Investigate replacing sort with nix eval

[bbenne10]

Nix ships with nix eval and builtins.compareVersions. Is there some reason we can't replace our version sorting/checks with this?

I think it'd be something like the following:

_require_version() {
  local cmd=$1 version=$2 required=$3
  if [ $(_nix eval --expr "builtins.compareVersions \"$required\" \"$version\"') = -1 ]; then
    _nix_direnv_error \
      "minimum required $(basename "$cmd") version is $required (installed: $version)"
    return 1
  fi

This should reduce our dependency on external tools (or maybe you can think of it as deepening our dependency on one we certainly can't remove?)

[Mic92]

Looks reasonable fast:

$ time nix eval --expr 'builtins.compareVersions "1.0.0" "2.0.0"'
nix eval --expr 'builtins.compareVersions "1.0.0" "2.0.0"'  0.01s user 0.01s system 99% cpu 0.017 total
$ time bash -c "echo '1.0.0' '2.0.0' | sort -C -V"
bash -c "echo '1.0.0' '2.0.0' | sort -C -V"  0.00s user 0.00s system 96% cpu 0.006 total

[Mic92]

Also we don't need to worry that much anymore. I think with the current flags, it works with coreutils/macOS/freebsd/openbsd/busybox/toybox.

[bbenne10]

I'm not particularly worried about this in the general sense. I happened to be poking in the nix builtins and nixpkgs.lib for unrelated reasons and stumbled on builtins.compareVersions. I may still put a PR together for this, just to explore it.