css-loader produces invalid es5 code

[timocov]

• Operating System: windows 10
• Node Version: 12.4
• NPM Version: 6.13.4
• webpack Version: 4.41.5
• css-loader Version: 3.4.0

Expected Behavior

No JS code produced.

Actual Behavior

css-loader produces

// Exports
module.exports = {
undefined
};

what is incorrect es5 code (also I don't think that having exported undefined key with undefined value is good here).

Code

I'll fill code later if it's really needed, but just looking into the code you're able to see difference between 3.3 and 3.4 versions.

Just look at https://github.com/webpack-contrib/css-loader/blob/v3.3.2/src/utils.js#L387-L389 and https://github.com/webpack-contrib/css-loader/blob/v3.4.0/src/utils.js#L417-L479. Previously (in 3.3.2) if exports length is 0 then it returns empty string. Now it doesn't check it and after if (exports.length > 0) { variable exportLocalsCode is undefined so that's why it produces incorrect output.

How Do We Reproduce?

I don't have working example right now, but it looks like that it fails if css module exports nothing (e.g. :global expression only).

[timocov]

Broken in 23bc1e9.

[alexander-akait]

Can you create reproducible test repo?

[alexander-akait]

Looks like bug, agree

[timocov]

I'll try. It isn't so easy to extract repro from huge project :)

[alexander-akait]

Reproduced, WIP