No builtin support for UUID

Should support for UUIDs be built in to persistent or should it be its own package? FYI, the own package version might look something like

{-# OPTIONS_GHC -fno-warn-orphans #-}

module Instances where

import Control.Error.Util
import Data.UUID (UUID)
import qualified Data.UUID as UUID
import qualified Data.ByteString.Lazy as BSL
import Database.Persist.Sql
import Web.HttpApiData

instance PersistField UUID where
  toPersistValue = PersistDbSpecific . BSL.toStrict . UUID.toByteString
  fromPersistValue (PersistDbSpecific t) =
    case UUID.fromByteString $ BSL.fromStrict t of
      Just x  -> Right x
      Nothing -> Left "Invalid UUID"
  fromPersistValue _ = Left "Not PersistDBSpecific"
instance PersistFieldSql UUID where
  sqlType _ = SqlOther "uuid"
instance PathPiece UUID where
  toPathPiece = toUrlPiece
  fromPathPiece = hush . parseUrlPiece
instance ToHttpApiData UUID where
  toUrlPiece = UUID.toText
instance FromHttpApiData UUID where
  parseUrlPiece uuid = note ("Error parsing UUID " <> uuid) . UUID.fromText $ uuid
instance ToJSON UUID where
  toJSON = toJSON . UUID.toText
instance FromJSON UUID where
  parseJSON uuid = maybe (fail $ "Error parsing UUID " <> show uuid) pure . UUID.fromText <=< parseJSON $ uuid

Start with the issue discussion and the proposed Instances module, including its Database.Persist.Sql UUID instances. Review the tradeoff between adding UUID support to persistent and maintaining it as a separate package; done requires a settled project direction and an agreed implementation scope.