Allow composite fused types.

Cython/Compiler/Nodes.py

@@ -1215,8 +1215,6 @@ class FusedTypeNode(CBaseTypeNode):
 
             if type in types:
                 error(type_node.pos, "Type specified multiple times")
-            elif type.is_fused:
-                error(type_node.pos, "Cannot fuse a fused type")
             else:
                 types.append(type)
 

Cython/Compiler/PyrexTypes.py

@@ -1339,7 +1339,13 @@ class FusedType(CType):
     exception_check = 0
 
     def __init__(self, types, name=None):
-        self.types = types
+        # Use list rather than set to preserve order.
+        flattened_types = [t for t in types if not t.is_fused]
+        subtypes = sum([t.types for t in types if t.is_fused], [])
+        for type in subtypes:
+            if type not in flattened_types:
+                flattened_types.append(type)
+        self.types = flattened_types
         self.name = name
 
     def declaration_code(self, entity_code, for_display = 0,

tests/errors/fused_types.pyx

@@ -67,7 +67,6 @@ func(x, y)
 _ERRORS = u"""
 10:15: fused_type does not take keyword arguments
 15:38: Type specified multiple times
-17:33: Cannot fuse a fused type
 26:4: Invalid use of fused types, type cannot be specialized
 26:4: Not enough types specified to specialize the function, int2_t is still fused
 27:4: Invalid use of fused types, type cannot be specialized

tests/run/fused_types.pyx

@@ -19,6 +19,7 @@ other_t = cython.fused_type(int, double)
 ctypedef double *p_double
 ctypedef int *p_int
 fused_type3 = cython.fused_type(int, double)
+fused_composite = cython.fused_type(fused_type2, fused_type3)
 
 def test_pure():
     """
@@ -349,3 +350,17 @@ def test_index_fused_args(cython.floating f, ints_t i):
     double int
     """
     _test_index_fused_args[cython.floating, ints_t](f, i)
+
+def test_composite(fused_composite x):
+    """
+    >>> test_composite('a')
+    'a'
+    >>> test_composite(3)
+    6
+    >>> test_composite(3.0)
+    6.0
+    """
+    if fused_composite is string_t:
+        return x
+    else:
+        return 2 * x