    {-# LANGUAGE FlexibleContexts #-}
    {-# LANGUAGE RankNTypes #-}

    -----------------------------------------------------------------------------
    -- |
    -- Module      :  Distribution.Simple.Register
    -- Copyright   :  Isaac Jones 2003-2004
    -- License     :  BSD3
    --
    -- Maintainer  :  cabal-devel@haskell.org
    -- Portability :  portable
    --
    -- This module deals with registering and unregistering packages. There are a
    -- couple ways it can do this, one is to do it directly. Another is to generate
    -- a script that can be run later to do it. The idea here being that the user
    -- is shielded from the details of what command to use for package registration
    -- for a particular compiler. In practice this aspect was not especially
    -- popular so we also provide a way to simply generate the package registration
    -- file which then must be manually passed to @ghc-pkg@. It is possible to
    -- generate registration information for where the package is to be installed,
    -- or alternatively to register the package in place in the build tree. The
    -- latter is occasionally handy, and will become more important when we try to
    -- build multi-package systems.
    --
    -- This module does not delegate anything to the per-compiler modules but just
    -- mixes it all in in this module, which is rather unsatisfactory. The script
    -- generation and the unregister feature are not well used or tested.

    module Distribution.Simple.Register (
        register,
        unregister,

        internalPackageDBPath,

        initPackageDB,
        doesPackageDBExist,
        createPackageDB,
        deletePackageDB,

        abiHash,
        invokeHcPkg,
        registerPackage,
        HcPkg.RegisterOptions(..),
        HcPkg.defaultRegisterOptions,
        generateRegistrationInfo,
        inplaceInstalledPackageInfo,
        absoluteInstalledPackageInfo,
        generalInstalledPackageInfo,
      ) where

    import Prelude ()
    import Distribution.Compat.Prelude

    import Distribution.Types.TargetInfo
    import Distribution.Types.LocalBuildInfo
    import Distribution.Types.ComponentLocalBuildInfo

    import Distribution.Simple.LocalBuildInfo
    import Distribution.Simple.BuildPaths
    import Distribution.Simple.BuildTarget

    import qualified Distribution.Simple.GHC   as GHC
    import qualified Distribution.Simple.GHCJS as GHCJS
    import qualified Distribution.Simple.LHC   as LHC
    import qualified Distribution.Simple.UHC   as UHC
    import qualified Distribution.Simple.HaskellSuite as HaskellSuite
    import qualified Distribution.Simple.PackageIndex as Index

    import Distribution.Backpack.DescribeUnitId
    import Distribution.Simple.Compiler
    import Distribution.Simple.Program
    import Distribution.Simple.Program.Script
    import qualified Distribution.Simple.Program.HcPkg as HcPkg
    import Distribution.Simple.Setup
    import Distribution.PackageDescription
    import Distribution.Package
    import Distribution.License (licenseToSPDX, licenseFromSPDX)
    import qualified Distribution.InstalledPackageInfo as IPI
    import Distribution.InstalledPackageInfo (InstalledPackageInfo)
    import Distribution.Simple.Utils
    import Distribution.Utils.MapAccum
    import Distribution.System
    import Distribution.Text
    import Distribution.Types.ComponentName
    import Distribution.Verbosity as Verbosity
    import Distribution.Version
    import Distribution.Compat.Graph (IsNode(nodeKey))

    import System.FilePath ((</>), (<.>), isAbsolute)
    import System.Directory

    import Data.List (partition)
    import qualified Data.ByteString.Lazy.Char8 as BS.Char8

    -- -----------------------------------------------------------------------------
    -- Registration

    register :: PackageDescription -> LocalBuildInfo
             -> RegisterFlags -- ^Install in the user's database?; verbose
             -> IO ()
    register pkg_descr lbi0 flags =
       -- Duncan originally asked for us to not register/install files
       -- when there was no public library.  But with per-component
       -- configure, we legitimately need to install internal libraries
       -- so that we can get them.  So just unconditionally install.
       doRegister
     where
      doRegister = do
        targets <- readTargetInfos verbosity pkg_descr lbi0 (regArgs flags)

        -- It's important to register in build order, because ghc-pkg
        -- will complain if a dependency is not registered.
        let componentsToRegister
                = neededTargetsInBuildOrder' pkg_descr lbi0 (map nodeKey targets)

        (_, ipi_mbs) <-
            mapAccumM `flip` installedPkgs lbi0 `flip` componentsToRegister $ \index tgt ->
                case targetComponent tgt of
                    CLib lib -> do
                        let clbi = targetCLBI tgt
                            lbi = lbi0 { installedPkgs = index }
                        ipi <- generateOne pkg_descr lib lbi clbi flags
                        return (Index.insert ipi index, Just ipi)
                    _   -> return (index, Nothing)

        registerAll pkg_descr lbi0 flags (catMaybes ipi_mbs)
       where
        verbosity = fromFlag (regVerbosity flags)

    generateOne :: PackageDescription -> Library -> LocalBuildInfo -> ComponentLocalBuildInfo
                -> RegisterFlags
                -> IO InstalledPackageInfo
    generateOne pkg lib lbi clbi regFlags
      = do
        absPackageDBs    <- absolutePackageDBPaths packageDbs
        installedPkgInfo <- generateRegistrationInfo
                               verbosity pkg lib lbi clbi inplace reloc distPref
                               (registrationPackageDB absPackageDBs)
        info verbosity (IPI.showInstalledPackageInfo installedPkgInfo)
        return installedPkgInfo
      where
        inplace   = fromFlag (regInPlace regFlags)
        reloc     = relocatable lbi
        -- FIXME: there's really no guarantee this will work.
        -- registering into a totally different db stack can
        -- fail if dependencies cannot be satisfied.
        packageDbs = nub $ withPackageDB lbi
                        ++ maybeToList (flagToMaybe  (regPackageDB regFlags))
        distPref  = fromFlag (regDistPref regFlags)
        verbosity = fromFlag (regVerbosity regFlags)

    registerAll :: PackageDescription -> LocalBuildInfo -> RegisterFlags
                -> [InstalledPackageInfo]
                -> IO ()
    registerAll pkg lbi regFlags ipis
      = do
        when (fromFlag (regPrintId regFlags)) $ do
          for_ ipis $ \installedPkgInfo ->
            -- Only print the public library's IPI
            when (packageId installedPkgInfo == packageId pkg
                  && IPI.sourceLibName installedPkgInfo == Nothing) $
              putStrLn (display (IPI.installedUnitId installedPkgInfo))

         -- Three different modes:
        case () of
         _ | modeGenerateRegFile   -> writeRegistrationFileOrDirectory
           | modeGenerateRegScript -> writeRegisterScript
           | otherwise             -> do
               for_ ipis $ \ipi -> do
                   setupMessage' verbosity "Registering" (packageId pkg)
                     (libraryComponentName (IPI.sourceLibName ipi))
                     (Just (IPI.instantiatedWith ipi))
                   registerPackage verbosity (compiler lbi) (withPrograms lbi)
                                   packageDbs ipi HcPkg.defaultRegisterOptions

      where
        modeGenerateRegFile = isJust (flagToMaybe (regGenPkgConf regFlags))
        regFile             = fromMaybe (display (packageId pkg) <.> "conf")
                                        (fromFlag (regGenPkgConf regFlags))

        modeGenerateRegScript = fromFlag (regGenScript regFlags)

        -- FIXME: there's really no guarantee this will work.
        -- registering into a totally different db stack can
        -- fail if dependencies cannot be satisfied.
        packageDbs = nub $ withPackageDB lbi
                        ++ maybeToList (flagToMaybe  (regPackageDB regFlags))
        verbosity = fromFlag (regVerbosity regFlags)

        writeRegistrationFileOrDirectory = do
          -- Handles overwriting both directory and file
          deletePackageDB regFile
          case ipis of
            [installedPkgInfo] -> do
              info verbosity ("Creating package registration file: " ++ regFile)
              writeUTF8File regFile (IPI.showInstalledPackageInfo installedPkgInfo)
            _ -> do
              info verbosity ("Creating package registration directory: " ++ regFile)
              createDirectory regFile
              let num_ipis = length ipis
                  lpad m xs = replicate (m - length ys) '0' ++ ys
                      where ys = take m xs
                  number i = lpad (length (show num_ipis)) (show i)
              for_ (zip ([1..] :: [Int]) ipis) $ \(i, installedPkgInfo) ->
                writeUTF8File (regFile </> (number i ++ "-" ++ display (IPI.installedUnitId installedPkgInfo)))
                              (IPI.showInstalledPackageInfo installedPkgInfo)

        writeRegisterScript =
          case compilerFlavor (compiler lbi) of
            JHC -> notice verbosity "Registration scripts not needed for jhc"
            UHC -> notice verbosity "Registration scripts not needed for uhc"
            _   -> withHcPkg verbosity
                   "Registration scripts are not implemented for this compiler"
                   (compiler lbi) (withPrograms lbi)
                   (writeHcPkgRegisterScript verbosity ipis packageDbs)

    generateRegistrationInfo :: Verbosity
                             -> PackageDescription
                             -> Library
                             -> LocalBuildInfo
                             -> ComponentLocalBuildInfo
                             -> Bool
                             -> Bool
                             -> FilePath
                             -> PackageDB
                             -> IO InstalledPackageInfo
    generateRegistrationInfo verbosity pkg lib lbi clbi inplace reloc distPref packageDb = do
      --TODO: eliminate pwd!
      pwd <- getCurrentDirectory

      installedPkgInfo <-
        if inplace
          -- NB: With an inplace installation, the user may run './Setup
          -- build' to update the library files, without reregistering.
          -- In this case, it is critical that the ABI hash not flip.
          then return (inplaceInstalledPackageInfo pwd distPref
                         pkg (mkAbiHash "inplace") lib lbi clbi)
        else do
            abi_hash <- abiHash verbosity pkg distPref lbi lib clbi
            if reloc
              then relocRegistrationInfo verbosity
                             pkg lib lbi clbi abi_hash packageDb
              else return (absoluteInstalledPackageInfo
                             pkg abi_hash lib lbi clbi)

      return installedPkgInfo

    -- | Compute the 'AbiHash' of a library that we built inplace.
    abiHash :: Verbosity
            -> PackageDescription
            -> FilePath
            -> LocalBuildInfo
            -> Library
            -> ComponentLocalBuildInfo
            -> IO AbiHash
    abiHash verbosity pkg distPref lbi lib clbi =
        case compilerFlavor comp of
         GHC | compilerVersion comp >= mkVersion [6,11] -> do
                fmap mkAbiHash $ GHC.libAbiHash verbosity pkg lbi' lib clbi
         GHCJS -> do
                fmap mkAbiHash $ GHCJS.libAbiHash verbosity pkg lbi' lib clbi
         _ -> return (mkAbiHash "")
      where
        comp = compiler lbi
        lbi' = lbi {
                  withPackageDB = withPackageDB lbi
                      ++ [SpecificPackageDB (internalPackageDBPath lbi distPref)]
               }

    relocRegistrationInfo :: Verbosity
                          -> PackageDescription
                          -> Library
                          -> LocalBuildInfo
                          -> ComponentLocalBuildInfo
                          -> AbiHash
                          -> PackageDB
                          -> IO InstalledPackageInfo
    relocRegistrationInfo verbosity pkg lib lbi clbi abi_hash packageDb =
      case (compilerFlavor (compiler lbi)) of
        GHC -> do fs <- GHC.pkgRoot verbosity lbi packageDb
                  return (relocatableInstalledPackageInfo
                            pkg abi_hash lib lbi clbi fs)
        _   -> die' verbosity
                  "Distribution.Simple.Register.relocRegistrationInfo: \
                   \not implemented for this compiler"

    initPackageDB :: Verbosity -> Compiler -> ProgramDb -> FilePath -> IO ()
    initPackageDB verbosity comp progdb dbPath =
        createPackageDB verbosity comp progdb False dbPath

    -- | Create an empty package DB at the specified location.
    createPackageDB :: Verbosity -> Compiler -> ProgramDb -> Bool
                    -> FilePath -> IO ()
    createPackageDB verbosity comp progdb preferCompat dbPath =
        case compilerFlavor comp of
          GHC   -> HcPkg.init (GHC.hcPkgInfo   progdb) verbosity preferCompat dbPath
          GHCJS -> HcPkg.init (GHCJS.hcPkgInfo progdb) verbosity False dbPath
          LHC   -> HcPkg.init (LHC.hcPkgInfo   progdb) verbosity False dbPath
          UHC   -> return ()
          HaskellSuite _ -> HaskellSuite.initPackageDB verbosity progdb dbPath
          _              -> die' verbosity $
                                  "Distribution.Simple.Register.createPackageDB: "
                               ++ "not implemented for this compiler"

    doesPackageDBExist :: FilePath -> NoCallStackIO Bool
    doesPackageDBExist dbPath = do
        -- currently one impl for all compiler flavours, but could change if needed
        dir_exists <- doesDirectoryExist dbPath
        if dir_exists
            then return True
            else doesFileExist dbPath

    deletePackageDB :: FilePath -> NoCallStackIO ()
    deletePackageDB dbPath = do
        -- currently one impl for all compiler flavours, but could change if needed
        dir_exists <- doesDirectoryExist dbPath
        if dir_exists
            then removeDirectoryRecursive dbPath
            else do file_exists <- doesFileExist dbPath
                    when file_exists $ removeFile dbPath

    -- | Run @hc-pkg@ using a given package DB stack, directly forwarding the
    -- provided command-line arguments to it.
    invokeHcPkg :: Verbosity -> Compiler -> ProgramDb -> PackageDBStack
                    -> [String] -> IO ()
    invokeHcPkg verbosity comp progdb dbStack extraArgs =
      withHcPkg verbosity "invokeHcPkg" comp progdb
        (\hpi -> HcPkg.invoke hpi verbosity dbStack extraArgs)

    withHcPkg :: Verbosity -> String -> Compiler -> ProgramDb
              -> (HcPkg.HcPkgInfo -> IO a) -> IO a
    withHcPkg verbosity name comp progdb f =
      case compilerFlavor comp of
        GHC   -> f (GHC.hcPkgInfo progdb)
        GHCJS -> f (GHCJS.hcPkgInfo progdb)
        LHC   -> f (LHC.hcPkgInfo progdb)
        _     -> die' verbosity ("Distribution.Simple.Register." ++ name ++ ":\
                      \not implemented for this compiler")

    registerPackage :: Verbosity
                    -> Compiler
                    -> ProgramDb
                    -> PackageDBStack
                    -> InstalledPackageInfo
                    -> HcPkg.RegisterOptions
                    -> IO ()
    registerPackage verbosity comp progdb packageDbs installedPkgInfo registerOptions =
      case compilerFlavor comp of
        GHC   -> GHC.registerPackage   verbosity progdb packageDbs installedPkgInfo registerOptions
        GHCJS -> GHCJS.registerPackage verbosity progdb packageDbs installedPkgInfo registerOptions
        _ | HcPkg.registerMultiInstance registerOptions
              -> die' verbosity "Registering multiple package instances is not yet supported for this compiler"
        LHC   -> LHC.registerPackage   verbosity      progdb packageDbs installedPkgInfo registerOptions
        UHC   -> UHC.registerPackage   verbosity comp progdb packageDbs installedPkgInfo
        JHC   -> notice verbosity "Registering for jhc (nothing to do)"
        HaskellSuite {} ->
          HaskellSuite.registerPackage verbosity      progdb packageDbs installedPkgInfo
        _    -> die' verbosity "Registering is not implemented for this compiler"

    writeHcPkgRegisterScript :: Verbosity
                             -> [InstalledPackageInfo]
                             -> PackageDBStack
                             -> HcPkg.HcPkgInfo
                             -> IO ()
    writeHcPkgRegisterScript verbosity ipis packageDbs hpi = do
      let genScript installedPkgInfo =
              let invocation  = HcPkg.registerInvocation hpi Verbosity.normal
                                  packageDbs installedPkgInfo
                                  HcPkg.defaultRegisterOptions
              in invocationAsSystemScript buildOS invocation
          scripts = map genScript ipis
          -- TODO: Do something more robust here
          regScript = unlines scripts

      info verbosity ("Creating package registration script: " ++ regScriptFileName)
      writeUTF8File regScriptFileName regScript
      setFileExecutable regScriptFileName

    regScriptFileName :: FilePath
    regScriptFileName = case buildOS of
                            Windows -> "register.bat"
                            _       -> "register.sh"

    -- -----------------------------------------------------------------------------
    -- Making the InstalledPackageInfo

    -- | Construct 'InstalledPackageInfo' for a library in a package, given a set
    -- of installation directories.
    --
    generalInstalledPackageInfo
      :: ([FilePath] -> [FilePath]) -- ^ Translate relative include dir paths to
                                    -- absolute paths.
      -> PackageDescription
      -> AbiHash
      -> Library
      -> LocalBuildInfo
      -> ComponentLocalBuildInfo
      -> InstallDirs FilePath
      -> InstalledPackageInfo
    generalInstalledPackageInfo adjustRelIncDirs pkg abi_hash lib lbi clbi installDirs =
      IPI.InstalledPackageInfo {
        IPI.sourcePackageId    = packageId pkg,
        IPI.installedUnitId    = componentUnitId clbi,
        IPI.installedComponentId_ = componentComponentId clbi,
        IPI.instantiatedWith   = componentInstantiatedWith clbi,
        IPI.sourceLibName      = libName lib,
        IPI.compatPackageKey   = componentCompatPackageKey clbi,
        -- If GHC >= 8.4 we register with SDPX, otherwise with legacy license
        IPI.license            =
            if ghc84
            then Left $ either id licenseToSPDX $ licenseRaw pkg
            else Right $ either licenseFromSPDX id $ licenseRaw pkg,
        IPI.copyright          = copyright   pkg,
        IPI.maintainer         = maintainer  pkg,
        IPI.author             = author      pkg,
        IPI.stability          = stability   pkg,
        IPI.homepage           = homepage    pkg,
        IPI.pkgUrl             = pkgUrl      pkg,
        IPI.synopsis           = synopsis    pkg,
        IPI.description        = description pkg,
        IPI.category           = category    pkg,
        IPI.abiHash            = abi_hash,
        IPI.indefinite         = componentIsIndefinite clbi,
        IPI.exposed            = libExposed  lib,
        IPI.exposedModules     = componentExposedModules clbi
                                 -- add virtual modules into the list of exposed modules for the
                                 -- package database as well.
                                 ++ map (\name -> IPI.ExposedModule name Nothing) (virtualModules bi),
        IPI.hiddenModules      = otherModules bi,
        IPI.trusted            = IPI.trusted IPI.emptyInstalledPackageInfo,
        IPI.importDirs         = [ libdir installDirs | hasModules ],
        IPI.libraryDirs        = libdirs,
        IPI.libraryDynDirs     = dynlibdirs,
        IPI.dataDir            = datadir installDirs,
        IPI.hsLibraries        = (if hasLibrary
                                  then [getHSLibraryName (componentUnitId clbi)]
                                  else []) ++ extraBundledLibs bi,
        IPI.extraLibraries     = extraLibs bi,
        IPI.extraGHCiLibraries = extraGHCiLibs bi,
        IPI.includeDirs        = absinc ++ adjustRelIncDirs relinc,
        IPI.includes           = includes bi,
        IPI.depends            = depends,
        IPI.abiDepends         = abi_depends,
        IPI.ccOptions          = [], -- Note. NOT ccOptions bi!
                                     -- We don't want cc-options to be propagated
                                     -- to C compilations in other packages.
        IPI.ldOptions          = ldOptions bi,
        IPI.frameworks         = frameworks bi,
        IPI.frameworkDirs      = extraFrameworkDirs bi,
        IPI.haddockInterfaces  = [haddockdir installDirs </> haddockName pkg],
        IPI.haddockHTMLs       = [htmldir installDirs],
        IPI.pkgRoot            = Nothing
      }
      where
        ghc84 = case compilerId $ compiler lbi of
            CompilerId GHC v -> v >= mkVersion [8, 4]
            _                -> False

        bi = libBuildInfo lib
        --TODO: unclear what the root cause of the
        -- duplication is, but we nub it here for now:
        depends = ordNub $ map fst (componentPackageDeps clbi)
        abi_depends = map add_abi depends
        add_abi uid = IPI.AbiDependency uid abi
          where
            abi = case Index.lookupUnitId (installedPkgs lbi) uid of
                    Nothing -> error $
                      "generalInstalledPackageInfo: missing IPI for " ++ display uid
                    Just ipi -> IPI.abiHash ipi
        (absinc, relinc) = partition isAbsolute (includeDirs bi)
        hasModules = not $ null (allLibModules lib clbi)
        comp = compiler lbi
        hasLibrary = (hasModules || not (null (cSources bi))
                                 || not (null (asmSources bi))
                                 || not (null (cmmSources bi))
                                 || not (null (cxxSources bi))
                                 || (not (null (jsSources bi)) &&
                                    compilerFlavor comp == GHCJS))
                   && not (componentIsIndefinite clbi)
        (libdirs, dynlibdirs)
          | not hasLibrary
          = (extraLibDirs bi, [])
          -- the dynamic-library-dirs defaults to the library-dirs if not specified,
          -- so this works whether the dynamic-library-dirs field is supported or not

          | libraryDynDirSupported comp
          = (libdir    installDirs : extraLibDirs bi,
             dynlibdir installDirs : extraLibDirs bi)

          | otherwise
          = (libdir installDirs : dynlibdir installDirs : extraLibDirs bi, [])
          -- the compiler doesn't understand the dynamic-library-dirs field so we
          -- add the dyn directory to the "normal" list in the library-dirs field

    -- | Construct 'InstalledPackageInfo' for a library that is in place in the
    -- build tree.
    --
    -- This function knows about the layout of in place packages.
    --
    inplaceInstalledPackageInfo :: FilePath -- ^ top of the build tree
                                -> FilePath -- ^ location of the dist tree
                                -> PackageDescription
                                -> AbiHash
                                -> Library
                                -> LocalBuildInfo
                                -> ComponentLocalBuildInfo
                                -> InstalledPackageInfo
    inplaceInstalledPackageInfo inplaceDir distPref pkg abi_hash lib lbi clbi =
        generalInstalledPackageInfo adjustRelativeIncludeDirs
                                    pkg abi_hash lib lbi clbi installDirs
      where
        adjustRelativeIncludeDirs = map (inplaceDir </>)
        libTargetDir = componentBuildDir lbi clbi
        installDirs =
          (absoluteComponentInstallDirs pkg lbi (componentUnitId clbi) NoCopyDest) {
            libdir     = inplaceDir </> libTargetDir,
            dynlibdir  = inplaceDir </> libTargetDir,
            datadir    = inplaceDir </> dataDir pkg,
            docdir     = inplaceDocdir,
            htmldir    = inplaceHtmldir,
            haddockdir = inplaceHtmldir
          }
        inplaceDocdir  = inplaceDir </> distPref </> "doc"
        inplaceHtmldir = inplaceDocdir </> "html" </> display (packageName pkg)

    -- | Construct 'InstalledPackageInfo' for the final install location of a
    -- library package.
    --
    -- This function knows about the layout of installed packages.
    --
    absoluteInstalledPackageInfo :: PackageDescription
                                 -> AbiHash
                                 -> Library
                                 -> LocalBuildInfo
                                 -> ComponentLocalBuildInfo
                                 -> InstalledPackageInfo
    absoluteInstalledPackageInfo pkg abi_hash lib lbi clbi =
        generalInstalledPackageInfo adjustReativeIncludeDirs
                                    pkg abi_hash lib lbi clbi installDirs
      where
        -- For installed packages we install all include files into one dir,
        -- whereas in the build tree they may live in multiple local dirs.
        adjustReativeIncludeDirs _
          | null (installIncludes bi) = []
          | otherwise                 = [includedir installDirs]
        bi = libBuildInfo lib
        installDirs = absoluteComponentInstallDirs pkg lbi (componentUnitId clbi) NoCopyDest

    relocatableInstalledPackageInfo :: PackageDescription
                                    -> AbiHash
                                    -> Library
                                    -> LocalBuildInfo
                                    -> ComponentLocalBuildInfo
                                    -> FilePath
                                    -> InstalledPackageInfo
    relocatableInstalledPackageInfo pkg abi_hash lib lbi clbi pkgroot =
        generalInstalledPackageInfo adjustReativeIncludeDirs
                                    pkg abi_hash lib lbi clbi installDirs
      where
        -- For installed packages we install all include files into one dir,
        -- whereas in the build tree they may live in multiple local dirs.
        adjustReativeIncludeDirs _
          | null (installIncludes bi) = []
          | otherwise                 = [includedir installDirs]
        bi = libBuildInfo lib

        installDirs = fmap (("${pkgroot}" </>) . shortRelativePath pkgroot)
                    $ absoluteComponentInstallDirs pkg lbi (componentUnitId clbi) NoCopyDest

    -- -----------------------------------------------------------------------------
    -- Unregistration

    unregister :: PackageDescription -> LocalBuildInfo -> RegisterFlags -> IO ()
    unregister pkg lbi regFlags = do
      let pkgid     = packageId pkg
          genScript = fromFlag (regGenScript regFlags)
          verbosity = fromFlag (regVerbosity regFlags)
          packageDb = fromFlagOrDefault (registrationPackageDB (withPackageDB lbi))
                                        (regPackageDB regFlags)
          unreg hpi =
            let invocation = HcPkg.unregisterInvocation
                               hpi Verbosity.normal packageDb pkgid
            in if genScript
                 then writeFileAtomic unregScriptFileName
                        (BS.Char8.pack $ invocationAsSystemScript buildOS invocation)
                 else runProgramInvocation verbosity invocation
      setupMessage verbosity "Unregistering" pkgid
      withHcPkg verbosity "unregistering is only implemented for GHC and GHCJS"
        (compiler lbi) (withPrograms lbi) unreg

    unregScriptFileName :: FilePath
    unregScriptFileName = case buildOS of
                              Windows -> "unregister.bat"
                              _       -> "unregister.sh"

    internalPackageDBPath :: LocalBuildInfo -> FilePath -> FilePath
    internalPackageDBPath lbi distPref =
          case compilerFlavor (compiler lbi) of
            UHC -> UHC.inplacePackageDbPath lbi
            _   -> distPref </> "package.conf.inplace"