Template Haskell boxes singleton unboxed tuples when splicing them

As noticed here, this program somehow compiles:

{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE UnboxedTuples #-}
module Bug where

import Language.Haskell.TH.Lib
import Language.Haskell.TH.Ppr
import Language.Haskell.TH.Syntax

f :: $([t| (# Int #) |]) -> Int
f x = x

g :: $(unboxedTupleT 1 `appT` conT ''Int) -> Int
g x = x

Despite the fact that (# Int #) and Int are most definitely //not// the same type! If you compile with -ddump-splices, you'll see what's going on:

$ /opt/ghc/head/bin/ghc Bug.hs -ddump-splices
[1 of 1] Compiling Bug              ( Bug.hs, Bug.o )
Bug.hs:12:8-40: Splicing type
    unboxedTupleT 1 `appT` conT ''Int ======> Int
Bug.hs:9:8-23: Splicing type [t| (# Int #) |] ======> Int

It appears that the splicing machinery is turning (# Int #) into Int behind the scenes. Luckily, this should be easy to fix. Patch coming soon.