fields: Add FormField.add_kid() method.

conservancy_beancount/pdfforms/fields.py

@@ -131,6 +131,12 @@ class FormField:
         except KeyError:
             return None
 
+    def add_kid(self, kid: 'FormField') -> None:
+        if kid.parent() is not None:
+            raise ValueError("given kid field already has a parent")
+        kid._source['Parent'] = self._source
+        self._source.setdefault('Kids', []).append(kid._source)
+
     def is_terminal(self) -> bool:
         return not self._get_value('Kids', None)
 

tests/test_pdfforms_fields.py

@@ -368,3 +368,11 @@ def test_recursive_as_mapping():
         _, _, expected_name = expected_key.rpartition('.')
         assert field.name() == expected_name
     assert next(actual, None) is None
+
+def test_add_kid():
+    parent = fieldsmod.FormField(field_source('parent'))
+    kid = fieldsmod.FormField(field_source('kid'))
+    parent.add_kid(kid)
+    actual, = parent.kids()
+    assert actual.name() == 'kid'
+    assert actual.parent().name() == 'parent'