[3.0.x] Fixed #31154 -- Added support for using enumeration types in templates.

Enumeration helpers are callables, so the template system tried to call
them with no arguments.

Thanks Rupert Baker for helping discover this.

Backport of 5166097d7c from master

django/db/models/enums.py

@@ -31,6 +31,7 @@ class ChoicesMeta(enum.EnumMeta):
         # that is passed in as "self" as the value to use when looking up the
         # label in the choices.
         cls.label = property(lambda self: cls._value2label_map_.get(self.value))
+        cls.do_not_call_in_templates = True
         return enum.unique(cls)
 
     def __contains__(cls, member):

docs/releases/3.0.3.txt

@@ -20,3 +20,6 @@ Bugfixes
 * Relaxed the system check added in Django 3.0 to reallow use of a sublanguage
   in the :setting:`LANGUAGE_CODE` setting, when a base language is available in
   Django but the sublanguage is not (:ticket:`31141`).
+
+* Added support for using enumeration types ``TextChoices``,
+  ``IntegerChoices``, and ``Choices`` in templates (:ticket:`31154`).

tests/model_enums/tests.py

@@ -4,6 +4,7 @@ import ipaddress
 import uuid
 
 from django.db import models
+from django.template import Context, Template
 from django.test import SimpleTestCase
 from django.utils.functional import Promise
 from django.utils.translation import gettext_lazy as _
@@ -149,6 +150,11 @@ class ChoicesTests(SimpleTestCase):
                 with self.subTest(member=member):
                     self.assertEqual(str(test[member.name]), str(member.value))
 
+    def test_templates(self):
+        template = Template('{{ Suit.DIAMOND.label }}|{{ Suit.DIAMOND.value }}')
+        output = template.render(Context({'Suit': Suit}))
+        self.assertEqual(output, 'Diamond|1')
+
 
 class Separator(bytes, models.Choices):
     FS = b'\x1c', 'File Separator'