Support optgroups in FilteredSelect

wagtail/admin/tests/test_widgets.py

@@ -322,3 +322,37 @@ class TestFilteredSelect(TestCase):
                 <option value="RU" data-filter-value="AS,EU">Russia</option>
             </select>
         ''')
+
+    def test_optgroups(self):
+        widget = widgets.FilteredSelect(choices=[
+            (None, '----'),
+            ('Big countries', [
+                ('FR', 'France', ['EU']),
+                ('JP', 'Japan', ['AS']),
+                ('RU', 'Russia', ['AS', 'EU']),
+                ('MOON', 'The moon'),
+            ]),
+            ('Small countries', [
+                ('AZ', 'Azerbaijan', ['AS']),
+                ('LI', 'Liechtenstein', ['EU']),
+            ]),
+            ('SK', 'Slovakia', ['EU'])
+        ], filter_field='id_continent')
+
+        html = widget.render('country', 'JP')
+        self.assertHTMLEqual(html, '''
+            <select name="country" data-widget="filtered-select" data-filter-field="id_continent">
+                <option value="">----</option>
+                <optgroup label="Big countries">
+                    <option value="FR" data-filter-value="EU">France</option>
+                    <option value="JP" selected data-filter-value="AS">Japan</option>
+                    <option value="RU" data-filter-value="AS,EU">Russia</option>
+                    <option value="MOON">The moon</option>
+                </optgroup>
+                <optgroup label="Small countries">
+                    <option value="AZ" data-filter-value="AS">Azerbaijan</option>
+                    <option value="LI" data-filter-value="EU">Liechtenstein</option>
+                </optgroup>
+                <option value="SK" data-filter-value="EU">Slovakia</option>
+            </select>
+        ''')

wagtail/admin/widgets/filtered_select.py

@@ -53,16 +53,25 @@ class FilteredSelect(forms.Select):
 
             subgroup = []
             if isinstance(option_label, (list, tuple)):
+                # this is an optgroup - we will iterate over the list in the second item of
+                # the tuple (which has been assigned to option_label)
                 group_name = option_value
                 subindex = 0
                 choices = option_label
             else:
+                # this is a top-level choice; put it in its own group with no name
                 group_name = None
                 subindex = None
-                choices = [(option_value, option_label)]
+                choices = [(option_value, option_label, filter_value)]
             groups.append((group_name, subgroup, index))
 
-            for subvalue, sublabel in choices:
+            for choice in choices:
+                try:
+                    (subvalue, sublabel, filter_value) = choice
+                except ValueError:
+                    (subvalue, sublabel) = choice
+                    filter_value = None
+
                 selected = (
                     str(subvalue) in value
                     and (not has_selected or self.allow_multiple_selected)