Support for the XPath concat() function.

lib/oga/xpath/evaluator.rb

@@ -786,8 +786,29 @@ module Oga
       end
 
       ##
-      # Processes an `(int)` node. This method simply returns the value as a
-      # Float.
+      # Processes the `concat()` function call.
+      #
+      # This function call converts its arguments to strings and concatenates
+      # them. In case of node sets the text of the set is used.
+      #
+      # @param [Oga::XML::NodeSet] context
+      # @param [Oga::XPath::Node] first
+      # @param [Oga::XPath::Node] second
+      # @param [Array<Oga::XPath::Node>] rest
+      #
+      def on_call_concat(context, first, second, *rest)
+        args   = [first, second] + rest
+        retval = ''
+
+        args.each do |arg|
+          retval << on_call_string(context, arg)
+        end
+
+        return retval
+      end
+
+      ##
+      # Processes an `(int)` node.
       #
       # @param [Oga::XPath::Node] ast_node
       # @param [Oga::XML::NodeSet] context

spec/oga/xpath/evaluator/calls/concat_spec.rb

@@ -0,0 +1,30 @@
+require 'spec_helper'
+
+describe Oga::XPath::Evaluator do
+  context 'concat() function' do
+    before do
+      @document  = parse('<root><a>foo</a><b>bar</b></root>')
+      @evaluator = described_class.new(@document)
+    end
+
+    example 'concatenate two strings' do
+      @evaluator.evaluate('concat("foo", "bar")').should == 'foobar'
+    end
+
+    example 'concatenate two integers' do
+      @evaluator.evaluate('concat(10, 20)').should == '1020'
+    end
+
+    example 'concatenate two floats' do
+      @evaluator.evaluate('concat(10.5, 20.5)').should == '10.520.5'
+    end
+
+    example 'concatenate two node sets' do
+      @evaluator.evaluate('concat(root/a, root/b)').should == 'foobar'
+    end
+
+    example 'concatenate a node set and a string' do
+      @evaluator.evaluate('concat(root/a, "baz")').should == 'foobaz'
+    end
+  end
+end