Fix crash in scan.infer_shape() and add test case.

theano/scan_module/scan_op.py

@@ -1265,8 +1265,13 @@ class Scan(PureOp):
         # if we are dealing with a repeat-until, then we do not know the
         # leading dimension so we replace it for every entry with Shape_i
         if self.as_while:
-            scan_outs = [(Shape_i(0)(o),) + x[1:]
-                         for o, x in izip(node.outputs, scan_outs)]
+            scan_outs_init = scan_outs
+            scan_outs = []
+            for o, x in izip(node.outputs, scan_outs_init):
+                if x is None:
+                    scan_outs.append(None)
+                else:
+                    scan_outs.append((Shape_i(0)(o),) + x[1:])
         return scan_outs
 
     def get_input_pos(self, output_index):

theano/scan_module/tests/test_scan.py

@@ -2519,6 +2519,25 @@ class T_Scan(unittest.TestCase):
         utt.assert_allclose(tx4, v_u[-1] + 4.)
         utt.assert_allclose(tx5, v_u[-1] + 5.)
 
+    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.
+
+        x = tensor.scalar()
+        srng = theano.tensor.shared_randomstreams.RandomStreams(0)
+
+        def inner_fct(previous_val):
+            new_val = previous_val + srng.uniform()
+            condition = theano.scan_module.until(previous_val > 50)
+            return new_val, condition
+
+        out, updates = theano.scan(inner_fct,
+                                   outputs_info=x,
+                                   n_steps=100)
+
+        g_out = tensor.grad(out.sum(), x)
+        fct = theano.function([x], out)
+
     # The following test will fail in DebugMode if there are
     # some problems in Scan.infer_shape
     def test_remove_stuff(self):