XML::LibXML defines setNamespace in the following way:

sub setNamespace {
    my $self = shift;
    my $n = $self->nodeName;
    if ( $self->_setNamespace(@_) ){
        if ( scalar @_ < 3 || $_[2] == 1 ){
            $self->setNodeName( $n );
        }
        return 1;
    }
    return 0;
}
[download]

where _setNamespace comes from its XS component, the important part (I guess) is the following:

       if ( nsPrefix == NULL && nsURI == NULL ) {
            /* special case: empty namespace */
            if ( (ns = xmlSearchNs(node->doc, node, NULL)) &&
                 ( ns->href && xmlStrlen( ns->href ) != 0 ) ) {
                /* won't take it */
                RETVAL = 0;
            } else if ( flag ) {
                /* no namespace */
                xmlSetNs(node, NULL);
                RETVAL = 1;
            } else {
                RETVAL = 0;
            }
        }
[download]

setNamespace returns 1, so I guess it goes the "else if" branch, but the namespace isn't removed from the node. xmlSetNs comes from libxml2 and is defined as (debugging ifdefs removed)

void
xmlSetNs(xmlNodePtr node, xmlNsPtr ns) {
    if (node == NULL) {
    return;
    }
    if ((node->type == XML_ELEMENT_NODE) ||
        (node->type == XML_ATTRIBUTE_NODE))
    node->ns = ns;
}
[download]

Anyone can explain why the namespace isn't changed?

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
[download]

Anyone can explain why the namespace isn't changed?

Hi,

Its some kind of bug, if I were setup to compile libxml2 I'd narrow it down with this addition to LibXML.xs

int
_setNamespaceNULL(self )
        SV * self
    PREINIT:
        xmlNodePtr node = PmmSvNode(self);
    INIT:
        if ( node == NULL ) {
            croak( "lost node" );
        }
    CODE:
        xmlSetNs(node, NULL);
        RETVAL = 1;
    OUTPUT:
        RETVAL
[download]

My knowledge of C is less than basic (yes, I used Basic a lot as a child).

But, I was able to compile the following and verify that libxml2 is able to clear the namespace, so the problem must lie in the XS land:

#include <stdio.h>
#include <libxml/tree.h>
#include <libxml/parser.h>
#include <libxml/xpath.h>
#include <libxml/xpathInternals.h>

int main (int argc, char **argv) {
  xmlInitParser();

  xmlDoc *document;
  document = xmlParseDoc("<r xmlns:p='http://p.p'><p:a>HERE</p:a></r>"
+);

  xmlXPathContext *xpc;
  xpc = xmlXPathNewContext(document);
  xmlXPathRegisterNs(xpc, "p", "http://p.p");

  xmlXPathObject *xp;
  xp = xmlXPathEvalExpression("/r/p:a", xpc);
  if (xp == NULL) return(1);

  xmlNodeSet *nodes;
  nodes = xp->nodesetval;

  xmlNode *node;
  node = nodes->nodeTab[0];

  xmlSetNs(node, NULL);

  xmlChar *s;
  int size;
  xmlDocDumpMemory(document, &s, &size);

  char *string;
  string = (char *)s;
  printf("%s", string);

  return(0);
}
[download]

Outputs:

<?xml version="1.0"?>
<r xmlns:p="http://p.p"><a>HERE</a></r>
[download]

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
[download]

Should work now.

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
[download]