Fix backwards compatibility with Rails 3 apps.

When we removed script/rails and introduced bin/rails, we accidentally
introduced a regression. If you install Rails 4 as a gem, then try to do
something in a Rails 3 application:

    $ rails g

This will throw the 'please type rails new foo' message rather than the
proper generator documentation message. This is because older apps don't
have bin/rails.

Therefore, we now *prefer* bin/rails, but still search for script/rails,
and exec the one we find.

railties/lib/rails/app_rails_loader.rb

@@ -3,12 +3,16 @@
 module Rails
   module AppRailsLoader
     RUBY = File.join(*RbConfig::CONFIG.values_at("bindir", "ruby_install_name")) + RbConfig::CONFIG["EXEEXT"]
-    EXECUTABLE = 'bin/rails'
+    EXECUTABLES = ['bin/rails', 'script/rails']
 
     def self.exec_app_rails
-      cwd = Dir.pwd
-      return unless in_rails_application_or_engine? || in_rails_application_or_engine_subdirectory?
-      exec RUBY, EXECUTABLE, *ARGV if in_rails_application_or_engine?
+      cwd   = Dir.pwd
+
+      exe   = find_executable
+      exe ||= find_executable_in_parent_path
+      return unless 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.
@@ -18,12 +22,16 @@ def self.exec_app_rails
       # could not chdir, no problem just return
     end
 
-    def self.in_rails_application_or_engine?
-      File.exists?(EXECUTABLE) && File.read(EXECUTABLE) =~ /(APP|ENGINE)_PATH/
+    def self.find_executable
+      EXECUTABLES.find do |exe|
+        File.exists?(exe) && File.read(exe) =~ /(APP|ENGINE)_PATH/
+      end
     end
 
-    def self.in_rails_application_or_engine_subdirectory?(path = Pathname.new(Dir.pwd))
-      File.exists?(File.join(path, EXECUTABLE)) || !path.root? && in_rails_application_or_engine_subdirectory?(path.parent)
+    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
     end
   end
 end

railties/lib/rails/cli.rb

@@ -3,9 +3,6 @@
 
 # If we are inside a Rails application this method performs an exec and thus
 # the rest of this script is not run.
-#
-# TODO: when we hit this, advise adding ./bin to $PATH instead. Then the
-# app's `rails` executable is run immediately.
 Rails::AppRailsLoader.exec_app_rails
 
 require 'rails/ruby_version_check'

railties/test/app_rails_loader_test.rb

@@ -2,40 +2,47 @@
 require 'rails/app_rails_loader'
 
 class AppRailsLoaderTest < ActiveSupport::TestCase
-  test "is in a rails application if bin/rails exists and contains APP_PATH" do
-    File.stubs(:exists?).returns(true)
-    File.stubs(:read).with('bin/rails').returns('APP_PATH')
-    assert Rails::AppRailsLoader.in_rails_application_or_engine?
-  end
 
-  test "is not in a rails application if bin/rails exists but doesn't contain APP_PATH" do
-    File.stubs(:exists?).returns(true)
-    File.stubs(:read).with('bin/rails').returns('railties bin/rails')
-    assert !Rails::AppRailsLoader.in_rails_application_or_engine?
+  setup do
+    File.stubs(:exists?).returns(false)
   end
 
-  test "is in a rails application if parent directory has bin/rails containing APP_PATH" do
-    File.stubs(:exists?).with("/foo/bar/bin/rails").returns(false)
-    File.stubs(:exists?).with("/foo/bin/rails").returns(true)
-    File.stubs(:read).with('/foo/bin/rails').returns('APP_PATH')
-    assert Rails::AppRailsLoader.in_rails_application_or_engine_subdirectory?(Pathname.new("/foo/bar"))
-  end
+  ['bin/rails', 'script/rails'].each do |exe|
+    test "is in a rails application if #{exe} exists and contains APP_PATH" do
+      File.stubs(:exists?).with(exe).returns(true)
+      File.stubs(:read).with(exe).returns('APP_PATH')
+      assert Rails::AppRailsLoader.find_executable
+    end
 
-  test "is not in a rails application if at the root directory and doesn't have bin/rails" do
-    Pathname.any_instance.stubs(:root?).returns true
-    assert !Rails::AppRailsLoader.in_rails_application_or_engine?
-  end
+    test "is not in a rails application if #{exe} exists but doesn't contain APP_PATH" do
+      File.stubs(:exists?).with(exe).returns(true)
+      File.stubs(:read).with(exe).returns("railties #{exe}")
+      assert !Rails::AppRailsLoader.find_executable
+    end
 
-  test "is in a rails engine if parent directory has bin/rails containing ENGINE_PATH" do
-    File.stubs(:exists?).with("/foo/bar/bin/rails").returns(false)
-    File.stubs(:exists?).with("/foo/bin/rails").returns(true)
-    File.stubs(:read).with('/foo/bin/rails').returns('ENGINE_PATH')
-    assert Rails::AppRailsLoader.in_rails_application_or_engine_subdirectory?(Pathname.new("/foo/bar"))
-  end
+    test "is in a rails application if parent directory has #{exe} containing APP_PATH" do
+      File.stubs(:exists?).with("/foo/bar/#{exe}").returns(false)
+      File.stubs(:exists?).with("/foo/#{exe}").returns(true)
+      File.stubs(:read).with("/foo/#{exe}").returns('APP_PATH')
+      assert Rails::AppRailsLoader.find_executable_in_parent_path(Pathname.new("/foo/bar"))
+    end
+
+    test "is not in a rails application if at the root directory and doesn't have #{exe}" do
+      Pathname.any_instance.stubs(:root?).returns true
+      assert !Rails::AppRailsLoader.find_executable
+    end
+
+    test "is in a rails engine if parent directory has #{exe} containing ENGINE_PATH" do
+      File.stubs(:exists?).with("/foo/bar/#{exe}").returns(false)
+      File.stubs(:exists?).with("/foo/#{exe}").returns(true)
+      File.stubs(:read).with("/foo/#{exe}").returns('ENGINE_PATH')
+      assert Rails::AppRailsLoader.find_executable_in_parent_path(Pathname.new("/foo/bar"))
+    end
 
-  test "is in a rails engine if bin/rails exists containing ENGINE_PATH" do
-    File.stubs(:exists?).returns(true)
-    File.stubs(:read).with('bin/rails').returns('ENGINE_PATH')
-    assert Rails::AppRailsLoader.in_rails_application_or_engine?
+    test "is in a rails engine if #{exe} exists containing ENGINE_PATH" do
+      File.stubs(:exists?).with(exe).returns(true)
+      File.stubs(:read).with(exe).returns('ENGINE_PATH')
+      assert Rails::AppRailsLoader.find_executable
+    end
   end
 end