Missing Typeable instances for built-in types

According to the PolyTypeable wiki, https://ghc.haskell.org/trac/ghc/wiki/GhcKinds/PolyTypeable, "Users can no longer giving manual instances of Typeable; they must be derived."

I cannot figure out how to do this for built-in types with missing Typeable instances. For example, my code requires a Typeable instance for 8-tuples. However, Typeable instances are natively only defined for 2- to 7-tuples:

Prelude> :m Data.Typeable
Prelude Data.Typeable> typeOf (1)
Integer
Prelude Data.Typeable> typeOf (1,2)
(Integer,Integer)
Prelude Data.Typeable> typeOf (1,2,3)
(Integer,Integer,Integer)
Prelude Data.Typeable> typeOf (1,2,3,4)
(Integer,Integer,Integer,Integer)
Prelude Data.Typeable> typeOf (1,2,3,4,5)
(Integer,Integer,Integer,Integer,Integer)
Prelude Data.Typeable> typeOf (1,2,3,4,5,6)
(Integer,Integer,Integer,Integer,Integer,Integer)
Prelude Data.Typeable> typeOf (1,2,3,4,5,6,7)
(Integer,Integer,Integer,Integer,Integer,Integer,Integer)
Prelude Data.Typeable> typeOf (1,2,3,4,5,6,7,8)

<interactive>:10:1:
    No instance for (Typeable (,,,,,,,)) arising from a use of ‘typeOf’
    In the expression: typeOf (1, 2, 3, 4, 5, 6, 7, 8)
    In an equation for ‘it’: it = typeOf (1, 2, 3, 4, 5, 6, 7, 8)
Prelude Data.Typeable>

Since my code does not define the type of 8-tuples (it is defined in the Prelude, or even in the compiler), it is not possible to "derive" a Typeable instance for it. With the old Typeable class, I could just define it myself:

instance (Typeable a, Typeable b, Typeable c, Typeable d, Typeable e, Typeable f, Typeable g, Typeable h) => Typeable (a,b,c,d,e,f,g,h) where
  typeOf _ = typerep
    where
      typerep = mkTyCon3 "GHC" "Tuple" "(,,,,,,,)" `mkTyConApp` [ typeOf (undefined :: a), typeOf (undefined :: b), typeOf (undefined :: c), typeOf (undefined :: d), typeOf (undefined :: e), typeOf (undefined :: f), typeOf (undefined :: g), typeOf (undefined :: h) ]

With the new Typeable class, I am completely stumped. How can I "derive" an instance for a pre-defined type?

I think this is a bug. Typeable instances should be pre-defined for all pre-defined types, including //n//-tuples for all //n//.

Trac metadata

Trac field	Value
Version	7.8.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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