From e077370ffcb3669a50a600e80356c2002e6b176d Mon Sep 17 00:00:00 2001
From: Julian Andres Klode <julian.klode@canonical.com>
Date: Fri, 8 Jul 2022 17:46:05 +0200
Subject: Mark broken reverse depends for upgrade

Currently the solver handles cases where a Breaks b (<< 1) and
if we install that a, upgrades b. However, where b Depends a (= 1),
b was removed again.

This addresses the problem by iterating over installed reverse
dependencies of upgrades and upgrading them so that both cases
work roughly similarly.

LP: #1974196
---
 apt-pkg/depcache.cc                     | 34 +++++++++++++++++++++++++++++++++
 test/integration/test-multiarch-allowed |  3 +--
 2 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/apt-pkg/depcache.cc b/apt-pkg/depcache.cc
index a5b586f5b..82b2fda99 100644
--- a/apt-pkg/depcache.cc
+++ b/apt-pkg/depcache.cc
@@ -1445,6 +1445,34 @@ static bool MarkInstall_RemoveConflictsIfNotUpgradeable(pkgDepCache &Cache, bool
    return not failedToRemoveSomething;
 }
 									/*}}}*/
+static bool MarkInstall_CollectReverseDepends(pkgDepCache &Cache, bool const DebugAutoInstall, pkgCache::VerIterator const &PV, unsigned long Depth, APT::PackageVector &toUpgrade) /*{{{*/
+{
+   auto CurrentVer = PV.ParentPkg().CurrentVer();
+   if (CurrentVer.end())
+      return true;
+   for (pkgCache::DepIterator D = PV.ParentPkg().RevDependsList(); D.end() == false; ++D)
+   {
+      auto ParentPkg = D.ParentPkg();
+      // Skip non-installed versions and packages already marked for upgrade
+      if (ParentPkg.CurrentVer() != D.ParentVer() || Cache[ParentPkg].Install())
+	 continue;
+      // We only handle important positive dependencies, RemoveConflictsIfNotUpgradeable handles negative
+      if (not Cache.IsImportantDep(D) || D.IsNegative())
+	 continue;
+      // The dependency was previously not satisfied (e.g. part of an or group) or will be satisfied, so it's OK
+      if (not D.IsSatisfied(CurrentVer) || D.IsSatisfied(PV))
+	 continue;
+      if (std::find(toUpgrade.begin(), toUpgrade.end(), ParentPkg) != toUpgrade.end())
+	 continue;
+
+      if (DebugAutoInstall)
+	 std::clog << OutputInDepth(Depth) << " Upgrading: " << APT::PrettyPkg(&Cache, ParentPkg) << " due to " << APT::PrettyDep(&Cache, D) << "\n";
+
+      toUpgrade.push_back(ParentPkg);
+   }
+   return true;
+}
+									/*}}}*/
 static bool MarkInstall_UpgradeOrRemoveConflicts(pkgDepCache &Cache, bool const DebugAutoInstall, unsigned long Depth, bool const ForceImportantDeps, APT::PackageVector &toUpgrade, bool const propagateProtected, bool const FromUser) /*{{{*/
 {
    bool failedToRemoveSomething = false;
@@ -1641,6 +1669,12 @@ bool pkgDepCache::MarkInstall(PkgIterator const &Pkg, bool AutoInst,
 	    return false;
 	 hasFailed = true;
       }
+      if (not MarkInstall_CollectReverseDepends(*this, DebugAutoInstall, PV, Depth, toUpgrade))
+      {
+	 if (failEarly)
+	    return false;
+	 hasFailed = true;
+      }
    }
 
    if (not FromUser && not MarkInstall_StateChange(Pkg, AutoInst, FromUser))
diff --git a/test/integration/test-multiarch-allowed b/test/integration/test-multiarch-allowed
index 69d0bfa10..db7f37169 100755
--- a/test/integration/test-multiarch-allowed
+++ b/test/integration/test-multiarch-allowed
@@ -64,8 +64,7 @@ Conf foo:i386 (1 unstable [i386])
 Conf needsfoo:i386 (1 unstable [i386])' aptget install needsfoo:i386 -s
 testfailureequal "$BADPREFIX
 The following packages have unmet dependencies:
- foo : Conflicts: foo:i386 but 1 is to be installed
- foo:i386 : Conflicts: foo but 1 is to be installed
+ needsfoo:i386 : Depends: foo:i386 but it is not installable
 E: Unable to correct problems, you have held broken packages." aptget install needsfoo:i386 foo:amd64 -s
 testfailureequal "$BADPREFIX
 The following packages have unmet dependencies:
-- 
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