stack/packages/mosaic/framework/skills/pnpm/references/best-practices-migration.md

name, description

name	description
migration-to-pnpm	Migrating from npm or Yarn to pnpm with minimal friction

Migration to pnpm

Guide for migrating existing projects from npm or Yarn to pnpm.

Quick Migration

From npm

# Remove npm lockfile and node_modules
rm -rf node_modules package-lock.json

# Install with pnpm
pnpm install

From Yarn

# Remove yarn lockfile and node_modules
rm -rf node_modules yarn.lock

# Install with pnpm
pnpm install

Import Existing Lockfile

pnpm can import existing lockfiles:

# Import from npm or yarn lockfile
pnpm import

# This creates pnpm-lock.yaml from:
# - package-lock.json (npm)
# - yarn.lock (yarn)
# - npm-shrinkwrap.json (npm)

Handling Common Issues

Phantom Dependencies

pnpm is strict about dependencies. If code imports a package not in package.json, it will fail.

Problem:

// Works with npm (hoisted), fails with pnpm
import lodash from 'lodash'; // Not in dependencies, installed by another package

Solution: Add missing dependencies explicitly:

pnpm add lodash

Missing Peer Dependencies

pnpm reports peer dependency issues by default.

Option 1: Let pnpm auto-install:

# .npmrc (default in pnpm v8+)
auto-install-peers=true

Option 2: Install manually:

pnpm add react react-dom

Option 3: Suppress warnings if acceptable:

{
  "pnpm": {
    "peerDependencyRules": {
      "ignoreMissing": ["react"]
    }
  }
}

Symlink Issues

Some tools don't work with symlinks. Use hoisted mode:

# .npmrc
node-linker=hoisted

Or hoist specific packages:

public-hoist-pattern[]=*eslint*
public-hoist-pattern[]=*babel*

Native Module Rebuilds

If native modules fail, try:

# Rebuild all native modules
pnpm rebuild

# Or reinstall
rm -rf node_modules
pnpm install

Monorepo Migration

From npm Workspaces

1. Create pnpm-workspace.yaml:

   packages:
     - 'packages/*'
   

2. Update internal dependencies to use workspace protocol:

   {
     "dependencies": {
       "@myorg/utils": "workspace:^"
     }
   }
   

3. Install:

   rm -rf node_modules packages/*/node_modules package-lock.json
   pnpm install
   

From Yarn Workspaces

1. Remove Yarn-specific files:

   rm yarn.lock .yarnrc.yml
   rm -rf .yarn
   

2. Create pnpm-workspace.yaml matching workspaces in package.json:

   packages:
     - 'packages/*'
   

3. Update package.json - remove Yarn workspace config if not needed:

   {
     // Remove "workspaces" field (optional, pnpm uses pnpm-workspace.yaml)
   }
   

4. Convert workspace references:

   // From Yarn
   "@myorg/utils": "*"
   
   // To pnpm
   "@myorg/utils": "workspace:*"
   

From Lerna

pnpm can replace Lerna for most use cases:

# Lerna: run script in all packages
lerna run build

# pnpm equivalent
pnpm -r run build

# Lerna: run in specific package
lerna run build --scope=@myorg/app

# pnpm equivalent
pnpm --filter @myorg/app run build

# Lerna: publish
lerna publish

# pnpm: use changesets instead
pnpm add -Dw @changesets/cli
pnpm changeset
pnpm changeset version
pnpm publish -r

Configuration Migration

.npmrc Settings

Most npm/Yarn settings work in pnpm's .npmrc:

# Registry settings (same as npm)
registry=https://registry.npmjs.org/
@myorg:registry=https://npm.myorg.com/

# Auth tokens (same as npm)
//registry.npmjs.org/:_authToken=${NPM_TOKEN}

# pnpm-specific additions
auto-install-peers=true
strict-peer-dependencies=false

Scripts Migration

Most scripts work unchanged. Update pnpm-specific patterns:

{
  "scripts": {
    // npm: recursive scripts
    "build:all": "npm run build --workspaces",
    // pnpm: use -r flag
    "build:all": "pnpm -r run build",

    // npm: run in specific workspace
    "dev:app": "npm run dev -w packages/app",
    // pnpm: use --filter
    "dev:app": "pnpm --filter @myorg/app run dev"
  }
}

CI/CD Migration

Update CI configuration:

# Before (npm)
- run: npm ci

# After (pnpm)
- uses: pnpm/action-setup@v4
- run: pnpm install --frozen-lockfile

Add to package.json for Corepack:

{
  "packageManager": "[email protected]"
}

Gradual Migration

For large projects, migrate gradually:

1. Start with CI: Use pnpm in CI, keep npm/yarn locally
2. Add pnpm-lock.yaml: Run pnpm import to create lockfile
3. Test thoroughly: Ensure builds work with pnpm
4. Update documentation: Update README, CONTRIBUTING
5. Remove old files: Delete old lockfiles after team adoption

Rollback Plan

If migration causes issues:

# Remove pnpm files
rm -rf node_modules pnpm-lock.yaml pnpm-workspace.yaml

# Restore npm
npm install

# Or restore Yarn
yarn install

Keep old lockfile in git history for easy rollback.