nixos/nncp: refactor configuration merging

[ehmry]

The NNCP utilities have poor support for configuration merging so use jq and hjson-cli instead.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 24.11 Release Notes (or backporting 23.11 and 24.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

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[nagy]

You could make use of systemd.services.<name>.path to make the script itself a bit shorter, but this is just a stylistic preference.

https://search.nixos.org/options?channel=unstable&show=systemd.services.%3Cname%3E.path

Further, to remove the need for temporary files, you could utilize the implicit stdout of the for loop to merge everything in one go:

for file in *.hjson ; do hjson-cli -j "$file" ; done| jq --slurp add

This is untested.

[ehmry]

@nagy, yes that does work and it's much cleaner, thanks.