Parsing support for :nth-last-child.

lib/oga/css/parser.y

@@ -379,26 +379,32 @@ end
   # @return [AST::Node]
   #
   def on_pseudo_class_nth_child(arg)
-    # literal 2, 4, etc
+    return generate_nth_child('preceding-sibling', arg)
+  end
+
+  ##
+  # Generates the AST for the `nth-last-child` pseudo class.
+  #
+  # @param [AST::Node] arg
+  # @return [AST::Node]
+  #
+  def on_pseudo_class_nth_last_child(arg)
+    return generate_nth_child('following-sibling', arg)
+  end
+
+  ##
+  # @param [String] count_axis
+  # @param [AST::Node] arg
+  # @return [AST::Node]
+  #
+  def generate_nth_child(count_axis, arg)
+    count_call = s(:call, 'count', s(:axis, count_axis, s(:test, nil, '*')))
+
+   # literal 2, 4, etc
     if arg.type == :int
-      node = s(
-        :eq,
-        s(
-          :call,
-          'count',
-          s(:axis, 'preceding-sibling', s(:test, nil, '*'))
-        ),
-        s(:int, arg.children[0] - 1)
-      )
+      node = s(:eq, count_call, s(:int, arg.children[0] - 1))
     else
       step, offset = *arg
-
-      count_call = s(
-        :call,
-        'count',
-        s(:axis, 'preceding-sibling', s(:test, nil, '*'))
-      )
-
       before_count = s(:add, count_call, s(:int, 1))
 
       if step and step.children[0] >= 0

spec/oga/css/parser/pseudo_classes/nth_last_child_spec.rb

@@ -0,0 +1,95 @@
+require 'spec_helper'
+
+describe Oga::CSS::Parser do
+  context ':nth-last-child pseudo class' do
+    example 'parse the x:nth-last-child(1) pseudo class' do
+      parse_css('x:nth-last-child(1)').should == parse_xpath(
+        'descendant-or-self::x[count(following-sibling::*) = 0]'
+      )
+    end
+
+    example 'parse the :nth-last-child(1) pseudo class' do
+      parse_css(':nth-last-child(1)').should == parse_xpath(
+        'descendant-or-self::*[count(following-sibling::*) = 0]'
+      )
+    end
+
+    example 'parse the :nth-last-child(2) pseudo class' do
+      parse_css(':nth-last-child(2)').should == parse_xpath(
+        'descendant-or-self::*[count(following-sibling::*) = 1]'
+      )
+    end
+
+    example 'parse the x:nth-last-child(even) pseudo class' do
+      parse_css('x:nth-last-child(even)').should == parse_xpath(
+        'descendant-or-self::x[((count(following-sibling::*) + 1) mod 2) = 0]'
+      )
+    end
+
+    example 'parse the x:nth-last-child(odd) pseudo class' do
+      parse_css('x:nth-last-child(odd)').should == parse_xpath(
+        'descendant-or-self::x[(count(following-sibling::*) + 1) >= 1 ' \
+          'and (((count(following-sibling::*) + 1) - 1) mod 2) = 0]'
+      )
+    end
+
+    example 'parse the x:nth-last-child(n) pseudo class' do
+      parse_css('x:nth-last-child(n)').should == parse_xpath(
+        'descendant-or-self::x[((count(following-sibling::*) + 1) mod 1) = 0]'
+      )
+    end
+
+    example 'parse the x:nth-last-child(-n) pseudo class' do
+      parse_css('x:nth-last-child(-n)').should == parse_xpath(
+        'descendant-or-self::x[((count(following-sibling::*) + 1) mod 1) = 0]'
+      )
+    end
+
+    example 'parse the x:nth-last-child(-n+6) pseudo class' do
+      parse_css('x:nth-last-child(-n+6)').should == parse_xpath(
+        'descendant-or-self::x[((count(following-sibling::*) + 1) <= 6) ' \
+          'and (((count(following-sibling::*) + 1) - 6) mod 1) = 0]'
+      )
+    end
+
+    example 'parse the x:nth-last-child(-n-6) pseudo class' do
+      parse_css('x:nth-last-child(-n-6)').should == parse_xpath(
+        'descendant-or-self::x[count(following-sibling::*) = -1]'
+      )
+    end
+
+    example 'parse the x:nth-last-child(2n) pseudo class' do
+      parse_css('x:nth-last-child(2n)').should == parse_css(
+        'x:nth-last-child(even)'
+      )
+    end
+
+    example 'parse the x:nth-last-child(2n+1) pseudo class' do
+      parse_css('x:nth-last-child(2n+1)').should == parse_xpath(
+        'descendant-or-self::x[(count(following-sibling::*) + 1) >= 1 ' \
+          'and (((count(following-sibling::*) + 1) - 1) mod 2) = 0]'
+      )
+    end
+
+    example 'parse the x:nth-last-child(2n-6) pseudo class' do
+      parse_css('x:nth-last-child(2n-6)').should == parse_xpath(
+        'descendant-or-self::x[(count(following-sibling::*) + 1) >= 2 ' \
+          'and (((count(following-sibling::*) + 1) - 2) mod 2) = 0]'
+      )
+    end
+
+    example 'parse the x:nth-last-child(-2n-6) pseudo class' do
+      parse_css('x:nth-last-child(-2n-6)').should == parse_xpath(
+        'descendant-or-self::x[((count(following-sibling::*) + 1) <= -2) ' \
+          'and (((count(following-sibling::*) + 1) - -2) mod 2) = 0]'
+      )
+    end
+
+    example 'parse the x:nth-last-child(-2n+6) pseudo class' do
+      parse_css('x:nth-last-child(-2n+6)').should == parse_xpath(
+        'descendant-or-self::x[((count(following-sibling::*) + 1) <= 6) ' \
+          'and (((count(following-sibling::*) + 1) - 6) mod 2) = 0]'
+      )
+    end
+  end
+end