Repair errors surfaced by the new tests

implementations/python/preserves/text.py

@@ -282,6 +282,14 @@ class Parser(TextCodec):
                 return tuple(vs)
             vs.append(self.next())
 
+    def read_set(self):
+        items = self.upto('}')
+        s = set()
+        for i in items:
+            if i in s: raise DecodeError('Duplicate value in set: ' + repr(i))
+            s.add(i)
+        return frozenset(s)
+
     def read_dictionary(self):
         acc = []
         while True:
@@ -344,7 +352,7 @@ class Parser(TextCodec):
             c = self.nextchar()
             if c == 'f': return self.wrap(False)
             if c == 't': return self.wrap(True)
-            if c == '{': return self.wrap(frozenset(self.upto('}')))
+            if c == '{': return self.wrap(self.read_set())
             if c == '"': return self.wrap(self.read_literal_binary())
             if c == 'x':
                 c = self.nextchar()

implementations/python/preserves/values.py

@@ -509,6 +509,8 @@ class ImmutableDict(dict):
                     v = next(i)
                 except StopIteration:
                     raise DecodeError("Missing dictionary value")
+                if k in result:
+                    raise DecodeError("Duplicate key: " + repr(k))
                 result_proxy.__setitem__(k, v)
         except StopIteration:
             pass