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.

2 files changed, 66 insertions, 17 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;
 }
 									/*}}}*/
diff --git a/apt-pkg/depcache.h b/apt-pkg/depcache.h
index 7358048ed..d9c95349b 100644
--- a/apt-pkg/depcache.h
+++ b/apt-pkg/depcache.h
@@ -442,16 +442,15 @@ class pkgDepCache : protected pkgCache::Namespace
    /** \return \b true if it's OK for MarkInstall to install
     *  the given package.
     *
-    *  See the default implementation for a simple example how this
-    *  method can be used.
-    *  Overriding implementations should use the hold-state-flag to cache
-    *  results from previous checks of this package - also it should
-    *  be used if the default resolver implementation is also used to
-    *  ensure that these packages are handled like "normal" dpkg holds.
+    *  The default implementation simply calls all IsInstallOk*
+    *  method mentioned below.
+    *
+    *  Overriding implementations should use the hold-state-flag to
+    *  cache results from previous checks of this package - if possible.
     *
     *  The parameters are the same as in the calling MarkInstall:
     *  \param Pkg       the package that MarkInstall wants to install.
-    *  \param AutoInst  needs a previous MarkInstall this package?
+    *  \param AutoInst  install this and all its dependencies
     *  \param Depth     recursive deep of this Marker call
     *  \param FromUser  was the install requested by the user?
     */
@@ -461,12 +460,8 @@ class pkgDepCache : protected pkgCache::Namespace
    /** \return \b true if it's OK for MarkDelete to remove
     *  the given package.
     *
-    *  See the default implementation for a simple example how this
-    *  method can be used.
-    *  Overriding implementations should use the hold-state-flag to cache
-    *  results from previous checks of this package - also it should
-    *  be used if the default resolver implementation is also used to
-    *  ensure that these packages are handled like "normal" dpkg holds.
+    *  The default implementation simply calls all IsDeleteOk*
+    *  method mentioned below, see also #IsInstallOk.
     *
     *  The parameters are the same as in the calling MarkDelete:
     *  \param Pkg       the package that MarkDelete wants to remove.
@@ -498,6 +493,15 @@ class pkgDepCache : protected pkgCache::Namespace
    pkgDepCache(pkgCache *Cache,Policy *Plcy = 0);
    virtual ~pkgDepCache();
 
+   protected:
+   // methods call by IsInstallOk
+   bool IsInstallOkMultiArchSameVersionSynced(PkgIterator const &Pkg,
+	 bool const AutoInst, unsigned long const Depth, bool const FromUser);
+
+   // methods call by IsDeleteOk
+   bool IsDeleteOkProtectInstallRequests(PkgIterator const &Pkg,
+	 bool const rPurge, unsigned long const Depth, bool const FromUser);
+
    private:
    bool IsModeChangeOk(ModeList const mode, PkgIterator const &Pkg,
 			unsigned long const Depth, bool const FromUser);