Distribution/Simple/Build.hs

    -----------------------------------------------------------------------------
    -- |
    -- 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 Distribution.Package
    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.Simple.Compiler hiding (Flag)
    import Distribution.PackageDescription hiding (Flag)
    import qualified Distribution.InstalledPackageInfo as IPI
    import qualified Distribution.ModuleName as ModuleName
    import Distribution.ModuleName (ModuleName)

    import Distribution.Simple.Setup
    import Distribution.Simple.BuildTarget
    import Distribution.Simple.PreProcess
    import Distribution.Simple.LocalBuildInfo
    import Distribution.Simple.Program.Types
    import Distribution.Simple.Program.Db
    import Distribution.Simple.BuildPaths
    import Distribution.Simple.Configure
    import Distribution.Simple.Register
    import Distribution.Simple.Test.LibV09
    import Distribution.Simple.Utils

    import Distribution.System
    import Distribution.Text
    import Distribution.Verbosity

    import qualified Data.Map as Map
    import qualified Data.Set as Set
    import Data.Either
             ( partitionEithers )
    import Data.List
             ( intersect )
    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 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 -> Platform
                     -> PackageDBStack -> IO ()
    startInterpreter verbosity programDb comp platform packageDBs =
      case compilerFlavor comp of
        GHC   -> GHC.startInterpreter   verbosity programDb comp platform packageDBs
        GHCJS -> GHCJS.startInterpreter verbosity programDb comp platform 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
        extras <- preprocessExtras comp lbi
        info verbosity "Building library..."
        let libbi = libBuildInfo lib
            lib' = lib { libBuildInfo = addExtraCSources libbi extras }
        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
            installedPkgInfo = inplaceInstalledPackageInfo pwd distPref pkg_descr
                                                           (AbiHash "") lib' lbi clbi

        registerPackage verbosity (compiler lbi) (withPrograms lbi) False
                        (withPackageDB lbi) installedPkgInfo

    buildComponent verbosity numJobs pkg_descr lbi suffixes
                   comp@(CExe exe) clbi _ = do
        preprocessComponent pkg_descr comp lbi False verbosity suffixes
        extras <- preprocessExtras comp lbi
        info verbosity $ "Building executable " ++ exeName exe ++ "..."
        let ebi = buildInfo exe
            exe' = exe { buildInfo = addExtraCSources ebi extras }
        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
        extras <- preprocessExtras comp lbi
        info verbosity $ "Building test suite " ++ testName test ++ "..."
        let ebi = buildInfo exe
            exe' = exe { buildInfo = addExtraCSources ebi extras }
        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
        extras <- preprocessExtras comp lbi
        info verbosity $ "Building test suite " ++ testName test ++ "..."
        buildLib verbosity numJobs pkg lbi lib libClbi
        -- NB: need to enable multiple instances here, because on 7.10+
        -- the package name is the same as the library, and we still
        -- want the registration to go through.
        registerPackage verbosity (compiler lbi) (withPrograms lbi) True
                        (withPackageDB lbi) ipi
        let ebi = buildInfo exe
            exe' = exe { buildInfo = addExtraCSources ebi extras }
        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
        extras <- preprocessExtras comp lbi
        info verbosity $ "Building benchmark " ++ benchmarkName bm ++ "..."
        let ebi = buildInfo exe
            exe' = exe { buildInfo = addExtraCSources ebi extras }
        buildExe verbosity numJobs pkg_descr lbi exe' exeClbi

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

    -- | Add extra C sources generated by preprocessing to build
    -- information.
    addExtraCSources :: BuildInfo -> [FilePath] -> BuildInfo
    addExtraCSources bi extras = bi { cSources = new }
      where new = Set.toList $ old `Set.union` exs
            old = Set.fromList $ cSources bi
            exs = Set.fromList extras

    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
        extras <- preprocessExtras comp lbi
        let libbi = libBuildInfo lib
            lib' = lib { libBuildInfo = libbi { cSources = cSources libbi ++ extras } }
        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
        extras <- preprocessExtras comp lbi
        let ebi = buildInfo exe
            exe' = exe { buildInfo = ebi { cSources = cSources ebi ++ extras } }
        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
        extras <- preprocessExtras comp lbi
        let ebi = buildInfo exe
            exe' = exe { buildInfo = ebi { cSources = cSources ebi ++ extras } }
        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
        extras <- preprocessExtras comp lbi
        let libbi = libBuildInfo lib
            lib' = lib { libBuildInfo = libbi { cSources = cSources libbi ++ extras } }
        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
        extras <- preprocessExtras comp lbi
        let ebi = buildInfo exe
            exe' = exe { buildInfo = ebi { cSources = cSources ebi ++ extras } }
        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,
                                   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
              }
        -- NB: temporary hack; I have a refactor which solves this
        cid = computeComponentId (package pkg_descr)
                                 (CTestName (testName test))
                                 (map ((\(SimpleUnitId cid0) -> cid0) . fst)
                                      (componentPackageDeps clbi))
                                 (flagAssignment lbi)
        uid = SimpleUnitId cid
        (pkg_name, compat_key) = computeCompatPackageKey
                                    (compiler lbi) (package pkg_descr)
                                    (CTestName (testName test)) uid
        libClbi = LibComponentLocalBuildInfo
                    { componentPackageDeps = componentPackageDeps clbi
                    , componentPackageRenaming = componentPackageRenaming clbi
                    , componentUnitId = uid
                    , componentCompatPackageKey = compat_key
                    , componentExposedModules = [IPI.ExposedModule m Nothing]
                    }
        pkg = pkg_descr {
                package      = (package pkg_descr) { pkgName = pkg_name }
              , buildDepends = targetBuildDepends $ testBuildInfo test
              , executables  = []
              , testSuites   = []
              , library      = Just lib
              }
        ipi    = inplaceInstalledPackageInfo pwd distPref pkg (AbiHash "") 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.empty
                             }
              }
        -- | The stub executable needs a new 'ComponentLocalBuildInfo'
        -- that exposes the relevant test suite library.
        exeClbi = ExeComponentLocalBuildInfo {
                    componentPackageDeps =
                        (IPI.installedUnitId ipi, packageId ipi)
                      : (filter (\(_, x) -> let PackageName name = pkgName x
                                            in name == "Cabal" || name == "base")
                                (componentPackageDeps clbi)),
                    componentPackageRenaming = Map.empty
                  }
    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
        existsAlready <- doesPackageDBExist dbPath
        when existsAlready $ deletePackageDB dbPath
        createPackageDB verbosity (compiler lbi) (withPrograms lbi) False dbPath
        return (SpecificPackageDB dbPath)
      where
          dbPath = case compilerFlavor (compiler lbi) of
            UHC -> UHC.inplacePackageDbPath lbi
            _   -> distPref </> "package.conf.inplace"

    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
      unless (not . null $ allBuildInfo pkg_descr) $ do
        let name = display (packageId pkg_descr)
        die $ "No libraries, executables, tests, or benchmarks "
           ++ "are enabled for package " ++ name ++ "."

      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"