GHC/Settings/Utils.hs

    module GHC.Settings.Utils where

    import Prelude -- See Note [Why do we import Prelude here?]

    import Data.Char (isSpace)
    import Data.Map (Map)
    import qualified Data.Map as Map

    import GHC.BaseDir
    import GHC.Platform.ArchOS

    maybeRead :: Read a => String -> Maybe a
    maybeRead str = case reads str of
      [(x, "")] -> Just x
      _ -> Nothing

    maybeReadFuzzy :: Read a => String -> Maybe a
    maybeReadFuzzy str = case reads str of
      [(x, s)] | all isSpace s -> Just x
      _ -> Nothing

    -- Note [Settings file]
    -- ~~~~~~~~~~~~~~~~~~~~
    --
    -- GHC has a file, `${top_dir}/settings`, which is the main source of run-time
    -- configuration. ghc-pkg needs just a little bit of it: the target platform CPU
    -- arch and OS. It uses that to figure out what subdirectory of `~/.ghc` is
    -- associated with the current version/target platform.
    --
    -- This module has just enough code to read key value pairs from the settings
    -- file, and read the target platform from those pairs.

    type RawSettings = Map String String

    -- | Read target Arch/OS from the settings
    getTargetArchOS
      :: FilePath     -- ^ Settings filepath (for error messages)
      -> RawSettings  -- ^ Raw settings file contents
      -> Either String ArchOS
    getTargetArchOS settingsFile settings =
      ArchOS <$> readRawSetting settingsFile settings "target arch"
             <*> readRawSetting settingsFile settings "target os"

    getRawSetting
      :: FilePath -> RawSettings -> String -> Either String String
    getRawSetting settingsFile settings key = case Map.lookup key settings of
      Just xs -> Right xs
      Nothing -> Left $ "No entry for " ++ show key ++ " in " ++ show settingsFile

    getRawFilePathSetting
      :: FilePath -> FilePath -> RawSettings -> String -> Either String String
    getRawFilePathSetting top_dir settingsFile settings key =
      expandTopDir top_dir <$> getRawSetting settingsFile settings key

    getRawBooleanSetting
      :: FilePath -> RawSettings -> String -> Either String Bool
    getRawBooleanSetting settingsFile settings key = do
      rawValue <- getRawSetting settingsFile settings key
      case rawValue of
        "YES" -> Right True
        "NO" -> Right False
        xs -> Left $ "Bad value for " ++ show key ++ ": " ++ show xs

    readRawSetting
      :: (Show a, Read a) => FilePath -> RawSettings -> String -> Either String a
    readRawSetting settingsFile settings key = case Map.lookup key settings of
      Just xs -> case maybeRead xs of
        Just v -> Right v
        Nothing -> Left $ "Failed to read " ++ show key ++ " value " ++ show xs
      Nothing -> Left $ "No entry for " ++ show key ++ " in " ++ show settingsFile