depclean: do not eliminate upgrades (bug 707108)

For depclean actions, prefer choices where all packages have been
pulled into the graph, except for choices that eliminate upgrades.
This solves the test case for bug 707108, where depclean eliminated
a new slot of python that had been pulled in by a world update.
This should also prevent non-deterministic elimination of the
latest vala slot that was reported in bug 693790.

NOTE: There's a common perception (expressed in bug 705700) that
emerge is pulling in an "unecessary" python slot in cases when that
python slot is not enabled in PYTHON_TARGETS. However, the so-called
"unnecessary" slot is practically indistinguishable from a desirable
upgrade such as the missed llvm slot upgrade that was reported in
bug 706278. Therefore, be advised that emerge must pull in the
highest visible slot (regardless of PYTHON_TARGETS) in order to
ensure that a desirable upgrade is not missed.

Fixes: f7d83d75c6b0 ("dep_zapdeps: adjust || preference for slot upgrades (bug 706278)")
Bug: https://bugs.gentoo.org/707108
Bug: https://bugs.gentoo.org/706278
Bug: https://bugs.gentoo.org/705700
Bug: https://bugs.gentoo.org/693790
Signed-off-by: Zac Medico <zmedico@gentoo.org>

2 files changed, 15 insertions, 12 deletions

diff --git a/lib/portage/dep/dep_check.py b/lib/portage/dep/dep_check.py
index a7ae2cfa4..8adb92da2 100644
--- a/lib/portage/dep/dep_check.py
+++ b/lib/portage/dep/dep_check.py
@@ -690,17 +690,12 @@ def dep_zapdeps(unreduced, reduced, myroot, use_binaries=0, trees=None,
 					# choice_1 will not be promoted, so move on
 					break
 				if (
-					# For removal actions, prefer choices where all packages
-					# have been pulled into the graph.
-					(graph_interface and graph_interface.removal_action and
-					choice_1.all_in_graph and not choice_2.all_in_graph)
-
 					# Prefer choices where all_installed_slots is True, except
 					# in cases where we want to upgrade to a new slot as in
 					# bug 706278. Don't compare new_slot_count here since that
 					# would aggressively override the preference order defined
 					# in the ebuild, breaking the test case for bug 645002.
-					or (choice_1.all_installed_slots and
+					(choice_1.all_installed_slots and
 					not choice_2.all_installed_slots and
 					not choice_2.want_update)
 				):
@@ -711,8 +706,6 @@ def dep_zapdeps(unreduced, reduced, myroot, use_binaries=0, trees=None,
 					break
 
 				intersecting_cps = cps.intersection(choice_2.cp_map)
-				if not intersecting_cps:
-					continue
 				has_upgrade = False
 				has_downgrade = False
 				for cp in intersecting_cps:
@@ -724,8 +717,18 @@ def dep_zapdeps(unreduced, reduced, myroot, use_binaries=0, trees=None,
 							has_upgrade = True
 						else:
 							has_downgrade = True
-							break
-				if has_upgrade and not has_downgrade:
+
+				if (
+					# Prefer upgrades.
+					(has_upgrade and not has_downgrade)
+
+					# For removal actions, prefer choices where all packages
+					# have been pulled into the graph, except for choices that
+					# eliminate upgrades.
+					or (graph_interface and graph_interface.removal_action and
+					choice_1.all_in_graph and not choice_2.all_in_graph and
+					not (has_downgrade and not has_upgrade))
+				):
 					# promote choice_1 in front of choice_2
 					choices.remove(choice_1)
 					index_2 = choices.index(choice_2)
diff --git a/lib/portage/tests/resolver/test_or_choices.py b/lib/portage/tests/resolver/test_or_choices.py
index 78946ccec..10c613e39 100644
--- a/lib/portage/tests/resolver/test_or_choices.py
+++ b/lib/portage/tests/resolver/test_or_choices.py
@@ -387,13 +387,13 @@ class OrChoicesTestCase(TestCase):
 		}
 
 		test_cases = (
-			# Demonstrate bug 707108, where a new python slot is erroneosly
+			# Test for bug 707108, where a new python slot was erroneously
 			# removed by emerge --depclean.
 			ResolverPlaygroundTestCase(
 				[],
 				options={"--depclean": True},
 				success=True,
-				cleanlist=['dev-lang/python-3.8'],
+				cleanlist=[],
 			),
 		)