SPECIALISE pragmas generated from Template Haskell are ignored

Hi,

I have the following program which contains a SPECIALISE pragma:

module Test(threeList) where

{-# NOINLINE three #-}
three :: Monad m => m Int
three = return 3
{-# SPECIALISE three :: [Int] #-}

threeList :: [Int]
threeList = three

The specialisation works and -ddump-simpl gives me the following:

a :: Int
[GblId, Caf=NoCafRefs, Str=DmdType m]
a = I# 3

threeList [InlPrag=NOINLINE] :: [Int]
[GblId, Caf=NoCafRefs, Str=DmdType]
threeList = : @ Int a ([] @ Int)

Suppose now I alter my program so that it uses Template Haskell to generate the SPECIALISE pragma:

{-# LANGUAGE TemplateHaskell #-}
module TestTH(threeList) where

import TH

{-# NOINLINE three #-}
three :: Monad m => m Int
three = return 3
$(specialise 'three)

threeList :: [Int]
threeList = three

{-# LANGUAGE TemplateHaskell #-}
module TH where

import Language.Haskell.TH

specialise :: Name -> DecsQ
specialise x = do
  listInt <- [t| [Int] |]
  return [ PragmaD (SpecialiseP x listInt Nothing) ]

The specialisation should work just as before. However, if I compile with -ddump-splices -ddump-simpl, I see that the correct pragma was spliced in but no specialisation happened and GHC generated icky code:

TestTH.hs:1:1: Splicing declarations
    specialise 'three
  ======>
    TestTH.hs:9:3-19
    {-# SPECIALIZE three :: [Int] #-}

==================== Tidy Core ====================
lvl :: Int
[GblId, Caf=NoCafRefs, Str=DmdType m]
lvl = I# 3

three [InlPrag=NOINLINE] :: forall (m :: * -> *). Monad m => m Int
[GblId, Arity=1, Caf=NoCafRefs, Str=DmdType U(AASA)]
three =
  \ (@ m::* -> *) ($dMonad :: Monad m) ->
    return @ m $dMonad @ Int lvl

threeList :: [Int]
[GblId,
 Str=DmdType,
 Unf=Unf{Src=<vanilla>, TopLvl=True, Arity=0, Value=False,
         ConLike=False, Cheap=False, Expandable=True,
         Guidance=IF_ARGS [] 2 0}]
threeList = three @ [] $fMonad[]

This happens on at least GHC 7.0.4 and 7.2.1.

Trac metadata

Trac field	Value
Version	7.2.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Template Haskell
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