solver3: Defer version selection where possible

If a dependency can be satisfied by all versions of a package,
add the package to the clause instead of the version object.

This works only if there are no providers for the package: Providers
are quite hard to enumerate over and make sure that all versions of
a package satisfy the provider dependency.

Implement arbitrary selection between packages and versions for
the CompareProviders class: We pick the best version for each package
and then pit them against each other.

1 files changed, 2 insertions, 0 deletions

diff --git a/apt-pkg/solver3.h b/apt-pkg/solver3.h
index 65cd9f017..e43e1065c 100644
--- a/apt-pkg/solver3.h
+++ b/apt-pkg/solver3.h
@@ -228,6 +228,8 @@ class Solver
    bool StrictPinning{_config->FindB("APT::Solver::Strict-Pinning", true)};
    // \brief If set, we install missing recommends and pick new best packages.
    bool FixPolicyBroken{_config->FindB("APT::Get::Fix-Policy-Broken")};
+   // \brief If set, we use strict pinning.
+   bool DeferVersionSelection{_config->FindB("APT::Solver::Defer-Version-Selection", true)};
 
    // \brief Discover a variable, translating the underlying dependencies to the SAT presentation
    void Discover(Var var);