Syntax Error: SassError: This file is already being loaded. With additionalData.

I create a new issue with the repo as recommend in the #908 issue.

• Operating System: macOS 11.2.3 (I think this isn’t important)
• Node Version: v14.15.4
• NPM Version: 6.14.10
• webpack Version: 4.46.0
• sass-loader Version: from 9.0.0

For version less than 9.0.0, which uses prependData, everything works fine.

Expected Behavior

additionalData should work like prependData.

Actual Behavior

additionalData causes compile error.

Code

 error  in ./src/scss/_problem.scss

Syntax Error: SassError: This file is already being loaded.
  ╷
1 │ @import "problem";
  │         ^^^^^^^^^
  ╵
  src/scss/_module.scss 1:9    @import
  src/scss/_problem.scss 2:19  root stylesheet

How Do We Reproduce?

Use this repo.

1. Clone. Run npm i.
2. Run npm run serve.
3. See error in console.

Webpack settings you can find in vue.config.js

[alexander-akait]

You can’t import the same file twice, if you need more information you can look at docs for sass and read about import, other solutions is migrate on @use

[alexander-akait]

You can exclude import for specific file, using:

additionalData: (content, loaderContext) => {
          if (loaderContext.resourcePath.endsWith('src/scss/_problem.scss')) {
            return content;
          }
          
          return `
          @import "~@/scss/_module.scss";
          ${content}
        `;
        }