Gomod2nix: mkGoEnv unable to find Go command

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As a follow on to my previous post:

I’m attempting to use gomod2nix’s mkGoEnv to acquire the dependencies, but it fails with the following:

error: go.mod specified Go version 1.20, but no compatible Go attribute could be found.

The relevant code from gomod2nix seems to be:

  # Return a Go attribute and error out if the Go version is older than was specified in go.mod.
  selectGo = attrs: goMod: attrs.go or (if goMod == null then buildPackages.go else
  (
    let
      goVersion = goMod.go;
      goAttrs = lib.reverseList (builtins.filter
        (
          attr: lib.hasPrefix "go_" attr && lib.versionAtLeast buildPackages.${attr}.version goVersion
        )
        (lib.attrNames buildPackages));
      goAttr = elemAt goAttrs 0;
    in
    (
      if goAttrs != [ ]
      then buildPackages.${goAttr}
      else throw "go.mod specified Go version ${goVersion}, but no compatible Go attribute could be found."
    )
  ));

I attempted the following in nix repl:

nix-repl> :l <nixpkgs>
Added 19222 variables.

nix-repl> :t buildPackages
a set

nix-repl> lib.reverseList (builtins.filter (attr: lib.hasPrefix "go_" attr && lib.versionAtLeast buildPackages.${attr}.version "1.20")(lib.attrNames buildPackages))
[ "go_1_20" ]

It’s not clear to me why gomod2nix isn’t able to find Go.