Avoid importing custom user models at load time in wagtail.admin.models

As per https://docs.djangoproject.com/en/5.0/topics/auth/customizing/#referencing-the-user-model , module-level code such as ForeignKey definitions should use `AUTH_USER_MODEL` rather than `get_user_model()`.

Probably fixes wagtail#12228 (unconfirmed)

CHANGELOG.txt

@@ -22,6 +22,7 @@ Changelog
 
  * Fix: Handle `child_block` being passed as a kwarg in ListBlock migrations (Matt Westcott)
  * Fix: Fix broken task type filter in workflow task chooser modal (Sage Abdullah)
+ * Fix: Prevent circular imports between `wagtail.admin.models` and custom user models (Matt Westcott)
 
 
 6.2 (01.08.2024)

docs/releases/6.2.1.md

@@ -16,3 +16,4 @@ depth: 1
 
  * Handle `child_block` being passed as a kwarg in ListBlock migrations (Matt Westcott)
  * Fix broken task type filter in workflow task chooser modal (Sage Abdullah)
+ * Prevent circular imports between `wagtail.admin.models` and custom user models (Matt Westcott)

wagtail/admin/models.py

@@ -1,4 +1,4 @@
-from django.contrib.auth import get_user_model
+from django.conf import settings
 from django.contrib.contenttypes.fields import GenericForeignKey
 from django.contrib.contenttypes.models import ContentType
 from django.db import models
@@ -76,7 +76,7 @@ def popular_tags_for_model(model, count=10):
 
 class EditingSession(models.Model):
     user = models.ForeignKey(
-        get_user_model(),
+        settings.AUTH_USER_MODEL,
         on_delete=models.CASCADE,
         related_name="editing_sessions",
     )

wagtail/test/customuser/models.py

@@ -5,11 +5,14 @@
 )
 from django.db import models
 
-# make sure we can import wagtail.admin.auth here without triggering a circular import
-# (which is easily done because it's dealing with django.contrib.auth views which depend
-# on the user model)
+# Custom user models are a common source of circular import errors, since the user model is often
+# referenced in Wagtail core code that we may want to import here. To prevent this, Wagtail should
+# avoid importing the user model at load time.
+# wagtail.admin.auth and wagtail.admin.views.generic are imported here as these have been
+# previously identified as sources of circular imports.
 from wagtail.admin.auth import permission_denied  # noqa: F401
 from wagtail.admin.panels import FieldPanel
+from wagtail.admin.views.generic import chooser as chooser_views  # noqa: F401
 
 from .fields import ConvertedValueField