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https://github.com/wamserma/flake-programs-sqlite

A simple flake to automagically specify programs.sqlite for command-not-found.
https://github.com/wamserma/flake-programs-sqlite

flakes nix

Last synced: 3 months ago
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A simple flake to automagically specify programs.sqlite for command-not-found.

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# programs.sqlite for Nix Flake based systems



[![Update Channel Info](https://github.com/wamserma/flake-programs-sqlite/actions/workflows/scrape.yml/badge.svg?branch=main)](https://github.com/wamserma/flake-programs-sqlite/actions/workflows/scrape.yml)



## TL;DR



(assuming a flake similar to )



Add to `inputs` in `flake.nix`:



```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:



```nix

{

  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-db`to the inputs of your system configuration (`configuration.nix`)

and to the configuration itself add:



```nix

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](https://github.com/NixOS/nixpkgs/blob/7c44c865ee736afba33ee8788b59e4a123800437/nixos/modules/programs/command-not-found/command-not-found.pl)

  that is hooked into this handler when

  the option [`programs.command-not-found.enable`](https://search.nixos.org/options?show=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 



## How?



The channel page is regularly scraped for the revision and file hashes, then a

[lookup table](./sources.json) 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



```sh

[ -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](https://github.com/bennofs/nix-index#usage-as-a-command-not-found-replacement)



## 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.