-----------------------------------------------------------------------------
-- |
-- Module      :  Distribution.Simple.Build
-- Copyright   :  Isaac Jones 2003-2005,
--                Ross Paterson 2006,
--                Duncan Coutts 2007-2008, 2012
-- License     :  BSD3
--
-- Maintainer  :  cabal-devel@haskell.org
-- Portability :  portable
--
-- This is the entry point to actually building the modules in a package. It
-- doesn't actually do much itself, most of the work is delegated to
-- compiler-specific actions. It does do some non-compiler specific bits like
-- running pre-processors.
--

module Distribution.Simple.Build (
    build, repl,
    startInterpreter,

    initialBuildSteps,
    writeAutogenFiles,
  ) where

import qualified Distribution.Simple.GHC   as GHC
import qualified Distribution.Simple.GHCJS as GHCJS
import qualified Distribution.Simple.JHC   as JHC
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.Build.Macros      as Build.Macros
import qualified Distribution.Simple.Build.PathsModule as Build.PathsModule

import Distribution.Package
         ( Package(..), PackageName(..), PackageIdentifier(..)
         , Dependency(..), thisPackageVersion, mkPackageKey, packageName )
import Distribution.Simple.Compiler
         ( Compiler, CompilerFlavor(..), compilerFlavor
         , PackageDB(..), PackageDBStack, packageKeySupported )
import Distribution.PackageDescription
         ( PackageDescription(..), BuildInfo(..), Library(..), Executable(..)
         , TestSuite(..), TestSuiteInterface(..), Benchmark(..)
         , BenchmarkInterface(..), defaultRenaming )
import qualified Distribution.InstalledPackageInfo as IPI
import qualified Distribution.ModuleName as ModuleName
import Distribution.ModuleName (ModuleName)

import Distribution.Simple.Setup
         ( Flag(..), BuildFlags(..), ReplFlags(..), fromFlag )
import Distribution.Simple.BuildTarget
         ( BuildTarget(..), readBuildTargets )
import Distribution.Simple.PreProcess
         ( preprocessComponent, PPSuffixHandler )
import Distribution.Simple.LocalBuildInfo
         ( LocalBuildInfo(compiler, buildDir, withPackageDB, withPrograms, pkgKey)
         , Component(..), componentName, getComponent, componentBuildInfo
         , ComponentLocalBuildInfo(..), pkgEnabledComponents
         , withComponentsInBuildOrder, componentsInBuildOrder
         , ComponentName(..), showComponentName
         , ComponentDisabledReason(..), componentDisabledReason
         , inplacePackageId, LibraryName(..) )
import Distribution.Simple.Program.Types
import Distribution.Simple.Program.Db
import qualified Distribution.Simple.Program.HcPkg as HcPkg
import Distribution.Simple.BuildPaths
         ( autogenModulesDir, autogenModuleName, cppHeaderName, exeExtension )
import Distribution.Simple.Register
         ( registerPackage, inplaceInstalledPackageInfo )
import Distribution.Simple.Test.LibV09 ( stubFilePath, stubName )
import Distribution.Simple.Utils
         ( createDirectoryIfMissingVerbose, rewriteFile
         , die, info, debug, warn, setupMessage )

import Distribution.Verbosity
         ( Verbosity )
import Distribution.Text
         ( display )

import qualified Data.Map as Map
import Data.Maybe
         ( maybeToList )
import Data.Either
         ( partitionEithers )
import Data.List
         ( intersect, intercalate )
import Control.Monad
         ( when, unless, forM_ )
import System.FilePath
         ( (</>), (<.>) )
import System.Directory
         ( getCurrentDirectory, removeDirectoryRecursive, doesDirectoryExist )

-- -----------------------------------------------------------------------------
-- |Build the libraries and executables in this package.

build    :: PackageDescription  -- ^ Mostly information from the .cabal file
         -> LocalBuildInfo      -- ^ Configuration information
         -> BuildFlags          -- ^ Flags that the user passed to build
         -> [ PPSuffixHandler ] -- ^ preprocessors to run before compiling
         -> IO ()
build pkg_descr lbi flags suffixes = do
  let distPref  = fromFlag (buildDistPref flags)
      verbosity = fromFlag (buildVerbosity flags)

  targets  <- readBuildTargets pkg_descr (buildArgs flags)
  targets' <- checkBuildTargets verbosity pkg_descr targets
  let componentsToBuild = map fst (componentsInBuildOrder lbi (map fst targets'))
  info verbosity $ "Component build order: "
                ++ intercalate ", " (map showComponentName componentsToBuild)

  initialBuildSteps distPref pkg_descr lbi verbosity
  when (null targets) $
    -- Only bother with this message if we're building the whole package
    setupMessage verbosity "Building" (packageId pkg_descr)

  internalPackageDB <- createInternalPackageDB verbosity lbi distPref

  withComponentsInBuildOrder pkg_descr lbi componentsToBuild $ \comp clbi ->
    let bi     = componentBuildInfo comp
        progs' = addInternalBuildTools pkg_descr lbi bi (withPrograms lbi)
        lbi'   = lbi {
                   withPrograms  = progs',
                   withPackageDB = withPackageDB lbi ++ [internalPackageDB]
                 }
    in buildComponent verbosity (buildNumJobs flags) pkg_descr
                      lbi' suffixes comp clbi distPref


repl     :: PackageDescription  -- ^ Mostly information from the .cabal file
         -> LocalBuildInfo      -- ^ Configuration information
         -> ReplFlags           -- ^ Flags that the user passed to build
         -> [ PPSuffixHandler ] -- ^ preprocessors to run before compiling
         -> [String]
         -> IO ()
repl pkg_descr lbi flags suffixes args = do
  let distPref  = fromFlag (replDistPref flags)
      verbosity = fromFlag (replVerbosity flags)

  targets  <- readBuildTargets pkg_descr args
  targets' <- case targets of
    []       -> return $ take 1 [ componentName c
                                | c <- pkgEnabledComponents pkg_descr ]
    [target] -> fmap (map fst) (checkBuildTargets verbosity pkg_descr [target])
    _        -> die $ "The 'repl' command does not support multiple targets at once."
  let componentsToBuild = componentsInBuildOrder lbi targets'
      componentForRepl  = last componentsToBuild
  debug verbosity $ "Component build order: "
                 ++ intercalate ", "
                      [ showComponentName c | (c,_) <- componentsToBuild ]

  initialBuildSteps distPref pkg_descr lbi verbosity

  internalPackageDB <- createInternalPackageDB verbosity lbi distPref

  let lbiForComponent comp lbi' =
        lbi' {
          withPackageDB = withPackageDB lbi ++ [internalPackageDB],
          withPrograms  = addInternalBuildTools pkg_descr lbi'
                            (componentBuildInfo comp) (withPrograms lbi')
        }

  -- build any dependent components
  sequence_
    [ let comp = getComponent pkg_descr cname
          lbi' = lbiForComponent comp lbi
       in buildComponent verbosity NoFlag
                         pkg_descr lbi' suffixes comp clbi distPref
    | (cname, clbi) <- init componentsToBuild ]

  -- REPL for target components
  let (cname, clbi) = componentForRepl
      comp = getComponent pkg_descr cname
      lbi' = lbiForComponent comp lbi
   in replComponent verbosity pkg_descr lbi' suffixes comp clbi distPref


-- | Start an interpreter without loading any package files.
startInterpreter :: Verbosity -> ProgramDb -> Compiler -> PackageDBStack -> IO ()
startInterpreter verbosity programDb comp packageDBs =
  case compilerFlavor comp of
    GHC   -> GHC.startInterpreter   verbosity programDb comp packageDBs
    GHCJS -> GHCJS.startInterpreter verbosity programDb comp packageDBs
    _     -> die "A REPL is not supported with this compiler."

buildComponent :: Verbosity
               -> Flag (Maybe Int)
               -> PackageDescription
               -> LocalBuildInfo
               -> [PPSuffixHandler]
               -> Component
               -> ComponentLocalBuildInfo
               -> FilePath
               -> IO ()
buildComponent verbosity numJobs pkg_descr lbi suffixes
               comp@(CLib lib) clbi distPref = do
    preprocessComponent pkg_descr comp lbi False verbosity suffixes
    info verbosity "Building library..."
    buildLib verbosity numJobs pkg_descr lbi lib clbi

    -- Register the library in-place, so exes can depend
    -- on internally defined libraries.
    pwd <- getCurrentDirectory
    let -- The in place registration uses the "-inplace" suffix, not an ABI hash
        ipkgid           = inplacePackageId (packageId installedPkgInfo)
        installedPkgInfo = inplaceInstalledPackageInfo pwd distPref pkg_descr
                                                       ipkgid lib lbi clbi

    registerPackage verbosity
      installedPkgInfo pkg_descr lbi True -- True meaning in place
      (withPackageDB lbi)


buildComponent verbosity numJobs pkg_descr lbi suffixes
               comp@(CExe exe) clbi _ = do
    preprocessComponent pkg_descr comp lbi False verbosity suffixes
    info verbosity $ "Building executable " ++ exeName exe ++ "..."
    buildExe verbosity numJobs pkg_descr lbi exe clbi


buildComponent verbosity numJobs pkg_descr lbi suffixes
               comp@(CTest test@TestSuite { testInterface = TestSuiteExeV10{} })
               clbi _distPref = do
    let exe = testSuiteExeV10AsExe test
    preprocessComponent pkg_descr comp lbi False verbosity suffixes
    info verbosity $ "Building test suite " ++ testName test ++ "..."
    buildExe verbosity numJobs pkg_descr lbi exe clbi


buildComponent verbosity numJobs pkg_descr lbi0 suffixes
               comp@(CTest
                 test@TestSuite { testInterface = TestSuiteLibV09{} })
               clbi -- This ComponentLocalBuildInfo corresponds to a detailed
                    -- test suite and not a real component. It should not
                    -- be used, except to construct the CLBIs for the
                    -- library and stub executable that will actually be
                    -- built.
               distPref = do
    pwd <- getCurrentDirectory
    let (pkg, lib, libClbi, lbi, ipi, exe, exeClbi) =
          testSuiteLibV09AsLibAndExe pkg_descr test clbi lbi0 distPref pwd
    preprocessComponent pkg_descr comp lbi False verbosity suffixes
    info verbosity $ "Building test suite " ++ testName test ++ "..."
    buildLib verbosity numJobs pkg lbi lib libClbi
    registerPackage verbosity ipi pkg lbi True $ withPackageDB lbi
    buildExe verbosity numJobs pkg_descr lbi exe exeClbi


buildComponent _ _ _ _ _
               (CTest TestSuite { testInterface = TestSuiteUnsupported tt })
               _ _ =
    die $ "No support for building test suite type " ++ display tt


buildComponent verbosity numJobs pkg_descr lbi suffixes
               comp@(CBench bm@Benchmark { benchmarkInterface = BenchmarkExeV10 {} })
               clbi _ = do
    let (exe, exeClbi) = benchmarkExeV10asExe bm clbi
    preprocessComponent pkg_descr comp lbi False verbosity suffixes
    info verbosity $ "Building benchmark " ++ benchmarkName bm ++ "..."
    buildExe verbosity numJobs pkg_descr lbi exe exeClbi


buildComponent _ _ _ _ _
               (CBench Benchmark { benchmarkInterface = BenchmarkUnsupported tt })
               _ _ =
    die $ "No support for building benchmark type " ++ display tt


replComponent :: Verbosity
              -> PackageDescription
              -> LocalBuildInfo
              -> [PPSuffixHandler]
              -> Component
              -> ComponentLocalBuildInfo
              -> FilePath
              -> IO ()
replComponent verbosity pkg_descr lbi suffixes
               comp@(CLib lib) clbi _ = do
    preprocessComponent pkg_descr comp lbi False verbosity suffixes
    replLib verbosity pkg_descr lbi lib clbi

replComponent verbosity pkg_descr lbi suffixes
               comp@(CExe exe) clbi _ = do
    preprocessComponent pkg_descr comp lbi False verbosity suffixes
    replExe verbosity pkg_descr lbi exe clbi


replComponent verbosity pkg_descr lbi suffixes
               comp@(CTest test@TestSuite { testInterface = TestSuiteExeV10{} })
               clbi _distPref = do
    let exe = testSuiteExeV10AsExe test
    preprocessComponent pkg_descr comp lbi False verbosity suffixes
    replExe verbosity pkg_descr lbi exe clbi


replComponent verbosity pkg_descr lbi0 suffixes
               comp@(CTest
                 test@TestSuite { testInterface = TestSuiteLibV09{} })
               clbi distPref = do
    pwd <- getCurrentDirectory
    let (pkg, lib, libClbi, lbi, _, _, _) =
          testSuiteLibV09AsLibAndExe pkg_descr test clbi lbi0 distPref pwd
    preprocessComponent pkg_descr comp lbi False verbosity suffixes
    replLib verbosity pkg lbi lib libClbi


replComponent _ _ _ _
              (CTest TestSuite { testInterface = TestSuiteUnsupported tt })
              _ _ =
    die $ "No support for building test suite type " ++ display tt


replComponent verbosity pkg_descr lbi suffixes
               comp@(CBench bm@Benchmark { benchmarkInterface = BenchmarkExeV10 {} })
               clbi _ = do
    let (exe, exeClbi) = benchmarkExeV10asExe bm clbi
    preprocessComponent pkg_descr comp lbi False verbosity suffixes
    replExe verbosity pkg_descr lbi exe exeClbi


replComponent _ _ _ _
              (CBench Benchmark { benchmarkInterface = BenchmarkUnsupported tt })
              _ _ =
    die $ "No support for building benchmark type " ++ display tt

----------------------------------------------------
-- Shared code for buildComponent and replComponent
--

-- | Translate a exe-style 'TestSuite' component into an exe for building
testSuiteExeV10AsExe :: TestSuite -> Executable
testSuiteExeV10AsExe test@TestSuite { testInterface = TestSuiteExeV10 _ mainFile } =
    Executable {
      exeName    = testName test,
      modulePath = mainFile,
      buildInfo  = testBuildInfo test
    }
testSuiteExeV10AsExe TestSuite{} = error "testSuiteExeV10AsExe: wrong kind"

-- | Translate a lib-style 'TestSuite' component into a lib + exe for building
testSuiteLibV09AsLibAndExe :: PackageDescription
                           -> TestSuite
                           -> ComponentLocalBuildInfo
                           -> LocalBuildInfo
                           -> FilePath
                           -> FilePath
                           -> (PackageDescription,
                               Library, ComponentLocalBuildInfo,
                               LocalBuildInfo,
                               IPI.InstalledPackageInfo_ ModuleName,
                               Executable, ComponentLocalBuildInfo)
testSuiteLibV09AsLibAndExe pkg_descr
                     test@TestSuite { testInterface = TestSuiteLibV09 _ m }
                     clbi lbi distPref pwd =
    (pkg, lib, libClbi, lbi', ipi, exe, exeClbi)
  where
    bi  = testBuildInfo test
    lib = Library {
            exposedModules = [ m ],
            reexportedModules = [],
            requiredSignatures = [],
            exposedSignatures = [],
            libExposed     = True,
            libBuildInfo   = bi
          }
    libClbi = LibComponentLocalBuildInfo
                { componentPackageDeps = componentPackageDeps clbi
                , componentPackageRenaming = componentPackageRenaming clbi
                , componentLibraries = [LibraryName (testName test)]
                , componentExposedModules = [IPI.ExposedModule m Nothing Nothing]
                }
    pkg = pkg_descr {
            package      = (package pkg_descr) {
                             pkgName = PackageName (testName test)
                           }
          , buildDepends = targetBuildDepends $ testBuildInfo test
          , executables  = []
          , testSuites   = []
          , library      = Just lib
          }
    -- Hack to make the library compile with the right package key.
    -- Probably the "right" way to do this is move this information to
    -- the ComponentLocalBuildInfo, but it seems odd that a single package
    -- can define multiple actual packages.
    lbi' = lbi {
        pkgKey = mkPackageKey (packageKeySupported (compiler lbi))
                              (package pkg) [] []
    }
    ipkgid = inplacePackageId (packageId pkg)
    ipi    = inplaceInstalledPackageInfo pwd distPref pkg ipkgid lib lbi libClbi
    testDir = buildDir lbi </> stubName test
          </> stubName test ++ "-tmp"
    testLibDep = thisPackageVersion $ package pkg
    exe = Executable {
            exeName    = stubName test,
            modulePath = stubFilePath test,
            buildInfo  = (testBuildInfo test) {
                           hsSourceDirs       = [ testDir ],
                           targetBuildDepends = testLibDep
                             : (targetBuildDepends $ testBuildInfo test),
                           targetBuildRenaming =
                            Map.insert (packageName pkg) defaultRenaming
                                (targetBuildRenaming $ testBuildInfo test)
                         }
          }
    -- | The stub executable needs a new 'ComponentLocalBuildInfo'
    -- that exposes the relevant test suite library.
    exeClbi = ExeComponentLocalBuildInfo {
                componentPackageDeps =
                    (IPI.installedPackageId ipi, packageId ipi)
                  : (filter (\(_, x) -> let PackageName name = pkgName x
                                        in name == "Cabal" || name == "base")
                            (componentPackageDeps clbi)),
                componentPackageRenaming =
                    Map.insert (packageName ipi) defaultRenaming
                               (componentPackageRenaming clbi)
              }
testSuiteLibV09AsLibAndExe _ TestSuite{} _ _ _ _ = error "testSuiteLibV09AsLibAndExe: wrong kind"


-- | Translate a exe-style 'Benchmark' component into an exe for building
benchmarkExeV10asExe :: Benchmark -> ComponentLocalBuildInfo
                     -> (Executable, ComponentLocalBuildInfo)
benchmarkExeV10asExe bm@Benchmark { benchmarkInterface = BenchmarkExeV10 _ f }
                     clbi =
    (exe, exeClbi)
  where
    exe = Executable {
            exeName    = benchmarkName bm,
            modulePath = f,
            buildInfo  = benchmarkBuildInfo bm
          }
    exeClbi = ExeComponentLocalBuildInfo {
                componentPackageDeps = componentPackageDeps clbi,
                componentPackageRenaming = componentPackageRenaming clbi
              }
benchmarkExeV10asExe Benchmark{} _ = error "benchmarkExeV10asExe: wrong kind"

-- | Initialize a new package db file for libraries defined
-- internally to the package.
createInternalPackageDB :: Verbosity -> LocalBuildInfo -> FilePath
                        -> IO PackageDB
createInternalPackageDB verbosity lbi distPref = do
    case compilerFlavor (compiler lbi) of
      GHC   -> createWith $ GHC.hcPkgInfo   (withPrograms lbi)
      GHCJS -> createWith $ GHCJS.hcPkgInfo (withPrograms lbi)
      LHC   -> createWith $ LHC.hcPkgInfo   (withPrograms lbi)
      _     -> return packageDB
    where
      dbDir = distPref </> "package.conf.inplace"
      packageDB = SpecificPackageDB dbDir
      createWith hpi = do
        exists <- doesDirectoryExist dbDir
        when exists $ removeDirectoryRecursive dbDir
        HcPkg.init hpi verbosity dbDir
        return packageDB

addInternalBuildTools :: PackageDescription -> LocalBuildInfo -> BuildInfo
                      -> ProgramDb -> ProgramDb
addInternalBuildTools pkg lbi bi progs =
    foldr updateProgram progs internalBuildTools
  where
    internalBuildTools =
      [ simpleConfiguredProgram toolName (FoundOnSystem toolLocation)
      | toolName <- toolNames
      , let toolLocation = buildDir lbi </> toolName </> toolName <.> exeExtension ]
    toolNames = intersect buildToolNames internalExeNames
    internalExeNames = map exeName (executables pkg)
    buildToolNames   = map buildToolName (buildTools bi)
      where
        buildToolName (Dependency (PackageName name) _ ) = name


-- TODO: build separate libs in separate dirs so that we can build
-- multiple libs, e.g. for 'LibTest' library-style test suites
buildLib :: Verbosity -> Flag (Maybe Int)
                      -> PackageDescription -> LocalBuildInfo
                      -> Library            -> ComponentLocalBuildInfo -> IO ()
buildLib verbosity numJobs pkg_descr lbi lib clbi =
  case compilerFlavor (compiler lbi) of
    GHC   -> GHC.buildLib   verbosity numJobs pkg_descr lbi lib clbi
    GHCJS -> GHCJS.buildLib verbosity numJobs pkg_descr lbi lib clbi
    JHC   -> JHC.buildLib   verbosity         pkg_descr lbi lib clbi
    LHC   -> LHC.buildLib   verbosity         pkg_descr lbi lib clbi
    UHC   -> UHC.buildLib   verbosity         pkg_descr lbi lib clbi
    HaskellSuite {} -> HaskellSuite.buildLib verbosity pkg_descr lbi lib clbi
    _    -> die "Building is not supported with this compiler."

buildExe :: Verbosity -> Flag (Maybe Int)
                      -> PackageDescription -> LocalBuildInfo
                      -> Executable         -> ComponentLocalBuildInfo -> IO ()
buildExe verbosity numJobs pkg_descr lbi exe clbi =
  case compilerFlavor (compiler lbi) of
    GHC   -> GHC.buildExe   verbosity numJobs pkg_descr lbi exe clbi
    GHCJS -> GHCJS.buildExe verbosity numJobs pkg_descr lbi exe clbi
    JHC   -> JHC.buildExe   verbosity         pkg_descr lbi exe clbi
    LHC   -> LHC.buildExe   verbosity         pkg_descr lbi exe clbi
    UHC   -> UHC.buildExe   verbosity         pkg_descr lbi exe clbi
    _     -> die "Building is not supported with this compiler."

replLib :: Verbosity -> PackageDescription -> LocalBuildInfo
                     -> Library            -> ComponentLocalBuildInfo -> IO ()
replLib verbosity pkg_descr lbi lib clbi =
  case compilerFlavor (compiler lbi) of
    -- 'cabal repl' doesn't need to support 'ghc --make -j', so we just pass
    -- NoFlag as the numJobs parameter.
    GHC   -> GHC.replLib   verbosity NoFlag pkg_descr lbi lib clbi
    GHCJS -> GHCJS.replLib verbosity NoFlag pkg_descr lbi lib clbi
    _     -> die "A REPL is not supported for this compiler."

replExe :: Verbosity -> PackageDescription -> LocalBuildInfo
                     -> Executable         -> ComponentLocalBuildInfo -> IO ()
replExe verbosity pkg_descr lbi exe clbi =
  case compilerFlavor (compiler lbi) of
    GHC   -> GHC.replExe   verbosity NoFlag pkg_descr lbi exe clbi
    GHCJS -> GHCJS.replExe verbosity NoFlag pkg_descr lbi exe clbi
    _     -> die "A REPL is not supported for this compiler."


initialBuildSteps :: FilePath -- ^"dist" prefix
                  -> PackageDescription  -- ^mostly information from the .cabal file
                  -> LocalBuildInfo -- ^Configuration information
                  -> Verbosity -- ^The verbosity to use
                  -> IO ()
initialBuildSteps _distPref pkg_descr lbi verbosity = do
  -- check that there's something to build
  let buildInfos =
          map libBuildInfo (maybeToList (library pkg_descr)) ++
          map buildInfo (executables pkg_descr)
  unless (any buildable buildInfos) $ do
    let name = display (packageId pkg_descr)
    die ("Package " ++ name ++ " can't be built on this system.")

  createDirectoryIfMissingVerbose verbosity True (buildDir lbi)

  writeAutogenFiles verbosity pkg_descr lbi

-- | Generate and write out the Paths_<pkg>.hs and cabal_macros.h files
--
writeAutogenFiles :: Verbosity
                  -> PackageDescription
                  -> LocalBuildInfo
                  -> IO ()
writeAutogenFiles verbosity pkg lbi = do
  createDirectoryIfMissingVerbose verbosity True (autogenModulesDir lbi)

  let pathsModulePath = autogenModulesDir lbi
                    </> ModuleName.toFilePath (autogenModuleName pkg) <.> "hs"
  rewriteFile pathsModulePath (Build.PathsModule.generate pkg lbi)

  let cppHeaderPath = autogenModulesDir lbi </> cppHeaderName
  rewriteFile cppHeaderPath (Build.Macros.generate pkg lbi)

-- | Check that the given build targets are valid in the current context.
--
-- Also swizzle into a more convenient form.
--
checkBuildTargets :: Verbosity -> PackageDescription -> [BuildTarget]
                  -> IO [(ComponentName, Maybe (Either ModuleName FilePath))]
checkBuildTargets _ pkg []      =
    return [ (componentName c, Nothing) | c <- pkgEnabledComponents pkg ]

checkBuildTargets verbosity pkg targets = do

    let (enabled, disabled) =
          partitionEithers
            [ case componentDisabledReason (getComponent pkg cname) of
                Nothing     -> Left  target'
                Just reason -> Right (cname, reason)
            | target <- targets
            , let target'@(cname,_) = swizzleTarget target ]

    case disabled of
      []                 -> return ()
      ((cname,reason):_) -> die $ formatReason (showComponentName cname) reason

    forM_ [ (c, t) | (c, Just t) <- enabled ] $ \(c, t) ->
      warn verbosity $ "Ignoring '" ++ either display id t ++ ". The whole "
                    ++ showComponentName c ++ " will be built. (Support for "
                    ++ "module and file targets has not been implemented yet.)"

    return enabled

  where
    swizzleTarget (BuildTargetComponent c)   = (c, Nothing)
    swizzleTarget (BuildTargetModule    c m) = (c, Just (Left  m))
    swizzleTarget (BuildTargetFile      c f) = (c, Just (Right f))

    formatReason cn DisabledComponent =
        "Cannot build the " ++ cn ++ " because the component is marked "
     ++ "as disabled in the .cabal file."
    formatReason cn DisabledAllTests =
        "Cannot build the " ++ cn ++ " because test suites are not "
     ++ "enabled. Run configure with the flag --enable-tests"
    formatReason cn DisabledAllBenchmarks =
        "Cannot build the " ++ cn ++ " because benchmarks are not "
     ++ "enabled. Re-run configure with the flag --enable-benchmarks"