Accessing a circular dependency early with re-export, an error occurs

Bug report

What is the current behavior?

This is a simplified example:

// src/barrel/a.js
export function a() {}

// src/barrel/b.js
import {a} from "./index";
console.log(a); // expected undefined
export function b() {}

// src/barrel/index.js
export * from "./b";
export * from "./a";

// src/index.js (entry point)
import {b} from "./barrel";
b();

When I run this example, I get an Cannot read property 'a' of undefined error in console.log(a); line of b.js.

What is the expected behavior?

I expect undefined to be printed to log without error.

I know that if I change the export order of index.js or import a.js directly from b.js it works fine. But I expect modules with unresolved circular imports to evaluate to undefined.

If I run the same code with Webpack 4(4.44.2), it prints undefined without error.

Other relevant information: webpack version: 5.10.1 Node.js version: 14.15.1 Operating System: Ubuntu 20.04.1 LTS (WSL) Additional tools: None

[alexander-akait]

Maybe better to stick on webpack@4 in this case

Even if the behavior is not supported, I think it is possible to implement a change to safely evaluate to undefined without throwing an error. (If necessary, I will try to send a PR.)

I think it is very hard/impossible to fix without breaking something other

[genshinw]

In the latest release (i.e. 5.26.2), it is undefined, fixed 😄

I meet the same issue like @HealGaren said when update to webpack@5.68 from webapck@4.46, Is this problem fixed?There was a risk to refactoring the legacy code.