gh-158984: Fix xmlns:prefix attributes set with setAttribute() in minidom

Take the prefix of an existing namespace declaration from the attribute
name instead of Attr.prefix, which is None for attributes created with
the DOM Level 1 API.

Author: sricursion

Lib/test/test_minidom.py

@@ -6,6 +6,7 @@
 from test import support
 import unittest
 
+import xml.dom.expatbuilder
 import xml.dom.minidom
 
 from xml.dom.minidom import parse, Attr, Node, Document, Element, parseString
@@ -683,6 +684,54 @@ def testWriteXMLExistingNamespaceDeclarations(self):
                 self.assertEqual(dom.documentElement.toxml(), str)
                 dom.unlink()
 
+    def testWriteXMLDOM1PrefixDeclaration(self):
+        # setAttribute() does not set the prefix of the attribute,
+        # but "xmlns:p" still declares the prefix "p".
+        dom = Document()
+        root = dom.appendChild(
+            dom.createElementNS("http://xml.python.org/ns", "p:root"))
+        root.setAttribute("xmlns:p", "http://xml.python.org/ns")
+        domstr = dom.documentElement.toxml()
+        dom.unlink()
+        self.assertEqual(domstr,
+                '<p:root xmlns:p="http://xml.python.org/ns"/>')
+        dom = parseString(domstr)
+        self.assertEqual(dom.documentElement.namespaceURI,
+                         "http://xml.python.org/ns")
+        dom.unlink()
+
+    def testWriteXMLDOM1PrefixDeclarationNoNamespace(self):
+        # A prefix declaration is not a declaration of the default namespace.
+        dom = Document()
+        root = dom.appendChild(dom.createElement("root"))
+        root.setAttribute("xmlns:xsi", "http://xml.python.org/ns")
+        self.assertEqual(dom.documentElement.toxml(),
+                '<root xmlns:xsi="http://xml.python.org/ns"/>')
+        dom.unlink()
+
+    def testWriteXMLDOM1PrefixDeclarationDefaultNamespace(self):
+        # The element still needs a declaration of its own default namespace.
+        dom = Document()
+        root = dom.appendChild(
+            dom.createElementNS("http://xml.python.org/ns", "root"))
+        root.setAttribute("xmlns:x", "http://xml.python.org/ns")
+        domstr = dom.documentElement.toxml()
+        dom.unlink()
+        self.assertEqual(domstr,
+                '<root xmlns="http://xml.python.org/ns" '
+                'xmlns:x="http://xml.python.org/ns"/>')
+        dom = parseString(domstr)
+        self.assertEqual(dom.documentElement.namespaceURI,
+                         "http://xml.python.org/ns")
+        dom.unlink()
+
+    def testWriteXMLParsedWithoutNamespaces(self):
+        src = ('<root xmlns:p="http://xml.python.org/ns">'
+               '<p:child/><other/></root>')
+        dom = xml.dom.expatbuilder.parseString(src, namespaces=False)
+        self.assertEqual(dom.documentElement.toxml(), src)
+        dom.unlink()
+
     def testWriteXMLNotANamespaceDeclaration(self):
         # an attribute whose name only starts with "xmlns" is not one
         dom = parseString('<root xmlns="http://xml.python.org/ns">'

Lib/xml/dom/minidom.py

@@ -433,7 +433,7 @@ def _fixup_namespaces(element, nsmap):
                 # Declarations already present in the document take precedence.
                 nsmap = _bind_namespace(
                     nsmap, inherited,
-                    attr.localName if attr.prefix else None, attr.value)
+                    attr.localName if ":" in name else None, attr.value)
                 attr_uri = None
             elif attr_uri == XML_NAMESPACE:
                 # The xml prefix is bound by definition.