[1.6.x] Fixed #23329 -- Allowed inherited and m2m fields to be referenced in the admin.

Thanks to Trac alias Markush2010 and ross for the detailed reports.

Backport of 3cbb759 from master

tests/admin_views/admin.py

@@ -30,7 +30,7 @@ from .models import (Article, Chapter, Account, Media, Child, Parent, Picture,
     AdminOrderedField, AdminOrderedModelMethod, AdminOrderedAdminMethod,
     AdminOrderedCallable, Report, Color2, UnorderedObject, MainPrepopulated,
     RelatedPrepopulated, UndeletableObject, UserMessenger, Simple, Choice,
-    ShortMessage, Telegram)
+    ShortMessage, Telegram, ReferencedByParent, ChildOfReferer, M2MReference)
 
 
 def callable_year(dt_value):
@@ -745,6 +745,9 @@ site.register(Report, ReportAdmin)
 site.register(MainPrepopulated, MainPrepopulatedAdmin)
 site.register(UnorderedObject, UnorderedObjectAdmin)
 site.register(UndeletableObject, UndeletableObjectAdmin)
+site.register(ReferencedByParent)
+site.register(ChildOfReferer)
+site.register(M2MReference)
 
 # We intentionally register Promo and ChapterXtra1 but not Chapter nor ChapterXtra2.
 # That way we cover all four cases:

tests/admin_views/models.py

@@ -687,3 +687,20 @@ class Simple(models.Model):
 class Choice(models.Model):
     choice = models.IntegerField(blank=True, null=True,
         choices=((1, 'Yes'), (0, 'No'), (None, 'No opinion')))
+
+# Models for #23329
+class ReferencedByParent(models.Model):
+    pass
+
+
+class ParentWithFK(models.Model):
+    fk = models.ForeignKey(ReferencedByParent)
+
+
+class ChildOfReferer(ParentWithFK):
+    pass
+
+
+class M2MReference(models.Model):
+    ref = models.ManyToManyField('self')
+

tests/admin_views/tests.py

@@ -595,6 +595,15 @@ class AdminViewBasicTest(AdminViewBasicTestCase):
         response = self.client.get("/test_admin/admin/admin_views/section/", {TO_FIELD_VAR: 'id'})
         self.assertEqual(response.status_code, 200)
 
+        # Specifying a field referenced by another model though a m2m should be allowed.
+        response = self.client.get("/test_admin/admin/admin_views/m2mreference/", {TO_FIELD_VAR: 'id'})
+        self.assertEqual(response.status_code, 200)
+
+        # Specifying a field that is not refered by any other model directly registered
+        # to this admin site but registered through inheritance should be allowed.
+        response = self.client.get("/test_admin/admin/admin_views/referencedbyparent/", {TO_FIELD_VAR: 'id'})
+        self.assertEqual(response.status_code, 200)
+
     def test_allowed_filtering_15103(self):
         """
         Regressions test for ticket 15103 - filtering on fields defined in a