This enables nushell integration by default for direnv, similar to
bash/zsh/fish. The slightly verbose way of setting this is to ensure
that peoples' existing nushell configuration isn't overwritten, only
appended to, as would be the case if we just used the integration
example from the nushell docs:
https://www.nushell.sh/cookbook/direnv.htmlCloses#3520
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
NixOS/nixpkgs@03310df843 disabled flake
support by default, so we now need to build a custom package and use it
if the user wants to `use flake` successfully. This should fix#2087.
