Monorepo Management

# Monorepo Management

Build efficient, scalable monorepos that enable code sharing, consistent tooling, and atomic changes across multiple packages and applications.

## When to Use This Skill

- Setting up new monorepo projects
- Migrating from multi-repo to monorepo
- Optimizing build and test performance
- Managing shared dependencies
- Implementing code sharing strategies
- Setting up CI/CD for monorepos
- Versioning and publishing packages
- Debugging monorepo-specific issues

## Core Concepts

### 1. Why Monorepos?

**Advantages:**

- Shared code and dependencies
- Atomic commits across projects
- Consistent tooling and standards
- Easier refactoring
- Simplified dependency management
- Better code visibility

**Challenges:**

- Build performance at scale
- CI/CD complexity
- Access control
- Large Git repository

### 2. Monorepo Tools

**Package Managers:**

- pnpm workspaces (recommended)
- npm workspaces
- Yarn workspaces

**Build Systems:**

- Turborepo (recommended for most)
- Nx (feature-rich, complex)
- Lerna (older, maintenance mode)

## Turborepo Setup

### Initial Setup

```bash
# Create new monorepo
npx create-turbo@latest my-monorepo
cd my-monorepo

# Structure:
# apps/
#   web/          - Next.js app
#   docs/         - Documentation site
# packages/
#   ui/           - Shared UI components
#   config/       - Shared configurations
#   tsconfig/     - Shared TypeScript configs
# turbo.json      - Turborepo configuration
# package.json    - Root package.json
```

### Configuration

```json
// turbo.json
{
  "$schema": "https://turbo.build/schema.json",
  "globalDependencies": ["**/.env.*local"],
  "pipeline": {
    "build": {
      "dependsOn": ["^build"],
      "outputs": ["dist/**", ".next/**", "!.next/cache/**"]
    },
    "test": {
      "dependsOn": ["build"],
      "outputs": ["coverage/**"]
    },
    "lint": {
      "outputs": []
    },
    "dev": {
      "cache": false,
      "persistent": true
    },
    "type-check": {
      "dependsOn": ["^build"],
      "outputs": []
    }
  }
}
```

```json
// package.json (root)
{
  "name": "my-monorepo",
  "private": true,
  "workspaces": ["apps/*", "packages/*"],
  "scripts": {
    "build": "turbo run build",
    "dev": "turbo run dev",
    "test": "turbo run test",
    "lint": "turbo run lint",
    "format": "prettier --write \"**/*.{ts,tsx,md}\"",
    "clean": "turbo run clean && rm -rf node_modules"
  },
  "devDependencies": {
    "turbo": "^1.10.0",
    "prettier": "^3.0.0",
    "typescript": "^5.0.0"
  },
  "packageManager": "pnpm@8.0.0"
}
```

### Package Structure

```json
// packages/ui/package.json
{
  "name": "@repo/ui",
  "version": "0.0.0",
  "private": true,
  "main": "./dist/index.js",
  "types": "./dist/index.d.ts",
  "exports": {
    ".": {
      "import": "./dist/index.js",
      "types": "./dist/index.d.ts"
    },
    "./button": {
      "import": "./dist/button.js",
      "types": "./dist/button.d.ts"
    }
  },
  "scripts": {
    "build": "tsup src/index.ts --format esm,cjs --dts",
    "dev": "tsup src/index.ts --format esm,cjs --dts --watch",
    "lint": "eslint src/",
    "type-check": "tsc --noEmit"
  },
  "devDependencies": {
    "@repo/tsconfig": "workspace:*",
    "tsup": "^7.0.0",
    "typescript": "^5.0.0"
  },
  "dependencies": {
    "react": "^18.2.0"
  }
}
```

## Detailed patterns and worked examples

Detailed pattern documentation lives in `references/details.md`. Read that file when the navigation tier above is insufficient.

## Best Practices

1. **Consistent Versioning**: Lock dependency versions across workspace
2. **Shared Configs**: Centralize ESLint, TypeScript, Prettier configs
3. **Dependency Graph**: Keep it acyclic, avoid circular dependencies
4. **Cache Effectively**: Configure inputs/outputs correctly
5. **Type Safety**: Share types between frontend/backend
6. **Testing Strategy**: Unit tests in packages, E2E in apps
7. **Documentation**: README in each package
8. **Release Strategy**: Use changesets for versioning

## Common Pitfalls

- **Circular Dependencies**: A depends on B, B depends on A
- **Phantom Dependencies**: Using deps not in package.json
- **Incorrect Cache Inputs**: Missing files in Turborepo inputs
- **Over-Sharing**: Sharing code that should be separate
- **Under-Sharing**: Duplicating code across packages
- **Large Monorepos**: Without proper tooling, builds slow down

## Publishing Packages

```bash
# Using Changesets
pnpm add -Dw @changesets/cli
pnpm changeset init

# Create changeset
pnpm changeset

# Version packages
pnpm changeset version

# Publish
pnpm changeset publish
```

```yaml
# .github/workflows/release.yml
- name: Create Release Pull Request or Publish
  uses: changesets/action@v1
  with:
    publish: pnpm release
  env:
    GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
    NPM_TOKEN: ${{ secrets.NPM_TOKEN }}
```