netplan: set: allow the removal of an entire devtype subtree

See LP: #1942930

Note that performance for this are horrendous, as we parse the whole
tree once for *each* removed netdef!

netplan/cli/commands/set.py

@@ -59,7 +59,14 @@ def split_tree_by_hint(self, set_tree) -> (str, dict):
         for devtype in network:
             if devtype in GLOBAL_KEYS:
                 continue  # special handling of global keys down below
-            for netdef in network.get(devtype, []):
+            devtype_content = network.get(devtype, [])
+            # Special case: removal of a whole devtype.
+            # We replace the devtype null node with a dict of all defined netdefs
+            # set to None.
+            if devtype_content is None:
+                devtype_content = {dev: None for dev in utils.netplan_get_ids_for_devtype(devtype, self.root_dir)}
+                network[devtype] = devtype_content
+            for netdef in devtype_content:
                 hint = FALLBACK_HINT
                 filename = utils.netplan_get_filename_by_id(netdef, self.root_dir)
                 if filename:

tests/test_cli_get_set.py

@@ -193,6 +193,21 @@ def test_set_delete(self):
             self.assertNotIn('addresses:', out)
             self.assertNotIn('eth0:', out)
 
+    def test_set_delete_subtree(self):
+        with open(self.path, 'w') as f:
+            f.write('''network:\n  version: 2\n  renderer: NetworkManager
+  ethernets:
+    eth0: {addresses: [1.2.3.4/24]}''')
+        self._set(['network.ethernets=null'])
+        self.assertTrue(os.path.isfile(self.path))
+        with open(self.path, 'r') as f:
+            out = f.read()
+            # print(out, flush=True) # debugging
+            self.assertIn('network:\n', out)
+            self.assertIn(' version: 2\n', out)
+            self.assertIn(' renderer: NetworkManager\n', out)
+            self.assertNotIn('ethernets:', out)
+
     def test_set_delete_file(self):
         with open(self.path, 'w') as f:
             f.write('''network: