[Nix-dev] nix-env -i can't find package override I defined

[Kirill Elagin]

It's not really that straightforward, because `nix-env` is a part of Nix,
but `configuration.nix` is a configuration of NixOS. Those are two
different projects.

Furthermore, it is not really correct to say that “`nix-env` reads” or
“does not read” `configuration.nix`. It reads the expression it was told to
read and all the overriding stuff etc. are just internal things of the
expression. In the case of `nix-env` without explicit `-f` it basically
reads `top-level/all-packages.nix`, and there we have `config` read from
`~/.nixpkgs/config.nix` (see the very beginning of
`top-level/all-packages.nix`) and then `config.packageOverrides` used to
modify the set of all packages.

So, I guess, the easiest way to achieve this is to explicitly merge
`packageOverrides` in your `~/.nixpkgs/config.nix` with the ones in
`configuration.nix`. In case you don’t want this code in
`~/.nixpkgs/config.nix` for some reason, you can just make
`top-level/all-packages.nix` read the config from another system-wide file
(e.g. by setting `$NIXPKGS_CONFIG` or altering `~/.nix-defexpr` and calling
`top-level/all-packages.nix` with a custom `config` argument there) and do
the importing `~/.nixpkgs/config.nix` and merging in that other system-wide
file.

In other words, there are many ways, but none of them is good enough to be
integrated into upstream nixpkgs, because nixpkgs are supposed to work on
non-NixOS and having it check whether `/etc/nixos/configuration.nix` exists
and read it in this case feels like a hack to me.
On Sun, Feb 22, 2015, 11:33 Bjørn Forsman <bjorn.forsman at gmail.com> wrote:

>
> 22. feb. 2015 08:29 skrev "Cody Goodman" <codygman.consulting at gmail.com>
> følgende:
> [...]
>
>
> > For some reason nix can't seem to find it...
> >
> > ~ $ grep -A3 helloEnv /etc/nixos/configuration.nix
> > 53:      helloEnv = pkgs.myEnvFun {
> > 54-            name = "someEnvName";
> > 55-            buildInputs = [ hello ];
> > 56-      };
> > ~ $ nix-env -i env-someEnvName
> > error: selector ‘env-someEnvName’ matches no derivations
>
> nix-env does not read configuration.nix. If you want that, put your
> packageOverrides in ~/.nixpkgs/config.nix instead.
>
> I've done the same mistake myself. I think it is a bit confusing that
> nix-env ignores the system-wide packageOverrides. I think it would be
> better if it merged those packageOverrides (if possible).
>
> - Bjørn
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