Improved home-manager nix-locate configuration, with an auto-updated index and a better command-not-found handler

command-not-found.sh

# Adapted from https://github.com/bennofs/nix-index/blob/master/command-not-found.sh

command_not_found_handle () {
    if [ -n "${MC_SID-}" ] || ! [ -t 1 ]; then
        >&2 echo "$1: command not found"
        return 127
    fi

    echo -n "searching nix-index..."
    ATTRS=$(@nix-locate@ --minimal --no-group --type x --type s --top-level --whole-name --at-root "/bin/$1")

    case `echo -n "$ATTRS" | grep -c "^"` in
        0)
            >&2 echo -ne "$(@tput@ el1)\r"
            >&2 echo "$1: command not found"
            ;;
        *)
            >&2 echo -ne "$(@tput@ el1)\r"
            >&2 echo "The program ‘$(@tput@ setaf 4)$1$(@tput@ sgr0)’ is currently not installed."
            >&2 echo "It is provided by the following derivation(s):"
            while read ATTR; do
                ATTR=$(echo "$ATTR" | sed 's|\.out$||') # Strip trailing '.out'
                >&2 echo "  $(@tput@ setaf 12)nixpkgs#$(@tput@ setaf 4)$ATTR$(@tput@ sgr0)"
            done <<< "$ATTRS"
    esac

    return 127
}

command_not_found_handler () {
    command_not_found_handle $@
    return $?
}

default.nix

{ config, pkgs, lib, ... }:

let
  # Automatically download the latest index from Mic92's nix-index-database.
  nix-locate = pkgs.writeShellScriptBin "nix-locate" ''
    set -euo pipefail
    mkdir -p ~/.cache/nix-index && cd ~/.cache/nix-index
    # Check for updates at most once a day
    if [ ! -f last-check ] || [ $(find last-check -mtime +1) ]; then
      filename="index-x86_64-$(uname | tr A-Z a-z)"
      # Prevent partial downloads
      [ -f files ] || rm -f $filename
      rm -f files
      wget -q -N --show-progress \
        https://github.com/Mic92/nix-index-database/releases/latest/download/$filename
      ln -sf $filename files
      touch last-check
    fi
    exec ${pkgs.nix-index}/bin/nix-locate "$@"
  '';

  # Modified version of command-not-found.sh that uses our wrapped version of
  # nix-locate, makes the output a bit less noisy, and adds color!
  command-not-found = pkgs.runCommandLocal "command-not-found.sh" { } ''
    mkdir -p $out/etc/profile.d
    substitute ${./command-not-found.sh}                  \
      $out/etc/profile.d/command-not-found.sh             \
      --replace @nix-locate@ ${nix-locate}/bin/nix-locate \
      --replace @tput@ ${pkgs.ncurses}/bin/tput
  '';
in {
  programs.nix-index = {
    enable = true;
    package = pkgs.symlinkJoin {
      name = "nix-index";
      # Don't provide 'bin/nix-index', since the index is updated automatically
      # and it is easy to forget that. It can always be run manually with
      # 'nix run nixpkgs#nix-index' if necessary.
      paths = [ nix-locate command-not-found ];
    };
  };
}

FYI: there now is a NixOS/home-manager module in the repo