__esModule property missing when dynamic module is concatenated

[Bobgy]

Bug report

What is the current behavior?
Some libraries depend on an exported module to have __esModule === true for understanding the export is an es module.

However, module concatenation doesn't work with this behavior that it doesn't have the __esModule property.

If the current behavior is a bug, please provide the steps to reproduce.
see the repo: https://github.com/Bobgy/webpack-concat-esmodule-bug-reproduction

What is the expected behavior?

regardless of a module is concatenated or not, it should have module.exports.__esModule === true

Other relevant information:
webpack version: 4.29.0
Node.js version: 8.12
Operating System: Ubuntu 18.04
Additional tools:

[Bobgy]

I'm not fully sure if this behavior is intended or not. Just tested this and it seems the behavior is the same from webpack 4.0

[sokra]

Yep, seem to be a bug..

[Bobgy]

Awesome, thank you for the quick fix!