A simple CSS linter

linter.rb

# inspired by twitter's RECESS
# http://twitter.github.io/recess/
# usage: git diff | ruby ~/linter.rb
class Linter

  def process
    @result = {}

    STDIN.each_line do |line|
      @line = line[2..-1]

      filename = line.scan(/^\+\+\+ b(.+)$/)
      unless filename.empty? # it's a filename!

        @filename = filename.first.first

        if @filename =~ /(css|sass|scss|less)$/
          @result[@filename] = []
        else # ignore non-CSS files
          @filename = nil
        end

        next
      end
      
      next unless @filename

      if line =~ /^\+ / # it's a change
        known_lints.each { |lint| send(lint) }
      end
    end

    @result.each do |filename, errors|
      unless errors.empty?
        puts "--- ERRORS IN #{filename}:"
        errors.each do |error|
          puts error
        end
      end
    end
  end

  def known_lints
    methods.grep /detect_/
  end

  def detect_no_ids
    if @line =~ /#\w+[^\w]/
      @result[@filename] << "Don’t style IDs: #@line"
    end
  end

  def detect_no_js_prefix
    if @line =~ /\.js-/
      @result[@filename] << "Don’t style .js- prefixed classnames: #@line"
    end
  end

  def detect_no_overqualifying
    if @line =~ /(div|label|a|input|span)(#|\.)\w+[^\w]/
      @result[@filename] << "Don’t overqualify your selectors: #@line"
    end
  end

  def detect_no_underscores
    if @line =~ /_/
      @result[@filename] << "Don’t use underscores when naming classes: #@line"
    end
  end

  def detect_no_camelcase
    if @line =~ /[A-Z]{1}/
      @result[@filename] << "Don’t use camelCase: #@line"
    end
  end

  def detect_zero_units
    if @line =~ / (0px|0em|0rem|0%)/
      @result[@filename] << "Don’t add the unit if zero: #@line"
    end
  end
end

Linter.new.process