immovable& operator=(const Immovable&) = delete; +}; + +Immovable get() { return {}; } +const Immovable i = get(); // OK +std::function f{&get}; // fails +const Immovable i2 = f(); + +const Immovable cget() { return {}; } +Immovable ci = cget(); // OK +std::function cf{&cget}; // fails +Immovable ci2 = cf(); diff --git a/libstdc++-v3/testsuite/20_util/is_invocable/91456.cc b/libstdc++-v3/testsuite/20_util/is_invocable/91456.cc new file mode 100644 index 00000000000..d510d221a7d --- /dev/null +++ b/libstdc++-v3/testsuite/20_util/is_invocable/91456.cc @@ -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 +// . + +// { dg-options "-std=gnu++17" } +// { dg-do compile { target c++17 } } + +#include + +#include + +struct Immovable { + Immovable() = default; + Immovable(const Immovable&) = delete; + Immovable& operator=(const Immovable&) = delete; +}; + +Immovable get() { return {}; } +const Immovable i = get(); // OK +std::function f{&get}; // fails +const Immovable i2 = f();