Bug #339606 - Fix broken 'missed update' message.

diff --git a/pym/_emerge/depgraph.py b/pym/_emerge/depgraph.py
index 7f5d168641cd0c43b313e0227cbaa4ed0b5d54ce..82433e8d96f5d07a51a487131ea695555dc89f84 100644 (file)
--- a/pym/_emerge/depgraph.py
+++ b/pym/_emerge/depgraph.py
@@ -875,17 +875,29 @@ class depgraph(object):
 
                                                backtrack_data = []
                                                all_parents = set()
-                                               for node, other_node in (existing_node, pkg), (pkg, existing_node):
+                                               # HACK: The ordering of backtrack_data can make
+                                               # a difference here. We choose an order such that
+                                               # the backtracker will first explore the choice with
+                                               # existing_node masked. The backtracker reverses the
+                                               # order twice, so the order it uses is the order shown
+                                               # here (the net result of two reversals is the same as
+                                               # no reversal). See bug #339606.
+                                               for to_be_selected, to_be_masked in (pkg, existing_node), (existing_node, pkg):
+                                                       # For missed update messages, find out which
+                                                       # atoms matched to_be_selected that did not
+                                                       # match to_be_masked.
                                                        parent_atoms = \
-                                                               self._dynamic_config._parent_atoms.get(node, set())
+                                                               self._dynamic_config._parent_atoms.get(to_be_selected, set())
                                                        if parent_atoms:
                                                                conflict_atoms = self._dynamic_config._slot_conflict_parent_atoms.intersection(parent_atoms)
                                                                if conflict_atoms:
                                                                        parent_atoms = conflict_atoms
                                                        all_parents.update(parent_atoms)
-                                                       if node < other_node:
+                                                       if to_be_selected >= to_be_masked:
+                                                               # We only care about the parent atoms
+                                                               # when they trigger a downgrade.
                                                                parent_atoms = set()
-                                                       backtrack_data.append((node, parent_atoms))
+                                                       backtrack_data.append((to_be_masked, parent_atoms))
 
                                                self._dynamic_config._backtrack_infos["slot conflict"] = backtrack_data
                                                self._dynamic_config._need_restart = True