From 0ad1f7db7bc540e376cca123964c99d5c11cb342 Mon Sep 17 00:00:00 2001
From: Edouard CHIN <edouard.chin@shopify.com>
Date: Wed, 29 Nov 2017 18:01:36 -0500
Subject: [PATCH] Decouple `config.asset_host` assignment from rails:

- There is two way to set the asset_host in rails: `config.action_controller.asset_host=` and `config.asset_host=` (the latter being usefull to both set action_mailer/action_controller asset_host)
- Opening this PR for two reasons:
  1. Getting the asset_host from `config.action_controller` currently works when the asset_host is defined using `config.asset_host` but I feel like this might be by chance:
    - When rails initialization process kicks in, the `action_controller.set_configs` initializer runs. A variable `options` is assigned and reference `config.action_controller`. The `options` variable get modified and by doing so modify the refernce to `config.action_controller` https://github.com/rails/rails/blob/1bee2fb600c07625b830afd33b43ead3364c9715/actionpack/lib/action_controller/railtie.rb#L50
  2. If a gem decide to set the asset_host automatically for any apps, the gem can do so inside an initializer.
     ```ruby
       initializer :set_asset_host do |app|
         app.config.asset_host = 'https://example.com'
       end
     ```
     This code won't have any effect in sprockets-rails and as a result any assets referenced inside css, i.e. (`.div { background-image: url('/assets/rails.png') }) will not be prefixed by the asset_host
---
 lib/sprockets/railtie.rb |  5 +++++
 test/test_railtie.rb     | 14 ++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/lib/sprockets/railtie.rb b/lib/sprockets/railtie.rb
index 3ff11003..fc11ff1f 100644
--- a/lib/sprockets/railtie.rb
+++ b/lib/sprockets/railtie.rb
@@ -201,6 +201,11 @@ def self.build_manifest(app)
       Sprockets::Manifest.new(app.assets, path, config.assets.manifest)
     end
 
+    config.after_initialize do |app|
+      config.action_controller.asset_host        ||= app.config.asset_host
+      config.action_controller.relative_url_root ||= app.config.relative_url_root
+    end
+
     config.after_initialize do |app|
       config = app.config
 
diff --git a/test/test_railtie.rb b/test/test_railtie.rb
index 8e964ee5..988dfe7a 100644
--- a/test/test_railtie.rb
+++ b/test/test_railtie.rb
@@ -410,4 +410,18 @@ def test_quiet_assets_inserts_middleware
     assert middleware.include?(Sprockets::Rails::QuietAssets)
     assert middleware.each_cons(2).include?([Sprockets::Rails::QuietAssets, Rails::Rack::Logger])
   end
+
+  def test_config_asset_host_can_be_set_inside_an_initializer
+    app.configure do
+      initializer 'asset_host_and_relative_url_root' do |app|
+        app.config.asset_host        = 'https://example.com'
+        app.config.relative_url_root = '/myassets'
+      end
+    end
+    app.initialize!
+    context_class = Sprockets::Railtie.build_environment(app).context_class
+
+    assert_equal 'https://example.com', context_class.config.asset_host
+    assert_equal '/myassets',           context_class.config.relative_url_root
+  end
 end