gistfile1.rb

#!/usr/bin/env ruby

require 'set'

cmd = "git diff --cached --name-only"
matches = { /\.sass/ => /\.css/, /\.haml/ => /\.html/ }

files = IO.popen(cmd).readlines.map(&:chomp)
fail = false

matches.each_key do |key|
  $; = '.'
  changed_src = files.grep(key).map(&:split).map(&:shift).to_set
  changed_dest = files.grep(matches[key]).map(&:split).map(&:shift).to_set
  diff = changed_src - changed_dest
  if diff.size > 0 then
    puts "DEGENERACY!"
    diff.each { |d| puts d }
    fail = true
  end
end

exit (fail ? 1 : 0)