Impossible to correctly use Turborepo with prebuilt option

Help
1

Current Behavior: I am deploying a Next.js monorepo using Turborepo. I need to run the build from inside the app directory (frontend/)so that Turbo can correctly hash the local Vercel environment files located in apps/frontend/.vercel/.env.*.local.
However, when I run vercel build from inside the frontend directory, Vercel appends the Project Setting “Root Directory” to the current path, resulting in a duplicate path error: Error: ENOENT: no such file or directory, lstat ‘…/Repo/frontend/frontend/.next/routes-manifest.json’
Expected Behavior: When running vercel build from the directory configured as the “Root Directory”, Vercel should detect that the context is already correct and look for artifacts in ./.next instead of appending the path again.
Code, configuration, and steps that reproduce this issue

  1. Directory Structure:
    / (Monorepo Root)
    ├── turbo.json
    ├
    │ └── frontend/ (Configured as “Root Directory” in Vercel)
    │ ├── next.config.js (Standard, no distDir override)
    │ ├── .vercel/ (Contains .env.preview.local needed for Turbo inputs)
    │ └── package.json
  2. turbo.json (Why I need to be in the folder): My build task relies on hashing the specific Vercel env files local to the app.
    JSON
    {
    “tasks”: {
    “build”: {
    “inputs”: [
    “$TURBO_DEFAULT$”,
    “.vercel/.env.preview.local”,
    “.vercel/.env.production.local”
    ],
    “outputs”: [“.next/", "!.next/cache/”]
    }
    }
    }
  3. Steps to Reproduce:
    cd frontend
    npx vercel pull (Downloads env vars to frontend/.vercel)
    npx vercel build
    Result: Build succeeds via Turbo, but Vercel CLI fails to find the output because it looks in frontend/frontend/.next.
  4. What I’ve tried:
    Running from Root: This fixes the path error, but Turbo fails to hash the environment files because they are nested inside frontend/.vercel and the root context doesn’t see them as inputs correctly.
    Setting rootDirectory: null in project.json: Vercel forces the paths frontend/frontend/.next. If I set rootDirectory: test, it will be the correct path frontend/test
    Project information
    Framework: Next.js
    Build Tool: Turborepo
    Environment: Vercel CLI (Local Build)
    Project Settings:
    Framework Preset: Next.js
    Root Directory: frontend
    Output Directory: Default (Empty)
    Build Command: cd ../.. && npx turbo run build --filter=frontend

I run the turbo build command from the monorepo’s root folder

5

Hey, @polo4096! Welcome to the Vercel Community :waving_hand:

It seems that th problem is that Vercel CLI is appending your configured “Root Directory” (frontend) to your current working directory, resulting in frontend/frontend/.next instead of just frontend/.next.

Could you try running vercel build from the monorepo root?

Instead of cd frontend && npx vercel build, try:

npx vercel build --cwd=frontend

Or configure this in vercel.json:

{
  "buildCommand": "cd ../.. && npx turbo run build --filter=frontend",
  "outputDirectory": "frontend/.next"
}