Support for querying attributes using XPath.

lib/oga/xpath/evaluator.rb

@@ -59,11 +59,7 @@ module Oga
         nodes = XML::NodeSet.new
 
         context.each do |xml_node|
-          # TODO: change this when attribute tests are implemented since those
-          # are not XML::Element instances.
-          if xml_node.is_a?(XML::Element) and node_matches?(xml_node, node)
-            nodes << xml_node
-          end
+          nodes << xml_node if node_matches?(xml_node, node)
         end
 
         return nodes
@@ -111,6 +107,18 @@ module Oga
         return nodes
       end
 
+      def on_axis_attribute(node, context)
+        nodes = XML::NodeSet.new
+
+        context.each do |xml_node|
+          next unless xml_node.is_a?(XML::Element)
+
+          nodes += on_test(node, xml_node.attributes)
+        end
+
+        return nodes
+      end
+
       def child_nodes(nodes)
         children = XML::NodeSet.new
 

spec/oga/xpath/evaluator/axes_spec.rb

@@ -77,4 +77,43 @@ describe Oga::XPath::Evaluator do
       end
     end
   end
+
+  context 'attribute axis' do
+    before do
+      document   = parse('<a foo="bar"><b x="y"></b></a>')
+      @evaluator = described_class.new(document)
+    end
+
+    context 'top-level attributes' do
+      before do
+        @set = @evaluator.evaluate('attribute::foo')
+      end
+
+      it_behaves_like :node_set, :length => 1
+
+      example 'return an Attribute instance' do
+        @set[0].is_a?(Oga::XML::Attribute).should == true
+      end
+
+      example 'return the correct attribute' do
+        @set[0].name.should == 'foo'
+      end
+    end
+
+    context 'nested attributes' do
+      before do
+        @set = @evaluator.evaluate('/a/attribute::x')
+      end
+
+      it_behaves_like :node_set, :length => 1
+
+      example 'return an Attribute instance' do
+        @set[0].is_a?(Oga::XML::Attribute).should == true
+      end
+
+      example 'return the correct attribute' do
+        @set[0].name.should == 'x'
+      end
+    end
+  end
 end