Support for the XPath "or" operator.

lib/oga/xpath/evaluator.rb

@@ -609,6 +609,23 @@ module Oga
         return on_call_boolean(context, left) && on_call_boolean(context, right)
       end
 
+      ##
+      # Processes the `or` operator.
+      #
+      # This operator returns `true` if one of the expressions evaluates to
+      # true, otherwise false is returned. If the first expression evaluates to
+      # `true` the second expression is ignored.
+      #
+      # @param [Oga::XPath::Node] ast_node
+      # @param [Oga::XML::NodeSet] context
+      # @return [TrueClass|FalseClass]
+      #
+      def on_or(ast_node, context)
+        left, right = *ast_node
+
+        return on_call_boolean(context, left) || on_call_boolean(context, right)
+      end
+
       ##
       # Delegates function calls to specific handlers.
       #

spec/oga/xpath/evaluator/operators/or_spec.rb

@@ -0,0 +1,40 @@
+require 'spec_helper'
+
+describe Oga::XPath::Evaluator do
+  context 'or operator' do
+    before do
+      @document  = parse('<root><a>1</a><b>1</b></root>')
+      @evaluator = described_class.new(@document)
+    end
+
+    example 'return true if both boolean literals are true' do
+      @evaluator.evaluate('true() or true()').should == true
+    end
+
+    example 'return true if one of the boolean literals is false' do
+      @evaluator.evaluate('true() or false()').should == true
+    end
+
+    example 'return true if the left node set is not empty' do
+      @evaluator.evaluate('root/a or root/x').should == true
+    end
+
+    example 'return true if the right node set is not empty' do
+      @evaluator.evaluate('root/x or root/b').should == true
+    end
+
+    example 'return true if both node sets are not empty' do
+      @evaluator.evaluate('root/a or root/b').should == true
+    end
+
+    example 'return false if both node sets are empty' do
+      @evaluator.evaluate('root/x or root/y').should == false
+    end
+
+    example 'skip the right expression if the left one evaluates to false' do
+      @evaluator.should_not receive(:on_call_false)
+
+      @evaluator.evaluate('true() or false()').should == true
+    end
+  end
+end