Allow specifying Dart Sass implementation

[christopher-francisco]

Description

For cases where you're not able to completely remove node-sass, causing sass-loader to pick it up, you can now explicitly specify you want to use Dart Sass through USE_DART_SASS=true env variable. See #9628 for the complete use case

Testing strategy

Manually tested it by doing the following

1. Created a new app with yarn create-react-app my-app
2. Added a few sass files with @use directive (only supported by Dart Sass)
3. Added sass dependnecy
4. Ran yarn start. Comiplation succeeded
5. Added node-sass dependency (we now have both)
6. Ran yarn start. Compilation failed
7. Ran USE_DART_SASS=true yarn start. Comiplation succeeded

Screenshot

You can see both sass and node-sass installed at the bottom right corner. App started with USE_DART_SASS=true yarn start

What's Missing?

• Find a way to automate a test similar to the one described above
• Updating documentation

Closes #9629

[facebook-github-bot]

Hi @christopher-francisco!

Thank you for your pull request and welcome to our community. We require contributors to sign our Contributor License Agreement, and we don't seem to have you on file.

In order for us to review and merge your code, please sign at https://code.facebook.com/cla. If you are contributing on behalf of someone else (eg your employer), the individual CLA may not be sufficient and your employer may need to sign the corporate CLA.

If you have received this in error or have any questions, please contact us at cla@fb.com. Thanks!

[just-boris]

Is there a chance to make it default in version 4.0 which is coming soon?

Dart-sass (or just sass, since it is transpiled to pure JS anyway) supports more features and should be used whenever you need sass, except some exotic use-cases.

[stale]

This pull request has been automatically marked as stale because it has not had any recent activity. It will be closed in 5 days if no further activity occurs.

[just-boris]

node-sass is deprecated, so this feature needs to be added, to allow consumers specifying the supported version of sass

[stale]

This pull request has been automatically marked as stale because it has not had any recent activity. It will be closed in 5 days if no further activity occurs.

[just-boris]

This is not stale