Fix indexing type inference.

Cython/Compiler/ExprNodes.py

@@ -2033,7 +2033,7 @@ class IndexNode(ExprNode):
         return None
 
     def type_dependencies(self, env):
-        return self.base.type_dependencies(env)
+        return self.base.type_dependencies(env) + self.index.type_dependencies(env)
 
     def infer_type(self, env):
         base_type = self.base.infer_type(env)

tests/run/type_inference.pyx

@@ -479,3 +479,10 @@ def large_literals():
     c, d = 10, 100000000000000000000000000000000
     assert typeof(c) == "long", typeof(c)
     assert typeof(d) == "Python object", typeof(d)
+
+
+# Regression test for trac #638.
+
+def bar(foo):
+    qux = foo
+    quux = foo[qux.baz]