Fixup code for use with rackup gem (may be used with rack 3) (#3061)

[MitchLewis930]

PR_060

[greptile-apps]

Greptile Overview

Greptile Summary

This PR adds compatibility for using Puma with Rack 3 by introducing support for the separate rackup gem. The changes refactor the Rack handler implementation to support both legacy Rack 2 (where rackup is built-in) and Rack 3 (where rackup is a separate gem).

Key Changes:

• Added conditional rackup gem dependency in Gemfile (only when not testing Rack 2)
• Refactored handler code into reusable Puma::RackHandler module that gets included by either Rack::Handler::Puma or Rackup::Handler::Puma based on runtime detection
• Updated rack_default.rb to conditionally define the default handler based on which gems are available
• Modified tests to dynamically select the appropriate handler module (Rack::Handler or Rackup::Handler) based on environment configuration

Minor Issue Found:

• Inconsistent error messages between rack_default.rb and handler/puma.rb when Rack 3 is used without the rackup gem

Confidence Score: 4/5

• This PR is safe to merge with low risk - it's a well-structured compatibility refactor
• The refactoring follows a clear pattern with runtime detection and conditional module definitions. The logic correctly handles all three scenarios (Rackup available, Rack < 3, Rack 3 without Rackup). Tests have been properly updated to work with both configurations. Only minor issue is inconsistent error messaging.
• No files require special attention - the inconsistent error message in lib/puma/rack_default.rb:23 is a minor style issue

Important Files Changed

Filename	Overview
Gemfile	Added conditional rackup gem dependency when not testing Rack 2
lib/puma/rack_default.rb	Added runtime detection for Rackup vs Rack with conditional module definitions, has inconsistent error message
lib/rack/handler/puma.rb	Refactored handler logic into shared Puma::RackHandler module with conditional registration for Rack/Rackup compatibility
test/test_rack_handler.rb	Updated tests to use RACK_HANDLER_MOD constant for dynamic handler selection based on environment

Sequence Diagram

sequenceDiagram
    participant App as Application
    participant RD as rack_default.rb
    participant RH as rack/handler/puma.rb
    participant Puma as Puma Server
    
    App->>RD: require rack_default
    RD->>RD: Check if Rackup defined
    
    alt Rackup gem installed
        RD->>RD: Define Rackup::Handler.default
        RD->>RH: Load handler (Rackup::Handler::Puma)
        RH->>RH: Include Puma::RackHandler in Rackup::Handler::Puma
    else Rack < 3
        RD->>RD: Define Rack::Handler.default
        RD->>RH: Load handler (Rack::Handler::Puma)
        RH->>RH: Include Puma::RackHandler in Rack::Handler::Puma
    else Rack 3 without Rackup
        RD->>App: Raise error
    end
    
    App->>RH: Call handler.run(app, options)
    RH->>Puma: Create Configuration
    RH->>Puma: Create Launcher
    RH->>Puma: Start server
    Puma-->>App: Server running

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_{4 files reviewed, 1 comment}

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[greptile-apps]

Error message differs from lib/rack/handler/puma.rb:135 ("You must install the rackup gem when using Rack 3")

Suggested change

	raise "Rack 3 must be used with the Rackup gem"
	raise "You must install the rackup gem when using Rack 3"

_{Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!}

Prompt To Fix With AI

This is a comment left during a code review.
Path: lib/puma/rack_default.rb
Line: 23:23

Comment:
Error message differs from `lib/rack/handler/puma.rb:135` ("You must install the rackup gem when using Rack 3")

```suggestion
  raise "You must install the rackup gem when using Rack 3"
```

<sub>Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!</sub>

How can I resolve this? If you propose a fix, please make it concise.