[register] allow to pass a debug_callback argument to Registry._select_best

1 files changed, 33 insertions, 0 deletions

diff --git a/logilab/common/registry.py b/logilab/common/registry.py
index 2a8a1c0..7820689 100644
--- a/logilab/common/registry.py
+++ b/logilab/common/registry.py
@@ -406,23 +406,56 @@ class Registry(dict):
         return None if not object apply (don't raise `NoSelectableObject` since
         it's costly when searching objects using `possible_objects`
         (e.g. searching for hooks).
+
+        An optional argument `debug_callback` can be passed, it will be called
+        once the selection is done and will return a dict of the following form::
+
+          {"all_objects": [], "end_score": 0, "winners": [],
+          "self": self, "args": args, "kwargs": kwargs, }
         """
+
+        debug_callback = kwargs.pop('debug_callback', None)
+
+        debug_registry_select_best = {
+            "all_objects": [],
+            "end_score": 0,
+            "winners": [],
+            "self": self,
+            "args": args,
+            "kwargs": kwargs,
+        }
+
         score, winners = 0, None
         for obj in objects:
             objectscore = obj.__select__(obj, *args, **kwargs)
+
+            if debug_callback:
+                debug_registry_select_best["all_objects"].append({"object": obj, "score": objectscore})
+
             if objectscore > score:
                 score, winners = objectscore, [obj]
+
             elif objectscore > 0 and objectscore == score:
                 winners.append(obj)
+
+        if debug_callback:
+            debug_registry_select_best["winners"] = winners.copy() if winners else []
+            debug_registry_select_best["end_score"] = score
+            debug_callback(debug_registry_select_best)
+
         if winners is None:
             return None
+
         if len(winners) > 1:
             # log in production environement / test, error while debugging
             msg = 'select ambiguity: %s\n(args: %s, kwargs: %s)'
+
             if self.debugmode:
                 # raise bare exception in debug mode
                 raise SelectAmbiguity(msg % (winners, args, kwargs.keys()))
+
             self.error(msg, winners, args, kwargs.keys())
+
         # return the result of calling the object
         return self.selected(winners[0], args, kwargs)