[1.8.x] Fixed #24146 -- Allowed model._meta.get_field() to be used after apps.models_ready

Backport of 19188826b4 from master

django/db/models/options.py

@@ -535,7 +535,7 @@ class Options(object):
         except KeyError:
             # If the app registry is not ready, reverse fields are
             # unavailable, therefore we throw a FieldDoesNotExist exception.
-            if not self.apps.ready:
+            if not self.apps.models_ready:
                 raise FieldDoesNotExist(
                     "%s has no field named %r. The app cache isn't ready yet, "
                     "so if this is an auto-created related field, it won't "

tests/admin_checks/models.py

@@ -49,6 +49,7 @@ class Book(models.Model):
 class AuthorsBooks(models.Model):
     author = models.ForeignKey(Author)
     book = models.ForeignKey(Book)
+    featured = models.BooleanField()
 
 
 class State(models.Model):

tests/admin_checks/tests.py

@@ -688,3 +688,20 @@ class SystemChecksTestCase(TestCase):
             )
         ]
         self.assertEqual(errors, expected)
+
+    def test_list_filter_works_on_through_field_even_when_apps_not_ready(self):
+        """
+        Ensure list_filter can access reverse fields even when the app registry
+        is not ready; refs #24146.
+        """
+        class BookAdminWithListFilter(admin.ModelAdmin):
+            list_filter = ['authorsbooks__featured']
+
+        # Temporarily pretending apps are not ready yet. This issue can happen
+        # if the value of 'list_filter' refers to a 'through__field'.
+        Book._meta.apps.ready = False
+        try:
+            errors = BookAdminWithListFilter.check(model=Book)
+            self.assertEqual(errors, [])
+        finally:
+            Book._meta.apps.ready = True

tests/model_meta/tests.py

@@ -178,7 +178,7 @@ class GetFieldByNameTests(OptionsBaseTests):
         opts = Person._meta
         # If apps registry is not ready, get_field() searches over only
         # forward fields.
-        opts.apps.ready = False
+        opts.apps.models_ready = False
         try:
             # 'data_abstract' is a forward field, and therefore will be found
             self.assertTrue(opts.get_field('data_abstract'))
@@ -191,7 +191,7 @@ class GetFieldByNameTests(OptionsBaseTests):
             with self.assertRaisesMessage(FieldDoesNotExist, msg):
                 opts.get_field('relating_baseperson')
         finally:
-            opts.apps.ready = True
+            opts.apps.models_ready = True
 
 
 class RelationTreeTests(TestCase):