Fix bug in infer_shape of Flatten

theano/tensor/basic.py

@@ -5778,13 +5778,20 @@ class Flatten(Op):
         in_shp, = in_shapes
         part1 = in_shp[:self.outdim - 1]
         part2 = in_shp[self.outdim - 1:]
-        # The if is needed as numpy.prod([]) return a float 1.0
-        # We do not want to force the other dtype to int32/64.
+
         if len(part2) > 1:
-            part2 = prod(part2, dtype='int64')
+            part2 = (prod(part2, dtype='int64'),)
+        elif len(part2) == 1:
+            # We do not want to force an upcast of part2 if its length is 1
+            pass
         else:
-            part2 = 1
-        out_shape = (part1 + (part2,))
+            if len(in_shp) == 0 and self.outdim == 1:
+                part2 = (1,)
+            else:
+                raise ValueError('invalid output ndimensions (%i) for tensor '
+                                 'of rank %i' % (self.outdim, len(in_shp)))
+
+        out_shape = (part1 + part2)
         return [out_shape]
 
     def grad(self, inp, grads):

theano/tensor/tests/test_basic.py

@@ -6505,17 +6505,26 @@ class TestInferShape(utt.InferShapeTester):
                         [admat_val, adtens4_val], TensorDot)
 
         # Flatten
-        adtens = tensor3()
-        adtens_val = rand(4, 5, 3)
-        outdim = 2
-        self._compile_and_check([adtens],
-                                [Flatten(outdim)(adtens)],
-                                [adtens_val], Flatten)
+        atens3 = tensor3()
+        atens3_val = rand(4, 5, 3)
+        for outdim in (3, 2, 1):
+            self._compile_and_check([atens3],
+                                    [Flatten(outdim)(atens3)],
+                                    [atens3_val], Flatten)
+
+        amat = matrix()
+        amat_val = rand(4, 5)
+        for outdim in (2, 1):
+            self._compile_and_check([amat],
+                                    [Flatten(outdim)(amat)],
+                                    [amat_val], Flatten)
 
+        avec = vector()
+        avec_val = rand(4)
         outdim = 1
-        self._compile_and_check([adtens],
-                                [Flatten(outdim)(adtens)],
-                                [adtens_val], Flatten)
+        self._compile_and_check([avec],
+                                [Flatten(outdim)(avec)],
+                                [avec_val], Flatten)
 
         # Eye
         aiscal = iscalar()
@@ -6536,6 +6545,8 @@ class TestInferShape(utt.InferShapeTester):
         # Shape
         # 'opt.Makevector' precludes optimizer from disentangling
         # elements of shape
+        adtens = tensor3()
+        adtens_val = rand(4, 5, 3)
         self._compile_and_check([adtens],
                                 [Shape()(adtens)],
                                 [adtens_val], (opt.MakeVector, Shape))