std::span as a template template argument doesn't compile with clang

I want to use std::span as a template template argument to a function.
gcc seems to accept the following code, but clang rejects.

#include <iostream>
#include <span>
#include <vector>

std::vector v{1,2,3,4,5,6};

template <template <typename> class S>
S<int> GetSpan()
{
    return v;
}

int main()
{
    auto x = GetSpan<std::span>();
    return 0;
}

Can someone please explain why this is the case ?

https://godbolt.org/z/Ks9M5oqKc

>Solution :

You are missing the second template parameter, the extent:

template <template <typename, std::size_t> class S>
S<int, std::dynamic_extent> GetSpan()
{
    return v;
}

To make it work with a custom span-like type as well as std::span you could possibly make it take a non-type parameter pack std::size_t... or auto....

template <template <typename, std::size_t...> class S>
auto GetSpan()
{
    return S(v);
}