Update packaging-existing-software.md

[olga-mcbfe]

update version of nixpkgs used to avoid multiple-hour cache build for first-time users trying to learn Nix

[fricklerhandwerk]

Thanks! Eventually all of these versions should be set automatically and all the examples tested to be working, but we're (by far) not there yet.

Although an old Nixpkgs release should not necessarily require you to build anything locally, all of that stuff is cached. Did you set up any custom cache configuration?

[willbush]

@fricklerhandwerk Think a Github action could update these pretty easy, but not sure how to test it easily. Guess we would need something like mdbook test, but for nix?

[fricklerhandwerk]

Updating is by far the easy part.

not sure how to test it easily

This is a discussion we had many times, and there are multiple attempts to build a testing framework, taking it from various angles. Someone needs to make these ideas usable by adopting, finishing, or implementing the respective pieces of technology. Here are a few recent notes relating to @djacu's contribution to the module system tutorial: https://discourse.nixos.org/t/2024-05-16-documentation-team-meeting-notes-128/45537

[olga-mcbfe]

Although an old Nixpkgs release should not necessarily require you to build anything locally, all of that stuff is cached. Did you set up any custom cache configuration?

I just installed nix and started to follow this tutorial. As far as I know I didn't have any custom cache configuration