Support for the XPath child axis.

lib/oga/xpath/evaluator.rb

@@ -150,7 +150,7 @@ module Oga
           while has_parent?(xml_node)
             xml_node = xml_node.parent
 
-            if node_matches?(xml_node, node)
+            if can_match_node?(xml_node) and node_matches?(xml_node, node)
               nodes << xml_node
               break
             end
@@ -206,6 +206,17 @@ module Oga
         return nodes
       end
 
+      ##
+      # Evaluates the `child` axis. This simply delegates work to {#on_test}.
+      #
+      # @param [Oga::XPath::Node] node
+      # @param [Oga::XML::NodeSet] context
+      # @return [Oga::XML::NodeSet]
+      #
+      def on_axis_child(node, context)
+        return on_test(node, context)
+      end
+
       ##
       # Returns a node set containing all the child nodes of the given set of
       # nodes.

spec/oga/xpath/evaluator/axes_spec.rb

@@ -34,6 +34,14 @@ describe Oga::XPath::Evaluator do
         @set[0].name.should == 'a'
       end
     end
+
+    context 'missing ancestors' do
+      before do
+        @set = @evaluator.evaluate('ancestor::foobar')
+      end
+
+      it_behaves_like :empty_node_set
+    end
   end
 
   context 'ancestor-or-self axis' do
@@ -115,5 +123,51 @@ describe Oga::XPath::Evaluator do
         @set[0].name.should == 'x'
       end
     end
+
+    context 'missing attributes' do
+      before do
+        @set = @evaluator.evaluate('attribute::bar')
+      end
+
+      it_behaves_like :empty_node_set
+    end
+  end
+
+  context 'child axis' do
+    before do
+      @evaluator = described_class.new(@document)
+    end
+
+    context 'direct children' do
+      before do
+        @set = @evaluator.evaluate('child::a')
+      end
+
+      it_behaves_like :node_set, :length => 1
+
+      example 'return the <a> node' do
+        @set[0].name.should == 'a'
+      end
+    end
+
+    context 'nested children' do
+      before do
+        @set = @evaluator.evaluate('child::a/child::b')
+      end
+
+      it_behaves_like :node_set, :length => 1
+
+      example 'return the <b> node' do
+        @set[0].name.should == 'b'
+      end
+    end
+
+    context 'invalid children' do
+      before do
+        @set = @evaluator.evaluate('child::foobar')
+      end
+
+      it_behaves_like :empty_node_set
+    end
   end
 end

spec/support/shared_examples.rb

@@ -7,3 +7,13 @@ shared_examples :node_set do |options|
     @set.length.should == options[:length]
   end
 end
+
+shared_examples :empty_node_set do
+  example 'return a NodeSet instance' do
+    @set.is_a?(Oga::XML::NodeSet).should == true
+  end
+
+  example 'return the right amount of rows' do
+    @set.empty?.should == true
+  end
+end