/usr/share/bash-completion/completions/lsblk is in util-linux 2.25.2-6.
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 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77  | _lsblk_module()
{
	local cur prev OPTS
	COMPREPLY=()
	cur="${COMP_WORDS[COMP_CWORD]}"
	prev="${COMP_WORDS[COMP_CWORD-1]}"
	LSBLK_COLS="NAME KNAME MAJ:MIN FSTYPE MOUNTPOINT
		LABEL UUID PARTTYPE PARTLABEL PARTUUID PARTFLAGS
		RA RO RM
		MODEL SIZE STATE OWNER GROUP MODE
		ALIGNMENT MIN-IO OPT-IO PHY-SEC LOG-SEC
		ROTA SCHED RQ-SIZE TYPE DISC-ALN
		DISC-GRAN DISC-MAX DISC-ZERO WSAME WWN
		RAND PKNAME HCTL TRAN REV VENDOR"
	case $prev in
		'-e'|'--exclude'|'-I'|'--include')
			local MAJOR I J
			MAJOR=''
			for I in /sys/dev/block/*; do
				J=${I##*/}
				MAJOR="$MAJOR ${J%%:*}"
			done
			# FIXME: how to append to a string with compgen?
			compopt -o nospace
			COMPREPLY=( $(compgen -W "$MAJOR" -S ',' -- $cur) )
			return 0
			;;
		'-o'|'--output')
			# FIXME: how to append to a string with compgen?
			compopt -o nospace
			COMPREPLY=( $(compgen -W "$LSBLK_COLS" -S ',' -- $cur) )
			return 0
			;;
		'-x'|'--sort')
			compopt -o nospace
			COMPREPLY=( $(compgen -W "$LSBLK_COLS"  -- $cur) )
			return 0
			;;
		'-h'|'--help'|'-V'|'--version')
			return 0
			;;
	esac
	case $cur in
		-*)
			OPTS="--all
				--bytes
				--nodeps
				--discard
				--exclude
				--fs
				--help
				--include
				--ascii
				--list
				--perms
				--noheadings
				--output
				--pairs
				--raw
				--inverse
				--topology
				--scsi
				--sort
				--help
				--version"
			COMPREPLY=( $(compgen -W "${OPTS[*]}" -- $cur) )
			return 0
			;;
	esac
	local DEVS
	DEVS=''; while read dev; do DEVS+="$dev " ; done < <(lsblk -pnro name)
	COMPREPLY=( $(compgen -W "$DEVS" -- $cur) )
	return 0
}
complete -F _lsblk_module lsblk
 |