Any way to unroll Generic instances?

Learn
1

Looking to know whether there’s any way to go from

data Foo = …
           deriving Generic
           deriving Bar [via Quux Foo]

to

data Foo = …

instance Bar Foo where
  …

without potentially introducing errors into the code.

2

Does --ddump-derivs work? The code will still need inlining and eta expansion since HLS doesn’t yet support that, so it’ll probably be too complex but unroll manually.

3

Nope, you get the raw definitions, so either an empty instance that falls back to its Generics-based default, or (if DerivingVia) a coercion to an unlisted instance.