gcc/testsuite/g++.dg/template/canon-type-17.C

// { dg-do compile { target c++11 } }
template<unsigned u> struct size_c{ static constexpr unsigned value = u; };
template<class... T> auto return_size(T... t) -> size_c<sizeof...(t)>;
template<class... T> auto return_size(T... t) -> size_c<sizeof...(t)>;
static_assert(decltype(return_size('a'))::value == 1u, "");