data: allow to customize free

When using sysrepo, we need to use sysrepo function to free dnode data.
Currently, the free method can't be overridden without hack.

This patch add the possibility to override the free method and will
allow the utilization with sysrepo-python.

Author: jeanseb6wind

libyang/data.py

@@ -205,7 +205,7 @@ class DNode:
     Data tree node.
     """
 
-    __slots__ = ("context", "cdata")
+    __slots__ = ("context", "cdata", "free_func")
 
     def __init__(self, context: "libyang.Context", cdata):
         """
@@ -216,6 +216,7 @@ def __init__(self, context: "libyang.Context", cdata):
         """
         self.context = context
         self.cdata = cdata  # C type: "struct lyd_node *"
+        self.free_func = None  # type: Callable[struct lyd_node *]
 
     def meta(self):
         ret = {}
@@ -791,7 +792,9 @@ def merge_data_dict(
 
     def free(self, with_siblings: bool = True) -> None:
         try:
-            if with_siblings:
+            if self.free_func:
+                self.free_func(self.cdata)  # pylint: disable=not-callable
+            elif with_siblings:
                 lib.lyd_free_all(self.cdata)
             else:
                 lib.lyd_free_tree(self.cdata)

tests/test_data.py

@@ -4,6 +4,7 @@
 import json
 import os
 import unittest
+from unittest import mock
 from unittest.mock import patch
 
 from _libyang import lib
@@ -394,6 +395,22 @@ def test_data_from_dict_module(self):
             dnode.free()
         self.assertEqual(json.loads(j), json.loads(self.JSON_CONFIG))
 
+    def test_data_from_dict_module_free_func(self):
+        module = self.ctx.get_module("yolo-system")
+
+        free_func = mock.Mock()
+        dnode = module.parse_data_dict(
+            self.DICT_CONFIG, strict=True, validate_present=True
+        )
+        dnode.free_func = free_func
+        self.assertIsInstance(dnode, DContainer)
+        try:
+            j = dnode.print_mem("json")
+        finally:
+            dnode.free()
+        self.assertEqual(json.loads(j), json.loads(self.JSON_CONFIG))
+        free_func.assert_called()
+
     DICT_CONFIG_WITH_PREFIX = {
         "yolo-system:conf": {
             "hostname": "foo",