A posteriori Nix shells

You have a dirty software environment and you want to get Nix shells with the same packages and versions.

Describe the different shells, packages, and desired versions in a YAML file:

- 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:

mop envs.yaml

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

• 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