Fixed descendant-or-self with a predicate.

Processing of this axis along with a predicate wouldn't quite work out. Even if
the predicate returned false the node would still be matched (which should not
be the case).

lib/oga/xpath/evaluator.rb

@@ -319,12 +319,8 @@ module Oga
         nodes = XML::NodeSet.new
 
         context.each do |context_node|
-          context_node.children.each do |node|
-            nodes << node if node_matches?(node, ast_node)
-          end
-
           context_node.each_node do |node|
-            nodes << node if node_matches?(node, ast_node)
+            nodes.concat(process(ast_node, XML::NodeSet.new([node])))
           end
         end
 

spec/oga/xpath/evaluator/axes/descendant_or_self_spec.rb

@@ -3,7 +3,7 @@ require 'spec_helper'
 describe Oga::XPath::Evaluator do
   context 'descendant-or-self axis' do
     before do
-      document = parse('<a><b><b><c></c></b></b></a>')
+      document = parse('<a><b><b><c class="x"></c></b></b></a>')
 
       @first_a   = document.children[0]
       @first_b   = @first_a.children[0]
@@ -40,6 +40,14 @@ describe Oga::XPath::Evaluator do
       end
     end
 
+    context 'nested descendants with a matching predicate' do
+      before do
+        @set = @evaluator.evaluate('descendant-or-self::c[@class="x"]')
+      end
+
+      it_behaves_like :node_set, :length => 1
+    end
+
     context 'descendants of a specific node' do
       before do
         @set = @evaluator.evaluate('a/descendant-or-self::b')
@@ -88,6 +96,22 @@ describe Oga::XPath::Evaluator do
       it_behaves_like :empty_node_set
     end
 
+    context 'direct descendants without a matching predicate' do
+      before do
+        @set = @evaluator.evaluate('descendant-or-self::a[@class]')
+      end
+
+      it_behaves_like :empty_node_set
+    end
+
+    context 'nested descendants without a matching predicate' do
+      before do
+        @set = @evaluator.evaluate('descendant-or-self::b[@class]')
+      end
+
+      it_behaves_like :empty_node_set
+    end
+
     context 'direct descendants using the short form' do
       before do
         @set = @evaluator.evaluate('//b')