[IMP] util.update_record_from_xml

Sometimes records get a field removed from their XML declaration. This creates a
divergence between new dbs and upgraded ones. The former will be initialised
with `NULL`/default values, whereas the latter will retain their current one.
This is usually handled in dedicated upgrade scripts with simple queries
un/setting the necessary columns. However, in some cases, these XML changes are
backported/noticed too late and need to be addressed in multiple versions.
That may create the pressure to target future versions, which creates a hidden
coupling between the xml declaration and the query, prone to turn into a bug.
It is one such example[^1] that inspired this PR.

Here `update_record_from_xml` is adapted to unset fields missing from the xml
declaration, if passed explicitely via the `fields` kwarg. This enables us to
leverage the foreward compatibility of `update_record_from_xml` in the scenario
described above, preventing the associated potential bugs.

[^1]: odoo/upgrade#9512

Author: Pirols

src/util/records.py

@@ -1039,7 +1039,8 @@ def update_record_from_xml(
                                    should also be updated.
     :param set(str) or None fields: optional list of fields to include in the XML declaration.
                                     If set, all other fields will be ignored. When set, record
-                                    won't be created if missing.
+                                    won't be created if missing and all fields not found in
+                                    the XML declaration will be set to NULL.
 
     .. warning::
        This functions uses the ORM, therefore it can only be used after **all** models
@@ -1147,9 +1148,13 @@ def add_ref(ref):
                 found = True
                 parent = node.getparent()
                 if node.tag == "record" and fields is not None:
+                    xml_fields = set()
                     for fn in node.xpath("./field[@name]"):
                         if fn.attrib["name"] not in fields:
                             node.remove(fn)
+                        xml_fields.add(fn.attrib["name"])
+                    # override requested fields not found in xml
+                    node.extend(lxml.builder.E.field(name=f, eval="False") for f in fields if f not in xml_fields)
                 new_root[0].append(node)
 
                 if node.tag == "menuitem" and parent.tag == "menuitem" and "parent_id" not in node.attrib: