solver3: Eagerly satisfy previously satisfied Recommends

When a user ran `apt install gpg`, the solver decided to remove
`gnupg` and `seahorse` because `seahorse` was only pulled in as
a Recommends of ubuntu-desktop and Recommends were resolved after
all other dependencies.

Solve this to most extent by introducing eager optionality: These
dependencies, while they do not take part in classic unit propagation,
are otherwise treated like hard dependencies and resolved as soon
as possible rather than after any hard dependencies.

This ensures that the Recommends of ubuntu-desktop on seahorse
is retained correctly, and as a result, gnupg is updated to the
latest version.

Oops: 6c8e32eb-665d-11f0-a985-fa163ec8ca8c

1 files changed, 5 insertions, 2 deletions

diff --git a/apt-pkg/solver3.cc b/apt-pkg/solver3.cc
index a386b967c..65e3940b4 100644
--- a/apt-pkg/solver3.cc
+++ b/apt-pkg/solver3.cc
@@ -223,8 +223,8 @@ bool APT::Solver::Work::operator<(APT::Solver::Work const &b) const
 {
    if ((not clause->optional && size < 2) != (not b.clause->optional && b.size < 2))
       return not b.clause->optional && b.size < 2;
-   if (clause->optional != b.clause->optional)
-      return clause->optional;
+   if (clause->eager != b.clause->eager)
+      return not clause->eager;
    if (clause->group != b.clause->group)
       return clause->group > b.clause->group;
    if ((size < 2) != (b.size < 2))
@@ -955,6 +955,7 @@ APT::Solver::Clause APT::Solver::TranslateOrGroup(pkgCache::DepIterator start, p
 	 if (unlikely(debug >= 3))
 	    std::cerr << "Promoting previously satisfied clause to hard dependency: " << clause.toString(cache, true) << std::endl;
 	 clause.optional = false;
+	 clause.eager = true;
       }
       else if (
 	 IsUpgrade && not(AllowRemove && AllowInstall)				    // promote Recommends to Depends in upgrade, not in dist-upgrade.
@@ -965,6 +966,7 @@ APT::Solver::Clause APT::Solver::TranslateOrGroup(pkgCache::DepIterator start, p
 	 if (unlikely(debug >= 3))
 	    std::cerr << "Promoting new clause to hard dependency: " << clause.toString(cache) << std::endl;
 	 clause.optional = false;
+	 clause.eager = true;
       }
       else if (not existing.end() && importantToKeep(start) && satisfied)
       {
@@ -975,6 +977,7 @@ APT::Solver::Clause APT::Solver::TranslateOrGroup(pkgCache::DepIterator start, p
 	 clause.solutions.erase(std::remove_if(clause.solutions.begin(), clause.solutions.end(), [this](auto var)
 					       { return var.CastPkg(cache)->CurrentVer == nullptr; }),
 				clause.solutions.end());
+	 clause.eager = true;
       }
    }