fix bug #693: side effects on complex coercion

Cython/Compiler/ExprNodes.py

@@ -7563,10 +7563,14 @@ class CoerceToPyTypeNode(CoercionNode):
     is_temp = 1
 
     def __init__(self, arg, env, type=py_object_type):
-        CoercionNode.__init__(self, arg)
         if not arg.type.create_to_py_utility_code(env):
-            error(arg.pos,
-                  "Cannot convert '%s' to Python object" % arg.type)
+            error(arg.pos, "Cannot convert '%s' to Python object" % arg.type)
+        elif arg.type.is_complex:
+            # special case: complex coercion is so complex that it
+            # uses a macro ("__pyx_PyComplex_FromComplex()"), for
+            # which the argument must be simple
+            arg = arg.coerce_to_simple(env)
+        CoercionNode.__init__(self, arg)
         if type is py_object_type:
             # be specific about some known types
             if arg.type.is_string:

tests/run/complex_coercion_sideeffects_T693.pyx

+# mode: run
+# ticket: 693
+
+cdef double complex func(double complex x):                                                  
+    print "hello"
+    return x
+
+def test_coercion():
+    """
+    >>> c = test_coercion()
+    hello
+    >>> c.real == 0.5
+    True
+    >>> c.imag == 1.5
+    True
+    """
+    cdef object x = func(0.5 + 1.5j)
+    return x