Regression - broken backward compatibility with rack 2 since passenger 6.0.24

[zzemla]

Issue report

Are you sure this is a bug in Passenger?

Yes.

Please try with the newest version of Passenger to avoid issues that have already been fixed

Present in the latest passenger gem

Question 1: What is the problem?

Expected behavior:

I'm able to use the latest passenger gem with rails apps that use rack 2.x.

Actual behavior:

This is not possible now due to gem dependency conflict.

How to reproduce it:

Start a new rails 7.2 project, and modify Gemfile by adding:

gem "passenger", "6.0.24"
gem "rack", "< 3"

With this bundle install will fail with version solving has failed error message:

$ bundle install
Fetching gem metadata from https://rubygems.org/.........
Resolving dependencies...
Could not find compatible versions

Because passenger >= 6.0.24 depends on rackup >= 2.0.0
  and rackup >= 2.0.0 depends on rack >= 3,
  passenger >= 6.0.24 requires rack >= 3.
So, because Gemfile depends on passenger = 6.0.24
  and Gemfile depends on rack < 3,
  version solving has failed.

More details:

Related to #2559 and cc5359c

Starting from version 6.0.24 passenger gem requires rackup >= 2.0.0 to work, which depends on rack >= 3.0. This breaks the ability to use the latest passenger version with rails apps that use rack 2.x

Rack 2 is still actively maintained and used by many Rails applications and gems.

I think this may be an unintended side effect, as passenger .gemspec specifies:

s.add_dependency 'rack', '>= 1.6.13'

but due to the recently added:

s.add_dependency 'rackup', '>= 2.0.0'

passenger now actually requires rack 3.x to work.

Possible fix:

This whole issue seems to stem from the fact that rackup 1.0.0 gem release was broken as it did not contain required files, and caused problems described in #2559

Since then, it appears that rackup 1.0.1 has been released specifically to address that issue:
rack/rackup#13 (comment)

The possible fix is to either change the dependency to:

s.add_dependency 'rackup', '>= 1.0.1'

or drop that dependency requirement at all, as I believe such issues with third-party gems should not be solved at the passenger .gemspec level.

Question 2: Passenger version and integration mode:

Both open source and enterprise versions are affected.

Question 3: OS or Linux distro, platform (including version):

Ubuntu 24.04 LTS.

Question 4: Passenger installation method:

[x] RubyGems + Gemfile
[ ] RubyGems, no Gemfile
[ ] Phusion APT repo
[ ] Phusion YUM repo
[ ] OS X Homebrew
[ ] source tarball
[ ] Other, please specify:

Question 5: Your app's programming language (including any version managers) and framework (including versions):

Ruby 3.2.3, Rails 7.2

Question 6: Are you using a PaaS and/or containerization? If so which one?

No.

Question 7: Anything else about your setup that we should know?

No.