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{ config, pkgs, ... }:
with pkgs.lib;
let
failed = map (x: x.message) (filter (x: !x.assertion) config.assertions);
in
{
options = {
assertions = mkOption {
default = [];
example = [ { assertion = false; msg = "you can't enable this for that reason"; } ];
merge = pkgs.lib.mergeListOption;
description = ''
This option allows modules to express conditions that must
hold for the evaluation of the system configuration to
succeed, along with associated error messages for the user.
'';
};
};
config = {
# This option is evaluated always. Thus the assertions are checked as well. hacky!
environment.systemPackages =
if [] == failed then []
else throw "\nFailed assertions:\n${concatStringsSep "\n" (map (x: "- ${x}") failed)}";
};
}
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