A posteriori Nix shell

Warning

Very fresh paint!

So you have a non-Nix software environment that you would like to reproduce in Nix?

You can try to use third party tools such as Devbox, but generating a proper Nix Flake also seems like a decent idea.

The Nix4Science flake provides a way to generate a flake.nix from a YAML description of the desired software environments.

Imagine that you need to nixify two seperate shells. One for your C++ code built with CMake, and the other one for some analysis in python.

You can then describe the desired environment in a YAML file such as the one below:

- shell: analysis
  packages:
    - name: python310
      version: "3.10.8"
      with_packages:
      - name: numpy
        version: "1.24.2"
      - name: matplotlib
        version: "3.7.1"
- shell: dev
  packages:
    - name: gcc
      version: "12.3.0"
    - name: cmake
      version: "3.24.3"

• shell sets the name of the shell

• packages is a list of pairs (name, version)

• for some packages (python, R, …), you can use the with_packages fields to add some packages (numpy and matplotlib in the example above)

Then run mop:

nix run n4s#mop -- envs.yaml

mop will generate a flake.nix file that tries to match as best as it can the desired environments.

Notes and Warnings

• mop calls Nixhub under the hood to retrieve the correct nixpkgs commits

• you do want to call a nix formatter on the generated flake.nix!!

• for now, the with_packages supports fully python, and partially R

• it might require you to edit the flake.nix to fill up some sha256 or hash