[Bug c++/102721] out-of-line member function definition fails to allow lambda in unevaluated-context of new feature in c++20

[nickhuang99 at hotmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102721

--- Comment #4 from qingzhe huang <nickhuang99 at hotmail dot com> ---
(In reply to Andrew Pinski from comment #2)
> Note it is not array related either:
> template<>
> void A<decltype(+[]{})>::foo(const decltype(+[]{}))
> {}

Yes, it is not array-related. But it is definitely member function issue with
out-of line definition. See this works fine:

template<class T>
void foo(const T){}

template<>
void foo<decltype(+[]{})>(const decltype(+[]{})); //declaration

template<>
void foo<decltype(+[]{})>(const decltype(+[]{}))
{}