    {-# LANGUAGE CPP #-}
    {-# LANGUAGE DeriveDataTypeable #-}
    -----------------------------------------------------------------------------
    -- |
    -- Module      :  Distribution.PackageDescription.Parse
    -- Copyright   :  Isaac Jones 2003-2005
    -- License     :  BSD3
    --
    -- Maintainer  :  cabal-devel@haskell.org
    -- Portability :  portable
    --
    -- This defined parsers and partial pretty printers for the @.cabal@ format.
    -- Some of the complexity in this module is due to the fact that we have to be
    -- backwards compatible with old @.cabal@ files, so there's code to translate
    -- into the newer structure.

    module Distribution.PackageDescription.Parse (
            -- * Package descriptions
            readPackageDescription,
            writePackageDescription,
            parsePackageDescription,
            showPackageDescription,

            -- ** Parsing
            ParseResult(..),
            FieldDescr(..),
            LineNo,

            -- ** Supplementary build information
            readHookedBuildInfo,
            parseHookedBuildInfo,
            writeHookedBuildInfo,
            showHookedBuildInfo,

            pkgDescrFieldDescrs,
            libFieldDescrs,
            executableFieldDescrs,
            binfoFieldDescrs,
            sourceRepoFieldDescrs,
            testSuiteFieldDescrs,
            flagFieldDescrs
      ) where

    import Distribution.ParseUtils hiding (parseFields)
    import Distribution.PackageDescription
    import Distribution.PackageDescription.Utils
    import Distribution.Package
    import Distribution.ModuleName
    import Distribution.Version
    import Distribution.Verbosity
    import Distribution.Compiler
    import Distribution.PackageDescription.Configuration
    import Distribution.Simple.Utils
    import Distribution.Text
    import Distribution.Compat.ReadP hiding (get)

    import Data.Char     (isSpace)
    import Data.Foldable (traverse_)
    import Data.Maybe    (listToMaybe, isJust)
    import Data.List     (nub, unfoldr, partition, (\\))
    import Control.Monad (liftM, foldM, when, unless, ap)
    #if __GLASGOW_HASKELL__ < 710
    import Data.Monoid         (Monoid(..))
    import Control.Applicative (Applicative(..))
    #endif
    import Control.Arrow    (first)
    import System.Directory (doesFileExist)
    import qualified Data.ByteString.Lazy.Char8 as BS.Char8

    import Text.PrettyPrint

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

    pkgDescrFieldDescrs :: [FieldDescr PackageDescription]
    pkgDescrFieldDescrs =
        [ simpleField "name"
               disp                   parse
               packageName            (\name pkg -> pkg{package=(package pkg){pkgName=name}})
     , simpleField "version"
               disp                   parse
               packageVersion         (\ver pkg -> pkg{package=(package pkg){pkgVersion=ver}})
     , simpleField "cabal-version"
               (either disp disp)     (liftM Left parse +++ liftM Right parse)
               specVersionRaw         (\v pkg -> pkg{specVersionRaw=v})
     , simpleField "build-type"
               (maybe empty disp)     (fmap Just parse)
               buildType              (\t pkg -> pkg{buildType=t})
     , simpleField "license"
               disp                   parseLicenseQ
               license                (\l pkg -> pkg{license=l})
       -- We have both 'license-file' and 'license-files' fields.
       -- Rather than declaring license-file to be deprecated, we will continue
       -- to allow both. The 'license-file' will continue to only allow single
       -- tokens, while 'license-files' allows multiple. On pretty-printing, we
       -- will use 'license-file' if there's just one, and use 'license-files'
       -- otherwise.
     , simpleField "license-file"
               showFilePath           parseFilePathQ
               (\pkg -> case licenseFiles pkg of
                          [x] -> x
                          _   -> "")
               (\l pkg -> pkg{licenseFiles=licenseFiles pkg ++ [l]})
     , listField "license-files"
               showFilePath           parseFilePathQ
               (\pkg -> case licenseFiles pkg of
                          [_] -> []
                          xs  -> xs)
               (\ls pkg -> pkg{licenseFiles=ls})
     , simpleField "copyright"
               showFreeText           parseFreeText
               copyright              (\val pkg -> pkg{copyright=val})
     , simpleField "maintainer"
               showFreeText           parseFreeText
               maintainer             (\val pkg -> pkg{maintainer=val})
     , simpleField "stability"
               showFreeText           parseFreeText
               stability              (\val pkg -> pkg{stability=val})
     , simpleField "homepage"
               showFreeText           parseFreeText
               homepage               (\val pkg -> pkg{homepage=val})
     , simpleField "package-url"
               showFreeText           parseFreeText
               pkgUrl                 (\val pkg -> pkg{pkgUrl=val})
     , simpleField "bug-reports"
               showFreeText           parseFreeText
               bugReports             (\val pkg -> pkg{bugReports=val})
     , simpleField "synopsis"
               showFreeText           parseFreeText
               synopsis               (\val pkg -> pkg{synopsis=val})
     , simpleField "description"
               showFreeText           parseFreeText
               description            (\val pkg -> pkg{description=val})
     , simpleField "category"
               showFreeText           parseFreeText
               category               (\val pkg -> pkg{category=val})
     , simpleField "author"
               showFreeText           parseFreeText
               author                 (\val pkg -> pkg{author=val})
     , listField "tested-with"
               showTestedWith         parseTestedWithQ
               testedWith             (\val pkg -> pkg{testedWith=val})
     , listFieldWithSep vcat "data-files"
               showFilePath           parseFilePathQ
               dataFiles              (\val pkg -> pkg{dataFiles=val})
     , simpleField "data-dir"
               showFilePath           parseFilePathQ
               dataDir                (\val pkg -> pkg{dataDir=val})
     , listFieldWithSep vcat "extra-source-files"
               showFilePath    parseFilePathQ
               extraSrcFiles          (\val pkg -> pkg{extraSrcFiles=val})
     , listFieldWithSep vcat "extra-tmp-files"
               showFilePath       parseFilePathQ
               extraTmpFiles          (\val pkg -> pkg{extraTmpFiles=val})
     , listFieldWithSep vcat "extra-doc-files"
               showFilePath    parseFilePathQ
               extraDocFiles          (\val pkg -> pkg{extraDocFiles=val})
     ]

    -- | Store any fields beginning with "x-" in the customFields field of
    --   a PackageDescription.  All other fields will generate a warning.
    storeXFieldsPD :: UnrecFieldParser PackageDescription
    storeXFieldsPD (f@('x':'-':_),val) pkg =
      Just pkg{ customFieldsPD =
                   customFieldsPD pkg ++ [(f,val)]}
    storeXFieldsPD _ _ = Nothing

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

    libFieldDescrs :: [FieldDescr Library]
    libFieldDescrs =
      [ listFieldWithSep vcat "exposed-modules" disp parseModuleNameQ
          exposedModules (\mods lib -> lib{exposedModules=mods})

      , commaListFieldWithSep vcat "reexported-modules" disp parse
          reexportedModules (\mods lib -> lib{reexportedModules=mods})

      , listFieldWithSep vcat "required-signatures" disp parseModuleNameQ
          requiredSignatures (\mods lib -> lib{requiredSignatures=mods})

      , listFieldWithSep vcat "exposed-signatures" disp parseModuleNameQ
          exposedSignatures (\mods lib -> lib{exposedSignatures=mods})

      , boolField "exposed"
          libExposed     (\val lib -> lib{libExposed=val})
      ] ++ map biToLib binfoFieldDescrs
      where biToLib = liftField libBuildInfo (\bi lib -> lib{libBuildInfo=bi})

    storeXFieldsLib :: UnrecFieldParser Library
    storeXFieldsLib (f@('x':'-':_), val) l@(Library { libBuildInfo = bi }) =
        Just $ l {libBuildInfo =
                     bi{ customFieldsBI = customFieldsBI bi ++ [(f,val)]}}
    storeXFieldsLib _ _ = Nothing

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

    executableFieldDescrs :: [FieldDescr Executable]
    executableFieldDescrs =
      [ -- note ordering: configuration must come first, for
        -- showPackageDescription.
        simpleField "executable"
                               showToken          parseTokenQ
                               exeName            (\xs    exe -> exe{exeName=xs})
      , simpleField "main-is"
                               showFilePath       parseFilePathQ
                               modulePath         (\xs    exe -> exe{modulePath=xs})
      ]
      ++ map biToExe binfoFieldDescrs
      where biToExe = liftField buildInfo (\bi exe -> exe{buildInfo=bi})

    storeXFieldsExe :: UnrecFieldParser Executable
    storeXFieldsExe (f@('x':'-':_), val) e@(Executable { buildInfo = bi }) =
        Just $ e {buildInfo = bi{ customFieldsBI = (f,val):customFieldsBI bi}}
    storeXFieldsExe _ _ = Nothing

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

    -- | An intermediate type just used for parsing the test-suite stanza.
    -- After validation it is converted into the proper 'TestSuite' type.
    data TestSuiteStanza = TestSuiteStanza {
           testStanzaTestType   :: Maybe TestType,
           testStanzaMainIs     :: Maybe FilePath,
           testStanzaTestModule :: Maybe ModuleName,
           testStanzaBuildInfo  :: BuildInfo
         }

    emptyTestStanza :: TestSuiteStanza
    emptyTestStanza = TestSuiteStanza Nothing Nothing Nothing mempty

    testSuiteFieldDescrs :: [FieldDescr TestSuiteStanza]
    testSuiteFieldDescrs =
        [ simpleField "type"
            (maybe empty disp)    (fmap Just parse)
            testStanzaTestType    (\x suite -> suite { testStanzaTestType = x })
        , simpleField "main-is"
            (maybe empty showFilePath)  (fmap Just parseFilePathQ)
            testStanzaMainIs      (\x suite -> suite { testStanzaMainIs = x })
        , simpleField "test-module"
            (maybe empty disp)    (fmap Just parseModuleNameQ)
            testStanzaTestModule  (\x suite -> suite { testStanzaTestModule = x })
        ]
        ++ map biToTest binfoFieldDescrs
      where
        biToTest = liftField testStanzaBuildInfo
                             (\bi suite -> suite { testStanzaBuildInfo = bi })

    storeXFieldsTest :: UnrecFieldParser TestSuiteStanza
    storeXFieldsTest (f@('x':'-':_), val) t@(TestSuiteStanza { testStanzaBuildInfo = bi }) =
        Just $ t {testStanzaBuildInfo = bi{ customFieldsBI = (f,val):customFieldsBI bi}}
    storeXFieldsTest _ _ = Nothing

    validateTestSuite :: LineNo -> TestSuiteStanza -> ParseResult TestSuite
    validateTestSuite line stanza =
        case testStanzaTestType stanza of
          Nothing -> return $
            emptyTestSuite { testBuildInfo = testStanzaBuildInfo stanza }

          Just tt@(TestTypeUnknown _ _) ->
            return emptyTestSuite {
              testInterface = TestSuiteUnsupported tt,
              testBuildInfo = testStanzaBuildInfo stanza
            }

          Just tt | tt `notElem` knownTestTypes ->
            return emptyTestSuite {
              testInterface = TestSuiteUnsupported tt,
              testBuildInfo = testStanzaBuildInfo stanza
            }

          Just tt@(TestTypeExe ver) ->
            case testStanzaMainIs stanza of
              Nothing   -> syntaxError line (missingField "main-is" tt)
              Just file -> do
                when (isJust (testStanzaTestModule stanza)) $
                  warning (extraField "test-module" tt)
                return emptyTestSuite {
                  testInterface = TestSuiteExeV10 ver file,
                  testBuildInfo = testStanzaBuildInfo stanza
                }

          Just tt@(TestTypeLib ver) ->
            case testStanzaTestModule stanza of
              Nothing      -> syntaxError line (missingField "test-module" tt)
              Just module_ -> do
                when (isJust (testStanzaMainIs stanza)) $
                  warning (extraField "main-is" tt)
                return emptyTestSuite {
                  testInterface = TestSuiteLibV09 ver module_,
                  testBuildInfo = testStanzaBuildInfo stanza
                }

      where
        missingField name tt = "The '" ++ name ++ "' field is required for the "
                            ++ display tt ++ " test suite type."

        extraField   name tt = "The '" ++ name ++ "' field is not used for the '"
                            ++ display tt ++ "' test suite type."

    -- ---------------------------------------------------------------------------
    -- The Benchmark type

    -- | An intermediate type just used for parsing the benchmark stanza.
    -- After validation it is converted into the proper 'Benchmark' type.
    data BenchmarkStanza = BenchmarkStanza {
           benchmarkStanzaBenchmarkType   :: Maybe BenchmarkType,
           benchmarkStanzaMainIs          :: Maybe FilePath,
           benchmarkStanzaBenchmarkModule :: Maybe ModuleName,
           benchmarkStanzaBuildInfo       :: BuildInfo
         }

    emptyBenchmarkStanza :: BenchmarkStanza
    emptyBenchmarkStanza = BenchmarkStanza Nothing Nothing Nothing mempty

    benchmarkFieldDescrs :: [FieldDescr BenchmarkStanza]
    benchmarkFieldDescrs =
        [ simpleField "type"
            (maybe empty disp)    (fmap Just parse)
            benchmarkStanzaBenchmarkType
            (\x suite -> suite { benchmarkStanzaBenchmarkType = x })
        , simpleField "main-is"
            (maybe empty showFilePath)  (fmap Just parseFilePathQ)
            benchmarkStanzaMainIs
            (\x suite -> suite { benchmarkStanzaMainIs = x })
        ]
        ++ map biToBenchmark binfoFieldDescrs
      where
        biToBenchmark = liftField benchmarkStanzaBuildInfo
                        (\bi suite -> suite { benchmarkStanzaBuildInfo = bi })

    storeXFieldsBenchmark :: UnrecFieldParser BenchmarkStanza
    storeXFieldsBenchmark (f@('x':'-':_), val)
        t@(BenchmarkStanza { benchmarkStanzaBuildInfo = bi }) =
            Just $ t {benchmarkStanzaBuildInfo =
                           bi{ customFieldsBI = (f,val):customFieldsBI bi}}
    storeXFieldsBenchmark _ _ = Nothing

    validateBenchmark :: LineNo -> BenchmarkStanza -> ParseResult Benchmark
    validateBenchmark line stanza =
        case benchmarkStanzaBenchmarkType stanza of
          Nothing -> return $
            emptyBenchmark { benchmarkBuildInfo = benchmarkStanzaBuildInfo stanza }

          Just tt@(BenchmarkTypeUnknown _ _) ->
            return emptyBenchmark {
              benchmarkInterface = BenchmarkUnsupported tt,
              benchmarkBuildInfo = benchmarkStanzaBuildInfo stanza
            }

          Just tt | tt `notElem` knownBenchmarkTypes ->
            return emptyBenchmark {
              benchmarkInterface = BenchmarkUnsupported tt,
              benchmarkBuildInfo = benchmarkStanzaBuildInfo stanza
            }

          Just tt@(BenchmarkTypeExe ver) ->
            case benchmarkStanzaMainIs stanza of
              Nothing   -> syntaxError line (missingField "main-is" tt)
              Just file -> do
                when (isJust (benchmarkStanzaBenchmarkModule stanza)) $
                  warning (extraField "benchmark-module" tt)
                return emptyBenchmark {
                  benchmarkInterface = BenchmarkExeV10 ver file,
                  benchmarkBuildInfo = benchmarkStanzaBuildInfo stanza
                }

      where
        missingField name tt = "The '" ++ name ++ "' field is required for the "
                            ++ display tt ++ " benchmark type."

        extraField   name tt = "The '" ++ name ++ "' field is not used for the '"
                            ++ display tt ++ "' benchmark type."

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

    binfoFieldDescrs :: [FieldDescr BuildInfo]
    binfoFieldDescrs =
     [ boolField "buildable"
               buildable          (\val binfo -> binfo{buildable=val})
     , commaListField  "build-tools"
               disp               parseBuildTool
               buildTools         (\xs  binfo -> binfo{buildTools=xs})
     , commaListFieldWithSep vcat "build-depends"
               disp                   parse
               targetBuildDepends (\xs binfo -> binfo{targetBuildDepends=xs})
     , spaceListField "cpp-options"
               showToken          parseTokenQ'
               cppOptions          (\val binfo -> binfo{cppOptions=val})
     , spaceListField "cc-options"
               showToken          parseTokenQ'
               ccOptions          (\val binfo -> binfo{ccOptions=val})
     , spaceListField "ld-options"
               showToken          parseTokenQ'
               ldOptions          (\val binfo -> binfo{ldOptions=val})
     , commaListField  "pkgconfig-depends"
               disp               parsePkgconfigDependency
               pkgconfigDepends   (\xs  binfo -> binfo{pkgconfigDepends=xs})
     , listField "frameworks"
               showToken          parseTokenQ
               frameworks         (\val binfo -> binfo{frameworks=val})
     , listField "extra-framework-dirs"
               showToken          parseFilePathQ
               extraFrameworkDirs (\val binfo -> binfo{extraFrameworkDirs=val})
     , listFieldWithSep vcat "c-sources"
               showFilePath       parseFilePathQ
               cSources           (\paths binfo -> binfo{cSources=paths})
     , listFieldWithSep vcat "js-sources"
               showFilePath       parseFilePathQ
               jsSources          (\paths binfo -> binfo{jsSources=paths})
     , simpleField "default-language"
               (maybe empty disp) (option Nothing (fmap Just parseLanguageQ))
               defaultLanguage    (\lang  binfo -> binfo{defaultLanguage=lang})
     , listField   "other-languages"
               disp               parseLanguageQ
               otherLanguages     (\langs binfo -> binfo{otherLanguages=langs})
     , listField   "default-extensions"
               disp               parseExtensionQ
               defaultExtensions  (\exts  binfo -> binfo{defaultExtensions=exts})
     , listField   "other-extensions"
               disp               parseExtensionQ
               otherExtensions    (\exts  binfo -> binfo{otherExtensions=exts})
     , listField   "extensions"
               disp               parseExtensionQ
               oldExtensions      (\exts  binfo -> binfo{oldExtensions=exts})

     , listFieldWithSep vcat "extra-libraries"
               showToken          parseTokenQ
               extraLibs          (\xs    binfo -> binfo{extraLibs=xs})
     , listFieldWithSep vcat "extra-ghci-libraries"
               showToken          parseTokenQ
               extraGHCiLibs      (\xs    binfo -> binfo{extraGHCiLibs=xs})
     , listField   "extra-lib-dirs"
               showFilePath       parseFilePathQ
               extraLibDirs       (\xs    binfo -> binfo{extraLibDirs=xs})
     , listFieldWithSep vcat "includes"
               showFilePath       parseFilePathQ
               includes           (\paths binfo -> binfo{includes=paths})
     , listFieldWithSep vcat "install-includes"
               showFilePath       parseFilePathQ
               installIncludes    (\paths binfo -> binfo{installIncludes=paths})
     , listField   "include-dirs"
               showFilePath       parseFilePathQ
               includeDirs        (\paths binfo -> binfo{includeDirs=paths})
     , listField   "hs-source-dirs"
               showFilePath       parseFilePathQ
               hsSourceDirs       (\paths binfo -> binfo{hsSourceDirs=paths})
     , listFieldWithSep vcat "other-modules"
               disp               parseModuleNameQ
               otherModules       (\val binfo -> binfo{otherModules=val})
     , optsField   "ghc-prof-options" GHC
               profOptions        (\val binfo -> binfo{profOptions=val})
     , optsField   "ghcjs-prof-options" GHCJS
               profOptions        (\val binfo -> binfo{profOptions=val})
     , optsField   "ghc-shared-options" GHC
               sharedOptions      (\val binfo -> binfo{sharedOptions=val})
     , optsField   "ghcjs-shared-options" GHCJS
               sharedOptions      (\val binfo -> binfo{sharedOptions=val})
     , optsField   "ghc-options"  GHC
               options            (\path  binfo -> binfo{options=path})
     , optsField   "ghcjs-options" GHCJS
               options            (\path  binfo -> binfo{options=path})
     , optsField   "jhc-options"  JHC
               options            (\path  binfo -> binfo{options=path})

     -- NOTE: Hugs and NHC are not supported anymore, but these fields are kept
     -- around for backwards compatibility.
     , optsField   "hugs-options" Hugs
               options            (const id)
     , optsField   "nhc98-options" NHC
               options            (const id)
     ]

    storeXFieldsBI :: UnrecFieldParser BuildInfo
    storeXFieldsBI (f@('x':'-':_),val) bi = Just bi{ customFieldsBI = (f,val):customFieldsBI bi }
    storeXFieldsBI _ _ = Nothing

    ------------------------------------------------------------------------------

    flagFieldDescrs :: [FieldDescr Flag]
    flagFieldDescrs =
        [ simpleField "description"
            showFreeText     parseFreeText
            flagDescription  (\val fl -> fl{ flagDescription = val })
        , boolField "default"
            flagDefault      (\val fl -> fl{ flagDefault = val })
        , boolField "manual"
            flagManual       (\val fl -> fl{ flagManual = val })
        ]

    ------------------------------------------------------------------------------

    sourceRepoFieldDescrs :: [FieldDescr SourceRepo]
    sourceRepoFieldDescrs =
        [ simpleField "type"
            (maybe empty disp)         (fmap Just parse)
            repoType                   (\val repo -> repo { repoType = val })
        , simpleField "location"
            (maybe empty showFreeText) (fmap Just parseFreeText)
            repoLocation               (\val repo -> repo { repoLocation = val })
        , simpleField "module"
            (maybe empty showToken)    (fmap Just parseTokenQ)
            repoModule                 (\val repo -> repo { repoModule = val })
        , simpleField "branch"
            (maybe empty showToken)    (fmap Just parseTokenQ)
            repoBranch                 (\val repo -> repo { repoBranch = val })
        , simpleField "tag"
            (maybe empty showToken)    (fmap Just parseTokenQ)
            repoTag                    (\val repo -> repo { repoTag = val })
        , simpleField "subdir"
            (maybe empty showFilePath) (fmap Just parseFilePathQ)
            repoSubdir                 (\val repo -> repo { repoSubdir = val })
        ]

    ------------------------------------------------------------------------------

    setupBInfoFieldDescrs :: [FieldDescr SetupBuildInfo]
    setupBInfoFieldDescrs =
        [ commaListFieldWithSep vcat "setup-depends"
            disp         parse
            setupDepends (\xs binfo -> binfo{setupDepends=xs})
        ]

    -- ---------------------------------------------------------------
    -- Parsing

    -- | Given a parser and a filename, return the parse of the file,
    -- after checking if the file exists.
    readAndParseFile :: (FilePath -> (String -> IO a) -> IO a)
                     -> (String -> ParseResult a)
                     -> Verbosity
                     -> FilePath -> IO a
    readAndParseFile withFileContents' parser verbosity fpath = do
      exists <- doesFileExist fpath
      unless exists
        (die $ "Error Parsing: file \"" ++ fpath ++ "\" doesn't exist. Cannot continue.")
      withFileContents' fpath $ \str -> case parser str of
        ParseFailed e -> do
            let (line, message) = locatedErrorMsg e
            dieWithLocation fpath line message
        ParseOk warnings x -> do
            mapM_ (warn verbosity . showPWarning fpath) $ reverse warnings
            return x

    readHookedBuildInfo :: Verbosity -> FilePath -> IO HookedBuildInfo
    readHookedBuildInfo =
        readAndParseFile withFileContents parseHookedBuildInfo

    -- |Parse the given package file.
    readPackageDescription :: Verbosity -> FilePath -> IO GenericPackageDescription
    readPackageDescription =
        readAndParseFile withUTF8FileContents parsePackageDescription

    stanzas :: [Field] -> [[Field]]
    stanzas [] = []
    stanzas (f:fields) = (f:this) : stanzas rest
      where
        (this, rest) = break isStanzaHeader fields

    isStanzaHeader :: Field -> Bool
    isStanzaHeader (F _ f _) = f == "executable"
    isStanzaHeader _ = False

    ------------------------------------------------------------------------------

    mapSimpleFields :: (Field -> ParseResult Field) -> [Field]
                    -> ParseResult [Field]
    mapSimpleFields f = mapM walk
      where
        walk fld@F{} = f fld
        walk (IfBlock l c fs1 fs2) = do
          fs1' <- mapM walk fs1
          fs2' <- mapM walk fs2
          return (IfBlock l c fs1' fs2')
        walk (Section ln n l fs1) = do
          fs1' <-  mapM walk fs1
          return (Section ln n l fs1')

    -- prop_isMapM fs = mapSimpleFields return fs == return fs

    -- names of fields that represents dependencies
    -- TODO: maybe build-tools should go here too?
    constraintFieldNames :: [String]
    constraintFieldNames = ["build-depends"]

    -- Possible refactoring would be to have modifiers be explicit about what
    -- they add and define an accessor that specifies what the dependencies
    -- are.  This way we would completely reuse the parsing knowledge from the
    -- field descriptor.
    parseConstraint :: Field -> ParseResult [Dependency]
    parseConstraint (F l n v)
        | n `elem` constraintFieldNames = runP l n (parseCommaList parse) v
    parseConstraint f = userBug $ "Constraint was expected (got: " ++ show f ++ ")"

    {-
    headerFieldNames :: [String]
    headerFieldNames = filter (\n -> not (n `elem` constraintFieldNames))
                     . map fieldName $ pkgDescrFieldDescrs
    -}

    libFieldNames :: [String]
    libFieldNames = map fieldName libFieldDescrs
                    ++ buildInfoNames ++ constraintFieldNames

    -- exeFieldNames :: [String]
    -- exeFieldNames = map fieldName executableFieldDescrs
    --                 ++ buildInfoNames

    buildInfoNames :: [String]
    buildInfoNames = map fieldName binfoFieldDescrs
                    ++ map fst deprecatedFieldsBuildInfo

    -- A minimal implementation of the StateT monad transformer to avoid depending
    -- on the 'mtl' package.
    newtype StT s m a = StT { runStT :: s -> m (a,s) }

    instance Functor f => Functor (StT s f) where
        fmap g (StT f) = StT $ fmap (first g)  . f

    #if __GLASGOW_HASKELL__ >= 710
    instance (Monad m) => Applicative (StT s m) where
    #else
    instance (Monad m, Functor m) => Applicative (StT s m) where
    #endif
        pure a = StT (\s -> return (a,s))
        (<*>) = ap

    instance Monad m => Monad (StT s m) where
    #if __GLASGOW_HASKELL__ < 710
        return a = StT (\s -> return (a,s))
    #endif
        StT f >>= g = StT $ \s -> do
                            (a,s') <- f s
                            runStT (g a) s'

    get :: Monad m => StT s m s
    get = StT $ \s -> return (s, s)

    modify :: Monad m => (s -> s) -> StT s m ()
    modify f = StT $ \s -> return ((),f s)

    lift :: Monad m => m a -> StT s m a
    lift m = StT $ \s -> m >>= \a -> return (a,s)

    evalStT :: Monad m => StT s m a -> s -> m a
    evalStT st s = liftM fst $ runStT st s

    -- Our monad for parsing a list/tree of fields.
    --
    -- The state represents the remaining fields to be processed.
    type PM a = StT [Field] ParseResult a

    -- return look-ahead field or nothing if we're at the end of the file
    peekField :: PM (Maybe Field)
    peekField = liftM listToMaybe get

    -- Unconditionally discard the first field in our state.  Will error when it
    -- reaches end of file.  (Yes, that's evil.)
    skipField :: PM ()
    skipField = modify tail

    --FIXME: this should take a ByteString, not a String. We have to be able to
    -- decode UTF8 and handle the BOM.

    -- | Parses the given file into a 'GenericPackageDescription'.
    --
    -- In Cabal 1.2 the syntax for package descriptions was changed to a format
    -- with sections and possibly indented property descriptions.
    parsePackageDescription :: String -> ParseResult GenericPackageDescription
    parsePackageDescription file = do

        -- This function is quite complex because it needs to be able to parse
        -- both pre-Cabal-1.2 and post-Cabal-1.2 files.  Additionally, it contains
        -- a lot of parser-related noise since we do not want to depend on Parsec.
        --
        -- If we detect an pre-1.2 file we implicitly convert it to post-1.2
        -- style.  See 'sectionizeFields' below for details about the conversion.

        fields0 <- readFields file `catchParseError` \err ->
                     let tabs = findIndentTabs file in
                     case err of
                       -- In case of a TabsError report them all at once.
                       TabsError tabLineNo -> reportTabsError
                       -- but only report the ones including and following
                       -- the one that caused the actual error
                                                [ t | t@(lineNo',_) <- tabs
                                                    , lineNo' >= tabLineNo ]
                       _ -> parseFail err

        let cabalVersionNeeded =
              head $ [ minVersionBound versionRange
                     | Just versionRange <- [ simpleParse v
                                            | F _ "cabal-version" v <- fields0 ] ]
                  ++ [Version [0] []]
            minVersionBound versionRange =
              case asVersionIntervals versionRange of
                []                            -> Version [0] []
                ((LowerBound version _, _):_) -> version

        handleFutureVersionParseFailure cabalVersionNeeded $ do

          let sf = sectionizeFields fields0  -- ensure 1.2 format

            -- figure out and warn about deprecated stuff (warnings are collected
            -- inside our parsing monad)
          fields <- mapSimpleFields deprecField sf

            -- Our parsing monad takes the not-yet-parsed fields as its state.
            -- After each successful parse we remove the field from the state
            -- ('skipField') and move on to the next one.
            --
            -- Things are complicated a bit, because fields take a tree-like
            -- structure -- they can be sections or "if"/"else" conditionals.

          flip evalStT fields $ do

              -- The header consists of all simple fields up to the first section
              -- (flag, library, executable).
            header_fields <- getHeader []

              -- Parses just the header fields and stores them in a
              -- 'PackageDescription'.  Note that our final result is a
              -- 'GenericPackageDescription'; for pragmatic reasons we just store
              -- the partially filled-out 'PackageDescription' inside the
              -- 'GenericPackageDescription'.
            pkg <- lift $ parseFields pkgDescrFieldDescrs
                                      storeXFieldsPD
                                      emptyPackageDescription
                                      header_fields

              -- 'getBody' assumes that the remaining fields only consist of
              -- flags, lib and exe sections.
            (repos, flags, mcsetup, mlib, exes, tests, bms) <- getBody
            warnIfRest  -- warn if getBody did not parse up to the last field.
              -- warn about using old/new syntax with wrong cabal-version:
            maybeWarnCabalVersion (not $ oldSyntax fields0) pkg
            checkForUndefinedFlags flags mlib exes tests
            return $ GenericPackageDescription
                       pkg { sourceRepos = repos, setupBuildInfo = mcsetup }
                       flags mlib exes tests bms

      where
        oldSyntax = all isSimpleField
        reportTabsError tabs =
            syntaxError (fst (head tabs)) $
              "Do not use tabs for indentation (use spaces instead)\n"
              ++ "  Tabs were used at (line,column): " ++ show tabs

        maybeWarnCabalVersion newsyntax pkg
          | newsyntax && specVersion pkg < Version [1,2] []
          = lift $ warning $
                 "A package using section syntax must specify at least\n"
              ++ "'cabal-version: >= 1.2'."

        maybeWarnCabalVersion newsyntax pkg
          | not newsyntax && specVersion pkg >= Version [1,2] []
          = lift $ warning $
                 "A package using 'cabal-version: "
              ++ displaySpecVersion (specVersionRaw pkg)
              ++ "' must use section syntax. See the Cabal user guide for details."
          where
            displaySpecVersion (Left version)       = display version
            displaySpecVersion (Right versionRange) =
              case asVersionIntervals versionRange of
                [] {- impossible -}           -> display versionRange
                ((LowerBound version _, _):_) -> display (orLaterVersion version)

        maybeWarnCabalVersion _ _ = return ()

        handleFutureVersionParseFailure cabalVersionNeeded parseBody =
          (unless versionOk (warning message) >> parseBody)
            `catchParseError` \parseError -> case parseError of
            TabsError _   -> parseFail parseError
            _ | versionOk -> parseFail parseError
              | otherwise -> fail message
          where versionOk = cabalVersionNeeded <= cabalVersion
                message   = "This package requires at least Cabal version "
                         ++ display cabalVersionNeeded

        -- "Sectionize" an old-style Cabal file.  A sectionized file has:
        --
        --  * all global fields at the beginning, followed by
        --
        --  * all flag declarations, followed by
        --
        --  * an optional library section, and an arbitrary number of executable
        --    sections (in any order).
        --
        -- The current implementation just gathers all library-specific fields
        -- in a library section and wraps all executable stanzas in an executable
        -- section.
        sectionizeFields :: [Field] -> [Field]
        sectionizeFields fs
          | oldSyntax fs =
              let
                -- "build-depends" is a local field now.  To be backwards
                -- compatible, we still allow it as a global field in old-style
                -- package description files and translate it to a local field by
                -- adding it to every non-empty section
                (hdr0, exes0) = break ((=="executable") . fName) fs
                (hdr, libfs0) = partition (not . (`elem` libFieldNames) . fName) hdr0

                (deps, libfs) = partition ((== "build-depends") . fName)
                                           libfs0

                exes = unfoldr toExe exes0
                toExe [] = Nothing
                toExe (F l e n : r)
                  | e == "executable" =
                      let (efs, r') = break ((=="executable") . fName) r
                      in Just (Section l "executable" n (deps ++ efs), r')
                toExe _ = cabalBug "unexpected input to 'toExe'"
              in
                hdr ++
               (if null libfs then []
                else [Section (lineNo (head libfs)) "library" "" (deps ++ libfs)])
                ++ exes
          | otherwise = fs

        isSimpleField F{} = True
        isSimpleField _ = False

        -- warn if there's something at the end of the file
        warnIfRest :: PM ()
        warnIfRest = do
          s <- get
          case s of
            [] -> return ()
            _ -> lift $ warning "Ignoring trailing declarations."  -- add line no.

        -- all simple fields at the beginning of the file are (considered) header
        -- fields
        getHeader :: [Field] -> PM [Field]
        getHeader acc = peekField >>= \mf -> case mf of
            Just f@F{} -> skipField >> getHeader (f:acc)
            _ -> return (reverse acc)

        --
        -- body ::= { repo | flag | library | executable | test }+   -- at most one lib
        --
        -- The body consists of an optional sequence of declarations of flags and
        -- an arbitrary number of executables and at most one library.
        getBody :: PM ([SourceRepo], [Flag]
                      ,Maybe SetupBuildInfo
                      ,Maybe (CondTree ConfVar [Dependency] Library)
                      ,[(String, CondTree ConfVar [Dependency] Executable)]
                      ,[(String, CondTree ConfVar [Dependency] TestSuite)]
                      ,[(String, CondTree ConfVar [Dependency] Benchmark)])
        getBody = peekField >>= \mf -> case mf of
          Just (Section line_no sec_type sec_label sec_fields)
            | sec_type == "executable" -> do
                when (null sec_label) $ lift $ syntaxError line_no
                  "'executable' needs one argument (the executable's name)"
                exename <- lift $ runP line_no "executable" parseTokenQ sec_label
                flds <- collectFields parseExeFields sec_fields
                skipField
                (repos, flags, csetup, lib, exes, tests, bms) <- getBody
                return (repos, flags, csetup, lib, (exename, flds): exes, tests, bms)

            | sec_type == "test-suite" -> do
                when (null sec_label) $ lift $ syntaxError line_no
                    "'test-suite' needs one argument (the test suite's name)"
                testname <- lift $ runP line_no "test" parseTokenQ sec_label
                flds <- collectFields (parseTestFields line_no) sec_fields

                -- Check that a valid test suite type has been chosen. A type
                -- field may be given inside a conditional block, so we must
                -- check for that before complaining that a type field has not
                -- been given. The test suite must always have a valid type, so
                -- we need to check both the 'then' and 'else' blocks, though
                -- the blocks need not have the same type.
                let checkTestType ts ct =
                        let ts' = mappend ts $ condTreeData ct
                            -- If a conditional has only a 'then' block and no
                            -- 'else' block, then it cannot have a valid type
                            -- in every branch, unless the type is specified at
                            -- a higher level in the tree.
                            checkComponent (_, _, Nothing) = False
                            -- If a conditional has a 'then' block and an 'else'
                            -- block, both must specify a test type, unless the
                            -- type is specified higher in the tree.
                            checkComponent (_, t, Just e) =
                                checkTestType ts' t && checkTestType ts' e
                            -- Does the current node specify a test type?
                            hasTestType = testInterface ts'
                                /= testInterface emptyTestSuite
                        -- If the current level of the tree specifies a type,
                        -- then we are done. If not, then one of the conditional
                        -- branches below the current node must specify a type.
                        -- Each node may have multiple immediate children; we
                        -- only one need one to specify a type because the
                        -- configure step uses 'mappend' to join together the
                        -- results of flag resolution.
                        in hasTestType || any checkComponent (condTreeComponents ct)
                if checkTestType emptyTestSuite flds
                    then do
                        skipField
                        (repos, flags, csetup, lib, exes, tests, bms) <- getBody
                        return (repos, flags, csetup, lib, exes,
                                (testname, flds) : tests, bms)
                    else lift $ syntaxError line_no $
                             "Test suite \"" ++ testname
                          ++ "\" is missing required field \"type\" or the field "
                          ++ "is not present in all conditional branches. The "
                          ++ "available test types are: "
                          ++ intercalate ", " (map display knownTestTypes)

            | sec_type == "benchmark" -> do
                when (null sec_label) $ lift $ syntaxError line_no
                    "'benchmark' needs one argument (the benchmark's name)"
                benchname <- lift $ runP line_no "benchmark" parseTokenQ sec_label
                flds <- collectFields (parseBenchmarkFields line_no) sec_fields

                -- Check that a valid benchmark type has been chosen. A type
                -- field may be given inside a conditional block, so we must
                -- check for that before complaining that a type field has not
                -- been given. The benchmark must always have a valid type, so
                -- we need to check both the 'then' and 'else' blocks, though
                -- the blocks need not have the same type.
                let checkBenchmarkType ts ct =
                        let ts' = mappend ts $ condTreeData ct
                            -- If a conditional has only a 'then' block and no
                            -- 'else' block, then it cannot have a valid type
                            -- in every branch, unless the type is specified at
                            -- a higher level in the tree.
                            checkComponent (_, _, Nothing) = False
                            -- If a conditional has a 'then' block and an 'else'
                            -- block, both must specify a benchmark type, unless the
                            -- type is specified higher in the tree.
                            checkComponent (_, t, Just e) =
                                checkBenchmarkType ts' t && checkBenchmarkType ts' e
                            -- Does the current node specify a benchmark type?
                            hasBenchmarkType = benchmarkInterface ts'
                                /= benchmarkInterface emptyBenchmark
                        -- If the current level of the tree specifies a type,
                        -- then we are done. If not, then one of the conditional
                        -- branches below the current node must specify a type.
                        -- Each node may have multiple immediate children; we
                        -- only one need one to specify a type because the
                        -- configure step uses 'mappend' to join together the
                        -- results of flag resolution.
                        in hasBenchmarkType || any checkComponent (condTreeComponents ct)
                if checkBenchmarkType emptyBenchmark flds
                    then do
                        skipField
                        (repos, flags, csetup, lib, exes, tests, bms) <- getBody
                        return (repos, flags, csetup, lib, exes,
                                tests, (benchname, flds) : bms)
                    else lift $ syntaxError line_no $
                             "Benchmark \"" ++ benchname
                          ++ "\" is missing required field \"type\" or the field "
                          ++ "is not present in all conditional branches. The "
                          ++ "available benchmark types are: "
                          ++ intercalate ", " (map display knownBenchmarkTypes)

            | sec_type == "library" -> do
                unless (null sec_label) $ lift $
                  syntaxError line_no "'library' expects no argument"
                flds <- collectFields parseLibFields sec_fields
                skipField
                (repos, flags, csetup, lib, exes, tests, bms) <- getBody
                when (isJust lib) $ lift $ syntaxError line_no
                  "There can only be one library section in a package description."
                return (repos, flags, csetup, Just flds, exes, tests, bms)

            | sec_type == "flag" -> do
                when (null sec_label) $ lift $
                  syntaxError line_no "'flag' needs one argument (the flag's name)"
                flag <- lift $ parseFields
                        flagFieldDescrs
                        warnUnrec
                        (MkFlag (FlagName (lowercase sec_label)) "" True False)
                        sec_fields
                skipField
                (repos, flags, csetup, lib, exes, tests, bms) <- getBody
                return (repos, flag:flags, csetup, lib, exes, tests, bms)

            | sec_type == "source-repository" -> do
                when (null sec_label) $ lift $ syntaxError line_no $
                     "'source-repository' needs one argument, "
                  ++ "the repo kind which is usually 'head' or 'this'"
                kind <- case simpleParse sec_label of
                  Just kind -> return kind
                  Nothing   -> lift $ syntaxError line_no $
                                 "could not parse repo kind: " ++ sec_label
                repo <- lift $ parseFields
                        sourceRepoFieldDescrs
                        warnUnrec
                        SourceRepo {
                          repoKind     = kind,
                          repoType     = Nothing,
                          repoLocation = Nothing,
                          repoModule   = Nothing,
                          repoBranch   = Nothing,
                          repoTag      = Nothing,
                          repoSubdir   = Nothing
                        }
                        sec_fields
                skipField
                (repos, flags, csetup, lib, exes, tests, bms) <- getBody
                return (repo:repos, flags, csetup, lib, exes, tests, bms)

            | sec_type == "custom-setup" -> do
                unless (null sec_label) $ lift $
                  syntaxError line_no "'setup' expects no argument"
                flds <- lift $ parseFields
                                 setupBInfoFieldDescrs
                                 warnUnrec
                                 mempty
                                 sec_fields
                skipField
                (repos, flags, csetup0, lib, exes, tests, bms) <- getBody
                when (isJust csetup0) $ lift $ syntaxError line_no
                  "There can only be one 'custom-setup' section in a package description."
                return (repos, flags, Just flds, lib, exes, tests, bms)

            | otherwise -> do
                lift $ warning $ "Ignoring unknown section type: " ++ sec_type
                skipField
                getBody
          Just f@(F {}) -> do
                _ <- lift $ syntaxError (lineNo f) $
                  "Plain fields are not allowed in between stanzas: " ++ show f
                skipField
                getBody
          Just f@(IfBlock {}) -> do
                _ <- lift $ syntaxError (lineNo f) $
                  "If-blocks are not allowed in between stanzas: " ++ show f
                skipField
                getBody
          Nothing -> return ([], [], Nothing, Nothing, [], [], [])

        -- Extracts all fields in a block and returns a 'CondTree'.
        --
        -- We have to recurse down into conditionals and we treat fields that
        -- describe dependencies specially.
        collectFields :: ([Field] -> PM a) -> [Field]
                      -> PM (CondTree ConfVar [Dependency] a)
        collectFields parser allflds = do

            let simplFlds = [ F l n v | F l n v <- allflds ]
                condFlds = [ f | f@IfBlock{} <- allflds ]
                sections = [ s | s@Section{} <- allflds ]

            mapM_
                (\(Section l n _ _) -> lift . warning $
                    "Unexpected section '" ++ n ++ "' on line " ++ show l)
                sections

            a <- parser simplFlds

            -- Dependencies must be treated specially: when we
            -- parse into a CondTree, not only do we parse them into
            -- the targetBuildDepends/etc field inside the
            -- PackageDescription, but we also have to put the
            -- combined dependencies into CondTree.
            --
            -- This information is, in principle, redundant, but
            -- putting it here makes it easier for the constraint
            -- solver to pick a flag assignment which supports
            -- all of the dependencies (because it only has
            -- to check the CondTree, rather than grovel everywhere
            -- inside the conditional bits).
            deps <- liftM concat
                  . mapM (lift . parseConstraint)
                  . filter isConstraint
                  $ simplFlds

            ifs <- mapM processIfs condFlds

            return (CondNode a deps ifs)
          where
            isConstraint (F _ n _) = n `elem` constraintFieldNames
            isConstraint _ = False

            processIfs (IfBlock l c t e) = do
                cnd <- lift $ runP l "if" parseCondition c
                t' <- collectFields parser t
                e' <- case e of
                       [] -> return Nothing
                       es -> do fs <- collectFields parser es
                                return (Just fs)
                return (cnd, t', e')
            processIfs _ = cabalBug "processIfs called with wrong field type"

        parseLibFields :: [Field] -> PM Library
        parseLibFields = lift . parseFields libFieldDescrs storeXFieldsLib emptyLibrary

        -- Note: we don't parse the "executable" field here, hence the tail hack.
        parseExeFields :: [Field] -> PM Executable
        parseExeFields = lift . parseFields (tail executableFieldDescrs)
                                            storeXFieldsExe emptyExecutable

        parseTestFields :: LineNo -> [Field] -> PM TestSuite
        parseTestFields line fields = do
            x <- lift $ parseFields testSuiteFieldDescrs storeXFieldsTest
                                    emptyTestStanza fields
            lift $ validateTestSuite line x

        parseBenchmarkFields :: LineNo -> [Field] -> PM Benchmark
        parseBenchmarkFields line fields = do
            x <- lift $ parseFields benchmarkFieldDescrs storeXFieldsBenchmark
                                    emptyBenchmarkStanza fields
            lift $ validateBenchmark line x

        checkForUndefinedFlags ::
            [Flag] ->
            Maybe (CondTree ConfVar [Dependency] Library) ->
            [(String, CondTree ConfVar [Dependency] Executable)] ->
            [(String, CondTree ConfVar [Dependency] TestSuite)] ->
            PM ()
        checkForUndefinedFlags flags mlib exes tests = do
            let definedFlags = map flagName flags
            traverse_ (checkCondTreeFlags definedFlags) mlib
            mapM_ (checkCondTreeFlags definedFlags . snd) exes
            mapM_ (checkCondTreeFlags definedFlags . snd) tests

        checkCondTreeFlags :: [FlagName] -> CondTree ConfVar c a -> PM ()
        checkCondTreeFlags definedFlags ct = do
            let fv = nub $ freeVars ct
            unless (all (`elem` definedFlags) fv) $
                fail $ "These flags are used without having been defined: "
                    ++ intercalate ", " [ n | FlagName n <- fv \\ definedFlags ]

    -- | Parse a list of fields, given a list of field descriptions,
    --   a structure to accumulate the parsed fields, and a function
    --   that can decide what to do with fields which don't match any
    --   of the field descriptions.
    parseFields :: [FieldDescr a]      -- ^ descriptions of fields we know how to
                                       --   parse
                -> UnrecFieldParser a  -- ^ possibly do something with
                                       --   unrecognized fields
                -> a                   -- ^ accumulator
                -> [Field]             -- ^ fields to be parsed
                -> ParseResult a
    parseFields descrs unrec ini fields =
        do (a, unknowns) <- foldM (parseField descrs unrec) (ini, []) fields
           unless (null unknowns) $ warning $ render $
             text "Unknown fields:" <+>
                  commaSep (map (\(l,u) -> u ++ " (line " ++ show l ++ ")")
                                (reverse unknowns))
             $+$
             text "Fields allowed in this section:" $$
               nest 4 (commaSep $ map fieldName descrs)
           return a
      where
        commaSep = fsep . punctuate comma . map text

    parseField :: [FieldDescr a]     -- ^ list of parseable fields
               -> UnrecFieldParser a -- ^ possibly do something with
                                     --   unrecognized fields
               -> (a,[(Int,String)]) -- ^ accumulated result and warnings
               -> Field              -- ^ the field to be parsed
               -> ParseResult (a, [(Int,String)])
    parseField (FieldDescr name _ parser : fields) unrec (a, us) (F line f val)
      | name == f = parser line val a >>= \a' -> return (a',us)
      | otherwise = parseField fields unrec (a,us) (F line f val)
    parseField [] unrec (a,us) (F l f val) = return $
      case unrec (f,val) a of        -- no fields matched, see if the 'unrec'
        Just a' -> (a',us)           -- function wants to do anything with it
        Nothing -> (a, (l,f):us)
    parseField _ _ _ _ = cabalBug "'parseField' called on a non-field"

    deprecatedFields :: [(String,String)]
    deprecatedFields =
        deprecatedFieldsPkgDescr ++ deprecatedFieldsBuildInfo

    deprecatedFieldsPkgDescr :: [(String,String)]
    deprecatedFieldsPkgDescr = [ ("other-files", "extra-source-files") ]

    deprecatedFieldsBuildInfo :: [(String,String)]
    deprecatedFieldsBuildInfo = [ ("hs-source-dir","hs-source-dirs") ]

    -- Handle deprecated fields
    deprecField :: Field -> ParseResult Field
    deprecField (F line fld val) = do
      fld' <- case lookup fld deprecatedFields of
                Nothing -> return fld
                Just newName -> do
                  warning $ "The field \"" ++ fld
                          ++ "\" is deprecated, please use \"" ++ newName ++ "\""
                  return newName
      return (F line fld' val)
    deprecField _ = cabalBug "'deprecField' called on a non-field"

    parseHookedBuildInfo :: String -> ParseResult HookedBuildInfo
    parseHookedBuildInfo inp = do
      fields <- readFields inp
      let ss@(mLibFields:exes) = stanzas fields
      mLib <- parseLib mLibFields
      biExes <- mapM parseExe (maybe ss (const exes) mLib)
      return (mLib, biExes)
      where
        parseLib :: [Field] -> ParseResult (Maybe BuildInfo)
        parseLib (bi@(F _ inFieldName _:_))
            | lowercase inFieldName /= "executable" = liftM Just (parseBI bi)
        parseLib _ = return Nothing

        parseExe :: [Field] -> ParseResult (String, BuildInfo)
        parseExe (F line inFieldName mName:bi)
            | lowercase inFieldName == "executable"
                = do bis <- parseBI bi
                     return (mName, bis)
            | otherwise = syntaxError line "expecting 'executable' at top of stanza"
        parseExe (_:_) = cabalBug "`parseExe' called on a non-field"
        parseExe [] = syntaxError 0 "error in parsing buildinfo file. Expected executable stanza"

        parseBI st = parseFields binfoFieldDescrs storeXFieldsBI emptyBuildInfo st

    -- ---------------------------------------------------------------------------
    -- Pretty printing

    writePackageDescription :: FilePath -> PackageDescription -> IO ()
    writePackageDescription fpath pkg = writeUTF8File fpath (showPackageDescription pkg)

    --TODO: make this use section syntax
    -- add equivalent for GenericPackageDescription
    showPackageDescription :: PackageDescription -> String
    showPackageDescription pkg = render $
         ppPackage pkg
      $$ ppCustomFields (customFieldsPD pkg)
      $$ (case library pkg of
            Nothing  -> empty
            Just lib -> ppLibrary lib)
      $$ vcat [ space $$ ppExecutable exe | exe <- executables pkg ]
      where
        ppPackage    = ppFields pkgDescrFieldDescrs
        ppLibrary    = ppFields libFieldDescrs
        ppExecutable = ppFields executableFieldDescrs

    ppCustomFields :: [(String,String)] -> Doc
    ppCustomFields flds = vcat (map ppCustomField flds)

    ppCustomField :: (String,String) -> Doc
    ppCustomField (name,val) = text name <> colon <+> showFreeText val

    writeHookedBuildInfo :: FilePath -> HookedBuildInfo -> IO ()
    writeHookedBuildInfo fpath = writeFileAtomic fpath . BS.Char8.pack
                                 . showHookedBuildInfo

    showHookedBuildInfo :: HookedBuildInfo -> String
    showHookedBuildInfo (mb_lib_bi, ex_bis) = render $
         (case mb_lib_bi of
            Nothing -> empty
            Just bi -> ppBuildInfo bi)
      $$ vcat [    space
                $$ text "executable:" <+> text name
                $$ ppBuildInfo bi
              | (name, bi) <- ex_bis ]
      where
        ppBuildInfo bi = ppFields binfoFieldDescrs bi
                      $$ ppCustomFields (customFieldsBI bi)

    -- replace all tabs used as indentation with whitespace, also return where
    -- tabs were found
    findIndentTabs :: String -> [(Int,Int)]
    findIndentTabs = concatMap checkLine
                   . zip [1..]
                   . lines
        where
          checkLine (lineno, l) =
              let (indent, _content) = span isSpace l
                  tabCols = map fst . filter ((== '\t') . snd) . zip [0..]
                  addLineNo = map (\col -> (lineno,col))
              in addLineNo (tabCols indent)

    --test_findIndentTabs = findIndentTabs $ unlines $
    --    [ "foo", "  bar", " \t baz", "\t  biz\t", "\t\t \t mib" ]