netplan.c: Don't drop files with just global values on 'set' (LP: #20…

…27584)

The "unlink" part at the bottom of netplan.c:netplan_state_update_yaml_hierarchy
seems to ignore any global values (such as "renderer") and operates on files
containing netdefs only.

The issue is happens due to a combination of the following PRs:
#254
#299

Which got SRUed into Jammy via 0.105-0ubuntu2~22.04.2

Here's a minimal reproducer:
```
netplan set network.renderer=NetworkManager --origin-hint=00-no-netdefs-just-globals
netplan set network.ethernets.eth99.dhcp4=true --origin-hint=90-some-netdefs
ls -l /etc/netplan/
netplan set network.ethernets.eth99=NULL
cat /etc/netplan/00-no-netdefs-just-globals.yaml
```

FR-4793

src/netplan.c

@@ -1214,6 +1214,22 @@ netplan_state_update_yaml_hierarchy(const NetplanState* np_state, const char* de
         }
     }
 
+    /* Add files containing a global renderer value to "perfile_netdefs", so
+     * they are updated on disk. */
+    if (np_state->global_renderer && g_hash_table_size(np_state->global_renderer) > 0) {
+        g_hash_table_iter_init(&hash_iter, np_state->global_renderer);
+        while (g_hash_table_iter_next (&hash_iter, &key, &value)) {
+            char *filename = key;
+            /* Anonymous globals will go to the default YAML (see above) */
+            if (g_strcmp0(filename, "") == 0)
+                continue;
+            /* Ignore the update of this file if it's already going to be
+             * written, caused by updated netdefs. */
+            if (!g_hash_table_contains(perfile_netdefs, filename))
+                g_hash_table_insert(perfile_netdefs, filename, NULL);
+        }
+    }
+
     g_hash_table_iter_init(&hash_iter, perfile_netdefs);
     while (g_hash_table_iter_next (&hash_iter, &key, &value)) {
         const char *filename = key;

tests/cli/test_get_set.py

@@ -248,6 +248,48 @@ def test_set_network_null_global(self):
         self.assertFalse(os.path.isfile(self.path))
         self.assertFalse(os.path.isfile(some_hint))
 
+    def test_set_no_netdefs_just_globals(self):  # LP: #2027584
+        keepme1 = os.path.join(self.workdir.name, 'etc', 'netplan',
+                               '00-no-netdefs-just-renderer.yaml')
+        with open(keepme1, 'w') as f:
+            f.write('''network: {renderer: NetworkManager}''')
+        keepme2 = os.path.join(self.workdir.name, 'etc', 'netplan',
+                               '00-no-netdefs-just-version.yaml')
+        with open(keepme2, 'w') as f:
+            f.write('''network: {version: 2}''')
+        deleteme = os.path.join(self.workdir.name, 'etc', 'netplan',
+                                '90-some-netdefs.yaml')
+        with open(deleteme, 'w') as f:
+            f.write('''network: {ethernets: {eth99: {dhcp4: true}}}''')
+
+        self._set(['ethernets.eth99=NULL'])
+        self.assertFalse(os.path.isfile(deleteme))
+        self.assertTrue(os.path.isfile(keepme1))
+        with open(keepme1, 'r') as f:
+            yml = yaml.safe_load(f)
+            self.assertEqual('NetworkManager', yml['network']['renderer'])
+        # XXX: It's probably fine to delete a file that just contains "version: 2"
+        #      Or is it? And what about other globals, such as OVS ports?
+        self.assertFalse(os.path.isfile(keepme2))
+
+    def test_set_clear_netdefs_keep_globals(self):  # LP: #2027584
+        keep = os.path.join(self.workdir.name, 'etc', 'netplan', '00-keep.yaml')
+        with open(keep, 'w') as f:
+            f.write('''network:
+  version: 2
+  renderer: NetworkManager
+  bridges:
+    br54:
+      addresses: [1.2.3.4/24]
+''')
+        self._set(['network.bridges.br54=NULL'])
+        self.assertTrue(os.path.isfile(keep))
+        with open(keep, 'r') as f:
+            yml = yaml.safe_load(f)
+            self.assertEqual(2, yml['network']['version'])
+            self.assertEqual('NetworkManager', yml['network']['renderer'])
+            self.assertNotIn('bridges', yml['network'])
+
     def test_set_invalid(self):
         with self.assertRaises(Exception) as context:
             self._set(['xxx.yyy=abc'])