SassC/Libsass has been deprecated for years and has been replaced by
Dart Sass. However, the dartsass-rails gem, maintained by the Rails
team, doesn't support sprockets integration and doesn't allow glob
imports (using `@import something/**/*` or similar). In particular,
dartsass-rails needs to start a separate browser that makes it less
straightforward to change a file and reload the browser.
So we're using sassc-embedded, which provides Dart Sass integration with
sprockets. While there's no guarantee this gem will be maintained a few
years from now, we know for sure that SassC/Libsass won't be maintained
at all, so using sassc-embedded is an improvement over our current
situation.
On my machine, this change reduces compilation times by about 35%.
Note we still depend on the `sassc-rails` gem, for two reasons.
First, we're still importing CSS/Sass content from a couple of gems
(mainly, social-share-button and font-awesome) and we don't know how to
import this content without the `sassc-rails` gem.
And, second, it provides support for glob imports. Without it, we'd have
to manually add every single (S)CSS file we import to the
`application.scss` file instead of being able to write things like
`@import admin/**/*";`.
Note we're removing the `sass` gem from `Gemfile.lock`. We should have
done it as part of e210682ac, but when we developed that branch, it
didn't contain the changes where we removed another gem depending on the
`sass` gem (which we removed in commit 2fa713c64), so Bundler didn't
delete it. However, now that we're changing the Gemfile, Bundler is
finally removing the no-longer-needed `sass` gem and its dependencies.
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