url_for not using default_url_options[:host] value - ruby-on-rails

Question

I've got a view for an ActionMailer that includes a few different links. I'm running it on localhost:3000 right now, and so I've set that as such in a file called setup_mail.rb in app/initializers (as indicated here):
ActionMailer::Base.default_url_options[:host] = "localhost:3000"
When I go to use url_for in the view, it doesn't seem to pull this value. If I then add :host => "localhost:3000" to each url_for tag, they work properly. But they don't work without that included.
I have another tag, project_url, which is as it appears: a link to a specified Project. This functions, including the host value, with just project_url(#project). Why would one work but not the other?
From everything I've read, setting the default_url_options[:host] in an initializer should allow me to omit the :host value in the url_for tag. Obviously, it's not the worst thing in the world to just add that value, but it seems unnecessary and it means that when I eventually host the project somewhere I'll have to go through and change that value all over the place. But worse than that, it's something that I don't understand. I'm still learning as I go here and so I'd like to know what I'm doing wrong.

Answer 1

The documentation is pretty clear on this
When you decide to set a default :host for your mailers, then you need to make sure to use the :only_path => false option when using url_for. Since the url_for view helper will generate relative URLs by default when a :host option isn’t explicitly provided, passing :only_path => false will ensure that absolute URLs are generated.
You could create your own helper to use instead of the url_for to force :only_path to be false
def your_url_for(options = {})
options.reverse_merge! only_path: false
url_for(options)
end
You could also monkey patch rails to force this as the default, but that's left up to you :)
This all would be in addition to adding
config.action_mailer.default_url_options = { host: "YOUR HOST" }
to config/application.rb or equivalent.

Answer 2

It seems :only_path option is false which is by default. so that is why you need to provide [:host] either explicitly for every tag or set default options for url_for which would apply to all tags. here is how to set default host:
put this code in your Application controller & it should work.
helper_method :url_for
def default_url_options(options)
{ host: 'localhost:3000' }
end
For more details check set url_for defaults

Answer 3

Instead of tampering with the global default setting which imho shouldn't be changed after initialization you can simply define a method default_url_options in your mailer just like you can do it in a controller:
class UserMailer < ActionMailer::Base
def default_url_options
{ host: Tenant.current(true).host }
end
def confirm(user)
#user = user
mail(to: #user.email, subject: t(".subject_confirm"))
end
end

Answer 4

You're setting the default in ActionMailer::Base, but appear to expect it to reset the default for ActionController::Base.
A <%= link_to %> inside your mailer view doesn't necessarily know anything about the fact that it's inside a mailer view.