solver3: Support comparing packages and versions

When comparing packages, we compare the best version for the
package. To determine the best version, the rules for comparisons
are applied normally.

This allows us to mix packages and versions in a clause as the
solutions for a dependency, which means we'll be able to defer
the selection of a particular version of a package to a later
time.

1 files changed, 15 insertions, 8 deletions

diff --git a/apt-pkg/solver3.cc b/apt-pkg/solver3.cc
index 09ba920fa..6288912f6 100644
--- a/apt-pkg/solver3.cc
+++ b/apt-pkg/solver3.cc
@@ -44,21 +44,28 @@ struct APT::Solver::CompareProviders3 /*{{{*/
    pkgCache::PkgIterator const Pkg;
    APT::Solver &Solver;
 
-   bool operator()(pkgCache::Version *AV, pkgCache::Version *BV)
+   pkgCache::VerIterator bestVersion(pkgCache::PkgIterator pkg)
    {
-      return (*this)(pkgCache::VerIterator(Cache, AV), pkgCache::VerIterator(Cache, BV));
+      pkgCache::VerIterator res = pkg.VersionList();
+      for (auto v = res; not v.end(); ++v)
+	 res = std::max(res, v, *this);
+      return res;
    }
    bool operator()(Var a, Var b)
    {
-      if (auto va = a.Ver(Cache))
-      {
-	 if (auto vb = b.Ver(Cache))
-	    return (*this)(va, vb);
-      }
-      abort();
+      pkgCache::VerIterator va = a.Ver(Cache);
+      pkgCache::VerIterator vb = b.Ver(Cache);
+      if (auto pa = a.Pkg(Cache))
+	 va = bestVersion(pa);
+      if (auto pb = b.Pkg(Cache))
+	 vb = bestVersion(pb);
+
+      assert(not va.end() && not vb.end());
+      return (*this)(va, vb);
    }
    bool operator()(pkgCache::VerIterator const &AV, pkgCache::VerIterator const &BV)
    {
+      assert(not AV.end() && not BV.end());
       pkgCache::PkgIterator const A = AV.ParentPkg();
       pkgCache::PkgIterator const B = BV.ParentPkg();
       // Compare versions for the same package. FIXME: Move this to the real implementation