Add a test case for previous crash

theano/scan_module/tests/test_scan.py

@@ -2519,6 +2519,35 @@ class T_Scan(unittest.TestCase):
         utt.assert_allclose(tx4, v_u[-1] + 4.)
         utt.assert_allclose(tx5, v_u[-1] + 5.)
 
+    def test_use_scan_direct_output(self):
+        # This test looks for a crash that happened when directly using the
+        # recurrent output of a scan node instead of taking the result
+        # returned by the scan() function
+
+        x = tensor.scalar()
+        seq = tensor.vector()
+        out, updates = theano.scan(lambda a, b : a + b, sequences=seq,
+                                   outputs_info=x)
+
+        # Obtain a reference to the scan output before the subtensor and
+        # compile a function with it as output
+        assert isinstance(out.owner.op, tensor.subtensor.Subtensor)
+        out = out.owner.inputs[0]
+        fct = theano.function([x, seq], out[:-1])
+
+        # Test the function to ensure valid outputs
+        floatX = theano.config.floatX
+
+        init_value = 5.0
+        seq_value = numpy.arange(4, dtype=floatX)
+        output = fct(init_value, seq_value)
+
+        expected_output = [init_value]
+        for i in seq_value[:-1]:
+            expected_output.append(expected_output[-1] + i)
+
+        utt.assert_allclose(output, expected_output)
+
     def test_infer_shape(self):
         # Test for a crash in scan.infer_shape when using both
         # an until condition and random sampling in the inner function.