Generated flake.nix for a go project doesn't work: error: undefined variable 'go_1_20'

[matta]

I am following zero-to-nix and tried running fh in a simple go project. The generated flake doesn't work. I am a complete newbie, so I'm not sure how to debug the problem.

The generated flake.nix and flake.lock are:

# This flake was initially generated by fh, the CLI for FlakeHub (version 0.1.10)
{
  # A helpful description of your flake
  description = "rfc20.org website";

  # Flake inputs
  inputs = {
    flake-schemas.url = "https://flakehub.com/f/DeterminateSystems/flake-schemas/*.tar.gz";

    nixpkgs.url = "https://flakehub.com/f/NixOS/nixpkgs/*.tar.gz";
  };

  # Flake outputs that other flakes can use
  outputs = { self, flake-schemas, nixpkgs }:
    let
      # Helpers for producing system-specific outputs
      supportedSystems = [ "x86_64-linux" "aarch64-darwin" "x86_64-darwin" "aarch64-linux" ];
      forEachSupportedSystem = f: nixpkgs.lib.genAttrs supportedSystems (system: f {
        pkgs = import nixpkgs { inherit system; };
      });
    in {
      # Schemas tell Nix about the structure of your flake's outputs
      schemas = flake-schemas.schemas;

      # Development environments
      devShells = forEachSupportedSystem ({ pkgs }: {
        default = pkgs.mkShell {
          # Pinned packages available in the environment
          packages = with pkgs; [
            go_1_20
            nixpkgs-fmt
          ];
        };
      });
    };
}

{
  "nodes": {
    "flake-schemas": {
      "locked": {
        "lastModified": 1721999734,
        "narHash": "sha256-G5CxYeJVm4lcEtaO87LKzOsVnWeTcHGKbKxNamNWgOw=",
        "rev": "0a5c42297d870156d9c57d8f99e476b738dcd982",
        "revCount": 75,
        "type": "tarball",
        "url": "https://api.flakehub.com/f/pinned/DeterminateSystems/flake-schemas/0.1.5/0190ef2f-61e0-794b-ba14-e82f225e55e6/source.tar.gz"
      },
      "original": {
        "type": "tarball",
        "url": "https://flakehub.com/f/DeterminateSystems/flake-schemas/%2A.tar.gz"
      }
    },
    "nixpkgs": {
      "locked": {
        "lastModified": 1722087241,
        "narHash": "sha256-2ShmEaFi0kJVOEEu5gmlykN5dwjWYWYUJmlRTvZQRpU=",
        "rev": "8c50662509100d53229d4be607f1a3a31157fa12",
        "revCount": 633516,
        "type": "tarball",
        "url": "https://api.flakehub.com/f/pinned/NixOS/nixpkgs/0.2405.633516%2Brev-8c50662509100d53229d4be607f1a3a31157fa12/0190f691-c019-7d99-b723-4b2dd6dfd38f/source.tar.gz"
      },
      "original": {
        "type": "tarball",
        "url": "https://flakehub.com/f/NixOS/nixpkgs/%2A.tar.gz"
      }
    },
    "root": {
      "inputs": {
        "flake-schemas": "flake-schemas",
        "nixpkgs": "nixpkgs"
      }
    }
  },
  "root": "root",
  "version": 7
}

The output of 'nix develop' is:

% nix develop
error:
       … while calling the 'derivationStrict' builtin
         at <nix/derivation-internal.nix>:9:12:
            8|
            9|   strict = derivationStrict drvAttrs;
             |            ^
           10|

       … while evaluating derivation 'nix-shell'
         whose name attribute is located at /nix/store/d6533m6b80n3c9lia5kvaz59ad3fynwk-source/pkgs/stdenv/generic/make-derivation.nix:333:7

       … while evaluating attribute 'nativeBuildInputs' of derivation 'nix-shell'
         at /nix/store/d6533m6b80n3c9lia5kvaz59ad3fynwk-source/pkgs/stdenv/generic/make-derivation.nix:377:7:
          376|       depsBuildBuild              = elemAt (elemAt dependencies 0) 0;
          377|       nativeBuildInputs           = elemAt (elemAt dependencies 0) 1;
             |       ^
          378|       depsBuildTarget             = elemAt (elemAt dependencies 0) 2;

       (stack trace truncated; use '--show-trace' to show the full, detailed trace)

       error: undefined variable 'go_1_20'
       at /nix/store/n6zxrknnddqz7hk4z8mijbzia23i43bc-source/flake.nix:30:13:
           29|           packages = with pkgs; [
           30|             go_1_20
             |             ^
           31|             nixpkgs-fmt

[matta]

I suppose the cool thing about flakes is that the repro is now available at:

nix develop "github:matta/rfc20?rev=7e841a805579a41d2677667cb2b76b05e2f554d5"

[cole-h]

You could try replacing go_1_20 with go_1_21, go_1_22, or go_1_23. go_1_20 was removed because it is EOL.