backtracking: discard extra rebuilds, bug #439688

3 files changed, 50 insertions, 8 deletions

diff --git a/pym/_emerge/depgraph.py b/pym/_emerge/depgraph.py
index e129a810d..fd5dfe806 100644
--- a/pym/_emerge/depgraph.py
+++ b/pym/_emerge/depgraph.py
@@ -415,6 +415,7 @@ class _dynamic_depgraph_config(object):
 		self._needed_use_config_changes = backtrack_parameters.needed_use_config_changes
 		self._runtime_pkg_mask = backtrack_parameters.runtime_pkg_mask
 		self._slot_operator_replace_installed = backtrack_parameters.slot_operator_replace_installed
+		self._prune_rebuilds = backtrack_parameters.prune_rebuilds
 		self._need_restart = False
 		# For conditions that always require user intervention, such as
 		# unsatisfied REQUIRED_USE (currently has no autounmask support).
@@ -633,7 +634,7 @@ class depgraph(object):
 				line = colorize("INFORM", line)
 			writemsg(line + "\n", noiselevel=-1)
 
-	def _show_missed_update(self):
+	def _get_missed_updates(self):
 
 		# In order to minimize noise, show only the highest
 		# missed update from each SLOT.
@@ -659,6 +660,12 @@ class depgraph(object):
 				missed_updates[k] = (pkg, mask_type, parent_atoms)
 				break
 
+		return missed_updates
+
+	def _show_missed_update(self):
+
+		missed_updates = self._get_missed_updates()
+
 		if not missed_updates:
 			return
 
@@ -2737,6 +2744,23 @@ class depgraph(object):
 			self.need_restart():
 			return False, myfavorites
 
+		if not self._dynamic_config._prune_rebuilds and \
+			self._dynamic_config._slot_operator_replace_installed and \
+			self._get_missed_updates():
+			# When there are missed updates, we might have triggered
+			# some unnecessary rebuilds (see bug #439688). So, prune
+			# all the rebuilds and backtrack with the problematic
+			# updates masked. The next backtrack run should pull in
+			# any rebuilds that are really needed, and this
+			# prune_rebuilds path should never be entered more than
+			# once in a series of backtracking nodes (in order to
+			# avoid a backtracking loop).
+			backtrack_infos = self._dynamic_config._backtrack_infos
+			config = backtrack_infos.setdefault("config", {})
+			config["prune_rebuilds"] = True
+			self._dynamic_config._need_restart = True
+			return False, myfavorites
+
 		# Any failures except those due to autounmask *alone* should return
 		# before this point, since the success_without_autounmask flag that's
 		# set below is reserved for cases where there are *zero* other
diff --git a/pym/_emerge/resolver/backtracking.py b/pym/_emerge/resolver/backtracking.py
index 5456ea455..c29b9d42a 100644
--- a/pym/_emerge/resolver/backtracking.py
+++ b/pym/_emerge/resolver/backtracking.py
@@ -1,4 +1,4 @@
-# Copyright 2010-2011 Gentoo Foundation
+# Copyright 2010-2012 Gentoo Foundation
 # Distributed under the terms of the GNU General Public License v2
 
 import copy
@@ -7,8 +7,8 @@ class BacktrackParameter(object):
 
 	__slots__ = (
 		"needed_unstable_keywords", "runtime_pkg_mask", "needed_use_config_changes", "needed_license_changes",
-		"rebuild_list", "reinstall_list", "needed_p_mask_changes",
-		"slot_operator_replace_installed"
+		"prune_rebuilds", "rebuild_list", "reinstall_list", "needed_p_mask_changes",
+		"slot_operator_mask_built", "slot_operator_replace_installed"
 	)
 
 	def __init__(self):
@@ -20,6 +20,8 @@ class BacktrackParameter(object):
 		self.rebuild_list = set()
 		self.reinstall_list = set()
 		self.slot_operator_replace_installed = set()
+		self.slot_operator_mask_built = set()
+		self.prune_rebuilds = False
 
 	def __deepcopy__(self, memo=None):
 		if memo is None:
@@ -36,6 +38,8 @@ class BacktrackParameter(object):
 		result.rebuild_list = copy.copy(self.rebuild_list)
 		result.reinstall_list = copy.copy(self.reinstall_list)
 		result.slot_operator_replace_installed = copy.copy(self.slot_operator_replace_installed)
+		result.slot_operator_mask_built = self.slot_operator_mask_built.copy()
+		result.prune_rebuilds = self.prune_rebuilds
 
 		# runtime_pkg_mask contains nested dicts that must also be copied
 		result.runtime_pkg_mask = {}
@@ -52,7 +56,9 @@ class BacktrackParameter(object):
 			self.needed_license_changes == other.needed_license_changes and \
 			self.rebuild_list == other.rebuild_list and \
 			self.reinstall_list == other.reinstall_list and \
-			self.slot_operator_replace_installed == other.slot_operator_replace_installed
+			self.slot_operator_replace_installed == other.slot_operator_replace_installed and \
+			self.slot_operator_mask_built == other.slot_operator_mask_built and \
+			self.prune_rebuilds == other.prune_rebuilds
 
 
 class _BacktrackNode(object):
@@ -193,6 +199,7 @@ class Backtracker(object):
 			elif change == "slot_conflict_abi":
 				new_node.terminal = False
 			elif change == "slot_operator_mask_built":
+				para.slot_operator_mask_built.update(data)
 				for pkg, mask_reasons in data.items():
 					para.runtime_pkg_mask.setdefault(pkg,
 						{}).update(mask_reasons)
@@ -202,6 +209,17 @@ class Backtracker(object):
 				para.rebuild_list.update(data)
 			elif change == "reinstall_list":
 				para.reinstall_list.update(data)
+			elif change == "prune_rebuilds":
+				para.prune_rebuilds = True
+				para.slot_operator_replace_installed.clear()
+				for pkg in para.slot_operator_mask_built:
+					runtime_masks = para.runtime_pkg_mask.get(pkg)
+					if runtime_masks is None:
+						continue
+					runtime_masks.pop("slot_operator_mask_built", None)
+					if not runtime_masks:
+						para.runtime_pkg_mask.pop(pkg)
+				para.slot_operator_mask_built.clear()
 
 		self._add(new_node, explore=explore)
 		self._current_node = new_node
diff --git a/pym/portage/tests/resolver/test_slot_conflict_rebuild.py b/pym/portage/tests/resolver/test_slot_conflict_rebuild.py
index e255e2a53..5ce2329e1 100644
--- a/pym/portage/tests/resolver/test_slot_conflict_rebuild.py
+++ b/pym/portage/tests/resolver/test_slot_conflict_rebuild.py
@@ -60,13 +60,13 @@ class SlotConflictRebuildTestCase(TestCase):
 
 		test_cases = (
 
-			# Demonstrate bug #439688, where a slot conflict prevents
-			# an upgrade and triggers unnecessary rebuilds.
+			# Test bug #439688, where a slot conflict prevents an
+			# upgrade and we don't want to trigger unnecessary rebuilds.
 			ResolverPlaygroundTestCase(
 				["@world"],
 				options = {"--update": True, "--deep": True},
 				success = True,
-				mergelist = ["app-misc/A-1", "app-misc/B-0"]),
+				mergelist = []),
 
 		)