# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1320090040 -3600
# Node ID 22dca03fcccba5781c0475903c276f8668268b87
# Parent  a6ddb1e042ea1384adb2baf579a04d82c5804150
Preserved empty usage observations when lists of object sets are combined and
when mapping dictionaries are updated.

diff -r a6ddb1e042ea -r 22dca03fcccb micropython/common.py
--- a/micropython/common.py	Mon Oct 31 19:09:47 2011 +0100
+++ b/micropython/common.py	Mon Oct 31 20:40:40 2011 +0100
@@ -62,6 +62,14 @@
     def __nonzero__(self):
         return self.objects != {}
 
+    # List methods.
+
+    def __add__(self, other):
+        obj = ObjectSet(self)
+        for key in other:
+            obj.add(key)
+        return obj
+
     # Set membership and comparisons.
 
     def __hash__(self):
@@ -131,7 +139,7 @@
         if value is None:
             new_dict[key] = None
         else:
-            new_dict[key] = set([value])
+            new_dict[key] = ObjectSet([value])
     return new_dict
 
 def merge_mapping_dicts(dicts):
@@ -148,11 +156,20 @@
 
     for old_dict in dicts:
         for key, value in old_dict.items():
-            if value is not None:
-                if not new_dict.has_key(key):
+            if not new_dict.has_key(key):
+                if value is not None:
                     new_dict[key] = ObjectSet(value)
                 else:
+                    new_dict[key] = None
+            elif new_dict[key] is not None:
+                if value is not None:
                     new_dict[key].update(value)
+                else:
+                    new_dict[key].add(value)
+            else:
+                if value is not None:
+                    objset = new_dict[key] = ObjectSet(value)
+                    objset.add(None)
 
 def combine_mapping_dicts(d1, d2):
 
@@ -186,14 +203,17 @@
     in 'd1' will not be added to 'd1'.
     """
 
-    d2_keys = d2.keys()
+    if d2 is not None:
+        d2_keys = d2.keys()
 
-    for key in d2_keys:
-        if not d1.has_key(key):
-            if not only_d1_keys:
-                combined[key] = d2[key]
-        else:
-            combined[key] = combine_op(d1[key], d2[key])
+        for key in d2_keys:
+            if not d1.has_key(key):
+                if not only_d1_keys:
+                    combined[key] = d2[key]
+            else:
+                combined[key] = combine_op(d1[key], d2[key])
+    else:
+        d2_keys = ()
 
     for key in d1.keys():
         if key not in d2_keys:
@@ -212,11 +232,11 @@
         if l2 is None:
             return None
         else:
-            return l2
+            return l2 + [None]
     elif l2 is None:
-        return l1
+        return l1 + [None]
 
-    combined = set([])
+    combined = ObjectSet()
     for i1 in l1:
         for i2 in l2:
             combined.add(i1.merge(i2))
@@ -292,6 +312,7 @@
     all_objtypes = set()
 
     for attrnames in usage:
+        attrnames = attrnames or ()
         objtypes = objtable.all_possible_objects_plus_status(attrnames)
         if not objtypes:
             print "Warning: usage in %r for %r finds no object supporting all attributes %r" % (