[3.1.x] Fixed #32110 -- Doc'd and tested enumerations for ChoiceField.choices.

Backport of 7f85498eef from master

docs/ref/forms/fields.txt

@@ -410,12 +410,13 @@ For each field, we describe the default widget used if you don't specify
     .. attribute:: choices
 
         Either an :term:`iterable` of 2-tuples to use as choices for this
-        field, or a callable that returns such an iterable. This argument
-        accepts the same formats as the ``choices`` argument to a model field.
-        See the :ref:`model field reference documentation on choices
-        <field-choices>` for more details. If the argument is a callable, it is
-        evaluated each time the field's form is initialized, in addition to
-        during rendering. Defaults to an empty list.
+        field, :ref:`enumeration <field-choices-enum-types>` choices, or a
+        callable that returns such an iterable. This argument accepts the same
+        formats as the ``choices`` argument to a model field. See the
+        :ref:`model field reference documentation on choices <field-choices>`
+        for more details. If the argument is a callable, it is evaluated each
+        time the field's form is initialized, in addition to during rendering.
+        Defaults to an empty list.
 
 ``TypedChoiceField``
 --------------------

tests/forms_tests/field_tests/test_choicefield.py

@@ -1,4 +1,5 @@
 from django.core.exceptions import ValidationError
+from django.db import models
 from django.forms import ChoiceField, Form
 from django.test import SimpleTestCase
 
@@ -87,3 +88,14 @@ class ChoiceFieldTest(FormFieldAssertionsMixin, SimpleTestCase):
             '<select id="id_f" name="f" disabled><option value="J">John</option>'
             '<option value="P">Paul</option></select>'
         )
+
+    def test_choicefield_enumeration(self):
+        class FirstNames(models.TextChoices):
+            JOHN = 'J', 'John'
+            PAUL = 'P', 'Paul'
+
+        f = ChoiceField(choices=FirstNames.choices)
+        self.assertEqual(f.clean('J'), 'J')
+        msg = "'Select a valid choice. 3 is not one of the available choices.'"
+        with self.assertRaisesMessage(ValidationError, msg):
+            f.clean('3')