    -----------------------------------------------------------------------------
    -- |
    -- Module      :  Distribution.Simple.Configure
    -- Copyright   :  Isaac Jones 2003-2005
    --
    -- Maintainer  :  cabal-devel@haskell.org
    -- Portability :  portable
    --
    -- This deals with the /configure/ phase. It provides the 'configure' action
    -- which is given the package description and configure flags. It then tries
    -- to: configure the compiler; resolves any conditionals in the package
    -- description; resolve the package dependencies; check if all the extensions
    -- used by this package are supported by the compiler; check that all the build
    -- tools are available (including version checks if appropriate); checks for
    -- any required @pkg-config@ packages (updating the 'BuildInfo' with the
    -- results)
    --
    -- Then based on all this it saves the info in the 'LocalBuildInfo' and writes
    -- it out to the @dist\/setup-config@ file. It also displays various details to
    -- the user, the amount of information displayed depending on the verbosity
    -- level.

    {- 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.Configure (configure,
                                          writePersistBuildConfig,
                                          getPersistBuildConfig,
                                          checkPersistBuildConfigOutdated,
                                          maybeGetPersistBuildConfig,
                                          localBuildInfoFile,
                                          getInstalledPackages,
                                          configCompiler, configCompilerAux,
                                          ccLdOptionsBuildInfo,
                                          tryGetConfigStateFile,
                                          checkForeignDeps,
                                         )
        where

    import Distribution.Simple.Compiler
        ( CompilerFlavor(..), Compiler(compilerId), compilerFlavor, compilerVersion
        , showCompilerId, unsupportedLanguages, unsupportedExtensions
        , PackageDB(..), PackageDBStack )
    import Distribution.Package
        ( PackageName(PackageName), PackageIdentifier(PackageIdentifier), PackageId
        , packageName, packageVersion, Package(..)
        , Dependency(Dependency), simplifyDependency
        , InstalledPackageId(..) )
    import Distribution.InstalledPackageInfo as Installed
        ( InstalledPackageInfo, InstalledPackageInfo_(..)
        , emptyInstalledPackageInfo )
    import qualified Distribution.Simple.PackageIndex as PackageIndex
    import Distribution.Simple.PackageIndex (PackageIndex)
    import Distribution.PackageDescription as PD
        ( PackageDescription(..), specVersion, GenericPackageDescription(..)
        , Library(..), hasLibs, Executable(..), BuildInfo(..), allExtensions
        , HookedBuildInfo, updatePackageDescription, allBuildInfo
        , FlagName(..), TestSuite(..) )
    import Distribution.PackageDescription.Configuration
        ( finalizePackageDescription, mapTreeData )
    import Distribution.PackageDescription.Check
        ( PackageCheck(..), checkPackage, checkPackageFiles )
    import Distribution.Simple.Program
        ( Program(..), ProgramLocation(..), ConfiguredProgram(..)
        , ProgramConfiguration, defaultProgramConfiguration
        , configureAllKnownPrograms, knownPrograms, lookupKnownProgram
        , userSpecifyArgss, userSpecifyPaths
        , requireProgram, requireProgramVersion
        , pkgConfigProgram, gccProgram, rawSystemProgramStdoutConf )
    import Distribution.Simple.Setup
        ( ConfigFlags(..), CopyDest(..), fromFlag, fromFlagOrDefault, flagToMaybe )
    import Distribution.Simple.InstallDirs
        ( InstallDirs(..), defaultInstallDirs, combineInstallDirs )
    import Distribution.Simple.LocalBuildInfo
        ( LocalBuildInfo(..), ComponentLocalBuildInfo(..)
        , absoluteInstallDirs, prefixRelativeInstallDirs, inplacePackageId )
    import Distribution.Simple.BuildPaths
        ( autogenModulesDir )
    import Distribution.Simple.Utils
        ( die, warn, info, setupMessage, createDirectoryIfMissingVerbose
        , intercalate, cabalVersion
        , withFileContents, writeFileAtomic
        , withTempFile )
    import Distribution.System
        ( OS(..), buildOS, buildPlatform )
    import Distribution.Version
             ( Version(..), anyVersion, orLaterVersion, withinRange, isAnyVersion )
    import Distribution.Verbosity
        ( Verbosity, lessVerbose )

    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 Control.Monad
        ( when, unless, foldM, filterM )
    import Data.List
        ( nub, partition, isPrefixOf, inits )
    import Data.Maybe
             ( isNothing, catMaybes )
    import Data.Monoid
        ( Monoid(..) )
    import System.Directory
        ( doesFileExist, getModificationTime, createDirectoryIfMissing, getTemporaryDirectory )
    import System.Exit
        ( ExitCode(..), exitWith )
    import System.FilePath
        ( (</>), isAbsolute )
    import qualified System.Info
        ( compilerName, compilerVersion )
    import System.IO
        ( hPutStrLn, stderr, hClose )
    import Distribution.Text
        ( Text(disp), display, simpleParse )
    import Text.PrettyPrint.HughesPJ
        ( comma, punctuate, render, nest, sep )
    import Distribution.Compat.Exception ( catchExit, catchIO )

    import Prelude hiding (catch)

    tryGetConfigStateFile :: (Read a) => FilePath -> IO (Either String a)
    tryGetConfigStateFile filename = do
      exists <- doesFileExist filename
      if not exists
        then return (Left missing)
        else withFileContents filename $ \str ->
          case lines str of
            [headder, rest] -> case checkHeader headder of
              Just msg -> return (Left msg)
              Nothing  -> case reads rest of
                [(bi,_)] -> return (Right bi)
                _        -> return (Left cantParse)
            _            -> return (Left cantParse)
      where
        checkHeader :: String -> Maybe String
        checkHeader header = case parseHeader header of
          Just (cabalId, compId)
            | cabalId
           == currentCabalId -> Nothing
            | otherwise      -> Just (badVersion cabalId compId)
          Nothing            -> Just cantParse

        missing   = "Run the 'configure' command first."
        cantParse = "Saved package config file seems to be corrupt. "
                 ++ "Try re-running the 'configure' command."
        badVersion cabalId compId
                  = "You need to re-run the 'configure' command. "
                 ++ "The version of Cabal being used has changed (was "
                 ++ display cabalId ++ ", now "
                 ++ display currentCabalId ++ ")."
                 ++ badcompiler compId
        badcompiler compId | compId == currentCompilerId = ""
                           | otherwise
                  = " Additionally the compiler is different (was "
                 ++ display compId ++ ", now "
                 ++ display currentCompilerId
                 ++ ") which is probably the cause of the problem."

    -- internal function
    tryGetPersistBuildConfig :: FilePath -> IO (Either String LocalBuildInfo)
    tryGetPersistBuildConfig distPref
        = tryGetConfigStateFile (localBuildInfoFile distPref)

    -- |Read the 'localBuildInfoFile'.  Error if it doesn't exist.  Also
    -- fail if the file containing LocalBuildInfo is older than the .cabal
    -- file, indicating that a re-configure is required.
    getPersistBuildConfig :: FilePath -> IO LocalBuildInfo
    getPersistBuildConfig distPref = do
      lbi <- tryGetPersistBuildConfig distPref
      either die return lbi

    -- |Try to read the 'localBuildInfoFile'.
    maybeGetPersistBuildConfig :: FilePath -> IO (Maybe LocalBuildInfo)
    maybeGetPersistBuildConfig distPref = do
      lbi <- tryGetPersistBuildConfig distPref
      return $ either (const Nothing) Just lbi

    -- |After running configure, output the 'LocalBuildInfo' to the
    -- 'localBuildInfoFile'.
    writePersistBuildConfig :: FilePath -> LocalBuildInfo -> IO ()
    writePersistBuildConfig distPref lbi = do
      createDirectoryIfMissing False distPref
      writeFileAtomic (localBuildInfoFile distPref)
                      (showHeader pkgid ++ '\n' : show lbi)
      where
        pkgid   = packageId (localPkgDescr lbi)

    showHeader :: PackageIdentifier -> String
    showHeader pkgid =
         "Saved package config for " ++ display pkgid
      ++ " written by " ++ display currentCabalId
      ++      " using " ++ display currentCompilerId
      where

    currentCabalId :: PackageIdentifier
    currentCabalId = PackageIdentifier (PackageName "Cabal") cabalVersion

    currentCompilerId :: PackageIdentifier
    currentCompilerId = PackageIdentifier (PackageName System.Info.compilerName)
                                          System.Info.compilerVersion

    parseHeader :: String -> Maybe (PackageIdentifier, PackageIdentifier)
    parseHeader header = case words header of
      ["Saved", "package", "config", "for", pkgid,
       "written", "by", cabalid, "using", compilerid]
        -> case (simpleParse pkgid :: Maybe PackageIdentifier,
                 simpleParse cabalid,
                 simpleParse compilerid) of
            (Just _,
             Just cabalid',
             Just compilerid') -> Just (cabalid', compilerid')
            _                  -> Nothing
      _                        -> Nothing

    -- |Check that localBuildInfoFile is up-to-date with respect to the
    -- .cabal file.
    checkPersistBuildConfigOutdated :: FilePath -> FilePath -> IO Bool
    checkPersistBuildConfigOutdated distPref pkg_descr_file = do
      t0 <- getModificationTime pkg_descr_file
      t1 <- getModificationTime $ localBuildInfoFile distPref
      return (t0 > t1)

    -- |@dist\/setup-config@
    localBuildInfoFile :: FilePath -> FilePath
    localBuildInfoFile distPref = distPref </> "setup-config"

    -- -----------------------------------------------------------------------------
    -- * Configuration
    -- -----------------------------------------------------------------------------

    -- |Perform the \"@.\/setup configure@\" action.
    -- Returns the @.setup-config@ file.
    configure :: (GenericPackageDescription, HookedBuildInfo)
              -> ConfigFlags -> IO LocalBuildInfo
    configure (pkg_descr0, pbi) cfg
      = do  let distPref = fromFlag (configDistPref cfg)
                verbosity = fromFlag (configVerbosity cfg)

            setupMessage verbosity "Configuring" (packageId pkg_descr0)

            createDirectoryIfMissingVerbose (lessVerbose verbosity) True distPref

            let programsConfig = userSpecifyArgss (configProgramArgs cfg)
                               . userSpecifyPaths (configProgramPaths cfg)
                               $ configPrograms cfg
                userInstall = fromFlag (configUserInstall cfg)
                packageDbs = implicitPackageDbStack userInstall
                               (flagToMaybe $ configPackageDB cfg)

            -- detect compiler
            (comp, programsConfig') <- configCompiler
              (flagToMaybe $ configHcFlavor cfg)
              (flagToMaybe $ configHcPath cfg) (flagToMaybe $ configHcPkg cfg)
              programsConfig (lessVerbose verbosity)
            let version = compilerVersion comp
                flavor  = compilerFlavor comp

            -- Create a PackageIndex that makes *any libraries that might be*
            -- defined internally to this package look like installed packages, in
            -- case an executable should refer to any of them as dependencies.
            --
            -- It must be *any libraries that might be* defined rather than the
            -- actual definitions, because these depend on conditionals in the .cabal
            -- file, and we haven't resolved them yet.  finalizePackageDescription
            -- does the resolution of conditionals, and it takes internalPackageSet
            -- as part of its input.
            --
            -- Currently a package can define no more than one library (which has
            -- the same name as the package) but we could extend this later.
            -- If we later allowed private internal libraries, then here we would
            -- need to pre-scan the conditional data to make a list of all private
            -- libraries that could possibly be defined by the .cabal file.
            let pid = packageId pkg_descr0
                internalPackage = emptyInstalledPackageInfo {
                    --TODO: should use a per-compiler method to map the source
                    --      package ID into an installed package id we can use
                    --      for the internal package set. The open-codes use of
                    --      InstalledPackageId . display here is a hack.
                    Installed.installedPackageId = InstalledPackageId $ display $ pid,
                    Installed.sourcePackageId = pid
                  }
                internalPackageSet = PackageIndex.fromList [internalPackage]
            installedPackageSet <- getInstalledPackages (lessVerbose verbosity) comp
                                          packageDbs programsConfig'

            let -- Constraint test function for the solver
                dependencySatisfiable =
                    not . null . PackageIndex.lookupDependency pkgs'
                  where
                    pkgs' = PackageIndex.insert internalPackage installedPackageSet
                enableTest t = t { testEnabled = fromFlag (configTests cfg) }
                flaggedTests = map (\(n, t) -> (n, mapTreeData enableTest t))
                                   (condTestSuites pkg_descr0)
                pkg_descr0'' = pkg_descr0 { condTestSuites = flaggedTests }

            (pkg_descr0', flags) <-
                    case finalizePackageDescription
                           (configConfigurationsFlags cfg)
                           dependencySatisfiable
                           Distribution.System.buildPlatform
                           (compilerId comp)
                           (configConstraints cfg)
                           pkg_descr0''
                    of Right r -> return r
                       Left missing ->
                           die $ "At least the following dependencies are missing:\n"
                             ++ (render . nest 4 . sep . punctuate comma
                                        . map (disp . simplifyDependency)
                                        $ missing)

            -- add extra include/lib dirs as specified in cfg
            -- we do it here so that those get checked too
            let pkg_descr = addExtraIncludeLibDirs pkg_descr0'

            when (not (null flags)) $
              info verbosity $ "Flags chosen: "
                            ++ intercalate ", " [ name ++ "=" ++ display value
                                                | (FlagName name, value) <- flags ]

            checkPackageProblems verbosity pkg_descr0
              (updatePackageDescription pbi pkg_descr)

            let selectDependencies =
                    (\xs -> ([ x | Left x <- xs ], [ x | Right x <- xs ]))
                  . map (selectDependency internalPackageSet installedPackageSet)

                (failedDeps, allPkgDeps) = selectDependencies (buildDepends pkg_descr)

                internalPkgDeps = [ pkgid | InternalDependency _ pkgid <- allPkgDeps ]
                externalPkgDeps = [ pkg   | ExternalDependency _ pkg   <- allPkgDeps ]

            when (not (null internalPkgDeps) && not (newPackageDepsBehaviour pkg_descr)) $
                die $ "The field 'build-depends: "
                   ++ intercalate ", " (map (display . packageName) internalPkgDeps)
                   ++ "' refers to a library which is defined within the same "
                   ++ "package. To use this feature the package must specify at "
                   ++ "least 'cabal-version: >= 1.8'."

            reportFailedDependencies failedDeps
            reportSelectedDependencies verbosity allPkgDeps

            packageDependsIndex <-
              case PackageIndex.dependencyClosure installedPackageSet
                      (map Installed.installedPackageId externalPkgDeps) of
                Left packageDependsIndex -> return packageDependsIndex
                Right broken ->
                  die $ "The following installed packages are broken because other"
                     ++ " packages they depend on are missing. These broken "
                     ++ "packages must be rebuilt before they can be used.\n"
                     ++ unlines [ "package "
                               ++ display (packageId pkg)
                               ++ " is broken due to missing package "
                               ++ intercalate ", " (map display deps)
                                | (pkg, deps) <- broken ]

            let pseudoTopPkg = emptyInstalledPackageInfo {
                    Installed.installedPackageId = InstalledPackageId (display (packageId pkg_descr)),
                    Installed.sourcePackageId = packageId pkg_descr,
                    Installed.depends = map Installed.installedPackageId externalPkgDeps
                  }
            case PackageIndex.dependencyInconsistencies
               . PackageIndex.insert pseudoTopPkg
               $ packageDependsIndex of
              [] -> return ()
              inconsistencies ->
                warn verbosity $
                     "This package indirectly depends on multiple versions of the same "
                  ++ "package. This is highly likely to cause a compile failure.\n"
                  ++ unlines [ "package " ++ display pkg ++ " requires "
                            ++ display (PackageIdentifier name ver)
                             | (name, uses) <- inconsistencies
                             , (pkg, ver) <- uses ]

            -- installation directories
            defaultDirs <- defaultInstallDirs flavor userInstall (hasLibs pkg_descr)
            let installDirs = combineInstallDirs fromFlagOrDefault
                                defaultDirs (configInstallDirs cfg)

            -- check languages and extensions
            let langlist = nub $ catMaybes $ map defaultLanguage (allBuildInfo pkg_descr)
            let langs = unsupportedLanguages comp langlist
            when (not (null langs)) $
              die $ "The package " ++ display (packageId pkg_descr0)
                 ++ " requires the following languages which are not "
                 ++ "supported by " ++ display (compilerId comp) ++ ": "
                 ++ intercalate ", " (map display langs)
            let extlist = nub $ concatMap allExtensions (allBuildInfo pkg_descr)
            let exts = unsupportedExtensions comp extlist
            when (not (null exts)) $
              die $ "The package " ++ display (packageId pkg_descr0)
                 ++ " requires the following language extensions which are not "
                 ++ "supported by " ++ display (compilerId comp) ++ ": "
                 ++ intercalate ", " (map display exts)

            let requiredBuildTools = concatMap buildTools (allBuildInfo pkg_descr)
            programsConfig'' <-
                  configureAllKnownPrograms (lessVerbose verbosity) programsConfig'
              >>= configureRequiredPrograms verbosity requiredBuildTools

            (pkg_descr', programsConfig''') <- configurePkgconfigPackages verbosity
                                                pkg_descr programsConfig''

            split_objs <-
               if not (fromFlag $ configSplitObjs cfg)
                    then return False
                    else case flavor of
                                GHC | version >= Version [6,5] [] -> return True
                                _ -> do warn verbosity
                                             ("this compiler does not support " ++
                                              "--enable-split-objs; ignoring")
                                        return False

            -- The allPkgDeps contains all the package deps for the whole package
            -- but we need to select the subset for this specific component.
            -- we just take the subset for the package names this component
            -- needs. Note, this only works because we cannot yet depend on two
            -- versions of the same package.
            let configLib lib = configComponent (libBuildInfo lib)
                configExe exe = (exeName exe, configComponent(buildInfo exe))
                configTest test = (testName test,
                        configComponent(testBuildInfo test))
                configComponent bi = ComponentLocalBuildInfo {
                  componentPackageDeps =
                    if newPackageDepsBehaviour pkg_descr'
                      then [ (installedPackageId pkg, packageId pkg)
                           | pkg <- selectSubset bi externalPkgDeps ]
                        ++ [ (inplacePackageId pkgid, pkgid)
                           | pkgid <- selectSubset bi internalPkgDeps ]
                      else [ (installedPackageId pkg, packageId pkg)
                           | pkg <- externalPkgDeps ]
                }
                selectSubset :: Package pkg => BuildInfo -> [pkg] -> [pkg]
                selectSubset bi pkgs =
                    [ pkg | pkg <- pkgs, packageName pkg `elem` names ]
                  where
                    names = [ name | Dependency name _ <- targetBuildDepends bi ]

            let lbi = LocalBuildInfo{
                        configFlags         = cfg,
                        extraConfigArgs     = [],  -- Currently configure does not
                                                   -- take extra args, but if it
                                                   -- did they would go here.
                        installDirTemplates = installDirs,
                        compiler            = comp,
                        buildDir            = distPref </> "build",
                        scratchDir          = fromFlagOrDefault
                                                (distPref </> "scratch")
                                                (configScratchDir cfg),
                        libraryConfig       = configLib `fmap` library pkg_descr',
                        executableConfigs   = configExe `fmap` executables pkg_descr',
                        testSuiteConfigs    = configTest `fmap` filter testEnabled (testSuites pkg_descr'),
                        installedPkgs       = packageDependsIndex,
                        pkgDescrFile        = Nothing,
                        localPkgDescr       = pkg_descr',
                        withPrograms        = programsConfig''',
                        withVanillaLib      = fromFlag $ configVanillaLib cfg,
                        withProfLib         = fromFlag $ configProfLib cfg,
                        withSharedLib       = fromFlag $ configSharedLib cfg,
                        withProfExe         = fromFlag $ configProfExe cfg,
                        withOptimization    = fromFlag $ configOptimization cfg,
                        withGHCiLib         = fromFlag $ configGHCiLib cfg,
                        splitObjs           = split_objs,
                        stripExes           = fromFlag $ configStripExes cfg,
                        withPackageDB       = packageDbs,
                        progPrefix          = fromFlag $ configProgPrefix cfg,
                        progSuffix          = fromFlag $ configProgSuffix cfg
                      }

            let dirs = absoluteInstallDirs pkg_descr lbi NoCopyDest
                relative = prefixRelativeInstallDirs (packageId pkg_descr) lbi

            unless (isAbsolute (prefix dirs)) $ die $
                "expected an absolute directory name for --prefix: " ++ prefix dirs

            info verbosity $ "Using " ++ display currentCabalId
                          ++ " compiled by " ++ display currentCompilerId
            info verbosity $ "Using compiler: " ++ showCompilerId comp
            info verbosity $ "Using install prefix: " ++ prefix dirs

            let dirinfo name dir isPrefixRelative =
                  info verbosity $ name ++ " installed in: " ++ dir ++ relNote
                  where relNote = case buildOS of
                          Windows | not (hasLibs pkg_descr)
                                 && isNothing isPrefixRelative
                                 -> "  (fixed location)"
                          _      -> ""

            dirinfo "Binaries"         (bindir dirs)     (bindir relative)
            dirinfo "Libraries"        (libdir dirs)     (libdir relative)
            dirinfo "Private binaries" (libexecdir dirs) (libexecdir relative)
            dirinfo "Data files"       (datadir dirs)    (datadir relative)
            dirinfo "Documentation"    (docdir dirs)     (docdir relative)

            sequence_ [ reportProgram verbosity prog configuredProg
                      | (prog, configuredProg) <- knownPrograms programsConfig''' ]

            return lbi

        where
          addExtraIncludeLibDirs pkg_descr =
              let extraBi = mempty { extraLibDirs = configExtraLibDirs cfg
                                   , PD.includeDirs = configExtraIncludeDirs cfg}
                  modifyLib l        = l{ libBuildInfo = libBuildInfo l `mappend` extraBi }
                  modifyExecutable e = e{ buildInfo    = buildInfo e    `mappend` extraBi}
              in pkg_descr{ library     = modifyLib        `fmap` library pkg_descr
                          , executables = modifyExecutable  `map` executables pkg_descr}

    -- -----------------------------------------------------------------------------
    -- Configuring package dependencies

    reportProgram :: Verbosity -> Program -> Maybe ConfiguredProgram -> IO ()
    reportProgram verbosity prog Nothing
        = info verbosity $ "No " ++ programName prog ++ " found"
    reportProgram verbosity prog (Just configuredProg)
        = info verbosity $ "Using " ++ programName prog ++ version ++ location
        where location = case programLocation configuredProg of
                FoundOnSystem p -> " found on system at: " ++ p
                UserSpecified p -> " given by user at: " ++ p
              version = case programVersion configuredProg of
                Nothing -> ""
                Just v  -> " version " ++ display v

    hackageUrl :: String
    hackageUrl = "http://hackage.haskell.org/package/"

    data ResolvedDependency = ExternalDependency Dependency InstalledPackageInfo
                            | InternalDependency Dependency PackageId -- should be a lib name

    data FailedDependency = DependencyNotExists PackageName
                          | DependencyNoVersion Dependency

    -- | Test for a package dependency and record the version we have installed.
    selectDependency :: PackageIndex  -- ^ Internally defined packages
                     -> PackageIndex  -- ^ Installed packages
                     -> Dependency
                     -> Either FailedDependency ResolvedDependency
    selectDependency internalIndex installedIndex
      dep@(Dependency pkgname vr) =
      -- If the dependency specification matches anything in the internal package
      -- index, then we prefer that match to anything in the second.
      -- For example:
      --
      -- Name: MyLibrary
      -- Version: 0.1
      -- Library
      --     ..
      -- Executable my-exec
      --     build-depends: MyLibrary
      --
      -- We want "build-depends: MyLibrary" always to match the internal library
      -- even if there is a newer installed library "MyLibrary-0.2".
      -- However, "build-depends: MyLibrary >= 0.2" should match the installed one.
      case PackageIndex.lookupPackageName internalIndex pkgname of
        [(_,[pkg])] | packageVersion pkg `withinRange` vr
               -> Right $ InternalDependency dep (packageId pkg)

        _      -> case PackageIndex.lookupDependency installedIndex dep of
          []   -> Left  $ DependencyNotExists pkgname
          pkgs -> Right $ ExternalDependency dep $
                    -- by default we just pick the latest
                    case last pkgs of
                      (_ver, instances) -> head instances -- the first preference

    reportSelectedDependencies :: Verbosity
                               -> [ResolvedDependency] -> IO ()
    reportSelectedDependencies verbosity deps =
      info verbosity $ unlines
        [ "Dependency " ++ display (simplifyDependency dep)
                        ++ ": using " ++ display pkgid
        | resolved <- deps
        , let (dep, pkgid) = case resolved of
                ExternalDependency dep' pkg'   -> (dep', packageId pkg')
                InternalDependency dep' pkgid' -> (dep', pkgid') ]

    reportFailedDependencies :: [FailedDependency] -> IO ()
    reportFailedDependencies []     = return ()
    reportFailedDependencies failed =
        die (intercalate "\n\n" (map reportFailedDependency failed))

      where
        reportFailedDependency (DependencyNotExists pkgname) =
             "there is no version of " ++ display pkgname ++ " installed.\n"
          ++ "Perhaps you need to download and install it from\n"
          ++ hackageUrl ++ display pkgname ++ "?"

        reportFailedDependency (DependencyNoVersion dep) =
            "cannot satisfy dependency " ++ display (simplifyDependency dep) ++ "\n"

    getInstalledPackages :: Verbosity -> Compiler
                         -> PackageDBStack -> ProgramConfiguration
                         -> IO PackageIndex
    getInstalledPackages verbosity comp packageDBs progconf = do
      info verbosity "Reading installed packages..."
      case compilerFlavor comp of
        GHC -> GHC.getInstalledPackages verbosity packageDBs progconf
        Hugs->Hugs.getInstalledPackages verbosity packageDBs progconf
        JHC -> JHC.getInstalledPackages verbosity packageDBs progconf
        LHC -> LHC.getInstalledPackages verbosity packageDBs progconf
        NHC -> NHC.getInstalledPackages verbosity packageDBs progconf
        UHC -> UHC.getInstalledPackages verbosity comp packageDBs progconf
        flv -> die $ "don't know how to find the installed packages for "
                  ++ display flv

    -- | Currently the user interface specifies the package dbs to use with just a
    -- single valued option, a 'PackageDB'. However internally we represent the
    -- stack of 'PackageDB's explictly as a list. This function converts encodes
    -- the package db stack implicit in a single packagedb.
    --
    implicitPackageDbStack :: Bool -> Maybe PackageDB -> PackageDBStack
    implicitPackageDbStack userInstall maybePackageDB
      | userInstall = GlobalPackageDB : UserPackageDB : extra
      | otherwise   = GlobalPackageDB : extra
      where
        extra = case maybePackageDB of
          Just (SpecificPackageDB db) -> [SpecificPackageDB db]
          _                           -> []

    newPackageDepsBehaviourMinVersion :: Version
    newPackageDepsBehaviourMinVersion = Version { versionBranch = [1,7,1], versionTags = [] }

    -- In older cabal versions, there was only one set of package dependencies for
    -- the whole package. In this version, we can have separate dependencies per
    -- target, but we only enable this behaviour if the minimum cabal version
    -- specified is >= a certain minimum. Otherwise, for compatibility we use the
    -- old behaviour.
    newPackageDepsBehaviour :: PackageDescription -> Bool
    newPackageDepsBehaviour pkg =
       specVersion pkg >= newPackageDepsBehaviourMinVersion

    -- -----------------------------------------------------------------------------
    -- Configuring program dependencies

    configureRequiredPrograms :: Verbosity -> [Dependency] -> ProgramConfiguration -> IO ProgramConfiguration
    configureRequiredPrograms verbosity deps conf =
      foldM (configureRequiredProgram verbosity) conf deps

    configureRequiredProgram :: Verbosity -> ProgramConfiguration -> Dependency -> IO ProgramConfiguration
    configureRequiredProgram verbosity conf (Dependency (PackageName progName) verRange) =
      case lookupKnownProgram progName conf of
        Nothing -> die ("Unknown build tool " ++ progName)
        Just prog
          -- requireProgramVersion always requires the program have a version
          -- but if the user says "build-depends: foo" ie no version constraint
          -- then we should not fail if we cannot discover the program version.
          | verRange == anyVersion -> do
              (_, conf') <- requireProgram verbosity prog conf
              return conf'
          | otherwise -> do
              (_, _, conf') <- requireProgramVersion verbosity prog verRange conf
              return conf'

    -- -----------------------------------------------------------------------------
    -- Configuring pkg-config package dependencies

    configurePkgconfigPackages :: Verbosity -> PackageDescription
                               -> ProgramConfiguration
                               -> IO (PackageDescription, ProgramConfiguration)
    configurePkgconfigPackages verbosity pkg_descr conf
      | null allpkgs = return (pkg_descr, conf)
      | otherwise    = do
        (_, _, conf') <- requireProgramVersion
                           (lessVerbose verbosity) pkgConfigProgram
                           (orLaterVersion $ Version [0,9,0] []) conf
        mapM_ requirePkg allpkgs
        lib'  <- updateLibrary (library pkg_descr)
        exes' <- mapM updateExecutable (executables pkg_descr)
        let pkg_descr' = pkg_descr { library = lib', executables = exes' }
        return (pkg_descr', conf')

      where
        allpkgs = concatMap pkgconfigDepends (allBuildInfo pkg_descr)
        pkgconfig = rawSystemProgramStdoutConf (lessVerbose verbosity)
                      pkgConfigProgram conf

        requirePkg dep@(Dependency (PackageName pkg) range) = do
          version <- pkgconfig ["--modversion", pkg]
                     `catchIO`   (\_ -> die notFound)
                     `catchExit` (\_ -> die notFound)
          case simpleParse version of
            Nothing -> die "parsing output of pkg-config --modversion failed"
            Just v | not (withinRange v range) -> die (badVersion v)
                   | otherwise                 -> info verbosity (depSatisfied v)
          where
            notFound     = "The pkg-config package " ++ pkg ++ versionRequirement
                        ++ " is required but it could not be found."
            badVersion v = "The pkg-config package " ++ pkg ++ versionRequirement
                        ++ " is required but the version installed on the"
                        ++ " system is version " ++ display v
            depSatisfied v = "Dependency " ++ display dep
                          ++ ": using version " ++ display v

            versionRequirement
              | isAnyVersion range = ""
              | otherwise          = " version " ++ display range

        updateLibrary Nothing    = return Nothing
        updateLibrary (Just lib) = do
          bi <- pkgconfigBuildInfo (pkgconfigDepends (libBuildInfo lib))
          return $ Just lib { libBuildInfo = libBuildInfo lib `mappend` bi }

        updateExecutable exe = do
          bi <- pkgconfigBuildInfo (pkgconfigDepends (buildInfo exe))
          return exe { buildInfo = buildInfo exe `mappend` bi }

        pkgconfigBuildInfo :: [Dependency] -> IO BuildInfo
        pkgconfigBuildInfo []      = return mempty
        pkgconfigBuildInfo pkgdeps = do
          let pkgs = nub [ display pkg | Dependency pkg _ <- pkgdeps ]
          ccflags <- pkgconfig ("--cflags" : pkgs)
          ldflags <- pkgconfig ("--libs"   : pkgs)
          return (ccLdOptionsBuildInfo (words ccflags) (words ldflags))

    -- | Makes a 'BuildInfo' from C compiler and linker flags.
    --
    -- This can be used with the output from configuration programs like pkg-config
    -- and similar package-specific programs like mysql-config, freealut-config etc.
    -- For example:
    --
    -- > ccflags <- rawSystemProgramStdoutConf verbosity prog conf ["--cflags"]
    -- > ldflags <- rawSystemProgramStdoutConf verbosity prog conf ["--libs"]
    -- > return (ccldOptionsBuildInfo (words ccflags) (words ldflags))
    --
    ccLdOptionsBuildInfo :: [String] -> [String] -> BuildInfo
    ccLdOptionsBuildInfo cflags ldflags =
      let (includeDirs',  cflags')   = partition ("-I" `isPrefixOf`) cflags
          (extraLibs',    ldflags')  = partition ("-l" `isPrefixOf`) ldflags
          (extraLibDirs', ldflags'') = partition ("-L" `isPrefixOf`) ldflags'
      in mempty {
           PD.includeDirs  = map (drop 2) includeDirs',
           PD.extraLibs    = map (drop 2) extraLibs',
           PD.extraLibDirs = map (drop 2) extraLibDirs',
           PD.ccOptions    = cflags',
           PD.ldOptions    = ldflags''
         }

    -- -----------------------------------------------------------------------------
    -- Determining the compiler details

    configCompilerAux :: ConfigFlags -> IO (Compiler, ProgramConfiguration)
    configCompilerAux cfg = configCompiler (flagToMaybe $ configHcFlavor cfg)
                                           (flagToMaybe $ configHcPath cfg)
                                           (flagToMaybe $ configHcPkg cfg)
                                           programsConfig
                                           (fromFlag (configVerbosity cfg))
      where
        programsConfig = userSpecifyArgss (configProgramArgs cfg)
                       . userSpecifyPaths (configProgramPaths cfg)
                       $ defaultProgramConfiguration

    configCompiler :: Maybe CompilerFlavor -> Maybe FilePath -> Maybe FilePath
                   -> ProgramConfiguration -> Verbosity
                   -> IO (Compiler, ProgramConfiguration)
    configCompiler Nothing _ _ _ _ = die "Unknown compiler"
    configCompiler (Just hcFlavor) hcPath hcPkg conf verbosity = do
      case hcFlavor of
          GHC  -> GHC.configure  verbosity hcPath hcPkg conf
          JHC  -> JHC.configure  verbosity hcPath hcPkg conf
          LHC  -> do (_,ghcConf) <- GHC.configure  verbosity Nothing hcPkg conf
                     LHC.configure  verbosity hcPath Nothing ghcConf
          Hugs -> Hugs.configure verbosity hcPath hcPkg conf
          NHC  -> NHC.configure  verbosity hcPath hcPkg conf
          UHC  -> UHC.configure  verbosity hcPath hcPkg conf
          _    -> die "Unknown compiler"

    -- Try to build a test C program which includes every header and links every
    -- lib. If that fails, try to narrow it down by preprocessing (only) and linking
    -- with individual headers and libs.  If none is the obvious culprit then give a
    -- generic error message.
    -- TODO: produce a log file from the compiler errors, if any.
    checkForeignDeps :: PackageDescription -> LocalBuildInfo -> Verbosity -> IO ()
    checkForeignDeps pkg lbi verbosity = do
      ifBuildsWith allHeaders (commonCcArgs ++ makeLdArgs allLibs) -- I'm feeling lucky
               (return ())
               (do missingLibs <- findMissingLibs
                   missingHdr  <- findOffendingHdr
                   explainErrors missingHdr missingLibs)
          where
            allHeaders = collectField PD.includes
            allLibs    = collectField PD.extraLibs

            ifBuildsWith headers args success failure = do
                ok <- builds (makeProgram headers) args
                if ok then success else failure

            findOffendingHdr =
                ifBuildsWith allHeaders ccArgs
                             (return Nothing)
                             (go . tail . inits $ allHeaders)
                where
                  go [] = return Nothing       -- cannot happen
                  go (hdrs:hdrsInits) =
                        -- Try just preprocessing first
                        ifBuildsWith hdrs cppArgs
                          -- If that works, try compiling too
                          (ifBuildsWith hdrs ccArgs
                            (go hdrsInits)
                            (return . Just . Right . last $ hdrs))
                          (return . Just . Left . last $ hdrs)

                  cppArgs = "-E":commonCppArgs -- preprocess only
                  ccArgs  = "-c":commonCcArgs  -- don't try to link

            findMissingLibs = ifBuildsWith [] (makeLdArgs allLibs)
                                           (return [])
                                           (filterM (fmap not . libExists) allLibs)

            libExists lib = builds (makeProgram []) (makeLdArgs [lib])

            commonCppArgs = hcDefines (compiler lbi)
                         ++ [ "-I" ++ autogenModulesDir lbi ]
                         ++ [ "-I" ++ dir | dir <- collectField PD.includeDirs ]
                         ++ ["-I."]
                         ++ collectField PD.cppOptions
                         ++ collectField PD.ccOptions
                         ++ [ "-I" ++ dir
                            | dep <- deps
                            , dir <- Installed.includeDirs dep ]
                         ++ [ opt
                            | dep <- deps
                            , opt <- Installed.ccOptions dep ]

            commonCcArgs  = commonCppArgs
                         ++ collectField PD.ccOptions
                         ++ [ opt
                            | dep <- deps
                            , opt <- Installed.ccOptions dep ]

            commonLdArgs  = [ "-L" ++ dir | dir <- collectField PD.extraLibDirs ]
                         ++ collectField PD.ldOptions
                         ++ [ "-L" ++ dir
                            | dep <- deps
                            , dir <- Installed.libraryDirs dep ]
                         --TODO: do we also need dependent packages' ld options?
            makeLdArgs libs = [ "-l"++lib | lib <- libs ] ++ commonLdArgs

            makeProgram hdrs = unlines $
                               [ "#include \""  ++ hdr ++ "\"" | hdr <- hdrs ] ++
                               ["int main(int argc, char** argv) { return 0; }"]

            collectField f = concatMap f allBi
            allBi = allBuildInfo pkg
            deps = PackageIndex.topologicalOrder (installedPkgs lbi)

            builds program args = do
                tempDir <- getTemporaryDirectory
                withTempFile tempDir ".c" $ \cName cHnd ->
                  withTempFile tempDir "" $ \oNname oHnd -> do
                    hPutStrLn cHnd program
                    hClose cHnd
                    hClose oHnd
                    _ <- rawSystemProgramStdoutConf verbosity
                      gccProgram (withPrograms lbi) (cName:"-o":oNname:args)
                    return True
               `catchIO`   (\_ -> return False)
               `catchExit` (\_ -> return False)

            explainErrors Nothing [] = return () -- should be impossible!
            explainErrors hdr libs = die $ unlines $
                 [ if plural
                     then "Missing dependencies on foreign libraries:"
                     else "Missing dependency on a foreign library:"
                 | missing ]
              ++ case hdr of
                   Just (Left h) -> ["* Missing (or bad) header file: " ++ h ]
                   _             -> []
              ++ case libs of
                   []    -> []
                   [lib] -> ["* Missing C library: " ++ lib]
                   _     -> ["* Missing C libraries: " ++ intercalate ", " libs]
              ++ [if plural then messagePlural else messageSingular | missing]
              ++ case hdr of
                   Just (Left  _) -> [ headerCppMessage ]
                   Just (Right h) -> [ (if missing then "* " else "")
                                       ++ "Bad header file: " ++ h
                                     , headerCcMessage ]
                   _              -> []

              where
                plural  = length libs >= 2
                -- Is there something missing? (as opposed to broken)
                missing = not (null libs)
                       || case hdr of Just (Left _) -> True; _ -> False

            messageSingular =
                 "This problem can usually be solved by installing the system "
              ++ "package that provides this library (you may need the "
              ++ "\"-dev\" version). If the library is already installed "
              ++ "but in a non-standard location then you can use the flags "
              ++ "--extra-include-dirs= and --extra-lib-dirs= to specify "
              ++ "where it is."
            messagePlural =
                 "This problem can usually be solved by installing the system "
              ++ "packages that provide these libraries (you may need the "
              ++ "\"-dev\" versions). If the libraries are already installed "
              ++ "but in a non-standard location then you can use the flags "
              ++ "--extra-include-dirs= and --extra-lib-dirs= to specify "
              ++ "where they are."
            headerCppMessage =
                 "If the header file does exist, it may contain errors that "
              ++ "are caught by the C compiler at the preprocessing stage. "
              ++ "In this case you can re-run configure with the verbosity "
              ++ "flag -v3 to see the error messages."
            headerCcMessage =
                 "The header file contains a compile error. "
              ++ "You can re-run configure with the verbosity flag "
              ++ "-v3 to see the error messages from the C compiler."

            --FIXME: share this with the PreProcessor module
            hcDefines :: Compiler -> [String]
            hcDefines comp =
              case compilerFlavor comp of
                GHC  -> ["-D__GLASGOW_HASKELL__=" ++ versionInt version]
                JHC  -> ["-D__JHC__=" ++ versionInt version]
                NHC  -> ["-D__NHC__=" ++ versionInt version]
                Hugs -> ["-D__HUGS__"]
                _    -> []
              where
                version = compilerVersion comp
                          -- TODO: move this into the compiler abstraction
                -- FIXME: this forces GHC's crazy 4.8.2 -> 408 convention on all
                -- the other compilers. Check if that's really what they want.
                versionInt :: Version -> String
                versionInt (Version { versionBranch = [] }) = "1"
                versionInt (Version { versionBranch = [n] }) = show n
                versionInt (Version { versionBranch = n1:n2:_ })
                  = -- 6.8.x -> 608
                    -- 6.10.x -> 610
                    let s1 = show n1
                        s2 = show n2
                        middle = case s2 of
                                 _ : _ : _ -> ""
                                 _         -> "0"
                    in s1 ++ middle ++ s2

    -- | Output package check warnings and errors. Exit if any errors.
    checkPackageProblems :: Verbosity
                         -> GenericPackageDescription
                         -> PackageDescription
                         -> IO ()
    checkPackageProblems verbosity gpkg pkg = do
      ioChecks      <- checkPackageFiles pkg "."
      let pureChecks = checkPackage gpkg (Just pkg)
          errors   = [ e | PackageBuildImpossible e <- pureChecks ++ ioChecks ]
          warnings = [ w | PackageBuildWarning    w <- pureChecks ++ ioChecks ]
      if null errors
        then mapM_ (warn verbosity) warnings
        else do mapM_ (hPutStrLn stderr . ("Error: " ++)) errors
                exitWith (ExitFailure 1)