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nixpkgs/nixos/modules/misc/label.nix

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Nix

{ config, lib, ... }:
with lib;
let
cfg = config.system.nixos;
in
{
options.system = {
nixos.label = mkOption {
type = types.str;
description = ''
NixOS version name to be used in the names of generated
outputs and boot labels.
If you ever wanted to influence the labels in your GRUB menu,
this is the option for you.
The default is <option>system.nixos.tags</option> separated by
"-" + "-" + <envar>NIXOS_LABEL_VERSION</envar> environment
variable (defaults to the value of
<option>system.nixos.version</option>).
Can be overriden by setting <envar>NIXOS_LABEL</envar>.
Useful for not loosing track of configurations built from different
nixos branches/revisions, e.g.:
<screen>
#!/bin/sh
today=`date +%Y%m%d`
branch=`(cd nixpkgs ; git branch 2>/dev/null | sed -n '/^\* / { s|^\* ||; p; }')`
revision=`(cd nixpkgs ; git rev-parse HEAD)`
export NIXOS_LABEL_VERSION="$today.$branch-''${revision:0:7}"
nixos-rebuild switch</screen>
'';
};
nixos.tags = mkOption {
type = types.listOf types.str;
default = [];
example = [ "with-xen" ];
description = ''
Strings to prefix to the default
<option>system.nixos.label</option>.
Useful for not loosing track of configurations built with
different options, e.g.:
<screen>
{
system.nixos.tags = [ "with-xen" ];
virtualisation.xen.enable = true;
}
</screen>
'';
};
};
config = {
# This is set here rather than up there so that changing it would
# not rebuild the manual
system.nixos.label = mkDefault (maybeEnv "NIXOS_LABEL"
(concatStringsSep "-" ((sort (x: y: x < y) cfg.tags)
++ [ (maybeEnv "NIXOS_LABEL_VERSION" cfg.version) ])));
};
}