https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102065
Bug ID: 102065
Summary: [C++20] Substitution failure of function instantiates
its argument
Product: gcc
Version: 11.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: seredinyegor at gmail dot com
Target Milestone: ---
Created attachment 51356
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=51356&action=edit
preprocessed file
Problem can be reproduced with:
- gcc version 11.2.0 (Ubuntu 11.2.0-1ubuntu2)
- gcc version 12.0.0 20210825 (experimental) (GCC)
Problem doesn't exist in:
- gcc version 10.3.0 (Ubuntu 10.3.0-1ubuntu1~20.04)
- Ubuntu clang version
13.0.0-++20210823084033+1f0b043ae709-1~exp1~20210823184829.58
CXXFLAGS: -std=c++20
Code:
#include <functional>
void elem_func(int) {}
template <
typename Sequence,
std::invocable<int> SequenceHandler
>
void func(
const Sequence& values,
SequenceHandler&& handler,
std::enable_if_t<std::is_pointer_v<Sequence>, int> = 0)
{
}
template <
typename T,
std::invocable<T> ValueHandler
>
void func(
T value,
ValueHandler&& handler,
std::enable_if_t<!std::is_pointer_v<T>, int> = 0)
{
}
int main()
{
func(
new int[1], // pointer => 1st func should be called
[](auto e) // lambda should be std::invocable<int> => decltype(e)==int
{
elem_func(e); // cannot call elem_func if decltype(e)==int* (2nd
func)
}
);
}
Compiler output:
sfinae_bug.cpp: In instantiation of ‘main()::<lambda(auto:3)> [with auto:3 =
int*]’:
/usr/include/c++/11/type_traits:2466:26: required by substitution of
‘template<class _Fn, class ... _Args> static std::__result_of_success<decltype
(declval<_Fn>()((declval<_Args>)()...)), std::__invoke_other>
std::__result_of_other_impl::_S_test(int) [with _Fn = main()::<lambda(auto:3)>;
_Args = {int*}]’
/usr/include/c++/11/type_traits:2477:55: required from ‘struct
std::__result_of_impl<false, false, main()::<lambda(auto:3)>, int*>’
/usr/include/c++/11/type_traits:2937:12: recursively required by substitution
of ‘template<class _Result, class _Ret> struct
std::__is_invocable_impl<_Result, _Ret, true, std::__void_t<typename
_CTp::type> > [with _Result = std::__invoke_result<main()::<lambda(auto:3)>,
int*>; _Ret = void]’
/usr/include/c++/11/type_traits:2937:12: required from ‘struct
std::is_invocable<main()::<lambda(auto:3)>, int*>’
/usr/include/c++/11/type_traits:3001:73: required from ‘constexpr const bool
std::is_invocable_v<main()::<lambda(auto:3)>, int*>’
/usr/include/c++/11/concepts:338:25: required by substitution of
‘template<class T, class ValueHandler> requires invocable<ValueHandler, T>
void func(T, ValueHandler&&, std::enable_if_t<(! is_pointer_v<T>), int>) [with
T = int*; ValueHandler = main()::<lambda(auto:3)>]’
sfinae_bug.cpp:29:9: required from here
sfinae_bug.cpp:33:23: error: invalid conversion from ‘int*’ to ‘int’
[-fpermissive]
33 | elem_func(e); // cannot call elem_func if decltype(e)==int*
(2nd func)
| ^
| |
| int*
