improve Node.js package manager detection

[josefaidt]

Is this feature request related to a new or existing Amplify category?

No response

Is this related to another service?

No response

Describe the feature you'd like to request

Improve detection of the developer's chosen Node.js package manager, which applies to the following workflows:

• auto-installing Node.js Function dependencies on build/push
• auto-installing dependencies in the Sandbox workflow

examples:

• Next.js is looking at process.env.npm_config_user_agent https://github.com/vercel/next.js/blob/canary/packages/create-next-app/helpers/get-pkg-manager.ts
• Vite is looking at process.env.npm_config_user_agent https://github.com/vitejs/vite/blob/main/packages/create-vite/src/index.ts#L312
• https://www.npmjs.com/package/preferred-pm
• Astro is using a package, https://www.npmjs.com/package/which-pm-runs

Describe the solution you'd like

Amplify CLI automatically detects the package manager of choice for JavaScript projects

// https://github.com/vercel/next.js/blob/canary/packages/create-next-app/helpers/get-pkg-manager.ts
export type PackageManager = 'npm' | 'pnpm' | 'yarn'

export function getPkgManager(): PackageManager {
  const userAgent = process.env.npm_config_user_agent

  if (userAgent) {
    if (userAgent.startsWith('yarn')) {
      return 'yarn'
    } else if (userAgent.startsWith('pnpm')) {
      return 'pnpm'
    } else {
      return 'npm'
    }
  } else {
    return 'npm'
  }
}

Describe alternatives you've considered

n/a

Additional context

• Support PNPM and Others #6382
• Option to not install function node_modules on push #4830
• Using yarn instead of npm to install function's dependencies #6035
• Support Yarn 2+ in lambda build with Amplify CLI #9726

Is this something that you'd be interested in working on?

• 👋 I may be able to implement this feature request

Would this feature include a breaking change?

• ⚠️ This feature might incur a breaking change

[danrivett]

I've submitted a PR (#14628) that partially addresses this by adding detection of the packageManager field in package.json (the corepack convention). The fix walks up the directory tree to find a packageManager field, mimicking corepack's own behavior, and gives it precedence over lock file / executable detection. This resolves the issue for pnpm/yarn monorepos using corepack.