Move Data ModuleName instance to Language.Haskell.Syntax.Module.Name

Fixes #25968.

compiler/GHC/Unit/Types.hs

-{-# OPTIONS_GHC -Wno-orphans #-} -- instance Data ModuleName
-
 {-# LANGUAGE FlexibleInstances #-}
 {-# LANGUAGE DeriveDataTypeable #-}
 {-# LANGUAGE DeriveTraversable #-}
@@ -117,13 +115,6 @@ data GenModule unit = Module
    }
    deriving (Eq,Ord,Data,Functor)
 
--- TODO: should be moved back into Language.Haskell.Syntax.Module.Name
-instance Data ModuleName where
-  -- don't traverse?
-  toConstr _   = abstractConstr "ModuleName"
-  gunfold _ _  = error "gunfold"
-  dataTypeOf _ = mkNoRepType "ModuleName"
-
 -- | A Module is a pair of a 'Unit' and a 'ModuleName'.
 type Module = GenModule Unit
 

compiler/Language/Haskell/Syntax/Module/Name.hs

@@ -3,6 +3,7 @@ module Language.Haskell.Syntax.Module.Name where
 import Prelude
 
 import Data.Char (isAlphaNum)
+import Data.Data
 import Control.DeepSeq
 import qualified Text.ParserCombinators.ReadP as Parse
 import System.FilePath
@@ -12,6 +13,14 @@ import GHC.Data.FastString
 -- | A ModuleName is essentially a simple string, e.g. @Data.List@.
 newtype ModuleName = ModuleName FastString deriving (Show, Eq)
 
+instance Data ModuleName where
+  -- don't traverse?
+  toConstr x   = constr
+    where
+      constr = mkConstr (dataTypeOf x) "{abstract:ModuleName}" [] Prefix
+  gunfold _ _  = error "gunfold"
+  dataTypeOf _ = mkNoRepType "ModuleName"
+
 instance Ord ModuleName where
   nm1 `compare` nm2 = stableModuleNameCmp nm1 nm2