Nushell has the option to source from the login.nu file in the case
that nushell is used as a login shell. This commit adds the login file
alongside the existing config and env files as another configuration
option.
Previously the nushell module did not differentiate between Linux and
Darwin when deciding where to place config files, whereas nushell
does. This commit fixes that.
Currently, dot directories and XDG base directories are used
inconsistently in the Home Manager option declarations. This creates
ambiguity for the user as to where the location of the file should be
albeit this is rarely encountered in practice as it is sufficient to
read upstream documentation. The rationale is to make declarations
consistent and make a clear distinction between hardcoded and modular
specifications.
References to ~/.config in relevant nixpkgs modules were untouched as
the location is hardcoded upstream[1]. Furthermore, modules of
programs which do not follow XDG specifications were also untouched.
Generalization of tilde(~) expansions to $HOME were also considered,
however there isn't sufficient rationale despite the use of $HOME
being more universal. The expansion is standardized in POSIX[2] and is
essentially portable across all shells, thus there is no pragmatic
value to introducing the change.
[1] https://github.com/nixos/nixpkgs/blob/master/pkgs/top-level/impure.nix
[2] https://pubs.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html#tag_02_06_01
