content: -----------------------------------------------------------------------------
  -- |
  -- Module      :  Distribution.Simple.Build
  -- Copyright   :  Isaac Jones 2003-2005,
  --                Ross Paterson 2006,
  --                Duncan Coutts 2007-2008, 2012
  --
  -- 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.
  --
  
  {- Copyright (c) 2003-2005, Isaac Jones
  All rights reserved.
  
  Redistribution and use in source and binary forms, with or without
  modification, are permitted provided that the following conditions are
  met:
  
      * Redistributions of source code must retain the above copyright
        notice, this list of conditions and the following disclaimer.
  
      * Redistributions in binary form must reproduce the above
        copyright notice, this list of conditions and the following
        disclaimer in the documentation and/or other materials provided
        with the distribution.
  
      * Neither the name of Isaac Jones nor the names of other
        contributors may be used to endorse or promote products derived
        from this software without specific prior written permission.
  
  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. -}
  
  module Distribution.Simple.Build (
      build, repl,
  
      initialBuildSteps,
      writeAutogenFiles,
    ) where
  
  import qualified Distribution.Simple.GHC  as GHC
  import qualified Distribution.Simple.JHC  as JHC
  import qualified Distribution.Simple.LHC  as LHC
  import qualified Distribution.Simple.NHC  as NHC
  import qualified Distribution.Simple.Hugs as Hugs
  import qualified Distribution.Simple.UHC  as UHC
  
  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 )
  import Distribution.Simple.Compiler
           ( CompilerFlavor(..), compilerFlavor, PackageDB(..) )
  import Distribution.PackageDescription
           ( PackageDescription(..), BuildInfo(..), Library(..), Executable(..)
           , TestSuite(..), TestSuiteInterface(..), Benchmark(..)
           , BenchmarkInterface(..) )
  import qualified Distribution.InstalledPackageInfo as IPI
  import qualified Distribution.ModuleName as ModuleName
  import Distribution.ModuleName (ModuleName)
  
  import Distribution.Simple.Setup
           ( BuildFlags(..), ReplFlags(..), fromFlag )
  import Distribution.Simple.BuildTarget
           ( BuildTarget(..), readBuildTargets )
  import Distribution.Simple.PreProcess
           ( preprocessComponent, PPSuffixHandler )
  import Distribution.Simple.LocalBuildInfo
           ( LocalBuildInfo(compiler, buildDir, withPackageDB, withPrograms)
           , 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 Distribution.Simple.BuildPaths
           ( autogenModulesDir, autogenModuleName, cppHeaderName, exeExtension )
  import Distribution.Simple.Register
           ( registerPackage, inplaceInstalledPackageInfo )
  import Distribution.Simple.Test ( stubFilePath, stubName )
  import Distribution.Simple.Utils
           ( createDirectoryIfMissingVerbose, rewriteFile
           , die, info, debug, warn, setupMessage )
  
  import Distribution.Verbosity
           ( Verbosity )
  import Distribution.Text
           ( display )
  
  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 )
  
  -- -----------------------------------------------------------------------------
  -- |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 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 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 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 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
  
  
  buildComponent :: Verbosity
                 -> PackageDescription
                 -> LocalBuildInfo
                 -> [PPSuffixHandler]
                 -> Component
                 -> ComponentLocalBuildInfo
                 -> FilePath
                 -> IO ()
  buildComponent verbosity pkg_descr lbi suffixes
                 comp@(CLib lib) clbi distPref = do
      preprocessComponent pkg_descr comp lbi False verbosity suffixes
      info verbosity "Building library..."
      buildLib verbosity pkg_descr lbi lib clbi
  
      -- Register the library in-place, so exes can depend
      -- on internally defined libraries.
      pwd <- getCurrentDirectory
      let installedPkgInfo =
            (inplaceInstalledPackageInfo pwd distPref pkg_descr lib lbi clbi) {
              -- The inplace registration uses the "-inplace" suffix,
              -- not an ABI hash.
              IPI.installedPackageId = inplacePackageId (packageId installedPkgInfo)
            }
      registerPackage verbosity
        installedPkgInfo pkg_descr lbi True -- True meaning inplace
        (withPackageDB lbi)
  
  
  buildComponent verbosity 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 pkg_descr lbi exe clbi
  
  
  buildComponent 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
      info verbosity $ "Building test suite " ++ testName test ++ "..."
      buildExe verbosity pkg_descr lbi exe clbi
  
  
  buildComponent verbosity pkg_descr lbi 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, ipi, exe, exeClbi) =
            testSuiteLibV09AsLibAndExe pkg_descr lbi test clbi distPref pwd
      preprocessComponent pkg_descr comp lbi False verbosity suffixes
      info verbosity $ "Building test suite " ++ testName test ++ "..."
      buildLib verbosity pkg lbi lib libClbi
      registerPackage verbosity ipi pkg lbi True $ withPackageDB lbi
      buildExe verbosity pkg_descr lbi exe exeClbi
  
  
  buildComponent _ _ _ _
                 (CTest TestSuite { testInterface = TestSuiteUnsupported tt })
                 _ _ =
      die $ "No support for building test suite type " ++ display tt
  
  
  buildComponent 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
      info verbosity $ "Building benchmark " ++ benchmarkName bm ++ "..."
      buildExe verbosity 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 lbi suffixes
                 comp@(CTest
                   test@TestSuite { testInterface = TestSuiteLibV09{} })
                 clbi distPref = do
      pwd <- getCurrentDirectory
      let (pkg, lib, libClbi, _, _, _) =
            testSuiteLibV09AsLibAndExe pkg_descr lbi test clbi 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
                             -> LocalBuildInfo
                             -> TestSuite
                             -> ComponentLocalBuildInfo
                             -> FilePath
                             -> FilePath
                             -> (PackageDescription,
                                 Library, ComponentLocalBuildInfo,
                                 IPI.InstalledPackageInfo_ ModuleName,
                                 Executable, ComponentLocalBuildInfo)
  testSuiteLibV09AsLibAndExe pkg_descr lbi
                       test@TestSuite { testInterface = TestSuiteLibV09 _ m }
                       clbi distPref pwd =
      (pkg, lib, libClbi, ipi, exe, exeClbi)
    where
      bi  = testBuildInfo test
      lib = Library {
              exposedModules = [ m ],
              libExposed     = True,
              libBuildInfo   = bi
            }
      libClbi = LibComponentLocalBuildInfo
                  { componentPackageDeps = componentPackageDeps clbi
                  , componentLibraries = [LibraryName (testName test)]
                  }
      pkg = pkg_descr {
              package      = (package pkg_descr) {
                               pkgName = PackageName (testName test)
                             }
            , buildDepends = targetBuildDepends $ testBuildInfo test
            , executables  = []
            , testSuites   = []
            , library      = Just lib
            }
      ipi = (inplaceInstalledPackageInfo pwd distPref pkg lib lbi libClbi) {
              IPI.installedPackageId = inplacePackageId $ packageId ipi
            }
      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)
                           }
            }
      -- | 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))
                }
  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
                }
  benchmarkExeV10asExe Benchmark{} _ = error "benchmarkExeV10asExe: wrong kind"
  
  -- | Initialize a new package db file for libraries defined
  -- internally to the package.
  createInternalPackageDB :: FilePath -> IO PackageDB
  createInternalPackageDB distPref = do
      let dbFile = distPref </> "package.conf.inplace"
          packageDB = SpecificPackageDB dbFile
      writeFile dbFile "[]"
      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 testsuites
  buildLib :: Verbosity -> PackageDescription -> LocalBuildInfo
                        -> Library            -> ComponentLocalBuildInfo -> IO ()
  buildLib verbosity pkg_descr lbi lib clbi =
    case compilerFlavor (compiler lbi) of
      GHC  -> GHC.buildLib  verbosity pkg_descr lbi lib clbi
      JHC  -> JHC.buildLib  verbosity pkg_descr lbi lib clbi
      LHC  -> LHC.buildLib  verbosity pkg_descr lbi lib clbi
      Hugs -> Hugs.buildLib verbosity pkg_descr lbi lib clbi
      NHC  -> NHC.buildLib  verbosity pkg_descr lbi lib clbi
      UHC  -> UHC.buildLib  verbosity pkg_descr lbi lib clbi
      _    -> die "Building is not supported with this compiler."
  
  buildExe :: Verbosity -> PackageDescription -> LocalBuildInfo
                        -> Executable         -> ComponentLocalBuildInfo -> IO ()
  buildExe verbosity pkg_descr lbi exe clbi =
    case compilerFlavor (compiler lbi) of
      GHC  -> GHC.buildExe  verbosity pkg_descr lbi exe clbi
      JHC  -> JHC.buildExe  verbosity pkg_descr lbi exe clbi
      LHC  -> LHC.buildExe  verbosity pkg_descr lbi exe clbi
      Hugs -> Hugs.buildExe verbosity pkg_descr lbi exe clbi
      NHC  -> NHC.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
      GHC  -> GHC.replLib verbosity 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 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"
  