NameError: uninitialized constant Paperclip::Storage::Fog::Excon (Zeitwerk?)

[viktorianer]

Describe the bug
First, thank you for keeping updating this cool gem.

I think we have found a bug, probably related to Rails Zeitwerk mode, where we get NameError, when we use Paperclip to store or update PDF files.

When we try to assign a document to a record with Paperclip attachment: bill.update document: pdf_document
We will see this error:

NameError: uninitialized constant Paperclip::Storage::Fog::Excon
from .bundle/ruby/3.0.0/gems/kt-paperclip-7.1.1/lib/paperclip/storage/fog.rb:120:in `rescue in block in flush_writes'
Caused by NameError: uninitialized constant Fog
from .bundle/ruby/3.0.0/gems/kt-paperclip-7.1.1/lib/paperclip/storage/fog.rb:232:in `connection'

See https://github.com/kreeti/kt-paperclip/blob/master/lib/paperclip/storage/fog.rb#L120

I also tried to activate config.autoloader = :classic mode, bud got the same error.

After adding gem "fog-aws", "~> 3.15.0", I got a new error:

TypeError: wrong argument type Class (expected Module)
from /home/nonroot/.bundle/ruby/3.0.0/gems/kt-paperclip-7.1.1/lib/paperclip/attachment.rb:425:in `extend'

See https://github.com/kreeti/kt-paperclip/blob/master/lib/paperclip/attachment.rb#L425

So, I have no idea, how to solve it.

Additional context
We are in process to upgrade old application from Rails 5 to 6.1 and Ruby 2.5.x to 3.0.4.
We followed Rails Guides, in order to upgrade, e.g.:

https://edgeguides.rubyonrails.org/upgrading_ruby_on_rails.html#autoloading
https://edgeguides.rubyonrails.org/classic_to_zeitwerk_howto.html
https://edgeguides.rubyonrails.org/autoloading_and_reloading_constants.html

[viktorianer]

I just tried to update to the latest version of kt-paperclip and aws-sdk-s3. On our review Heroku instance, it works now! But I get this error in local environment (macOS 12.5.1 or Docker Alpine).

Because I do not have credentials for S3 bucket, I tried with defaults from README, where storage: :fog is set to fog. And maybe this is the issue here?!

Why I should use fog for local development?