[1.11.x] Fixed #26522 -- Fixed a nondeterministic AssertionError in QuerySet combining.

Thanks Andrew Brown for the test case.

Backport of 9bbb6e2d2536c4ac20dc13a94c1f80494e51f8d9 from master

2 files changed, 20 insertions, 3 deletions

diff --git a/tests/queries/models.py b/tests/queries/models.py
index ab03b9c248..fd76623c33 100644
--- a/tests/queries/models.py
+++ b/tests/queries/models.py
@@ -709,6 +709,11 @@ class Classroom(models.Model):
     students = models.ManyToManyField(Student, related_name='classroom')
 
 
+class Teacher(models.Model):
+    schools = models.ManyToManyField(School)
+    friends = models.ManyToManyField('self')
+
+
 class Ticket23605AParent(models.Model):
     pass
 
diff --git a/tests/queries/tests.py b/tests/queries/tests.py
index 6633985f81..877cf8091e 100644
--- a/tests/queries/tests.py
+++ b/tests/queries/tests.py
@@ -28,9 +28,9 @@ from .models import (
     ProxyCategory, ProxyObjectA, ProxyObjectB, Ranking, Related,
     RelatedIndividual, RelatedObject, Report, ReportComment, ReservedName,
     Responsibility, School, SharedConnection, SimpleCategory, SingleObject,
-    SpecialCategory, Staff, StaffUser, Student, Tag, Task, Ticket21203Child,
-    Ticket21203Parent, Ticket23605A, Ticket23605B, Ticket23605C, TvChef, Valid,
-    X,
+    SpecialCategory, Staff, StaffUser, Student, Tag, Task, Teacher,
+    Ticket21203Child, Ticket21203Parent, Ticket23605A, Ticket23605B,
+    Ticket23605C, TvChef, Valid, X,
 )
 
 
@@ -1391,6 +1391,18 @@ class Queries4Tests(TestCase):
         self.assertEqual(len(combined), 1)
         self.assertEqual(combined[0].name, 'a1')
 
+    def test_join_reuse_order(self):
+        # Join aliases are reused in order. This shouldn't raise AssertionError
+        # because change_map contains a circular reference (#26522).
+        s1 = School.objects.create()
+        s2 = School.objects.create()
+        s3 = School.objects.create()
+        t1 = Teacher.objects.create()
+        otherteachers = Teacher.objects.exclude(pk=t1.pk).exclude(friends=t1)
+        qs1 = otherteachers.filter(schools=s1).filter(schools=s2)
+        qs2 = otherteachers.filter(schools=s1).filter(schools=s3)
+        self.assertQuerysetEqual(qs1 | qs2, [])
+
     def test_ticket7095(self):
         # Updates that are filtered on the model being updated are somewhat
         # tricky in MySQL.