From fe066ce2d6f71603f525c6d887fddf632fedba8b Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Thu, 7 Nov 2019 14:15:46 +0530
Subject: [PATCH] Conversion: CSS selectors with unknown pseudo-elements should
 not match any tags. See #1827700 (Private bug)

---
 src/css_selectors/select.py | 46 +++++++++++++++++++++++++++----------
 1 file changed, 34 insertions(+), 12 deletions(-)

diff --git a/src/css_selectors/select.py b/src/css_selectors/select.py
index 2626a8fe8c..ce6b2df178 100644
--- a/src/css_selectors/select.py
+++ b/src/css_selectors/select.py
@@ -13,7 +13,7 @@ from itertools import chain
 from lxml import etree
 
 from css_selectors.errors import ExpressionError
-from css_selectors.parser import parse, ascii_lower, Element
+from css_selectors.parser import parse, ascii_lower, Element, FunctionalPseudoElement
 from css_selectors.ordered_set import OrderedSet
 
 from polyglot.builtins import iteritems, itervalues
@@ -182,8 +182,7 @@ class Select(object):
         seen = set()
         if root is not None:
             root = frozenset(self.itertag(root))
-        for selector in get_parsed_selector(selector):
-            parsed_selector = selector.parsed_tree
+        for parsed_selector in get_parsed_selector(selector):
             for item in self.iterparsedselector(parsed_selector):
                 if item not in seen and (root is None or item in root):
                     yield item
@@ -581,31 +580,54 @@ def allow_all(cache, item):
     return True
 
 
-def select_pseudo(cache, pseudo):
+def get_func_for_pseudo(cache, ident):
     try:
-        func = cache.dispatch_map[pseudo.ident.replace('-', '_')]
+        func = cache.dispatch_map[ident.replace('-', '_')]
     except KeyError:
-        if pseudo.ident == 'root':
-            yield cache.root
-            return
-
-        if pseudo.ident in cache.ignore_inappropriate_pseudo_classes:
+        if ident in cache.ignore_inappropriate_pseudo_classes:
             func = allow_all
         else:
             raise ExpressionError(
-                "The pseudo-class :%s is not supported" % pseudo.ident)
+                "The pseudo-class :%s is not supported" % ident)
 
     try:
         func.is_pseudo
     except AttributeError:
         raise ExpressionError(
-            "The pseudo-class :%s is invalid" % pseudo.ident)
+            "The pseudo-class :%s is invalid" % ident)
+    return func
+
+
+def select_selector(cache, selector):
+    if selector.pseudo_element is None:
+        for item in cache.iterparsedselector(selector.parsed_tree):
+            yield item
+        return
+    if isinstance(selector.pseudo_element, FunctionalPseudoElement):
+        raise ExpressionError(
+            "The pseudo-element ::%s is not supported" % selector.pseudo_element.name)
+    func = get_func_for_pseudo(cache, selector.pseudo_element)
+    for item in cache.iterparsedselector(selector.parsed_tree):
+        if func(cache, item):
+            yield item
+
+
+def select_pseudo(cache, pseudo):
+    func = get_func_for_pseudo(cache, pseudo.ident)
+    if func is select_root:
+        yield cache.root
+        return
 
     for item in cache.iterparsedselector(pseudo.selector):
         if func(cache, item):
             yield item
 
 
+@pseudo_func
+def select_root(cache, elem):
+    return elem is cache.root
+
+
 @pseudo_func
 def select_first_child(cache, elem):
     try: