"wrong argument type" exception when using ActionMailer in Rails 3

Question

I'm totally lost on this one. In a Rails 3.2.12 app, I'm trying to send an email with ActionMailer and getting this exception:

TypeError: wrong argument type Class (expected Module) from /Users/trcull/.rvm/gems/ruby-1.9.3-p125@featureviz/gems/actionpack-3.2.12/lib/abstract_controller/helpers.rb:153:in `include'

I've stripped my mailer down to bare minimum. It doesn't even send mail! Here it is in its entirety:

class SupportNewUserMailer < ActionMailer::Base
  def new_user
    puts "hi"
  end
end

Seriously, that's it. Then I call it from the Rails console like this and get the exception:

1.9.3p125 :001 > SupportNewUserMailer.new_user

No idea what's going on here. I have another mailer in the same app and it works fine.

Also, in case they are relevant, here's my configuration in development:

config.action_mailer.default_url_options = { :host => 'localhost:3000' }
config.action_mailer.delivery_method = :smtp
config.action_mailer.perform_deliveries = true
config.action_mailer.raise_delivery_errors = true
config.action_mailer.smtp_settings = {
  :authentication => :plain,
  :address => "smtp.mailgun.org",
  :port => 587,
  :domain => "redacted",
  :user_name => "redacted",
  :password => "redacted"
}

PS: yes, I tried declaring it as a class method (even though the docs say not to) and get the same result:

class SupportNewUserMailer < ActionMailer::Base
  def self.new_user
    puts "hi"
  end
end

Yields:

TypeError: wrong argument type Class (expected Module) from /Users/trcull/.rvm/gems/ruby-1.9.3-p125@featureviz/gems/actionpack-3.2.12/lib/abstract_controller/helpers.rb:153:in `include'

PPS: no, it's not a problem finding the class. If I change the declaration to this (note, no longer inheriting from ActionMailer::Base):

class SupportNewUserMailer 
  def self.new_user
    puts "hi"
  end
end

Then I can call it just fine with no errors and it prints "hi" to the screen as expected:

1.9.3p125 :001 > SupportNewUserMailer.new_user
hi
 => nil 
1.9.3p125 :002 >

Did you use include anywhere in your program? then show us that. TypeError: wrong argument type Class (expected Module) clearly saying you used class name in the include section. — Arup Rakshit

Tim Cull Tim Cull · Accepted Answer · 2013-09-05T20:08:30

I have a partial answer to my own question, though I don't understand why it works and would love to know a better explanation.

If I simply use a different name for my class, it works fine. So, for example, this works fine:

class NewUserMailer < ActionMailer::Base
  def new_user()
    puts "hi"
  end
end

Which would seem to suggest that using the word "Support" at the beginning of the class name is bad. But I tried a different class name that also starts with "Support" and that works fine, too:

class SupportStackOverflowMailer < ActionMailer::Base
  def new_user()
    puts "hi"
  end
end

It's just specifically the name "SupportNewUserMailer" that it doesn't like. I've confirmed that I don't have a different class with the same name anywhere in my project (though who knows if a gem does?). Is there some kind of class meta cache thing that's borked?

EDIT:

Finally figured it out. I had a "SupportNewUserMailerHelper" class declared under /lib. Apparently Rails was trying to associate that class as a helper for my mailer class through some automagical wizardty that was exploding. Deleting the helper class got rid of the problem.

"wrong argument type" exception when using ActionMailer in Rails 3

1 Answers