Fix compatibility issue with Sprockets Rails 3.0.0

Sprockets Rails now unset `Rails.application.assets` when
`config.assets.compile` is false, causing an issue as we were relying on
that hash. The workaround here is to read the manifest file directly
by using `Sprockets::Railtie.build_manifest`.

Note that this patch requires the manifest file to exists, so you have
to run `rake assets:precompile` to generate the manifest file first.

Also adding Rails 4.2 using Sprockets Rails 2.3 to the build matrix.

See issue rails/sprockets-rails#237 for more detail.

Fix #12

.travis.yml

@@ -13,6 +13,7 @@ gemfile:
   - gemfiles/rails_4_0.gemfile
   - gemfiles/rails_4_1.gemfile
   - gemfiles/rails_4_2.gemfile
+  - gemfiles/rails_4_2_sprockets_2.gemfile
   - gemfiles/rails_5_0.gemfile
 
 matrix:

Appraisals

@@ -18,6 +18,11 @@ appraise "rails-4-2" do
   gem "rails", "~> 4.2.0"
 end
 
+appraise "rails-4-2-sprockets-2" do
+  gem "rails", "~> 4.2.0"
+  gem "sprockets-rails", "~> 2.3.0"
+end
+
 appraise "rails-5-0" do
   gem "rails", "~> 5.0.0.beta1"
 end

gemfiles/rails_4_2_sprockets_2.gemfile

@@ -0,0 +1,8 @@
+# This file was generated by Appraisal
+
+source "https://rubygems.org"
+
+gem "rails", "~> 4.2.0"
+gem "sprockets-rails", "~> 2.3.0"
+
+gemspec :path => "../"

lib/sprockets-redirect.rb

@@ -4,7 +4,10 @@ module Sprockets
   class RedirectRailtie < ::Rails::Railtie
     initializer "insert_sprockets_redirect_middleware" do |app|
       if !::Rails.configuration.assets.compile && ::Rails.configuration.assets.digest
-        app.middleware.insert 0, Sprockets::Redirect, ::Rails.application.assets,
+        app.middleware.insert 0,
+          Sprockets::Redirect,
+          ::Rails.application.assets ||
+            Sprockets::Railtie.build_manifest(::Rails.application).assets,
           :prefix => ::Rails.configuration.assets.prefix,
           :asset_host => ::Rails.configuration.action_controller.asset_host
       end

lib/sprockets/redirect.rb

@@ -69,7 +69,11 @@ def logical_path
     end
 
     def digest_path
-      @environment[logical_path].digest_path
+      if @environment[logical_path].respond_to?(:digest_path)
+        @environment[logical_path].digest_path
+      else
+        @environment[logical_path]
+      end
     end
 
     # Sends a redirect header back to browser

test/integration_test.rb

@@ -12,6 +12,7 @@ def test_build_app_and_add_gem
     create_rails_app
     append_gemfile
     create_test_file
+    precompile_assets
     assert_middleware_injection
     assert_asset_redirection
   end
@@ -49,6 +50,13 @@ def append_gemfile
       f.puts
       f.puts 'gem "sprockets-redirect", :path => "../../"'
       f.puts 'gem "test-unit"'
+
+      begin
+        require "sprockets/rails/version"
+        f.puts %(gem "sprockets-rails", "#{Sprockets::Rails::VERSION}")
+      rescue LoadError
+        # Unable to determine Sprockets::Rails version, so we just ignore it.
+      end
     end
 
     reset_bundler_environment_variables
@@ -80,6 +88,10 @@ def test_asset_redirection
     end
   end
 
+  def precompile_assets
+    in_app_dir { run_command "bundle exec rake assets:precompile" }
+  end
+
   def assert_middleware_injection
     output = in_app_dir { run_command 'bundle exec rake middleware' }
     assert_match(/use Sprockets::Redirect/, output)