[PATCH] PR libstdc++/91456 make INVOKE<R> work with uncopyable prvalues
Jonathan Wakely
jwakely@redhat.com
Thu Aug 15 16:07:00 GMT 2019
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.
Tested x86_64-linux, committed to trunk.
I might backport this to gcc-9-branch too, after some time on trunk.
-------------- next part --------------
commit a9ae95a61b2d8b5ccbbaff1f9bd0b3ed70c600ed
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Thu Aug 15 15:46:39 2019 +0100
PR libstdc++/91456 make INVOKE<R> 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<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.
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<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.
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<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
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
+// <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();
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
+// <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();
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