Webpack upgrade breaks TypeScript interface exports

[rodogir]

Bug report

Describe the bug

TypeScript interfaces and type aliases that are exported in an object break the dev and prod build. The build will fail with a Module parse failed: Export 'XYZ' is not defined message.

To clarify what I mean with object export, here is a small example:

interface MyInterface {};
export { MyInterface };

This used to work fine in Next 7. The bug was probably introduced in https://github.com/zeit/next.js/releases/tag/v8.0.0-canary.12. Version v8.0.0-canary.11 does not have this problem.

To Reproduce

1. Setup https://github.com/zeit/next.js/tree/canary/examples/with-typescript
2. Make sure it runs correctly
3. Open any component (e.g. components/List.tsx)
4. Add export { Props }; to the last line
5. The build breaks

System information

• OS: Windows 10
• Version of Next.js: 8.0.3

[toshi1127]

@timneutkens
I could confirm that it would work by canceling #6114.
How should I fix it ...?

[rodogir]

I did some further research after this problem also started appearing in fresh Next.js 7 and non-next builds. It seems that this is bug in babel:
See: babel/babel#9766 and babel/babel#9763.