[bug] support for `next.config.ts`

[mehdibha]

To Reproduce

When i've switch to next.config.ts, i had this error:

> www@0.1.0 dev C:\Users\mehdi\OneDrive\Bureau\dotUI\www
> next dev --turbo

node:internal/errors:497
    ErrorCaptureStackTrace(err);
    ^

Error: Package subpath './next' is not defined by "exports" in C:\Users\mehdi\OneDrive\Bureau\dotUI\www\node_modules\fumadocs-mdx\package.json
    at new NodeError (node:internal/errors:406:5)
    at exportsNotFound (node:internal/modules/esm/resolve:268:10)
    at packageExportsResolve (node:internal/modules/esm/resolve:542:13)
    at resolveExports (node:internal/modules/cjs/loader:547:36)  
    at Module._findPath (node:internal/modules/cjs/loader:621:31)
    at Module._resolveFilename (node:internal/modules/cjs/loader:1034:27)
    at C:\Users\mehdi\OneDrive\Bureau\dotUI\node_modules\.pnpm\next@15.0.3_react-dom@19.0.0-rc-66855b96-20241106_react@19.0.0-rc-66855b96-20241106__react@19.0.0-rc-66855b96-20241106\node_modules\next\dist\server\require-hook.js:55:36
    at Module._load (node:internal/modules/cjs/loader:901:27)    
    at Module.require (node:internal/modules/cjs/loader:1115:19) 
    at mod.require (C:\Users\mehdi\OneDrive\Bureau\dotUI\node_modules\.pnpm\next@15.0.3_react-dom@19.0.0-rc-66855b96-20241106_react@19.0.0-rc-66855b96-20241106__react@19.0.0-rc-66855b96-20241106\node_modules\next\dist\server\require-hook.js:65:28) {
  code: 'ERR_PACKAGE_PATH_NOT_EXPORTED'
}

Node.js v20.9.0

Current vs. Expected behavior

The project should start correctly when running development server.

Provide environment information

Node.js 20.9
Next.js 15.0.3

Which area(s) are affected? (Select all that apply)

Content Sources (e.g. Fumadocs MDX, Content Collections)

Additional context

No response

[fuma-nama]

You can try to rename it to next.config.mts

I remember Next.js doesn't support mts extensions, causing ESM packages to have problems so you still need to use mjs. Not sure if it's supported now.