Added check test to ensure that model field choices can not be callab…

…les.

django/db/models/fields/__init__.py

@@ -15,7 +15,7 @@
 from django.db.models.constants import LOOKUP_SEP
 from django.db.models.query_utils import DeferredAttribute, RegisterLookupMixin
 from django.utils import timezone
-from django.utils.choices import normalize_choices
+from django.utils.choices import CallableChoiceIterator, normalize_choices
 from django.utils.datastructures import DictWrapper
 from django.utils.dateparse import (
     parse_date,
@@ -315,7 +315,9 @@ def _check_choices(self):
         if not self.choices:
             return []
 
-        if not is_iterable(self.choices) or isinstance(self.choices, str):
+        if not is_iterable(self.choices) or isinstance(
+            self.choices, (str, CallableChoiceIterator)
+        ):
             return [
                 checks.Error(
                     "'choices' must be a mapping (e.g. a dictionary) or an iterable "

tests/invalid_models_tests/test_ordinary_fields.py

@@ -391,6 +391,26 @@ class Model(models.Model):
                     ],
                 )
 
+    def test_choices_callable(self):
+        def get_choices():
+            return [(i, i) for i in range(3)]
+
+        class Model(models.Model):
+            field = models.CharField(max_length=10, choices=get_choices)
+
+        field = Model._meta.get_field("field")
+        self.assertEqual(
+            field.check(),
+            [
+                Error(
+                    "'choices' must be a mapping (e.g. a dictionary) or an iterable "
+                    "(e.g. a list or tuple).",
+                    obj=field,
+                    id="fields.E004",
+                ),
+            ],
+        )
+
     def test_bad_db_index_value(self):
         class Model(models.Model):
             field = models.CharField(max_length=10, db_index="bad")