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

1 files changed, 40 insertions, 4 deletions

diff --git a/test/integration/test-solver3-evaluation b/test/integration/test-solver3-evaluation
index 71d117f7d..f5a10f5fa 100755
--- a/test/integration/test-solver3-evaluation
+++ b/test/integration/test-solver3-evaluation
@@ -11,8 +11,8 @@ insertinstalledpackage 'apport' 'all' '3'
 insertpackage 'unstable' 'x' 'all' '3' 'Depends: a | b'
 insertpackage 'unstable' 'y' 'all' '3' 'Depends: b | a'
 insertpackage 'unstable' 'a' 'all' '3' 'Depends: c'
-insertpackage 'unstable' 'b' 'all' '3'
-insertpackage 'unstable' 'c' 'all' '3'
+insertpackage 'unstable' 'b' 'all' '3' 'Source: src'
+insertpackage 'unstable' 'c' 'all' '3' 'Source: src'
 insertpackage 'unstable' 'unrelated' 'all' '3'
 
 setupaptarchive
@@ -20,6 +20,7 @@ setupaptarchive
 rm rootdir/etc/apt/apt.conf.d/disable-solver3-context
 mkdir rootdir/var/log/apt
 
+msgmsg "Test 'worse  result'"
 testsuccess aptget install y x --solver internal -s -o Dir::Apport=var/crash
 
 testsuccess sed -i "s/^Date:.*/Date: Sun Mar  9 00:08:41 2025/" rootdir/var/crash/apt-edsp.$(id -u).crash
@@ -59,7 +60,7 @@ Package: b
 Architecture: all
 Version: 3
 APT-ID: 3
-Source: b
+Source: src
 Source-Version: 3
 Priority: optional
 Section: other
@@ -73,7 +74,7 @@ Package: c
 Architecture: all
 Version: 3
 APT-ID: 4
-Source: c
+Source: src
 Source-Version: 3
 Priority: optional
 Section: other
@@ -126,6 +127,7 @@ APT-Pin: 100
 APT-Candidate: yes
 " apthelper cat-file rootdir/var/log/apt/edsp.log.zst
 
+msgmsg "Test that solver 3.0 explanations are shown"
 testfailureequal "Reading package lists...
 Building dependency tree...
 Package 'c' is not installed, so not removed
@@ -147,6 +149,8 @@ E: The following information from --solver 3.0 may provide additional context:
       - c:amd64 is not selected for install" apt install -s a c- --solver internal
 
 
+msgmsg "Test for 'did not find a result'"
+
 rm rootdir/var/crash/apt-edsp.$(id -u).crash
 
 testsuccessequal "Reading package lists...
@@ -180,3 +184,35 @@ ErrorMessage:
     - c:amd64 is not selected for install
 AptSolverDump:
 $(cat rootdir/var/log/apt/edsp.log.zst | base64 | sed 's#^# #')" cat rootdir/var/crash/apt-edsp.$(id -u).crash
+
+msgmsg "Test that more upgrades are not better in installs"
+# FIXME: This will fail once 3.0 solver tries upgrading by source package.
+insertinstalledpackage 'b' 'all' '2' 'Source: src'
+insertinstalledpackage  'c' 'all' '2' 'Source: src'
+
+# No "Writing error report..."
+testsuccess rm rootdir/var/crash/apt-edsp.$(id -u).crash
+testsuccessequal "Reading package lists...
+Building dependency tree...
+Solving dependencies...
+The following additional packages will be installed:
+  c
+The following packages will be upgraded:
+  b c
+2 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
+Inst b [2] (3 unstable [all])
+Inst c [2] (3 unstable [all])
+Conf b (3 unstable [all])
+Conf c (3 unstable [all])"  apt install --solver internal b  -s
+
+testfailure test -e rootdir/var/crash/apt-edsp.$(id -u).crash
+
+# Safety check to check that the 3.0 result actually looks worse
+testsuccessequal "Reading package lists...
+Building dependency tree...
+Solving dependencies...
+The following packages will be upgraded:
+  b
+1 upgraded, 0 newly installed, 0 to remove and 1 not upgraded.
+Inst b [2] (3 unstable [all])
+Conf b (3 unstable [all])"  apt install --solver 3.0 b  -s