Switch to the new Sprockets processor

[eugenijusr]

Starting version 4 Sprockets is removing the register_engine method which registers JSX transformers using Tilt based templates breaking this gem for the current Rails 5 master. This has been deprecated since Sprockets version 3:
https://github.com/rails/sprockets/blob/master/UPGRADING.md

This PR adds a JSX Processor and registers it via register_processor as application/jsx mime type. Is there a reserved mime type for JSX templates?

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[rmosolgo]

Hmmm as you can see in the specs, this @output is getting assigned in the first use, but then never being reassigned. This causes all inputs to have the same output!

Is there a downside to simply

class Processor 
  def self.call(input)
    JSX::transform(input[:data])
  end 
end

?

[eugenijusr]

I think this was done for performance reasons in the Tilt template version of this. For these Sprocket processors there is a way to do a similar thing by implementing an optional cache_key method.

[rmosolgo]

Thanks for updating us!

I don't think there is a special mime type for .jsx. They're usually requested & served as JavaScript files, so I think the normal JS mime type is good enough!

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[rmosolgo]

from https://github.com/rails/sprockets#return-hash:

Returning a String is shorthand for returning { data: str }

Can we return a string only? Do we need any metadata?

[rmosolgo]

✨ Thanks again for getting us up-to-date (and getting me up to date 😝) !