Add a test

theano/compile/tests/test_builders.py

@@ -266,6 +266,38 @@ class T_OpFromGraph(unittest_tools.InferShapeTester):
 
         # TODO list override case
 
+    @test_params
+    def test_connection_pattern_override(self, cls_ofg):
+        x, y = T.vectors('xy')
+
+        def f1(x, y):
+            del x
+            # but we know how to backpropagate for x for some reasons
+            # and we don't care about the gradient wrt y.
+            return y + T.round(y)
+
+        def f1_back(inputs, output_gradients):
+            return [
+                output_gradients[0],
+                theano.gradient.disconnected_type()]
+
+        op = cls_ofg(
+            inputs=[x, y],
+            outputs=[f1(x, y)],
+            grad_overrides=f1_back,
+            connection_pattern=[[True], [False]],  # This is new
+            on_unused_input='ignore')  # This is new
+
+        c = op(x, y)
+
+        g1 = theano.grad(c.sum(), x)
+
+        out = g1.eval({
+            x: np.ones((5,), dtype=np.float32),
+            y: np.ones((5,), dtype=np.float32)})
+        assert np.allclose(out, [1.] *5)
+            # array([ 1.,  1.,  1.,  1.,  1.])
+
     @test_params
     def test_nested(self, cls_ofg):
         x, y = T.vectors('xy')