Bizarre pretty-printing of inferred Coercible constraint in partial type signature

Consider the following GHCi session:

$ ghci
GHCi, version 8.4.1: http://www.haskell.org/ghc/  :? for help
Loaded GHCi configuration from /home/rgscott/.ghci
λ> import Data.Type.Coercion
λ> foo :: _ => Coercion a b; foo = Coercion

<interactive>:2:8: error:
    • Found type wildcard ‘_’
        standing for ‘Coercible a b :: TYPE ('GHC.Types.TupleRep '[])’
      Where: ‘a’, ‘b’ are rigid type variables bound by
               the inferred type of foo :: Coercible a b => Coercion a b
               at <interactive>:2:27-40
      To use the inferred type, enable PartialTypeSignatures
    • In the type signature: foo :: _ => Coercion a b
λ> :set -fprint-explicit-kinds 
λ> foo :: _ => Coercion a b; foo = Coercion

<interactive>:4:8: error:
    • Found type wildcard ‘_’
        standing for ‘(a :: *) ~~ (b :: *) :: TYPE
                                                ('GHC.Types.TupleRep ('[] GHC.Types.RuntimeRep))’
      Where: ‘a’, ‘b’ are rigid type variables bound by
               the inferred type of
                 foo :: ((a :: *) ~~ (b :: *)) => Coercion * a b
               at <interactive>:4:27-40
      To use the inferred type, enable PartialTypeSignatures
    • In the type signature: foo :: _ => Coercion a b

There are two things quite strange about this:

1. In both error messages, GHC claims that Coercible a b/a ~~ b has kind TYPE (TupleRep '[]). This is wrong, and should be Coercible.
2. For some reason, enabling -fprint-explicit-kinds causes the inferred constraint to be (~~) instead of Coercible, which is just plain wrong.

Trac metadata

Trac field	Value
Version	8.4.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture