[xslt] Bug regarding libxslt and XML_USE_BUFFER_CONTENT

[Thorsten Meinl <Thorsten meinl bnv-bamberg de>]

Hello everybody,

I think I just found a serious bug in libxslt 1.0.9. I compiled 
libxml2-2.4.12 with XML_USE_BUFFER_CONTENT (god knows why :-)). Afterwards 
libxslt fell over hundreds of errors while running the tests. I think the 
problem is very easy:
There is a define IS_BLANK_NODE in xslt.c which tests for "empty" nodes:

<snip outOf="xslt.c">
#define IS_BLANK_NODE(n) \
    (((n)->type == XML_TEXT_NODE) && (xsltIsBlank((n)->content)))
</snip>

The second statement does not works for -DXML_USE_BUFFER_CONTENT, because the 
xmlNodePtr looks slightly different in this case:

<snip from="libxml/tree.h">
#ifndef XML_USE_BUFFER_CONTENT
    xmlChar         *content;   /* the content */
#else
    xmlBufferPtr     content;   /* the content in a buffer */
#endif
</snip>

So content is a pointer to something else and therefore xsltIsBlank reads 
garbage and fails. So my suggestion to solve it in this place (maybe it 
crashes in several other places):

<snip from="xslt.c">
#ifndef XML_USE_BUFFER_CONTENT
  #define IS_BLANK_NODE(n) \
      (((n)->type == XML_TEXT_NODE) && (xsltIsBlank((n)->content)))
#else
  #define IS_BLANK_NODE(n) \
      (((n)->type == XML_TEXT_NODE) && (xsltIsBlank((n)->content->content)))
#endif
</snip>

Maybe you could also mention this problem in README or INSTALL.

Greetings

Thorsten