Log email sending and check for PII when sending asynchronous email

[mitchellhenke]

🛠 Summary of changes

Builds on #7106 to check for PII when sending async emails since they get saved in the database!

I don't love the approach of instance_variable_get and instance_variable_set, and would very much have preferred to use the instrumented deliver method from ActionMailer, but it doesn't include the arguments given to the Mailer (like user, which we want to log, or the action the mail was derived from).

The only other hook that exists after the mail is delivered is the email observer delivered_email. A list of all the hooks in the order that they happen:

  # UserMailer#before_action
  # UserMailer#after_action
  # IdentityMailLogSubscriber#process
  # EmailDeliveryObserver.delivering_email
  # Email actually sent
  # IdentityMailLogSubscriber#deliver
  # EmailDeliveryObserver.delivered_email

[zachmargolis]

🤔 what if we only applied the lint to UserMailer and its subclasses instead of ApplicationMailer?

[mitchellhenke]

I think that'd make sense, I don't know how to do that off-hand from a brief look at the current linter.

[zachmargolis]

ok! I'll poke around at it for a follow-up

[zachmargolis]

LGTM

[zachmargolis]

I just remembered we can use prepend to avoid alias_method dances in #7165

So here we could define somewhere the file:

module DeliverLaterArgumentChecker
  def deliver_later(...)
    MailerSensitiveInformationChecker.check_for_sensitive_pii!(@params, @args, @action)
    super(...)
  end
end

and turn this into:

Suggested change

	alias_method :original_deliver_later, :deliver_later
	prepend DeliverLaterArgumentChecker

[mitchellhenke]

Thanks for reminding me, added in b8f658b