Support for the XPath "=" operator.

lib/oga/xpath/evaluator.rb

@@ -706,6 +706,42 @@ module Oga
         return on_call_number(context, left) - on_call_number(context, right)
       end
 
+      ##
+      # Processes the `=` operator.
+      #
+      # This operator evaluates the expression on the left and right and returns
+      # `true` if they are equal. This operator can be used to compare strings,
+      # numbers and node sets. When using node sets the text of the set is
+      # compared instead of the nodes themselves. That is, nodes with different
+      # names but the same text are considered to be equal.
+      #
+      # @param [Oga::XPath::Node] ast_node
+      # @param [Oga::XML::NodeSet] context
+      # @return [TrueClass|FalseClass]
+      #
+      def on_eq(ast_node, context)
+        left  = process(ast_node.children[0], context)
+        right = process(ast_node.children[1], context)
+
+        if left.is_a?(XML::NodeSet)
+          left = left.text
+        end
+
+        if right.is_a?(XML::NodeSet)
+          right = right.text
+        end
+
+        if left.is_a?(Numeric) and !right.is_a?(Numeric)
+          right = to_float(right)
+        end
+
+        if left.is_a?(String) and !right.is_a?(String)
+          right = to_string(right)
+        end
+
+        return left == right
+      end
+
       ##
       # Delegates function calls to specific handlers.
       #
@@ -903,14 +939,7 @@ module Oga
         if convert.respond_to?(:text)
           return convert.text
         else
-          # If we have a number that has a zero decimal (e.g. 10.0) we want to
-          # get rid of that decimal. For this we'll first convert the number to
-          # an integer.
-          if convert.is_a?(Float) and convert.modulo(1).zero?
-            convert = convert.to_i
-          end
-
-          return convert.to_s
+          return to_string(convert)
         end
       end
 
@@ -950,7 +979,7 @@ module Oga
           convert = current_node.text
         end
 
-        return Float(convert) rescue Float::NAN
+        return to_float(convert)
       end
 
       ##
@@ -1528,6 +1557,35 @@ module Oga
         return ast_node.respond_to?(:parent) && !!ast_node.parent
       end
 
+      ##
+      # Converts the given value to a float. If the value can't be converted to
+      # a float NaN is returned instead.
+      #
+      # @param [Mixed] value
+      # @return [Float]
+      #
+      def to_float(value)
+        return Float(value) rescue Float::NAN
+      end
+
+      ##
+      # Converts the given value to a string according to the XPath string
+      # conversion rules.
+      #
+      # @param [Mixed] value
+      # @return [String]
+      #
+      def to_string(value)
+        # If we have a number that has a zero decimal (e.g. 10.0) we want to
+        # get rid of that decimal. For this we'll first convert the number to
+        # an integer.
+        if value.is_a?(Float) and value.modulo(1).zero?
+          value = value.to_i
+        end
+
+        return value.to_s
+      end
+
       ##
       # Stores the node in the node stack, yields the block and removes the node
       # from the stack.

spec/oga/xpath/evaluator/general_spec.rb

@@ -154,4 +154,24 @@ describe Oga::XPath::Evaluator do
       @evaluator.has_parent?(@parent).should == false
     end
   end
+
+  context '#to_string' do
+    example 'convert a float to a string' do
+      @evaluator.to_string(10.5).should == '10.5'
+    end
+
+    example 'convert a float without decimals to a string' do
+      @evaluator.to_string(10.0).should == '10'
+    end
+  end
+
+  context '#to_float' do
+    example 'convert a string to a float' do
+      @evaluator.to_float('10').should == 10.0
+    end
+
+    example "return NaN for values that can't be converted to floats" do
+      @evaluator.to_float('a').should be_nan
+    end
+  end
 end

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

@@ -0,0 +1,50 @@
+require 'spec_helper'
+
+describe Oga::XPath::Evaluator do
+  context 'equal operator' do
+    before do
+      @document  = parse('<root><a>10</a><b>10</b></root>')
+      @evaluator = described_class.new(@document)
+    end
+
+    example 'return true if two numbers are equal' do
+      @evaluator.evaluate('10 = 10').should == true
+    end
+
+    example 'return false if two numbers are not equal' do
+      @evaluator.evaluate('10 = 15').should == false
+    end
+
+    example 'return true if a number and a string are equal' do
+      @evaluator.evaluate('10 = "10"').should == true
+    end
+
+    example 'return true if two strings are equal' do
+      @evaluator.evaluate('"10" = "10"').should == true
+    end
+
+    example 'return true if a string and a number are equal' do
+      @evaluator.evaluate('"10" = 10').should == true
+    end
+
+    example 'return false if two strings are not equal' do
+      @evaluator.evaluate('"a" = "b"').should == false
+    end
+
+    example 'return true if two node sets are equal' do
+      @evaluator.evaluate('root/a = root/b').should == true
+    end
+
+    example 'return false if two node sets are not equal' do
+      @evaluator.evaluate('root/a = root/c').should == false
+    end
+
+    example 'return true if a node set and a number are equal' do
+      @evaluator.evaluate('root/a = 10').should == true
+    end
+
+    example 'return true if a node set and a string are equal' do
+      @evaluator.evaluate('root/a = "10"').should == true
+    end
+  end
+end