Title : NixOS optional features in packages
Author: Solène
Date : 14 October 2020
Tags : nixos linux
As a claws-mail user, I like to have calendar support in the mail
client to be able to "accept" invitations. In the default NixOS
claws-mail package, the vcalendar module isn't installed with the
package. Still, it is possible to add support for the vcalendar
module without ugly hack.
It turns out, by default, the claws-mail package in Nixpkg has an
optional build option for the vcalendar module, we need to tell
nixpkg we want this module and claws-mail will be compiled.
As stated in the [NixOS
manual](https://nixos.org/manual/nixos/stable/#sec-customising-packages),
the optionals features can't be searched yet. So what's possible
is to search for your package in the [NixOS packages
search](https://search.nixos.org/packages), click on the package
name to get to the details and click on the link named "Nix expression"
that will open a link to the package definition on GitHUB, [claws-mail
nix
expression](https://github.com/NixOS/nixpkgs/blob/nixos-unstable/pkgs/applications/networking/mailreaders/claws-mail/default.nix#L111)
As you can see on the claws-mail nix expression code, there are lot
of lines with **optional**, those are features we can enable. Here
is a sample:
[..]
++ optional (!enablePluginArchive) "--disable-archive-plugin"
++ optional (!enablePluginLitehtmlViewer) "--disable-litehtml_viewer-plugin"
++ optional (!enablePluginPdf) "--disable-pdf_viewer-plugin"
++ optional (!enablePluginPython) "--disable-python-plugin"
[..]
In your `configuration.nix` file, where you define the package list
you want, you can tell you want to enable the plugin vcalendar,
this is done as in the following example:
environment.systemPackages = with pkgs; [
kakoune git firefox irssi minetest
(pkgs.claws-mail.override { enablePluginVcalendar = true;})
];
When you rebuild your system to match the configuration definition,
claws-mail will be compiled with the extras options you defined.
Now, I have claws-mail with vCalendar support.
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