/usr/share/bash-completion/completions/chcpu is in util-linux 2.31.1-0.4ubuntu3.
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 55 56 57 58 59  | _chcpu_module()
{
	local cur prev OPTS
	COMPREPLY=()
	cur="${COMP_WORDS[COMP_CWORD]}"
	prev="${COMP_WORDS[COMP_CWORD-1]}"
	case $prev in
		'-e'|'--enable')
			local prefix realcur CPULIST_ALL CPULIST
			realcur="${cur##*,}"
			prefix="${cur%$realcur}"
			CPULIST_ALL=$(sed 's/^/{/; s/-/../g; s/,/} {/g; s/$/}/' /sys/devices/system/cpu/offline)
			for WORD in $(eval echo $CPULIST_ALL); do
				if ! [[ $prefix == *"$WORD"* ]]; then
					CPULIST="$WORD $CPULIST"
				fi
			done
			compopt -o nospace
			COMPREPLY=( $(compgen -P "$prefix" -W "$CPULIST" -S ',' -- $realcur) )
			return 0
			;;
		'-d'|'--disable')
			local prefix realcur CPULIST_ALL CPULIST
			realcur="${cur##*,}"
			prefix="${cur%$realcur}"
			CPULIST_ALL=$(sed 's/^/{/; s/-/../g; s/,/} {/g; s/$/}/' /sys/devices/system/cpu/online)
			for WORD in $(eval echo $CPULIST_ALL); do
				if ! [[ $prefix == *"$WORD"* ]]; then
					CPULIST="$WORD $CPULIST"
				fi
			done
			compopt -o nospace
			COMPREPLY=( $(compgen -P "$prefix" -W "$CPULIST" -S ',' -- $realcur) )
			return 0
			;;
		'-c'|'--configure'|'-g'|'--deconfigure')
			COMPREPLY=( $(compgen -W "cpu-list" -- $cur) )
			return 0
			;;
		'-p'|'--dispatch')
			COMPREPLY=( $(compgen -W "horizontal vertical" -- $cur) )
			return 0
			;;
		'-h'|'--help'|'-V'|'--version')
			return 0
			;;
	esac
	OPTS="--help
		--enable
		--disable
		--configure
		--deconfigure
		--dispatch
		--rescan
		--version"
	COMPREPLY=( $(compgen -W "${OPTS[*]}" -- $cur) )
	return 0
}
complete -F _chcpu_module chcpu
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