1 files changed, 64 insertions, 0 deletions
diff --git a/railties/lib/rails/app_loader.rb b/railties/lib/rails/app_loader.rb
new file mode 100644
index 0000000000..a9fe21824e
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+++ b/railties/lib/rails/app_loader.rb
@@ -0,0 +1,64 @@
+require 'pathname'
+require 'rails/version'
+
+module Rails
+  module AppLoader # :nodoc:
+    extend self
+
+    RUBY = Gem.ruby
+    EXECUTABLES = ['bin/rails', 'script/rails']
+    BUNDLER_WARNING = <<EOS
+Looks like your app's ./bin/rails is a stub that was generated by Bundler.
+
+In Rails #{Rails::VERSION::MAJOR}, your app's bin/ directory contains executables that are versioned
+like any other source code, rather than stubs that are generated on demand.
+
+Here's how to upgrade:
+
+  bundle config --delete bin    # Turn off Bundler's stub generator
+  rake rails:update:bin         # Use the new Rails 4 executables
+  git add bin                   # Add bin/ to source control
+
+You may need to remove bin/ from your .gitignore as well.
+
+When you install a gem whose executable you want to use in your app,
+generate it and add it to source control:
+
+  bundle binstubs some-gem-name
+  git add bin/new-executable
+
+EOS
+
+    def exec_app
+      original_cwd = Dir.pwd
+
+      loop do
+        if exe = find_executable
+          contents = File.read(exe)
+
+          if contents =~ /(APP|ENGINE)_PATH/
+            exec RUBY, exe, *ARGV
+            break # non reachable, hack to be able to stub exec in the test suite
+          elsif exe.end_with?('bin/rails') && contents.include?('This file was generated by Bundler')
+            $stderr.puts(BUNDLER_WARNING)
+            Object.const_set(:APP_PATH, File.expand_path('config/application', Dir.pwd))
+            require File.expand_path('../boot', APP_PATH)
+            require 'rails/commands'
+            break
+          end
+        end
+
+        # If we exhaust the search there is no executable, this could be a
+        # call to generate a new application, so restore the original cwd.
+        Dir.chdir(original_cwd) and return if Pathname.new(Dir.pwd).root?
+
+        # Otherwise keep moving upwards in search of an executable.
+        Dir.chdir('..')
+      end
+    end
+
+    def find_executable
+      EXECUTABLES.find { |exe| File.file?(exe) }
+    end
+  end
+end