cooker/event: Add an event which lists all stamps reachable after parsing

index 577d808..d2b5ceb 100644
@@ -1477,6 +1477,11 @@ class BBCooker:
             self.handlePrefProviders()
             self.recipecache.bbfile_priority = self.collection.collection_priorities(self.recipecache.pkg_fn, self.data)
             self.state = state.running
+
+            # Send an event listing all stamps reachable after parsing
+            # which the metadata may use to clean up stale data
+            event = bb.event.ReachableStamps(self.recipecache.stamp)
+            bb.event.fire(event, self.expanded_data)
             return None
 
         return True

index fec6a05..ba0de11 100644
@@ -497,6 +497,16 @@ class TargetsTreeGenerated(Event):
         Event.__init__(self)
         self._model = model
 
+class ReachableStamps(Event):
+    """
+    An event listing all stamps reachable after parsing
+    which the metadata may use to clean up stale data
+    """
+
+    def __init__(self, stamps):
+        Event.__init__(self)
+        self.stamps = stamps
+
 class FilesMatchingFound(Event):
     """
     Event when a list of files matching the supplied pattern has