Tooling for the simple-package-paths Nix RFC

Implementation

• Index the tree for references. If .git exists, use ls-tree equivalent
• Check the validity of the pkgs/unit directory
  • Should only contain correctly-named subdirectories
    • Not needed, Nix evaluation can check that (but only enabled in CI for performance)
  • Shouldn't reference files outside, neither be referenced from outside
• all-packages.nix, aliases.nix and unit directories are non-intersecting
  • Not needed, Nix evaluation can check that (but only enabled in CI for performance)
• Loop through all definitions in all-packages.nix
  • If the definition could be migrated:
    • If --mode=migrate, migrate the code, output a message
    • If --mode=warn, output a warning message only
      • If in GitHub Actions, create a code annotation
    • If --mode=error, output an error message, fail at the end
      • If in GitHub Actions, create a code annotation

Perhaps create code annotations only when they're in a file that's changed by the PR