[juliank, r=adconrad] Improve autoremove behaviour by minimizing manual installs

debian/changelog

@@ -1,3 +1,10 @@
+livecd-rootfs (2.537) UNRELEASED; urgency=medium
+
+  * Minimize the number of manually installed packages in images by marking
+    dependencies of metapackages as automatically installed.
+
+ -- Julian Andres Klode <juliank@ubuntu.com>  Tue, 18 Sep 2018 08:55:04 +0200
+
 livecd-rootfs (2.536) cosmic; urgency=medium
 
   * Fix live-server journald config snippet to actually disable journald rate

debian/control

@@ -26,6 +26,7 @@ Depends: ${misc:Depends},
          parted,
          procps,
          python-minimal | python,
+         python3-apt,
          python3-software-properties,
          qemu-utils,
          rsync,

debian/install

@@ -1,2 +1,3 @@
 live-build usr/share/livecd-rootfs
 get-ppa-fingerprint usr/share/livecd-rootfs
+minimize-manual usr/share/livecd-rootfs

live-build/auto/build

@@ -445,6 +445,8 @@ EOF
 	(cd chroot && find usr/share/doc -maxdepth 1 -type d | xargs du -s | sort -nr)
 	echo END docdirs
 
+	/usr/share/livecd-rootfs/minimize-manual chroot
+
 	lb binary "$@"
 	touch binary.success
 ) 2>&1 | tee binary.log

minimize-manual

@@ -0,0 +1,52 @@
+#!/usr/bin/python3
+"""Minimize the number of manually installed packages in the image.
+
+Finds all manually installed meta packages, and marks their dependencies
+as automatically installed.
+"""
+import sys
+
+import apt
+
+
+def is_root(pkg):
+    """Check if the package is a root package (manually inst. meta)"""
+    return (pkg.is_installed and
+            not pkg.is_auto_installed and
+            (pkg.section == "metapackages" or
+             pkg.section.endswith("/metapackages")))
+
+
+def main():
+    """Main function"""
+    cache = apt.Cache(rootdir=sys.argv[1] if len(sys.argv) > 1 else None)
+    roots = set(pkg for pkg in cache if is_root(pkg))
+    workset = set(roots)
+    seen = set()
+
+    with cache.actiongroup():
+        while True:
+            print("Iteration", file=sys.stderr)
+            to_proc = workset - seen
+            if not to_proc:
+                break
+            for pkg in sorted(to_proc):
+                print("    Visiting", pkg, file=sys.stderr)
+
+                if pkg not in roots:
+                    pkg.mark_auto()
+
+                for dep in (pkg.installed.dependencies +
+                            pkg.installed.recommends):
+                    for bdep in dep.or_dependencies:
+                        for ver in bdep.target_versions:
+                            if ver.package.is_installed:
+                                workset.add(ver.package)
+
+                seen.add(pkg)
+
+        cache.commit()
+
+
+if __name__ == '__main__':
+    main()