[libxml2] Fix handling of XML-1.0 XML namespace declaration

[Daniel Veillard <veillard src gnome org>]

commit aa54d37cd75399722f012e37f17d9ffeeddba556
Author: Daniel Veillard <veillard redhat com>
Date:   Thu Sep 9 18:17:47 2010 +0200

    Fix handling of XML-1.0 XML namespace declaration
    
    Usually 'xml' namespace for XML-1.0 declaration does not need
    to be carried but Mike Hommey raised the problem that the SVG
    XSD file fails to parse due to a mishandling.
    - SAX2.c: failure to create a namespace should not be interpreted
      as a memory allocation error
    - tree.c: document better xmlNewNs behaviour, and fix it in the
      case the 'xml' prefix is being used.

 SAX2.c |    8 ++++++--
 tree.c |   15 +++++++++++++--
 2 files changed, 19 insertions(+), 4 deletions(-)
---
diff --git a/SAX2.c b/SAX2.c
index 84c1f00..c0482c0 100644
--- a/SAX2.c
+++ b/SAX2.c
@@ -2242,8 +2242,12 @@ xmlSAX2StartElementNs(void *ctx,
 	    if ((URI != NULL) && (prefix == pref))
 		ret->ns = ns;
 	} else {
-	    xmlSAX2ErrMemory(ctxt, "xmlSAX2StartElementNs");
-	    return;
+            /*
+             * any out of memory error would already have been raised
+             * but we can't be garanteed it's the actual error due to the
+             * API, best is to skip in this case
+             */
+	    continue;
 	}
 #ifdef LIBXML_VALID_ENABLED
 	if ((!ctxt->html) && ctxt->validate && ctxt->wellFormed &&
diff --git a/tree.c b/tree.c
index 1e1a23a..24db82a 100644
--- a/tree.c
+++ b/tree.c
@@ -721,8 +721,19 @@ xmlNewNs(xmlNodePtr node, const xmlChar *href, const xmlChar *prefix) {
     if ((node != NULL) && (node->type != XML_ELEMENT_NODE))
 	return(NULL);
 
-    if ((prefix != NULL) && (xmlStrEqual(prefix, BAD_CAST "xml")))
-	return(NULL);
+    if ((prefix != NULL) && (xmlStrEqual(prefix, BAD_CAST "xml"))) {
+        /* xml namespace is predefined, no need to add it */
+        if (xmlStrEqual(href, XML_XML_NAMESPACE))
+            return(NULL);
+
+        /*
+         * Problem, this is an attempt to bind xml prefix to a wrong
+         * namespace, which breaks
+         * Namespace constraint: Reserved Prefixes and Namespace Names
+         * from XML namespace. But documents authors may not care in
+         * their context so let's proceed.
+         */
+    }
 
     /*
      * Allocate a new Namespace and fill the fields.