experiments.css cannot be disabled when experiments.futureDefaults is enabled

[jdanil]

Bug report

What is the current behavior?

When experiements.futureDefaults is enabled but experiments.css is disabled, webpack fails with the following error.

Error: Conflict: Multiple chunks emit assets to the same filename main.css

I believe this behaviour was introduced in 5.67.0 via (#15200). Specifically...

webpack/lib/config/normalization.js

Line 185 in 1489b91

options === true ? {} : options === false ? undefined : options

When experiments.css is set to false, its value is normalised as undefined. So the experiments.futureDefaults value is used in its place here...

webpack/lib/config/defaults.js

Line 164 in 1489b91

applyExperimentsDefaults(options.experiments, {

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

webpack.config.js

{
  experiments: {
    css: false,
    futureDefaults: true,
  },
}

What is the expected behavior?

webpack should build successfully with experiments.css disabled.

I would like to be able to enable experiments.futureDefaults so that I can ensure compatibility with the next major webpack version. But for some experiments, like experiments.css, I would like to be able opt-out for now until I better understand the upgrade path.

Other relevant information:
webpack version: 5.72.0
Node.js version: 16.14.2
Operating System: Ubuntu

[alexander-akait]

Thanks for a report, feel free to send a fix

[sokra]

You can opt-out of that by changing the default module type for .css files to something else.

e. g. in your rule with test: /\.css$/i set type: "javascript/auto"