/lib/partman/check.d/13encrypted_home_present is in ubiquity 2.10.16.
This file is owned by root:root, with mode 0o755.
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  | #! /bin/sh
# Look for an encrypted home directory.
. /lib/partman/lib/base.sh
working="$(mktemp -d)"
tmpl=user-setup/force-encrypt-home
db_set $tmpl false
for dev in $DEVICES/*; do
	[ -d "$dev" ] || continue
	cd $dev
	partitions=
	open_dialog PARTITIONS
	while { read_line num id size type fs path name; [ "$id" ]; }; do
		[ "$fs" != free ] || continue
		partitions="$partitions $id,$path"
	done
	close_dialog
	for part in $partitions; do
		id="${part%%,*}"
		path="${part#*,}"
		[ -f "$id/method" ] || continue
		[ ! -f "$id/format" ] || continue
		[ ! -f "$id/formatted" ] || continue
		[ -f "$id/acting_filesystem" ] || continue
		[ -f "$id/mountpoint" ] || continue
		mountpoint="$(cat "$id/mountpoint")"
		case $mountpoint in
		/|/home)
			mount "$path" "$working" 3>&-
			if [ "$mountpoint" = / ]; then
				dir="$working/home"
			else
				dir="$working"
			fi
			for d in "$dir"/*; do
				[ -e "$d/.ecryptfs" ] || [ -L "$d/.ecryptfs" ] || continue
				if ! db_set $tmpl true; then
					db_register debian-installer/dummy "$tmpl"
					db_set "$tmpl" true
					db_subst "$tmpl" ID "$tmpl"
				fi
				umount "$path"
				exit 0
			done
			umount "$working"
			;;
		esac
	done
done
exit 0
 |