Automatic extension detection from package.yaml for Floskell

[Krantz-XRF]

I have several extensions enabled in my package.yaml file in the default-extensions field (e.g. DerivingStrategies), so floskell fails to parse the source file (on seeing deriving stock for example) and reports a syntax error.

Is there any possibility that we automatically detect the default-extensions field in package.yaml file and pass them to floskell? Or perhaps by default enabling some extensions that in general don't break otherwise well-formed programs (e.g. DerivingStrategies, StandaloneDeriving, etc.)?

[Krantz-XRF]

I see that extensions can be specified in floskell configuration files, but two copies of the default extensions seem a bit difficult to maintain. If the extensions can be automatically extracted from package.yaml and passed to floskell, some human labour would be saved.

[fendor]

I think that should be rather trivial now. We have access to the DynFlags within IdeGhcM, and the used language extensions are in the DynFlags.

[lukel97]

Might this need to be addressed upstream?

[fendor]

It can be addressed upstream, but we can easily fix it here, imo. Might also be useful for #1374
EDIT: unless floskell maintainers say they want to support that, I think adding this upstream is just re-implementing what we already know here. We know the exact flags used to compile a file, including the language extensions. floskell would need to re-implement all the stuff we are doing with the cradles.