Support for parsing the :root pseudo class.

lib/oga/css/parser.y

@@ -237,10 +237,10 @@ rule
 
   pseudo_class
     # :root
-    : pseudo_name { s(:pseudo, nil, val[0]) }
+    : pseudo_name { on_pseudo_class(val[0]) }
 
     # :nth-child(2)
-    | pseudo_name pseudo_args { s(:pseudo, nil, val[0], val[1]) }
+    | pseudo_name pseudo_args { on_pseudo_class(val[0], val[1]) }
     ;
 
   pseudo_name
@@ -253,19 +253,34 @@ rule
 
   pseudo_arg
     : integer
-    #| odd
+    | odd
-    #| even
+    | even
-    #| nth
+    | nth
     | selector
     ;
 
+  nth
+    : T_NTH                 { s(:nth) }
+    | T_MINUS T_NTH         { s(:nth) }
+    | integer T_NTH         { s(:nth, val[0]) }
+    | integer T_NTH integer { s(:nth, val[0], val[2]) }
+    ;
+
+  odd
+    : T_ODD { s(:nth, s(:int, 2), s(:int, 1)) }
+    ;
+
+  even
+    : T_EVEN { s(:nth, s(:int, 2)) }
+    ;
+
   string
     : T_STRING { s(:string, val[0]) }
     ;
 
   integer
-   : T_INT { s(:int, val[0].to_i) }
+    : T_INT { s(:int, val[0].to_i) }
-   ;
+    ;
 end
 
 ---- inner
@@ -313,4 +328,23 @@ end
     return ast
   end
 
+  ##
+  # @param [String] name
+  # @param [AST::Node] arg
+  # @return [AST::Node]
+  #
+  def on_pseudo_class(name, arg = nil)
+    handler = "on_pseudo_class_#{name.gsub('-', '_')}"
+
+    return arg ? send(handler, arg) : send(handler)
+  end
+
+  ##
+  # Generates the AST for the `root` pseudo class.
+  #
+  # @return [AST::Node]
+  #
+  def on_pseudo_class_root
+    return s(:call, 'not', s(:axis, 'parent', s(:test, nil, '*')))
+  end
 # vim: set ft=racc:

spec/oga/css/parser/pseudo_classes_spec.rb

@@ -3,11 +3,15 @@ require 'spec_helper'
 describe Oga::CSS::Parser do
   context 'pseudo classes' do
     example 'parse the x:root pseudo class' do
-      parse_css('x:root').should == s(:pseudo, s(:test, nil, 'x'), 'root')
+      parse_css('x:root').should == parse_xpath(
+        'descendant-or-self::x[not(parent::*)]'
+      )
     end
 
     example 'parse the :root pseudo class' do
-      parse_css(':root').should == s(:pseudo, nil, 'root')
+      parse_css(':root').should == parse_xpath(
+        'descendant-or-self::*[not(parent::*)]'
+      )
     end
 
     example 'parse the x:nth-child(1) pseudo class' do