From 295ab44a3063fb7790d8a558a161fc1bd801f998 Mon Sep 17 00:00:00 2001
From: Julian Andres Klode <julian.klode@canonical.com>
Date: Fri, 4 Apr 2025 15:25:01 +0200
Subject: solver3: Consider more upgrades more costly when not upgrading

We inadvertently considered more upgrades as a better solution in
all cases, but if we are *installing* rather than upgrading, we
should count upgrades as a negative.

Change the code to accomodate that. This requires a few more
tricks:

- We remove the keep count check. This does not appear to work
  correctly and would have prevented the fix. We are already
  counting all possible changes, so why bother.

- We need to subtract the upgrade count from the install count
  (upgrades are a class of installs) since we now allow comparing
  solutions with different upgrade counts for install counts.

- After comparing the "new install count", we now compare upgrade
  count too, in the opposite direction of upgrading.

To test, we abuse that solver 3.0 does not upgrade all packages
in a source package when using the install command.

LP: #2105395
---
 apt-private/private-install.cc | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

(limited to 'apt-private')

diff --git a/apt-private/private-install.cc b/apt-private/private-install.cc
index 7103c6dc7..7c9a27290 100644
--- a/apt-private/private-install.cc
+++ b/apt-private/private-install.cc
@@ -983,6 +983,7 @@ bool DoCacheManipulationFromCommandLine(CommandLine &CmdL, std::vector<PseudoPkg
      // Fallback to 3.0 if we don't get a result or apport is installed
      if (not invalidCombinations && _config->Find("APT::Solver", "internal") == "internal" && (not res || (not Cache->FindPkg("apport").end() && Cache->FindPkg("apport")->CurrentVer)))
      {
+	bool isUpgrade = distUpgradeMode || UpgradeMode != APT::Upgrade::ALLOW_EVERYTHING;
 	auto internalBroken = Cache->BrokenCount();
 	auto internalDel = Cache->DelCount();
 	auto internalInst = Cache->InstCount();
@@ -1006,6 +1007,11 @@ bool DoCacheManipulationFromCommandLine(CommandLine &CmdL, std::vector<PseudoPkg
 	      errors.push_back(str);
 	_config->Set("APT::Solver", "internal");
 	_error->RevertToStack();
+
+	// Cost factors to compare two solutions
+	auto solver3Cost = std::make_tuple(Cache->DelCount(), isUpgrade  ? -Cache->UpgradeCount() : 0, Cache->InstCount() - Cache->UpgradeCount(), Cache->UpgradeCount());
+	auto internalCost = std::make_tuple(internalDel, isUpgrade ? -internalUpgrade : 0, internalInst - internalUpgrade, internalUpgrade);
+
 	// An error summary for apport.
 	std::string error;
 	if (solver3Res && Cache->BrokenCount())
@@ -1027,7 +1033,7 @@ bool DoCacheManipulationFromCommandLine(CommandLine &CmdL, std::vector<PseudoPkg
 	   solver3.commit();
 	   res = true;
 	}
-	else if (std::make_tuple(Cache->DelCount(), -Cache->UpgradeCount(), Cache->KeepCount(), Cache->InstCount()) > std::make_tuple(internalDel, -internalUpgrade, internalKeep, internalInst))
+	else if (solver3Cost > internalCost)
 	{
 	   error = "Failure: The 3.0 solver produced a worse result";
 	}
-- 
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