Sample custom nixpkgs repository for custom Hydra channels

Foreword: work in progress, use at your own risk.

This repository is an example of how to create a custom set of packages with a dedicated channel extending the official nixpkgs.

The idea is to have a base for nixpkgs based projects.

Files

default.nix

This is the entry point of the main package set. The main package set consist of the main <nixpkgs> extendended with the customPkgs set.

The custom packages are accessible in a dedicated set (pkgs.customPkgs) or under pkgs top level.

exaple:

$ nix-build -A trivial

is equivalent to

$ nix-build -A customPkgs.trivial

Having the custom packages in a dedicated set becomes handy when dealing with Hydra.

pkgs/default.nix

Is more or less the equivalent to the official nixpkgs ./pkgs/top-level/all-packages.nix for the custom packages.

release.nix

The beast. This file is the hardest to understand, so it is better to have some basic knowledge of the nix expression language and Hydra before diving in.

lib/default.nix

This imports the custom library functions in a custom namespace.

Playing with this repository

clone localy and build some useless packages!

$ nix-build -A trivial
$ ./result/bin/trivial

Play with this repo and Hydra

Hydra is fun! Building useless packages with it is even more.

First, you should set some hydra server to play with. It is a piece of cake with nixos-unstable and nixops.

TODO: add nixops hydra expressions and instructions

In hydra, create a projet with a jobset.

For projects, the only important things are to check Enabled and Visible in the list of projects.

Jobsets are little more complicated to configure, but it is not that hard:

State should be enabled
Check interval to 10 sec (for fast feedback on testing)
Scheduling shares to 1
Inputs are the way to override what is passed to release.nix, but release.nix is also an input we will set 2 inputs:
- hydra-pg Git Checkout git://github.com/ericsagnes/hydra-pg (release.nix in this repo)
- nixpkgs Git Checkout git://github.com/nixos/nixpkgs-channels.git nixos-unstable (official nixpkgs, is is possible to change the branch name)
Going back up, Nix Expression: release.nix in hydra-pg

To summarize. Hydra will evaluate release.nix from hydra-pg (this repository) passing the nixpkgs input as a function argument. (release.nix is a function)

Then, apply changes and the jobset will evaluate and if everything work as it should a channel will be available in the Channels tab of the jobset.

The generated channel can be used like any normal nix channel.

TODO

Figure how publish channel binary cache
more comments, better comments
add NixOS modules

ericsagnes/hydra-pg