Simple static analyser for one-letter variable names.

analyzer.rb

require 'parser'
require 'parser/current'

module OneLetterVariableDetector
  class NodeAnalyzer < Struct.new(:node, :path)
    def analyze
      return unless node && node.respond_to?(:type)

      if node.type == :lvasgn || node.type == :lvar
        if lvar_name.size == 1
          puts "One letter local variable \"#{lvar_name}\" in #{path}:#{node.source_map.line}"
        end
      end

      if node.type == :ivasgn || node.type == :ivar
        if ivar_name.size == 1
          puts "One letter instance variable \"@#{ivar_name}\" in #{path}:#{node.source_map.line}"
        end
      end
    end

    private
    def lvar_name
      node.to_a.first.to_s.gsub(":", "")
    end

    def ivar_name
      node.to_a.first.to_s.gsub("@", "")
    end
  end

  class CodeAnalyzer < Struct.new(:path)
    def analyze
      Parser::CurrentRuby.parse(code).to_a.each do |lexem|
        scan_node(lexem)
      end
    end

    private
    def scan_node(node)
      node_analyzer = NodeAnalyzer.new(node, path)
      node_analyzer.analyze

      if node.respond_to?(:to_a) && node.to_a.respond_to?(:each)
        node.to_a.each do |subnode|
          scan_node(subnode)
        end
      end
    end

    def code
      @code ||= File.read(path)
    end
  end

  class FileScanner
    def scan(path)
      if File.directory?(path)
        scan_dir(path)
      else
        scan_file(path)
      end
    end

    private
    def scan_dir(path)
      Dir["#{path}/**/*.rb"].each do |file|
        scan_file(file)
      end
    end

    def scan_file(path)
      begin
        analyzer = CodeAnalyzer.new(path)
        analyzer.analyze
      rescue Exception => e
        # comment if you want to skip invalid files
        raise e
      end
    end
  end
end

scanner = OneLetterVariableDetector::FileScanner.new
scanner.scan(PATH_TO_FILE_OR_DIR)