In our own products we relied on installation scripts to create directories with correct ownership and permissions. I think it's responsibility of lib's user to make sure needed paths exist.

It may appear simple when it's something as innocent as ~/.config, but that's not always the case. Even with ~/.config consider the case when user runs your app with sudo by mistake. Such directory would cause a lot of headache.

In general I suggest to run validation and directory creation early in your app to address this problem. Then you can gracefully handle cases when $HOME and $EUID represent different users.

I agree that auto-creating directories could be dangerous, but we already auto-create a file, so much of the same concerns hold there. I did worry about it for a bit but it then end - it comes down ensuring sane paths are used. On my systems under sudo '~' expands to '/root'; so it's not a weird outcome. Any use of sudo is dangerous; I don't think this is any worse than say 'rm'

Perhaps this should be an option - wouldn't want to put OS-specifics like this (windows - for example won't need this) is the library use; the whole point of library is abstract away Os specific cases.