https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111357
Bug ID: 111357
Summary: __integer_pack fails to work with values of dependent
type convertible to integers
Product: gcc
Version: 13.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: frankhb1989 at gmail dot com
Target Milestone: ---
Case:
#include <cstddef>
#include <type_traits>
#include <tuple>
using std::size_t;
#if __cpp_lib_integer_sequence >= 201304L
using std::index_sequence;
using std::make_index_sequence;
#else
template<size_t... V>
struct index_sequence
{};
template<class>
struct succ;
template<size_t... V>
struct succ<index_sequence<V...>>
{
using type = index_sequence<V..., sizeof...(V)>;
};
template<size_t N>
struct iseq
{
using type = typename succ<typename iseq<N - 1>::type>::type;
};
template<>
struct iseq<0>
{
using type = index_sequence<>;
};
template<size_t N>
using make_index_sequence = typename iseq<N>::type;
#endif
template<size_t... V>
void g(index_sequence<V...>)
{}
template<typename T>
struct R
{
using S = make_index_sequence<std::tuple_size<std::tuple<T>>{}>;
R() noexcept(noexcept(g(S())))
{}
};
int main()
{
R<int>();
}
Output of x86-64 gcc 13.2 (Compiler #1)
<source>: In instantiation of 'R<T>::R() [with T = int]':
<source>:55:9: required from here
<source>:49:33: error: argument to '__integer_pack' must be between 0 and
268435452
49 | R() noexcept(noexcept(g(S())))
| ^~~
This should work as -std=c++11 which uses a naive implementation of
make_index_sequence here.
I mark it as a libstdc++ bug of conformance for the case. The root cause seems
a bug of the implementation in the frontend, but I'm not that sure, because the
document of __integer_pack does not mention such cases explicitly. (The error
message here is obviously confusing, though.)
