Cannot compile descendant XPath expression generated by CSS selector

[Martin Aspeli]

Using this rule:

<drop css:content="dl.portletNavigationTree a img" />

I get this error:

XSLTParseError: xsltCompilePattern : failed to compile '//dl[contains(concat(' ', normalize-space(@class), ' '), ' portletNavigationTree ')]/descendant::a/descendant::img'

This expression would work:

//dl[contains(concat(' ', normalize-space(@class), ' '), ' portletNavigationTree ')]//a//img

[Laurence Rowe (lrowe)]

xsl:template match is more restrictive than plain xpath: http://www.w3.org/TR/xslt#Patterns
"The syntax for patterns is a subset of the syntax for expressions. In particular, location paths that meet certain restrictions can be used as patterns."
"A Pattern is a set of location path patterns separated by |. A location path pattern is a location path whose steps all use only the child or attribute axes. Although patterns must not use the descendant-or-self axis, patterns may use the // operator as well as the / operator."

A minimal test case here would be "body a":

>>> from lxml import etree, cssselect
>>> match = cssselect.css_to_xpath('body a', '//')
>>> match
u'//body/descendant::a'
>>> doc = etree.XML('''<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"><xsl:template match=""/></xsl:stylesheet>''')
>>> template = doc.getchildren()[0]
>>> template.set('match', match)
>>> etree.XSLT(doc)
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "xslt.pxi", line 399, in lxml.etree.XSLT.__init__ (src/lxml/lxml.etree.c:108752)
XSLTParseError: xsltCompilePattern : failed to compile '//body/descendant::a'

I guess we should probably file this as a bug report against lxml.

Laurence

[scoder (scoder)]

The cssselect.py module was not designed to work with XSLT specifically. It's meant as a translator to general XPath expressions.

I would accept a patch that simplifies the XPath expressions without changing their behaviour.

[Laurence Rowe (lrowe)]

Make css_to_xpath more compatible with location paths.

In lxml.cssselect, use the xpath 'A//B' (short for 'A/descendant-or-self::node()/B') instead of 'A/descendant::B' for the css descendant selector ('A B'). This makes a few edge cases to be consistent with the selector behavior in WebKit and Firefox, and makes more css
expressions valid location paths (for use in xsl:template match).

https://github.com/lxml/lxml/pull/1

[scoder (scoder)]

Pull request was merged. Thanks.

[scoder (scoder)]

Fixed in lxml 2.3.1.