forms: only update item options if there are new values (#40216)

tests/test_form_pages.py

@@ -6913,6 +6913,22 @@ def test_field_live_select_content_based_on_prefill(pub, http_requests):
     assert resp.html.find('option', {'value': 'a'})
     assert http_requests.get_last('url') == 'http://remote.example.net/json-list?plop=HELLO WORLD'
 
+    # check with autocomplete and a remote source with id
+    NamedDataSource.wipe()
+    data_source = NamedDataSource(name='foobar')
+    data_source.data_source = {'type': 'json', 'value': 'http://remote.example.net/json?plop={{form_var_bar}}'}
+    data_source.query_parameter = 'q'
+    data_source.id_parameter = 'id'
+    data_source.store()
+
+    formdef.fields[1].display_mode = 'autocomplete'
+    formdef.fields[1].data_source['type'] = 'foobar'
+    formdef.store()
+    app = get_app(pub)
+    resp = app.get('/foo/')
+    assert 'f1' in resp.form.fields
+    assert 'f2' in resp.form.fields
+
 
 def test_field_live_comment_content(pub, http_requests):
     FormDef.wipe()

wcs/forms/root.py

@@ -427,8 +427,9 @@ class FormPage(Directory, FormTemplateMixin):
                     with get_publisher().substitutions.temporary_feed(
                             transient_formdata, force_mode='lazy'):
                         field.perform_more_widget_changes(form, kwargs)
-                        widget.options = kwargs['options']
-                        widget.options_with_attributes = kwargs['options_with_attributes']
+                        if 'options' in kwargs and 'options_with_attributes' in kwargs:
+                            widget.options = kwargs['options']
+                            widget.options_with_attributes = kwargs['options_with_attributes']
 
         self.html_top(self.formdef.name)