Support XDG or platform-specific paths for .erlang and .erlang.cookie files

[hauleth]

Is your feature request related to a problem? Please describe.

Due to unfortunate decision of early UNIX developers to use path[0] == '.' instead of strcmp(path, ".") || strcmp(path, "..") in ls when filtering out the default paths, people started to using "dotfiles" stored in the $HOME of the current user to provide configuration and runtime commands for various files. Erlang currently follows that unfortunate trend in form of .erlang and .erlang.cookie files. To solve that mess that is all the dotfiles in home directory and all of mixing of configuration, caches, logs, data, etc. in the same directories and/or more files in home directory. Erlang already uses platform-specific paths for shell history, but .erlang and .erlang.cookie are still where these were before.

Describe the solution you'd like

Use either XDG Base Directory specification on all OSes or platform-specific approach for all files. This could be implemented in a way that "old" paths are fallbacks if the "new" files do not exists.

Describe alternatives you've considered

Do nothing.

[garazdawi]

I had a look at this. Doing it for .erlang is no problem.

However for .erlang.cookie I'm unsure about where the generated cookie should be placed. I think that in order to keep backward compatibility, it would need to be placed in ~/.erlang.cookie. That way jinterface, erl_interface and old erlang versions would still use the same default created cookie.

[hauleth]

The .erlang.cookie can be phased out in multi-step approach. It first can be left as is, and read XDG cookie if exists, then make position of .erlang.cookie configurable, then warn if .erlang.cookie position is not set, and then move to the new position. In that way the transition should be done somewhere around OTP 30.