From bc174e6ea0ce676c5a7f467bda9739e6ef6b6186 Mon Sep 17 00:00:00 2001
From: Petter Friberg <petter_friberg@hotmail.com>
Date: Tue, 4 Jan 2022 23:06:46 +0100
Subject: [PATCH] Fixed #33410 -- Fixed recursive capturing of callbacks by
 TestCase.captureOnCommitCallbacks().

Regression in d89f976bddb49fb168334960acc8979c3de991fa.
---
 django/test/testcases.py  | 12 ++++-----
 docs/releases/4.0.2.txt   |  3 ++-
 tests/test_utils/tests.py | 52 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 59 insertions(+), 8 deletions(-)

diff --git a/django/test/testcases.py b/django/test/testcases.py
index 685cbe2bd4f..9759680f0f0 100644
--- a/django/test/testcases.py
+++ b/django/test/testcases.py
@@ -1253,18 +1253,16 @@ class TestCase(TransactionTestCase):
         try:
             yield callbacks
         finally:
-            callback_count = len(connections[using].run_on_commit)
             while True:
-                run_on_commit = connections[using].run_on_commit[start_count:]
-                callbacks[:] = [func for sids, func in run_on_commit]
-                if execute:
-                    for callback in callbacks:
+                callback_count = len(connections[using].run_on_commit)
+                for _, callback in connections[using].run_on_commit[start_count:]:
+                    callbacks.append(callback)
+                    if execute:
                         callback()
 
                 if callback_count == len(connections[using].run_on_commit):
                     break
-                start_count = callback_count - 1
-                callback_count = len(connections[using].run_on_commit)
+                start_count = callback_count
 
 
 class CheckCondition:
diff --git a/docs/releases/4.0.2.txt b/docs/releases/4.0.2.txt
index 002e8910178..b1f1fb9c76c 100644
--- a/docs/releases/4.0.2.txt
+++ b/docs/releases/4.0.2.txt
@@ -9,4 +9,5 @@ Django 4.0.2 fixes several bugs in 4.0.1.
 Bugfixes
 ========
 
-* ...
+* Fixed a bug in Django 4.0 where ``TestCase.captureOnCommitCallbacks()`` could
+  execute callbacks multiple times (:ticket:`33410`).
diff --git a/tests/test_utils/tests.py b/tests/test_utils/tests.py
index 2addc1fdde6..3380a1c67e7 100644
--- a/tests/test_utils/tests.py
+++ b/tests/test_utils/tests.py
@@ -1829,6 +1829,58 @@ class CaptureOnCommitCallbacksTests(TestCase):
         self.assertEqual(len(callbacks), 2)
         self.assertIs(self.callback_called, True)
 
+    def test_execute_tree(self):
+        """
+        A visualisation of the callback tree tested. Each node is expected to
+        be visited only once:
+
+        └─branch_1
+          ├─branch_2
+          │ ├─leaf_1
+          │ └─leaf_2
+          └─leaf_3
+        """
+        branch_1_call_counter = 0
+        branch_2_call_counter = 0
+        leaf_1_call_counter = 0
+        leaf_2_call_counter = 0
+        leaf_3_call_counter = 0
+
+        def leaf_1():
+            nonlocal leaf_1_call_counter
+            leaf_1_call_counter += 1
+
+        def leaf_2():
+            nonlocal leaf_2_call_counter
+            leaf_2_call_counter += 1
+
+        def leaf_3():
+            nonlocal leaf_3_call_counter
+            leaf_3_call_counter += 1
+
+        def branch_1():
+            nonlocal branch_1_call_counter
+            branch_1_call_counter += 1
+            transaction.on_commit(branch_2)
+            transaction.on_commit(leaf_3)
+
+        def branch_2():
+            nonlocal branch_2_call_counter
+            branch_2_call_counter += 1
+            transaction.on_commit(leaf_1)
+            transaction.on_commit(leaf_2)
+
+        with self.captureOnCommitCallbacks(execute=True) as callbacks:
+            transaction.on_commit(branch_1)
+
+        self.assertEqual(branch_1_call_counter, 1)
+        self.assertEqual(branch_2_call_counter, 1)
+        self.assertEqual(leaf_1_call_counter, 1)
+        self.assertEqual(leaf_2_call_counter, 1)
+        self.assertEqual(leaf_3_call_counter, 1)
+
+        self.assertEqual(callbacks, [branch_1, branch_2, leaf_3, leaf_1, leaf_2])
+
 
 class DisallowedDatabaseQueriesTests(SimpleTestCase):
     def test_disallowed_database_connections(self):