[react-scripts 3.4.0] SCSS file with import statement cause resolve-url-loader: CSS error

Created by: simoneb

Describe the bug

After upgrading from react-scripts 3.2.0 to 3.4.0 in a project which imports a simple SCSS file with an @import statement, running yarn build consistently fails with:

$ react-scripts build
Creating an optimized production build...
Failed to compile.

./src/index.scss
Error: resolve-url-loader: CSS error
  Invalid mapping: {"generated":{"line":1,"column":63},"source":"file:///home/circleci/project/src/index.scss","original":{"column":null},"name":null}

Steps to reproduce

Here's a very simple repro created by:

• npx create-react-app
• yarn add node-sass
• create a index.scss file containing @import url("https://fonts.googleapis.com/css?family=Open+Sans");
• import index.scss from App.js

Links

• Repro url: https://github.com/simoneb/cra-3.4.0-sass-repro
• CircleCI build showing the build error: https://app.circleci.com/jobs/github/simoneb/cra-3.4.0-sass-repro/1