fix type inference for target of with statement

Cython/Compiler/TypeInference.py

@@ -65,6 +65,11 @@ class MarkAssignments(CythonTransform):
             # Could use this info to infer cdef class attributes...
             pass
 
+    def visit_WithTargetAssignmentStatNode(self, node):
+        self.mark_assignment(node.lhs, node.rhs)
+        self.visitchildren(node)
+        return node
+
     def visit_SingleAssignmentNode(self, node):
         self.mark_assignment(node.lhs, node.rhs)
         self.visitchildren(node)

tests/run/type_inference.pyx

@@ -529,6 +529,24 @@ def large_literals():
     assert typeof(d) == "Python object", typeof(d)
 
 
+class EmptyContextManager(object):
+    def __enter__(self):
+        return None
+    def __exit__(self, *args):
+        return 0
+
+def with_statement():
+    """
+    >>> with_statement()
+    Python object
+    'Python object'
+    """
+    x = 1.0
+    with EmptyContextManager() as x:
+        print(typeof(x))
+    return typeof(x)
+
+
 # Regression test for trac #638.
 
 def bar(foo):