<===> input.scss
a {
  b: {
    @debug "debug";
    foo: bar;
  }
}
<===> error
Error: Illegal nesting: Only properties may be nested beneath properties.
        on line 3 of input.scss
  Use --trace for backtrace.

<===> output-dart-sass.css
a {
  b-foo: bar;
}

<===> warning-dart-sass
spec/errors/fn-debug/property-dart-sass/input.scss:3 DEBUG: debug