DerivingVia gives syntax errors for valid code

[kozross]

Problem

Suppose we have this code:

newtype Trit = Trit (Maybe Bool)
    deriving Eq via (Maybe Bool)

GHC will compile this code just fine, but hindent complains that there's a parse error on 'via'.

• [X] I checked the issue tracker for existing issues about this problem.
• [X] I'm using the latest version of hindent.

[kozross]

This appears to be an issue upstream with haskell-src-exts.

[domenkozar]

FYI: https://github.com/ennocramer/floskell (fork of hindent) seems to support derivingvia.

[toku-sa-n]

Closing as the current master can format the code.