    {-# LANGUAGE CPP #-}
    module Distribution.Compat.Process (
        -- * Redefined functions
        proc,
        -- * Additions
        enableProcessJobs,
        ) where

    import           System.Process (CreateProcess)
    import qualified System.Process as Process

    #if defined(mingw32_HOST_OS) && MIN_VERSION_process(1,6,9)
    import           System.IO.Unsafe (unsafePerformIO)
    import           System.Win32.Info.Version (dwMajorVersion, dwMinorVersion, getVersionEx)
    #endif

    -------------------------------------------------------------------------------
    -- enableProcessJobs
    -------------------------------------------------------------------------------

    #if defined(mingw32_HOST_OS) && MIN_VERSION_process(1,6,9)
    -- This exception, needed to support Windows 7, could be removed when
    -- the lowest GHC version cabal supports is a GHC that doesn’t support
    -- Windows 7 any more.
    {-# NOINLINE isWindows8OrLater #-}
    isWindows8OrLater :: Bool
    isWindows8OrLater = unsafePerformIO $ do
      v <- getVersionEx
      pure $ (dwMajorVersion v, dwMinorVersion v) >= (6, 2)
    #endif

    -- | Enable process jobs to ensure accurate determination of process completion
    -- in the presence of @exec(3)@ on Windows.
    --
    -- Unfortunately the process job support is badly broken in @process@ releases
    -- prior to 1.6.9, so we disable it in these versions, despite the fact that
    -- this means we may see sporadic build failures without jobs.
    --
    -- On Windows 7 or before the jobs are disabled due to the fact that
    -- processes on these systems can only have one job. This prevents
    -- spawned process from assigning jobs to its own children. Suppose
    -- process A spawns process B. The B process has a job assigned (call
    -- it J1) and when it tries to spawn a new process C the C
    -- automatically inherits the job. But at it also tries to assign a
    -- new job J2 to C since it doesn’t have access J1. This fails on
    -- Windows 7 or before.
    enableProcessJobs :: CreateProcess -> CreateProcess
    #if defined(mingw32_HOST_OS) && MIN_VERSION_process(1,6,9)
    enableProcessJobs cp = cp {Process.use_process_jobs = isWindows8OrLater}
    #else
    enableProcessJobs :: CreateProcess -> CreateProcess
    enableProcessJobs CreateProcess
    cp = CreateProcess
    cp
    #endif

    -------------------------------------------------------------------------------
    -- process redefinitions
    -------------------------------------------------------------------------------

    -- | 'System.Process.proc' with process jobs enabled when appropriate,
    -- and defaulting 'delegate_ctlc' to 'True'.
    proc :: FilePath -> [String] -> CreateProcess
    proc :: FilePath -> [FilePath] -> CreateProcess
    proc FilePath
    path [FilePath]
    args = CreateProcess -> CreateProcess
    enableProcessJobs (FilePath -> [FilePath] -> CreateProcess
    Process.proc FilePath
    path [FilePath]
    args) { delegate_ctlc :: Bool
    Process.delegate_ctlc = Bool
    True }