nixpkgs is a treasure

Nix and NixOS continue to be the best way to manage and build software that I've found. Every project has a shell.nix file in the root where I can define the specific software needed to work on that project along with any necessary environment variables or $PATH modifications. I ran into an issue this week though where I needed an "old" version of Go (1.20) but the version had already been removed from nixpkgs. How can I pull in an "unlisted" version into my shell.nix?

It's actually pretty straightforward, utilize fetchTarball to pull in nixpkgs based on a commit where the version was present sometime in the past. You can mix that import in with regular/"current" packages with no issue like so:

{ pkgs ? import <nixpkgs> {} }:

let oldGo = import (builtins.fetchTarball {
    url = "https://github.com/NixOS/nixpkgs/archive/33c51330782cb486764eb598d5907b43dc87b4c2.tar.gz";
    sha256 = "sha256:0nflmpfp3pk704vhlvlgh5vgwl8qciqi18mcpl32k79qjziwmih8";
    }) {};
in 

pkgs.mkShell {
  buildInputs = [
    oldGo.go_1_20
    pkgs.gopls
    pkgs.nodejs_18
  ];
  
  hardeningDisable = [ "fortify" ];

  shellHook = ''
    mkdir -p .go .npm
    export GOPATH=$PWD/.go
    export NODE_PATH=$PWD/.npm
    export NPM_CONFIG_PREFIX=$NODE_PATH
    export PATH=$PWD/.yarn/sdks/typescript/bin:$PWD/.go/bin:$PATH:$NODE_PATH/bin
  '';
}

Notice I can reference the "nixpkgs" tarball/snapshot, oldGo, and pull in the version of Go I need?! nixpkgs is such a treasure trove of software, it's absolutely incredible!