Use Dir.glob in find_root_with_flag to return correct case

As of Ruby 2.2, Dir.glob returns matches with the correct case as opposed
to in previous versions where the matches were returned with the case of
the pattern. In certain scenarios on Mac OS X the app can be booted with
the incorrect case, e.g. incorrect case on Pow symlink). This is because
the app is built by Rack::Builder evaluating a string from the config.ru
file and passing the incorrectly cased path to the eval method.

As Dir.glob is the only method in Ruby 2.2 that appears to do this case
correction currently we need to rewrite the find_root_with_flag method
to use it so that it corrects the case for when the applications paths
instance is created.

Fixes #18660.

actionpack/lib/action_controller/metal/helpers.rb

@@ -73,7 +73,7 @@ def helper_attr(*attrs)
 
       # Provides a proxy to access helpers methods from outside the view.
       def helpers
-        @helper_proxy ||= begin 
+        @helper_proxy ||= begin
           proxy = ActionView::Base.new
           proxy.config = config.inheritable_copy
           proxy.extend(_helpers)

railties/CHANGELOG.md

+*   Use Dir.glob in `find_root_with_flag` so that correct case is used on Mac OS X.
+
+    Fixes #18660.
+
+    *Andrew White*
+
+
 ## Rails 4.2.1 (March 19, 2015) ##
 
 *   Add a new-line to the end of route method generated code.

railties/lib/rails/engine.rb

@@ -663,16 +663,20 @@ def has_migrations? #:nodoc:
     end
 
     def self.find_root_with_flag(flag, root_path, default=nil) #:nodoc:
+      root_paths = [File.join(root_path, flag)]
 
-      while root_path && File.directory?(root_path) && !File.exist?("#{root_path}/#{flag}")
-        parent = File.dirname(root_path)
-        root_path = parent != root_path && parent
+      while root_path != (root_path = File.dirname(root_path))
+        root_paths << File.join(root_path, flag)
       end
 
-      root = File.exist?("#{root_path}/#{flag}") ? root_path : default
+      matches = Dir.glob(root_paths, File::FNM_CASEFOLD)
+      matches.sort_by!(&:size)
+      match = matches.last
+
+      root = match ? File.dirname(match) : default
       raise "Could not find root path for #{self}" unless root
 
-      Pathname.new File.realpath root
+      Pathname.new(File.realpath(root))
     end
 
     def default_middleware_stack #:nodoc:

railties/test/application/rackup_test.rb

@@ -40,4 +40,38 @@ def teardown
       assert_equal 'UTC', Rails.application.config.time_zone
     end
   end
+
+  class CaseInsensitiveRackupTest < ActiveSupport::TestCase
+    include ActiveSupport::Testing::Isolation
+
+    def app_path(*args)
+      tmp_path(*%w[OtherApp] + args)
+    end
+
+    def rackup
+      require "rack"
+      app, _ = Rack::Builder.parse_file("#{app_path.downcase}/config.ru")
+      app
+    end
+
+    def setup
+      build_app
+      boot_rails
+    end
+
+    def teardown
+      teardown_app
+    end
+
+    test "rails app is present" do
+      assert File.exist?(app_path("config"))
+    end
+
+    test "config.ru can be racked up" do
+      Dir.chdir app_path do
+        @app = rackup
+        assert_welcome get("/")
+      end
+    end
+  end
 end