Template Haskell declaration splice causes subsequent declarations to fall out of scope

When using Template Haskell to splice in instance declarations, it is possible to cause identifiers following it to fall out of scope:

-- DeriveJSON.hs
{-# LANGUAGE TemplateHaskell #-}
module DeriveJSON where

import Data.Aeson.TH

data ADT = ADT

instance Show ADT
    where show = adtFun

$(deriveJSON defaultOptions ''ADT)

adtFun :: ADT -> String
adtFun = undefined

ghc DeriveJSON.hs gives the following error:

[1 of 1] Compiling DeriveJSON       ( DeriveJSON.hs, DeriveJSON.o )

DeriveJSON.hs:10:18: Not in scope: ‘adtFun’

Since deriveJSON simply returns a Q [Dec], I don't see why this code shouldn't compile as is.

I can find two workarounds at the moment:

• Move the instance Show ADT declaration after the $(deriveJSON defaultOptions ''ADT) line.
• Move the $(deriveJSON defaultOptions ''ADT) line after the adtFun function declaration.

Trac metadata

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