add direnv setup

home/common/.direnvrc

@@ -0,0 +1,62 @@
+use_nix() {
+  local path="$(nix-instantiate --find-file nixpkgs)"
+
+  if [ -f "${path}/.version-suffix" ]; then
+    local version="$(< $path/.version-suffix)"
+  elif [ -f "${path}/.git" ]; then
+    local version="$(< $(< ${path}/.git/HEAD))"
+  fi
+
+  local cache=".direnv/cache-${version:-unknown}"
+
+  local update_drv=0
+  if [[ ! -e "$cache" ]] || \
+    [[ "$HOME/.direnvrc" -nt "$cache" ]] || \
+    [[ .envrc -nt "$cache" ]] || \
+    [[ default.nix -nt "$cache" ]] || \
+    [[ shell.nix -nt "$cache" ]];
+  then
+    [ -d .direnv ] || mkdir .direnv
+    nix-shell --show-trace --pure "$@" --run "\"$direnv\" dump bash" > "$cache"
+    update_drv=1
+  else
+    log_status using cached derivation
+  fi
+  local term_backup=$TERM path_backup=$PATH
+  if [ -n ${TMPDIR+x} ]; then
+    local tmp_backup=$TMPDIR
+  fi
+
+  eval "$(< $cache)"
+  export PATH=$PATH:$path_backup TERM=$term_backup TMPDIR=$tmp_backup
+  if [ -n ${tmp_backup+x} ]; then
+    export TMPDIR=${tmp_backup}
+  else
+    unset TMPDIR
+  fi
+
+  # `nix-shell --pure` sets invalid ssl certificate paths
+  if [ "${SSL_CERT_FILE:-}" = /no-cert-file.crt ]; then
+    unset SSL_CERT_FILE
+  fi
+  if [ "${NIX_SSL_CERT_FILE:-}" = /no-cert-file.crt ]; then
+    unset NIX_SSL_CERT_FILE
+  fi
+
+  # This part is based on https://discourse.nixos.org/t/what-is-the-best-dev-workflow-around-nix-shell/418/4
+  if [ "$out" ] && (( $update_drv )); then
+    local drv_link=".direnv/drv"
+    local drv="$(nix show-derivation $out | grep -E -o -m1 '/nix/store/.*.drv')"
+    local stripped_pwd=${PWD/\//}
+    local escaped_pwd=${stripped_pwd//-/--}
+    local escaped_pwd=${escaped_pwd//\//-}
+    ln -fs "$drv" "$drv_link"
+    ln -fs "$PWD/$drv_link" "/nix/var/nix/gcroots/per-user/$LOGNAME/$escaped_pwd"
+    log_status renewed cache and derivation link
+  fi
+
+  if [[ $# = 0 ]]; then
+    watch_file default.nix
+    watch_file shell.nix
+  fi
+}