panic with RecordWildCards: find_tycon ghc-prim:GHC.Types.[]

The following crashes in 7.4.2, 7.6.3, 7.7:

{-# LANGUAGE RecordWildCards #-}
data R = R {r :: Int}
f x = undefined [] {r = x}
main = return ()

with the message:

~/$ ghc --make tycon_panic.hs 
[1 of 1] Compiling Main             ( tycon_panic.hs, tycon_panic.o )
ghc: panic! (the 'impossible' happened)
  (GHC version 7.4.2 for x86_64-unknown-linux):
	find_tycon
    ghc-prim:GHC.Types.[]{(w) d 6m}
    []

Instead it should signal a type error (as it does with no RecordWildCards).

Trac metadata

Trac field	Value
Version	7.6.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
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