Preserve apt preferences created by any package we install (i.e. ubuntu-advantage-tools) against live-build's attempt to delete them. (LP: #1855354)

debian/changelog

@@ -1,3 +1,11 @@
+livecd-rootfs (2.408.57) UNRELEASED; urgency=medium
+
+  * Preserve apt preferences created by any package we install (i.e.
+    ubuntu-advantage-tools) against live-build's attempt to delete them.
+    (LP: #1855354)
+
+ -- Michael Hudson-Doyle <michael.hudson@ubuntu.com>  Thu, 19 Dec 2019 15:43:56 +1300
+
 livecd-rootfs (2.408.56) xenial; urgency=medium
 
   * Backport enabling of adding extra snaps to ubuntu-core images via the

live-build/auto/build

@@ -220,6 +220,12 @@ EOF
 
 	lb chroot "$@"
 
+	if [ -d chroot/etc/apt/preferences.d.save ]; then
+		# https://twitter.com/infinite_scream
+		mv chroot/etc/apt/preferences.d.save/* chroot/etc/apt/preferences.d/
+		rmdir chroot/etc/apt/preferences.d.save
+	fi
+
 	if [ "${SUBPROJECT:-}" = minimized ]; then
 		# and if initramfs-tools was configured before our kernel,
 		# /etc/kernel/postinst.d/initramfs-tools will have created

live-build/auto/config

@@ -875,6 +875,19 @@ EOF
 		;;
 esac
 
+if [ $PROJECT != ubuntu-cpc ]; then
+	cat > config/hooks/100-preserve-apt-prefs.chroot <<\EOF
+#! /bin/sh -ex
+
+# live-build "helpfully" removes /etc/apt/preferences.d/* so we put a
+# copy somewhere it won't touch it.
+
+if [ -n "$(ls -A /etc/apt/preferences.d)" ]; then
+    cp -a /etc/apt/preferences.d /etc/apt/preferences.d.save
+fi
+EOF
+fi
+
 if $BINARY_REMOVE_LINUX; then
 	cat > config/binary_rootfs/excludes << EOF
 boot/vmlinu?-*

live-build/ubuntu-cpc/hooks.d/chroot/100-preserve-apt-prefs.chroot

@@ -0,0 +1,8 @@
+#! /bin/sh -ex
+
+# live-build "helpfully" removes /etc/apt/preferences.d/* so we put a
+# copy somewhere it won't touch it.
+
+if [ -n "$(ls -A /etc/apt/preferences.d)" ]; then
+    cp -a /etc/apt/preferences.d /etc/apt/preferences.d.save
+fi