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mononix/Mononix/Nix Flakes.md

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3 part tutorial by Eelco Dolstra

  • solves the problem where build inputs are dependent on environment variables, the nix channels, and so forth. These are inconsistent across systems.
  • no standard way to compose nix projects
  • packages can provide their own flake.nix file
    • nix shell github:edolstra/dwarffs --command dwarffs --version
  • flakes must declare dependencies, and dependencies must be locked to specific versions
  • nix flake metadata will show the flake's dependencies
  • nix flake show will show all of the outputs
  • defaultPackage.<system> must be a derivation
  • flakes are specified with a URL-like syntax: github:edolstra/dwarffs or git+https://github.com/NixOS/patchelf. The flake registery maps symbolic identifiers to actual locations. nixpkgs is equivalent to github:NixOS/nixpkgs.
  • Registry can be locally overridden: nix registry add nixpkgs ~/my-nixpkgs

Flake structure:

  • description -- string
  • inputs -- dictionary which declares all inputs
    • inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-20.03";
  • outputs -- function which takes all of the inputs and produces a result
    • `outputs = { self, nixpkgs }: { }``
    • defaultPackage.<system>
    • devShell.<system>
    • packages.<system>

All of the so-called "trivial" builders are built on the assumption that a project will be built separately, and that every project lives at the root of the repo. This actually can't work in my case because I do use monorepos and put many crates into a project, and don't necessarily publish all of them to crates.io.