From 30eb4290d8e193114d3780d1bf46a0416ba89bc8 Mon Sep 17 00:00:00 2001
From: Vyron Vasileiadis <hi@fedonman.com>
Date: Sat, 17 Oct 2026 21:43:26 +0300
Subject: [PATCH] gh-159637: Fix renaming an attribute to a prefixed name in
 minidom

Document.renameNode() set the new prefix of an attribute before its
new namespace, so the prefix was validated against the old namespace.
Renaming an attribute with no namespace to a prefixed name in a
namespace raised NamespaceErr after the attribute had been removed
from its element.

Set the namespace first, and check the prefix before removing the
attribute, so that a rejected rename leaves the element unchanged.
---
 Lib/test/test_minidom.py | 22 ++++++++++++++++++++++
 Lib/xml/dom/minidom.py   |  4 +++-
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/Lib/test/test_minidom.py b/Lib/test/test_minidom.py
index 446bbe096bd19d..b5028ee126ccee 100644
--- a/Lib/test/test_minidom.py
+++ b/Lib/test/test_minidom.py
@@ -1880,6 +1880,28 @@ def testRenameAttribute(self):
         self.checkRenameNodeSharedConstraints(doc, attr)
         doc.unlink()
 
+    def testRenameAttributeToPrefixedName(self):
+        doc = parseString("<doc a='v' b='w'/>")
+        elem = doc.documentElement
+        attr = elem.getAttributeNode("a")
+        attr = doc.renameNode(attr, "http://xml.python.org/ns", "p:c")
+        self.assertEqual(attr.name, "p:c")
+        self.assertEqual(attr.prefix, "p")
+        self.assertEqual(attr.localName, "c")
+        self.assertEqual(attr.namespaceURI, "http://xml.python.org/ns")
+        self.assertIsNone(elem.getAttributeNode("a"))
+        self.assertIs(elem.getAttributeNodeNS("http://xml.python.org/ns", "c"),
+                      attr)
+
+        # A rejected rename leaves the attribute on its element.
+        attr = elem.getAttributeNode("b")
+        self.assertRaises(xml.dom.NamespaceErr, doc.renameNode, attr,
+                          "http://xml.python.org/ns", "xml:lang")
+        self.assertEqual(attr.name, "b")
+        self.assertIsNone(attr.namespaceURI)
+        self.assertIs(elem.getAttributeNode("b"), attr)
+        doc.unlink()
+
     def testRenameElement(self):
         doc = parseString("<doc/>")
         elem = doc.documentElement
diff --git a/Lib/xml/dom/minidom.py b/Lib/xml/dom/minidom.py
index 7cb652a323dcc2..5ab58c76f032ad 100644
--- a/Lib/xml/dom/minidom.py
+++ b/Lib/xml/dom/minidom.py
@@ -2129,15 +2129,17 @@ def renameNode(self, n, namespaceURI, name):
             prefix = None
             localName = None
         if n.nodeType == Node.ATTRIBUTE_NODE:
+            if prefix is not None:
+                _check_prefix(prefix, namespaceURI, True)
             element = n.ownerElement
             if element is not None:
                 is_id = n._is_id
                 element.removeAttributeNode(n)
         else:
             element = None
+        n.namespaceURI = namespaceURI
         n.prefix = prefix
         n._localName = localName
-        n.namespaceURI = namespaceURI
         n.nodeName = name
         if n.nodeType == Node.ELEMENT_NODE:
             n.tagName = name