document finding unpersisted files

[KiaraGrouwstra]

hi there,
i feel like one challenge in using impermanence has been to figure out what state needs persisting.

for example, given persist dirs like /persist/home/$USER (and in my case a disko LUKS partition on disk main), i tried to answer that question using a script like:

# list-ephemeral.sh
# usage example: sh list-ephemeral.sh $HOME | $PAGER
user="$(whoami)"
DIR="${1:-$HOME}"
enquote_pattern="s@\(.*\)@-path '\1' -prune -o@g"
prepend_pattern="s@\(.*\)@-path '$HOME/\1' -prune -o@g"

system_global_dirs=$(nix eval ".#nixosConfigurations.default.config.environment.persistence.\"/persist\".directories" --json | jq -r '.[].dirPath' | sed "$enquote_pattern")
system_global_files=$(nix eval ".#nixosConfigurations.default.config.environment.persistence.\"/persist\".files" --json | jq -r '.[].filePath' | sed "$enquote_pattern")
system_user_dirs=$(nix eval ".#nixosConfigurations.default.config.environment.persistence.\"/persist\".users.$user.directories" --json | jq -r '.[].dirPath' | sed "$enquote_pattern")
system_user_files=$(nix eval ".#nixosConfigurations.default.config.environment.persistence.\"/persist\".users.$user.files" --json | jq -r '.[].filePath' | sed "$enquote_pattern")
home_dirs=$(nix eval ".#nixosConfigurations.default.config.home-manager.users.$user.home.persistence.\"/persist/home/$user\".directories" --json | jq -r '.[]' | sed "$prepend_pattern")
home_files=$(nix eval ".#nixosConfigurations.default.config.home-manager.users.$user.home.persistence.\"/persist/home/$user\".files" --json | jq -r '.[]' | sed "$prepend_pattern")
disk_subvolumes=$(nix eval ".#nixosConfigurations.default.config.disko.devices.disk.\"main\".content.partitions.luks.content.content.subvolumes" --json | jq -r '.[].mountpoint | select(. != "/")' | sed "$enquote_pattern")

cmd="find '$DIR' \
      $system_global_dirs \
      $system_global_files \
      $system_user_dirs \
      $system_user_files \
      $home_dirs \
      $home_files \
      $disk_subvolumes \
  -type f -printf '%p\\n'"

# shellcheck disable=SC2086
eval $cmd