boot.rb

# add this to the bottom of config/boot.rb, before Rails.boot!

class Rails::Boot
  def run
    load_initializer
    extend_environment
    Rails::Initializer.run(:set_load_path)
  end

  def extend_environment
    Rails::Initializer.class_eval do
      old_load = instance_method(:load_environment)
      define_method(:load_environment) do
        Bundler.require :default, Rails.env
        old_load.bind(self).call
      end
    end
  end
end


# and add this to the very end, after Rails.boot! to load all Gem Plugins

class Rails::Plugin::GemLocator
  # find the original that we patch in rails/lib/rails/plugin/locator.rb:80
  def plugins
    specs     = Bundler.load.specs_for(:default, Rails.env)
    specs    += Gem.loaded_specs.values.select do |spec|
      spec.loaded_from && # prune stubs
        # File.exist?(File.join(spec.full_gem_path, "rails", "init.rb"))
        (File.exist?(File.join(spec.full_gem_path, "rails", "init.rb")) || File.exist?(File.join(spec.full_gem_path, "init.rb")))
    end
    specs.compact!

    require "rubygems/dependency_list"

    deps = Gem::DependencyList.new
    deps.add(*specs) unless specs.empty?

    deps.dependency_order.collect do |spec|
      Rails::GemPlugin.new(spec, nil)
    end
  end
end

Gemfile

# include at least one source and the rails gem
source :gemcutter
gem 'rails', '~> 2.3.5', :require => nil

group :development do
  # bundler requires these gems in development
  gem 'rails-footnotes'
end

group :test do
  # bundler requires these gems while running tests
  gem 'rspec'
end

preinitializer.rb

# this code goes in config/preinitializer.rb, which you should create if it doesn't exist

begin
  # Require the preresolved locked set of gems.
  require File.expand_path('../../.bundle/environment', __FILE__)
rescue LoadError
  # Fallback on doing the resolve at runtime.
  require "rubygems"
  require "bundler"
  Bundler.setup
end

I get an error trying this with rails 2.3.12, bundler 1.0.10, and devise 1.0.11

undefined method specs_for' for #Bundler::Runtime:0x10105d2f8 (NoMethodError)`

Any suggestions?

My issue was occurring because I was attempting to use devise in a custom rails engine in my project.

I updated the code above so that errors weren't thrown and but ultimately decided to remove the rails engine and move associated code back into the main project.

class Rails::Plugin::GemLocator
  # find the original that we patch in rails/lib/rails/plugin/locator.rb:80
  def plugins
    specs     = Bundler.definition.specs_for([]).to_a
    gem_specs = Gem.loaded_specs.values.select do |spec|
      spec.loaded_from && # prune stubs
        # File.exist?(File.join(spec.full_gem_path, "rails", "init.rb"))
        (File.exist?(File.join(spec.full_gem_path, "rails", "init.rb")) || File.exist?(File.join(spec.full_gem_path, "init.rb")))
    end
    specs += gem_specs

    require "rubygems/dependency_list"

    deps = Gem::DependencyList.new
    deps.add(*specs) unless specs.empty?

    deps.dependency_order.collect do |spec|
      Rails::GemPlugin.new(spec, nil)
    end
  end
end

Glad that you found the solution yourself. The code above is for a quite ancient bundler version (0.9.5 I belive) so I'm not too suprised that it does not work with the current version anymore.