path: root/compiler/GHC/Unit/Finder.hs

{-
(c) The University of Glasgow, 2000-2006

-}


{-# LANGUAGE FlexibleContexts #-}

-- | Module finder
module GHC.Unit.Finder (
    FindResult(..),
    InstalledFindResult(..),
    FinderOpts(..),
    FinderCache,
    initFinderCache,
    flushFinderCaches,
    findImportedModule,
    findPluginModule,
    findExactModule,
    findHomeModule,
    findExposedPackageModule,
    mkHomeModLocation,
    mkHomeModLocation2,
    mkHiOnlyModLocation,
    mkHiPath,
    mkObjPath,
    addHomeModuleToFinder,
    uncacheModule,
    mkStubPaths,

    findObjectLinkableMaybe,
    findObjectLinkable,

    -- Hash cache
    lookupFileCache
  ) where

import GHC.Prelude

import GHC.Platform.Ways

import GHC.Builtin.Names ( gHC_PRIM )

import GHC.Unit.Types
import GHC.Unit.Module
import GHC.Unit.Home
import GHC.Unit.State
import GHC.Unit.Finder.Types

import GHC.Data.Maybe    ( expectJust )
import qualified GHC.Data.ShortText as ST

import GHC.Utils.Misc
import GHC.Utils.Outputable as Outputable
import GHC.Utils.Panic

import GHC.Linker.Types
import GHC.Types.PkgQual

import GHC.Fingerprint
import Data.IORef
import System.Directory
import System.FilePath
import Control.Monad
import Data.Time
import qualified Data.Map as M


type FileExt = String   -- Filename extension
type BaseName = String  -- Basename of file

-- -----------------------------------------------------------------------------
-- The Finder

-- The Finder provides a thin filesystem abstraction to the rest of
-- the compiler.  For a given module, it can tell you where the
-- source, interface, and object files for that module live.

-- It does *not* know which particular package a module lives in.  Use
-- Packages.lookupModuleInAllUnits for that.

-- -----------------------------------------------------------------------------
-- The finder's cache


initFinderCache :: IO FinderCache
initFinderCache = FinderCache <$> newIORef emptyInstalledModuleEnv
                              <*> newIORef M.empty

-- remove all the home modules from the cache; package modules are
-- assumed to not move around during a session; also flush the file hash
-- cache
flushFinderCaches :: FinderCache -> HomeUnit -> IO ()
flushFinderCaches (FinderCache ref file_ref) home_unit = do
  atomicModifyIORef' ref $ \fm -> (filterInstalledModuleEnv is_ext fm, ())
  atomicModifyIORef' file_ref $ \_ -> (M.empty, ())
 where
  is_ext mod _ = not (isHomeInstalledModule home_unit mod)

addToFinderCache :: FinderCache -> InstalledModule -> InstalledFindResult -> IO ()
addToFinderCache (FinderCache ref _) key val =
  atomicModifyIORef' ref $ \c -> (extendInstalledModuleEnv c key val, ())

removeFromFinderCache :: FinderCache -> InstalledModule -> IO ()
removeFromFinderCache (FinderCache ref _) key =
  atomicModifyIORef' ref $ \c -> (delInstalledModuleEnv c key, ())

lookupFinderCache :: FinderCache -> InstalledModule -> IO (Maybe InstalledFindResult)
lookupFinderCache (FinderCache ref _) key = do
   c <- readIORef ref
   return $! lookupInstalledModuleEnv c key

lookupFileCache :: FinderCache -> FilePath -> IO Fingerprint
lookupFileCache (FinderCache _ ref) key = do
   c <- readIORef ref
   case M.lookup key c of
     Nothing -> do
       hash <- getFileHash key
       atomicModifyIORef' ref $ \c -> (M.insert key hash c, ())
       return hash
     Just fp -> return fp

-- -----------------------------------------------------------------------------
-- The three external entry points


-- | Locate a module that was imported by the user.  We have the
-- module's name, and possibly a package name.  Without a package
-- name, this function will use the search path and the known exposed
-- packages to find the module, if a package is specified then only
-- that package is searched for the module.

findImportedModule
  :: FinderCache
  -> FinderOpts
  -> UnitState
  -> Maybe HomeUnit
  -> ModuleName
  -> PkgQual
  -> IO FindResult
findImportedModule fc fopts units mhome_unit mod_name mb_pkg =
  case mb_pkg of
    NoPkgQual  -> unqual_import
    ThisPkg _  -> home_import
    OtherPkg _ -> pkg_import
  where
    home_import
      | Just home_unit <- mhome_unit
      = findHomeModule fc fopts home_unit mod_name
      | otherwise
      = pure $ NoPackage (panic "findImportedModule: no home-unit")

    pkg_import    = findExposedPackageModule fc fopts units mod_name mb_pkg

    unqual_import = home_import
                    `orIfNotFound`
                    findExposedPackageModule fc fopts units mod_name NoPkgQual

-- | Locate a plugin module requested by the user, for a compiler
-- plugin.  This consults the same set of exposed packages as
-- 'findImportedModule', unless @-hide-all-plugin-packages@ or
-- @-plugin-package@ are specified.
findPluginModule :: FinderCache -> FinderOpts -> UnitState -> Maybe HomeUnit -> ModuleName -> IO FindResult
findPluginModule fc fopts units (Just home_unit) mod_name =
  findHomeModule fc fopts home_unit mod_name
  `orIfNotFound`
  findExposedPluginPackageModule fc fopts units mod_name
findPluginModule fc fopts units Nothing mod_name =
  findExposedPluginPackageModule fc fopts units mod_name

-- | Locate a specific 'Module'.  The purpose of this function is to
-- create a 'ModLocation' for a given 'Module', that is to find out
-- where the files associated with this module live.  It is used when
-- reading the interface for a module mentioned by another interface,
-- for example (a "system import").

findExactModule :: FinderCache -> FinderOpts -> UnitState -> Maybe HomeUnit -> InstalledModule -> IO InstalledFindResult
findExactModule fc fopts unit_state mhome_unit mod = do
  case mhome_unit of
    Just home_unit
      | isHomeInstalledModule home_unit mod
      -> findInstalledHomeModule fc fopts home_unit (moduleName mod)
    _ -> findPackageModule fc unit_state fopts mod

-- -----------------------------------------------------------------------------
-- Helpers

-- | Given a monadic actions @this@ and @or_this@, first execute
-- @this@.  If the returned 'FindResult' is successful, return
-- it; otherwise, execute @or_this@.  If both failed, this function
-- also combines their failure messages in a reasonable way.
orIfNotFound :: Monad m => m FindResult -> m FindResult -> m FindResult
orIfNotFound this or_this = do
  res <- this
  case res of
    NotFound { fr_paths = paths1, fr_mods_hidden = mh1
             , fr_pkgs_hidden = ph1, fr_unusables = u1, fr_suggestions = s1 }
     -> do res2 <- or_this
           case res2 of
             NotFound { fr_paths = paths2, fr_pkg = mb_pkg2, fr_mods_hidden = mh2
                      , fr_pkgs_hidden = ph2, fr_unusables = u2
                      , fr_suggestions = s2 }
              -> return (NotFound { fr_paths = paths1 ++ paths2
                                  , fr_pkg = mb_pkg2 -- snd arg is the package search
                                  , fr_mods_hidden = mh1 ++ mh2
                                  , fr_pkgs_hidden = ph1 ++ ph2
                                  , fr_unusables = u1 ++ u2
                                  , fr_suggestions = s1  ++ s2 })
             _other -> return res2
    _other -> return res

-- | Helper function for 'findHomeModule': this function wraps an IO action
-- which would look up @mod_name@ in the file system (the home package),
-- and first consults the 'hsc_FC' cache to see if the lookup has already
-- been done.  Otherwise, do the lookup (with the IO action) and save
-- the result in the finder cache and the module location cache (if it
-- was successful.)
homeSearchCache :: FinderCache -> HomeUnit -> ModuleName -> IO InstalledFindResult -> IO InstalledFindResult
homeSearchCache fc home_unit mod_name do_this = do
  let mod = mkHomeInstalledModule home_unit mod_name
  modLocationCache fc mod do_this

findExposedPackageModule :: FinderCache -> FinderOpts -> UnitState -> ModuleName -> PkgQual -> IO FindResult
findExposedPackageModule fc fopts units mod_name mb_pkg =
  findLookupResult fc fopts
    $ lookupModuleWithSuggestions units mod_name mb_pkg

findExposedPluginPackageModule :: FinderCache -> FinderOpts -> UnitState -> ModuleName -> IO FindResult
findExposedPluginPackageModule fc fopts units mod_name =
  findLookupResult fc fopts
    $ lookupPluginModuleWithSuggestions units mod_name NoPkgQual

findLookupResult :: FinderCache -> FinderOpts -> LookupResult -> IO FindResult
findLookupResult fc fopts r = case r of
     LookupFound m pkg_conf -> do
       let im = fst (getModuleInstantiation m)
       r' <- findPackageModule_ fc fopts im (fst pkg_conf)
       case r' of
        -- TODO: ghc -M is unlikely to do the right thing
        -- with just the location of the thing that was
        -- instantiated; you probably also need all of the
        -- implicit locations from the instances
        InstalledFound loc   _ -> return (Found loc m)
        InstalledNoPackage   _ -> return (NoPackage (moduleUnit m))
        InstalledNotFound fp _ -> return (NotFound{ fr_paths = fp, fr_pkg = Just (moduleUnit m)
                                         , fr_pkgs_hidden = []
                                         , fr_mods_hidden = []
                                         , fr_unusables = []
                                         , fr_suggestions = []})
     LookupMultiple rs ->
       return (FoundMultiple rs)
     LookupHidden pkg_hiddens mod_hiddens ->
       return (NotFound{ fr_paths = [], fr_pkg = Nothing
                       , fr_pkgs_hidden = map (moduleUnit.fst) pkg_hiddens
                       , fr_mods_hidden = map (moduleUnit.fst) mod_hiddens
                       , fr_unusables = []
                       , fr_suggestions = [] })
     LookupUnusable unusable ->
       let unusables' = map get_unusable unusable
           get_unusable (m, ModUnusable r) = (moduleUnit m, r)
           get_unusable (_, r)             =
             pprPanic "findLookupResult: unexpected origin" (ppr r)
       in return (NotFound{ fr_paths = [], fr_pkg = Nothing
                          , fr_pkgs_hidden = []
                          , fr_mods_hidden = []
                          , fr_unusables = unusables'
                          , fr_suggestions = [] })
     LookupNotFound suggest -> do
       let suggest'
             | finder_enableSuggestions fopts = suggest
             | otherwise = []
       return (NotFound{ fr_paths = [], fr_pkg = Nothing
                       , fr_pkgs_hidden = []
                       , fr_mods_hidden = []
                       , fr_unusables = []
                       , fr_suggestions = suggest' })

modLocationCache :: FinderCache -> InstalledModule -> IO InstalledFindResult -> IO InstalledFindResult
modLocationCache fc mod do_this = do
  m <- lookupFinderCache fc mod
  case m of
    Just result -> return result
    Nothing     -> do
        result <- do_this
        addToFinderCache fc mod result
        return result

-- This returns a module because it's more convenient for users
addHomeModuleToFinder :: FinderCache -> HomeUnit -> ModuleName -> ModLocation -> IO Module
addHomeModuleToFinder fc home_unit mod_name loc = do
  let mod = mkHomeInstalledModule home_unit mod_name
  addToFinderCache fc mod (InstalledFound loc mod)
  return (mkHomeModule home_unit mod_name)

uncacheModule :: FinderCache -> HomeUnit -> ModuleName -> IO ()
uncacheModule fc home_unit mod_name = do
  let mod = mkHomeInstalledModule home_unit mod_name
  removeFromFinderCache fc mod

-- -----------------------------------------------------------------------------
--      The internal workers

findHomeModule :: FinderCache -> FinderOpts -> HomeUnit -> ModuleName -> IO FindResult
findHomeModule fc fopts  home_unit mod_name = do
  let uid       = homeUnitAsUnit home_unit
  r <- findInstalledHomeModule fc fopts home_unit mod_name
  return $ case r of
    InstalledFound loc _ -> Found loc (mkHomeModule home_unit mod_name)
    InstalledNoPackage _ -> NoPackage uid -- impossible
    InstalledNotFound fps _ -> NotFound {
        fr_paths = fps,
        fr_pkg = Just uid,
        fr_mods_hidden = [],
        fr_pkgs_hidden = [],
        fr_unusables = [],
        fr_suggestions = []
      }

-- | Implements the search for a module name in the home package only.  Calling
-- this function directly is usually *not* what you want; currently, it's used
-- as a building block for the following operations:
--
--  1. When you do a normal package lookup, we first check if the module
--  is available in the home module, before looking it up in the package
--  database.
--
--  2. When you have a package qualified import with package name "this",
--  we shortcut to the home module.
--
--  3. When we look up an exact 'Module', if the unit id associated with
--  the module is the current home module do a look up in the home module.
--
--  4. Some special-case code in GHCi (ToDo: Figure out why that needs to
--  call this.)
findInstalledHomeModule :: FinderCache -> FinderOpts -> HomeUnit -> ModuleName -> IO InstalledFindResult
findInstalledHomeModule fc fopts home_unit mod_name = do
  homeSearchCache fc home_unit mod_name $
   let
     home_path = finder_importPaths fopts
     hisuf = finder_hiSuf fopts
     mod = mkHomeInstalledModule home_unit mod_name

     source_exts =
      [ ("hs",    mkHomeModLocationSearched fopts mod_name "hs")
      , ("lhs",   mkHomeModLocationSearched fopts mod_name "lhs")
      , ("hsig",  mkHomeModLocationSearched fopts mod_name "hsig")
      , ("lhsig", mkHomeModLocationSearched fopts mod_name "lhsig")
      ]

     -- we use mkHomeModHiOnlyLocation instead of mkHiOnlyModLocation so that
     -- when hiDir field is set in dflags, we know to look there (see #16500)
     hi_exts = [ (hisuf,                mkHomeModHiOnlyLocation fopts mod_name)
               , (addBootSuffix hisuf,  mkHomeModHiOnlyLocation fopts mod_name)
               ]

        -- In compilation manager modes, we look for source files in the home
        -- package because we can compile these automatically.  In one-shot
        -- compilation mode we look for .hi and .hi-boot files only.
     exts | finder_lookupHomeInterfaces fopts = hi_exts
          | otherwise                         = source_exts
   in

   -- special case for GHC.Prim; we won't find it in the filesystem.
   -- This is important only when compiling the base package (where GHC.Prim
   -- is a home module).
   if mod `installedModuleEq` gHC_PRIM
         then return (InstalledFound (error "GHC.Prim ModLocation") mod)
         else searchPathExts home_path mod exts


-- | Search for a module in external packages only.
findPackageModule :: FinderCache -> UnitState -> FinderOpts -> InstalledModule -> IO InstalledFindResult
findPackageModule fc unit_state fopts mod = do
  let pkg_id = moduleUnit mod
  case lookupUnitId unit_state pkg_id of
     Nothing -> return (InstalledNoPackage pkg_id)
     Just u  -> findPackageModule_ fc fopts mod u

-- | Look up the interface file associated with module @mod@.  This function
-- requires a few invariants to be upheld: (1) the 'Module' in question must
-- be the module identifier of the *original* implementation of a module,
-- not a reexport (this invariant is upheld by "GHC.Unit.State") and (2)
-- the 'UnitInfo' must be consistent with the unit id in the 'Module'.
-- The redundancy is to avoid an extra lookup in the package state
-- for the appropriate config.
findPackageModule_ :: FinderCache -> FinderOpts -> InstalledModule -> UnitInfo -> IO InstalledFindResult
findPackageModule_ fc fopts mod pkg_conf = do
  massertPpr (moduleUnit mod == unitId pkg_conf)
             (ppr (moduleUnit mod) <+> ppr (unitId pkg_conf))
  modLocationCache fc mod $

    -- special case for GHC.Prim; we won't find it in the filesystem.
    if mod `installedModuleEq` gHC_PRIM
          then return (InstalledFound (error "GHC.Prim ModLocation") mod)
          else

    let
       tag = waysBuildTag (finder_ways fopts)

             -- hi-suffix for packages depends on the build tag.
       package_hisuf | null tag  = "hi"
                     | otherwise = tag ++ "_hi"

       package_dynhisuf = waysBuildTag (addWay WayDyn (finder_ways fopts)) ++ "_hi"

       mk_hi_loc = mkHiOnlyModLocation fopts package_hisuf package_dynhisuf

       import_dirs = map ST.unpack $ unitImportDirs pkg_conf
        -- we never look for a .hi-boot file in an external package;
        -- .hi-boot files only make sense for the home package.
    in
    case import_dirs of
      [one] | finder_bypassHiFileCheck fopts ->
            -- there's only one place that this .hi file can be, so
            -- don't bother looking for it.
            let basename = moduleNameSlashes (moduleName mod)
                loc = mk_hi_loc one basename
            in return $ InstalledFound loc mod
      _otherwise ->
            searchPathExts import_dirs mod [(package_hisuf, mk_hi_loc)]

-- -----------------------------------------------------------------------------
-- General path searching

searchPathExts :: [FilePath]      -- paths to search
               -> InstalledModule -- module name
               -> [ (
                     FileExt,                             -- suffix
                     FilePath -> BaseName -> ModLocation  -- action
                    )
                  ]
               -> IO InstalledFindResult

searchPathExts paths mod exts = search to_search
  where
    basename = moduleNameSlashes (moduleName mod)

    to_search :: [(FilePath, ModLocation)]
    to_search = [ (file, fn path basename)
                | path <- paths,
                  (ext,fn) <- exts,
                  let base | path == "." = basename
                           | otherwise   = path </> basename
                      file = base <.> ext
                ]

    search [] = return (InstalledNotFound (map fst to_search) (Just (moduleUnit mod)))

    search ((file, loc) : rest) = do
      b <- doesFileExist file
      if b
        then return $ InstalledFound loc mod
        else search rest

mkHomeModLocationSearched :: FinderOpts -> ModuleName -> FileExt
                          -> FilePath -> BaseName -> ModLocation
mkHomeModLocationSearched fopts mod suff path basename =
  mkHomeModLocation2 fopts mod (path </> basename) suff


-- -----------------------------------------------------------------------------
-- Constructing a home module location

-- This is where we construct the ModLocation for a module in the home
-- package, for which we have a source file.  It is called from three
-- places:
--
--  (a) Here in the finder, when we are searching for a module to import,
--      using the search path (-i option).
--
--  (b) The compilation manager, when constructing the ModLocation for
--      a "root" module (a source file named explicitly on the command line
--      or in a :load command in GHCi).
--
--  (c) The driver in one-shot mode, when we need to construct a
--      ModLocation for a source file named on the command-line.
--
-- Parameters are:
--
-- mod
--      The name of the module
--
-- path
--      (a): The search path component where the source file was found.
--      (b) and (c): "."
--
-- src_basename
--      (a): (moduleNameSlashes mod)
--      (b) and (c): The filename of the source file, minus its extension
--
-- ext
--      The filename extension of the source file (usually "hs" or "lhs").

mkHomeModLocation :: FinderOpts -> ModuleName -> FilePath -> ModLocation
mkHomeModLocation dflags mod src_filename =
   let (basename,extension) = splitExtension src_filename
   in mkHomeModLocation2 dflags mod basename extension

mkHomeModLocation2 :: FinderOpts
                   -> ModuleName
                   -> FilePath  -- Of source module, without suffix
                   -> String    -- Suffix
                   -> ModLocation
mkHomeModLocation2 fopts mod src_basename ext =
   let mod_basename = moduleNameSlashes mod

       obj_fn = mkObjPath  fopts src_basename mod_basename
       dyn_obj_fn = mkDynObjPath  fopts src_basename mod_basename
       hi_fn  = mkHiPath   fopts src_basename mod_basename
       dyn_hi_fn  = mkDynHiPath   fopts src_basename mod_basename
       hie_fn = mkHiePath  fopts src_basename mod_basename

   in (ModLocation{ ml_hs_file   = Just (src_basename <.> ext),
                        ml_hi_file   = hi_fn,
                        ml_dyn_hi_file = dyn_hi_fn,
                        ml_obj_file  = obj_fn,
                        ml_dyn_obj_file = dyn_obj_fn,
                        ml_hie_file  = hie_fn })

mkHomeModHiOnlyLocation :: FinderOpts
                        -> ModuleName
                        -> FilePath
                        -> BaseName
                        -> ModLocation
mkHomeModHiOnlyLocation fopts mod path basename =
   let loc = mkHomeModLocation2 fopts mod (path </> basename) ""
   in loc { ml_hs_file = Nothing }

-- This function is used to make a ModLocation for a package module. Hence why
-- we explicitly pass in the interface file suffixes.
mkHiOnlyModLocation :: FinderOpts -> Suffix -> Suffix -> FilePath -> String
                    -> ModLocation
mkHiOnlyModLocation fopts hisuf dynhisuf path basename
 = let full_basename = path </> basename
       obj_fn = mkObjPath fopts full_basename basename
       dyn_obj_fn = mkDynObjPath fopts full_basename basename
       hie_fn = mkHiePath fopts full_basename basename
   in ModLocation{    ml_hs_file   = Nothing,
                             ml_hi_file   = full_basename <.> hisuf,
                                -- Remove the .hi-boot suffix from
                                -- hi_file, if it had one.  We always
                                -- want the name of the real .hi file
                                -- in the ml_hi_file field.
                             ml_dyn_obj_file = dyn_obj_fn,
                             -- MP: TODO
                             ml_dyn_hi_file  = full_basename <.> dynhisuf,
                             ml_obj_file  = obj_fn,
                             ml_hie_file  = hie_fn
                  }

-- | Constructs the filename of a .o file for a given source file.
-- Does /not/ check whether the .o file exists
mkObjPath
  :: FinderOpts
  -> FilePath           -- the filename of the source file, minus the extension
  -> String             -- the module name with dots replaced by slashes
  -> FilePath
mkObjPath fopts basename mod_basename = obj_basename <.> osuf
  where
                odir = finder_objectDir fopts
                osuf = finder_objectSuf fopts

                obj_basename | Just dir <- odir = dir </> mod_basename
                             | otherwise        = basename

-- | Constructs the filename of a .dyn_o file for a given source file.
-- Does /not/ check whether the .dyn_o file exists
mkDynObjPath
  :: FinderOpts
  -> FilePath           -- the filename of the source file, minus the extension
  -> String             -- the module name with dots replaced by slashes
  -> FilePath
mkDynObjPath fopts basename mod_basename = obj_basename <.> dynosuf
  where
                odir = finder_objectDir fopts
                dynosuf = finder_dynObjectSuf fopts

                obj_basename | Just dir <- odir = dir </> mod_basename
                             | otherwise        = basename


-- | Constructs the filename of a .hi file for a given source file.
-- Does /not/ check whether the .hi file exists
mkHiPath
  :: FinderOpts
  -> FilePath           -- the filename of the source file, minus the extension
  -> String             -- the module name with dots replaced by slashes
  -> FilePath
mkHiPath fopts basename mod_basename = hi_basename <.> hisuf
 where
                hidir = finder_hiDir fopts
                hisuf = finder_hiSuf fopts

                hi_basename | Just dir <- hidir = dir </> mod_basename
                            | otherwise         = basename

-- | Constructs the filename of a .dyn_hi file for a given source file.
-- Does /not/ check whether the .dyn_hi file exists
mkDynHiPath
  :: FinderOpts
  -> FilePath           -- the filename of the source file, minus the extension
  -> String             -- the module name with dots replaced by slashes
  -> FilePath
mkDynHiPath fopts basename mod_basename = hi_basename <.> dynhisuf
 where
                hidir = finder_hiDir fopts
                dynhisuf = finder_dynHiSuf fopts

                hi_basename | Just dir <- hidir = dir </> mod_basename
                            | otherwise         = basename

-- | Constructs the filename of a .hie file for a given source file.
-- Does /not/ check whether the .hie file exists
mkHiePath
  :: FinderOpts
  -> FilePath           -- the filename of the source file, minus the extension
  -> String             -- the module name with dots replaced by slashes
  -> FilePath
mkHiePath fopts basename mod_basename = hie_basename <.> hiesuf
 where
                hiedir = finder_hieDir fopts
                hiesuf = finder_hieSuf fopts

                hie_basename | Just dir <- hiedir = dir </> mod_basename
                             | otherwise          = basename



-- -----------------------------------------------------------------------------
-- Filenames of the stub files

-- We don't have to store these in ModLocations, because they can be derived
-- from other available information, and they're only rarely needed.

mkStubPaths
  :: FinderOpts
  -> ModuleName
  -> ModLocation
  -> FilePath

mkStubPaths fopts mod location
  = let
        stubdir = finder_stubDir fopts

        mod_basename = moduleNameSlashes mod
        src_basename = dropExtension $ expectJust "mkStubPaths"
                                                  (ml_hs_file location)

        stub_basename0
            | Just dir <- stubdir = dir </> mod_basename
            | otherwise           = src_basename

        stub_basename = stub_basename0 ++ "_stub"
     in
        stub_basename <.> "h"

-- -----------------------------------------------------------------------------
-- findLinkable isn't related to the other stuff in here,
-- but there's no other obvious place for it

findObjectLinkableMaybe :: Module -> ModLocation -> IO (Maybe Linkable)
findObjectLinkableMaybe mod locn
   = do let obj_fn = ml_obj_file locn
        maybe_obj_time <- modificationTimeIfExists obj_fn
        case maybe_obj_time of
          Nothing -> return Nothing
          Just obj_time -> liftM Just (findObjectLinkable mod obj_fn obj_time)

-- Make an object linkable when we know the object file exists, and we know
-- its modification time.
findObjectLinkable :: Module -> FilePath -> UTCTime -> IO Linkable
findObjectLinkable mod obj_fn obj_time = return (LM obj_time mod [DotO obj_fn])
  -- We used to look for _stub.o files here, but that was a bug (#706)
  -- Now GHC merges the stub.o into the main .o (#3687)