Reject inconsistent backtrack parameters

If backtracking masks a package that caused another package to
be masked, we declare this backtracking node as invalid. The
backtracker should be able to find another node that gives a
valid solution if one exists. This fixes bug 375573.

3 files changed, 68 insertions, 5 deletions

diff --git a/pym/_emerge/depgraph.py b/pym/_emerge/depgraph.py
index 19773c2d9..8b2bfd378 100644
--- a/pym/_emerge/depgraph.py
+++ b/pym/_emerge/depgraph.py
@@ -1121,11 +1121,6 @@ class depgraph(object):
 									all_match = False
 									break
 
-							if to_be_selected >= to_be_masked:
-								# We only care about the parent atoms
-								# when they trigger a downgrade.
-								parent_atoms = set()
-
 							fallback_data.append((to_be_masked, parent_atoms))
 
 							if all_match:
diff --git a/pym/_emerge/resolver/backtracking.py b/pym/_emerge/resolver/backtracking.py
index dcdaee0cb..e072275fe 100644
--- a/pym/_emerge/resolver/backtracking.py
+++ b/pym/_emerge/resolver/backtracking.py
@@ -84,6 +84,9 @@ class Backtracker(object):
 		Adds a newly computed backtrack parameter. Makes sure that it doesn't already exist and
 		that we don't backtrack deeper than we are allowed by --backtrack.
 		"""
+		if not self._check_runtime_pkg_mask(node.parameter.runtime_pkg_mask):
+			return
+
 		if node.mask_steps <= self._max_depth and node not in self._nodes:
 			if explore:
 				self._unexplored_nodes.append(node)
@@ -105,6 +108,28 @@ class Backtracker(object):
 	def __len__(self):
 		return len(self._unexplored_nodes)
 
+	def _check_runtime_pkg_mask(self, runtime_pkg_mask):
+		"""
+		If a package gets masked that caused other packages to be masked
+		before, we revert the mask for other packages (bug 375573).
+		"""
+
+		for pkg in runtime_pkg_mask:
+
+			if "missing dependency" in runtime_pkg_mask[pkg]:
+				continue
+
+			entry_is_valid = False
+
+			for ppkg, patom in runtime_pkg_mask[pkg].get("slot conflict", set()):
+				if ppkg not in runtime_pkg_mask:
+					entry_is_valid = True
+					break
+
+			if not entry_is_valid:
+				return False
+
+		return True
 
 	def _feedback_slot_conflict(self, conflict_data):
 		for pkg, parent_atoms in conflict_data:
diff --git a/pym/portage/tests/resolver/test_backtracking.py b/pym/portage/tests/resolver/test_backtracking.py
index fc493062c..600f68216 100644
--- a/pym/portage/tests/resolver/test_backtracking.py
+++ b/pym/portage/tests/resolver/test_backtracking.py
@@ -167,3 +167,46 @@ class BacktrackingTestCase(TestCase):
 				self.assertEqual(test_case.test_success, True, test_case.fail_msg)
 		finally:
 			playground.cleanup()
+
+
+	def testBacktrackNoWrongRebuilds(self):
+		"""
+		Ensure we remove backtrack masks if the reason for the mask gets masked itself.
+		"""
+
+		ebuilds = {
+			"dev-libs/A-1": { },
+			"dev-libs/A-2": { },
+			"dev-libs/B-1": { "RDEPEND": "dev-libs/D"},
+			"dev-libs/C-1": { },
+			"dev-libs/C-2": { "RDEPEND": ">=dev-libs/A-2" },
+			"dev-libs/D-1": { "RDEPEND": "<dev-libs/A-2" },
+			}
+
+		installed = {
+			"dev-libs/A-1": { },
+			"dev-libs/B-1": { "RDEPEND": "dev-libs/D" },
+			"dev-libs/C-1": { },
+			"dev-libs/D-1": { "RDEPEND": "<dev-libs/A-2" },
+			}
+
+		world = [ "dev-libs/B", "dev-libs/C" ]
+
+		options = {'--update' : True, '--deep' : True, '--selective' : True}
+
+		test_cases = (
+				ResolverPlaygroundTestCase(
+					["@world"],
+					options = options,
+					mergelist = [],
+					success = True),
+			)
+
+		playground = ResolverPlayground(ebuilds=ebuilds, installed=installed, world=world)
+
+		try:
+			for test_case in test_cases:
+				playground.run_TestCase(test_case)
+				self.assertEqual(test_case.test_success, True, test_case.fail_msg)
+		finally:
+			playground.cleanup()