make SpecifyShape.grad work and test it.

theano/tensor/basic.py

@@ -1568,8 +1568,13 @@ class SpecifyShape(Op):
         assert len(new_shape)==len(xshape)
         return [new_shape]
 
-    def grad(self, (x,), (gz,)):
-        return [gz]
+    def grad(self, (x, s), (gz,)):
+        # Should I set an SpecifyShape on gz? I think so
+        # But I don't do it now as we need to make an optimization
+        # to remove that op from the graph to don't block other optimization
+        # Should I do an optimizer that will remove the SpecifyShape? I think Yes
+        return [gz, None]
+        return [specify_shape(gz,s), None]
 
 specify_shape = SpecifyShape()
 

theano/tensor/tests/test_sharedvar.py

@@ -418,6 +418,12 @@ def makeSharedTester(shared_constructor_,
             if theano.config.mode!='FAST_COMPILE':
                 assert len(topo_cst)==0
 
+            # Test that we can take the grad.
+            shape_grad = tensor.grad(x1_specify_shape.sum(), x1_shared)
+            shape_constant_fct_grad = theano.function([], shape_grad)
+            theano.printing.debugprint(shape_constant_fct_grad)
+            shape_constant_fct_grad()
+
             #Test that we can replace with values of the different shape
             # but that will raise an error in some case, but not all
             specify_shape_fct()