Fix spec compliance error for DOMDocument::getElementsByTagNameNS

ext/dom/php_dom.c

@@ -1270,10 +1270,15 @@ xmlNode *dom_get_elements_by_tag_name_ns_raw(xmlNodePtr nodep, char *ns, char *l
 {
 	xmlNodePtr ret = NULL;
 
+	/* Note: The spec says that ns == '' must be transformed to ns == NULL. In other words, they are equivalent.
+	 *       PHP however does not do this and internally uses the empty string everywhere when the user provides ns == NULL.
+	 *       This is because for PHP ns == NULL has another meaning: "match every namespace" instead of "match the empty namespace". */
+	bool ns_match_any = ns == NULL || (ns[0] == '*' && ns[1] == '\0');
+
 	while (nodep != NULL && (*cur <= index || index == -1)) {
 		if (nodep->type == XML_ELEMENT_NODE) {
 			if (xmlStrEqual(nodep->name, (xmlChar *)local) || xmlStrEqual((xmlChar *)"*", (xmlChar *)local)) {
-				if (ns == NULL || (!strcmp(ns, "") && nodep->ns == NULL) || (nodep->ns != NULL && (xmlStrEqual(nodep->ns->href, (xmlChar *)ns) || xmlStrEqual((xmlChar *)"*", (xmlChar *)ns)))) {
+				if (ns_match_any || (!strcmp(ns, "") && nodep->ns == NULL) || (nodep->ns != NULL && xmlStrEqual(nodep->ns->href, (xmlChar *)ns))) {
 					if (*cur == index) {
 						ret = nodep;
 						break;

ext/dom/tests/DOMDocument_getElementsByTagNameNS_match_any_namespace.phpt

@@ -0,0 +1,82 @@
+--TEST--
+DOMDocument::getElementsByTagNameNS() match any namespace
+--EXTENSIONS--
+dom
+--FILE--
+<?php
+
+/* Sample document taken from https://www.php.net/manual/en/domdocument.getelementsbytagname.php */
+$xml = <<<EOD
+<?xml version="1.0" ?>
+<chapter xmlns:xi="http://www.w3.org/2001/XInclude">
+<title>Books of the other guy..</title>
+<para>
+ <xi:include href="book.xml">
+  <xi:fallback>
+   <error>xinclude: book.xml not found</error>
+  </xi:fallback>
+ </xi:include>
+ <include>
+  This is another namespace
+ </include>
+</para>
+</chapter>
+EOD;
+$dom = new DOMDocument;
+
+// load the XML string defined above
+$dom->loadXML($xml);
+
+function test($namespace, $local) {
+    global $dom;
+    $namespace_str = $namespace !== NULL ? "'$namespace'" : "null";
+    echo "-- getElementsByTagNameNS($namespace_str, '$local') --\n";
+    foreach ($dom->getElementsByTagNameNS($namespace, $local) as $element) {
+        echo 'local name: ', $element->localName, ', prefix: ', $element->prefix, "\n";
+    }
+}
+
+// Should *also* include objects even without a namespace
+test(null, '*');
+// Should *also* include objects even without a namespace
+test('*', '*');
+// Should *only* include objects without a namespace
+test('', '*');
+// Should *only* include objects with the specified namespace
+test('http://www.w3.org/2001/XInclude', '*');
+// Should not give any output
+test('', 'fallback');
+// Should not give any output, because the null namespace is the same as the empty namespace
+test(null, 'fallback');
+// Should only output the include from the empty namespace
+test(null, 'include');
+
+?>
+--EXPECT--
+-- getElementsByTagNameNS(null, '*') --
+local name: chapter, prefix: 
+local name: title, prefix: 
+local name: para, prefix: 
+local name: error, prefix: 
+local name: include, prefix: 
+-- getElementsByTagNameNS('*', '*') --
+local name: chapter, prefix: 
+local name: title, prefix: 
+local name: para, prefix: 
+local name: include, prefix: xi
+local name: fallback, prefix: xi
+local name: error, prefix: 
+local name: include, prefix: 
+-- getElementsByTagNameNS('', '*') --
+local name: chapter, prefix: 
+local name: title, prefix: 
+local name: para, prefix: 
+local name: error, prefix: 
+local name: include, prefix: 
+-- getElementsByTagNameNS('http://www.w3.org/2001/XInclude', '*') --
+local name: include, prefix: xi
+local name: fallback, prefix: xi
+-- getElementsByTagNameNS('', 'fallback') --
+-- getElementsByTagNameNS(null, 'fallback') --
+-- getElementsByTagNameNS(null, 'include') --
+local name: include, prefix: