[Dynamic-to-Static] Fix bug in loop_transformer: loop vars should contain the var from ancestor-for-node (#28735)

python/paddle/fluid/dygraph/dygraph_to_static/loop_transformer.py

@@ -294,11 +294,21 @@ class NameVisitor(gast.NodeVisitor):
             return True
         return False
 
+    def _is_ancestor_node(self, ancestor_node, node):
+        parent_node = self._get_parent_node(node)
+
+        while parent_node is not None:
+            if parent_node == ancestor_node:
+                return True
+            parent_node = self._get_parent_node(parent_node)
+        return False
+
     def _get_parent_node(self, node):
         wrapper_node = self.node_to_wrapper_map.get(node)
         if wrapper_node:
-            parent_node = wrapper_node.parent.node
-            return parent_node
+            if wrapper_node.parent:
+                parent_node = wrapper_node.parent.node
+                return parent_node
         return None
 
     def _remove_unnecessary_vars(self, loop_vars, loop_node):
@@ -355,9 +365,22 @@ class NameVisitor(gast.NodeVisitor):
                         if child_node.id in target_var_names:
                             vars_of_list_generator.add(child_node)
 
-            # 2. Get target vars or vars from target vars used in for-loop.
-            elif isinstance(parent_node,
-                            gast.For) and parent_node is not loop_node:
+            # 2. Get target vars or vars from target vars used in for-loop but the for-loop is
+            #   1) not the "loop_node" itself
+            #   2) not the ancestor of the "loop_node"
+            #
+            # For examples:
+            #   for k in range(x):   # if it's this "loop_node", i or j both should be target vars.
+            #      # do something
+            #
+            #   for i in range(a):   # if it's this "loop_node", k or j should be in target vars but i should not.
+            #     for j in range(a): # if it's this "loop_node", k should be in target_vars but i or j should not.
+            #       x = i+j
+            elif isinstance(parent_node, gast.For):
+                if parent_node is loop_node:
+                    continue
+                if self._is_ancestor_node(parent_node, loop_node):
+                    continue
                 # 2.1 target vars in gast.For node.
                 target_node = parent_node.target
                 if isinstance(target_node, gast.Tuple):

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

@@ -161,7 +161,7 @@ def nested_for_loop_dyfunc():
     three = fluid.layers.fill_constant(shape=[1], value=3, dtype="int32")
     for j in range(two):
         for i in range(10):
-            a = 2
+            a = 2 + j
 
     for i in range(three):
         b = fluid.layers.zeros(shape=[1], dtype='float32')
@@ -216,16 +216,25 @@ class TestNameVisitor(unittest.TestCase):
         self.loop_var_names = [
             set(["j", "two"]),
             set(["i", "three", "b"]),
-            set(["i"]),
+            set(["i", "j"]),
         ]
         self.create_var_names = [set(), set(["b"]), set()]
+
         i = 0
         for node in gast.walk(gast_root):
             if isinstance(node, (gast.While, gast.For)):
                 loop_var_names, create_var_names = name_visitor.get_loop_var_names(
                     node)
-                self.assertEqual(loop_var_names, self.loop_var_names[i])
-                self.assertEqual(create_var_names, self.create_var_names[i])
+                self.assertEqual(
+                    loop_var_names,
+                    self.loop_var_names[i],
+                    msg="loop_var_names : {}, \nexpected loop_var_names : {}".
+                    format(loop_var_names, self.loop_var_names[i]))
+                self.assertEqual(
+                    create_var_names,
+                    self.create_var_names[i],
+                    msg="i = {}\ncreate_var_names : {}, \nexpected create_var_names : {}".
+                    format(i, create_var_names, self.create_var_names[i]))
                 i += 1