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Devenv Configuration

This project uses devenv.sh as a convenient and more intuitive wrapper around Nix which still provides us with the same level of control and reproducibility over the software environment. You can find an API reference and various guides on their docs website.

Config Files

The configuration can be found in several places: - devenv.nix, devenv.yaml in the project root - The contents of the nix/ folder in the repository - Various default.nix package definition and overlay.nix files placed near relevant code

Main Config Files

The devenv.yaml configures devenv itself and defines the nixpkgs inputs (similar to flake.nix inputs) used by the environment. Moreover, in this project, devenv.nix is intended to only contain configuration that applies to the entire system (for example, importing overlays). Instead of putting configuration into the main devenv.nix environment, everything is abstracted into a profile, allowing easy isolation of tech stacks.

The nix/ Folder

This folder is where most of the Nix-related code is organised, based on the file tree here: 

nix
├── extra-packages # (1)!
│   ├── colcon
│   │   └── colcon plugins and patches
│   ├── patches
│   │   └── manually patched packages
│   └── ros-packages
│       └── auto generated with nix2ros
├── machines # (2)!
│   └── home
│       └── home-manager Nix config
├── profiles # (3)!
│   └── profile-name.nix
├── overlays.nix # (4)!
├── profiles.nix # (5)!
├── ros-workspace.nix # (6)!
├── scripts.nix # (7)!
└── treefmt.nix # (8)!

  1. All the Nix packages that we maintain or patch live in here. At the time of writing, this includes the ROS2 packages that we develop for Perseus, along with some patches/plugins for colcon and third-party ROS2 packages.
  2. Machines refers to the compute units that we configure using home-manager.
  3. Each profile is defined in its own file, which can be found in this folder.
  4. This is the main overlay.nix, which is imported by devenv, connecting it to the overlay tree in the repository.
  5. Similar to the overlay.nix file above, profiles.nix imports all the profile files.
  6. Some shared logic for setting up ROS2 environments has been abstracted here from the dev and prod profiles.
  7. Wraps the scripts so they can be executed as a terminal command anywhere inside the devenv shell.
  8. Configuration for the treefmt formatter.

Other Files

The remaining config files take two forms:

  • Nix package derivations for native and shared software
  • Nix overlays

These files are scattered throughout the codebase because it makes more organisational sense to place them next to the code they relate to. Nix overlays can be somewhat confusing at first, but in essence, they add our packages to nixpkgs and modify existing packages in nixpkgs.

Devenv Maintenance

Most of the maintenance required to keep the devenv environment running smoothly is periodically running devenv gc to delete unused builds and save disk space. Running devenv update to update the lock file should only be done by someone with a good understanding of the whole repository, as it may potentially break dependencies.