1 files changed, 45 insertions, 21 deletions

diff --git a/railties/lib/rails/app_rails_loader.rb b/railties/lib/rails/app_rails_loader.rb
index 44f4d3dabc..fbb83fa10e 100644
--- a/railties/lib/rails/app_rails_loader.rb
+++ b/railties/lib/rails/app_rails_loader.rb
@@ -2,36 +2,60 @@ require 'pathname'
 
 module Rails
   module AppRailsLoader
-    RUBY = File.join(*RbConfig::CONFIG.values_at("bindir", "ruby_install_name")) + RbConfig::CONFIG["EXEEXT"]
+    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 4, 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 self.exec_app_rails
-      cwd   = Dir.pwd
+      original_cwd = Dir.pwd
 
-      exe   = find_executable
-      exe ||= find_executable_in_parent_path
-      return unless exe
+      loop do
+        if exe = find_executable
+          contents = File.read(exe)
 
-      exec RUBY, exe, *ARGV if find_executable
-      Dir.chdir("..") do
-        # Recurse in a chdir block: if the search fails we want to be sure
-        # the application is generated in the original working directory.
-        exec_app_rails unless cwd == Dir.pwd
-      end
-    rescue SystemCallError
-      # could not chdir, no problem just return
-    end
+          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
 
-    def self.find_executable
-      EXECUTABLES.find do |exe|
-        File.exists?(exe) && File.read(exe) =~ /(APP|ENGINE)_PATH/
+        # 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 a executable.
+        Dir.chdir('..')
       end
     end
 
-    def self.find_executable_in_parent_path(path = Pathname.new(Dir.pwd))
-      EXECUTABLES.find do |exe|
-        File.exists?(File.join(path, exe)) || !path.root? && find_executable_in_parent_path(path.parent)
-      end
+    def self.find_executable
+      EXECUTABLES.find { |exe| File.exists?(exe) }
     end
   end
 end