GHC panic on type wildcard in left-hand side of data family

While playing around with data families I received the following output by ghc/ghci:

ghc: panic! (the 'impossible' happened)
  (GHC version 7.10.3 for x86_64-unknown-linux):
        rnHsTyKi HsWildcardTy

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

I had accidentally left a wildcard _ on the left-hand side of a data instance definition.

To reproduce enter the following code into a file and try to load that file into ghci, or try to compile it with ghc:

data family Bug x
data instance Bug _ = Bug

The expected behavior would be a (non-panic) error message of some sort.

Trac metadata

Trac field	Value
Version	7.10.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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