add flake-compat to flake.nix and use sha256 in default.nix

[sysedwinistrator]

Motivation

Make default.nix pure

Context

Forum thread
I have no idea why default.nix was used at all when referring to the package from a flake. However, as adding flake-compat to flake.nix is the way the its (and nix') author recommend using it, I don't see the harm of doing exactly that to ensure default.nix works when called in pure evaluation mode, even if few people actually need to do this.

Advantages:

• flake-compat is pinned and default.nix is pure

Disadvantages:

• flake-compat has to be updated manually by updating flake input

Checklist for maintainers

Maintainers: tick if completed or explain if not relevant

• agreed on idea
• agreed on implementation strategy
• tests, as appropriate
  • functional tests - tests/**.sh
  • unit tests - src/*/tests
  • integration tests - tests/nixos/*
• documentation in the manual
• code and comments are self-explanatory
• commit message explains why the change was made
• new feature or incompatible change: updated release notes

Priorities

Add 👍 to pull requests you find important.

[thufschmitt]

Thanks, that's very sensible, indeed 👍

[thufschmitt]

@sysedwinistrator any reason you marked this as a draft?

[sysedwinistrator]

@sysedwinistrator any reason you marked this as a draft?

I just opened the PR while trying to help someone on the forums, and it struck me as odd that out of all projects, Nix itself doesn't use flake-compat the way it's recommended in the repo, so I actually wanted to check first whether this isn't intentional (I don't want to break my favorite package manager, do I).
Since you already approved, I guess that's not the case 😄

[thufschmitt]

Ahah, makes sense! I think the main reason is that this got introduced without thinking about it too much, and for some reason no one got bitten by it yet ;)

Let's just merge it then!

[nixos-discourse]

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/use-a-custom-nix-on-a-flake-proyect/26065/5