Implements border width parsing

Per specs on http://www.w3.org/TR/CSS21/box.html#value-def-border-width
and http://www.w3.org/TR/CSS/

Author: zmoazeni

lib/csscss.rb

@@ -21,3 +21,5 @@
 require "csscss/parser/list_style"
 require "csscss/parser/margin"
 require "csscss/parser/padding"
+require "csscss/parser/border_width"
+

lib/csscss/parser/border_width.rb

@@ -0,0 +1,37 @@
+module Csscss
+  module Parser
+    module BorderWidth
+      extend Parser::Base
+
+      class Parser < Parslet::Parser
+        include Color
+
+        rule(:border_width_side) {
+          symbol_list(%w(thin medium thick inherit)) | length
+        }
+
+        rule(:border_width) {
+          (
+           symbol("inherit") >> eof | (
+             border_width_side.maybe.as(:top)    >>
+             border_width_side.maybe.as(:right)  >>
+             border_width_side.maybe.as(:bottom) >>
+             border_width_side.maybe.as(:left)
+           )
+          ).as(:border_width)
+        }
+
+        root(:border_width)
+      end
+
+      class Transformer < Parslet::Transform
+        @property = :border_width
+        extend MultiWidthTransformer
+
+        def self.side_declaration(side, value)
+          Declaration.from_parser("border-#{side}-width", value)
+        end
+      end
+    end
+  end
+end

test/csscss/parser/border_width_test.rb

@@ -0,0 +1,30 @@
+require "test_helper"
+
+module Csscss::Parser
+  module BorderWidth
+    describe BorderWidth do
+      include CommonParserTests
+
+      before do
+        @parser = Parser.new
+        @trans = Transformer.new
+      end
+
+      it "converts shorthand rules to longhand" do
+        trans("thin thick inherit 10em").must_equal([
+          dec("border-top-width", "thin"),
+          dec("border-right-width", "thick"),
+          dec("border-bottom-width", "inherit"),
+          dec("border-left-width", "10em")
+        ])
+
+        trans("thin thick").must_equal([
+          dec("border-top-width", "thin"),
+          dec("border-right-width", "thick"),
+          dec("border-bottom-width", "thin"),
+          dec("border-left-width", "thick")
+        ])
+      end
+    end
+  end
+end