Add a nix shell

[rossabaker]

Like http4s/http4s#3005, but particularly useful here, where a newer JDK is required.

[ChristopherDavenport]

What does this do for us nix novices?

[rossabaker]

If I run nix-shell from this directory, I am dropped into a bash session that has an SBT that runs on JDK11, regardless of what sbt or java (if any) is globally installed on the system. All dependencies required to build the project, including the documentation, are available within this shell, at a consistent revision as pinned by nixpkgs-version.json.

The .envrc file is a direnv integration that makes this happen without an explicit call into nix-shell. If I cd into this directory, or open any of its files in my editor, I have a fully configured development environment for this project. If I cd into the core repo after http4s/http4s#3005, I get JDK8 and the hugo we need to build the site.

[amesgen]

I don't use nix (apart from GHCJS experiments), do you still want to get this merged? @rossabaker

[rossabaker]

I have a gitignored version. I find it particularly useful on this project, because it's the only one I use on Java 11. I'll refresh it with an updated version, but if it doesn't bother you, I'd appreciate having it around.

[amesgen]

Actually, I have been converted to NixOS recently, and I would love to nixify this repo! Do you think the setup in typelevel/case-insensitive#210 is still a playground, or can we adopt it also here (I can prepare a PR)?

[rossabaker]

I think it would be great to add it. It's particularly useful on this repo, which requires JDK 11, which is awkwardly between the 8 of Scala or the 17 that's current.

I'm experimenting on my personal config with workflows to automate flake updates, but as a baseline, what's merged on case-insensitive is good. Note that I'm assuming flakes.

[amesgen]

Superseded by #556