Turbopack module resolution fails for installed packages in Next.js 16.0.6

Submit this at: https://github.com/vercel/next.js/issues/new

Description

Next.js 16.0.6 with Turbopack fails to resolve react-map-gl and mapbox-gl packages during build, despite the packages being correctly installed in node_modules.

To Reproduce

Environment:

• Next.js: 16.0.6
• react-map-gl: 8.1.0
• mapbox-gl: 3.16.0
• Platform: Vercel deployment (also reproducible locally)

Steps:

1. Install react-map-gl and mapbox-gl via npm
2. Import from react-map-gl/mapbox in a component
3. Run next build

Code:

import Map from 'react-map-gl/mapbox'
import { Marker, NavigationControl } from 'react-map-gl/mapbox'

Expected Behavior

Build should succeed since packages are installed in node_modules.

Actual Behavior

Build fails with:

Error: Turbopack build failed with 1 errors:
./components/intersections/intersection-map.tsx:4:1
Module not found: Can't resolve 'react-map-gl'

Evidence

Packages confirmed installed:

$ npm list react-map-gl mapbox-gl
[email protected]
├── [email protected]
└─┬ [email protected]
  ├─┬ @vis.gl/[email protected]
  │ └── [email protected] deduped
  └── [email protected] deduped

Packages exist in node_modules:

$ ls node_modules | grep -E 'react-map|mapbox'
@mapbox
mapbox-gl
react-map-gl

Yet Turbopack still reports "Module not found".

Attempted Fixes (None Worked)

• ✗ Dynamic imports with ssr: false
• ✗ Adding transpilePackages: ['react-map-gl', 'mapbox-gl']
• ✗ Adding Turbopack resolveAlias config
• ✗ Regenerating package-lock.json from scratch
• ✗ Fresh npm ci install (deleted node_modules)
• ✗ Clearing all Vercel build cache
• ✗ Using different branch names
• ✗ Adding postinstall scripts to force package installation

All attempts showed packages installed but Turbopack couldn't resolve them.

Workaround

Downgrading to Next.js 15.5.7 (which uses webpack) resolves the issue completely with identical code and dependencies.

Additional Context

Build Logs Show Packages Installed

From Vercel build with Next.js 16:

11:24:30.936 added 233 packages, and audited 234 packages in 11s
11:24:30.962 === CHECKING PACKAGES ===
11:24:31.355 [email protected] /vercel/path0
11:24:31.355 ├── [email protected]
11:24:31.356 └─┬ [email protected]
11:24:31.364 @mapbox
11:24:31.364 mapbox-gl
11:24:31.364 react-map-gl
11:24:31.364 === END CHECK ===
[Then Turbopack build fails with "Module not found"]

Import Paths

The package exports these paths correctly:

"exports": {
  "./mapbox": {
    "types": "./dist/mapbox.d.ts",
    "require": "./dist/mapbox.cjs",
    "import": "./dist/mapbox.js"
  },
  "./maplibre": { ... }
}

We're importing from the correct exported path (react-map-gl/mapbox).

Impact

• Blocks using popular map libraries (react-map-gl, mapbox-gl, maplibre-gl) in Next.js 16
• Forces downgrade to Next.js 15 (which triggers security warnings)
• Likely affects other packages with similar export structures

System Info

• OS: macOS (Darwin 25.0.0) and Vercel deployment environment
• Node: v20+ LTS
• Package manager: npm
• Next.js: 16.0.6 (Turbopack) - FAILS
• Next.js: 15.5.7 (webpack) - WORKS

Labels

bug, Turbopack, module-resolution

This issue is blocking production deployment of mapping features in our application.