Support for the XPath count() function.

lib/oga/xpath/evaluator.rb

@@ -601,7 +601,7 @@ module Oga
       # @return [Oga::XML::NodeSet]
       #
       def on_call(ast_node, context)
-        name, args = *ast_node
+        name, *args = *ast_node
 
         handler = name.gsub('-', '_')
 
@@ -633,6 +633,36 @@ module Oga
         return index.to_f
       end
 
+      ##
+      # Processes the `count()` function call. This function counts the amount
+      # of nodes in `expression` and returns the result as a float.
+      #
+      # @param [Oga::XML::NodeSet] context
+      # @param [Oga::XPath::Node] expression
+      # @return [Float]
+      #
+      def on_call_count(context, expression)
+        retval = process(expression, context)
+
+        unless retval.is_a?(XML::NodeSet)
+          raise TypeError, 'count() can only operate on NodeSet instances'
+        end
+
+        return retval.length.to_f
+      end
+
+      ##
+      # Processes an `(int)` node. This method simply returns the value as a
+      # Float.
+      #
+      # @param [Oga::XPath::Node] ast_node
+      # @param [Oga::XML::NodeSet] context
+      # @return [Float]
+      #
+      def on_int(ast_node, context)
+        return ast_node.children[0].to_f
+      end
+
       ##
       # Returns a node set containing all the child nodes of the given set of
       # nodes.

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

@@ -0,0 +1,38 @@
+require 'spec_helper'
+
+describe Oga::XPath::Evaluator do
+  context 'count() function' do
+    before do
+      @document  = parse('<root><a><b></b></a><a></a></root>')
+      @evaluator = described_class.new(@document)
+    end
+
+    example 'return the amount of nodes as a Float' do
+      @evaluator.evaluate('count(root)').is_a?(Float).should == true
+    end
+
+    example 'count the amount of <root> nodes' do
+      @evaluator.evaluate('count(root)').should == 1
+    end
+
+    example 'count the amount of <a> nodes' do
+      @evaluator.evaluate('count(root/a)').should == 2
+    end
+
+    example 'count the amount of <b> nodes' do
+      @evaluator.evaluate('count(root/a/b)').should == 1
+    end
+
+    example 'raise ArgumentError if no arguments are given' do
+      block = lambda { @evaluator.evaluate('count()') }
+
+      block.should raise_error(ArgumentError)
+    end
+
+    example 'raise TypeError if the argument is not a NodeSet' do
+      block = lambda { @evaluator.evaluate('count(1)') }
+
+      block.should raise_error(TypeError)
+    end
+  end
+end

spec/oga/xpath/evaluator/types/int_spec.rb

@@ -0,0 +1,19 @@
+require 'spec_helper'
+
+describe Oga::XPath::Evaluator do
+  context 'integer types' do
+    before do
+      document  = parse('<a></a>')
+      evaluator = described_class.new(document)
+      @number   = evaluator.evaluate('1')
+    end
+
+    example 'return literal integers' do
+      @number.should == 1
+    end
+
+    example 'return integers as floats' do
+      @number.is_a?(Float).should == true
+    end
+  end
+end