GHC 7.10.1 panic due to wildcard in data family instance

The following simple program causes GHC 7.10.1 (for x86_64-apple-darwin) to panic (rnHsTyKi HsWildcardTy):

 {-# LANGUAGE TypeFamilies, GADTs, DataKinds, PolyKinds #-}
    
data MyKind = A | B

data family Sing (a :: k)

data instance Sing (_ :: MyKind) where
    SingA :: Sing A
    SingB :: Sing B

Because data family instances must be fully saturated, we must give some name to the parameter; but because our instance is a GADT, the name of that parameter is meaningless, so using the wildcard makes complete sense here.

Trac metadata

Trac field	Value
Version	7.10.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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