command-not-found: drop perl dependency

[Mic92]

Faster startup and remove some perl packages from the default nixos closure.
Eventually we could remove perl completely from the default nixos closure.
It now also uses nix run when NIX_AUTO_RUN is set.

Motivation for this change

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nix-review --run "nix-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

Notify maintainers

cc @

[Mic92]

I tested export NIX_AUTO_INSTALL=1, export NIX_AUTO_RUN=1 and without any of those.

[Mic92]

Is nixpkgs. correct here or should it be nixos.?

[edolstra]

nixpkgs., however it will become nixpkgs# in the future.

[bjornfor]

Small typo in commit subject.

[Mic92]

fixed

[edolstra]

This to me is not really an improvement: it replaces a 51-line Perl script with a 141-line C++ program. As an aside, if we really want to get rid of Perl, then Rust is the way to go IMHO.

BTW, I think we can get rid of the auto-install feature, it was added as a bit of a joke and nobody uses it.

[edolstra]

nix run should be avoided, it's experimental and won't work in Nix 2.4 unless you pass --experimental-features nix-command.

[Mic92]

@edolstra is this going away in future or when does it become stable?

[bjornfor]

FYI, nix run is used a few places in nixpkgs (and the manual) already.

[Mic92]

Not only nix run also nix copy and nix build (for example in the installer).

[edolstra]

Yeah, we should replace those by nix-build etc. (or add --experimental-features nix-command to those invocations, but that's tricky because it could override the user's experimental-features setting).

[edolstra]

BTW, maybe we should get rid of NIX_AUTO_RUN as well, automatically downloading/running binaries is not a very secure thing to do...

[Mic92]

Let's say not safe instead of secure.

[edolstra]

These char * are a bit unidiomatic C++ IMHO.

[edolstra]

These are unnecessary, compilation will fail anyway if they're not defined.

[Mic92]

This to me is not really an improvement: it replaces a 51-line Perl script with a 141-line C++ program. As an aside, if we really want to get rid of Perl, then Rust is the way to go IMHO.

BTW, I think we can get rid of the auto-install feature, it was added as a bit of a joke and nobody uses it.

I choose C++:

• because it was proposed here: [WIP] Port switch-to-configuration script to Python #48378 (comment)
• it was accepted here: nixos-option C++ rewrite with --all #68193
• the sqlite interface is already in C, which made the building part quite simple and avoids having to cross-compile rust, when cross-compiling NixOS.

I am not sure the Rust version would be much shorter. The C++ is now 99 lines compared to 55 lines Perl. But it also generates more error messages and starts faster.
I guess I just wait for nix run to become stable - it is better suited for this use case since nix-shell exports all tons of unneeded environment variables and takes more time to execute as it spawns a shell with setup hooks.

[Mic92]

Old closure size: 82.9M
New closure size: 33.6M

New one is faster but it probably hardly matters:

Old:

$ time command-not-found sqlite3
0.03s user 0.00s system 98% cpu 0.034 total

New:

$ time command-not-found sqlite3
0.00s user 0.00s system 87% cpu 0.004 total

The C++ program is now +28 lines longer.

Does this looks fine now?

[bjornfor]

-1 on removing NIX_AUTO_INSTALL, since I'm using it. Or at least remove it in a separate PR with a release note entry.

[Mic92]

I am fine with whatever the consensus is.

[doronbehar]

BTW for the record, nix-index (Rust written) has a database and a "command-not-found" shell function which can be used:

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

Though from my experience it feels somewhat slower to that of the original command-not-found implementation.

[Mic92]

There is also a rust version alternative: #88517