Deprecate `*_path` methods in mailers

Email does not support relative links since there is no implicit host. Therefore all links inside of emails must be fully qualified URLs. All path helpers are now deprecated. When removed, the error will give early indication to developers to use `*_url` methods instead.

Currently if a developer uses a `*_path` helper, their tests and `mail_view` will not catch the mistake. The only way to see the error is by sending emails in production. Preventing sending out emails with non-working path's is the desired end goal of this PR.

Currently path helpers are mixed-in to controllers (the ActionMailer::Base acts as a controller). All `*_url` and `*_path` helpers are made available through the same module. This PR separates this behavior into two modules so we can extend the `*_path` methods to add a Deprecation to them. Once deprecated we can use this same area to raise a NoMethodError and add an informative message directing the developer to use `*_url` instead.

The module with warnings is only mixed in when a controller returns false from the newly added `supports_relative_path?`.

Paired @sgrif & @schneems

1 files changed, 52 insertions, 0 deletions

diff --git a/railties/test/application/mailer_previews_test.rb b/railties/test/application/mailer_previews_test.rb
index 8b91a1171f..55e917c3ec 100644
--- a/railties/test/application/mailer_previews_test.rb
+++ b/railties/test/application/mailer_previews_test.rb
@@ -417,6 +417,58 @@ module ApplicationTests
       assert_match '<option selected value="?part=text%2Fplain">View as plain-text email</option>', last_response.body
     end
 
+    test "*_path helpers emit a deprecation" do
+
+      app_file "config/routes.rb", <<-RUBY
+        Rails.application.routes.draw do
+          get 'foo', to: 'foo#index'
+        end
+      RUBY
+
+      mailer 'notifier', <<-RUBY
+        class Notifier < ActionMailer::Base
+          default from: "from@example.com"
+
+          def path_in_view
+            mail to: "to@example.org"
+          end
+
+          def path_in_mailer
+            @url = foo_path
+            mail to: "to@example.org"
+          end
+        end
+      RUBY
+
+      html_template 'notifier/path_in_view', "<%= link_to 'foo', foo_path %>"
+
+      mailer_preview 'notifier', <<-RUBY
+        class NotifierPreview < ActionMailer::Preview
+          def path_in_view
+            Notifier.path_in_view
+          end
+
+          def path_in_mailer
+            Notifier.path_in_mailer
+          end
+        end
+      RUBY
+
+      app('development')
+
+      assert_deprecated do
+        get "/rails/mailers/notifier/path_in_view.html"
+        assert_equal 200, last_response.status
+      end
+
+      html_template 'notifier/path_in_mailer', "No ERB in here"
+
+      assert_deprecated do
+        get "/rails/mailers/notifier/path_in_mailer.html"
+        assert_equal 200, last_response.status
+      end
+    end
+
     private
       def build_app
         super