another fix for the 'descendant' problem in cssselect to undo a serio…

…us performance regression in 2.3.1

--HG--
extra : rebase_source : 2c4c89423870a16cc9aedc19532032d2a10bae5e

CHANGES.txt

@@ -20,6 +20,13 @@ Features added
 Bugs fixed
 ----------
 
+* Fixed the "descendant" bug in cssselect a second time (after a first
+  fix in lxml 2.3.1).  The previous change resulted in a serious
+  performance regression for the XPath based evaluation of the
+  translated expression.  Note that this breaks the usage of some of
+  the generated XPath expressions as XSLT location paths that
+  previously worked in 2.3.1.
+
 Other changes
 --------------
 
@@ -69,10 +76,11 @@ Bugs fixed
 * Assertion error in lxml.html.cleaner when discarding top-level elements.
 
 * 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).
+  'A/descendant-or-self::node()/B') instead of 'A/descendant::B' for
+  the css descendant selector ('A B').  This makes a few edge cases
+  like ``"div *:last-child"`` consistent with the selector behavior in
+  WebKit and Firefox, and makes more css expressions valid location
+  paths (for use in xsl:template match).
 
 * In lxml.html, non-selected ``<option>`` tags no longer show up in the
   collected form values.

src/lxml/cssselect.py

@@ -494,7 +494,7 @@ def xpath(self):
 
     def _xpath_descendant(self, xpath, sub):
         # when sub is a descendant in any way of xpath
-        xpath.join('//', sub.xpath())
+        xpath.join('/descendant-or-self::*/', sub.xpath())
         return xpath
 
     def _xpath_child(self, xpath, sub):

src/lxml/tests/test_css.txt

@@ -95,7 +95,7 @@ Now of translation:
     >>> xpath('E:nth-last-of-type(1)')
     */e[position() = last() - 1]
     >>> xpath('div E:nth-last-of-type(1) .aclass')
-    div//e[position() = last() - 1]//*[contains(concat(' ', normalize-space(@class), ' '), ' aclass ')]
+    div/descendant-or-self::*/e[position() = last() - 1]/descendant-or-self::*/*[contains(concat(' ', normalize-space(@class), ' '), ' aclass ')]
     >>> xpath('E:first-child')
     */*[name() = 'e' and (position() = 1)]
     >>> xpath('E:last-child')
@@ -119,15 +119,15 @@ Now of translation:
     >>> xpath('E:not(:contains("foo"))')
     e[not(contains(css:lower-case(string(.)), 'foo'))]
     >>> xpath('E F')
-    e//f
+    e/descendant-or-self::*/f
     >>> xpath('E > F')
     e/f
     >>> xpath('E + F')
     e/following-sibling::*[name() = 'f' and (position() = 1)]
     >>> xpath('E ~ F')
     e/following-sibling::f
     >>> xpath('div#container p')
-    div[@id = 'container']//p
+    div[@id = 'container']/descendant-or-self::*/p
     >>> xpath('p *:only-of-type')
     Traceback (most recent call last):
         ...