CI Optimization Guide

This document explains the CI optimization strategy implemented for React on Rails.

Overview

The CI pipeline has been optimized to:

1. Skip unnecessary workflows for documentation-only changes
2. Run reduced test matrices on PRs (full matrix only on master)
3. Provide local CI tooling to run appropriate tests before pushing

Optimization Strategies

1. Path-Based Filtering

All workflows now use paths-ignore to skip when only certain files change:

on:
  pull_request:
    paths-ignore:
      - '**.md'
      - 'docs/**'

Benefits:

• Documentation changes don't trigger CI
• Workflows skip when irrelevant files change
• Reduces GitHub Actions minutes usage

2. Change Detection

The main test workflow includes a detect-changes job that:

• Analyzes which files changed
• Determines if tests are needed
• Skips downstream jobs for docs-only changes

Example:

jobs:
  detect-changes:
    runs-on: ubuntu-22.04
    outputs:
      skip_tests: ${{ steps.changes.outputs.skip_tests }}
    steps:
      - name: Detect changes
        # ... analyzes git diff

3. Reduced Test Matrix on PRs

On PRs, we run a reduced test matrix for faster feedback:

Benefits:

• ~75% reduction in CI time for PRs
• Faster feedback for developers
• Full coverage still runs on master before release

Implementation:

matrix:
  ruby-version: ${{ github.ref == 'refs/heads/master' && fromJSON('["3.2", "3.4"]') || fromJSON('["3.4"]') }}
  node-version: ${{ github.ref == 'refs/heads/master' && fromJSON('["20", "22"]') || fromJSON('["22"]') }}

4. Smart Path Filtering per Workflow

Each workflow ignores paths that don't affect its tests:

• JS tests: Skip when only Ruby files change (lib/**, spec/react_on_rails/**)
• Ruby tests: Skip when only JS files change (packages/react-on-rails/src/**)
• All tests: Skip for docs-only changes

Local CI Tools

bin/ci-local - Smart Local CI Runner

Runs appropriate CI checks based on your changes:

# Auto-detect what to test based on changes
bin/ci-local

# Run all CI checks (same as master)
bin/ci-local --all

# Run only fast checks
bin/ci-local --fast

# Compare against specific branch
bin/ci-local origin/develop

Features:

• Analyzes your git diff
• Skips unnecessary tests
• Shows clear success/failure summary
• Provides feedback before pushing

script/ci-changes-detector - Change Analysis Tool

Analyzes which files changed and recommends CI jobs:

# Check changes since master
script/ci-changes-detector origin/master

# Check changes between any refs
script/ci-changes-detector origin/develop HEAD

Output:

=== CI Changes Analysis ===
Changed file categories:
  • Ruby source code
  • JavaScript/TypeScript code

Recommended CI jobs:
  ✓ Lint (Ruby + JS)
  ✓ RSpec gem tests
  ✓ JS unit tests
  ✓ Dummy app integration tests

/run-ci Claude Command

Claude Code command for interactive CI execution:

/run-ci

Claude will:

1. Analyze your changes
2. Show recommended CI jobs
3. Ask which option you prefer
4. Execute and report results

CI Workflow Reference

Workflows and Their Triggers

Expected Time Savings

Before Optimization

• PR with code changes: ~45 minutes (all matrices)
• PR with docs changes: ~45 minutes (unnecessary)
• Total CI time per day: High

After Optimization

• PR with code changes: ~12 minutes (reduced matrix)
• PR with docs changes: 0 minutes (skipped)
• Master merge: ~45 minutes (full matrix)
• Total CI time saved: ~70%

Best Practices

For Developers

1. Run local CI before pushing:

   bin/ci-local

2. Use fast mode for quick checks:

   bin/ci-local --fast

3. Separate doc changes from code changes:

   • Docs-only PRs skip CI entirely
   • Mixed PRs run full CI

4. Trust the PR CI:

   • Reduced matrix is sufficient for most changes
   • Master branch validates full matrix before release

For Maintainers

1. Monitor CI performance:

   • Check GitHub Actions usage
   • Identify slow tests
   • Adjust matrix as needed

2. Update path filters:

   • Add new file patterns as project evolves
   • Keep filters accurate

3. Review master CI failures:

   • Master runs full matrix
   • Catches edge cases not found in PR CI

Troubleshooting

CI not skipping for docs changes

Check if:

• Changes are truly docs-only (use git diff --name-only)
• Path patterns match your files
• Workflow has correct paths-ignore

CI taking too long on PRs

• Ensure you're not on master branch
• Check if matrix reduction is working
• Use bin/ci-local --fast for local testing

Tests pass locally but fail in CI

• Different dependency versions
• Environment differences
• Run bin/ci-local --all to match CI exactly

Future Improvements

Potential further optimizations:

1. Parallel test execution within jobs
2. Smarter caching of dependencies
3. Test splitting for faster execution
4. Conditional job dependencies based on changes
5. Reusable workflows to reduce duplication

Related Files

• script/ci-changes-detector - Change detection script
• bin/ci-local - Local CI runner
• .claude/commands/run-ci.md - Claude command
• .github/workflows/*.yml - All CI workflows