ModuleConcatenationPlugin is setting modules[].reasons[].moduleId to null in some cases

[joeljeske]

Bug report

What is the current behavior?

It would appear that when using ModuleConcatenationPlugin (which is default for mode = production), that the modules that it concatenated do not properly have module ids in the output stats. More specifically, if a reason for given module is from a module that has been concatenated, then the moduleId of that reason is null. I would not expect that to be the case.

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

Reproduction Project:
https://github.com/joeljeske/webpack-module-concatenation-plugin-issue

What is the expected behavior?

Every reason for module should have a moduleId that corresponds with the id of a module

Other relevant information:
webpack version: 4.19.1
Node.js version: v8.11.3
Operating System: MacOS 10.13.4
Additional tools: N/A

[sokra]

Concatenated modules don't have ids. All modules have identifiers.

[joeljeske]

How would you recommend that I traverse the dependency tree using the stats? Is there any way to do this?

[sokra]

You can use moduleIdentifier and identifier. This is always set and unique.

Best build a Map<string, Module> with identifer as key.

[alexander-akait]

Answer above