[SOLVED] Deriving Generic from data declared in another file fails

Deriving Generic from data declared in another file fails

I have these two modules:

module Server where
import Data.JSON.Schema.Generic (gSchema)
import Data.JSON.Schema.Types (JSONSchema(schema))
import Two
instance JSONSchema Data where 
    schema = gSchema
main :: IO ()
main = undefined

{-# LANGUAGE DeriveGeneric #-}
module Two where
import GHC.Generics (Generic)
data Data = Data {
    scName :: String
} deriving Generic

When trying to build the project containing these two files, the ghc in linking phase throws several errors looking like this: (They only differ in the (.data+0XXXX) part).

dist/dist-sandbox-190abc84/build/libHSserver-0.1.a(Server.o):(.data+0x1b8): undefined reference to `serverzm0zi1_Two_zdfGenericData_closure'

And final message is:

collect2: error: ld returned 1 exit status

I tried this with ghc 7.8.3 and 7.6.3 and they both behave similarly.

I can make this functionality work if put all the code into one module.

Can anyone explain, what's happening here, please?

Solution

I'm using GHC 7.8.3 (from the Haskell Platform). Below is a cabal.config file with the specific versions used in the sandbox.

constraints: aeson ==0.8.0.2,
             array ==0.5.0.0,
             attoparsec ==0.12.1.2,
             base ==4.7.0.1,
             bytestring ==0.10.4.0,
             containers ==0.5.5.1,
             deepseq ==1.3.0.2,
             dlist ==0.7.1,
             generic ==0.1.0.0,
             generic-aeson ==0.2.0.2,
             generic-deriving ==1.7.0,
             ghc-prim ==0.3.1.0,
             hashable ==1.2.2.0,
             integer-gmp ==0.5.1.0,
             json-schema ==0.7.1.1,
             mtl ==2.1.3.1,
             old-locale ==1.0.0.6,
             pretty ==1.1.1.1,
             primitive ==0.5.2.1,
             rts ==1.0,
             scientific ==0.3.3.2,
             syb ==0.4.1,
             tagged ==0.7.3,
             template-haskell ==2.9.0.0,
             text ==1.1.1.3,
             time ==1.4.2,
             transformers ==0.3.0.0,
             unordered-containers ==0.2.5.1,
             vector ==0.10.9.1