configdict: T9269: no phantom removal when a multi node gains a value

A multi node with a single value is a plain string in the JSON rendering
of the config tree, and only becomes a list once it holds several values.
leaf_node_changed() tested for a string before diffing the lists, so
appending a value reported the already configured one as gone.

Adding a second bond member thus produced an "interface_remove" entry for
the first, and BondIf.update() released it right after enslaving the new
one, leaving the bond with the new member only.

Normalize to a list and reuse list_diff(). Only the string to list append
changes, from [old] to []. interface.py was immune as it re-applies
list_diff() to address_old, protocols_static_arp.py was not.

1 files changed, 6 insertions, 1 deletions

diff --git a/python/vyos/configdict.py b/python/vyos/configdict.py
index ff784251a..da2e9792c 100644
--- a/python/vyos/configdict.py
+++ b/python/vyos/configdict.py
@@ -133,8 +133,13 @@ def leaf_node_changed(conf, path):
             return True
         if old is None:
             return []
+        # A multi node holding a single value is a plain string in the JSON
+        # rendering of the config tree, and only becomes a list once it holds
+        # several values. Normalize before diffing, else appending a value to a
+        # single-valued multi node reports the already configured value as gone
+        # just because its representation changed from string to list
         if isinstance(old, str):
-            return [old]
+            old = [old]
         if isinstance(old, list):
             if isinstance(new, str):
                 new = [new]