Fix typespec with (...) -> any(), closes #1974

[josevalim]

@gomoripeti this is fixed in main but it will require Elixir v1.18+.

@garazdawi in the long term, we probably want the code that converts a typespec into a string with links to be part of Erlang/OTP? Perhaps by adding some sort of fallback to the existing pretty printing function? Or perhaps, instead of converting it to Elixir AST and traversing it, we'd traverse the Erlang AST typespec directly.

[josevalim]

💚 💙 💜 💛 ❤️

[garazdawi]

Or perhaps, instead of converting it to Elixir AST and traversing it, we'd traverse the Erlang AST typespec directly.

I think this would be a better option. IIRC it should be possible to use erl_syntax_lib:fold to get something relatively close to what we have today.

[garazdawi]

I found a regression with this change. If you do:

-spec foo(fun()) -> ok.

It will try to create a link for a local type called fun/0, while fun() is actually syntax (as opposed to function() which is more like a type()). Any ideas on how to solve this would be appreciated. I will work around it by replacing it with function() for now and will start digging to see if I can come up with a solution.