Offer the option to use parameterization for shared processing of headers and ivars (#27825)

Offer the option to use parameterization for shared processing of headers and ivars

3 files changed, 148 insertions, 7 deletions

diff --git a/actionmailer/lib/action_mailer.rb b/actionmailer/lib/action_mailer.rb
index cf2c0f37e3..211190560a 100644
--- a/actionmailer/lib/action_mailer.rb
+++ b/actionmailer/lib/action_mailer.rb
@@ -42,6 +42,7 @@ module ActionMailer
   autoload :DeliveryMethods
   autoload :InlinePreviewInterceptor
   autoload :MailHelper
+  autoload :Parameterized
   autoload :Preview
   autoload :Previews, "action_mailer/preview"
   autoload :TestCase
diff --git a/actionmailer/lib/action_mailer/base.rb b/actionmailer/lib/action_mailer/base.rb
index 5aa3c4fa97..c0c030ac3e 100644
--- a/actionmailer/lib/action_mailer/base.rb
+++ b/actionmailer/lib/action_mailer/base.rb
@@ -288,20 +288,19 @@ module ActionMailer
   #             content_description: 'This is a description'
   #   end
   #
-  # Finally, Action Mailer also supports passing <tt>Proc</tt> objects into the default hash, so you
-  # can define methods that evaluate as the message is being generated:
+  # Finally, Action Mailer also supports passing <tt>Proc</tt> and <tt>Lambda</tt> objects into the default hash,
+  # so you can define methods that evaluate as the message is being generated:
   #
   #   class NotifierMailer < ApplicationMailer
-  #     default 'X-Special-Header' => Proc.new { my_method }
+  #     default 'X-Special-Header' => Proc.new { my_method }, to: -> { @inviter.email_address }
   #
   #     private
-  #
   #       def my_method
   #         'some complex call'
   #       end
   #   end
   #
-  # Note that the proc is evaluated right at the start of the mail message generation, so if you
+  # Note that the proc/lambda is evaluated right at the start of the mail message generation, so if you
   # set something in the default hash using a proc, and then set the same thing inside of your
   # mailer method, it will get overwritten by the mailer method.
   #
@@ -324,7 +323,6 @@ module ActionMailer
   #     end
   #
   #     private
-  #
   #       def add_inline_attachment!
   #         attachments.inline["footer.jpg"] = File.read('/path/to/filename.jpg')
   #       end
@@ -434,6 +432,7 @@ module ActionMailer
   class Base < AbstractController::Base
     include DeliveryMethods
     include Rescuable
+    include Parameterized
     include Previews
 
     abstract!
@@ -888,7 +887,7 @@ module ActionMailer
         default_values = self.class.default.map do |key, value|
           [
             key,
-            value.is_a?(Proc) ? instance_eval(&value) : value
+            value.is_a?(Proc) ? instance_exec(&value) : value
           ]
         end.to_h
 
diff --git a/actionmailer/lib/action_mailer/parameterized.rb b/actionmailer/lib/action_mailer/parameterized.rb
new file mode 100644
index 0000000000..dadb074c47
--- /dev/null
+++ b/actionmailer/lib/action_mailer/parameterized.rb
@@ -0,0 +1,141 @@
+module ActionMailer
+  # Provides the option to parameterize mailers in other to share ivar setup, processing, and common headers.
+  #
+  # Consider this example that does not use parameterization:
+  #
+  #   class InvitationsMailer < ApplicationMailer
+  #     def account_invitation(inviter, invitee)
+  #       @account = inviter.account
+  #       @inviter = inviter
+  #       @invitee = invitee
+  #
+  #       subject = "#{@inviter.name} invited you to their Basecamp (#{@account.name})"
+  #
+  #       mail \
+  #         subject:   subject,
+  #         to:        invitee.email_address,
+  #         from:      common_address(inviter),
+  #         reply_to:  inviter.email_address_with_name
+  #     end
+  #
+  #     def project_invitation(project, inviter, invitee)
+  #       @account = inviter.account
+  #       @project = project
+  #       @inviter = inviter
+  #       @invitee = invitee
+  #       @summarizer = ProjectInvitationSummarizer.new(@project.bucket)
+  #
+  #       subject = "#{@inviter.name.familiar} added you to a project in Basecamp (#{@account.name})"
+  #
+  #       mail \
+  #         subject:   subject,
+  #         to:        invitee.email_address,
+  #         from:      common_address(inviter),
+  #         reply_to:  inviter.email_address_with_name
+  #     end
+  #
+  #     def bulk_project_invitation(projects, inviter, invitee)
+  #       @account  = inviter.account
+  #       @projects = projects.sort_by(&:name)
+  #       @inviter  = inviter
+  #       @invitee  = invitee
+  #
+  #       subject = "#{@inviter.name.familiar} added you to some new stuff in Basecamp (#{@account.name})"
+  #
+  #       mail \
+  #         subject:   subject,
+  #         to:        invitee.email_address,
+  #         from:      common_address(inviter),
+  #         reply_to:  inviter.email_address_with_name
+  #     end
+  #   end
+  #
+  #   InvitationsMailer.account_invitation(person_a, person_b).deliver_later
+  #
+  # Using parameterized mailers, this can be rewritten as:
+  #
+  #   class InvitationsMailer < ApplicationMailer
+  #     before_action { @inviter, @invitee = params[:inviter], params[:invitee] }
+  #     before_action { @account = params[:inviter].account }
+  #
+  #     default to:       -> { @invitee.email_address },
+  #             from:     -> { common_address(@inviter) },
+  #             reply_to: -> { @inviter.email_address_with_name }
+  #
+  #     def account_invitation
+  #       mail subject: "#{@inviter.name} invited you to their Basecamp (#{@account.name})"
+  #     end
+  #
+  #     def project_invitation
+  #       @project    = params[:project]
+  #       @summarizer = ProjectInvitationSummarizer.new(@project.bucket)
+  #
+  #        mail subject: "#{@inviter.name.familiar} added you to a project in Basecamp (#{@account.name})"
+  #     end
+  #
+  #     def bulk_project_invitation
+  #       @projects = params[:projects].sort_by(&:name)
+  #
+  #       mail subject: "#{@inviter.name.familiar} added you to some new stuff in Basecamp (#{@account.name})"
+  #     end
+  #   end
+  #
+  #   InvitationsMailer.with(inviter: person_a, invitee: person_b).account_invitation.deliver_later
+  #
+  # That's a big improvement! It's also fully backwards compatible. So you can start to gradually transition
+  # mailers that stand to benefit the most from parameterization one by one and leave the others behind.
+  module Parameterized
+    extend ActiveSupport::Concern
+
+    included do
+      attr_accessor :params
+    end
+
+    class_methods do
+      def with(params)
+        ActionMailer::Parameterized::Mailer.new(self, params)
+      end
+    end
+
+    class Mailer
+      def initialize(mailer, params)
+        @mailer, @params = mailer, params
+      end
+
+      def method_missing(method_name, *args)
+        if @mailer.action_methods.include?(method_name.to_s)
+          ActionMailer::Parameterized::MessageDelivery.new(@mailer, method_name, *args).tap { |pmd| pmd.params = @params }
+        else
+          super
+        end
+      end
+    end
+
+    class MessageDelivery < ActionMailer::MessageDelivery
+      attr_accessor :params
+
+      private
+        def processed_mailer
+          @processed_mailer ||= @mailer_class.new.tap do |mailer|
+            mailer.params = params
+            mailer.process @action, *@args
+          end
+        end
+
+        def enqueue_delivery(delivery_method, options = {})
+          if processed?
+            super
+          else
+            args = @mailer_class.name, @action.to_s, delivery_method.to_s, @params, *@args
+            ActionMailer::Parameterized::DeliveryJob.set(options).perform_later(*args)
+          end
+        end
+    end
+
+    class DeliveryJob < ActionMailer::DeliveryJob # :nodoc:
+      def perform(mailer, mail_method, delivery_method, params, *args) #:nodoc:
+        mailer.constantize.with(params).public_send(mail_method, *args).send(delivery_method)
+      end
+    end
+  end
+end