Bug: Enable template tag richtext to convert lazy text strings

wagtail/templatetags/wagtailcore_tags.py

@@ -3,6 +3,7 @@
 from django.template.defaulttags import token_kwargs
 from django.template.loader import render_to_string
 from django.utils.encoding import force_str
+from django.utils.functional import Promise
 from django.utils.html import conditional_escape
 
 from wagtail import VERSION, __version__
@@ -120,6 +121,8 @@ def richtext(value):
     elif value is None:
         html = ""
     else:
+        if isinstance(value, Promise):
+            value = str(value)
         if isinstance(value, str):
             html = expand_db_html(value)
         else:

wagtail/tests/tests.py

@@ -9,6 +9,7 @@
 from django.test.utils import override_settings
 from django.urls.exceptions import NoReverseMatch
 from django.utils.safestring import SafeString
+from django.utils.translation import gettext_lazy
 
 from wagtail.coreutils import (
     get_dummy_request,
@@ -536,6 +537,10 @@ def test_call_with_text(self):
         self.assertEqual(result, "Hello world!")
         self.assertIsInstance(result, SafeString)
 
+    def test_call_with_lazy(self):
+        result = richtext(gettext_lazy("test"))
+        self.assertEqual(result, "test")
+
     def test_call_with_none(self):
         result = richtext(None)
         self.assertEqual(result, "")