Add support for multiple preview_path

actionmailer/lib/action_mailer/base.rb

@@ -335,9 +335,7 @@ module ActionMailer
   # Methods must return a <tt>Mail::Message</tt> object which can be generated by calling the mailer
   # method without the additional <tt>deliver_now</tt> / <tt>deliver_later</tt>. The location of the
   # mailer previews directory can be configured using the <tt>preview_paths</tt> option which has a default
-  # of <tt>test/mailers/previews</tt>:
-  #
-  #   config.action_mailer.preview_paths = "#{Rails.root}/lib/mailer_previews"
+  # of <tt>test/mailers/previews</tt>
   #
   # An overview of all previews is accessible at <tt>http://localhost:3000/rails/mailers</tt>
   # on a running development server instance.

actionmailer/lib/action_mailer/preview.rb

@@ -5,9 +5,9 @@ module Previews #:nodoc:
     extend ActiveSupport::Concern
 
     included do
-      # Set the location of mailer previews through app configuration:
+      # Add the location of mailer previews through app configuration:
       #
-      #     config.action_mailer.preview_paths = "#{Rails.root}/lib/mailer_previews"
+      #     config.action_mailer.preview_paths << "#{Rails.root}/lib/mailer_previews"
       #
       mattr_accessor :preview_paths, instance_writer: false
 
@@ -96,7 +96,7 @@ def preview_name
       protected
         def load_previews #:nodoc:
           if preview_paths
-            Dir["#{preview_paths}/**/*_preview.rb"].each{ |file| require_dependency file }
+            preview_paths.existent.each{ |file| require_dependency file }
           end
         end
 

actionmailer/lib/action_mailer/railtie.rb

@@ -22,7 +22,7 @@ class Railtie < Rails::Railtie # :nodoc:
       options.show_previews = Rails.env.development? if options.show_previews.nil?
 
       if options.show_previews
-        options.preview_paths  ||= defined?(Rails.root) ? "#{Rails.root}/test/mailers/previews" : nil
+        options.preview_paths ||= paths["test/mailers/previews"]
       end
 
       # make sure readers methods get compiled
@@ -54,11 +54,5 @@ class Railtie < Rails::Railtie # :nodoc:
         config.compile_methods! if config.respond_to?(:compile_methods!)
       end
     end
-
-    config.after_initialize do
-      if ActionMailer::Base.preview_paths
-        ActiveSupport::Dependencies.autoload_paths << ActionMailer::Base.preview_paths
-      end
-    end
   end
 end

actionpack/test/controller/resources_test.rb

@@ -346,13 +346,13 @@ def test_with_new_action
       end
 
       preview_options = {:action => 'preview'}
-      preview_paths   = "/messages/new/preview"
+      preview_path    = "/messages/new/preview"
       assert_restful_routes_for :messages do |options|
-        assert_recognizes(options.merge(preview_options), :path => preview_paths, :method => :post)
+        assert_recognizes(options.merge(preview_options), :path => preview_path, :method => :post)
       end
 
       assert_restful_named_routes_for :messages do |options|
-        assert_named_route preview_paths, :preview_new_message_path, preview_options
+        assert_named_route preview_path, :preview_new_message_path, preview_options
       end
     end
   end
@@ -368,13 +368,13 @@ def test_with_new_action_with_name_prefix
       end
 
       preview_options = {:action => 'preview', :thread_id => '1'}
-      preview_paths   = "/threads/1/messages/new/preview"
+      preview_path    = "/threads/1/messages/new/preview"
       assert_restful_routes_for :messages, :path_prefix => 'threads/1/', :name_prefix => 'thread_', :options => { :thread_id => '1' } do |options|
-        assert_recognizes(options.merge(preview_options), :path => preview_paths, :method => :post)
+        assert_recognizes(options.merge(preview_options), :path => preview_path, :method => :post)
       end
 
       assert_restful_named_routes_for :messages, :path_prefix => 'threads/1/', :name_prefix => 'thread_', :options => { :thread_id => '1' } do |options|
-        assert_named_route preview_paths, :preview_new_thread_message_path, preview_options
+        assert_named_route preview_path, :preview_new_thread_message_path, preview_options
       end
     end
   end
@@ -390,13 +390,13 @@ def test_with_formatted_new_action_with_name_prefix
       end
 
       preview_options = {:action => 'preview', :thread_id => '1', :format => 'xml'}
-      preview_paths   = "/threads/1/messages/new/preview.xml"
+      preview_path    = "/threads/1/messages/new/preview.xml"
       assert_restful_routes_for :messages, :path_prefix => 'threads/1/', :name_prefix => 'thread_', :options => { :thread_id => '1' } do |options|
-        assert_recognizes(options.merge(preview_options), :path => preview_paths, :method => :post)
+        assert_recognizes(options.merge(preview_options), :path => preview_path, :method => :post)
       end
 
       assert_restful_named_routes_for :messages, :path_prefix => 'threads/1/', :name_prefix => 'thread_', :options => { :thread_id => '1' } do |options|
-        assert_named_route preview_paths, :preview_new_thread_message_path, preview_options
+        assert_named_route preview_path, :preview_new_thread_message_path, preview_options
       end
     end
   end

guides/source/configuring.md

@@ -453,10 +453,10 @@ There are a number of settings available on `config.action_mailer`:
     config.action_mailer.interceptors = ["MailInterceptor"]
     ```
 
-* `config.action_mailer.preview_paths` specifies the location of mailer previews.
+* `config.action_mailer.preview_paths` adds the location of mailer previews.
 
     ```ruby
-    config.action_mailer.preview_paths = "#{Rails.root}/lib/mailer_previews"
+    config.action_mailer.preview_paths << "#{Rails.root}/lib/mailer_previews"
     ```
 
 * `config.action_mailer.show_previews` enable or disable mailer previews. By default this is `true` in development.

railties/lib/rails/engine/configuration.rb

@@ -67,6 +67,8 @@ def paths
           paths.add "vendor",              load_path: true
           paths.add "vendor/assets",       glob: "*"
 
+          paths.add "test/mailers/previews", glob: "**/*_preview.rb"
+
           paths
         end
       end

railties/test/application/mailer_previews_test.rb

@@ -102,6 +102,42 @@ def foo
       assert_match '<li><a href="/rails/mailers/notifier/foo">foo</a></li>', last_response.body
     end
 
+    test "mailer previews are loaded from a custom preview_path when it's multiple" do
+      add_to_config "config.action_mailer.preview_path = ['#{app_path}/lib/notifier_previews', '#{app_path}/lib/confirm_previews']"
+
+      ['notifier', 'confirm'].each do |keyword|
+        mailer keyword, <<-RUBY
+          class #{keyword.camelize} < ActionMailer::Base
+            default from: "from@example.com"
+
+            def foo
+              mail to: "to@example.org"
+            end
+          end
+        RUBY
+
+        text_template "#{keyword}/foo", <<-RUBY
+          Hello, World!
+        RUBY
+
+        app_file "lib/#{keyword}_previews/notifier_preview.rb", <<-RUBY
+          class #{keyword.camelize}Preview < ActionMailer::Preview
+            def foo
+              #{keyword.camelize}.foo
+            end
+          end
+        RUBY
+      end
+
+      app('development')
+
+      get "/rails/mailers"
+      assert_match '<h3><a href="/rails/mailers/notifier">Notifier</a></h3>', last_response.body
+      assert_match '<li><a href="/rails/mailers/notifier/foo">foo</a></li>', last_response.body
+      assert_match '<h3><a href="/rails/mailers/confirm">Confirm</a></h3>', last_response.body
+      assert_match '<li><a href="/rails/mailers/confirm/foo">foo</a></li>', last_response.body
+    end
+
     test "mailer previews are reloaded across requests" do
       app('development')