Simple script for scanning a file for possible model references, then filtering out those which no longer exist in app/models.

dead_models.rb

#!/usr/bin/env ruby

require 'rubygems'
require 'machete'

rails_root = ARGV[0]
file = ARGV[1]

if rails_root.nil? || !File.exists?(rails_root) || file.nil? || !File.exists?(file)
  warn "Usage: dead_models <rails root> <source file>"
  exit(1)
end

source = File.read(file)

def model_pattern
  patterns = [
    'SendWithArguments<name ^= :find, receiver = ConstantAccess>',
    'SendWithArguments<name ^= :destroy, receiver = ConstantAccess>',
    'SendWithArguments<name ^= :create, receiver = ConstantAccess>',
    'SendWithArguments<name ^= :update, receiver = ConstantAccess>',
    'SendWithArguments<name ^= :save, receiver = ConstantAccess>',
    'SendWithArguments<name ^= :reload, receiver = ConstantAccess>',
  ].join("|")
end

# Stolen from rails sources
def underscore(camel_cased_word)
  word = camel_cased_word.to_s.dup
  word.gsub!(/::/, '/')
  word.gsub!(/([A-Z]+)([A-Z][a-z])/,'\1_\2')
  word.gsub!(/([a-z\d])([A-Z])/,'\1_\2')
  word.tr!("-", "_")
  word.downcase!
  word
end

nodes = Machete.find(source.to_ast, model_pattern)

calls = nodes.map { |node| [file, node.receiver.line, node.receiver.name.to_s, "#{underscore(node.receiver.name.to_s)}.rb"] }

calls.each do |call|
  ref_file, ref_line, model, model_file = *call
  path = File.join(rails_root, "app", "models", model_file)
  puts "Model #{model} referenced from #{ref_file}:#{ref_line} is probably dead." unless File.exists?(path)
end