Derived Data instance requires Data instances for unused type parameters

First reported here: http://www.haskell.org/pipermail/glasgow-haskell-users/2010-April/018785.html

With this module:

{-# LANGUAGE DeriveDataTypeable #-}

import Data.Data
import Data.Typeable

newtype FSVec s a = FSVec {unFSVec :: [a]}
    deriving (Eq, Typeable, Data)

1. 12 now has a Data s requirement on the Data (FSVec s a) instance.

With 6.10.4:

*Main> :i FSVec
newtype FSVec s a = FSVec {unFSVec :: [a]}
        -- Defined at q.hs:7:8-12
instance (Eq a) => Eq (FSVec s a) -- Defined at q.hs:8:14-15
instance (Data a, Typeable s) => Data (FSVec s a)
  -- Defined at q.hs:8:28-31
instance Typeable2 FSVec -- Defined at q.hs:8:18-25

With 6.12 (and the HEAD):

*Main> :i FSVec
newtype FSVec s a = FSVec {unFSVec :: [a]}
        -- Defined at q.hs:7:8-12
instance (Eq a) => Eq (FSVec s a) -- Defined at q.hs:8:14-15
instance (Data s, Data a) => Data (FSVec s a)
  -- Defined at q.hs:8:28-31
instance Typeable2 FSVec -- Defined at q.hs:8:18-25

Trac metadata

Trac field	Value
Version	6.12.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
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