David Alexandru Ilie ba9f073cc2 Add a Turbopack error for missing root layouts (#97639) ...

## Summary

Turbopack currently builds an App Router page without a root layout,
leaving the problem to surface later at runtime. Report it while
building the app structure instead:

`route/page.js doesn't have a root layout. To fix this error, make sure
every page has a root layout.`

The check uses the layouts already inherited during directory-tree
traversal, so route groups and apps with multiple root layouts keep
working. Route handlers are unaffected.

Webpack behavior is intentionally unchanged in this PR.

## Verification

- `HEADLESS=true pnpm test-dev-turbo
test/e2e/app-dir/create-root-layout/create-root-layout.test.ts`
- `HEADLESS=true pnpm test-start-turbo
test/e2e/app-dir/create-root-layout/create-root-layout.test.ts`
- `HEADLESS=true pnpm test-dev-webpack
test/e2e/app-dir/create-root-layout/create-root-layout.test.ts`
- `HEADLESS=true pnpm test-start-webpack
test/e2e/app-dir/create-root-layout/create-root-layout.test.ts`
- `HEADLESS=true pnpm test-dev-turbo
test/e2e/app-dir/root-layout/root-layout.test.ts`

2026-08-21 15:07:42 +01:00

..

app/route

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app-find-available-dir/(group)/route

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app-group-layout/(group)

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create-root-layout.test.ts

Add a Turbopack error for missing root layouts (#97639)

2026-08-21 15:07:42 +01:00

next.config.js

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