solver3: Upgrade by source package

Implement the "APT::Get::Upgrade-By-Source-Package" option as
the classic solver does.

Here this is equally straight forward now: We enqueue optional, but
eager, clauses of the form

    foo=2 -> foo-data=2

for each sibling in the source version, assuming they are currently
installed, and the selection is not the current version.

This softly enforces upgrades of already installed siblings, but
in non-strict-pinning mode it will not affect the selection of
new packages to be installed.

A more complete solution to version selection by source package
also seems feasible, where we change the "priority" of versions
in the solver dynamically - currently they are statically evaluated.
Such that, when you select foo=2, and something installs foo-data,
foo-data would be installed in version 2 even if version 3 were its
candidate.

1 files changed, 19 insertions, 0 deletions

diff --git a/apt-pkg/solver3.cc b/apt-pkg/solver3.cc
index 6d818ed67..bfc187ea6 100644
--- a/apt-pkg/solver3.cc
+++ b/apt-pkg/solver3.cc
@@ -972,6 +972,25 @@ void DependencySolver::Discover(Var var)
 	    RegisterClause(std::move(clause));
 	 }
 
+	 if (UpgradeBySourcePackage && Ver != Ver.ParentPkg().CurrentVer())
+	 {
+	    // For this version selection, if I have other binaries in the source package that are currently installed,
+	    // mark them for upgrade using an eager optional dependency (which is executed soon, but can be skipped)
+	    for (auto sibling = Ver.SourceVersion().Group().VersionsInSource(); not sibling.end(); sibling = sibling.NextInSource())
+	    {
+	       // Package is the same; not installed or at right version, don't need to upgrade
+	       if (sibling->ParentPkg == Ver->ParentPkg || not sibling.ParentPkg()->CurrentVer || sibling.ParentPkg().CurrentVer() == sibling)
+		  continue;
+	       // Package has a different source version than us, so it's not relevant
+	       if (strcmp(sibling.SourceVersion().VerStr(), Ver.SourceVersion().VerStr()) != 0)
+		  continue;
+	       Clause clause{Var(Ver), Group::SelectVersion, true /* optional */};
+	       clause.eager = true;
+	       clause.solutions = {Var(sibling)};
+	       RegisterClause(std::move(clause));
+	    }
+	 }
+
 	 for (auto dep = Ver.DependsList(); not dep.end();)
 	 {
 	    // Compute a single dependency element (glob or)