Fix crash in ParentNode::append() when dealing with a fragment containing text nodes

Credits for test: phpgt/Dom#454.

Closes GH-14206.

Author: nielsdos

NEWS

@@ -20,6 +20,8 @@ PHP                                                                        NEWS
   . Fix references not handled correctly in C14N. (nielsdos)
   . Fix crash when calling childNodes next() when iterator is exhausted.
     (nielsdos)
+  . Fix crash in ParentNode::append() when dealing with a fragment
+    containing text nodes. (nielsdos)
 
 - Hash:
   . ext/hash: Swap the checking order of `__has_builtin` and `__GNUC__`

ext/dom/parentnode.c

@@ -150,6 +150,22 @@ static xmlDocPtr dom_doc_from_context_node(xmlNodePtr contextNode)
 	}
 }
 
+/* Citing from the docs (https://gnome.pages.gitlab.gnome.org/libxml2/devhelp/libxml2-tree.html#xmlAddChild):
+ * "Add a new node to @parent, at the end of the child (or property) list merging adjacent TEXT nodes (in which case @cur is freed)".
+ * So we must use a custom way of adding that does not merge. */
+static void dom_add_child_without_merging(xmlNodePtr parent, xmlNodePtr child)
+{
+	if (parent->children == NULL) {
+		parent->children = child;
+	} else {
+		xmlNodePtr last = parent->last;
+		last->next = child;
+		child->prev = last;
+	}
+	parent->last = child;
+	child->parent = parent;
+}
+
 xmlNode* dom_zvals_to_fragment(php_libxml_ref_obj *document, xmlNode *contextNode, zval *nodes, int nodesc)
 {
 	int i;
@@ -183,7 +199,7 @@ xmlNode* dom_zvals_to_fragment(php_libxml_ref_obj *document, xmlNode *contextNod
 			 * So we must take a copy if this situation arises to prevent a use-after-free. */
 			bool will_free = newNode->type == XML_TEXT_NODE && fragment->last && fragment->last->type == XML_TEXT_NODE;
 			if (will_free) {
-				newNode = xmlCopyNode(newNode, 1);
+				newNode = xmlCopyNode(newNode, 0);
 			}
 
 			if (newNode->type == XML_DOCUMENT_FRAG_NODE) {
@@ -192,9 +208,7 @@ xmlNode* dom_zvals_to_fragment(php_libxml_ref_obj *document, xmlNode *contextNod
 				while (newNode) {
 					xmlNodePtr next = newNode->next;
 					xmlUnlinkNode(newNode);
-					if (!xmlAddChild(fragment, newNode)) {
-						goto err;
-					}
+					dom_add_child_without_merging(fragment, newNode);
 					newNode = next;
 				}
 			} else if (!xmlAddChild(fragment, newNode)) {

ext/dom/tests/ParentNode_append_fragment_text_coalesce.phpt

@@ -0,0 +1,21 @@
+--TEST--
+Text coalesce bug when appending fragment with text nodes
+--EXTENSIONS--
+dom
+--FILE--
+<?php
+$document = new DOMDocument();
+$document->loadXML('<root/>');
+
+$sut = $document->createDocumentFragment();
+for($i = 0; $i < 10; $i++) {
+	$textNode = $document->createTextNode("Node$i");
+	$sut->append($textNode);
+}
+
+$document->documentElement->append($sut);
+echo $document->saveXML();
+?>
+--EXPECT--
+<?xml version="1.0"?>
+<root>Node0Node1Node2Node3Node4Node5Node6Node7Node8Node9</root>