Pure Python Set objects were also not marking themselves changed on addition....

Pure Python Set objects were also not marking themselves changed on addition. This impacted things like zope.index.topic.filter

BTrees/_base.py

@@ -559,6 +559,7 @@ class Set(_BucketBase):
         index = self._search(key)
         if index < 0:
             index = -index - 1
+            self._p_changed = True
             self._keys.insert(index, key)
             return True, None
         return False, None

BTrees/tests/common.py

@@ -1421,6 +1421,32 @@ class NormalSetTests(Base):
         self.assertTrue(t._p_changed)
         self.assertEqual(t, t._p_jar.registered)
 
+    def testAddingOneSetsChanged(self):
+        # A bug in the BTree Set Python implementation once caused
+        # adding an object not to set _p_changed
+        t = self._makeOne()
+        # Note that for the property to actually hold, we have to fake a
+        # _p_jar and _p_oid
+        t._p_oid = b'\0\0\0\0\0'
+        class Jar(object):
+            def __init__(self):
+                self._cache = self
+                self.registered = None
+
+            def mru(self, arg):
+                pass
+            def readCurrent(self, arg):
+                pass
+            def register(self, arg):
+                self.registered = arg
+
+        t._p_jar = Jar()
+        t.add(0)
+        self.assertTrue(t._p_changed)
+        self.assertEqual(t, t._p_jar.registered)
+
+        # Whether or not doing `t.add(0)` again would result in
+        # _p_changed being set depends on whether this is a TreeSet or a plain Set
 
 class ExtendedSetTests(NormalSetTests):
 

CHANGES.rst

@@ -5,7 +5,7 @@
 ------------------
 
 - Fix _p_changed when removing items from small pure-Python
-  BTrees/TreeSets. See:
+  BTrees/TreeSets and when adding to Sets. See:
   https://github.com/zopefoundation/BTrees/issues/13