Enhance slice to support 0 shape Tensor (#45861)

* Enhance slice to support 0 dims Tensor

* Add UT

paddle/fluid/pybind/eager_method.cc

@@ -759,8 +759,10 @@ static PyObject* tensor__getitem_index_not_tensor(TensorObject* self,
       decrease_axis, none_axes, infer_flags, list_select_idxs;
   // if index is a list, list_select_flag will be true
   bool list_select_flag = false;
+  // Note(0x45f): Using defined() instead of initialized()
+  // to support slice tensor which shape like [0, 0, 0].
   PADDLE_ENFORCE_EQ(
-      self->tensor.initialized(),
+      self->tensor.defined(),
       true,
       platform::errors::InvalidArgument(
           "tensor %s has not been initialized, we can only slice initialized "

python/paddle/fluid/tests/unittests/dygraph_to_static/test_slice.py

@@ -284,5 +284,23 @@ class TestPaddleStridedSlice(unittest.TestCase):
         np.testing.assert_array_equal(sl.numpy(), array_slice)
 
 
+def slice_zero_shape_tensor(x):
+    y = x[1:2]
+    return y
+
+
+class TestSliceZeroShapeTensor(unittest.TestCase):
+
+    def test_slice(self):
+        paddle.disable_static()
+        x = paddle.ones([0, 0, 0, 0])
+        y = slice_zero_shape_tensor(x)
+        np.testing.assert_equal(y.shape, [0, 0, 0, 0])
+
+        static_func = paddle.jit.to_static(slice_zero_shape_tensor)
+        y = static_func(x)
+        np.testing.assert_equal(y.shape, [0, 0, 0, 0])
+
+
 if __name__ == '__main__':
     unittest.main()