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diff --git a/railties/lib/rails/source_annotation_extractor.rb b/railties/lib/rails/source_annotation_extractor.rb
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+# Implements the logic behind the rake tasks for annotations like
+#
+#   rake notes
+#   rake notes:optimize
+#
+# and friends. See <tt>rake -T notes</tt> and <tt>railties/lib/tasks/annotations.rake</tt>.
+#
+# Annotation objects are triplets <tt>:line</tt>, <tt>:tag</tt>, <tt>:text</tt> that
+# represent the line where the annotation lives, its tag, and its text. Note
+# the filename is not stored.
+#
+# Annotations are looked for in comments and modulus whitespace they have to
+# start with the tag optionally followed by a colon. Everything up to the end
+# of the line (or closing ERb comment tag) is considered to be their text.
+class SourceAnnotationExtractor
+  class Annotation < Struct.new(:line, :tag, :text)
+
+    # Returns a representation of the annotation that looks like this:
+    #
+    #   [126] [TODO] This algorithm is simple and clearly correct, make it faster.
+    #
+    # If +options+ has a flag <tt>:tag</tt> the tag is shown as in the example above.
+    # Otherwise the string contains just line and text.
+    def to_s(options={})
+      s = "[%3d] " % line
+      s << "[#{tag}] " if options[:tag]
+      s << text
+    end
+  end
+
+  # Prints all annotations with tag +tag+ under the root directories +app+, +lib+,
+  # and +test+ (recursively). Only filenames with extension +.builder+, +.rb+,
+  # +.rxml+, +.rjs+, +.rhtml+, or +.erb+ are taken into account. The +options+
+  # hash is passed to each annotation's +to_s+.
+  #
+  # This class method is the single entry point for the rake tasks.
+  def self.enumerate(tag, options={})
+    extractor = new(tag)
+    extractor.display(extractor.find, options)
+  end
+
+  attr_reader :tag
+
+  def initialize(tag)
+    @tag = tag
+  end
+
+  # Returns a hash that maps filenames under +dirs+ (recursively) to arrays
+  # with their annotations. Only files with annotations are included, and only
+  # those with extension +.builder+, +.rb+, +.rxml+, +.rjs+, +.rhtml+, and +.erb+
+  # are taken into account.
+  def find(dirs=%w(app lib test))
+    dirs.inject({}) { |h, dir| h.update(find_in(dir)) }
+  end
+
+  # Returns a hash that maps filenames under +dir+ (recursively) to arrays
+  # with their annotations. Only files with annotations are included, and only
+  # those with extension +.builder+, +.rb+, +.rxml+, +.rjs+, +.rhtml+, and +.erb+
+  # are taken into account.
+  def find_in(dir)
+    results = {}
+
+    Dir.glob("#{dir}/*") do |item|
+      next if File.basename(item)[0] == ?.
+
+      if File.directory?(item)
+        results.update(find_in(item))
+      elsif item =~ /\.(builder|(r(?:b|xml|js)))$/
+        results.update(extract_annotations_from(item, /#\s*(#{tag}):?\s*(.*)$/))
+      elsif item =~ /\.(rhtml|erb)$/
+        results.update(extract_annotations_from(item, /<%\s*#\s*(#{tag}):?\s*(.*?)\s*%>/))
+      end
+    end
+
+    results
+  end
+
+  # If +file+ is the filename of a file that contains annotations this method returns
+  # a hash with a single entry that maps +file+ to an array of its annotations.
+  # Otherwise it returns an empty hash.
+  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
+
+  # Prints the mapping from filenames to annotations in +results+ ordered by filename.
+  # The +options+ hash is passed to each annotation's +to_s+.
+  def display(results, options={})
+    results.keys.sort.each do |file|
+      puts "#{file}:"
+      results[file].each do |note|
+        puts "  * #{note.to_s(options)}"
+      end
+      puts
+    end
+  end
+end
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