    -----------------------------------------------------------------------------
    -- |
    -- Module      :  Distribution.PackageDescription
    -- Copyright   :  Isaac Jones 2003-2005
    --
    -- Maintainer  :  cabal-devel@haskell.org
    -- Portability :  portable
    --
    -- This defines the data structure for the @.cabal@ file format. There are
    -- several parts to this structure. It has top level info and then 'Library',
    -- 'Executable', and 'TestSuite' sections each of which have associated
    -- 'BuildInfo' data that's used to build the library, exe, or test. To further
    -- complicate things there is both a 'PackageDescription' and a
    -- 'GenericPackageDescription'. This distinction relates to cabal
    -- configurations. When we initially read a @.cabal@ file we get a
    -- 'GenericPackageDescription' which has all the conditional sections.
    -- Before actually building a package we have to decide
    -- on each conditional. Once we've done that we get a 'PackageDescription'.
    -- It was done this way initially to avoid breaking too much stuff when the
    -- feature was introduced. It could probably do with being rationalised at some
    -- point to make it simpler.

    {- 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.PackageDescription (
            -- * Package descriptions
            PackageDescription(..),
            emptyPackageDescription,
            specVersion,
            descCabalVersion,
            BuildType(..),
            knownBuildTypes,

            -- ** Libraries
            Library(..),
            emptyLibrary,
            withLib,
            hasLibs,
            libModules,

            -- ** Executables
            Executable(..),
            emptyExecutable,
            withExe,
            hasExes,
            exeModules,

            -- * Tests
            TestSuite(..),
            TestSuiteInterface(..),
            TestType(..),
            testType,
            knownTestTypes,
            emptyTestSuite,
            hasTests,
            withTest,
            testModules,
            enabledTests,

            -- * Build information
            BuildInfo(..),
            emptyBuildInfo,
            allBuildInfo,
            allLanguages,
            allExtensions,
            usedExtensions,
            hcOptions,

            -- ** Supplementary build information
            HookedBuildInfo,
            emptyHookedBuildInfo,
            updatePackageDescription,

            -- * package configuration
            GenericPackageDescription(..),
            Flag(..), FlagName(..), FlagAssignment,
            CondTree(..), ConfVar(..), Condition(..),

            -- * Source repositories
            SourceRepo(..),
            RepoKind(..),
            RepoType(..),
            knownRepoTypes,
      ) where

    import Data.List   (nub, intersperse)
    import Data.Maybe  (maybeToList)
    import Data.Monoid (Monoid(mempty, mappend))
    import Control.Monad (MonadPlus(mplus))
    import Text.PrettyPrint.HughesPJ as Disp
    import qualified Distribution.Compat.ReadP as Parse
    import qualified Data.Char as Char (isAlphaNum, isDigit, toLower)

    import Distribution.Package
             ( PackageName(PackageName), PackageIdentifier(PackageIdentifier)
             , Dependency, Package(..) )
    import Distribution.ModuleName ( ModuleName )
    import Distribution.Version
             ( Version(Version), VersionRange, anyVersion, orLaterVersion
             , asVersionIntervals, LowerBound(..) )
    import Distribution.License  (License(AllRightsReserved))
    import Distribution.Compiler (CompilerFlavor)
    import Distribution.System   (OS, Arch)
    import Distribution.Text
             ( Text(..), display )
    import Language.Haskell.Extension
             ( Language, Extension )

    -- -----------------------------------------------------------------------------
    -- The PackageDescription type

    -- | This data type is the internal representation of the file @pkg.cabal@.
    -- It contains two kinds of information about the package: information
    -- which is needed for all packages, such as the package name and version, and
    -- information which is needed for the simple build system only, such as
    -- the compiler options and library name.
    --
    data PackageDescription
        =  PackageDescription {
            -- the following are required by all packages:
            package        :: PackageIdentifier,
            license        :: License,
            licenseFile    :: FilePath,
            copyright      :: String,
            maintainer     :: String,
            author         :: String,
            stability      :: String,
            testedWith     :: [(CompilerFlavor,VersionRange)],
            homepage       :: String,
            pkgUrl         :: String,
            bugReports     :: String,
            sourceRepos    :: [SourceRepo],
            synopsis       :: String, -- ^A one-line summary of this package
            description    :: String, -- ^A more verbose description of this package
            category       :: String,
            customFieldsPD :: [(String,String)], -- ^Custom fields starting
                                                 -- with x-, stored in a
                                                 -- simple assoc-list.
            buildDepends   :: [Dependency],
            -- | The version of the Cabal spec that this package description uses.
            -- For historical reasons this is specified with a version range but
            -- only ranges of the form @>= v@ make sense. We are in the process of
            -- transitioning to specifying just a single version, not a range.
            specVersionRaw :: Either Version VersionRange,
            buildType      :: Maybe BuildType,
            -- components
            library        :: Maybe Library,
            executables    :: [Executable],
            testSuites     :: [TestSuite],
            dataFiles      :: [FilePath],
            dataDir        :: FilePath,
            extraSrcFiles  :: [FilePath],
            extraTmpFiles  :: [FilePath]
        }
        deriving (Show, Read, Eq)

    instance Package PackageDescription where
      packageId = package

    -- | The version of the Cabal spec that this package should be interpreted
    -- against.
    --
    -- Historically we used a version range but we are switching to using a single
    -- version. Currently we accept either. This function converts into a single
    -- version by ignoring upper bounds in the version range.
    --
    specVersion :: PackageDescription -> Version
    specVersion pkg = case specVersionRaw pkg of
      Left  version      -> version
      Right versionRange -> case asVersionIntervals versionRange of
                              []                            -> Version [0] []
                              ((LowerBound version _, _):_) -> version

    -- | The range of versions of the Cabal tools that this package is intended to
    -- work with.
    --
    -- This function is deprecated and should not be used for new purposes, only to
    -- support old packages that rely on the old interpretation.
    --
    descCabalVersion :: PackageDescription -> VersionRange
    descCabalVersion pkg = case specVersionRaw pkg of
      Left  version      -> orLaterVersion version
      Right versionRange -> versionRange
    {-# DEPRECATED descCabalVersion "Use specVersion instead" #-}

    emptyPackageDescription :: PackageDescription
    emptyPackageDescription
        =  PackageDescription {
                          package      = PackageIdentifier (PackageName "")
                                                           (Version [] []),
                          license      = AllRightsReserved,
                          licenseFile  = "",
                          specVersionRaw = Right anyVersion,
                          buildType    = Nothing,
                          copyright    = "",
                          maintainer   = "",
                          author       = "",
                          stability    = "",
                          testedWith   = [],
                          buildDepends = [],
                          homepage     = "",
                          pkgUrl       = "",
                          bugReports   = "",
                          sourceRepos  = [],
                          synopsis     = "",
                          description  = "",
                          category     = "",
                          customFieldsPD = [],
                          library      = Nothing,
                          executables  = [],
                          testSuites   = [],
                          dataFiles    = [],
                          dataDir      = "",
                          extraSrcFiles = [],
                          extraTmpFiles = []
                         }

    -- | The type of build system used by this package.
    data BuildType
      = Simple      -- ^ calls @Distribution.Simple.defaultMain@
      | Configure   -- ^ calls @Distribution.Simple.defaultMainWithHooks defaultUserHooks@,
                    -- which invokes @configure@ to generate additional build
                    -- information used by later phases.
      | Make        -- ^ calls @Distribution.Make.defaultMain@
      | Custom      -- ^ uses user-supplied @Setup.hs@ or @Setup.lhs@ (default)
      | UnknownBuildType String
                    -- ^ a package that uses an unknown build type cannot actually
                    --   be built. Doing it this way rather than just giving a
                    --   parse error means we get better error messages and allows
                    --   you to inspect the rest of the package description.
                    deriving (Show, Read, Eq)

    knownBuildTypes :: [BuildType]
    knownBuildTypes = [Simple, Configure, Make, Custom]

    instance Text BuildType where
      disp (UnknownBuildType other) = Disp.text other
      disp other                    = Disp.text (show other)

      parse = do
        name <- Parse.munch1 Char.isAlphaNum
        return $ case name of
          "Simple"    -> Simple
          "Configure" -> Configure
          "Custom"    -> Custom
          "Make"      -> Make
          _           -> UnknownBuildType name

    -- ---------------------------------------------------------------------------
    -- The Library type

    data Library = Library {
            exposedModules    :: [ModuleName],
            libExposed        :: Bool, -- ^ Is the lib to be exposed by default?
            libBuildInfo      :: BuildInfo
        }
        deriving (Show, Eq, Read)

    instance Monoid Library where
      mempty = Library {
        exposedModules = mempty,
        libExposed     = True,
        libBuildInfo   = mempty
      }
      mappend a b = Library {
        exposedModules = combine exposedModules,
        libExposed     = libExposed a && libExposed b, -- so False propagates
        libBuildInfo   = combine libBuildInfo
      }
        where combine field = field a `mappend` field b

    emptyLibrary :: Library
    emptyLibrary = mempty

    -- |does this package have any libraries?
    hasLibs :: PackageDescription -> Bool
    hasLibs p = maybe False (buildable . libBuildInfo) (library p)

    -- |'Maybe' version of 'hasLibs'
    maybeHasLibs :: PackageDescription -> Maybe Library
    maybeHasLibs p =
       library p >>= \lib -> if buildable (libBuildInfo lib)
                               then Just lib
                               else Nothing

    -- |If the package description has a library section, call the given
    --  function with the library build info as argument.
    withLib :: PackageDescription -> (Library -> IO ()) -> IO ()
    withLib pkg_descr f =
       maybe (return ()) f (maybeHasLibs pkg_descr)

    -- | Get all the module names from the library (exposed and internal modules)
    libModules :: Library -> [ModuleName]
    libModules lib = exposedModules lib
                  ++ otherModules (libBuildInfo lib)

    -- ---------------------------------------------------------------------------
    -- The Executable type

    data Executable = Executable {
            exeName    :: String,
            modulePath :: FilePath,
            buildInfo  :: BuildInfo
        }
        deriving (Show, Read, Eq)

    instance Monoid Executable where
      mempty = Executable {
        exeName    = mempty,
        modulePath = mempty,
        buildInfo  = mempty
      }
      mappend a b = Executable{
        exeName    = combine' exeName,
        modulePath = combine modulePath,
        buildInfo  = combine buildInfo
      }
        where combine field = field a `mappend` field b
              combine' field = case (field a, field b) of
                          ("","") -> ""
                          ("", x) -> x
                          (x, "") -> x
                          (x, y) -> error $ "Ambiguous values for executable field: '"
                                      ++ x ++ "' and '" ++ y ++ "'"

    emptyExecutable :: Executable
    emptyExecutable = mempty

    -- |does this package have any executables?
    hasExes :: PackageDescription -> Bool
    hasExes p = any (buildable . buildInfo) (executables p)

    -- | Perform the action on each buildable 'Executable' in the package
    -- description.
    withExe :: PackageDescription -> (Executable -> IO ()) -> IO ()
    withExe pkg_descr f =
      sequence_ [f exe | exe <- executables pkg_descr, buildable (buildInfo exe)]

    -- | Get all the module names from an exe
    exeModules :: Executable -> [ModuleName]
    exeModules exe = otherModules (buildInfo exe)

    -- ---------------------------------------------------------------------------
    -- The TestSuite type

    -- | A \"test-suite\" stanza in a cabal file.
    --
    data TestSuite = TestSuite {
            testName      :: String,
            testInterface :: TestSuiteInterface,
            testBuildInfo :: BuildInfo,
            testEnabled   :: Bool
            -- TODO: By having a 'testEnabled' field in the PackageDescription, we
            -- are mixing build status information (i.e., arguments to 'configure')
            -- with static package description information. This is undesirable, but
            -- a better solution is waiting on the next overhaul to the
            -- GenericPackageDescription -> PackageDescription resolution process.
        }
        deriving (Show, Read, Eq)

    -- | The test suite interfaces that are currently defined. Each test suite must
    -- specify which interface it supports.
    --
    -- More interfaces may be defined in future, either new revisions or totally
    -- new interfaces.
    --
    data TestSuiteInterface =

         -- | Test interface \"exitcode-stdio-1.0\". The test-suite takes the form
         -- of an executable. It returns a zero exit code for success, non-zero for
         -- failure. The stdout and stderr channels may be logged. It takes no
         -- command line parameters and nothing on stdin.
         --
         TestSuiteExeV10 Version FilePath

         -- | Test interface \"detailed-0.9\". The test-suite takes the form of a
         -- library containing a designated module that exports \"tests :: [Test]\".
         --
       | TestSuiteLibV09 Version ModuleName

         -- | A test suite that does not conform to one of the above interfaces for
         -- the given reason (e.g. unknown test type).
         --
       | TestSuiteUnsupported TestType
       deriving (Eq, Read, Show)

    instance Monoid TestSuite where
        mempty = TestSuite {
            testName      = mempty,
            testInterface = mempty,
            testBuildInfo = mempty,
            testEnabled   = False
        }

        mappend a b = TestSuite {
            testName      = combine' testName,
            testInterface = combine  testInterface,
            testBuildInfo = combine  testBuildInfo,
            testEnabled   = if testEnabled a then True else testEnabled b
        }
            where combine   field = field a `mappend` field b
                  combine' f = case (f a, f b) of
                            ("", x) -> x
                            (x, "") -> x
                            (x, y) -> error "Ambiguous values for test field: '"
                                ++ x ++ "' and '" ++ y ++ "'"

    instance Monoid TestSuiteInterface where
        mempty  =  TestSuiteUnsupported (TestTypeUnknown mempty (Version [] []))
        mappend a (TestSuiteUnsupported _) = a
        mappend _ b                        = b

    emptyTestSuite :: TestSuite
    emptyTestSuite = mempty

    -- | Does this package have any test suites?
    hasTests :: PackageDescription -> Bool
    hasTests = any (buildable . testBuildInfo) . testSuites

    -- | Get all the enabled test suites from a package.
    enabledTests :: PackageDescription -> [TestSuite]
    enabledTests = filter testEnabled . testSuites

    -- | Perform an action on each buildable 'TestSuite' in a package.
    withTest :: PackageDescription -> (TestSuite -> IO ()) -> IO ()
    withTest pkg_descr f =
        mapM_ f $ filter (buildable . testBuildInfo) $ enabledTests pkg_descr

    -- | Get all the module names from a test suite.
    testModules :: TestSuite -> [ModuleName]
    testModules test = (case testInterface test of
                         TestSuiteLibV09 _ m -> [m]
                         _                   -> [])
                    ++ otherModules (testBuildInfo test)

    -- | The \"test-type\" field in the test suite stanza.
    --
    data TestType = TestTypeExe Version     -- ^ \"type: exitcode-stdio-x.y\"
                  | TestTypeLib Version     -- ^ \"type: detailed-x.y\"
                  | TestTypeUnknown String Version -- ^ Some unknown test type e.g. \"type: foo\"
        deriving (Show, Read, Eq)

    knownTestTypes :: [TestType]
    knownTestTypes = [ TestTypeExe (Version [1,0] [])
                       -- 'detailed-0.9' test type is disabled in Cabal-1.10.x
                       -- needs more work on the details of the library interface
                  {- , TestTypeLib (Version [0,9] []) -} ]

    instance Text TestType where
      disp (TestTypeExe ver)          = text "exitcode-stdio-" <> disp ver
      disp (TestTypeLib ver)          = text "detailed-"       <> disp ver
      disp (TestTypeUnknown name ver) = text name <> char '-' <> disp ver

      parse = do
        cs   <- Parse.sepBy1 component (Parse.char '-')
        _    <- Parse.char '-'
        ver  <- parse
        let name = concat (intersperse "-" cs)
        return $! case lowercase name of
          "exitcode-stdio" -> TestTypeExe ver
          "detailed"       -> TestTypeLib ver
          _                -> TestTypeUnknown name ver

        where
          component = do
            cs <- Parse.munch1 Char.isAlphaNum
            if all Char.isDigit cs then Parse.pfail else return cs
            -- each component must contain an alphabetic character, to avoid
            -- ambiguity in identifiers like foo-1 (the 1 is the version number).

    testType :: TestSuite -> TestType
    testType test = case testInterface test of
      TestSuiteExeV10 ver _         -> TestTypeExe ver
      TestSuiteLibV09 ver _         -> TestTypeLib ver
      TestSuiteUnsupported testtype -> testtype

    -- ---------------------------------------------------------------------------
    -- The BuildInfo type

    -- Consider refactoring into executable and library versions.
    data BuildInfo = BuildInfo {
            buildable         :: Bool,      -- ^ component is buildable here
            buildTools        :: [Dependency], -- ^ tools needed to build this bit
            cppOptions        :: [String],  -- ^ options for pre-processing Haskell code
            ccOptions         :: [String],  -- ^ options for C compiler
            ldOptions         :: [String],  -- ^ options for linker
            pkgconfigDepends  :: [Dependency], -- ^ pkg-config packages that are used
            frameworks        :: [String], -- ^support frameworks for Mac OS X
            cSources          :: [FilePath],
            hsSourceDirs      :: [FilePath], -- ^ where to look for the haskell module hierarchy
            otherModules      :: [ModuleName], -- ^ non-exposed or non-main modules

            defaultLanguage   :: Maybe Language,-- ^ language used when not explicitly specified
            otherLanguages    :: [Language],    -- ^ other languages used within the package
            defaultExtensions :: [Extension],   -- ^ language extensions used by all modules
            otherExtensions   :: [Extension],   -- ^ other language extensions used within the package
            oldExtensions     :: [Extension],   -- ^ the old extensions field, treated same as 'defaultExtensions'

            extraLibs         :: [String], -- ^ what libraries to link with when compiling a program that uses your package
            extraLibDirs      :: [String],
            includeDirs       :: [FilePath], -- ^directories to find .h files
            includes          :: [FilePath], -- ^ The .h files to be found in includeDirs
            installIncludes   :: [FilePath], -- ^ .h files to install with the package
            options           :: [(CompilerFlavor,[String])],
            ghcProfOptions    :: [String],
            ghcSharedOptions  :: [String],
            customFieldsBI    :: [(String,String)], -- ^Custom fields starting
                                                    -- with x-, stored in a
                                                    -- simple assoc-list.
            targetBuildDepends :: [Dependency] -- ^ Dependencies specific to a library or executable target
        }
        deriving (Show,Read,Eq)

    instance Monoid BuildInfo where
      mempty = BuildInfo {
        buildable         = True,
        buildTools        = [],
        cppOptions        = [],
        ccOptions         = [],
        ldOptions         = [],
        pkgconfigDepends  = [],
        frameworks        = [],
        cSources          = [],
        hsSourceDirs      = [],
        otherModules      = [],
        defaultLanguage   = Nothing,
        otherLanguages    = [],
        defaultExtensions = [],
        otherExtensions   = [],
        oldExtensions     = [],
        extraLibs         = [],
        extraLibDirs      = [],
        includeDirs       = [],
        includes          = [],
        installIncludes   = [],
        options           = [],
        ghcProfOptions    = [],
        ghcSharedOptions  = [],
        customFieldsBI    = [],
        targetBuildDepends = []
      }
      mappend a b = BuildInfo {
        buildable         = buildable a && buildable b,
        buildTools        = combine    buildTools,
        cppOptions        = combine    cppOptions,
        ccOptions         = combine    ccOptions,
        ldOptions         = combine    ldOptions,
        pkgconfigDepends  = combine    pkgconfigDepends,
        frameworks        = combineNub frameworks,
        cSources          = combineNub cSources,
        hsSourceDirs      = combineNub hsSourceDirs,
        otherModules      = combineNub otherModules,
        defaultLanguage   = combineMby defaultLanguage,
        otherLanguages    = combineNub otherLanguages,
        defaultExtensions = combineNub defaultExtensions,
        otherExtensions   = combineNub otherExtensions,
        oldExtensions     = combineNub oldExtensions,
        extraLibs         = combine    extraLibs,
        extraLibDirs      = combineNub extraLibDirs,
        includeDirs       = combineNub includeDirs,
        includes          = combineNub includes,
        installIncludes   = combineNub installIncludes,
        options           = combine    options,
        ghcProfOptions    = combine    ghcProfOptions,
        ghcSharedOptions  = combine    ghcSharedOptions,
        customFieldsBI    = combine    customFieldsBI,
        targetBuildDepends = combineNub targetBuildDepends
      }
        where
          combine    field = field a `mappend` field b
          combineNub field = nub (combine field)
          combineMby field = field b `mplus` field a

    emptyBuildInfo :: BuildInfo
    emptyBuildInfo = mempty

    -- | The 'BuildInfo' for the library (if there is one and it's buildable) and
    -- all the buildable executables. Useful for gathering dependencies.
    allBuildInfo :: PackageDescription -> [BuildInfo]
    allBuildInfo pkg_descr = [ bi | Just lib <- [library pkg_descr]
                                  , let bi = libBuildInfo lib
                                  , buildable bi ]
                          ++ [ bi | exe <- executables pkg_descr
                                  , let bi = buildInfo exe
                                  , buildable bi ]
                          ++ [ bi | tst <- testSuites pkg_descr
                                  , let bi = testBuildInfo tst
                                  , buildable bi ]
      --FIXME: many of the places where this is used, we actually want to look at
      --       unbuildable bits too, probably need separate functions

    -- | The 'Language's used by this component
    --
    allLanguages :: BuildInfo -> [Language]
    allLanguages bi = maybeToList (defaultLanguage bi)
                   ++ otherLanguages bi

    -- | The 'Extension's that are used somewhere by this component
    --
    allExtensions :: BuildInfo -> [Extension]
    allExtensions bi = usedExtensions bi
                    ++ otherExtensions bi

    -- | The 'Extensions' that are used by all modules in this component
    --
    usedExtensions :: BuildInfo -> [Extension]
    usedExtensions bi = oldExtensions bi
                     ++ defaultExtensions bi

    type HookedBuildInfo = (Maybe BuildInfo, [(String, BuildInfo)])

    emptyHookedBuildInfo :: HookedBuildInfo
    emptyHookedBuildInfo = (Nothing, [])

    -- |Select options for a particular Haskell compiler.
    hcOptions :: CompilerFlavor -> BuildInfo -> [String]
    hcOptions hc bi = [ opt | (hc',opts) <- options bi
                            , hc' == hc
                            , opt <- opts ]

    -- ------------------------------------------------------------
    -- * Source repos
    -- ------------------------------------------------------------

    -- | Information about the source revision control system for a package.
    --
    -- When specifying a repo it is useful to know the meaning or intention of the
    -- information as doing so enables automation. There are two obvious common
    -- purposes: one is to find the repo for the latest development version, the
    -- other is to find the repo for this specific release. The 'ReopKind'
    -- specifies which one we mean (or another custom one).
    --
    -- A package can specify one or the other kind or both. Most will specify just
    -- a head repo but some may want to specify a repo to reconstruct the sources
    -- for this package release.
    --
    -- The required information is the 'RepoType' which tells us if it's using
    -- 'Darcs', 'Git' for example. The 'repoLocation' and other details are
    -- interpreted according to the repo type.
    --
    data SourceRepo = SourceRepo {
      -- | The kind of repo. This field is required.
      repoKind     :: RepoKind,

      -- | The type of the source repository system for this repo, eg 'Darcs' or
      -- 'Git'. This field is required.
      repoType     :: Maybe RepoType,

      -- | The location of the repository. For most 'RepoType's this is a URL.
      -- This field is required.
      repoLocation :: Maybe String,

      -- | 'CVS' can put multiple \"modules\" on one server and requires a
      -- module name in addition to the location to identify a particular repo.
      -- Logically this is part of the location but unfortunately has to be
      -- specified separately. This field is required for the 'CVS' 'RepoType' and
      -- should not be given otherwise.
      repoModule   :: Maybe String,

      -- | The name or identifier of the branch, if any. Many source control
      -- systems have the notion of multiple branches in a repo that exist in the
      -- same location. For example 'Git' and 'CVS' use this while systems like
      -- 'Darcs' use different locations for different branches. This field is
      -- optional but should be used if necessary to identify the sources,
      -- especially for the 'RepoThis' repo kind.
      repoBranch   :: Maybe String,

      -- | The tag identify a particular state of the repository. This should be
      -- given for the 'RepoThis' repo kind and not for 'RepoHead' kind.
      --
      repoTag      :: Maybe String,

      -- | Some repositories contain multiple projects in different subdirectories
      -- This field specifies the subdirectory where this packages sources can be
      -- found, eg the subdirectory containing the @.cabal@ file. It is interpreted
      -- relative to the root of the repository. This field is optional. If not
      -- given the default is \".\" ie no subdirectory.
      repoSubdir   :: Maybe FilePath
    }
      deriving (Eq, Read, Show)

    -- | What this repo info is for, what it represents.
    --
    data RepoKind =
        -- | The repository for the \"head\" or development version of the project.
        -- This repo is where we should track the latest development activity or
        -- the usual repo people should get to contribute patches.
        RepoHead

        -- | The repository containing the sources for this exact package version
        -- or release. For this kind of repo a tag should be given to give enough
        -- information to re-create the exact sources.
      | RepoThis

      | RepoKindUnknown String
      deriving (Eq, Ord, Read, Show)

    -- | An enumeration of common source control systems. The fields used in the
    -- 'SourceRepo' depend on the type of repo. The tools and methods used to
    -- obtain and track the repo depend on the repo type.
    --
    data RepoType = Darcs | Git | SVN | CVS
                  | Mercurial | GnuArch | Bazaar | Monotone
                  | OtherRepoType String
      deriving (Eq, Ord, Read, Show)

    knownRepoTypes :: [RepoType]
    knownRepoTypes = [Darcs, Git, SVN, CVS
                     ,Mercurial, GnuArch, Bazaar, Monotone]

    repoTypeAliases :: RepoType -> [String]
    repoTypeAliases Bazaar    = ["bzr"]
    repoTypeAliases Mercurial = ["hg"]
    repoTypeAliases GnuArch   = ["arch"]
    repoTypeAliases _         = []

    instance Text RepoKind where
      disp RepoHead                = Disp.text "head"
      disp RepoThis                = Disp.text "this"
      disp (RepoKindUnknown other) = Disp.text other

      parse = do
        name <- ident
        return $ case lowercase name of
          "head" -> RepoHead
          "this" -> RepoThis
          _      -> RepoKindUnknown name

    instance Text RepoType where
      disp (OtherRepoType other) = Disp.text other
      disp other                 = Disp.text (lowercase (show other))
      parse = fmap classifyRepoType ident

    classifyRepoType :: String -> RepoType
    classifyRepoType s =
      case lookup (lowercase s) repoTypeMap of
        Just repoType' -> repoType'
        Nothing        -> OtherRepoType s
      where
        repoTypeMap = [ (name, repoType')
                      | repoType' <- knownRepoTypes
                      , name <- display repoType' : repoTypeAliases repoType' ]

    ident :: Parse.ReadP r String
    ident = Parse.munch1 (\c -> Char.isAlphaNum c || c == '_' || c == '-')

    lowercase :: String -> String
    lowercase = map Char.toLower

    -- ------------------------------------------------------------
    -- * Utils
    -- ------------------------------------------------------------

    updatePackageDescription :: HookedBuildInfo -> PackageDescription -> PackageDescription
    updatePackageDescription (mb_lib_bi, exe_bi) p
        = p{ executables = updateExecutables exe_bi    (executables p)
           , library     = updateLibrary     mb_lib_bi (library     p)
           }
        where
          updateLibrary :: Maybe BuildInfo -> Maybe Library -> Maybe Library
          updateLibrary (Just bi) (Just lib) = Just (lib{libBuildInfo = bi `mappend` libBuildInfo lib})
          updateLibrary Nothing   mb_lib     = mb_lib

           --the lib only exists in the buildinfo file.  FIX: Is this
           --wrong?  If there aren't any exposedModules, then the library
           --won't build anyway.  add to sanity checker?
          updateLibrary (Just bi) Nothing     = Just emptyLibrary{libBuildInfo=bi}

          updateExecutables :: [(String, BuildInfo)] -- ^[(exeName, new buildinfo)]
                            -> [Executable]          -- ^list of executables to update
                            -> [Executable]          -- ^list with exeNames updated
          updateExecutables exe_bi' executables' = foldr updateExecutable executables' exe_bi'

          updateExecutable :: (String, BuildInfo) -- ^(exeName, new buildinfo)
                           -> [Executable]        -- ^list of executables to update
                           -> [Executable]        -- ^libst with exeName updated
          updateExecutable _                 []         = []
          updateExecutable exe_bi'@(name,bi) (exe:exes)
            | exeName exe == name = exe{buildInfo = bi `mappend` buildInfo exe} : exes
            | otherwise           = exe : updateExecutable exe_bi' exes

    -- ---------------------------------------------------------------------------
    -- The GenericPackageDescription type

    data GenericPackageDescription =
        GenericPackageDescription {
            packageDescription :: PackageDescription,
            genPackageFlags       :: [Flag],
            condLibrary        :: Maybe (CondTree ConfVar [Dependency] Library),
            condExecutables    :: [(String, CondTree ConfVar [Dependency] Executable)],
            condTestSuites     :: [(String, CondTree ConfVar [Dependency] TestSuite)]
          }
        deriving (Show, Eq)

    instance Package GenericPackageDescription where
      packageId = packageId . packageDescription

    --TODO: make PackageDescription an instance of Text.

    -- | A flag can represent a feature to be included, or a way of linking
    --   a target against its dependencies, or in fact whatever you can think of.
    data Flag = MkFlag
        { flagName        :: FlagName
        , flagDescription :: String
        , flagDefault     :: Bool
        , flagManual      :: Bool
        }
        deriving (Show, Eq)

    -- | A 'FlagName' is the name of a user-defined configuration flag
    newtype FlagName = FlagName String
        deriving (Eq, Ord, Show, Read)

    -- | A 'FlagAssignment' is a total or partial mapping of 'FlagName's to
    -- 'Bool' flag values. It represents the flags chosen by the user or
    -- discovered during configuration. For example @--flags=foo --flags=-bar@
    -- becomes @[("foo", True), ("bar", False)]@
    --
    type FlagAssignment = [(FlagName, Bool)]

    -- | A @ConfVar@ represents the variable type used.
    data ConfVar = OS OS
                 | Arch Arch
                 | Flag FlagName
                 | Impl CompilerFlavor VersionRange
        deriving (Eq, Show)

    --instance Text ConfVar where
    --    disp (OS os) = "os(" ++ display os ++ ")"
    --    disp (Arch arch) = "arch(" ++ display arch ++ ")"
    --    disp (Flag (ConfFlag f)) = "flag(" ++ f ++ ")"
    --    disp (Impl c v) = "impl(" ++ display c
    --                       ++ " " ++ display v ++ ")"

    -- | A boolean expression parameterized over the variable type used.
    data Condition c = Var c
                     | Lit Bool
                     | CNot (Condition c)
                     | COr (Condition c) (Condition c)
                     | CAnd (Condition c) (Condition c)
        deriving (Show, Eq)

    --instance Text c => Text (Condition c) where
    --  disp (Var x) = text (show x)
    --  disp (Lit b) = text (show b)
    --  disp (CNot c) = char '!' <> parens (ppCond c)
    --  disp (COr c1 c2) = parens $ sep [ppCond c1, text "||" <+> ppCond c2]
    --  disp (CAnd c1 c2) = parens $ sep [ppCond c1, text "&&" <+> ppCond c2]

    data CondTree v c a = CondNode
        { condTreeData        :: a
        , condTreeConstraints :: c
        , condTreeComponents  :: [( Condition v
                                  , CondTree v c a
                                  , Maybe (CondTree v c a))]
        }
        deriving (Show, Eq)

    --instance (Text v, Text c) => Text (CondTree v c a) where
    --  disp (CondNode _dat cs ifs) =
    --    (text "build-depends: " <+>
    --      disp cs)
    --    $+$
    --    (vcat $ map ppIf ifs)
    --  where
    --    ppIf (c,thenTree,mElseTree) =
    --        ((text "if" <+> ppCond c <> colon) $$
    --          nest 2 (ppCondTree thenTree disp))
    --        $+$ (maybe empty (\t -> text "else: " $$ nest 2 (ppCondTree t disp))
    --                   mElseTree)