Implement CWG 1780

[llvmbot]

Bugzilla Link	26166
Version	trunk
OS	Windows NT
Reporter	LLVM Bugzilla Contributor

Extended Description

auto l = [] () -> void {};
struct s {friend void decltype(l)::operator()() const;};

The above spuriously succeeds.

NB: For unbeknown reasons, the trailing return type is necessary. How come the return type differs from void if it isn't supplied? E.g. in the same sample program without -> void, the assertion

static_assert(std::is_same<decltype(&decltype(l)::operator()), void(decltype(l)::*)() const>{});

succeeds.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

[cor3ntin]

Can't reproduce (as far back as 3.5)

[frederick-vs-ja]

@cor3ntin This is still reproducible - demo.

[cor3ntin]

@frederick-vs-ja what is the behavior you expect to see?
https://godbolt.org/z/zYqfGje3T

I guess this is the issue https://godbolt.org/z/q5hx43fn8

Edit: nvm, we just don't implement a core issue...