Per my understanding Rails edge is currently locked to rack 3.0+ and (sadly) not fully compatible yet. There is no easy way to use Rack 2.x+ for now.

If you would like to use rack 3 + webrick I think something like this should work (not tested):

# Gemfile
gem 'rackup'
...
# test helper
Capybara.register_server :webrick do |app, port, host, **options|
  require 'rackup/handler/webrick'
  options = { Host: host, Port: port, AccessLog: [], Logger: WEBrick::Log.new(nil, 0) }.merge(options)
  Rackup::Handler::WEBrick.run(app, **options)
end

Capybara.server = :webrick

Ah, so rails edge is actually known to not actually be working properly? In the sense that it requires rack 3, but is known to not yet work with it? So much for my plan of testing against Rails edge! I had thought that Rails edge should always be in an internally consistent working state, i guess I misunderstood!

Thanks for that demo code, i will try it out, super helpful! (update: Does appear to work!)

But regardless of what Rails is doing or does -- should Capybara.server = :webrick already work with rack 3, since rack 3 is long-released, and capybara can be used without Rails too? Does capybara need like conditional logic for what webrick should do depending on rack 2 or 3? or a separate :webrick_rack_3 registration?

Indeed Capybara needs to be updated (to either work with both Rack 2 and 3 or just one of them), the changes are in the Rack 3 upgrade guide: https://github.com/rack/rack/blob/7acfe495c907c4b219125309f97f7309e64a563c/UPGRADE-GUIDE.md#binrackup-rackserver-rackhandlerand--racklobster-were-moved-to-a-separate-gem

In the sense that it requires rack 3, but is known to not yet work with it?

Just wanted to add some clarification here: Rails edge allows either Rack 2.x or 3.x.

3.x was first allowed in rails/rails#47133 so that compatibility could be fixed across multiple PRs since the diff ended up really big in a single PR.

You should be able to prevent a Rack 3.x resolution with something like gem "rack", "< 3" in your Gemfile/gemspec. Rails itself does this to test against both major versions of Rack:

https://github.com/rails/rails/blob/c8190750f9d28b831f9b38b4ded8a3ee5b41fd9d/Gemfile#L72

and capybara gemspec allows any rack >= 1.6.0 -- should Capybara.server = :webrick be fixed to work with rack 3?

probably a good idea to add a < 4 too once 3.x compatibility is fixed

@skipkayhil ahh, thanks for clarification. I was a little confused since there was a lot of changes related to actionpack gemspec happening at short time.

(update: I at first had trouble getting a rack 2 resolution with "rack", "< 3" in an app with current rails edge -- bundler was refusing to resolve it, claiming conflicts. But a rack 2 resolution was possible, bundler was just having trouble with it for it's own reasons on an existing Gemfile.lock, and eventually after messing with it, adding and removing different restrictions from my gemfile, I got bundler to resolve with rack 2)

Issue here is that Capybaras tests depend on sinatra which doesn't yet have a versions which supports rack 3, so we can't currently add rack 3 to the automated tests.

Trial "fix" merged here - 2db340d - please give it a try and let me know - we can reopen if anything else is required

Thank you for the workaround commit for :webrick server in capybara!

simi's local workaround at #2640 (comment) also works fine for me, and is reasonable.

The bigger concern is of course the block on capybara running CI for rack 3! Would it be useful to make an open issue here to track that, for people curious to find? And I wonder the most realistic path to resolving that. The sinatra project does not currently seem to have resources engaged for adding support for rack 3. sinatra/sinatra#1797 Swapping sinatra out in capybara CI may or may not be desirable/feasible. (swapping it out for... roda? The roda gemspec does not specify any rack version requirements, not sure if that actually means it is fully supported for rack 3; I haven't found it's CI to see what it builds with; some posts in Github Discussions and Issues seem to suggest some people are using it with rack 3).

@jrochkind Feel free to try out sinatra/sinatra#1857 :-)

@dentarg Looks like Rack::File was removed, and it needs to be Rack::Files::Iterator at https://github.com/dentarg/sinatra/blob/rack-3/lib/sinatra/base.rb#L294 now -- not sure where else in the code that may affect

@twalpole Yes, but not until Rack 3.1: rack/rack#1811 (will try to address that too)

@dentarg Files is available in Rack 2.x too --- it's just that File was an alias of it --- should be able to just swap to using Files in both 2 and 3

I noticed