GHC/SysTools/BaseDir.hs

    {-# LANGUAGE CPP #-}
    {-# LANGUAGE ScopedTypeVariables #-}

    {-
    -----------------------------------------------------------------------------
    --
    -- (c) The University of Glasgow 2001-2017
    --
    -- Finding the compiler's base directory.
    --
    -----------------------------------------------------------------------------
    -}

    module GHC.SysTools.BaseDir
      ( expandTopDir, expandToolDir
      , findTopDir, findToolDir
      , tryFindTopDir
      ) where

    #include "HsVersions.h"

    import GHC.Prelude

    -- See note [Base Dir] for why some of this logic is shared with ghc-pkg.
    import GHC.BaseDir

    import GHC.Utils.Panic

    import System.Environment (lookupEnv)
    import System.FilePath

    -- Windows
    #if defined(mingw32_HOST_OS)
    import System.Directory (doesDirectoryExist)
    #endif

    #if defined(mingw32_HOST_OS)
    # if defined(i386_HOST_ARCH)
    #  define WINDOWS_CCONV stdcall
    # elif defined(x86_64_HOST_ARCH)
    #  define WINDOWS_CCONV ccall
    # else
    #  error Unknown mingw32 arch
    # endif
    #endif

    {-
    Note [topdir: How GHC finds its files]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    GHC needs various support files (library packages, RTS etc), plus
    various auxiliary programs (cp, gcc, etc).  It starts by finding topdir,
    the root of GHC's support files

    On Unix:
      - ghc always has a shell wrapper that passes a -B<dir> option

    On Windows:
      - ghc never has a shell wrapper.
      - we can find the location of the ghc binary, which is
            $topdir/<foo>/<something>.exe
        where <something> may be "ghc", "ghc-stage2", or similar
      - we strip off the "<foo>/<something>.exe" to leave $topdir.

    from topdir we can find package.conf, ghc-asm, etc.

    Note [tooldir: How GHC finds mingw on Windows]

    GHC has some custom logic on Windows for finding the mingw
    toolchain and perl. Depending on whether GHC is built
    with the make build system or Hadrian, and on whether we're
    running a bindist, we might find the mingw toolchain and perl
    either under $topdir/../{mingw, perl}/ or
    $topdir/../../{mingw, perl}/.

    -}

    -- | Expand occurrences of the @$tooldir@ interpolation in a string
    -- on Windows, leave the string untouched otherwise.
    expandToolDir :: Maybe FilePath -> String -> String
    #if defined(mingw32_HOST_OS)
    expandToolDir (Just tool_dir) s = expandPathVar "tooldir" tool_dir s
    expandToolDir Nothing         _ = panic "Could not determine $tooldir"
    #else
    expandToolDir _ s = s
    #endif

    -- | Returns a Unix-format path pointing to TopDir.
    findTopDir :: Maybe String -- Maybe TopDir path (without the '-B' prefix).
               -> IO String    -- TopDir (in Unix format '/' separated)
    findTopDir m_minusb = do
      maybe_exec_dir <- tryFindTopDir m_minusb
      case maybe_exec_dir of
          -- "Just" on Windows, "Nothing" on unix
          Nothing -> throwGhcExceptionIO $
              InstallationError "missing -B<dir> option"
          Just dir -> return dir

    tryFindTopDir
      :: Maybe String -- ^ Maybe TopDir path (without the '-B' prefix).
      -> IO (Maybe String) -- ^ TopDir (in Unix format '/' separated)
    tryFindTopDir (Just minusb) = return $ Just $ normalise minusb
    tryFindTopDir Nothing
        = do -- The _GHC_TOP_DIR environment variable can be used to specify
             -- the top dir when the -B argument is not specified. It is not
             -- intended for use by users, it was added specifically for the
             -- purpose of running GHC within GHCi.
             maybe_env_top_dir <- lookupEnv "_GHC_TOP_DIR"
             case maybe_env_top_dir of
                 Just env_top_dir -> return $ Just env_top_dir
                 -- Try directory of executable
                 Nothing -> getBaseDir

    -- See Note [tooldir: How GHC finds mingw and perl on Windows]
    -- Returns @Nothing@ when not on Windows.
    -- When called on Windows, it either throws an error when the
    -- tooldir can't be located, or returns @Just tooldirpath@.
    findToolDir
      :: FilePath -- ^ topdir
      -> IO (Maybe FilePath)
    #if defined(mingw32_HOST_OS)
    findToolDir top_dir = go 0 (top_dir </> "..")
      where maxDepth = 3
            go :: Int -> FilePath -> IO (Maybe FilePath)
            go k path
              | k == maxDepth = throwGhcExceptionIO $
                  InstallationError "could not detect mingw toolchain"
              | otherwise = do
                  oneLevel <- doesDirectoryExist (path </> "mingw")
                  if oneLevel
                    then return (Just path)
                    else go (k+1) (path </> "..")
    #else
    findToolDir _ = return Nothing
    #endif