Introduce suspenders:email generator (#1162)

Creates [email interceptor][] to ensure emails are sent to preconfigured
addresses in non-production environments. Drops support for [Recipient
Interceptor][], since this functionality is supported in Rails Core.

In order to enable the interceptor, set `EMAIL_RECIPIENTS` to a
comma-separated list.

```sh
INTERCEPTOR_ADDRESSES="user_1@example.com,user_2@example.com" bin/rails s
```

Configures [default_url_options][] in `test` and `development`
environments so that `*_url` helpers will work.

Note that we do not configure `production`, since we've determined the
`delivery_method` is something each project will configure
independently. This means we'll just use the [default configuration][],
which is `smtp`.

[email interceptor]: https://guides.rubyonrails.org/action_mailer_basics.html#intercepting-emails
[Recipient Interceptor]: https://github.com/croaky/recipient_interceptor
[default_url_options]: https://guides.rubyonrails.org/action_mailer_basics.html#generating-urls-in-action-mailer-views
[default configuration]: https://guides.rubyonrails.org/configuring.html#config-action-mailer-delivery-method

NEWS.md

@@ -13,6 +13,7 @@ Unreleased
 * Introduce `suspenders:setup` generator
 * Introduce `suspenders:tasks` generator
 * Introduce `suspenders:db:migrate` task
+* Introduce `suspenders:email` generator
 
 20230113.0 (January, 13, 2023)
 

README.md

@@ -159,6 +159,20 @@ bin/rails suspenders:rake
 bin/rails suspenders:db:migrate
 ```
 
+### Email
+
+Intercepts emails in non-production environments by setting `INTERCEPTOR_ADDRESSES`.
+
+```sh
+INTERCEPTOR_ADDRESSES="user_1@example.com,user_2@example.com" bin/rails s
+```
+
+Configures `default_url_options` in `test` and `development`.
+
+```
+bin/rails g suspenders:email
+```
+
 ## Contributing
 
 See the [CONTRIBUTING] document.

lib/generators/suspenders/email_generator.rb

@@ -0,0 +1,52 @@
+module Suspenders
+  module Generators
+    class EmailGenerator < Rails::Generators::Base
+      source_root File.expand_path("../../templates/email", __FILE__)
+      desc <<~TEXT
+        Intercepts emails in non-production environments by setting `INTERCEPTOR_ADDRESSES`.
+
+        ```sh
+        INTERCEPTOR_ADDRESSES="user_1@example.com,user_2@example.com" bin/rails s
+        ```
+
+        Configures `default_url_options` in `test` and `development`.
+      TEXT
+
+      def create_email_interceptor
+        copy_file "email_interceptor.rb", "app/mailers/email_interceptor.rb"
+      end
+
+      def create_email_interceptor_initializer
+        initializer "email_interceptor.rb", <<~RUBY
+          Rails.application.configure do
+            if ENV["INTERCEPTOR_ADDRESSES"].present?
+              config.action_mailer.interceptors = %w[EmailInterceptor]
+            end
+          end
+        RUBY
+      end
+
+      def configure_email_interceptor
+        environment do
+          %(
+            config.to_prepare do
+              EmailInterceptor.config.interceptor_addresses = ENV.fetch("INTERCEPTOR_ADDRESSES", "").split(",")
+            end
+          )
+        end
+      end
+
+      # TODO: Remove once https://github.com/rails/rails/pull/51191 is in latest
+      # Rails release
+      def configure_development_environment
+        environment %(config.action_mailer.default_url_options = { host: "localhost", port: 3000 }), env: "development"
+      end
+
+      # TODO: Remove once https://github.com/rails/rails/pull/51191 is in latest
+      # Rails release
+      def configure_test_environment
+        environment %(config.action_mailer.default_url_options = { host: "www.example.com" }), env: "test"
+      end
+    end
+  end
+end

lib/generators/templates/email/email_interceptor.rb

@@ -0,0 +1,11 @@
+class EmailInterceptor
+  include ActiveSupport::Configurable
+
+  config_accessor :interceptor_addresses, default: []
+
+  def self.delivering_email(message)
+    to = interceptor_addresses
+
+    message.to = to if to.any?
+  end
+end

test/generators/suspenders/email_generator_test.rb

@@ -0,0 +1,91 @@
+require "test_helper"
+require "generators/suspenders/email_generator"
+
+module Suspenders
+  module Generators
+    class EmailGeneratorTest < Rails::Generators::TestCase
+      include Suspenders::TestHelpers
+
+      tests Suspenders::Generators::EmailGenerator
+      destination Rails.root
+      setup :prepare_destination
+      teardown :restore_destination
+
+      test "creates a mailer intercepter" do
+        expected = <<~RUBY
+          class EmailInterceptor
+            include ActiveSupport::Configurable
+
+            config_accessor :interceptor_addresses, default: []
+
+            def self.delivering_email(message)
+              to = interceptor_addresses
+
+              message.to = to if to.any?
+            end
+          end
+        RUBY
+
+        run_generator
+
+        assert_file app_root("app/mailers/email_interceptor.rb") do |file|
+          assert_equal expected, file
+        end
+      end
+
+      test "creates initializer" do
+        expected = <<~RUBY