From f4eb9ab014545b521fb261b80adfa6d138e7e092 Mon Sep 17 00:00:00 2001
From: Seth Michael Larson <seth@python.org>
Date: Wed, 3 Dec 2025 01:16:37 -0600
Subject: [PATCH] gh-142145: Remove quadratic behavior in node ID cache
 clearing (GH-142146)

* Remove quadratic behavior in node ID cache clearing

Co-authored-by: Jacob Walls <38668450+jacobtylerwalls@users.noreply.github.com>

* Add news fragment

---------
(cherry picked from commit 08d8e18ad81cd45bc4a27d6da478b51ea49486e4)

Co-authored-by: Seth Michael Larson <seth@python.org>
Co-authored-by: Jacob Walls <38668450+jacobtylerwalls@users.noreply.github.com>
---
 Lib/test/test_minidom.py                                                 |   18 ++++++++++
 Lib/xml/dom/minidom.py                                                   |    9 -----
 Misc/NEWS.d/next/Security/2025-12-01-09-36-45.gh-issue-142145.tcAUhg.rst |    1 
 3 files changed, 20 insertions(+), 8 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Security/2025-12-01-09-36-45.gh-issue-142145.tcAUhg.rst

Index: Python-3.9.25/Lib/test/test_minidom.py
===================================================================
--- Python-3.9.25.orig/Lib/test/test_minidom.py	2025-12-19 23:24:47.176384491 +0100
+++ Python-3.9.25/Lib/test/test_minidom.py	2025-12-19 23:27:27.634483015 +0100
@@ -2,6 +2,7 @@
 
 import copy
 import pickle
+import time
 import io
 from test import support
 import unittest
@@ -162,6 +163,23 @@
         self.confirm(dom.documentElement.childNodes[-1].data == "Hello")
         dom.unlink()
 
+    def testAppendChildNoQuadraticComplexity(self):
+        impl = getDOMImplementation()
+
+        newdoc = impl.createDocument(None, "some_tag", None)
+        top_element = newdoc.documentElement
+        children = [newdoc.createElement(f"child-{i}") for i in range(1, 2 ** 15 + 1)]
+        element = top_element
+
+        start = time.time()
+        for child in children:
+            element.appendChild(child)
+            element = child
+        end = time.time()
+
+        # This example used to take at least 30 seconds.
+        self.assertLess(end - start, 1)
+
     def testAppendChildFragment(self):
         dom, orig, c1, c2, c3, frag = self._create_fragment_test_nodes()
         dom.documentElement.appendChild(frag)
Index: Python-3.9.25/Lib/xml/dom/minidom.py
===================================================================
--- Python-3.9.25.orig/Lib/xml/dom/minidom.py	2025-10-31 19:40:52.000000000 +0100
+++ Python-3.9.25/Lib/xml/dom/minidom.py	2025-12-19 23:27:27.635128214 +0100
@@ -292,13 +292,6 @@
     childNodes.append(node)
     node.parentNode = self
 
-def _in_document(node):
-    # return True iff node is part of a document tree
-    while node is not None:
-        if node.nodeType == Node.DOCUMENT_NODE:
-            return True
-        node = node.parentNode
-    return False
 
 def _write_data(writer, data):
     "Writes datachars to writer."
@@ -1537,7 +1530,7 @@
     if node.nodeType == Node.DOCUMENT_NODE:
         node._id_cache.clear()
         node._id_search_stack = None
-    elif _in_document(node):
+    elif node.ownerDocument:
         node.ownerDocument._id_cache.clear()
         node.ownerDocument._id_search_stack= None
 
Index: Python-3.9.25/Misc/NEWS.d/next/Security/2025-12-01-09-36-45.gh-issue-142145.tcAUhg.rst
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ Python-3.9.25/Misc/NEWS.d/next/Security/2025-12-01-09-36-45.gh-issue-142145.tcAUhg.rst	2025-12-19 23:27:27.635403950 +0100
@@ -0,0 +1 @@
+Remove quadratic behavior in ``xml.minidom`` node ID cache clearing.