Multiple declarations of uniquely generated name

I originally reported this problem in the syb-with-class bug tracker but I think it's a bug in TH possibly related to #5362 (closed).

After increasing the version range of template-haskell in syb-with-class to:

template-haskell >= 2.4 && < 2.7

the package fails to build on ghc-7.2.1 with the following error:

$ cabal build --ghc-option=-ddump-splices
Preprocessing library syb-with-class-0.6.1.2...
Building syb-with-class-0.6.1.2...
[4 of 4] Compiling Data.Generics.SYB.WithClass.Instances ( Data/Generics/SYB/WithClass/Instances.hs, dist/build/Data/Generics/SYB/WithClass/Instances.o )
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Loading package array-0.3.0.3 ... linking ... done.
Loading package containers-0.4.1.0 ... linking ... done.
Loading package pretty-1.1.0.0 ... linking ... done.
Loading package template-haskell ... linking ... done.
Loading package bytestring-0.9.2.0 ... linking ... done.
Loading package ffi-1.0 ... linking ... done.
Data/Generics/SYB/WithClass/Instances.hs:1:1: Splicing declarations
    deriveTypeable ['DataType]
  ======>
    Data/Generics/SYB/WithClass/Instances.hs:544:3-29
    instance Typeable DataType where
        { typeOf _
            = mkTyConApp
                (mkTyCon "Data.Generics.SYB.WithClass.Basics.DataType")
                ghc-prim:GHC.Types.[] }
Data/Generics/SYB/WithClass/Instances.hs:1:1: Splicing declarations
    deriveData ['ByteString]
  ======>
    Data/Generics/SYB/WithClass/Instances.hs:726:4-28
    constr_a2Ya :: Constr
    constr_a2Ya = mkConstr dataType_a2Y9 "PS" [] Prefix
    dataType_a2Y9 :: DataType
    dataType_a2Y9 = mkDataType "ByteString" [constr_a2Ya]
    instance (Data ctx (ForeignPtr Word8),
              Data ctx Int,
              Sat (ctx ByteString),
              Sat (ctx (ForeignPtr Word8)),
              Sat (ctx Int)) =>
             Data ctx ByteString where
        { gfoldl _ _f_a2Yb z_a2Yc x_a2Yd
            = case x_a2Yd of {
                Data.ByteString.Internal.PS arg_a2Ye arg_a2Yf arg_a2Yg
                  -> _f_a2Yb
                       (_f_a2Yb
                          (_f_a2Yb (z_a2Yc Data.ByteString.Internal.PS) arg_a2Ye) arg_a2Yf)
                       arg_a2Yg }
          gunfold _ _k_a2Yh z_a2Yi c_a2Yj
            = case constrIndex c_a2Yj of {
                1 -> _k_a2Yh
                       (_k_a2Yh (_k_a2Yh (z_a2Yi Data.ByteString.Internal.PS)))
                _ -> error "gunfold: fallthrough" }
          toConstr _ x_a2Yk
            = case x_a2Yk of {
                Data.ByteString.Internal.PS _ _ _ -> constr_a2Ya }
          dataTypeOf _ _ = dataType_a2Y9 }
Data/Generics/SYB/WithClass/Instances.hs:1:1: Splicing declarations
    deriveData ['L.ByteString]
  ======>
    Data/Generics/SYB/WithClass/Instances.hs:727:4-30
    constr_a30f :: Constr
    constr_a30f = mkConstr dataType_a30e "Empty" [] Prefix
    constr_a30g :: Constr
    constr_a30g = mkConstr dataType_a30e "Chunk" [] Prefix
    dataType_a30e :: DataType
    dataType_a30e = mkDataType "ByteString" [constr_a30f, constr_a30g]
    instance (Data ctx ByteString,
              Data ctx L.ByteString,
              Sat (ctx L.ByteString),
              Sat (ctx ByteString)) =>
             Data ctx L.ByteString where
        { gfoldl _ _f_a30h z_a30i x_a30j
            = case x_a30j of {
                Data.ByteString.Lazy.Internal.Empty
                  -> z_a30i Data.ByteString.Lazy.Internal.Empty
                Data.ByteString.Lazy.Internal.Chunk arg_a30k arg_a30l
                  -> _f_a30h
                       (_f_a30h (z_a30i Data.ByteString.Lazy.Internal.Chunk) arg_a30k)
                       arg_a30l }
          gunfold _ _k_a30m z_a30n c_a30o
            = case constrIndex c_a30o of {
                1 -> z_a30n Data.ByteString.Lazy.Internal.Empty
                2 -> _k_a30m (_k_a30m (z_a30n Data.ByteString.Lazy.Internal.Chunk))
                _ -> error "gunfold: fallthrough" }
          toConstr _ x_a30p
            = case x_a30p of {
                Data.ByteString.Lazy.Internal.Empty -> constr_a30f
                Data.ByteString.Lazy.Internal.Chunk _ _ -> constr_a30g }
          dataTypeOf _ _ = dataType_a30e }

Data/Generics/SYB/WithClass/Instances.hs:727:4:
    Multiple declarations of `dataType'
    Declared at: Data/Generics/SYB/WithClass/Instances.hs:726:4
                 Data/Generics/SYB/WithClass/Instances.hs:727:4

Data/Generics/SYB/WithClass/Instances.hs:727:4:
    Multiple declarations of `constr'
    Declared at: Data/Generics/SYB/WithClass/Instances.hs:726:4
                 Data/Generics/SYB/WithClass/Instances.hs:727:4
                 Data/Generics/SYB/WithClass/Instances.hs:727:4

The weird thing is that the generated names dataType_a2Y9, dataType_a30e, constr_a2Ya and constr_a30 are all unique.

Trac metadata

Trac field	Value
Version	7.0.4
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Template Haskell
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