[Nix-dev] Moving some of the NixOS setup to nixpkgs

[Nicolas Pierron]

Hi,

First of all I want to thanks Thomas, for his pull request on the Vim
configuration [1].  One of the most interesting part, from my point of
view, is to give the Configuration Management aspect of NixOS
configuration to manage user environments.

Jan, suggested a similar idea except that the module lies in the
derivation files of the packages.  Even if I do not like the approach
of storing the modules inside the derivation, I think this is the
rough idea we should be aim at, at least at the package level.

Jan also suggested to have activations scripts, which is an idea
coming from NixOS.  Having such a thing would be very convenient at
the user level, but leads to multiple questions to know what does it
maps to at user profile.

(as I am waiting to get feedback / reviews for the Nix's secret branch [2])
I started to work on a system (NixUP) which would be identical and
compatible with NixOS, the idea would be to have another tool for
managing user profiles, which would be similar to what nixos-rebuild
do, and nixos-option should almost the same way.

By compatible, I want us to be able to have modules which are
targeting both NixOS options and NixUP options.  Also, ideally NixUP
modules should be valid sub-modules for the "users.extraUsers" option,
such as anything which can be handled at the user level can also be
handled at the system level. (such as openssh.authorizedKeys.keys)

Among the thing that I am trying to get right at the moment, is what
does it means to activate a user profile?  Should the activation of a
user profile be done only when you switch to a new profile (changing
$HOME/.zshrc), or should it be something done only once we are logged
in (ssh-agent), or should it be something which is done every time we
start a terminal?

I think that all these use cases deserved to be considered as valid
activations, and then the question is how do we manage them properly.

So far, on all my computers, I have been managing my user
configuration with a private git repository hosted on a server.  I
think this is time to change and to update it to use a new model based
on NixOS module system.

One of the thing that I want everybody to keep in mind, is that doing
such system implies that we should not be relying on the operating
system.  We should not assume that a user can use systemd processes,
and this implies that we will have to support multiple backends.

Maybe, later, we could be writing some default abstraction based on
the operation system on which the user environment is running
(host.system = "debian"), or even infer it in a similar way as
hardware-config.nix.

Also note, that NixUp should NOT be considered as a replacement of
nix-env or Nixpkgs.  Managing a configuration of one user does not
replace the management of a user environment.  nix-env provides some
convenient imperative management such as one-click-install, which are
not working with the module system (so far).

[1] https://github.com/NixOS/nixpkgs/pull/4493
[2] https://github.com/NixOS/nix/pull/329

-- 
Nicolas Pierron
http://www.linkedin.com/in/nicolasbpierron - http://nbp.name/