- Got it parsing a single plugin and emitting the config description.

doc/docgen.rb

@@ -0,0 +1,88 @@
+require "rubygems"
+
+class LogStashConfigDocGenerator
+  COMMENT_RE = /^ *#(.*)/
+
+  def initialize
+    @rules = {
+      COMMENT_RE => lambda { |m| add_comment(m[1]) },
+      /^ *config .*/ => lambda { |m| add_config(m[0]) },
+      /^ *config_name .*/ => lambda { |m| set_config_name(m[0]) },
+      /^ *(class|def|module) / => lambda { |m| clear_comments },
+    }
+  end
+
+  def parse(string)
+    buffer = ""
+    @comments = []
+    @settings = {}
+    string.split("\n").each do |line|
+      # Join long lines
+      if line =~ COMMENT_RE
+        # nothing
+      else
+        # Join extended lines
+        if line =~ /(, *$)|(\\$)/
+          buffer += line.gsub(/\\$/, "")
+          next
+        end
+      end
+
+      line = buffer + line
+      buffer = ""
+
+      @rules.each do |re, action|
+        m = re.match(line)
+        if m
+          action.call(m)
+        end
+      end # RULES.each
+    end # string.split("\n").each
+  end
+
+  def add_comment(comment)
+    @comments << comment
+  end
+
+  def add_config(code)
+    # call the code, which calls 'config' in this class.
+    # This will let us align comments with config options.
+    name, opts = eval(code)
+    @settings[name] = opts.merge(:description => @comments.join("\n"))
+    clear_comments
+  end # def add_config
+
+  def set_config_name(code)
+    name = eval(code)
+    @name = name
+  end # def set_config_name
+
+  # pretend to be the config DSL and just get the name
+  def config(name, opts={})
+    return name, opts
+  end # def config
+
+  # pretend to be the config dsl's 'config_name' method
+  def config_name(name)
+    return name
+  end # def config_name
+
+  def clear_comments
+    @comments.clear
+  end # def clear_comments
+
+  def generate(file)
+    string = File.new(file).read
+    parse(string)
+    require file
+    puts LogStash::Config::Registry.registry[@name]
+    @settings.each do |name, description|
+      p name => description
+    end
+  end
+end
+
+if __FILE__ == $0
+  gen = LogStashConfigDocGenerator.new
+  gen.generate(ARGV[0])
+end