improve maybe-* hook conditions

hooks/maybe-jessie-or-older/extract00.sh

@@ -2,15 +2,24 @@
 
 set -eu
 
-# if dpkg is new enough, do nothing
-# we cannot ask dpkg-query about the version because dpkg is only extracted
-# but not installed at this point
-dpkg_ver="$(chroot "$1" dpkg --version | grep --extended-regexp --only-matching '[0-9]+\.[0-9.]+')"
-if dpkg --compare-versions "$dpkg_ver" ge 1.17.11; then
-	echo "dpkg version $dpkg_ver is >= 1.17.11 -- not running jessie-or-older extract00 hook" >&2
+# we need to check the version of dpkg
+# since at this point packages are just extracted but not installed, we cannot use dpkg-query
+# since we want to support chrootless, we cannot run dpkg --version inside the chroot
+# to avoid this hook depending on dpkg-dev being installed, we do not parse the extracted changelog with dpkg-parsechangelog
+# we also want to avoid parsing the changelog because /usr/share/doc might've been added to dpkg --path-exclude
+# instead, we just ask apt about the latest version of dpkg it knows of
+# this should only fail in situations where there are multiple versions of dpkg in different suites
+ver=$(env --chdir="$1" APT_CONFIG="$MMDEBSTRAP_APT_CONFIG" apt-cache show --no-all-versions dpkg 2>/dev/null | sed -ne 's/^Version: \(.*\)$/\1/p' || printf '')
+if [ -z "$ver" ]; then
+	echo "no package called dpkg can be installed -- not running jessie-or-older extract00 hook" >&2
+	exit 0
+fi
+
+if dpkg --compare-versions "$ver" ge 1.17.11; then
+	echo "dpkg version $ver is >= 1.17.11 -- not running jessie-or-older extract00 hook" >&2
 	exit 0
 else
-	echo "dpkg version $dpkg_ver is << 1.17.11 -- running jessie-or-older extract00 hook" >&2
+	echo "dpkg version $ver is << 1.17.11 -- running jessie-or-older extract00 hook" >&2
 fi
 
 # resolve the script path using several methods in order:

hooks/maybe-jessie-or-older/extract01.sh

@@ -2,18 +2,44 @@
 
 set -eu
 
-# If the init package has not been extracted, then it is not part of the
-# Essential:yes set and we do not need this workaround. This holds true for the
-# init package version 1.34 and later. Instead of asking apt about the init
-# version (which might not be the same version that was picked to be installed)
-# we check for the presence of the init package by checking whether
-# /usr/share/doc/init/copyright exists.
-
-if [ -e "$1/usr/share/doc/init/copyright" ]; then
-	echo "the init package is not Essential:yes -- not running jessie-or-older extract01 hook" >&2
+# The jessie-or-older extract01 hook has to be run up to the point where the
+# Essential:yes field was removed from the init package (with
+# init-system-helpers 1.34). Since the essential packages have only been
+# extracted but not installed, we cannot use dpkg-query to find out its
+# version. Since /usr/share/doc might be missing due to dpkg --path-exclude, we
+# also cannot check whether /usr/share/doc/init/copyright exists. There also
+# was a time (before init-system-helpers 1.20) where there was no init package
+# at all where we also want to apply this hook. So we just ask apt about the
+# candidate version for init-system-helpers. This should only fail in
+# situations where there are multiple versions of init-system-helpers in
+# different suites.
+ver=$(env --chdir="$1" APT_CONFIG="$MMDEBSTRAP_APT_CONFIG" apt-cache show --no-all-versions init-system-helpers 2>/dev/null | sed -ne 's/^Version: \(.*\)$/\1/p' || printf '')
+if [ -z "$ver" ]; then
+	# there is no package called init-system-helpers, so either:
+	#  - this is so old that init-system-helpers didn't exist yet
+	#  - we are in a future where init-system-helpers doesn't exist anymore
+	#  - something strange is going on
+	# we should only call the hook in the first case
+	ver=$(env --chdir="$1" APT_CONFIG="$MMDEBSTRAP_APT_CONFIG" apt-cache show --no-all-versions base-files 2>/dev/null | sed -ne 's/^Version: \(.*\)$/\1/p' || printf '')
+	if [ -z "$ver" ]; then
+		echo "neither init-system-helpers nor base-files can be installed -- not running jessie-or-older extract01 hook" >&2
 		exit 0
+	fi
+
+	# Jessie is Debian 8
+	if dpkg --compare-versions "$ver" ge 8; then
+		echo "there is no init-system-helpers but base-files version $ver is >= 8 -- not running jessie-or-older extract01 hook" >&2
+		exit 0
+	else
+		echo "there is no init-system-helpers but base-files version $ver is << 8 -- running jessie-or-older extract01 hook" >&2
+	fi
 else
-	echo "the init package is Essential:yes -- running jessie-or-older extract01 hook" >&2
+	if dpkg --compare-versions "$ver" ge 1.34; then
+		echo "init-system-helpers version $ver is >= 1.34 -- not running jessie-or-older extract01 hook" >&2
+		exit 0
+	else
+		echo "init-system-helpers version $ver is << 1.34 -- running jessie-or-older extract01 hook" >&2
+	fi
 fi
 
 # resolve the script path using several methods in order:

hooks/maybe-merged-usr/essential00.sh

@@ -2,13 +2,24 @@
 
 set -eu
 
-# if the usr-is-merged package cannot be installed with apt, do nothing
-if ! env --chdir="$1" APT_CONFIG="$MMDEBSTRAP_APT_CONFIG" apt-cache show --no-all-versions usr-is-merged > /dev/null 2>&1; then
-	echo "no package called usr-is-merged found -- not running merged-usr essential hook" >&2
+ver=$(dpkg-query --root="$1" -f '${db:Status-Status} ${Source} ${Version}' --show usr-is-merged 2>/dev/null || printf '')
+case "$ver" in
+	'')
+		echo "no package called usr-is-merged is installed -- not running merged-usr essential hook" >&2
 		exit 0
-else
-	echo "package usr-is-merged found -- running merged-usr essential hook" >&2
-fi
+		;;
+	'installed mmdebstrap-dummy-usr-is-merged 1')
+		echo "dummy usr-is-merged package installed -- running merged-usr essential hook" >&2
+		;;
+	'installed usrmerge '*)
+		echo "usr-is-merged package from src:usrmerge installed -- not running merged-usr essential hook" >&2
+		exit 0
+		;;
+	*)
+		echo "unexpected situation for package usr-is-merged: $ver" >&2
+		exit 1
+		;;
+esac
 
 # resolve the script path using several methods in order:
 #  1. using dirname -- "$0"