Panic with promoted types that Typeable doesn't support

The following program panics on GHC 8.2 and later:

{-# LANGUAGE DataKinds #-}
{-# LANGUAGE ImpredicativeTypes #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE TypeApplications #-}
module Bug where

import Type.Reflection

newtype Foo = MkFoo (forall a. a)

foo :: TypeRep MkFoo
foo = typeRep @MkFoo

$ /opt/ghc/8.6.1/bin/ghc Bug.hs
[1 of 1] Compiling Bug              ( Bug.hs, Bug.o )
GHC error in desugarer lookup in Bug:
  attempting to use module ‘main:Bug’ (Bug.hs) which is not loaded
ghc: panic! (the 'impossible' happened)
  (GHC version 8.6.1 for x86_64-unknown-linux):
        initDs

Trac metadata

Trac field	Value
Version	8.6.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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