/usr/share/bash-completion/completions/gapplication is in libglib2.0-bin 2.42.1-1+b1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54  | # Check for bash
[ -z "$BASH_VERSION" ] && return
####################################################################################################
__app() {
  case "${COMP_CWORD}" in
    1)
      COMPREPLY=($(compgen -W "help version list-apps launch action list-actions" -- "${COMP_WORDS[1]}"))
      return 0
      ;;
    2)
      case "${COMP_WORDS[1]}" in
        launch|action|list-actions)
          COMPREPLY=($(compgen -W "`gapplication list-apps`" -- "${COMP_WORDS[2]}"))
          return 0
          ;;
        *)
          COMPREPLY=()
          return 0
          ;;
      esac
      ;;
  esac
  # Otherwise, what we will do is based on the command in ${COMP_WORDS[1]}
  case "${COMP_WORDS[1]}" in
    action)
      # Word 3 is the action name.  This is the only one we can help with.
      if [ "${COMP_CWORD}" == 3 ]; then
        COMPREPLY=($(compgen -W "`gapplication list-actions "${COMP_WORDS[2]}"`" -- "${COMP_WORDS[3]}"))
        return 0
      else
        COMPREPLY=()
        return 0
      fi
      ;;
    launch)
      # Filenames...
      COMPREPLY=($(compgen -A file "${COMP_WORDS[COMP_CWORD]}"))
      return 0
      ;;
    *)
      # Nothing else should be out this far...
      COMPREPLY=()
      return 0
  esac
}
####################################################################################################
complete -F __app gapplication
 |