dnode: add iter_tree

The DNode.diff function result is hard to use because it is not possible
to iterate on the node tree. Add DNode.iter_tree for this purpose. The
code mimics the LYD_TREE_DFS_BEGIN/LYD_TREE_DFS_END libyang macros, but
in python.

Another possibility was to use the macros directly and call a python
callback, but it is easier to maintain this way.

Signed-off-by: Samuel Gauthier <samuel.gauthier@6wind.com>

Author: samuel-gauthier

libyang/data.py

@@ -553,6 +553,23 @@ def merge(
         if ret != lib.LY_SUCCESS:
             raise self.context.error("merge failed")
 
+    def iter_tree(self) -> Iterator["DNode"]:
+        n = next_n = self.cdata
+        while n != ffi.NULL:
+            yield self.new(self.context, n)
+
+            next_n = lib.lyd_child(n)
+            if next_n == ffi.NULL:
+                if n == self.cdata:
+                    break
+                next_n = n.next
+            while next_n == ffi.NULL:
+                n = n.parent
+                if n.parent == self.cdata.parent:
+                    break
+                next_n = n.next
+            n = next_n
+
     def print(
         self,
         fmt: str,

tests/test_data.py

@@ -749,6 +749,34 @@ def test_data_diff(self):
         dnode1.free()
         dnode2.free()
 
+    TREE = [
+        "/yolo-system:conf",
+        "/yolo-system:conf/hostname",
+        "/yolo-system:conf/url[proto='https'][host='github.com']",
+        "/yolo-system:conf/url[proto='https'][host='github.com']/proto",
+        "/yolo-system:conf/url[proto='https'][host='github.com']/host",
+        "/yolo-system:conf/url[proto='https'][host='github.com']/path",
+        "/yolo-system:conf/url[proto='https'][host='github.com']/enabled",
+        "/yolo-system:conf/url[proto='http'][host='foobar.com']",
+        "/yolo-system:conf/url[proto='http'][host='foobar.com']/proto",
+        "/yolo-system:conf/url[proto='http'][host='foobar.com']/host",
+        "/yolo-system:conf/url[proto='http'][host='foobar.com']/port",
+        "/yolo-system:conf/url[proto='http'][host='foobar.com']/path",
+        "/yolo-system:conf/url[proto='http'][host='foobar.com']/enabled",
+        "/yolo-system:conf/number[.='1000']",
+        "/yolo-system:conf/number[.='2000']",
+        "/yolo-system:conf/number[.='3000']",
+        "/yolo-system:conf/speed",
+    ]
+
+    def test_iter_tree(self):
+        dnode = self.ctx.parse_data_mem(self.JSON_CONFIG, "json", validate_present=True)
+        try:
+            paths = [d.path() for d in dnode.iter_tree()]
+            self.assertEqual(paths, self.TREE)
+        finally:
+            dnode.free()
+
     def test_find_one(self):
         dnode = self.ctx.parse_data_mem(self.JSON_CONFIG, "json", validate_present=True)
         self.assertIsInstance(dnode, DContainer)