flake: remove redundant transitive dependencies

[jeremyschlatter]

I added the github:tweag/nickel flake to a project today and noticed that it pulled in a bunch of redundant transitive dependencies. This commit cleans those up. The impact is visible in the lock file, which now has 13 fewer nodes:

nickel on master fsh ❯ python -c 'import json; print(len(json.load(open("flake.lock"))["nodes"]))'
29

nickel on flake-inputs fsh ❯ python -c 'import json; print(len(json.load(open("flake.lock"))["nodes"]))'
16

Things done:

• added several more follows relationships for de-duplication

• updated to latest rust-overlay flake which drops flake-utils dependency

• set follows = "" for a few unused dependencies. See null flake input NixOS/nix#7807.

[yannham]

Thanks, it does trim the flake.lock quite a bit.

What do you think about NixOS/nix#7807 (comment), related to follows = ""? I'm a bit reluctant with those kind of hacks, because if somebody else has to handle a CI breakage (say, upon a flake.lock update) and don't know about it, it can turn out to be painful.

[jeremyschlatter]

I was conflicted about it. I think it's quite reasonable to not use follows = "" for that reason. I pushed a commit that removes it. You can see the diff here: 43125b5

[yannham]

@jeremyschlatter Thanks. I believe there's still one empty follows for the flake-compat input of pre-commit-hooks.

[jeremyschlatter]

@yannham Whoops, thanks for catching that. Fixed.

[yannham]

I'm taking over here. There are unrelated clippy failures (this change induced a flake.lock update, and the rustc version was bumped, which made clippy more restrictive), and some of them (e.g. the transmute) aren't trivial to fix.