prevent MarkInstall of unsynced Multi-Arch:same siblings

Multi-Arch: same packages can be co-installed, but need to have the same
version for all installed packages (aka "siblings"). Otherwise the
unsynced versions will fight against each other and the auto-install as
wel as the problem resolver will later have to decide between holding the
packages or to remove one of the siblings (usually a foreign) taking a
bunch of packages (like the entire foreign setup) with them.

The idea here is now to be more pro-active: MarkInstall will fail for
a package if the siblings aren't synced, so we don't allow a situation
in which a resolver has to decide if to hold or to remove-upgrade under
the assumption that the remove-upgrade decision is always wrong and
doesn't deserve to be explored (expect valid out-of-syncs of course).

Thats a pretty bold move to take for a library which is used by
different solvers so this check is done in IsInstallOk and can be
overridden if front-ends want to.

1 files changed, 49 insertions, 4 deletions

diff --git a/apt-pkg/depcache.cc b/apt-pkg/depcache.cc
index 9f8422fec..2c6eb43bf 100644
--- a/apt-pkg/depcache.cc
+++ b/apt-pkg/depcache.cc
@@ -865,6 +865,11 @@ bool pkgDepCache::MarkDelete(PkgIterator const &Pkg, bool rPurge,
 bool pkgDepCache::IsDeleteOk(PkgIterator const &Pkg,bool rPurge,
 			      unsigned long Depth, bool FromUser)
 {
+   return IsDeleteOkProtectInstallRequests(Pkg, rPurge, Depth, FromUser);
+}
+bool pkgDepCache::IsDeleteOkProtectInstallRequests(PkgIterator const &Pkg,
+      bool const rPurge, unsigned long const Depth, bool const FromUser)
+{
    if (FromUser == false && Pkg->CurrentVer == 0)
    {
       StateCache &P = PkgState[Pkg->ID];
@@ -1047,9 +1052,10 @@ bool pkgDepCache::MarkInstall(PkgIterator const &Pkg,bool AutoInst,
       return true;
    }
 
-   // check if we are allowed to install the package
-   if (IsInstallOk(Pkg,AutoInst,Depth,FromUser) == false)
-      return false;
+   // check if we are allowed to install the package (if we haven't already)
+   if (P.Mode != ModeInstall || P.InstallVer != P.CandidateVer)
+      if (IsInstallOk(Pkg,AutoInst,Depth,FromUser) == false)
+	 return false;
 
    ActionGroup group(*this);
    P.iFlags &= ~AutoKept;
@@ -1271,11 +1277,50 @@ bool pkgDepCache::MarkInstall(PkgIterator const &Pkg,bool AutoInst,
 									/*}}}*/
 // DepCache::IsInstallOk - check if it is ok to install this package	/*{{{*/
 // ---------------------------------------------------------------------
-/* The default implementation does nothing.
+/* The default implementation checks if the installation of an M-A:same
+   package would lead us into a version-screw and if so forbids it.
    dpkg holds are enforced by the private IsModeChangeOk */
 bool pkgDepCache::IsInstallOk(PkgIterator const &Pkg,bool AutoInst,
 			      unsigned long Depth, bool FromUser)
 {
+   return IsInstallOkMultiArchSameVersionSynced(Pkg,AutoInst, Depth, FromUser);
+}
+bool pkgDepCache::IsInstallOkMultiArchSameVersionSynced(PkgIterator const &Pkg,
+      bool const AutoInst, unsigned long const Depth, bool const FromUser)
+{
+   if (FromUser == true) // as always: user is always right
+      return true;
+
+   // ignore packages with none-M-A:same candidates
+   VerIterator const CandVer = PkgState[Pkg->ID].CandidateVerIter(*this);
+   if (unlikely(CandVer.end() == true) || CandVer == Pkg.CurrentVer() ||
+	 (CandVer->MultiArch & pkgCache::Version::Same) != pkgCache::Version::Same)
+      return true;
+
+   GrpIterator const Grp = Pkg.Group();
+   for (PkgIterator P = Grp.PackageList(); P.end() == false; P = Grp.NextPkg(P))
+   {
+      // not installed or version synced: fine by definition
+      // (simple string-compare as stuff like '1' == '0:1-0' can't happen here)
+      if (P->CurrentVer == 0 || strcmp(Pkg.CandVersion(), P.CandVersion()) == 0)
+	 continue;
+      // packages loosing M-A:same can be out-of-sync
+      VerIterator CV = PkgState[P->ID].CandidateVerIter(*this);
+      if (unlikely(CV.end() == true) ||
+	    (CV->MultiArch & pkgCache::Version::Same) != pkgCache::Version::Same)
+	 continue;
+
+      // not downloadable means the package is obsolete, so allow out-of-sync
+      if (CV.Downloadable() == false)
+	 continue;
+
+      PkgState[Pkg->ID].iFlags |= AutoKept;
+      if (unlikely(DebugMarker == true))
+	 std::clog << OutputInDepth(Depth) << "Ignore MarkInstall of " << Pkg
+	    << " as its M-A:same siblings are not version-synced" << std::endl;
+      return false;
+   }
+
    return true;
 }
 									/*}}}*/