.direnvrc

#!/bin/bash
#
#     Cache nix-shell environment
#
#         - watch all *.nix files, ~/.direnvrc and .envrc
#         - based on https://github.com/direnv/direnv/wiki/Nix
#
use_nix() {
  local cache_dir="$HOME/.cache/direnv/$(pwd)"
  mkdir -p "$cache_dir"
  local files="$HOME/.direnvrc .envrc *.nix"
  local cache="$cache_dir/direnv.$(nix-instantiate *.nix | shasum -a 256 | head -c 16)"
  local redo=false

  if ! test -e "$cache"; then
    echo "nix-instantiate returned new value."
    redo=true
  else
    for f in $files; do
        if test $f -nt "$cache"; then
            echo "File $f is newer than cache."
            redo=true
            continue
        fi
    done
  fi

  if $redo; then
    local tmp="$(mktemp "${cache}.tmp-XXXXXXXX")"
    trap "rm -rf '$tmp'" EXIT
    nix-shell --show-trace "$@" --run 'direnv dump' > "$tmp" && \
    mv "$tmp" "$cache"
  else
    echo "Using cached direnv."
  fi
  direnv_load cat "$cache"
  if [[ $# = 0 ]]; then
    for f in $files; do
        watch_file $f
    done
  fi
}

# GistId: 0ac310801f23e329d9714c505d91cfb3

Fix for picking up unwanted *.nix files (build tools, etc) https://gist.github.com/lionello/4ba29a03c128fefdf3ed52d5e7d5ac4c