fields: correctly check data source tuple size (#8719)

tests/test_datasource.py

@@ -193,3 +193,22 @@ def test_data_source_slug_name():
     data_source = NamedDataSource(name='foo bar')
     data_source.store()
     assert data_source.slug == 'foo_bar'
+
+def test_optional_item_field_with_data_source():
+    NamedDataSource.wipe()
+    data_source = NamedDataSource(name='foobar')
+    data_source.data_source = {'type': 'formula',
+            'value': repr([('1', 'un'), ('2', 'deux')])}
+    data_source.store()
+
+    field = fields.ItemField()
+    field.id = 1
+    field.required = False
+    field.data_source = {
+        'type': 'foobar', # use the named data source defined earlier
+    }
+    form = Form()
+    field.add_to_form(form)
+    widget = form.get_widget('f1')
+    assert widget is not None
+    assert widget.options == [(None, '---', 'None'), ('1', 'un', '1'), ('2', 'deux', '2')]

wcs/fields.py

@@ -864,7 +864,7 @@ class ItemField(WidgetField):
         if options and not self.required:
             if type(options[0]) is str:
                 options[:0] = [None]
-            elif len(options) == 2:
+            elif len(options[0]) == 2:
                 options[:0] = [(None, '---')]
             elif len(options[0]) == 3:
                 options[:0] = [(None, '---', None)]