DriverPipeline.hs 102 KB
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{-# LANGUAGE CPP, NamedFieldPuns, NondecreasingIndentation #-}
{-# OPTIONS_GHC -fno-cse #-}
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-- -fno-cse is needed for GLOBAL_VAR's to behave properly

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-----------------------------------------------------------------------------
--
-- GHC Driver
--
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-- (c) The University of Glasgow 2005
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--
-----------------------------------------------------------------------------

module DriverPipeline (
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        -- Run a series of compilation steps in a pipeline, for a
        -- collection of source files.
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   oneShot, compileFile,
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        -- Interfaces for the batch-mode driver
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   linkBinary,
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        -- Interfaces for the compilation manager (interpreted/batch-mode)
   preprocess,
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   compileOne, compileOne',
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   link,
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        -- Exports for hooks to override runPhase and link
   PhasePlus(..), CompPipeline(..), PipeEnv(..), PipeState(..),
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   phaseOutputFilename, getOutputFilename, getPipeState, getPipeEnv,
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   hscPostBackendPhase, getLocation, setModLocation, setDynFlags,
   runPhase, exeFileName,
   mkExtraObjToLinkIntoBinary, mkNoteObjsToLinkIntoBinary,
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   maybeCreateManifest,
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   linkingNeeded, checkLinkInfo, writeInterfaceOnlyMode
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  ) where

#include "HsVersions.h"

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import PipelineMonad
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import Packages
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import HeaderInfo
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import DriverPhases
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import SysTools
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import Elf
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import HscMain
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import Finder
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import HscTypes hiding ( Hsc )
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import Outputable
import Module
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import ErrUtils
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import DynFlags
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import Config
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import Panic
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import Util
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import StringBuffer     ( hGetStringBuffer )
import BasicTypes       ( SuccessFlag(..) )
import Maybes           ( expectJust )
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import SrcLoc
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import LlvmCodeGen      ( llvmFixupAsm )
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import MonadUtils
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import Platform
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import TcRnTypes
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import Hooks
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import qualified GHC.LanguageExtensions as LangExt
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import Exception
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import System.Directory
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import System.FilePath
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import System.IO
import Control.Monad
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import Data.List        ( isSuffixOf )
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import Data.Maybe
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import Data.Version
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-- ---------------------------------------------------------------------------
-- Pre-process
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-- | Just preprocess a file, put the result in a temp. file (used by the
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-- compilation manager during the summary phase).
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--
-- We return the augmented DynFlags, because they contain the result
-- of slurping in the OPTIONS pragmas
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preprocess :: HscEnv
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           -> (FilePath, Maybe Phase) -- ^ filename and starting phase
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           -> IO (DynFlags, FilePath)
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preprocess hsc_env (filename, mb_phase) =
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  ASSERT2(isJust mb_phase || isHaskellSrcFilename filename, text filename)
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  runPipeline anyHsc hsc_env (filename, fmap RealPhase mb_phase)
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        Nothing Temporary Nothing{-no ModLocation-} []{-no foreign objects-}
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-- ---------------------------------------------------------------------------
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-- | Compile
--
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-- Compile a single module, under the control of the compilation manager.
--
-- This is the interface between the compilation manager and the
-- compiler proper (hsc), where we deal with tedious details like
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-- reading the OPTIONS pragma from the source file, converting the
-- C or assembly that GHC produces into an object file, and compiling
-- FFI stub files.
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--
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-- NB.  No old interface can also mean that the source has changed.

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compileOne :: HscEnv
           -> ModSummary      -- ^ summary for module being compiled
           -> Int             -- ^ module N ...
           -> Int             -- ^ ... of M
           -> Maybe ModIface  -- ^ old interface, if we have one
           -> Maybe Linkable  -- ^ old linkable, if we have one
           -> SourceModified
           -> IO HomeModInfo   -- ^ the complete HomeModInfo, if successful

compileOne = compileOne' Nothing (Just batchMsg)

compileOne' :: Maybe TcGblEnv
            -> Maybe Messager
            -> HscEnv
            -> ModSummary      -- ^ summary for module being compiled
            -> Int             -- ^ module N ...
            -> Int             -- ^ ... of M
            -> Maybe ModIface  -- ^ old interface, if we have one
            -> Maybe Linkable  -- ^ old linkable, if we have one
            -> SourceModified
            -> IO HomeModInfo   -- ^ the complete HomeModInfo, if successful

compileOne' m_tc_result mHscMessage
            hsc_env0 summary mod_index nmods mb_old_iface maybe_old_linkable
            source_modified0
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 = do
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   debugTraceMsg dflags1 2 (text "compile: input file" <+> text input_fnpp)
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   (status, hmi0) <- hscIncrementalCompile
                        always_do_basic_recompilation_check
                        m_tc_result mHscMessage
                        hsc_env summary source_modified mb_old_iface (mod_index, nmods)

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   let flags = hsc_dflags hsc_env0
     in do unless (gopt Opt_KeepHiFiles flags) $
               addFilesToClean flags [ml_hi_file $ ms_location summary]
           unless (gopt Opt_KeepOFiles flags) $
               addFilesToClean flags [ml_obj_file $ ms_location summary]

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   case (status, hsc_lang) of
        (HscUpToDate, _) ->
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            -- TODO recomp014 triggers this assert. What's going on?!
            -- ASSERT( isJust maybe_old_linkable || isNoLink (ghcLink dflags) )
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            return hmi0 { hm_linkable = maybe_old_linkable }
        (HscNotGeneratingCode, HscNothing) ->
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            let mb_linkable = if isHsBootOrSig src_flavour
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                                then Nothing
                                -- TODO: Questionable.
                                else Just (LM (ms_hs_date summary) this_mod [])
            in return hmi0 { hm_linkable = mb_linkable }
        (HscNotGeneratingCode, _) -> panic "compileOne HscNotGeneratingCode"
        (_, HscNothing) -> panic "compileOne HscNothing"
        (HscUpdateBoot, HscInterpreted) -> do
            return hmi0
        (HscUpdateBoot, _) -> do
            touchObjectFile dflags object_filename
            return hmi0
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        (HscUpdateSig, HscInterpreted) ->
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            let linkable = LM (ms_hs_date summary) this_mod []
            in return hmi0 { hm_linkable = Just linkable }
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        (HscUpdateSig, _) -> do
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            output_fn <- getOutputFilename next_phase
                            Temporary basename dflags next_phase (Just location)

            -- #10660: Use the pipeline instead of calling
            -- compileEmptyStub directly, so -dynamic-too gets
            -- handled properly
            _ <- runPipeline StopLn hsc_env
                              (output_fn,
                               Just (HscOut src_flavour
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                                            mod_name HscUpdateSig))
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                              (Just basename)
                              Persistent
                              (Just location)
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                              []
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            o_time <- getModificationUTCTime object_filename
            let linkable = LM o_time this_mod [DotO object_filename]
            return hmi0 { hm_linkable = Just linkable }
        (HscRecomp cgguts summary, HscInterpreted) -> do
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            (hasStub, comp_bc, spt_entries) <-
                hscInteractive hsc_env cgguts summary
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            stub_o <- case hasStub of
                      Nothing -> return []
                      Just stub_c -> do
                          stub_o <- compileStub hsc_env stub_c
                          return [DotO stub_o]

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            let hs_unlinked = [BCOs comp_bc spt_entries]
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                unlinked_time = ms_hs_date summary
              -- Why do we use the timestamp of the source file here,
              -- rather than the current time?  This works better in
              -- the case where the local clock is out of sync
              -- with the filesystem's clock.  It's just as accurate:
              -- if the source is modified, then the linkable will
              -- be out of date.
            let linkable = LM unlinked_time (ms_mod summary)
                           (hs_unlinked ++ stub_o)
            return hmi0 { hm_linkable = Just linkable }
        (HscRecomp cgguts summary, _) -> do
            output_fn <- getOutputFilename next_phase
                            Temporary basename dflags next_phase (Just location)
            -- We're in --make mode: finish the compilation pipeline.
            _ <- runPipeline StopLn hsc_env
                              (output_fn,
                               Just (HscOut src_flavour mod_name (HscRecomp cgguts summary)))
                              (Just basename)
                              Persistent
                              (Just location)
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                              []
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                  -- The object filename comes from the ModLocation
            o_time <- getModificationUTCTime object_filename
            let linkable = LM o_time this_mod [DotO object_filename]
            return hmi0 { hm_linkable = Just linkable }

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 where dflags0     = ms_hspp_opts summary
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       this_mod    = ms_mod summary
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       location    = ms_location summary
       input_fn    = expectJust "compile:hs" (ml_hs_file location)
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       input_fnpp  = ms_hspp_file summary
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       mod_graph   = hsc_mod_graph hsc_env0
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       needsTH     = any (xopt LangExt.TemplateHaskell . ms_hspp_opts) mod_graph
       needsQQ     = any (xopt LangExt.QuasiQuotes     . ms_hspp_opts) mod_graph
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       needsLinker = needsTH || needsQQ
       isDynWay    = any (== WayDyn) (ways dflags0)
       isProfWay   = any (== WayProf) (ways dflags0)
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       internalInterpreter = not (gopt Opt_ExternalInterpreter dflags0)
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       src_flavour = ms_hsc_src summary
       mod_name = ms_mod_name summary
       next_phase = hscPostBackendPhase dflags src_flavour hsc_lang
       object_filename = ml_obj_file location

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       -- #8180 - when using TemplateHaskell, switch on -dynamic-too so
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       -- the linker can correctly load the object files.  This isn't necessary
       -- when using -fexternal-interpreter.
       dflags1 = if needsLinker && dynamicGhc && internalInterpreter &&
                    not isDynWay && not isProfWay
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                  then gopt_set dflags0 Opt_BuildDynamicToo
                  else dflags0

       basename = dropExtension input_fn

       -- We add the directory in which the .hs files resides) to the import
       -- path.  This is needed when we try to compile the .hc file later, if it
       -- imports a _stub.h file that we created here.
       current_dir = takeDirectory basename
       old_paths   = includePaths dflags1
       dflags      = dflags1 { includePaths = current_dir : old_paths }
       hsc_env     = hsc_env0 {hsc_dflags = dflags}

       -- Figure out what lang we're generating
       hsc_lang = hscTarget dflags

       -- -fforce-recomp should also work with --make
       force_recomp = gopt Opt_ForceRecomp dflags
       source_modified
         | force_recomp = SourceModified
         | otherwise = source_modified0

       always_do_basic_recompilation_check = case hsc_lang of
                                             HscInterpreted -> True
                                             _ -> False
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-----------------------------------------------------------------------------
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-- stub .h and .c files (for foreign export support), and cc files.
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-- The _stub.c file is derived from the haskell source file, possibly taking
-- into account the -stubdir option.
--
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-- The object file created by compiling the _stub.c file is put into a
-- temporary file, which will be later combined with the main .o file
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-- (see the MergeForeigns phase).
--
-- Moreover, we also let the user emit arbitrary C/C++/ObjC/ObjC++ files
-- from TH, that are then compiled and linked to the module. This is
-- useful to implement facilities such as inline-c.

compileForeign :: HscEnv -> ForeignSrcLang -> FilePath -> IO FilePath
compileForeign hsc_env lang stub_c = do
        let phase = case lang of
              LangC -> Cc
              LangCxx -> Ccxx
              LangObjc -> Cobjc
              LangObjcxx -> Cobjcxx
        (_, stub_o) <- runPipeline StopLn hsc_env
                       (stub_c, Just (RealPhase phase))
                       Nothing Temporary Nothing{-no ModLocation-} []
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        return stub_o
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compileStub :: HscEnv -> FilePath -> IO FilePath
compileStub hsc_env stub_c = compileForeign hsc_env LangC stub_c

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compileEmptyStub :: DynFlags -> HscEnv -> FilePath -> ModLocation -> ModuleName -> IO ()
compileEmptyStub dflags hsc_env basename location mod_name = do
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  -- To maintain the invariant that every Haskell file
  -- compiles to object code, we make an empty (but
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  -- valid) stub object file for signatures.  However,
  -- we make sure this object file has a unique symbol,
  -- so that ranlib on OS X doesn't complain, see
  -- http://ghc.haskell.org/trac/ghc/ticket/12673
  -- and https://github.com/haskell/cabal/issues/2257
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  empty_stub <- newTempName dflags "c"
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  let src = text "int" <+> ppr (mkModule (thisPackage dflags) mod_name) <+> text "= 0;"
  writeFile empty_stub (showSDoc dflags (pprCode CStyle src))
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  _ <- runPipeline StopLn hsc_env
                  (empty_stub, Nothing)
                  (Just basename)
                  Persistent
                  (Just location)
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                  []
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  return ()

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-- ---------------------------------------------------------------------------
-- Link
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link :: GhcLink                 -- interactive or batch
     -> DynFlags                -- dynamic flags
     -> Bool                    -- attempt linking in batch mode?
     -> HomePackageTable        -- what to link
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     -> IO SuccessFlag

-- For the moment, in the batch linker, we don't bother to tell doLink
-- which packages to link -- it just tries all that are available.
-- batch_attempt_linking should only be *looked at* in batch mode.  It
-- should only be True if the upsweep was successful and someone
-- exports main, i.e., we have good reason to believe that linking
-- will succeed.

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link ghcLink dflags
  = lookupHook linkHook l dflags ghcLink dflags
  where
    l LinkInMemory _ _ _
      = if cGhcWithInterpreter == "YES"
        then -- Not Linking...(demand linker will do the job)
             return Succeeded
        else panicBadLink LinkInMemory
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    l NoLink _ _ _
      = return Succeeded
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    l LinkBinary dflags batch_attempt_linking hpt
      = link' dflags batch_attempt_linking hpt
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    l LinkStaticLib dflags batch_attempt_linking hpt
      = link' dflags batch_attempt_linking hpt
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    l LinkDynLib dflags batch_attempt_linking hpt
      = link' dflags batch_attempt_linking hpt
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panicBadLink :: GhcLink -> a
panicBadLink other = panic ("link: GHC not built to link this way: " ++
                            show other)

link' :: DynFlags                -- dynamic flags
      -> Bool                    -- attempt linking in batch mode?
      -> HomePackageTable        -- what to link
      -> IO SuccessFlag

link' dflags batch_attempt_linking hpt
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   | batch_attempt_linking
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   = do
        let
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            staticLink = case ghcLink dflags of
                          LinkStaticLib -> True
                          _ -> platformBinariesAreStaticLibs (targetPlatform dflags)

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            home_mod_infos = eltsHpt hpt
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            -- the packages we depend on
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            pkg_deps  = concatMap (map fst . dep_pkgs . mi_deps . hm_iface) home_mod_infos
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            -- the linkables to link
            linkables = map (expectJust "link".hm_linkable) home_mod_infos
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        debugTraceMsg dflags 3 (text "link: linkables are ..." $$ vcat (map ppr linkables))
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        -- check for the -no-link flag
        if isNoLink (ghcLink dflags)
          then do debugTraceMsg dflags 3 (text "link(batch): linking omitted (-c flag given).")
                  return Succeeded
          else do
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        let getOfiles (LM _ _ us) = map nameOfObject (filter isObject us)
            obj_files = concatMap getOfiles linkables
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            exe_file = exeFileName staticLink dflags
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        linking_needed <- linkingNeeded dflags staticLink linkables pkg_deps
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        if not (gopt Opt_ForceRecomp dflags) && not linking_needed
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           then do debugTraceMsg dflags 2 (text exe_file <+> text "is up to date, linking not required.")
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                   return Succeeded
           else do
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        compilationProgressMsg dflags ("Linking " ++ exe_file ++ " ...")
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        -- Don't showPass in Batch mode; doLink will do that for us.
        let link = case ghcLink dflags of
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                LinkBinary    -> linkBinary
                LinkStaticLib -> linkStaticLibCheck
                LinkDynLib    -> linkDynLibCheck
                other         -> panicBadLink other
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        link dflags obj_files pkg_deps
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        debugTraceMsg dflags 3 (text "link: done")
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        -- linkBinary only returns if it succeeds
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        return Succeeded

   | otherwise
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   = do debugTraceMsg dflags 3 (text "link(batch): upsweep (partially) failed OR" $$
                                text "   Main.main not exported; not linking.")
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        return Succeeded
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linkingNeeded :: DynFlags -> Bool -> [Linkable] -> [InstalledUnitId] -> IO Bool
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linkingNeeded dflags staticLink linkables pkg_deps = do
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        -- if the modification time on the executable is later than the
        -- modification times on all of the objects and libraries, then omit
        -- linking (unless the -fforce-recomp flag was given).
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  let exe_file = exeFileName staticLink dflags
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  e_exe_time <- tryIO $ getModificationUTCTime exe_file
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  case e_exe_time of
    Left _  -> return True
    Right t -> do
        -- first check object files and extra_ld_inputs
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        let extra_ld_inputs = [ f | FileOption _ f <- ldInputs dflags ]
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        e_extra_times <- mapM (tryIO . getModificationUTCTime) extra_ld_inputs
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        let (errs,extra_times) = splitEithers e_extra_times
        let obj_times =  map linkableTime linkables ++ extra_times
        if not (null errs) || any (t <) obj_times
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            then return True
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            else do

        -- next, check libraries. XXX this only checks Haskell libraries,
        -- not extra_libraries or -l things from the command line.
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        let pkg_hslibs  = [ (collectLibraryPaths dflags [c], lib)
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                          | Just c <- map (lookupInstalledPackage dflags) pkg_deps,
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                            lib <- packageHsLibs dflags c ]

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        pkg_libfiles <- mapM (uncurry (findHSLib dflags)) pkg_hslibs
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        if any isNothing pkg_libfiles then return True else do
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        e_lib_times <- mapM (tryIO . getModificationUTCTime)
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                          (catMaybes pkg_libfiles)
        let (lib_errs,lib_times) = splitEithers e_lib_times
        if not (null lib_errs) || any (t <) lib_times
           then return True
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           else checkLinkInfo dflags pkg_deps exe_file

-- Returns 'False' if it was, and we can avoid linking, because the
-- previous binary was linked with "the same options".
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checkLinkInfo :: DynFlags -> [InstalledUnitId] -> FilePath -> IO Bool
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checkLinkInfo dflags pkg_deps exe_file
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 | not (platformSupportsSavingLinkOpts (platformOS (targetPlatform dflags)))
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 -- ToDo: Windows and OS X do not use the ELF binary format, so
 -- readelf does not work there.  We need to find another way to do
 -- this.
 = return False -- conservatively we should return True, but not
                -- linking in this case was the behaviour for a long
                -- time so we leave it as-is.
 | otherwise
 = do
   link_info <- getLinkInfo dflags pkg_deps
   debugTraceMsg dflags 3 $ text ("Link info: " ++ link_info)
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   m_exe_link_info <- readElfNoteAsString dflags exe_file
                          ghcLinkInfoSectionName ghcLinkInfoNoteName
   let sameLinkInfo = (Just link_info == m_exe_link_info)
   debugTraceMsg dflags 3 $ case m_exe_link_info of
     Nothing -> text "Exe link info: Not found"
     Just s
       | sameLinkInfo -> text ("Exe link info is the same")
       | otherwise    -> text ("Exe link info is different: " ++ s)
   return (not sameLinkInfo)
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platformSupportsSavingLinkOpts :: OS -> Bool
platformSupportsSavingLinkOpts os
  | os == OSSolaris2 = False -- see #5382
  | otherwise        = osElfTarget os

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-- See Note [LinkInfo section]
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ghcLinkInfoSectionName :: String
ghcLinkInfoSectionName = ".debug-ghc-link-info"
   -- if we use the ".debug" prefix, then strip will strip it by default
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-- Identifier for the note (see Note [LinkInfo section])
ghcLinkInfoNoteName :: String
ghcLinkInfoNoteName = "GHC link info"

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findHSLib :: DynFlags -> [String] -> String -> IO (Maybe FilePath)
findHSLib dflags dirs lib = do
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  let batch_lib_file = if WayDyn `notElem` ways dflags
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                       then "lib" ++ lib <.> "a"
                       else mkSOName (targetPlatform dflags) lib
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  found <- filterM doesFileExist (map (</> batch_lib_file) dirs)
  case found of
    [] -> return Nothing
    (x:_) -> return (Just x)

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-- -----------------------------------------------------------------------------
-- Compile files in one-shot mode.

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oneShot :: HscEnv -> Phase -> [(String, Maybe Phase)] -> IO ()
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oneShot hsc_env stop_phase srcs = do
  o_files <- mapM (compileFile hsc_env stop_phase) srcs
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  doLink (hsc_dflags hsc_env) stop_phase o_files
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compileFile :: HscEnv -> Phase -> (FilePath, Maybe Phase) -> IO FilePath
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compileFile hsc_env stop_phase (src, mb_phase) = do
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   exists <- doesFileExist src
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   when (not exists) $
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        throwGhcExceptionIO (CmdLineError ("does not exist: " ++ src))
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   let
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        dflags    = hsc_dflags hsc_env
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        split     = gopt Opt_SplitObjs dflags
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        mb_o_file = outputFile dflags
        ghc_link  = ghcLink dflags      -- Set by -c or -no-link
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        -- When linking, the -o argument refers to the linker's output.
        -- otherwise, we use it as the name for the pipeline's output.
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        output
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         -- If we are dong -fno-code, then act as if the output is
         -- 'Temporary'. This stops GHC trying to copy files to their
         -- final location.
         | HscNothing <- hscTarget dflags = Temporary
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         | StopLn <- stop_phase, not (isNoLink ghc_link) = Persistent
                -- -o foo applies to linker
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         | isJust mb_o_file = SpecificFile
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                -- -o foo applies to the file we are compiling now
         | otherwise = Persistent

        stop_phase' = case stop_phase of
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                        As _ | split -> SplitAs
                        _            -> stop_phase
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   ( _, out_file) <- runPipeline stop_phase' hsc_env
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                            (src, fmap RealPhase mb_phase) Nothing output
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                            Nothing{-no ModLocation-} []
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   return out_file


doLink :: DynFlags -> Phase -> [FilePath] -> IO ()
doLink dflags stop_phase o_files
  | not (isStopLn stop_phase)
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  = return ()           -- We stopped before the linking phase
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  | otherwise
  = case ghcLink dflags of
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        NoLink        -> return ()
        LinkBinary    -> linkBinary         dflags o_files []
        LinkStaticLib -> linkStaticLibCheck dflags o_files []
        LinkDynLib    -> linkDynLibCheck    dflags o_files []
        other         -> panicBadLink other
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-- ---------------------------------------------------------------------------
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-- | Run a compilation pipeline, consisting of multiple phases.
--
-- This is the interface to the compilation pipeline, which runs
-- a series of compilation steps on a single source file, specifying
-- at which stage to stop.
--
-- The DynFlags can be modified by phases in the pipeline (eg. by
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-- OPTIONS_GHC pragmas), and the changes affect later phases in the
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-- pipeline.
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runPipeline
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  :: Phase                      -- ^ When to stop
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  -> HscEnv                     -- ^ Compilation environment
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  -> (FilePath,Maybe PhasePlus) -- ^ Input filename (and maybe -x suffix)
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  -> Maybe FilePath             -- ^ original basename (if different from ^^^)
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  -> PipelineOutput             -- ^ Output filename
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  -> Maybe ModLocation          -- ^ A ModLocation, if this is a Haskell module
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  -> [FilePath]                 -- ^ foreign objects
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  -> IO (DynFlags, FilePath)    -- ^ (final flags, output filename)
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runPipeline stop_phase hsc_env0 (input_fn, mb_phase)
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             mb_basename output maybe_loc foreign_os
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    = do let
             dflags0 = hsc_dflags hsc_env0

             -- Decide where dump files should go based on the pipeline output
             dflags = dflags0 { dumpPrefix = Just (basename ++ ".") }
             hsc_env = hsc_env0 {hsc_dflags = dflags}

             (input_basename, suffix) = splitExtension input_fn
             suffix' = drop 1 suffix -- strip off the .
             basename | Just b <- mb_basename = b
                      | otherwise             = input_basename

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             -- If we were given a -x flag, then use that phase to start from
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             start_phase = fromMaybe (RealPhase (startPhase suffix')) mb_phase
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             isHaskell (RealPhase (Unlit _)) = True
             isHaskell (RealPhase (Cpp   _)) = True
             isHaskell (RealPhase (HsPp  _)) = True
             isHaskell (RealPhase (Hsc   _)) = True
             isHaskell (HscOut {})           = True
             isHaskell _                     = False
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             isHaskellishFile = isHaskell start_phase

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             env = PipeEnv{ stop_phase,
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                            src_filename = input_fn,
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                            src_basename = basename,
                            src_suffix = suffix',
                            output_spec = output }

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         when (isBackpackishSuffix suffix') $
           throwGhcExceptionIO (UsageError
                       ("use --backpack to process " ++ input_fn))

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         -- We want to catch cases of "you can't get there from here" before
         -- we start the pipeline, because otherwise it will just run off the
         -- end.
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         let happensBefore' = happensBefore dflags
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         case start_phase of
             RealPhase start_phase' ->
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                 -- See Note [Partial ordering on phases]
                 -- Not the same as: (stop_phase `happensBefore` start_phase')
                 when (not (start_phase' `happensBefore'` stop_phase ||
                            start_phase' `eqPhase` stop_phase)) $
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                       throwGhcExceptionIO (UsageError
                                   ("cannot compile this file to desired target: "
                                      ++ input_fn))
             HscOut {} -> return ()
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         debugTraceMsg dflags 4 (text "Running the pipeline")
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         r <- runPipeline' start_phase hsc_env env input_fn
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                           maybe_loc foreign_os
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         -- If we are compiling a Haskell module, and doing
         -- -dynamic-too, but couldn't do the -dynamic-too fast
         -- path, then rerun the pipeline for the dyn way
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         let dflags = hsc_dflags hsc_env
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         -- NB: Currently disabled on Windows (ref #7134, #8228, and #5987)
         when (not $ platformOS (targetPlatform dflags) == OSMinGW32) $ do
           when isHaskellishFile $ whenCannotGenerateDynamicToo dflags $ do
               debugTraceMsg dflags 4
                   (text "Running the pipeline again for -dynamic-too")
               let dflags' = dynamicTooMkDynamicDynFlags dflags
               hsc_env' <- newHscEnv dflags'
               _ <- runPipeline' start_phase hsc_env' env input_fn
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                                 maybe_loc foreign_os
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               return ()
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         return r

runPipeline'
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  :: PhasePlus                  -- ^ When to start
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  -> HscEnv                     -- ^ Compilation environment
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  -> PipeEnv
  -> FilePath                   -- ^ Input filename
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  -> Maybe ModLocation          -- ^ A ModLocation, if this is a Haskell module
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  -> [FilePath]                 -- ^ foreign objects, if we have one
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  -> IO (DynFlags, FilePath)    -- ^ (final flags, output filename)
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runPipeline' start_phase hsc_env env input_fn
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             maybe_loc foreign_os
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  = do
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  -- Execute the pipeline...
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  let state = PipeState{ hsc_env, maybe_loc, foreign_os = foreign_os }
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  evalP (pipeLoop start_phase input_fn) env state
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-- ---------------------------------------------------------------------------
-- outer pipeline loop

-- | pipeLoop runs phases until we reach the stop phase
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pipeLoop :: PhasePlus -> FilePath -> CompPipeline (DynFlags, FilePath)
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pipeLoop phase input_fn = do
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  env <- getPipeEnv
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  dflags <- getDynFlags
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  -- See Note [Partial ordering on phases]
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  let happensBefore' = happensBefore dflags
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      stopPhase = stop_phase env
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  case phase of
   RealPhase realPhase | realPhase `eqPhase` stopPhase            -- All done
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     -> -- Sometimes, a compilation phase doesn't actually generate any output
        -- (eg. the CPP phase when -fcpp is not turned on).  If we end on this
        -- stage, but we wanted to keep the output, then we have to explicitly
        -- copy the file, remembering to prepend a {-# LINE #-} pragma so that
        -- further compilation stages can tell what the original filename was.
        case output_spec env of
        Temporary ->
            return (dflags, input_fn)
        output ->
            do pst <- getPipeState
               final_fn <- liftIO $ getOutputFilename
                                        stopPhase output (src_basename env)
                                        dflags stopPhase (maybe_loc pst)
               when (final_fn /= input_fn) $ do
                  let msg = ("Copying `" ++ input_fn ++"' to `" ++ final_fn ++ "'")
                      line_prag = Just ("{-# LINE 1 \"" ++ src_filename env ++ "\" #-}\n")
                  liftIO $ copyWithHeader dflags msg line_prag input_fn final_fn
               return (dflags, final_fn)


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     | not (realPhase `happensBefore'` stopPhase)
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        -- Something has gone wrong.  We'll try to cover all the cases when
        -- this could happen, so if we reach here it is a panic.
        -- eg. it might happen if the -C flag is used on a source file that
        -- has {-# OPTIONS -fasm #-}.
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     -> panic ("pipeLoop: at phase " ++ show realPhase ++
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           " but I wanted to stop at phase " ++ show stopPhase)
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   _
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     -> do liftIO $ debugTraceMsg dflags 4
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                                  (text "Running phase" <+> ppr phase)
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           (next_phase, output_fn) <- runHookedPhase phase input_fn dflags
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           r <- pipeLoop next_phase output_fn
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           case phase of
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               HscOut {} ->
                   whenGeneratingDynamicToo dflags $ do
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                       setDynFlags $ dynamicTooMkDynamicDynFlags dflags
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                       -- TODO shouldn't ignore result:
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                       _ <- pipeLoop phase input_fn
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                       return ()
               _ ->
                   return ()
           return r
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runHookedPhase :: PhasePlus -> FilePath -> DynFlags
               -> CompPipeline (PhasePlus, FilePath)
runHookedPhase pp input dflags =
  lookupHook runPhaseHook runPhase dflags pp input dflags

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-- -----------------------------------------------------------------------------
-- In each phase, we need to know into what filename to generate the
-- output.  All the logic about which filenames we generate output
-- into is embodied in the following function.
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-- | Computes the next output filename after we run @next_phase@.
-- Like 'getOutputFilename', but it operates in the 'CompPipeline' monad
-- (which specifies all of the ambient information.)
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phaseOutputFilename :: Phase{-next phase-} -> CompPipeline FilePath
phaseOutputFilename next_phase = do
  PipeEnv{stop_phase, src_basename, output_spec} <- getPipeEnv
  PipeState{maybe_loc, hsc_env} <- getPipeState
  let dflags = hsc_dflags hsc_env
  liftIO $ getOutputFilename stop_phase output_spec
                             src_basename dflags next_phase maybe_loc

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-- | Computes the next output filename for something in the compilation
-- pipeline.  This is controlled by several variables:
--
--      1. 'Phase': the last phase to be run (e.g. 'stopPhase').  This
--         is used to tell if we're in the last phase or not, because
--         in that case flags like @-o@ may be important.
--      2. 'PipelineOutput': is this intended to be a 'Temporary' or
--         'Persistent' build output?  Temporary files just go in
--         a fresh temporary name.
--      3. 'String': what was the basename of the original input file?
--      4. 'DynFlags': the obvious thing
--      5. 'Phase': the phase we want to determine the output filename of.
--      6. @Maybe ModLocation@: the 'ModLocation' of the module we're
--         compiling; this can be used to override the default output
--         of an object file.  (TODO: do we actually need this?)
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getOutputFilename
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  :: Phase -> PipelineOutput -> String
  -> DynFlags -> Phase{-next phase-} -> Maybe ModLocation -> IO FilePath
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getOutputFilename stop_phase output basename dflags next_phase maybe_location
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 | is_last_phase, Persistent   <- output = persistent_fn
 | is_last_phase, SpecificFile <- output = case outputFile dflags of
                                           Just f -> return f
                                           Nothing ->
                                               panic "SpecificFile: No filename"
 | keep_this_output                      = persistent_fn
 | otherwise                             = newTempName dflags suffix
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    where
          hcsuf      = hcSuf dflags
          odir       = objectDir dflags
          osuf       = objectSuf dflags
          keep_hc    = gopt Opt_KeepHcFiles dflags
          keep_s     = gopt Opt_KeepSFiles dflags
          keep_bc    = gopt Opt_KeepLlvmFiles dflags

          myPhaseInputExt HCc       = hcsuf
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          myPhaseInputExt MergeForeign = osuf
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          myPhaseInputExt StopLn    = osuf
          myPhaseInputExt other     = phaseInputExt other

          is_last_phase = next_phase `eqPhase` stop_phase

          -- sometimes, we keep output from intermediate stages
          keep_this_output =
               case next_phase of
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                       As _    | keep_s     -> True
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                       LlvmOpt | keep_bc    -> True
                       HCc     | keep_hc    -> True
                       _other               -> False

          suffix = myPhaseInputExt next_phase

          -- persistent object files get put in odir
          persistent_fn
             | StopLn <- next_phase = return odir_persistent
             | otherwise            = return persistent

          persistent = basename <.> suffix

          odir_persistent
             | Just loc <- maybe_location = ml_obj_file loc
             | Just d <- odir = d </> persistent
             | otherwise      = persistent
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-- -----------------------------------------------------------------------------
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-- | Each phase in the pipeline returns the next phase to execute, and the
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-- name of the file in which the output was placed.
--
-- We must do things dynamically this way, because we often don't know
-- what the rest of the phases will be until part-way through the
-- compilation: for example, an {-# OPTIONS -fasm #-} at the beginning
-- of a source file can change the latter stages of the pipeline from
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-- taking the LLVM route to using the native code generator.
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--
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runPhase :: PhasePlus   -- ^ Run this phase
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         -> FilePath    -- ^ name of the input file
         -> DynFlags    -- ^ for convenience, we pass the current dflags in
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         -> CompPipeline (PhasePlus,           -- next phase to run
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                          FilePath)            -- output filename
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        -- Invariant: the output filename always contains the output
        -- Interesting case: Hsc when there is no recompilation to do
        --                   Then the output filename is still a .o file
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-------------------------------------------------------------------------------
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-- Unlit phase
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runPhase (RealPhase (Unlit sf)) input_fn dflags
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  = do
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       output_fn <- phaseOutputFilename (Cpp sf)
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       let flags = [ -- The -h option passes the file name for unlit to
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                     -- put in a #line directive
                     SysTools.Option     "-h"
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                     -- See Note [Don't normalise input filenames].
                   , SysTools.Option $ escape input_fn
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                   , SysTools.FileOption "" input_fn
                   , SysTools.FileOption "" output_fn
                   ]

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       liftIO $ SysTools.runUnlit dflags flags
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       return (RealPhase (Cpp sf), output_fn)
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  where
       -- escape the characters \, ", and ', but don't try to escape
       -- Unicode or anything else (so we don't use Util.charToC
       -- here).  If we get this wrong, then in
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       -- Coverage.isGoodTickSrcSpan where we check that the filename in
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       -- a SrcLoc is the same as the source filenaame, the two will
       -- look bogusly different. See test:
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       -- libraries/hpc/tests/function/subdir/tough2.hs
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       escape ('\\':cs) = '\\':'\\': escape cs
       escape ('\"':cs) = '\\':'\"': escape cs
       escape ('\'':cs) = '\\':'\'': escape cs
       escape (c:cs)    = c : escape cs
       escape []        = []
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-------------------------------------------------------------------------------
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-- Cpp phase : (a) gets OPTIONS out of file
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--             (b) runs cpp if necessary
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runPhase (RealPhase (Cpp sf)) input_fn dflags0
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  = do
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       src_opts <- liftIO $ getOptionsFromFile dflags0 input_fn
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       (dflags1, unhandled_flags, warns)
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           <- liftIO $ parseDynamicFilePragma dflags0 src_opts
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       setDynFlags dflags1
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       liftIO $ checkProcessArgsResult dflags1 unhandled_flags
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       if not (xopt LangExt.Cpp dflags1) then do
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           -- we have to be careful to emit warnings only once.
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           unless (gopt Opt_Pp dflags1) $
               liftIO $ handleFlagWarnings dflags1 warns
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           -- no need to preprocess CPP, just pass input file along
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           -- to the next phase of the pipeline.
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           return (RealPhase (HsPp sf), input_fn)
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        else do
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            output_fn <- phaseOutputFilename (HsPp sf)
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            liftIO $ doCpp dflags1 True{-raw-}
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                           input_fn output_fn
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            -- re-read the pragmas now that we've preprocessed the file
            -- See #2464,#3457
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            src_opts <- liftIO $ getOptionsFromFile dflags0 output_fn
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            (dflags2, unhandled_flags, warns)
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                <- liftIO $ parseDynamicFilePragma dflags0 src_opts
            liftIO $ checkProcessArgsResult dflags2 unhandled_flags
            unless (gopt Opt_Pp dflags2) $
                liftIO $ handleFlagWarnings dflags2 warns
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            -- the HsPp pass below will emit warnings
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            setDynFlags dflags2
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            return (RealPhase (HsPp sf), output_fn)
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-------------------------------------------------------------------------------
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-- HsPp phase
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runPhase (RealPhase (HsPp sf)) input_fn dflags
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  = do
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       if not (gopt Opt_Pp dflags) then
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           -- no need to preprocess, just pass input file along
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           -- to the next phase of the pipeline.
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          return (RealPhase (Hsc sf), input_fn)
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        else do
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            PipeEnv{src_basename, src_suffix} <- getPipeEnv
            let orig_fn = src_basename <.> src_suffix
            output_fn <- phaseOutputFilename (Hsc sf)
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            liftIO $ SysTools.runPp dflags
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                           ( [ SysTools.Option     orig_fn
                             , SysTools.Option     input_fn
                             , SysTools.FileOption "" output_fn
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                             ]
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                           )
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            -- re-read pragmas now that we've parsed the file (see #3674)
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            src_opts <- liftIO $ getOptionsFromFile dflags output_fn
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            (dflags1, unhandled_flags, warns)
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                <- liftIO $ parseDynamicFilePragma dflags src_opts
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            setDynFlags dflags1
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            liftIO $ checkProcessArgsResult dflags1 unhandled_flags
            liftIO $ handleFlagWarnings dflags1 warns
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            return (RealPhase (Hsc sf), output_fn)
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-----------------------------------------------------------------------------
-- Hsc phase

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-- Compilation of a single module, in "legacy" mode (_not_ under
-- the direction of the compilation manager).
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runPhase (RealPhase (Hsc src_flavour)) input_fn dflags0
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 = do   -- normal Hsc mode, not mkdependHS
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        PipeEnv{ stop_phase=stop,
                 src_basename=basename,
                 src_suffix=suff } <- getPipeEnv
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  -- we add the current directory (i.e. the directory in which
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  -- the .hs files resides) to the include path, since this is
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  -- what gcc does, and it's probably what you want.
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        let current_dir = takeDirectory basename
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            paths = includePaths dflags0
            dflags = dflags0 { includePaths = current_dir : paths }

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        setDynFlags dflags

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  -- gather the imports and module name
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        (hspp_buf,mod_name,imps,src_imps) <- liftIO $ do
          do
            buf <- hGetStringBuffer input_fn
            (src_imps,imps,L _ mod_name) <- getImports dflags buf input_fn (basename <.> suff)
            return (Just buf, mod_name, imps, src_imps)
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  -- Take -o into account if present
  -- Very like -ohi, but we must *only* do this if we aren't linking
  -- (If we're linking then the -o applies to the linked thing, not to
  -- the object file for one module.)
  -- Note the nasty duplication with the same computation in compileFile above
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        location <- getLocation src_flavour mod_name
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        let o_file = ml_obj_file location -- The real object file
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            hi_file = ml_hi_file location
            dest_file | writeInterfaceOnlyMode dflags
                            = hi_file