Add fallback backtrack_data, in case logic fails.

This adds some safety in the depgraph._add_pkg() slot conflict code,
in case the new logic fails somehow (it shouldn't, but given all
the complexities, who knows?). Also, add some more debug output.

diff --git a/pym/_emerge/depgraph.py b/pym/_emerge/depgraph.py
index ab34a411ae34b0a14dd80fd2812494fb36765108..5ab42f68e1f4a55248bc96a548b857e0a2f02716 100644 (file)
--- a/pym/_emerge/depgraph.py
+++ b/pym/_emerge/depgraph.py
@@ -874,6 +874,7 @@ class depgraph(object):
                                                self._process_slot_conflicts()
 
                                                backtrack_data = []
+                                               fallback_data = []
                                                all_parents = set()
                                                # The ordering of backtrack_data can make
                                                # a difference here, because both mask actions may lead
@@ -904,16 +905,26 @@ class depgraph(object):
                                                                        all_match = False
                                                                        break
 
-                                                       if all_match:
-                                                               # 'to_be_masked' does not violate any parent atom, which means
-                                                               # there is no point in masking it.
-                                                               continue
-
                                                        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((to_be_masked, parent_atoms))
+
+                                                       fallback_data.append((to_be_masked, parent_atoms))
+
+                                                       if all_match:
+                                                               # 'to_be_masked' does not violate any parent atom, which means
+                                                               # there is no point in masking it.
+                                                               pass
+                                                       else:
+                                                               backtrack_data.append((to_be_masked, parent_atoms))
+
+                                               if not backtrack_data:
+                                                       # This shouldn't happen, but fall back to th old
+                                                       # behavior if this gets triggered somehow.
+                                                       backtrack_data = fallback_data
+
+                                               to_be_masked = backtrack_data[-1][0]
 
                                                self._dynamic_config._backtrack_infos["slot conflict"] = backtrack_data
                                                self._dynamic_config._need_restart = True
@@ -922,8 +933,11 @@ class depgraph(object):
                                                        msg.append("")
                                                        msg.append("")
                                                        msg.append("backtracking due to slot conflict:")
+                                                       if backtrack_data is fallback_data:
+                                                               msg.append("!!! backtrack_data fallback")
                                                        msg.append("   first package:  %s" % existing_node)
                                                        msg.append("   second package: %s" % pkg)
+                                                       msg.append("  package to mask: %s" % to_be_masked)
                                                        msg.append("      slot: %s" % pkg.slot_atom)
                                                        msg.append("   parents: %s" % ", ".join( \
                                                                "(%s, '%s')" % (ppkg, atom) for ppkg, atom in all_parents))