Exception when encountering instance declarations without class name

[guest]

Code

instance Bounded b => (a -> b) where
 minBound = const minBound
 maxBound = const maxBound

GHC 7.4.1 "crashes" with an exception if the class name is missing.

*** Exception: compiler/rename/RnSource.lhs:429:14-81: Irrefutable pattern failed for pattern Data.Maybe.Just (inst_tyvars,
                                                        _,
                                                        SrcLoc.L _ cls,
                                                        _)

[simonpj]

Another dup of #5951. Please re-open if you think it isn't a dup.