[xslt] Streaming XPath compilation in xsltXPathCompile()

["Kasimier Buchcik" <k buchcik 4commerce de>]

Hi,

xsltXPathCompile() in xsltutils.c could be further optimized,
as it currently won't use the optimized streaming XPath
for simple expressions if the expression contains prefixed
name tests, due to the fact that xmlPatterncompile needs
a list of in-scope namespace for prefixed name tests.
So we get the time-penalty for trying to stream-compile the
expression but we don't get the efficiency for its execution.

xsltXPathCompile() is used in attrvt.c and keys.c.

Call-stack:
xsltXPathCompile (xsltutils.c)
--> xmlXPathCtxtCompile (Libxsml2, xpath.c)
--> xmlXPathTryStreamCompile (Libxml2, xpath.c)
--> xmlPatterncompile (Libxml2, pattern.c)
--> xmlCompileStepPattern (Libxml2, pattern.c)
where we hit the following:
if (i >= ctxt->nb_namespaces) {
	ERROR5(NULL, NULL, NULL,
		"xmlCompileStepPattern : no namespace bound to prefix
%s\n",

A way to fix this would be to feed the xmlXPathContext with
the current in-scope namespaces. *But*, on the other side,
this will generate a copy of all the given in-scope namespaces
in xmlXPathTryStreamCompile(); I'm not sure if we want a copy
of such a list for every compiled expression. So I really don't know
would be the optimal solution here.

If there was a chance of adjusting xmlXPathTryStreamCompile() to *not*
to copy the list (maybe per context option), then this would be the
ideal solution, I think.

Regards,

Kasimier