Problems upgrading gems

issue に記載されている依存関係の制約から始め、assets/stylesheets/application.css.scss を調査します。特に @import の使用箇所を確認してください。プロジェクトで sprockets-sass を置き換えるべきか、その stylesheet を修正すべきかを判断し、選択した方針によって Sinatra、Rack、Sprockets、Ruby のアップグレードが可能になることを検証します。完了の条件は、stylesheet のコンパイルを壊さずに依存関係の競合が解消されていることです。

As it stands several key gems cannot be upgraded because of version conflicts. Specifically, v4 of sinatra depends on rack (>= 3, < 4) and that conflicts with sprockets-sass. This is because DevDocs depends on sprockets-sass, but the latest version of that is only compatible with sprockets < 4 and finally sprockets 3.75 (the highest version compatible with sprockets-sass) requires rack <3.

In short, we can't upgrade sinatra or rack because there's no compatible version of sprockets-sass and that's unmaintained at this point.

What sprocket-sass is doing

It enables @import statements to work in .scss files, including when the imported file is an ERB that in turn compiles to SCSS (that compiles to CSS). The main place this happens is
https://github.com/freeCodeCamp/devdocs/blob/2c5b5bd25985101fa2f06c28bb9bae15d821bfbc/assets/stylesheets/application.css.scss

What can be done

I see two potential paths forward

1. Fork sprockets-sass and make it compatible with sprockets 4 (and Ruby 3)
2. Inline the imports and convert application.css.scss to application.css.scss.erb, which should work since the issue sprockets-sass solved was specifically @importing files, not compiling .erb files.

I'm not sure how long 1. would take. I looked into it, but I didn't make much headway.

Option 2. would be ugly, but not awful. Reason being, the imported files are not used more than once, so the code wouldn't get any less DRY. We would end up with one massive file, though.