Ruby script that rewrite source code collapsing nested modules definitions

ruby_collapse_nested_module_defs.rb

src = STDIN.read

# iterate on "1st level" module definitions
src.dup.scan(/^module [^;]+$.+?^end/m) do |mod|
  # get the nested modules' definitions
  mdefs = mod.scan(/^ *module [^\n]+$(?=\n +module)/m).map(&:to_s)
  # stop if there is no nested module definition
  next if mdefs.empty?
  ndefs = mdefs.size
  # get the last definition that's not extracted because of the look ahead
  mdefs << mod.match(/\A(?:^ *module [^\n]+\n)+(^ +module [^\n]+)/m)[1].to_s
  # collapse nested modules' definitions
  mdefs = mdefs.join("\n")
  newmod = mod.gsub(/\A#{mdefs}/m, mdefs.gsub(/\n^ +module /m, '::'))
  # removes useless closure of modules' blocks
  newmod.gsub!(/(^ +end\n){#{ndefs}}end\Z/m, 'end')
  # re-indent the code contained in the module
  newmod.gsub!(/^ {#{ndefs * 2}}/, '')
  # replace the module's definition in the source code
  src.sub!(mod, newmod)
end

puts src