class SourceAnnotationExtractor

def extract_annotations_from(file, pattern)

Otherwise it returns an empty hash.
a hash with a single entry that maps +file+ to an array of its annotations.
If +file+ is the filename of a file that contains annotations this method returns 
def extract_annotations_from(file, pattern)
  lineno = 0
  result = File.readlines(file).inject([]) do |list, line|
    lineno += 1
    next list unless line =~ pattern
    list << Annotation.new(lineno, $1, $2)
  end
  result.empty? ? {} : { file => result }
end