Distribution/Simple/Build.hs

    -----------------------------------------------------------------------------
    -- |
    -- 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"