hooks/merged-usr/essential00.sh: avoid chroot in chrootless mode

hooks/merged-usr/essential00.sh

@@ -8,8 +8,20 @@ fi
 
 TARGET="$1"
 
-APT_CONFIG=$MMDEBSTRAP_APT_CONFIG apt-get --yes install -oDPkg::Chroot-Directory="$TARGET" usr-is-merged
-
-chroot "$TARGET" dpkg-query --showformat '${db:Status-Status}\n' --show usr-is-merged | grep -q '^installed$'
-chroot "$TARGET" dpkg-query --showformat '${Source}\n' --show usr-is-merged | grep -q '^usrmerge$'
-dpkg --compare-versions "1" "lt" "$(chroot "$TARGET" dpkg-query --showformat '${Version}\n' --show usr-is-merged)"
+if [ "${MMDEBSTRAP_MODE:-}" = "chrootless" ]; then
+	APT_CONFIG=$MMDEBSTRAP_APT_CONFIG apt-get --yes install \
+		-oDPkg::Options::=--force-not-root \
+		-oDPkg::Options::=--force-script-chrootless \
+		-oDPkg::Options::=--root="$TARGET" \
+		-oDPkg::Options::=--log="$TARGET/var/log/dpkg.log" \
+		usr-is-merged
+	export DPKG_ROOT="$TARGET"
+	dpkg-query --showformat '${db:Status-Status}\n' --show usr-is-merged | grep -q '^installed$'
+	dpkg-query --showformat '${Source}\n' --show usr-is-merged | grep -q '^usrmerge$'
+	dpkg --compare-versions "1" "lt" "$(dpkg-query --showformat '${Version}\n' --show usr-is-merged)"
+else
+	APT_CONFIG=$MMDEBSTRAP_APT_CONFIG apt-get --yes install -oDPkg::Chroot-Directory="$TARGET" usr-is-merged
+	chroot "$TARGET" dpkg-query --showformat '${db:Status-Status}\n' --show usr-is-merged | grep -q '^installed$'
+	chroot "$TARGET" dpkg-query --showformat '${Source}\n' --show usr-is-merged | grep -q '^usrmerge$'
+	dpkg --compare-versions "1" "lt" "$(chroot "$TARGET" dpkg-query --showformat '${Version}\n' --show usr-is-merged)"
+fi