__webpack_require__(null) when using manual splitChunks, concatenateModules

[Knagis]

Bug report

What is the current behavior?

This might be closely related to #11770.

// EXTERNAL MODULE: ./packages/path/SomeModule.ts
var SomeModule = __webpack_require__(null);

obviously moduleId null does not work... This module is one that is extracted into a common chunk as part of concatenated module with some ID like 784404 - an ID that is not referenced anywhere at all.

If the current behavior is a bug, please provide the steps to reproduce.

Reproduces in our huge monorepo, so far no luck in creating a small reproduction. Even in our repo, building just the parts affected do not reproduce it, only building everything (~40 entries) produces the error.

Some notes:

• reproduces in production mode
• building with devTool: false.
• setting innerGraph: false does not affect the issue.
• setting concatenateModules: false "fixes" the issue
• setting usedExports: "global" also "fixes" the issue

What is the expected behavior?

Correctly generated chunks with no missing modules.

Btw, moduleId: null if it does happen, should perhaps throw during build since it will never work at runtime.

Other relevant information:
webpack version: 5.3.0
Node.js version: 12.13.1
Operating System: any
Additional tools:

[Knagis]

usedExports: "global" also prevents the issue

[sokra]

Hmm yes that really sounds related to that. To me it sounds like a bug in the module concatenation, especially the algorithm that selects which modules are concatenated. Probably related to the runtime filtering. I have one idea which I can try to figure out how to reproduce it (note to myself: entry A -> c -> d, entry B -> d, c and d force to chunk, c + d concatenated, maybe c -> d conditional).

[sokra]

Ok I found something. Looks really like your issue. I'm pretty sure #11861 fixes your issue, but it would be great if you could test it in your codebase.

"webpack": "webpack/webpack#bugfix/11856

[Knagis]

Yes, just tested and this issue is fixed in the branch.

[YikaJ]

webpack@5.31.0 still get this problem

concatenateModules: false can fix it。

@Knagis @sokra Could you reopen this issue?

[paradite]

same issue here with webpack@5.31.2. We are doing a re-export of modules if that helps.

---

Update: it turns out from webpack/webpack.js.org#4837 the solution is to just remove new webpack.optimize.ModuleConcatenationPlugin(), which solved the error for me.

[zdila]

I've just migrated our project from webpack 4 to webpack 5 and also experience this issue. Referenced null module is not instructed to be a chunk. It constains a single object that is default-exported:

export default {
   // some properties
}

Removing new webpack.optimize.ModuleConcatenationPlugin() fixed the problem.