fix: global-error for dynamic routes

What?

Based on similar issues, I decided to investigate why I encountered the same problem with the global-error.tsx file when the root layout.tsx thrown an error.

Initially, I suspected that the i18n library (next-intl) I used in my main project was the cause. However, I later realized that the problem lies in dynamic routes.

Why?

Many users, including myself, find it unintuitive from the official documentation about i18n and the example on github.com that the global-error.tsx file should be placed in the root of the app/ directory instead of app/[lang]/. The documentation and example do not cover this detail, which leads users to place global-error.tsx in app/[lang]/. As a result, when global-error.tsx cannot catch errors in root layout.tsx, users report this as a new issue on Next.js's GitHub, as seen in the related issues linked above.

How?

My bug fix allows the global-error.tsx file to be placed not only in the root of app/ but also in app/[lang]/. This fix eliminates the need to update the documentation to specify where the global-error.tsx file should be placed or to change the example on github.com to clarify this point.

p.s. you can use any dynamic route for your i18n Next.js applications; lang is just an example as shown in the official documentation.

Fixes #66905

vercel / next.js