When to Use This Skill

Analyze Rails apps and provide upgrade assessments

Use this skill when working with analyze rails apps and provide upgrade assessments.

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:

First, check

Gemfile.lock

for the exact installed version (look for

rails (x.y.z)

)

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: Package Purpose Version Alignment @hotwired/turbo-rails Turbo Drive/Frames/Streams Should match Rails version era @hotwired/stimulus Stimulus JS framework Generally stable across Rails versions @rails/actioncable WebSocket support Should match Rails version @rails/activestorage Direct uploads Should match Rails version @rails/actiontext Rich text editing Should match Rails version @rails/request.js Rails UJS replacement Should match Rails version era 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: Factor Small Medium Large Version jump Patch only Minor version Major version Breaking changes None Few, well-documented Many, significant Config changes Minimal Moderate Extensive Deprecations None active Some to address Many requiring refactoring Dependencies Compatible Some updates needed Major dependency updates Key Changes to Address List the most important changes the user needs to handle: Configuration file updates Deprecated methods/features to update New required dependencies Database migrations needed Breaking API changes Recommended Upgrade Steps Update test suite and ensure passing Review deprecation warnings in current version Update Gemfile with new Rails version Run bundle update rails Update JavaScript dependencies (see JS Dependencies section) DO NOT run rails app:update directly - use the selective merge process below Run database migrations Run test suite 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} When to Use This Skill Analyze Rails apps and provide upgrade assessments Use this skill when working with analyze rails apps and provide upgrade assessments. 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: Category Action Example New files Create directly config/initializers/new_framework_defaults_X_Y.rb Unchanged locally Safe to overwrite public/404.html (if not customized) Customized locally Manual merge needed config/application.rb , bin/dev Comment-only changes Usually skip Minor comment updates in config files 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: Current local version (their customizations) New Rails default (from railsdiff) 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: Start the Rails server and check for errors: bin/dev

or bin/rails server

Check the Rails console: bin/rails console Run the test suite: bin/rails test Review deprecation warnings in logs Step 10: Finalize Framework Defaults After verifying the app works: Review config/initializers/new_framework_defaults_X_Y.rb Enable each new default one by one, testing after each Once all defaults are enabled and tested, update config/application.rb : config . load_defaults X . Y

Update to new version

Delete the new_framework_defaults_X_Y.rb file When to Use This Skill Analyze Rails apps and provide upgrade assessments Use this skill when working with analyze rails apps and provide upgrade assessments. 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 Never overwrite without checking - Always check for local customizations first Preserve user intent - Local customizations exist for a reason Minimal changes - Only add what's necessary for the new Rails version Transparency - Show the user exactly what will change before doing it Reversibility - User should be able to git checkout to restore if needed