-ddump-splices output doesn't match generated code for data instances inside instances.

Using the following code:

{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE TypeFamilies #-}

module Test where

import Language.Haskell.TH

class C a where
    data D a

bang :: DecsQ
bang = return [
    InstanceD [] (AppT (ConT ''C) (ConT ''Int)) [
        DataInstD [] ''D [ConT ''Int] [
            NormalC (mkName "T") []] []]]

{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE TypeFamilies #-}

import Language.Haskell.TH
import Test

$(bang)

When compiling the second file in GHCi with -ddump-splices set, the output is:

th-test2.hs:1:1: Splicing declarations
    bang
  ======>
    th-test2.hs:9:3-6
    instance C Int where
      data instance D Int = T
Ok, modules loaded: Test, Main.

This compiles successfully, but the dumped splice is clearly incorrect (which I confirmed by attempting to splice this code manually into the same place).

Trac metadata

Trac field	Value
Version	7.6.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Template Haskell
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