fix refnanny code for del statement inside of generators

Cython/Compiler/ExprNodes.py

@@ -1861,6 +1861,8 @@ class NameNode(AtomicExprNode):
                     code.put_error_if_unbound(self.pos, self.entry)
 
                 if self.entry.type.is_pyobject:
+                    if self.entry.in_closure:
+                        code.put_gotref(self.result()) # generator
                     code.put_decref(self.result(), self.ctype())
                     code.putln('%s = NULL;' % self.result())
                 else:

tests/run/generators_py.py

@@ -350,3 +350,15 @@ def test_generator_cleanup():
         yield 1
     finally:
         print('cleanup')
+
+def test_del_in_generator():
+    """
+    >>> [ s for s in test_del_in_generator() ]
+    ['abcabcabc', 'abcabcabc']
+    """
+    x = len('abc') * 'abc'
+    a = x
+    yield x
+    del x
+    yield a
+    del a