Add nix flake

[tirimia]

This PR enables building lychee via nix flake by simply running nix build.
Simultaneously, nix develop will open a shell with the environment required to build and develop it.

[mre]

@thomas-zahner, @niklaskorz, any thoughts?

[thomas-zahner]

@tirimia Did you see #1565? It's pretty much a duplicate of this PR. The main difference is that with my PR I didn't have nix build in mind. I do like the idea, so eventually we could use Nix to build in CI.

Is it possible to easily specify the Rust version in this flake? If not I would probably prefer my approach.

[tirimia]

That’s the beauty of using the fenix flake and reading the toolchain configuration, that’s already taken care of and we then also know we provision rust like the non-nix users of the repo 🥳

In general though, I personally avoid thinking of the specific version of software when working with nix as it’s rolling release and if I need something specific, importing a pinned version of nixpkgs is still an open option.

A further advantage of this PR is that people can reference this flake and use lychee without having to figure out how to build it on their own. You can also directly call it with nix run github:lycheeverse/lychee

[thomas-zahner]

@tirimia Ah I see, thanks for the clarification. I agree that this is probably the better approach. Does this mean that nixpkgs could simply reference our flake?

[thomas-zahner]

Also would you mind if we add an .envrc file to the project, as in my PR?
Sorry if my questions seem weird or stupid, I'm quite new to Nix 😅

[tirimia]

@tirimia Ah I see, thanks for the clarification. I agree that this is probably the better approach. Does this mean that nixpkgs could simply reference our flake?

Nixpkgs offers a reference to its packages via flakes as a convenience; flakes are not “officially” stable.

You can, however, reference this flake in your own or in the command line

[tirimia]

Also would you mind if we add an .envrc file to the project, as in my PR? Sorry if my questions seem weird or stupid, I'm quite new to Nix 😅

I would avoid that. Direnv docs recommend you add .envrc and .direnv to your global git ignore. Committing it forces people to use the flake if they use direnv, and it also prevents people from having their own configuration

As for the “stupid” questions: nix is a beast, the craft of tech is impossible to master in its entirety. Don’t judge yourself for not knowing things, enjoy that you get to learn 💃

[niklaskorz]

Also would you mind if we add an .envrc file to the project, as in my PR? Sorry if my questions seem weird or stupid, I'm quite new to Nix 😅

I would avoid that. Direnv docs recommend you add .envrc and .direnv to your global git ignore. Committing it forces people to use the flake if they use direnv, and it also prevents people from having their own configuration

As for the “stupid” questions: nix is a beast, the craft of tech is impossible to master in its entirety. Don’t judge yourself for not knowing things, enjoy that you get to learn 💃

As for .direnv, yes, that should be gitignored. But it's common practice to track the .envrc.

[thomas-zahner]

@tirimia @niklaskorz thank you for the answers and improvements. The flake now targets my platform but it still does not build because of the pinned SHA which is not the same on my platform. With the current version I get a mismatch: error: hash mismatch in fixed-output derivation.

We can't simply remove the argument because it seems to be required: error: in pure evaluation mode, 'fetchurl' requires a 'sha256'.

When an empty string is provided or if nixpkgs.lib.fakeSha256 is used, the following error will occur

       error: hash mismatch in fixed-output derivation ...:
         specified: sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=
            got:    sha256-s1RPtyvDGJaX/BisLT+ifVfuhDT1nZkZ1NcK8sbwELM=

So now I see two possibilities:

• Specify the hashes for every single platform. But I'm not sure if this is possible or if this makes sense as it seems quite cumbersome.
• Just switch to rust-overlay as in my PR