Support for data families in generics

Currently DeriveGeneric doesn't handle data families correctly, so that the following module

{-# LANGUAGE TypeFamilies, DeriveGeneric #-}
module FamilyDerive where
import GHC.Generics

data family F a
data instance F Int = FInt deriving Generic

fails to compile, with error

/tmp/FamilyDerive.hs:6:15:
    Couldn't match type `Rep (F Int)' with `M1 t0 t1 (M1 t2 t3 U1)'
    The type variables `t0', `t1', `t2', `t3' are ambiguous
    Possible fix: add a type signature that fixes these type variable(s)
    Expected type: Rep (F Int) x
      Actual type: M1 t0 t1 (M1 t2 t3 U1) x
    In the pattern: M1 (M1 U1)
    In an equation for `to': to (M1 (M1 U1)) = FInt
    In the instance declaration for `Generic (F Int)'

It turns out to require only small changes to GHC to handle data families. I've attached patches.

Trac metadata

Trac field	Value
Version	7.4.1
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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