How to ban a single extension

[phadej]

The documentation snippet in readme

- extensions:
  - default: false
  - name: [DeriveDataTypeable, GeneralizedNewtypeDeriving]
  - {name: CPP, within: CompatLayer}

is "everything is forbidden, except these are allowed".

is there a way to specify "everything is allowed, except these are forbidden"?

[chungyc]

I think this would be

- extensions:
  - default: true
  - {name: DisallowedExtension, within: []}