Rails Upgrade Analyzer

Analyze the current Rails application and provide a comprehensive upgrade assessment with selective file merging.

Step 1: Verify Rails Application

Check that we're in a Rails application by looking for these files:

• Gemfile (must exist and contain 'rails')
• config/application.rb (Rails application config)
• config/environment.rb (Rails environment)

If any of these are missing or don't indicate a Rails app, stop and inform the user this doesn't appear to be a Rails application.

Step 2: Get Current Rails Version

Extract the current Rails version from:

1. First, check Gemfile.lock for the exact installed version (look for rails (x.y.z))
2. If not found, check Gemfile for the version constraint

Report the exact current version (e.g., 7.1.3).

Step 3: Find Latest Rails Version

Use the GitHub CLI to fetch the latest Rails release:

gh api repos/rails/rails/releases/latest --jq '.tag_name'

This returns the latest stable version tag (e.g., v8.0.1). Strip the 'v' prefix for comparison.

Also check recent tags to understand the release landscape:

gh api repos/rails/rails/tags --jq '.[0:10] | .[].name'

Step 4: Determine Upgrade Type

Compare current and latest versions to classify the upgrade:

• Patch upgrade: Same major.minor, different patch (e.g., 7.1.3 → 7.1.5)
• Minor upgrade: Same major, different minor (e.g., 7.1.3 → 7.2.0)
• Major upgrade: Different major version (e.g., 7.1.3 → 8.0.0)

Step 5: Fetch Upgrade Guide

Use WebFetch to get the official Rails upgrade guide:

URL: https://guides.rubyonrails.org/upgrading_ruby_on_rails.html

Look for sections relevant to the version jump. The guide is organized by target version with sections like:

• "Upgrading from Rails X.Y to Rails X.Z"
• Breaking changes
• Deprecation warnings
• Configuration changes
• Required migrations

Extract and summarize the relevant sections for the user's specific upgrade path.

Step 6: Fetch Rails Diff

Use WebFetch to get the diff between versions from railsdiff.org:

URL: https://railsdiff.org/{current_version}/{target_version}

For example: https://railsdiff.org/7.1.3/8.0.0

This shows:

• Changes to default configuration files
• New files that need to be added
• Modified initializers
• Updated dependencies
• Changes to bin/ scripts

Summarize the key file changes.

Step 7: Check JavaScript Dependencies

Rails applications often include JavaScript packages that should be updated alongside Rails. Check for and report on these dependencies.

7.1: Identify JS Package Manager

Check which package manager the app uses:

# Check for package.json (npm/yarn)
ls package.json 2>/dev/null

# Check for importmap (Rails 7+)
ls config/importmap.rb 2>/dev/null

7.2: Check Rails-Related JS Packages

If package.json exists, check for these Rails-related packages:

# Extract current versions of Rails-related packages
cat package.json | grep -E '"@hotwired/|"@rails/|"stimulus"|"turbo-rails"' || echo "No Rails JS packages found"

Key packages to check:

7.3: Check for Updates

For npm/yarn projects, check for available updates:

# Using npm
npm outdated @hotwired/turbo-rails @hotwired/stimulus @rails/actioncable @rails/activestorage 2>/dev/null

# Or check latest versions directly
npm view @hotwired/turbo-rails version 2>/dev/null
npm view @rails/actioncable version 2>/dev/null

7.4: Check Importmap Pins (if applicable)

If the app uses importmap-rails, check config/importmap.rb for pinned versions:

cat config/importmap.rb | grep -E 'pin.*turbo|pin.*stimulus|pin.*@rails' || echo "No importmap pins found"

To update importmap pins:

bin/importmap pin @hotwired/turbo-rails
bin/importmap pin @hotwired/stimulus

7.5: JS Dependency Summary

Include in the upgrade summary:

### JavaScript Dependencies

**Package Manager**: [npm/yarn/importmap/none]

| Package | Current | Latest | Action |
|---------|---------|--------|--------|
| @hotwired/turbo-rails | 8.0.4 | 8.0.12 | Update recommended |
| @rails/actioncable | 7.1.0 | 8.0.0 | Update with Rails |
| ... | ... | ... | ... |

**Recommended JS Updates:**
- Run `npm update @hotwired/turbo-rails` (or yarn equivalent)
- Run `npm update @rails/actioncable @rails/activestorage` to match Rails version

Step 8: Generate Upgrade Summary

Provide a comprehensive summary including all findings from Steps 1-7:

Version Information

• Current version: X.Y.Z
• Latest version: A.B.C
• Upgrade type: [Patch/Minor/Major]

Upgrade Complexity Assessment

Rate the upgrade as Small, Medium, or Large based on:

Key Changes to Address

List the most important changes the user needs to handle:

1. Configuration file updates
2. Deprecated methods/features to update
3. New required dependencies
4. Database migrations needed
5. Breaking API changes

Recommended Upgrade Steps

1. Update test suite and ensure passing
2. Review deprecation warnings in current version
3. Update Gemfile with new Rails version
4. Run bundle update rails
5. Update JavaScript dependencies (see JS Dependencies section)
6. DO NOT run rails app:update directly - use the selective merge process below
7. Run database migrations
8. Run test suite
9. Review and update deprecated code

Resources

• Rails Upgrade Guide: https://guides.rubyonrails.org/upgrading_ruby_on_rails.html
• Rails Diff: https://railsdiff.org/{current}/{target}
• Release Notes: https://github.com/rails/rails/releases/tag/v{target}

Step 9: Selective File Update (replaces rails app:update)

IMPORTANT: Do NOT run rails app:update as it overwrites files without considering local customizations. Instead, follow this selective merge process:

9.1: Detect Local Customizations

Before any upgrade, identify files with local customizations:

# Check for uncommitted changes
git status

# List config files that differ from a fresh Rails app
# These are the files we need to be careful with
git diff HEAD --name-only -- config/ bin/ public/

Create a mental list of files in these categories:

• Custom config files: Files with project-specific settings (i18n, mailer, etc.)
• Modified bin scripts: Scripts with custom behavior (bin/dev with foreman, etc.)
• Standard files: Files that haven't been customized

9.2: Analyze Required Changes from Railsdiff

Based on the railsdiff output from Step 6, categorize each changed file:

9.3: Create Upgrade Plan

Present the user with a clear upgrade plan:

## Upgrade Plan: Rails X.Y.Z → A.B.C

### New Files (will be created):
- config/initializers/new_framework_defaults_A_B.rb
- bin/ci (new CI script)

### Safe to Update (no local customizations):
- public/400.html
- public/404.html
- public/500.html

### Needs Manual Merge (local customizations detected):
- config/application.rb
  └─ Local: i18n configuration
  └─ Rails: [describe new Rails changes if any]

- config/environments/development.rb
  └─ Local: letter_opener mailer config
  └─ Rails: [describe new Rails changes]

- bin/dev
  └─ Local: foreman + Procfile.dev setup
  └─ Rails: changed to simple ruby script

### Skip (comment-only or irrelevant changes):
- config/puma.rb (only comment changes)

9.4: Execute Upgrade Plan

After user confirms the plan:

For New Files:

Create them directly using the content from railsdiff or by extracting from a fresh Rails app:

# Generate a temporary fresh Rails app to extract new files
cd /tmp && rails new rails_template --skip-git --skip-bundle
# Then copy needed files

Or use the Rails generator for specific files:

bin/rails app:update:configs  # Only updates config files, still interactive

For Safe Updates:

Overwrite these files as they have no local customizations.

For Manual Merges:

For each file needing merge, show the user:

1. Current local version (their customizations)
2. New Rails default (from railsdiff)
3. Suggested merged version that:
   • Keeps all local customizations
   • Adds only essential new Rails functionality
   • Removes deprecated settings

Example merge for config/application.rb:

# KEEP local customizations:
config.i18n.available_locales = [:de, :en]
config.i18n.default_locale = :de
config.i18n.fallbacks = [:en]

# ADD new Rails 8.1 settings if needed:
# (usually none required - new defaults come via new_framework_defaults file)

9.5: Handle Active Storage Migrations

After file updates, run any new migrations:

bin/rails db:migrate

Check for new migrations that were added:

ls -la db/migrate/ | tail -10

9.6: Verify Upgrade

After completing the merge:

1. Start the Rails server and check for errors:

   bin/dev  # or bin/rails server

2. Check the Rails console:

   bin/rails console

3. Run the test suite:

   PARALLEL=1 COVERAGE=1 bin/rails test

4. Review deprecation warnings in logs

Step 10: Finalize Framework Defaults

After verifying the app works:

1. Review config/initializers/new_framework_defaults_X_Y.rb
2. Enable each new default one by one, testing after each
3. Once all defaults are enabled and tested, update config/application.rb:

   config.load_defaults X.Y  # Update to new version

4. Delete the new_framework_defaults_X_Y.rb file

Error Handling

• If gh CLI is not authenticated, instruct the user to run gh auth login
• If railsdiff.org doesn't have the exact versions, try with major.minor.0 versions
• If the app is already on the latest version, congratulate the user and note any upcoming releases
• If local customizations would be lost, ALWAYS stop and show the user what would be overwritten before proceeding

Key Principles

1. Never overwrite without checking - Always check for local customizations first
2. Preserve user intent - Local customizations exist for a reason
3. Minimal changes - Only add what's necessary for the new Rails version
4. Transparency - Show the user exactly what will change before doing it
5. Reversibility - User should be able to git checkout to restore if needed