don't consider holds for autoremoval

We can't remove packages which are held back by the user with a hold, so
marking them (or its dependencies) as garbage will lead our autoremover
into madness – and given that the package is important enough that the
user has held it back it can't be garbage (at least at the moment), so
even if a front-end wants to use the info just for information display
its a good idea to not consider it garbage for them.

Closes: 724995

apt-pkg/depcache.cc

@@ -896,6 +896,7 @@ char const* PrintMode(char const mode)
 	 case pkgDepCache::ModeInstall: return "Install";
 	 case pkgDepCache::ModeKeep: return "Keep";
 	 case pkgDepCache::ModeDelete: return "Delete";
+	 case pkgDepCache::ModeGarbage: return "Garbage";
 	 default: return "UNKNOWN";
 	 }
 }
@@ -1726,8 +1727,6 @@ bool pkgDepCache::MarkRequired(InRootSetFunc &userFunc)
    follow_recommends = MarkFollowsRecommends();
    follow_suggests   = MarkFollowsSuggests();
 
-
-
    // do the mark part, this is the core bit of the algorithm
    for(PkgIterator p = PkgBegin(); !p.end(); ++p)
    {
@@ -1738,7 +1737,9 @@ bool pkgDepCache::MarkRequired(InRootSetFunc &userFunc)
 	  // be nice even then a required package violates the policy (#583517)
 	  // and do the full mark process also for required packages
 	  (p.CurrentVer().end() != true &&
-	   p.CurrentVer()->Priority == pkgCache::State::Required))
+	   p.CurrentVer()->Priority == pkgCache::State::Required) ||
+	  // packages which can't be changed (like holds) can't be garbage
+	  (IsModeChangeOk(ModeGarbage, p, 0, false) == false))
       {
 	 // the package is installed (and set to keep)
 	 if(PkgState[p->ID].Keep() && !p.CurrentVer().end())

apt-pkg/depcache.h

@@ -128,7 +128,7 @@ class pkgDepCache : protected pkgCache::Namespace
    enum InternalFlags {AutoKept = (1 << 0), Purge = (1 << 1), ReInstall = (1 << 2), Protected = (1 << 3)};
       
    enum VersionTypes {NowVersion, InstallVersion, CandidateVersion};
-   enum ModeList {ModeDelete = 0, ModeKeep = 1, ModeInstall = 2};
+   enum ModeList {ModeDelete = 0, ModeKeep = 1, ModeInstall = 2, ModeGarbage = 3};
 
    /** \brief Represents an active action group.
     *

test/integration/test-apt-get-autoremove

@@ -49,3 +49,23 @@ Install: unrelated:i386 (1), debhelper:i386 (8.0.0), po-debconf:i386 (1.0.16, au
 Remove: debhelper:i386 (8.0.0)
 
 Remove: po-debconf:i386 (1.0.16)'
+
+testsuccess aptget install debhelper -y
+testdpkginstalled 'unrelated' 'debhelper' 'po-debconf'
+testsuccess aptmark auto debhelper
+
+testmarkedauto 'debhelper' 'po-debconf'
+testequal 'Reading package lists...
+Building dependency tree...
+Reading state information...
+The following packages will be REMOVED:
+  debhelper po-debconf
+0 upgraded, 0 newly installed, 2 to remove and 0 not upgraded.
+Remv debhelper [8.0.0]
+Remv po-debconf [1.0.16]' aptget autoremove -s
+
+testsuccess aptmark hold debhelper
+testequal 'Reading package lists...
+Building dependency tree...
+Reading state information...
+0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.' aptget autoremove -s