feat(turbopack): add chunkLoadingGlobal config option (#93488)
### What?
Adds a new `chunkLoadingGlobal` option to the `turbopack` config in
`next.config.js` that overrides the global variable name used for
Turbopack chunk loading (defaults to `TURBOPACK`).
```js
// next.config.js
module.exports = {
turbopack: {
chunkLoadingGlobal: 'myApp',
},
}
```
### Why?
When multiple Turbopack-built apps run on the same page (e.g. horizontal
micro-frontends), they each try to use `globalThis.TURBOPACK` which
causes conflicts. This option allows each app to use its own isolated
global, mirroring webpack's `output.chunkLoadingGlobal`.
The `chunk_loading_global` method was already wired into Turbopack in
#88790 — this PR exposes it via Next.js config.
A reason is
[vercel/remote-components#239](https://github.com/vercel/remote-components/pull/239),
which uses this option to eliminate four brittle `globalThis.TURBOPACK`
regex rename transforms in the remote-components runtime. Those
transforms target Turbopack's internal variable naming and have already
required updates as Turbopack's output format evolved. With
`chunkLoadingGlobal` set at build time, Turbopack handles the renaming
natively and those transforms become unnecessary.
### How?
- `config-shared.ts` / `config-schema.ts` — adds `chunkLoadingGlobal?:
string` to `TurbopackOptions` with Zod validation
- `next_config.rs` — adds the field to `TurbopackConfig` and a
`turbopack_chunk_loading_global()` accessor
- `next_client/context.rs` — threads it through
`ClientChunkingContextOptions` and calls
`builder.chunk_loading_global()` when set
- `project.rs` — wires the config into the client chunking context
options
Only applies to the browser/client chunking context — server and edge
runtimes don't have this concept.
### Test plan
- `pnpm test-start-turbo
test/production/app-dir/turbopack-chunk-loading-global/turbopack-chunk-loading-global.test.ts`
<!-- NEXT_JS_LLM_PR -->
---------
Co-authored-by: Niklas Mischkulnig <4586894+mischnic@users.noreply.github.com>
