programs.sqlite for Nix Flake based systems

TL;DR

(assuming a flake similar to https://nixos.wiki/wiki/Flakes#Using_nix_flakes_with_NixOS)

Add to inputs in flake.nix:

flake-programs-sqlite.url = "github:wamserma/flake-programs-sqlite";
flake-programs-sqlite.inputs.nixpkgs.follows = "nixpkgs";

Then just add the module.

NixOS module

Usage with a minimal system flake:

{
  inputs.nixpkgs.url = github:NixOS/nixpkgs/nixos-22.11;
  inputs.flake-programs-sqlite.url = "github:wamserma/flake-programs-sqlite";
  inputs.flake-programs-sqlite.inputs.nixpkgs.follows = "nixpkgs";

  outputs = inputs@{ self, nixpkgs, ... }: {

    nixosConfigurations.mymachine = nixpkgs.lib.nixosSystem {
      system = "x86_64-linux";
      modules =
        [
          (import configuration.nix)
          inputs.flake-programs-sqlite.nixosModules.programs-sqlite
        ];
    };
  };
}

The module's functionality is enabled as soon as the module is imported.

alternative: without using a module

Add flake-programs-sqlite to the arguments of the flake's outputs function.

Add programs-sqlite-db = flake-programs-sqlite.packages.${system}.programs-sqlite to the specialArgs argument of lib.nixosSystem.

Add programs-sqlite-dbto the inputs of your system configuration (configuration.nix) and to the configuration itself add:

programs.command-not-found.dbPath = programs-sqlite-db;

Why?

NixOS systems configured with flakes and thus lacking channels usually have a broken command-not-found. The reason is that the backing database programs.sqlite is only available on channels. The problem is that the channel URL can not be determined from the nixpkgs revision alone, as it also contains a build number.

command-not-what?

Bash and other shells have a special handler that is invoked when an unknown command is issued to the shell. For bash this is command_not_found_handler.

command-not-found is a Perl script that is hooked into this handler when the option programs.command-not-found.enable is set to true. This perl script evaluates a pre-made database to suggest packages that might be able to provide the command.

The pre-made database is generated as part of a channel, hence pure-flake-systems do not have access to it. This flake extracts the database from the channels and passes it to the command-not-found script to restore functionality that was previously only available when using channels.

This is an attempt to provide a usable solution, motivated by https://discourse.nixos.org/t/how-to-specify-programs-sqlite-for-command-not-found-from-flakes/22722/3

How?

The channel page is regularly scraped for the revision and file hashes, then a lookup table from revisions to URL and hashes is amended with any new information. The lookup table is used to create a fixed-output-derivation (FOD) for programs.sqlite based on the revision of nixpkgs passed as input of this flake.

Usage

see TL:DR above

Development

The flake provides a minimal devshell, but hacking on the code with a editor and running nix run .#updater is valid, too.

Development happens on the tooling branch, which is then merged into the main branch. Updates to the JSON file go directly to main. Releases of the tooling are also cut from the tooling branch. There are no releases for the JSON files.

Fetching selected channel revisions

e.g. to fetch info for older revisions/releases from before this project was started

[ -f sources.json ] || echo {} > sources.json
nix run github:wamserma/flake-programs-sqlite#updater -- --dir:. --channel:https://releases.nixos.org/nixos/20.03/nixos-20.03.2400.ff1b66eaea4

Multiple channels/revisions may be passed for a single run.
If no channel is given, the current channels are guessed and their latest revisions are fetched.

Alternatives

• nix-index

Licensing

The Nim code to scrape the metadata is released under MIT License.
The Nix code to provide the FODs is released under MIT License.
The database itself (JSON) is public domain.