3.15.0 makes ViewComponent incompatible with use in an ActionMailer::Base subclass with a #format method

[jrochkind]

This is a pretty niche conflict, but it took me a while to figure out, so figured I should report it at least for searchability for anyone else running into it.

As far as I can tell, #format is not a reserved method name in ActionMailer, or an existing method in ActionMailer. I have an ActionMailer that contains a #format method. It's .erb renders a ViewComponent.

This worked fine up to view_component 3.14.0, but started causing a problem exactly in view_component 3.15.0 (I determined through testing). Rails 7.2.2

The problem looks like:

ActionView::Template::Error:
       private method `format' called for an instance of OralHistoryRequest
     # /Users/jrochkind/.gem/ruby/3.3.4/gems/view_component-3.15.0/lib/view_component/base.rb:112:in `render_in'
     # ./app/views/oral_history_delivery_mailer/oral_history_delivery_email.html.erb:12:in `block in _app_views_oral_history_delivery_mailer_oral_history_delivery_email_html_erb___597500510261675183_408460'

Where the second line is just the line in my mailer ERB that tries to render a SomeViewComponent.new -- any at all will do.

The line mentioned at view_component-3.15.0/lib/view_component/base.rb:112 is pretty opaque to me, but... aha.

view_component/lib/view_component/base.rb

Line 112 in 0dc9342

if compiler.renders_template_for?(@__vc_variant, request&.format&.to_sym)

This is observed in the process of running rspec-based tests, so it's possible it only appears as an artifact of testing harness, but does not look like it.

Changing the name of my mailer method #request to something else eliminates the problem.

OK, so it looks like then that line above in ViewComponent thinks that if the "container" for the ViewComponent (in this case a mailer) has a public #request method, then it's actually a controller (not a mailer), and the #request method is returning an ActionDispatch::Request which will have a public #format method it wants to use.

But in fact, it's in an ActionMailer, and that's my own #request method not rails, and it returns my own model object for my own use, and my own model object's #format is actually the (always in the way!) Kernel#format method which nobody wants or cares about and we always forget about, making this an even more confusing issue to debug!

This is a pretty edge case situation -- ViewComponent used in an ActionMailer that has it's own custom method named #request -- but it was surprising to run into a breakage on a minor version ViewComponent upgrade, and also fairly confusing to debug.

Perhaps it can be easily fixed though (don't assume public #format is a controller wtih an ActionDispatch::Request, check something else like class of receiver or returned object?) , or get better error message or docs or something?