Conditional 'process convert: :format' always changes file extension

[langalex]

Given an uploader:

class MyUploader < CarrierWave::Uploader::Base
  process convert: :webp, if: :should_convert_to_webp?

  def should_convert_to_webp?(filename)
    ..
  end
end

The file extension is always changed to webp, even if should_convert_to_webp? returns false.

The error was introduced in 3.0.5:

module CarrierWave
  module Uploader
    module Processing
        def process(*args)
          new_processors = args.inject({}) do |hash, arg|
            arg = { arg => [] } unless arg.is_a?(Hash)
            hash.merge!(arg)
          end

          condition_type = new_processors.keys.detect { |key| [:if, :unless].include?(key) }
          condition = new_processors.delete(:if) || new_processors.delete(:unless)
          new_processors.each do |processor, processor_args|
            self.processors += [[processor, processor_args, condition, condition_type]]

            if processor == :convert
              # Treat :convert specially, since it should trigger the file extension change
              force_extension processor_args
            end
          end
        end
      end # ClassMethods
    end
  end
end

The if processor == :convert clause runs on the class level, ignoring the condition which is evaluated on the instance level, when an actual file is uploaded.

[mshibuya]

Sorry but it turned out that this issue is hard to resolve in a non-breaking way. I've added a warning message in fb287f3, so users can be aware of this.

For the time being I would suggest working around this by using conditional versions, like:

class CarrierwaveUploader < CarrierWave::Uploader::Base
  ...

  version :webp, if: :should_convert_to_webp? do
    process convert: :webp
  end

  def should_convert_to_webp?(file)
    file.content_type == 'image/jpeg'
  end

  def url(*args)
    if version_active?(:webp)
      webp.url(*args)
    else
      super
    end
  end
end