[Bug c++/91023] Unification Fails for parameter pack

[christoph.hoeger at celeraone dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91023

--- Comment #1 from Christoph Höger <christoph.hoeger at celeraone dot com> ---
Since it might help investigating the issue, here is a workaround:


#include <variant>
#include <optional>

template <typename T, typename S>
struct Foo
{
};

template <typename... T, typename S>
std::optional<std::variant<T...>>
parse_variant(const Foo<T, S> &... variants)
{
    return {};
}

struct A {};
struct B {};

using var_test = std::variant<A, B>;

Foo<A, var_test> a()
{
    return {};
}

Foo<B, var_test> b()
{
    return {};
}

int main()
{
    const auto x =  parse_variant(a(), b());
    return 0;
}