Panic with piResultTys1

{-# LANGUAGE DataKinds           #-}
{-# LANGUAGE ScopedTypeVariables #-}

twacePowDec :: t m' r -> t m r
twacePowDec = undefined

data Bench a

bench :: (a -> b) -> a -> Bench params
bench f = undefined

bench_twacePow :: forall t m m' r . _ => t m' r -> Bench '(t,m,m',r)
bench_twacePow = bench (twacePowDec :: t m' r -> t m r)

produces (in GHCi):

GHCi, version 8.0.1: http://www.haskell.org/ghc/  :? for help
[1 of 1] Compiling Main             ( Bug.hs, interpreted )

Bug.hs:13:58: error:
    • Expected a type, but
      ‘'(t, m, m', r)’ has kind
      ‘(k1 -> k2 -> *, k0, k1, k2)’
    • In the first argument of ‘Bench’, namely ‘'(t, m, m', r)’
      In the type ‘t m' r -> Bench '(t, m, m', r)’

Bug.hs:14:52: error:
    • Expected kind ‘k1’, but ‘m’ has kind ‘k0’
    • In the first argument of ‘t’, namely ‘m’
      In an expression type signature: t m' r -> t m r
      In the first argument of ‘bench’, namely
        ‘(twacePowDec :: t m' r -> t m r)’
    • Relevant bindings includeghc: panic! (the 'impossible' happened)
  (GHC version 8.0.1 for x86_64-unknown-linux):
	piResultTys1
  k_a18K[tau:3]
  [m'_a17U[sk], r_a17V[sk]]

The intent was to use this code with -XPartialTypeSignatures, but the bug occurs with or without that extension.

Trac metadata

Trac field	Value
Version	8.0.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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