Nixpkgs/Create and debug packages: Difference between revisions

There is a chapter about hacking packages and modules in the NixOS manual: http://nixos.org/nixos/manual/index.html#ch-development

Writing packages is covered in https://nixos.org/manual/nixpkgs/stable/#chap-quick-start and writing modules in http://nixos.org/nixos/manual

If you've read the manual and still don't know how to go about creating a package read on.

The nix repositories are hosted here: https://github.com/nixos

The code for nix packages is managed in the nixpkgs repository. NixOS services, and other system configuration options are managed in the nixos sub-directory of the nixpkgs repository.

# Clone your fork <code>git clone git@github.com:YOUR-GITHUB-ACCOUNT-NAME/nixpkgs.git</code>

# Read the repo build instructions. Many times the instructions won't be 100% clear in the README, but there might be some script for CI that will be more precise. This should give you a rough idea of how hard it will be to package it. For example, if it uses a standard, vanilla build, it will probably be easy to package. If on the contrary there are no CI scripts, or no build instructions, or the build instructions are complicated, things could be rough.  

# Look in nixpkgs for a similar package to use as reference. Many times you can just copy/paste a similar package, change the <code>src</code> attribute and things will just work. E.g. if you're packaging a project written in Go, find a package for an existing Go application. Each language has its own supporting Nix functions and a more or less standard way of dealing with things. For example Go has <code>buildGoPackage</code>. Rust has <code>buildRustPackage</code>. Python has <code>buildPythonApplication</code>. The official documentation for these is generally good. These functions will typically do most of the heavy lifting and you probably just have to point them to the repo and they will do the rest. There are also specific functions for wrapping e.g. GNOME applications. It pays off to have a look at the [https://nixos.org/manual/nixpkgs/stable/#chap-language-support table of contents for these functions in the docs].  

# If there isn't a specific function for the build/language you'll need to use stdenv.mkDerivation directly but don't despair (yet!). mkDerivation has built-in support for GNU make, CMake, and possibly others too (?) so you probably won't have to spell out every single command necessary to build the project.

# Figure out at least some dependencies from the project repo. Doesn't have to be perfect, but something to get you started. See if they're available in nixpkgs. If any dependency is missing you'll need to package that as well! Common libraries are usually available though.

# Write the default.nix. <br/>

Do it in some empty local directory and at the top just say <code>with import <nixpkgs> {};</code>, don't worry too much about declaring every dependency as a parameter for now as it will only slow you down. Again, use some similar package as reference.

# Build it with <code>nix build -L</code>. Iterate on tweaking default.nix and running nix build until it builds. At this stage you will start dealing with build quirks of the project, if the are any. Compile-time errors will hopefully point out what you're missing. For example [https://github.com/NixOS/nixpkgs/blob/643ce4bd0f057bc0b90f0faebeb83a3b14f01674/pkgs/tools/package-management/micromamba/default.nix#L6-L10 micromamba needs a specialized build of libsolv].

# Sometimes the definitions for other distros won't be enough by nix's standards. If that's the case, use <code>ldd</code> and/or <code>strace</code> to find the rest of the dependencies. If you're not familiar with <code>ldd</code>/<code>strace</code> see https://unix.stackexchange.com/questions/120015/how-to-find-out-the-dynamic-libraries-executables-loads-when-run

# Now that your package builds and runs, it's time to move it to nixpkgs. Read https://github.com/NixOS/nixpkgs/blob/master/CONTRIBUTING.md , make sure your package is up to the standards e.g. add a suitable [https://nixos.org/manual/nixpkgs/stable/#sec-standard-meta-attributes <code>meta</code> section].