src/Distribution/PackageDescription/Parsec.hs

    {-# LANGUAGE CPP                 #-}
    {-# LANGUAGE FlexibleContexts    #-}
    {-# LANGUAGE OverloadedStrings   #-}
    {-# LANGUAGE Rank2Types          #-}
    {-# LANGUAGE ScopedTypeVariables #-}
    -----------------------------------------------------------------------------
    -- |
    -- Module      :  Distribution.PackageDescription.Parsec
    -- 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.

    module Distribution.PackageDescription.Parsec (
        -- * Package descriptions
        readGenericPackageDescription,
        parseGenericPackageDescription,
        parseGenericPackageDescriptionMaybe,

        -- ** Parsing
        ParseResult,
        runParseResult,

        -- * New-style spec-version
        scanSpecVersion,

        -- ** Supplementary build information
        readHookedBuildInfo,
        parseHookedBuildInfo,
        ) where

    import Distribution.Compat.Prelude
    import Prelude ()

    import Control.Monad.State.Strict                    (StateT, execStateT)
    import Control.Monad.Trans.Class                     (lift)
    import Distribution.CabalSpecVersion
    import Distribution.Compat.Lens
    import Distribution.FieldGrammar
    import Distribution.FieldGrammar.Parsec              (NamelessField (..))
    import Distribution.Fields.ConfVar                   (parseConditionConfVar)
    import Distribution.Fields.Field                     (FieldName, getName)
    import Distribution.Fields.LexerMonad                (LexWarning, toPWarnings)
    import Distribution.Fields.Parser
    import Distribution.Fields.ParseResult
    import Distribution.PackageDescription
    import Distribution.PackageDescription.Configuration (freeVars, transformAllBuildInfos)
    import Distribution.PackageDescription.FieldGrammar
    import Distribution.PackageDescription.Quirks        (patchQuirks)
    import Distribution.Parsec                           (parsec, simpleParsecBS)
    import Distribution.Parsec.FieldLineStream           (fieldLineStreamFromBS)
    import Distribution.Parsec.Position                  (Position (..), zeroPos)
    import Distribution.Parsec.Warning                   (PWarnType (..))
    import Distribution.Pretty                           (prettyShow)
    import Distribution.Simple.Utils                     (fromUTF8BS, toUTF8BS)
    import Distribution.Utils.Generic                    (breakMaybe, unfoldrM, validateUTF8)
    import Distribution.Verbosity                        (Verbosity)
    import Distribution.Version                          (Version, mkVersion, versionNumbers)

    import qualified Data.ByteString                                   as BS
    import qualified Data.ByteString.Char8                             as BS8
    import qualified Data.Map.Strict                                   as Map
    import qualified Data.Set                                          as Set
    import qualified Distribution.Compat.Newtype                       as Newtype
    import qualified Distribution.Compat.NonEmptySet                   as NES
    import qualified Distribution.Types.BuildInfo.Lens                 as L
    import qualified Distribution.Types.Executable.Lens                as L
    import qualified Distribution.Types.ForeignLib.Lens                as L
    import qualified Distribution.Types.GenericPackageDescription.Lens as L
    import qualified Distribution.Types.PackageDescription.Lens        as L
    import qualified Distribution.Types.SetupBuildInfo.Lens            as L
    import qualified Text.Parsec                                       as P

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

    -- | Parse the given package file.
    readGenericPackageDescription :: Verbosity -> FilePath -> IO GenericPackageDescription
    readGenericPackageDescription = readAndParseFile parseGenericPackageDescription

    ------------------------------------------------------------------------------
    -- | 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.
    --
    parseGenericPackageDescription :: BS.ByteString -> ParseResult GenericPackageDescription
    parseGenericPackageDescription bs = do
        -- set scanned version
        setCabalSpecVersion ver

        csv <- case ver of
            -- if we get too new version, fail right away
            Just v -> case cabalSpecFromVersionDigits (versionNumbers v) of
                Just csv -> return (Just csv)
                Nothing  -> parseFatalFailure zeroPos $
                    "Unsupported cabal-version " ++ prettyShow v ++ ". See https://github.com/haskell/cabal/issues/4899."
            _ -> pure Nothing

        case readFields' bs'' of
            Right (fs, lexWarnings) -> do
                when patched $
                    parseWarning zeroPos PWTQuirkyCabalFile "Legacy cabal file"
                -- UTF8 is validated in a prepass step, afterwards parsing is lenient.
                parseGenericPackageDescription' csv lexWarnings invalidUtf8 fs
            -- TODO: better marshalling of errors
            Left perr -> parseFatalFailure pos (show perr) where
                ppos = P.errorPos perr
                pos  = Position (P.sourceLine ppos) (P.sourceColumn ppos)
      where
        (patched, bs') = patchQuirks bs
        ver = scanSpecVersion bs'

        invalidUtf8 = validateUTF8 bs'

        -- if there are invalid utf8 characters, we make the bytestring valid.
        bs'' = case invalidUtf8 of
            Nothing -> bs'
            Just _  -> toUTF8BS (fromUTF8BS bs')

    -- | 'Maybe' variant of 'parseGenericPackageDescription'
    parseGenericPackageDescriptionMaybe :: BS.ByteString -> Maybe GenericPackageDescription
    parseGenericPackageDescriptionMaybe =
        either (const Nothing) Just . snd . runParseResult . parseGenericPackageDescription

    fieldlinesToBS :: [FieldLine ann] -> BS.ByteString
    fieldlinesToBS = BS.intercalate "\n" . map (\(FieldLine _ bs) -> bs)

    -- Monad in which sections are parsed
    type SectionParser = StateT SectionS ParseResult

    -- | State of section parser
    data SectionS = SectionS
        { _stateGpd           :: !GenericPackageDescription
        , _stateCommonStanzas :: !(Map String CondTreeBuildInfo)
        }

    stateGpd :: Lens' SectionS GenericPackageDescription
    stateGpd f (SectionS gpd cs) = (\x -> SectionS x cs) <$> f gpd
    {-# INLINE stateGpd #-}

    stateCommonStanzas :: Lens' SectionS (Map String CondTreeBuildInfo)
    stateCommonStanzas f (SectionS gpd cs) = SectionS gpd <$> f cs
    {-# INLINE stateCommonStanzas #-}

    -- Note [Accumulating parser]
    --
    -- This parser has two "states":
    -- * first we parse fields of PackageDescription
    -- * then we parse sections (libraries, executables, etc)
    parseGenericPackageDescription'
        :: Maybe CabalSpecVersion
        -> [LexWarning]
        -> Maybe Int
        -> [Field Position]
        -> ParseResult GenericPackageDescription
    parseGenericPackageDescription' scannedVer lexWarnings utf8WarnPos fs = do
        parseWarnings (toPWarnings lexWarnings)
        for_ utf8WarnPos $ \pos ->
            parseWarning zeroPos PWTUTF $ "UTF8 encoding problem at byte offset " ++ show pos
        let (syntax, fs') = sectionizeFields fs
        let (fields, sectionFields) = takeFields fs'

        -- cabal-version
        specVer <- case scannedVer of
            Just v  -> return v
            Nothing -> case Map.lookup "cabal-version" fields >>= safeLast of
                Nothing                        -> return CabalSpecV1_0
                Just (MkNamelessField pos fls) -> do
                    -- version will be parsed twice, therefore we parse without warnings.
                    v <- withoutWarnings $
                        Newtype.unpack' SpecVersion <$>
                        -- Use version with || and && but before addition of ^>= and removal of -any
                        runFieldParser pos parsec CabalSpecV1_24 fls

                    -- if it were at the beginning, scanner would found it
                    when (v >= CabalSpecV2_2) $ parseFailure pos $
                        "cabal-version should be at the beginning of the file starting with spec version 2.2. " ++
                        "See https://github.com/haskell/cabal/issues/4899"

                    return v

        -- reset cabal version, it might not be set
        let specVer' = mkVersion (cabalSpecToVersionDigits specVer)
        setCabalSpecVersion (Just specVer')

        -- Package description
        pd <- parseFieldGrammar specVer fields packageDescriptionFieldGrammar

        -- Check that scanned and parsed versions match.
        unless (specVer == specVersion pd) $ parseFailure zeroPos $
            "Scanned and parsed cabal-versions don't match " ++
            prettyShow (SpecVersion specVer) ++ " /= " ++ prettyShow (SpecVersion (specVersion pd))

        maybeWarnCabalVersion syntax pd

        -- Sections
        let gpd = emptyGenericPackageDescription
                & L.packageDescription .~ pd
        gpd1 <- view stateGpd <$> execStateT (goSections specVer sectionFields) (SectionS gpd Map.empty)

        let gpd2 = postProcessInternalDeps specVer gpd1
        checkForUndefinedFlags gpd2
        checkForUndefinedCustomSetup gpd2
        -- See nothunks test, without this deepseq we get (at least):
        -- Thunk in ThunkInfo {thunkContext = ["PackageIdentifier","PackageDescription","GenericPackageDescription"]}
        --
        -- TODO: re-benchmark, whether `deepseq` is important (both cabal-benchmarks and solver-benchmarks)
        -- TODO: remove the need for deepseq if `deepseq` in fact matters
        -- NOTE: IIRC it does affect (maximal) memory usage, which causes less GC pressure
        gpd2 `deepseq` return gpd2
      where
        safeLast :: [a] -> Maybe a
        safeLast = listToMaybe . reverse

        newSyntaxVersion :: CabalSpecVersion
        newSyntaxVersion = CabalSpecV1_2

        maybeWarnCabalVersion :: Syntax -> PackageDescription -> ParseResult ()
        maybeWarnCabalVersion syntax pkg
          | syntax == NewSyntax && specVersion pkg < newSyntaxVersion
          = parseWarning zeroPos PWTNewSyntax $
                 "A package using section syntax must specify at least\n"
              ++ "'cabal-version: >= 1.2'."

        maybeWarnCabalVersion syntax pkg
          | syntax == OldSyntax && specVersion pkg >= newSyntaxVersion
          = parseWarning zeroPos PWTOldSyntax $
                 "A package using 'cabal-version: "
              ++ prettyShow (SpecVersion (specVersion pkg))
              ++ "' must use section syntax. See the Cabal user guide for details."

        maybeWarnCabalVersion _ _ = return ()

    goSections :: CabalSpecVersion -> [Field Position] -> SectionParser ()
    goSections specVer = traverse_ process
      where
        process (Field (Name pos name) _) =
            lift $ parseWarning pos PWTTrailingFields $
                "Ignoring trailing fields after sections: " ++ show name
        process (Section name args secFields) =
            parseSection name args secFields

        snoc x xs = xs ++ [x]

        hasCommonStanzas = specHasCommonStanzas specVer

        -- we need signature, because this is polymorphic, but not-closed
        parseCondTree'
            :: L.HasBuildInfo a
            => ParsecFieldGrammar' a       -- ^ grammar
            -> (BuildInfo -> a)
            -> Map String CondTreeBuildInfo  -- ^ common stanzas
            -> [Field Position]
            -> ParseResult (CondTree ConfVar [Dependency] a)
        parseCondTree' = parseCondTreeWithCommonStanzas specVer

        parseSection :: Name Position -> [SectionArg Position] -> [Field Position] -> SectionParser ()
        parseSection (Name pos name) args fields
            | hasCommonStanzas == NoCommonStanzas, name == "common" = lift $ do
              parseWarning pos PWTUnknownSection $ "Ignoring section: common. You should set cabal-version: 2.2 or larger to use common stanzas."

            | name == "common" = do
                commonStanzas <- use stateCommonStanzas
                name' <- lift $ parseCommonName pos args
                biTree <- lift $ parseCondTree' buildInfoFieldGrammar id commonStanzas fields

                case Map.lookup name' commonStanzas of
                    Nothing -> stateCommonStanzas .= Map.insert name' biTree commonStanzas
                    Just _  -> lift $ parseFailure pos $
                        "Duplicate common stanza: " ++ name'

            | name == "library" && null args = do
                prev <- use $ stateGpd . L.condLibrary
                when (isJust prev) $ lift $ parseFailure pos $
                    "Multiple main libraries; have you forgotten to specify a name for an internal library?"

                commonStanzas <- use stateCommonStanzas
                let name'' = LMainLibName
                lib <- lift $ parseCondTree' (libraryFieldGrammar name'') (libraryFromBuildInfo name'') commonStanzas fields
                --
                -- TODO check that not set
                stateGpd . L.condLibrary ?= lib

            -- Sublibraries
            -- TODO: check cabal-version
            | name == "library" = do
                commonStanzas <- use stateCommonStanzas
                name' <- parseUnqualComponentName pos args
                let name'' = LSubLibName name'
                lib   <- lift $ parseCondTree' (libraryFieldGrammar name'') (libraryFromBuildInfo name'') commonStanzas fields
                -- TODO check duplicate name here?
                stateGpd . L.condSubLibraries %= snoc (name', lib)

            -- TODO: check cabal-version
            | name == "foreign-library" = do
                commonStanzas <- use stateCommonStanzas
                name' <- parseUnqualComponentName pos args
                flib  <- lift $ parseCondTree' (foreignLibFieldGrammar name') (fromBuildInfo' name') commonStanzas fields

                let hasType ts = foreignLibType ts /= foreignLibType mempty
                unless (onAllBranches hasType flib) $ lift $ parseFailure pos $ concat
                    [ "Foreign library " ++ show (prettyShow name')
                    , " is missing required field \"type\" or the field "
                    , "is not present in all conditional branches. The "
                    , "available test types are: "
                    , intercalate ", " (map prettyShow knownForeignLibTypes)
                    ]

                -- TODO check duplicate name here?
                stateGpd . L.condForeignLibs %= snoc (name', flib)

            | name == "executable" = do
                commonStanzas <- use stateCommonStanzas
                name' <- parseUnqualComponentName pos args
                exe   <- lift $ parseCondTree' (executableFieldGrammar name') (fromBuildInfo' name') commonStanzas fields
                -- TODO check duplicate name here?
                stateGpd . L.condExecutables %= snoc (name', exe)

            | name == "test-suite" = do
                commonStanzas <- use stateCommonStanzas
                name'      <- parseUnqualComponentName pos args
                testStanza <- lift $ parseCondTree' testSuiteFieldGrammar (fromBuildInfo' name') commonStanzas fields
                testSuite  <- lift $ traverse (validateTestSuite pos) testStanza

                let hasType ts = testInterface ts /= testInterface mempty
                unless (onAllBranches hasType testSuite) $ lift $ parseFailure pos $ concat
                    [ "Test suite " ++ show (prettyShow name')
                    , " is missing required field \"type\" or the field "
                    , "is not present in all conditional branches. The "
                    , "available test types are: "
                    , intercalate ", " (map prettyShow knownTestTypes)
                    ]

                -- TODO check duplicate name here?
                stateGpd . L.condTestSuites %= snoc (name', testSuite)

            | name == "benchmark" = do
                commonStanzas <- use stateCommonStanzas
                name'       <- parseUnqualComponentName pos args
                benchStanza <- lift $ parseCondTree' benchmarkFieldGrammar (fromBuildInfo' name') commonStanzas fields
                bench       <- lift $ traverse (validateBenchmark pos) benchStanza

                let hasType ts = benchmarkInterface ts /= benchmarkInterface mempty
                unless (onAllBranches hasType bench) $ lift $ parseFailure pos $ concat
                    [ "Benchmark " ++ show (prettyShow name')
                    , " is missing required field \"type\" or the field "
                    , "is not present in all conditional branches. The "
                    , "available benchmark types are: "
                    , intercalate ", " (map prettyShow knownBenchmarkTypes)
                    ]

                -- TODO check duplicate name here?
                stateGpd . L.condBenchmarks %= snoc (name', bench)

            | name == "flag" = do
                name'  <- parseNameBS pos args
                name'' <- lift $ runFieldParser' [pos] parsec specVer (fieldLineStreamFromBS name') `recoverWith` mkFlagName ""
                flag   <- lift $ parseFields specVer fields (flagFieldGrammar name'')
                -- Check default flag
                stateGpd . L.genPackageFlags %= snoc flag

            | name == "custom-setup" && null args = do
                sbi <- lift $ parseFields specVer fields  (setupBInfoFieldGrammar False)
                stateGpd . L.packageDescription . L.setupBuildInfo ?= sbi

            | name == "source-repository" = do
                kind <- lift $ case args of
                    [SecArgName spos secName] ->
                        runFieldParser' [spos] parsec specVer (fieldLineStreamFromBS secName) `recoverWith` RepoHead
                    [] -> do
                        parseFailure pos "'source-repository' requires exactly one argument"
                        pure RepoHead
                    _ -> do
                        parseFailure pos $ "Invalid source-repository kind " ++ show args
                        pure RepoHead

                sr <- lift $ parseFields specVer fields (sourceRepoFieldGrammar kind)
                stateGpd . L.packageDescription . L.sourceRepos %= snoc sr

            | otherwise = lift $
                parseWarning pos PWTUnknownSection $ "Ignoring section: " ++ show name

    parseName :: Position -> [SectionArg Position] -> SectionParser String
    parseName pos args = fromUTF8BS <$> parseNameBS pos args

    parseNameBS :: Position -> [SectionArg Position] -> SectionParser BS.ByteString
    -- TODO: use strict parser
    parseNameBS pos args = case args of
        [SecArgName _pos secName] ->
             pure secName
        [SecArgStr _pos secName] ->
             pure secName
        [] -> do
             lift $ parseFailure pos "name required"
             pure ""
        _ -> do
             -- TODO: pretty print args
             lift $ parseFailure pos $ "Invalid name " ++ show args
             pure ""

    parseCommonName :: Position -> [SectionArg Position] -> ParseResult String
    parseCommonName pos args = case args of
        [SecArgName _pos secName] ->
             pure $ fromUTF8BS secName
        [SecArgStr _pos secName] ->
             pure $ fromUTF8BS secName
        [] -> do
             parseFailure pos $ "name required"
             pure ""
        _ -> do
             -- TODO: pretty print args
             parseFailure pos $ "Invalid name " ++ show args
             pure ""

    -- TODO: avoid conversion to 'String'.
    parseUnqualComponentName :: Position -> [SectionArg Position] -> SectionParser UnqualComponentName
    parseUnqualComponentName pos args = mkUnqualComponentName <$> parseName pos args

    -- | Parse a non-recursive list of fields.
    parseFields
        :: CabalSpecVersion
        -> [Field Position] -- ^ fields to be parsed
        -> ParsecFieldGrammar' a
        -> ParseResult a
    parseFields v fields grammar = do
        let (fs0, ss) = partitionFields fields
        traverse_ (traverse_ warnInvalidSubsection) ss
        parseFieldGrammar v fs0 grammar

    warnInvalidSubsection :: Section Position -> ParseResult ()
    warnInvalidSubsection (MkSection (Name pos name) _ _) =
        void $ parseFailure pos $ "invalid subsection " ++ show name

    parseCondTree
        :: forall a. L.HasBuildInfo a
        => CabalSpecVersion
        -> HasElif                        -- ^ accept @elif@
        -> ParsecFieldGrammar' a          -- ^ grammar
        -> Map String CondTreeBuildInfo   -- ^ common stanzas
        -> (BuildInfo -> a)               -- ^ constructor from buildInfo
        -> (a -> [Dependency])            -- ^ condition extractor
        -> [Field Position]
        -> ParseResult (CondTree ConfVar [Dependency] a)
    parseCondTree v hasElif grammar commonStanzas fromBuildInfo cond = go
      where
        go fields0 = do
            (fields, endo) <-
                if v >= CabalSpecV3_0
                then processImports v fromBuildInfo commonStanzas fields0
                else traverse (warnImport v) fields0 >>= \fields1 -> return (catMaybes fields1, id)

            let (fs, ss) = partitionFields fields
            x <- parseFieldGrammar v fs grammar
            branches <- concat <$> traverse parseIfs ss
            return $ endo $ CondNode x (cond x) branches

        parseIfs :: [Section Position] -> ParseResult [CondBranch ConfVar [Dependency] a]
        parseIfs [] = return []
        parseIfs (MkSection (Name _ name) test fields : sections) | name == "if" = do
            test' <- parseConditionConfVar test
            fields' <- go fields
            (elseFields, sections') <- parseElseIfs sections
            return (CondBranch test' fields' elseFields : sections')
        parseIfs (MkSection (Name pos name) _ _ : sections) = do
            parseWarning pos PWTInvalidSubsection $ "invalid subsection " ++ show name
            parseIfs sections

        parseElseIfs
            :: [Section Position]
            -> ParseResult (Maybe (CondTree ConfVar [Dependency] a), [CondBranch ConfVar [Dependency] a])
        parseElseIfs [] = return (Nothing, [])
        parseElseIfs (MkSection (Name pos name) args fields : sections) | name == "else" = do
            unless (null args) $
                parseFailure pos $ "`else` section has section arguments " ++ show args
            elseFields <- go fields
            sections' <- parseIfs sections
            return (Just elseFields, sections')

        parseElseIfs (MkSection (Name _ name) test fields : sections) | hasElif == HasElif, name == "elif" = do
            test' <- parseConditionConfVar test
            fields' <- go fields
            (elseFields, sections') <- parseElseIfs sections
            -- we parse an empty 'Fields', to get empty value for a node
            a <- parseFieldGrammar v mempty grammar
            return (Just $ CondNode a (cond a) [CondBranch test' fields' elseFields], sections')

        parseElseIfs (MkSection (Name pos name) _ _ : sections) | name == "elif" = do
            parseWarning pos PWTInvalidSubsection $ "invalid subsection \"elif\". You should set cabal-version: 2.2 or larger to use elif-conditionals."
            (,) Nothing <$> parseIfs sections

        parseElseIfs sections = (,) Nothing <$> parseIfs sections

    {- Note [Accumulating parser]

    Note: Outdated a bit

    In there parser, @'FieldDescr' a@ is transformed into @Map FieldName (a ->
    FieldParser a)@.  The weird value is used because we accumulate structure of
    @a@ by folding over the fields.  There are various reasons for that:

    * Almost all fields are optional

    * This is simple approach so declarative bi-directional format (parsing and
    printing) of structure could be specified (list of @'FieldDescr' a@)

    * There are surface syntax fields corresponding to single field in the file:
      @license-file@ and @license-files@

    * This is quite safe approach.

    When/if we re-implement the parser to support formatting preservging roundtrip
    with new AST, this all need to be rewritten.
    -}

    -------------------------------------------------------------------------------
    -- Common stanzas
    -------------------------------------------------------------------------------

    -- $commonStanzas
    --
    -- [Note: Common stanzas]
    --
    -- In Cabal 2.2 we support simple common stanzas:
    --
    -- * Commons stanzas define 'BuildInfo'
    --
    -- * import "fields" can only occur at top of other stanzas (think: imports)
    --
    -- In particular __there aren't__
    --
    -- * implicit stanzas
    --
    -- * More specific common stanzas (executable, test-suite).
    --
    --
    -- The approach uses the fact that 'BuildInfo' is a 'Monoid':
    --
    -- @
    -- mergeCommonStanza' :: HasBuildInfo comp => BuildInfo -> comp -> comp
    -- mergeCommonStanza' bi = over L.BuildInfo (bi <>)
    -- @
    --
    -- Real 'mergeCommonStanza' is more complicated as we have to deal with
    -- conditional trees.
    --
    -- The approach is simple, and have good properties:
    --
    -- * Common stanzas are parsed exactly once, even if not-used. Thus we report errors in them.
    --
    type CondTreeBuildInfo = CondTree ConfVar [Dependency] BuildInfo

    -- | Create @a@ from 'BuildInfo'.
    -- This class is used to implement common stanza parsing.
    --
    -- Law: @view buildInfo . fromBuildInfo = id@
    --
    -- This takes name, as 'FieldGrammar's take names too.
    class L.HasBuildInfo a => FromBuildInfo a where
        fromBuildInfo' :: UnqualComponentName -> BuildInfo -> a

    libraryFromBuildInfo :: LibraryName -> BuildInfo -> Library
    libraryFromBuildInfo n bi = emptyLibrary
        { libName       = n
        , libVisibility = case n of
            LMainLibName  -> LibraryVisibilityPublic
            LSubLibName _ -> LibraryVisibilityPrivate
        , libBuildInfo  = bi
        }

    instance FromBuildInfo BuildInfo  where fromBuildInfo' _ = id
    instance FromBuildInfo ForeignLib where fromBuildInfo' n bi = set L.foreignLibName n $ set L.buildInfo bi emptyForeignLib
    instance FromBuildInfo Executable where fromBuildInfo' n bi = set L.exeName        n $ set L.buildInfo bi emptyExecutable

    instance FromBuildInfo TestSuiteStanza where
        fromBuildInfo' _ bi = TestSuiteStanza Nothing Nothing Nothing bi

    instance FromBuildInfo BenchmarkStanza where
        fromBuildInfo' _ bi = BenchmarkStanza Nothing Nothing Nothing bi

    parseCondTreeWithCommonStanzas
        :: forall a. L.HasBuildInfo a
        => CabalSpecVersion
        -> ParsecFieldGrammar' a       -- ^ grammar
        -> (BuildInfo -> a)              -- ^ construct fromBuildInfo
        -> Map String CondTreeBuildInfo  -- ^ common stanzas
        -> [Field Position]
        -> ParseResult (CondTree ConfVar [Dependency] a)
    parseCondTreeWithCommonStanzas v grammar fromBuildInfo commonStanzas fields = do
        (fields', endo) <- processImports v fromBuildInfo commonStanzas fields
        x <- parseCondTree v hasElif grammar commonStanzas fromBuildInfo (view L.targetBuildDepends) fields'
        return (endo x)
      where
        hasElif = specHasElif v

    processImports
        :: forall a. L.HasBuildInfo a
        => CabalSpecVersion
        -> (BuildInfo -> a)              -- ^ construct fromBuildInfo
        -> Map String CondTreeBuildInfo  -- ^ common stanzas
        -> [Field Position]
        -> ParseResult ([Field Position], CondTree ConfVar [Dependency] a -> CondTree ConfVar [Dependency] a)
    processImports v fromBuildInfo commonStanzas = go []
      where
        hasCommonStanzas = specHasCommonStanzas v

        getList' :: List CommaFSep Token String -> [String]
        getList' = Newtype.unpack

        go acc (Field (Name pos name) _ : fields) | name == "import", hasCommonStanzas == NoCommonStanzas = do
            parseWarning pos PWTUnknownField "Unknown field: import. You should set cabal-version: 2.2 or larger to use common stanzas"
            go acc fields
        -- supported:
        go acc (Field (Name pos name) fls : fields) | name == "import" = do
            names <- getList' <$> runFieldParser pos parsec v fls
            names' <- for names $ \commonName ->
                case Map.lookup commonName commonStanzas of
                    Nothing -> do
                        parseFailure pos $ "Undefined common stanza imported: " ++ commonName
                        pure Nothing
                    Just commonTree ->
                        pure (Just commonTree)

            go (acc ++ catMaybes names') fields

        -- parse actual CondTree
        go acc fields = do
            fields' <- catMaybes <$> traverse (warnImport v) fields
            pure $ (fields', \x -> foldr (mergeCommonStanza fromBuildInfo) x acc)

    -- | Warn on "import" fields, also map to Maybe, so errorneous fields can be filtered
    warnImport :: CabalSpecVersion -> Field Position -> ParseResult (Maybe (Field Position))
    warnImport v (Field (Name pos name) _) | name ==  "import" = do
        if specHasCommonStanzas v == NoCommonStanzas
        then parseWarning pos PWTUnknownField "Unknown field: import. You should set cabal-version: 2.2 or larger to use common stanzas"
        else parseWarning pos PWTUnknownField "Unknown field: import. Common stanza imports should be at the top of the enclosing section"
        return Nothing
    warnImport _ f = pure (Just f)

    mergeCommonStanza
        :: L.HasBuildInfo a
        => (BuildInfo -> a)
        -> CondTree ConfVar [Dependency] BuildInfo
        -> CondTree ConfVar [Dependency] a
        -> CondTree ConfVar [Dependency] a
    mergeCommonStanza fromBuildInfo (CondNode bi _ bis) (CondNode x _ cs) =
        CondNode x' (x' ^. L.targetBuildDepends) cs'
      where
        -- new value is old value with buildInfo field _prepended_.
        x' = x & L.buildInfo %~ (bi <>)

        -- tree components are appended together.
        cs' = map (fmap fromBuildInfo) bis ++ cs

    -------------------------------------------------------------------------------
    -- Branches
    -------------------------------------------------------------------------------

    -- Check that a property holds on all branches of a condition tree
    onAllBranches :: forall v c a. Monoid a => (a -> Bool) -> CondTree v c a -> Bool
    onAllBranches p = go mempty
      where
        -- If the current level of the tree satisfies the property, then we are
        -- done. If not, then one of the conditional branches below the current node
        -- must satisfy it. Each node may have multiple immediate children; we only
        -- one need one to satisfy the property because the configure step uses
        -- 'mappend' to join together the results of flag resolution.
        go :: a -> CondTree v c a -> Bool
        go acc ct = let acc' = acc `mappend` condTreeData ct
                    in p acc' || any (goBranch acc') (condTreeComponents ct)

        -- Both the 'true' and the 'false' block must satisfy the property.
        goBranch :: a -> CondBranch v c a -> Bool
        goBranch _   (CondBranch _ _ Nothing) = False
        goBranch acc (CondBranch _ t (Just e))  = go acc t && go acc e

    -------------------------------------------------------------------------------
    -- Post parsing checks
    -------------------------------------------------------------------------------

    -- | Check that we
    --
    -- * don't use undefined flags (very bad)
    -- * define flags which are unused (just bad)
    --
    checkForUndefinedFlags :: GenericPackageDescription -> ParseResult ()
    checkForUndefinedFlags gpd = do
        let definedFlags, usedFlags :: Set.Set FlagName
            definedFlags = toSetOf (L.genPackageFlags . traverse . getting flagName) gpd
            usedFlags    = getConst $ L.allCondTrees f gpd

        -- Note: we can check for defined, but unused flags here too.
        unless (usedFlags `Set.isSubsetOf` definedFlags) $ parseFailure zeroPos $
            "These flags are used without having been defined: " ++
            intercalate ", " [ unFlagName fn | fn <- Set.toList $ usedFlags `Set.difference` definedFlags ]
      where
        f :: CondTree ConfVar c a -> Const (Set.Set FlagName) (CondTree ConfVar c a)
        f ct = Const (Set.fromList (freeVars ct))

    -- | Since @cabal-version: 1.24@ one can specify @custom-setup@.
    -- Let us require it.
    --
    checkForUndefinedCustomSetup :: GenericPackageDescription -> ParseResult ()
    checkForUndefinedCustomSetup gpd = do
        let pd  = packageDescription gpd
        let csv = specVersion pd

        when (buildType pd == Custom && isNothing (setupBuildInfo pd)) $
            when (csv >= CabalSpecV1_24) $ parseFailure zeroPos $
                "Since cabal-version: 1.24 specifying custom-setup section is mandatory"

    -------------------------------------------------------------------------------
    -- Post processing of internal dependencies
    -------------------------------------------------------------------------------

    -- Note [Dependencies on sublibraries]
    -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    --
    -- This is solution to https://github.com/haskell/cabal/issues/6083
    --
    -- Before 'cabal-version: 3.0' we didn't have a syntax specially
    -- for referring to internal libraries. Internal library names
    -- shadowed the outside ones.
    --
    -- Since 'cabal-version: 3.0' we have ability to write
    --
    --     build-depends: some-package:its-sub-lib >=1.2.3
    --
    -- This allows us to refer also to local packages by `this-package:sublib`.
    -- So since 'cabal-version: 3.4' to refer to *any*
    -- sublibrary we must use the two part syntax. Here's small table:
    --
    --                   | pre-3.4             |      3.4 and after            |
    -- ------------------|---------------------|-------------------------------|
    -- pkg-name          | may refer to sublib | always refers to external pkg |
    -- pkg-name:sublib   | refers to sublib    | refers to sublib              |
    -- pkg-name:pkg-name | may refer to sublib | always refers to external pkg |
    --
    -- In pre-3.4 case, if a package 'this-pkg' has a sublibrary 'pkg-name',
    -- all dependency definitions will refer to that sublirary.
    --
    -- In 3.4 and after case, 'pkg-name' will always refer to external package,
    -- and to use internal library you have to say 'this-pkg:pkg-name'.
    --
    -- In summary, In 3.4 and after, the internal names don't shadow,
    -- as there is an explicit syntax to refer to them,
    -- i.e. what you write is what you get;
    -- For pre-3.4 we post-process the file.
    --
    -- Similarly, we process mixins.
    -- See https://github.com/haskell/cabal/issues/6281
    --

    postProcessInternalDeps :: CabalSpecVersion -> GenericPackageDescription -> GenericPackageDescription
    postProcessInternalDeps specVer gpd
        | specVer >= CabalSpecV3_4 = gpd
        | otherwise                = transformAllBuildInfos transformBI transformSBI gpd
      where
        transformBI :: BuildInfo -> BuildInfo
        transformBI
            = over L.targetBuildDepends (concatMap transformD)
            . over L.mixins (map transformM)

        transformSBI :: SetupBuildInfo -> SetupBuildInfo
        transformSBI = over L.setupDepends (concatMap transformD)

        transformD :: Dependency -> [Dependency]
        transformD (Dependency pn vr ln)
            | uqn `Set.member` internalLibs
            , LMainLibName `NES.member` ln
            = case NES.delete LMainLibName ln of
                Nothing  -> [dep]
                Just ln' -> [dep, Dependency pn vr ln']
          where
            uqn = packageNameToUnqualComponentName pn
            dep = Dependency thisPn vr (NES.singleton (LSubLibName uqn))

        transformD d = [d]

        transformM :: Mixin -> Mixin
        transformM (Mixin pn LMainLibName incl)
            | uqn `Set.member` internalLibs
            = mkMixin thisPn (LSubLibName uqn) incl
          where
            uqn = packageNameToUnqualComponentName pn

        transformM m = m

        thisPn :: PackageName
        thisPn = pkgName (package (packageDescription gpd))

        internalLibs :: Set UnqualComponentName
        internalLibs = Set.fromList
            [ n
            | (n, _) <- condSubLibraries gpd
            ]

    -------------------------------------------------------------------------------
    -- Old syntax
    -------------------------------------------------------------------------------

    -- TODO: move to own module

    -- | "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 ann] -> (Syntax, [Field ann])
    sectionizeFields fs = case classifyFields fs of
        Just fields -> (OldSyntax, convert fields)
        Nothing     -> (NewSyntax, fs)
      where
        -- return 'Just' if all fields are simple fields
        classifyFields :: [Field ann] -> Maybe [(Name ann, [FieldLine ann])]
        classifyFields = traverse f
          where
            f (Field name fieldlines) = Just (name, fieldlines)
            f _                      = Nothing

        trim = BS.dropWhile isSpace' . BS.reverse . BS.dropWhile isSpace' . BS.reverse
        isSpace' = (== 32)

        convert :: [(Name ann, [FieldLine ann])] -> [Field ann]
        convert fields =
          let
            toField (name, ls) = Field name ls
            -- "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") . getName . fst) fields
            (hdr, libfs0) = partition (not . (`elem` libFieldNames) . getName . fst) hdr0

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

            exes = unfoldr toExe exes0
            toExe [] = Nothing
            toExe ((Name pos n, ls) : r)
              | n == "executable" =
                  let (efs, r') = break ((== "executable") . getName . fst) r
                  in Just (Section (Name pos "executable") [SecArgName pos $ trim $ fieldlinesToBS ls] (map toField $ deps ++ efs), r')
            toExe _ = error "unexpected input to 'toExe'"

            lib = case libfs of
                []                         -> []
                ((Name pos _,  _) : _) ->
                    [Section (Name pos "library") [] (map toField $ deps ++ libfs)]

          in map toField hdr ++ lib ++ exes

    -- | See 'sectionizeFields'.
    data Syntax = OldSyntax | NewSyntax
        deriving (Eq, Show)

    -- TODO:
    libFieldNames :: [FieldName]
    libFieldNames = fieldGrammarKnownFieldList (libraryFieldGrammar LMainLibName)

    -------------------------------------------------------------------------------
    -- Suplementary build information
    -------------------------------------------------------------------------------

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

    parseHookedBuildInfo :: BS.ByteString -> ParseResult HookedBuildInfo
    parseHookedBuildInfo bs = case readFields' bs of
        Right (fs, lexWarnings) -> do
            parseHookedBuildInfo' lexWarnings fs
        -- TODO: better marshalling of errors
        Left perr -> parseFatalFailure zeroPos (show perr)

    parseHookedBuildInfo'
        :: [LexWarning]
        -> [Field Position]
        -> ParseResult HookedBuildInfo
    parseHookedBuildInfo' lexWarnings fs = do
        parseWarnings (toPWarnings lexWarnings)
        (mLibFields, exes) <- stanzas fs
        mLib <- parseLib mLibFields
        biExes <- traverse parseExe exes
        return (mLib, biExes)
      where
        parseLib :: Fields Position -> ParseResult (Maybe BuildInfo)
        parseLib fields
            | Map.null fields = pure Nothing
            | otherwise       = Just <$> parseFieldGrammar cabalSpecLatest fields buildInfoFieldGrammar

        parseExe :: (UnqualComponentName, Fields Position) -> ParseResult (UnqualComponentName, BuildInfo)
        parseExe (n, fields) = do
            bi <- parseFieldGrammar cabalSpecLatest fields buildInfoFieldGrammar
            pure (n, bi)

        stanzas :: [Field Position] -> ParseResult (Fields Position, [(UnqualComponentName, Fields Position)])
        stanzas fields = do
            let (hdr0, exes0) = breakMaybe isExecutableField fields
            hdr <- toFields hdr0
            exes <- unfoldrM (traverse toExe) exes0
            pure (hdr, exes)

        toFields :: [Field Position] -> ParseResult (Fields Position)
        toFields fields = do
            let (fields', ss) = partitionFields fields
            traverse_ (traverse_ warnInvalidSubsection) ss
            pure fields'

        toExe
            :: ([FieldLine Position], [Field Position])
            -> ParseResult ((UnqualComponentName, Fields Position), Maybe ([FieldLine Position], [Field Position]))
        toExe (fss, fields) = do
            name <- runFieldParser zeroPos parsec cabalSpecLatest fss
            let (hdr0, rest) = breakMaybe isExecutableField fields
            hdr <- toFields hdr0
            pure ((name, hdr), rest)

        isExecutableField (Field (Name _ name) fss)
            | name == "executable" = Just fss
            | otherwise            = Nothing
        isExecutableField _ = Nothing

    -------------------------------------------------------------------------------
    -- Scan of spec version
    -------------------------------------------------------------------------------

    -- | Quickly scan new-style spec-version
    --
    -- A new-style spec-version declaration begins the .cabal file and
    -- follow the following case-insensitive grammar (expressed in
    -- RFC5234 ABNF):
    --
    -- @
    -- newstyle-spec-version-decl = "cabal-version" *WS ":" *WS newstyle-pec-version *WS
    --
    -- spec-version               = NUM "." NUM [ "." NUM ]
    --
    -- NUM    = DIGIT0 / DIGITP 1*DIGIT0
    -- DIGIT0 = %x30-39
    -- DIGITP = %x31-39
    -- WS = %20
    -- @
    --
    scanSpecVersion :: BS.ByteString -> Maybe Version
    scanSpecVersion bs = do
        fstline':_ <- pure (BS8.lines bs)

        -- parse <newstyle-spec-version-decl>
        -- normalise: remove all whitespace, convert to lower-case
        let fstline = BS.map toLowerW8 $ BS.filter (/= 0x20) fstline'
        ["cabal-version",vers] <- pure (BS8.split ':' fstline)

        -- parse <spec-version>
        --
        -- This is currently more tolerant regarding leading 0 digits.
        --
        ver <- simpleParsecBS vers
        guard $ case versionNumbers ver of
                  [_,_]   -> True
                  [_,_,_] -> True
                  _       -> False

        pure ver
      where
        -- | Translate ['A'..'Z'] to ['a'..'z']
        toLowerW8 :: Word8 -> Word8
        toLowerW8 w | 0x40 < w && w < 0x5b = w+0x20
                    | otherwise            = w