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 (2.525.36) 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 (2.525.35) bionic; urgency=medium
 
   * Did not expect the bionic branch being so outdated. Backport support

live-build/auto/build

@@ -261,6 +261,12 @@ 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
 		# force removal of initramfs-tools, which we assert is not
 		# required for any minimized images but is still pulled in by

live-build/auto/config

@@ -1039,6 +1039,19 @@ rm -f /etc/fstab
 EOF
 fi
 
+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 [ $PROJECT = ubuntukylin ]; then
 	cat > config/hooks/100-ubuntukylin.chroot <<EOF
 #! /bin/sh

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