/etc/bash_completion.d/devscripts.chdist is in devscripts 2.14.1.
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  | have chdist &&
_chdist ()
{
  local cur=$2 prev=$3
  local options='--help -h --data-dir -d --arch -a'
  local commands='create apt-get apt-cache apt-rdepends
           src2bin bin2src
	   compare-packages compare-bin-packages
	   compare-versions compare-bin-versions
	   grep-dctrl-packages grep-dctrl-sources
	   list'
  local archs='i386 amd64 powerpc m68k sparc alpha hppa arm mips mipsel ia64 armel s390 ppc64 sh armeb m32r'
  local dists=$(ls $HOME/.chdist 2>/dev/null)
  COMPREPLY=()
  case "$prev" in
     -@(-arch|a))
        COMPREPLY=( $( compgen -W "$archs" -- $cur ) )
        return 0
      ;;
     -@(-data-dir|d))
        _filedir
        return 0
     ;;
    -@(-help|h)|list)
        return 0
    ;;
    create|apt-get|apt-cache|apt-rdepends|src2bin|bin2src|compare-packages|compare-bin-packages|compare-versions|compare-bin-versions|grep-dctrl-packages|grep-dctrl-sources)
        COMPREPLY=( $( compgen -W "$dists" -- $cur ) )
	return 0
  esac
  if [[ "$cur" == -* ]]; then
    # return one of the possible options
    COMPREPLY=( $( compgen -W "$options" -- $cur ) )
  else
    # return one of the possible commands
    COMPREPLY=( $( compgen -W "$commands" -- $cur ) )
  fi
  return 0
}
[ -n "${have:-}" ] && complete -F _chdist $filenames chdist
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