[Template-haskell] change in [d| |] and creating instances in template-haskell 2.7

[Jeremy Shaw]

Hello,

I have some code that likes like this, which works in template-haskell  
2.5 / GHC 7.0.3:

---------------
{-# Language TemplateHaskell, TypeFamilies #-}
module Show where

import Language.Haskell.TH

class Bar a where
   bar :: a -> String

inferBar :: Name -> Q [Dec]
inferBar typeName =
   do s <- [d| bar _ = "sucker"
             |]
      d <- instanceD (return []) (appT (conT ''Bar) (conT typeName))  
(map return s)
      return [d]

-----------------

$(inferBar ''Bool)

But, in template-haskell 2.6 / GHC 7.2.1, I get an error,

    Warning: No explicit method nor default method for `bar'
     In the instance declaration for `Bar Bool'

Comparing the output of -ddump-splices we see in GHC 7.0.3/ TH 2.5, we  
have:

bar-test.hs:1:1: Splicing declarations
     inferBar 'Bool
   ======>
     bar-test.hs:4:3-17
     instance Bar Bool where
         { bar _ = "sucker" }

But in GHC 7.2.1 / TH 2.6 we have:

bar-test.hs:1:1: Splicing declarations
     inferBar 'Bool
   ======>
     bar-test.hs:4:3-17
     instance Bar Bool where
         { bar_acAU _ = "sucker" }

The difference being that instead 'bar' we have 'bar_acAU'.  So maybe  
that is why it can't find the method 'bar' in the instance  
declaration? Though, I would kind of expect an error like,

`bar_acAU' is not a (visible) method of class `Bar'.

Am I doing something wrong? Should I file a bug ?

Thanks!

- jeremy