<===> input.scss
foo {
  @extend &;
}

<===> error
Error: Can't extend &: can't extend parent selectors
        on line 2 of input.scss
  Use --trace for backtrace.

<===> error-libsass
Error: Parent selectors aren't allowed here.
        on line 2:11 of input.scss
>>   @extend &;
   ----------^

<===> error-dart-sass
Error: Parent selectors aren't allowed here.
  ,
2 |   @extend &;
  |           ^
  '
  input.scss 2:11  root stylesheet