Implement app_config_for helper

Author: tangrufus

README.md

@@ -39,7 +39,8 @@ TODO.
 
 ### `Rails.app_env`
 
-`Rails.app_env` is like `Rails.env` but it is set by the `APP_ENV` environment variable (`ENV["APP_ENV"]`).
+`Rails.app_env` is like [`Rails.env`](https://api.rubyonrails.org/classes/Rails.html#method-c-env) but it is set by the
+`APP_ENV` environment variable (`ENV["APP_ENV"]`).
 
 It is optimization for `staging` and `review` ([the two extra Heroku pipeline stages](https://devcenter.heroku.com/articles/pipelines)),
 so it doesn't need to rely on the slower delegation through `method_missing` that `ActiveSupport::EnvironmentInquirer`
@@ -59,6 +60,17 @@ Rails.env.production? # => true
 
 In case `ENV["APP_ENV"]` is blank, `Rails.app_env` falls back to `Rails.env`.
 
+### `Rails.application.app_config_for`
+
+`Rails.application.app_config_for` wraps[`Rails.application.config_for`](https://api.rubyonrails.org/classes/Rails/Application.html#method-i-config_for)
+with `{env: Rails.app_env}` as the second argument.
+
+```ruby
+# These two lines are equivalent.
+Rails.application.app_config_for(:foo)
+Rails.application.config_for(:foo, env: Rails.app_env)
+```
+
 ### Credentials
 
 `Rails APP_ENV` overrides the default Rails credentials `content_path` and `key_path` according to `Rails.app_env`.

lib/rails/app_env.rb

@@ -1,6 +1,7 @@
 require_relative "app_env/version"
 require_relative "app_env/environment_inquirer"
-require_relative "app_env/helpers"
+require_relative "app_env/rails_helpers"
+require_relative "app_env/application_helpers"
 require_relative "app_env/credentials"
 require_relative "app_env/railtie"
 

lib/rails/app_env/application_helpers.rb

@@ -0,0 +1,9 @@
+module Rails
+  module AppEnv
+    module ApplicationHelpers
+      def app_config_for(name)
+        config_for(name, env: Rails.app_env)
+      end
+    end
+  end
+end

lib/rails/app_env/helpers.rb renamed to lib/rails/app_env/rails_helpers.rb

@@ -1,6 +1,6 @@
 module Rails
   module AppEnv
-    module Helpers
+    module RailsHelpers
       def app_env
         @_app_env ||= EnvironmentInquirer.new(ENV["APP_ENV"] || Rails.env)
       end

lib/rails/app_env/railtie.rb

@@ -1,22 +1,27 @@
 module Rails
   module AppEnv
     class Railtie < Rails::Railtie
-      initializer :load_helpers, before: :initialize_logger do
-        Rails.extend(Helpers)
+      config.before_configuration do
+        Rails.extend(RailsHelpers)
+        Rails.application.extend(ApplicationHelpers)
       end
 
-      initializer :set_credentials, before: :initialize_logger do
+      config.before_configuration do
+        # TODO: Allow opt-out.
         Rails::AppEnv::Credentials.initialize!
       end
 
       config.after_initialize do
-        Rails::Info.property "Application environment", Rails.app_env
+        Rails::Info.property "Application environment" do
+          Rails.app_env
+        end
       end
 
       console do |app|
+        # TODO: Allow opt-out.
         require_relative "console"
-
         app.config.console = Rails::AppEnv::Console.new(app)
+
         puts "Loading #{Rails.app_env} application environment (rails-app_env #{Rails::AppEnv::VERSION})" # standard:disable Rails/Output
       end
     end

test/features/app_config_for_test.rb

@@ -0,0 +1,25 @@
+require "minitest/mock"
+require_relative "../test_helper"
+require_relative "env_helpers"
+
+module Rails::AppEnv::FeaturesTest
+  class AppConfigForTest < ActiveSupport::TestCase
+    include EnvHelpers
+
+    test "Rails.application.app_config_for delegates to Rails.application.config_for" do
+      app_env = "foo"
+      expected = Object.new
+
+      mock = Minitest::Mock.new
+      mock.expect(:call, expected, [:bar], env: app_env)
+
+      with_app_env(app_env) do
+        Rails.application.stub(:config_for, mock) do
+          assert_same expected, Rails.application.app_config_for(:bar)
+        end
+      end
+
+      mock.verify
+    end
+  end
+end