[3.10] gh-142145: Remove quadratic behavior in node ID cache clearing (GH-142146)

Lib/test/test_minidom.py

@@ -2,14 +2,15 @@
 
 importcopy
 importpickle
+importtime
 importio
 fromtestimportsupport
 importunittest
 
 importpyexpat
 importxml.dom.minidom
 
-fromxml.dom.minidomimportparse, Attr, Node, Document, parseString
+fromxml.dom.minidomimportparse, Attr, Node, Document, Element, parseString
 fromxml.dom.minidomimportgetDOMImplementation
 fromxml.parsers.expatimportExpatError
 
@@ -177,6 +178,36 @@ def testAppendChild(self):
 self.confirm(dom.documentElement.childNodes[-1].data=="Hello")
 dom.unlink()
 
+@support.requires_resource('cpu')
+deftestAppendChildNoQuadraticComplexity(self):
+impl=getDOMImplementation()
+
+newdoc=impl.createDocument(None, "some_tag", None)
+top_element=newdoc.documentElement
+children= [newdoc.createElement(f"child-{i}") foriinrange(1, 2**15+1)]
+element=top_element
+
+start=time.monotonic()
+forchildinchildren:
+element.appendChild(child)
+element=child
+end=time.monotonic()
+
+# This example used to take at least 30 seconds.
+# Conservative assertion due to the wide variety of systems and
+# build configs timing based tests wind up run under.
+# A --with-address-sanitizer --with-pydebug build on a rpi5 still
+# completes this loop in <0.5 seconds.
+self.assertLess(end-start, 4)
+
+deftestSetAttributeNodeWithoutOwnerDocument(self):
+# regression test for gh-142754
+elem=Element("test")
+attr=Attr("id")
+attr.value="test-id"
+elem.setAttributeNode(attr)
+self.assertEqual(elem.getAttribute("id"), "test-id")
+
 deftestAppendChildFragment(self):
 dom, orig, c1, c2, c3, frag=self._create_fragment_test_nodes()
 dom.documentElement.appendChild(frag)

Lib/xml/dom/minidom.py

@@ -292,13 +292,6 @@ def _append_child(self, node):
 childNodes.append(node)
 node.parentNode=self
 
-def_in_document(node):
-# return True iff node is part of a document tree
-whilenodeisnotNone:
-ifnode.nodeType==Node.DOCUMENT_NODE:
-returnTrue
-node=node.parentNode
-returnFalse
 
 def_write_data(writer, data):
 "Writes datachars to writer."
@@ -355,6 +348,7 @@ class Attr(Node):
 def__init__(self, qName, namespaceURI=EMPTY_NAMESPACE, localName=None,
 prefix=None):
 self.ownerElement=None
+self.ownerDocument=None
 self._name=qName
 self.namespaceURI=namespaceURI
 self._prefix=prefix
@@ -680,6 +674,7 @@ class Element(Node):
 
 def__init__(self, tagName, namespaceURI=EMPTY_NAMESPACE, prefix=None,
 localName=None):
+self.ownerDocument=None
 self.parentNode=None
 self.tagName=self.nodeName=tagName
 self.prefix=prefix
@@ -1539,7 +1534,7 @@ def _clear_id_cache(node):
 ifnode.nodeType==Node.DOCUMENT_NODE:
 node._id_cache.clear()
 node._id_search_stack=None
-elif_in_document(node):
+elifnode.ownerDocument:
 node.ownerDocument._id_cache.clear()
 node.ownerDocument._id_search_stack=None
 

Misc/NEWS.d/next/Security/2025-12-01-09-36-45.gh-issue-142145.tcAUhg.rst

@@ -0,0 +1,6 @@
+Remove quadratic behavior in ``xml.minidom`` node ID cache clearing. In order
+to do this without breaking existing users, we also add the *ownerDocument*
+attribute to :mod:`xml.dom.minidom` elements and attributes created by directly
+instantiating the ``Element`` or ``Attr`` class. Note that this way of creating
+nodes is not supported; creator functions like
+:py:meth:`xml.dom.Document.documentElement` should be used instead.