Sometimes, you may still run into this error when you start the Rails server in development or run assets:precompile (while deploying to a server, for instance):
cannot load such file -- sassc /tmp/build/vendor/bundle/ruby/3.1.2/gems/bootsnap-1.13.0/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:34:in `require' /tmp/build/vendor/bundle/ruby/3.1.2/gems/zeitwerk-2.6.12/lib/zeitwerk/kernel.rb:35:in `require' /tmp/build/vendor/bundle/ruby/3.1.2/gems/sprockets-4.1.1/lib/sprockets/autoload/sassc.rb:2:in `<main>' ...
And you think, "but I'm not even using SASS! # £$^%" It can be a real headscratcher.
Why it happens
It's most probably a local caching issue.
If you tried out one of the SASS gems in your app and later removed it or switched to a branch which does not have SASS at all, you may still run into this error because some files got cached locally.
How to fix it
Clear the temporary cache by running this on the command line in your app's root directory:
rails tmp:cache:clear