[HeteroGraph] Fix the failure of apply_nodes when the input function …

…changes feature size for all nodes (dmlc#2223)

* Fix

* Fix

python/dgl/heterograph.py

@@ -4016,10 +4016,10 @@ def apply_nodes(self, func, v=ALL, ntype=None, inplace=False):
         ntid = self.get_ntype_id(ntype)
         ntype = self.ntypes[ntid]
         if is_all(v):
-            v = self.nodes(ntype)
+            v_id = self.nodes(ntype)
         else:
-            v = utils.prepare_tensor(self, v, 'v')
-        ndata = core.invoke_node_udf(self, v, ntype, func, orig_nid=v)
+            v_id = utils.prepare_tensor(self, v, 'v')
+        ndata = core.invoke_node_udf(self, v_id, ntype, func, orig_nid=v_id)
         self._set_n_repr(ntid, v, ndata)
 
     def apply_edges(self, func, edges=ALL, etype=None, inplace=False):

tests/compute/test_heterograph.py

@@ -1295,6 +1295,8 @@ def _check_typed_subgraph2(g, sg):
 def test_apply(idtype):
     def node_udf(nodes):
         return {'h': nodes.data['h'] * 2}
+    def node_udf2(nodes):
+        return {'h': F.sum(nodes.data['h'], dim=1, keepdims=True)}
     def edge_udf(edges):
         return {'h': edges.data['h'] * 2 + edges.src['h']}
 
@@ -1314,6 +1316,11 @@ def edge_udf(edges):
     g['plays'].apply_edges(edge_udf)
     assert F.array_equal(g['plays'].edata['h'], F.ones((4, 5)) * 12)
 
+    # Test the case that feature size changes
+    g.nodes['user'].data['h'] = F.ones((3, 5))
+    g.apply_nodes(node_udf2, ntype='user')
+    assert F.array_equal(g.nodes['user'].data['h'], F.ones((3, 1)) * 5)
+
     # test fail case
     # fail due to multiple types
     with pytest.raises(DGLError):