[Bug] webpackImporter:true (default) loses path context on Windows when resolving SCSS imports inside node_modules

[anarefolio]

Bug description

On Windows (native, no WSL), when webpackImporter is true (the default),
sass-loader fails to resolve relative SCSS imports inside node_modules packages.

The same code works perfectly on Linux/macOS.

To Reproduce

1. Windows 10/11, Node.js 24, native (no WSL)
2. Have a SCSS file that imports from a package which has internal relative imports:

// your file
@import '@primer/css/color-modes/index.scss';

// inside node_modules/@primer/css/color-modes/index.scss
@import './themes/light.scss'; // FAILS on Windows

Error

Error: Can't find stylesheet to import.
@import './themes/light.scss'
node_modules@primer\css\color-modes\index.scss

Root cause

With webpackImporter: true, webpack's resolver handles all imports. On Windows,
webpack's resolver loses the working directory context when processing relative
imports inside node_modules packages, causing them to fail.

Fix

Setting webpackImporter: false and using modern-compiler API with loadPaths: ['node_modules'] resolves the issue — sass uses its own native resolver which handles Windows paths correctly.

This was confirmed and documented in:

• fix: resolve Windows native SCSS import failures in dev server github/docs#44118
• [Bug] Windows: sass-loader fails to resolve SCSS imports from node_modules in webpack mode (not Turbopack) vercel/next.js#93583

Suggested fix

Consider defaulting to modern-compiler API when dart-sass is detected,
or documenting that Windows users need webpackImporter: false.

Environment

• OS: Windows 11, x64
• Node: 24.15.0
• sass-loader: (bundled in next@16.2.3)
• sass: 1.97.3

[alexander-akait]

Hello, can you create reproducible test repo? I can't reproduce, thanks

[anarefolio]

sass-repro-next.zip

Hi Alexander, I managed to reproduce the issue on Windows 11.
Interestingly, a raw Webpack setup worked fine, but the bug triggers consistently when using Next.js (which uses a compiled version of sass-loader).
Reproduction Steps:
Unzip the attached sass-repro-next.zip
Run npm install
Run npm run dev
The terminal will show: Error: Can't find stylesheet to import. @import './themes/light.scss'
It seems the path context is being lost specifically when resolving relative imports inside node_modules on Windows. I've attached the minimal Next.js repo below.