dirnode: return to 'delete fails if the child wasn't actually there' semantics, to make tests pass. There's a switch to enable/disable this

src/allmydata/dirnode.py

@@ -39,12 +39,15 @@ def split_netstring(data, numstrings, allow_leftover=False):
     return tuple(elements)
 
 class Deleter:
-    def __init__(self, node, name):
+    def __init__(self, node, name, must_exist=True):
         self.node = node
         self.name = name
+        self.must_exist = True
     def modify(self, old_contents):
         children = self.node._unpack_contents(old_contents)
         if self.name not in children:
+            if self.must_exist:
+                raise KeyError(self.name)
             self.old_child = None
             return None
         self.old_child, metadata = children[self.name]

src/allmydata/test/common.py

@@ -102,10 +102,12 @@ class FakeMutableFileNode:
         self.all_contents[self.storage_index] = new_contents
         return defer.succeed(None)
     def modify(self, modifier):
+        return defer.maybeDeferred(self._modify, modifier)
+    def _modify(self, modifier):
         assert not self.is_readonly()
         old_contents = self.all_contents[self.storage_index]
         self.all_contents[self.storage_index] = modifier(old_contents)
-        return defer.succeed(None)
+        return None
 
 
 def make_mutable_file_uri():