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Hendrik LiebauandGitHub
d2e6b6c0e4
When SSR fails in development — whether the failing page is in the App Router or the Pages Router — Next.js falls back to rendering the Pages Router `/_error` page and serializes the original error into `__NEXT_DATA__.err`. The client bootstrap in `packages/next/src/client/ index.tsx` later re-throws a fresh `new Error(initialErr.message)` so that the dev overlay picks it up. The error-code SWC plugin stamps that new `Error` with the generic code mapped to `%s` in `errors.json` because the message argument is an identifier, not a statically-known string, which is how the overlay ended up showing the wrong code for errors like `UseCacheTimeoutError`. The pipeline has two problems on the way to the overlay. First, `errorToJSON` in `packages/next/src/server/render.tsx` only copies the error's standard fields (`name`, `source`, `message`, `stack`, `digest`) into `__NEXT_DATA__.err`, so the real `__NEXT_ERROR_CODE` attached to the thrown error never reaches the client. Second, the subsequent rewrap in `getServerError` at `packages/next/src/server/dev/node-stack- frames.ts` creates yet another `new Error(...)` that the plugin stamps with the same generic code, clobbering anything the caller might have set on the rewrapped instance. This change plumbs the code through. `errorToJSON` now also emits `__NEXT_ERROR_CODE` using `extractNextErrorCode` so the value survives JSON serialization into `__NEXT_DATA__.err`; the type in `packages/next/src/shared/lib/utils.ts` is updated to match. Both rewrap sites — the client bootstrap and `getServerError` — copy the code from the source error onto the fresh `Error` via `Object.defineProperty` with `enumerable: false` and `configurable: true`, matching how the plugin itself stores the property, which overrides the generic code the plugin stamped on the rewrapped instance. The `use-cache-hanging` e2e test snapshot is updated from `E394` to `E236` now that the real code surfaces in the dev overlay.