Make layers.reshape/expand/slice in dygraph support var inputs. (#22920)

* Make layers.reshape/expand/slice in dygraph support var inputs.
Make transpose support size 0.
test=develop

* Update layers.expand and layers.slice to support var inputs.
test=develop

python/paddle/fluid/layers/nn.py

@@ -5948,18 +5948,11 @@ def reshape(x, shape, actual_shape=None, act=None, inplace=False, name=None):
             warnings.warn(
                 "Inplace on reshape is not allowed and will be discarded in dygraph mode currently."
             )
-        attrs = {}
         if isinstance(shape, (list, tuple)):
-            if utils._contain_var(shape):
-                raise TypeError(
-                    "The type of 'shape' in reshape must be list[int] or tuple(int) in Dygraph mode, but "
-                    "received %s, which contains Variable." % type(shape))
-            attrs['shape'] = shape
-        else:
-            raise TypeError(
-                "The type of 'shape' in reshape must be list[int] or tuple(int) in Dygraph mode, but "
-                "received %s." % type(shape))
-
+            shape = [
+                item.numpy()[0] if isinstance(item, Variable) else item
+                for item in shape
+            ]
             out, _ = core.ops.reshape2(x, 'shape', shape)
             return dygraph_utils._append_activation_in_dygraph(out, act)
 
@@ -9770,14 +9763,10 @@ def expand(x, expand_times, name=None):
     """
     if in_dygraph_mode():
         if isinstance(expand_times, (list, tuple)):
-            if utils._contain_var(expand_times):
-                raise TypeError(
-                    "The type of 'expand_times' in expand must be list[int] or tuple(int) in Dygraph mode, but "
-                    "received %s, which contains Variable." % type(shape))
-        else:
-            raise TypeError(
-                "The type of 'expand_times' in expand must be list[int] or tuple(int) in Dygraph mode, but "
-                "received %s." % type(shape))
+            expand_times = [
+                item.numpy()[0] if isinstance(item, Variable) else item
+                for item in expand_times
+            ]
 
             return core.ops.expand(x, 'expand_times', expand_times)
 
@@ -10318,25 +10307,16 @@ def slice(input, axes, starts, ends):
     """
     if in_dygraph_mode():
         infer_flags = list(1 for i in range(len(axes)))
-        if isinstance(starts, (list, tuple)):
-            if utils._contain_var(starts):
-                raise TypeError(
-                    "The type of 'starts' in slice must be list[int] or tuple(int) in Dygraph mode, but "
-                    "received %s, which contains Variable." % type(shape))
-        else:
-            raise TypeError(
-                "The type of 'starts' in slice must be list[int] or tuple(int) in Dygraph mode, but "
-                "received %s." % type(shape))
-
-        if isinstance(ends, (list, tuple)):
-            if utils._contain_var(ends):
-                raise TypeError(
-                    "The type of 'ends' in slice must be list[int] or tuple(int) in Dygraph mode, but "
-                    "received %s, which contains Variable." % type(shape))
-        else:
-            raise TypeError(
-                "The type of 'ends' in slice must be list[int] or tuple(int) in Dygraph mode, but "
-                "received %s." % type(shape))
+        if isinstance(starts, (list, tuple)) and isinstance(ends,
+                                                            (list, tuple)):
+            starts = [
+                item.numpy()[0] if isinstance(item, Variable) else item
+                for item in starts
+            ]
+            ends = [
+                item.numpy()[0] if isinstance(item, Variable) else item
+                for item in ends
+            ]
 
             return core.ops.slice(input, 'axes', axes, 'starts', starts, 'ends',
                                   ends, 'infer_flags', infer_flags)

python/paddle/fluid/layers/rnn.py

@@ -725,7 +725,7 @@ class BeamSearchDecoder(Decoder):
                 data type is same as `x`.     
         """
         # TODO: avoid fake shape in compile-time like tile_beam_merge_with_batch
-        return nn.reshape(x, shape=(-1, self.beam_size) + x.shape[1:])
+        return nn.reshape(x, shape=[-1, self.beam_size] + list(x.shape[1:]))
 
     def _merge_batch_beams(self, x):
         """
@@ -741,7 +741,7 @@ class BeamSearchDecoder(Decoder):
                 data type is same as `x`.     
         """
         # TODO: avoid fake shape in compile-time like tile_beam_merge_with_batch
-        return nn.reshape(x, shape=(-1, ) + x.shape[2:])
+        return nn.reshape(x, shape=[-1] + list(x.shape[2:]))
 
     def _expand_to_beam_size(self, x):
         """