Webpack 5: weback.config.js doesn't seem to support a function that returns a config array anymore

[eamodio]

Bug report

What is the current behavior?

See my current webpack.config.js: https://github.com/eamodio/vscode-gitlens/blob/2bfc0360b46933f715379016aed4084ad4e75fae/webpack.config.js

It works fine in Webpack 4, but results in

Compilation Results

 Version: 5.0.0-beta.22
 Built: Sun Jul 26 2020 00:41:05 GMT-0400 (Eastern Daylight Time)
 Compile Time: 36ms
 Output Directory: C:\Users\Eric\code\eamodio\vscode-gitlens\dist
 Hash: dbd0e35abb9cf7150b07

┌────────────┬───────────────────────────────┐
│ Entrypoint │ Bundle                        │
├────────────┼───────────────────────────────┤
│ main       │  Bundle Name       │ main.js  │
│            │  Compared For Emit │ false    │
│            │  Bundle size       │ 0.64 kb  │
│            │                               │
│            │ Modules:                      │
│            │                               │
└────────────┴───────────────────────────────┘

[webpack-cli] Module not found: Error: Can't resolve './index.js' in 'C:\Users\Eric\code\eamodio\vscode-gitlens'

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

Using this branch: https://github.com/eamodio/vscode-gitlens/commits/feature/webpack5

1. Clone
2. Run yarn
3. Run yarn build

What is the expected behavior?

It should generate multiple bundles.

Other relevant information:
webpack version: 5.0.0-beta.22
Node.js version: v12.16.2
Operating System: Window 10
Additional tools:

[alexander-akait]

/cc @webpack/cli-team Can we add tests (or we already have tests)?

[anshumanv]

I'll take a look

[anshumanv]

webpack-cli/packages/webpack-cli/lib/groups/ConfigGroup.js

Line 99 in f1876c1

const newOptions = configOptions(this.args.env);

@evilebottnawi first thing I noticed is that we aren't passing the 2nd param argv to the config function, need to support that too, will check