Introduce FinderLocations for decoupling Finder from DynFlags

20 files changed, 200 insertions, 103 deletions

diff --git a/compiler/GHC.hs b/compiler/GHC.hs
index f419e21534..a95757b8fd 100644
--- a/compiler/GHC.hs
+++ b/compiler/GHC.hs
@@ -310,6 +310,7 @@ import GHC.Driver.Errors.Types
 import GHC.Driver.CmdLine
 import GHC.Driver.Session
 import GHC.Driver.Backend
+import GHC.Driver.Config.Finder (initFinderOpts)
 import GHC.Driver.Config.Parser (initParserOpts)
 import GHC.Driver.Config.Logger (initLogFlags)
 import GHC.Driver.Config.Diagnostic
@@ -1659,9 +1660,10 @@ findModule mod_name maybe_pkg = withSession $ \hsc_env -> do
   let home_unit = hsc_home_unit hsc_env
   let units     = hsc_units hsc_env
   let dflags    = hsc_dflags hsc_env
+  let fopts     = initFinderOpts dflags
   case maybe_pkg of
     Just pkg | not (isHomeUnit home_unit (fsToUnit pkg)) && pkg /= fsLit "this" -> liftIO $ do
-      res <- findImportedModule fc units home_unit dflags mod_name maybe_pkg
+      res <- findImportedModule fc fopts units home_unit mod_name maybe_pkg
       case res of
         Found _ m -> return m
         err       -> throwOneError $ noModError hsc_env noSrcSpan mod_name err
@@ -1670,11 +1672,13 @@ findModule mod_name maybe_pkg = withSession $ \hsc_env -> do
       case home of
         Just m  -> return m
         Nothing -> liftIO $ do
-           res <- findImportedModule fc units home_unit dflags mod_name maybe_pkg
+           res <- findImportedModule fc fopts units home_unit mod_name maybe_pkg
            case res of
              Found loc m | not (isHomeModule home_unit m) -> return m
                          | otherwise -> modNotLoadedError dflags m loc
              err -> throwOneError $ noModError hsc_env noSrcSpan mod_name err
+  where
+
 
 modNotLoadedError :: DynFlags -> Module -> ModLocation -> IO a
 modNotLoadedError dflags m loc = throwGhcExceptionIO $ CmdLineError $ showSDoc dflags $
@@ -1699,7 +1703,8 @@ lookupModule mod_name Nothing = withSession $ \hsc_env -> do
       let fc     = hsc_FC hsc_env
       let units  = hsc_units hsc_env
       let dflags = hsc_dflags hsc_env
-      res <- findExposedPackageModule fc units dflags mod_name Nothing
+      let fopts  = initFinderOpts dflags
+      res <- findExposedPackageModule fc fopts units mod_name Nothing
       case res of
         Found _ m -> return m
         err       -> throwOneError $ noModError hsc_env noSrcSpan mod_name err
diff --git a/compiler/GHC/Driver/Backpack.hs b/compiler/GHC/Driver/Backpack.hs
index 8581865dbf..8e7bbf49d5 100644
--- a/compiler/GHC/Driver/Backpack.hs
+++ b/compiler/GHC/Driver/Backpack.hs
@@ -21,6 +21,7 @@ import GHC.Prelude
 
 -- In a separate module because it hooks into the parser.
 import GHC.Driver.Backpack.Syntax
+import GHC.Driver.Config.Finder (initFinderOpts)
 import GHC.Driver.Config.Parser (initParserOpts)
 import GHC.Driver.Config.Diagnostic
 import GHC.Driver.Monad
@@ -742,9 +743,10 @@ summariseRequirement pn mod_name = do
     hsc_env <- getSession
     let dflags = hsc_dflags hsc_env
     let home_unit = hsc_home_unit hsc_env
+    let fopts = initFinderOpts dflags
 
     let PackageName pn_fs = pn
-    location <- liftIO $ mkHomeModLocation2 dflags mod_name
+    location <- liftIO $ mkHomeModLocation2 fopts mod_name
                  (unpackFS pn_fs </> moduleNameSlashes mod_name) "hsig"
 
     env <- getBkpEnv
@@ -828,13 +830,14 @@ hsModuleToModSummary pn hsc_src modname
     -- Use the PACKAGE NAME to find the location
     let PackageName unit_fs = pn
         dflags = hsc_dflags hsc_env
+        fopts = initFinderOpts dflags
     -- Unfortunately, we have to define a "fake" location in
     -- order to appease the various code which uses the file
     -- name to figure out where to put, e.g. object files.
     -- To add insult to injury, we don't even actually use
     -- these filenames to figure out where the hi files go.
     -- A travesty!
-    location0 <- liftIO $ mkHomeModLocation2 dflags modname
+    location0 <- liftIO $ mkHomeModLocation2 fopts modname
                              (unpackFS unit_fs </>
                               moduleNameSlashes modname)
                               (case hsc_src of
diff --git a/compiler/GHC/Driver/CodeOutput.hs b/compiler/GHC/Driver/CodeOutput.hs
index 6108e529af..7382ec9a10 100644
--- a/compiler/GHC/Driver/CodeOutput.hs
+++ b/compiler/GHC/Driver/CodeOutput.hs
@@ -27,6 +27,7 @@ import GHC.Cmm              ( RawCmmGroup )
 import GHC.Cmm.CLabel
 
 import GHC.Driver.Session
+import GHC.Driver.Config.Finder (initFinderOpts)
 import GHC.Driver.Config.CmmToAsm (initNCGConfig)
 import GHC.Driver.Ppr
 import GHC.Driver.Backend
@@ -209,7 +210,7 @@ outputForeignStubs
            Maybe FilePath) -- C file created
 outputForeignStubs logger tmpfs dflags unit_state mod location stubs
  = do
-   let stub_h = mkStubPaths dflags (moduleName mod) location
+   let stub_h = mkStubPaths (initFinderOpts dflags) (moduleName mod) location
    stub_c <- newTempName logger tmpfs (tmpDir dflags) TFL_CurrentModule "c"
 
    case stubs of
diff --git a/compiler/GHC/Driver/Config/Finder.hs b/compiler/GHC/Driver/Config/Finder.hs
new file mode 100644
index 0000000000..4fa4278c09
--- /dev/null
+++ b/compiler/GHC/Driver/Config/Finder.hs
@@ -0,0 +1,26 @@
+module GHC.Driver.Config.Finder (
+    FinderOpts(..),
+    initFinderOpts
+  ) where
+
+import GHC.Prelude
+
+import GHC.Driver.Session
+import GHC.Unit.Finder
+
+-- | Create a new 'FinderOpts' from DynFlags.
+initFinderOpts :: DynFlags -> FinderOpts
+initFinderOpts flags = FinderOpts
+  { finder_importPaths = importPaths flags
+  , finder_lookupHomeInterfaces = isOneShot (ghcMode flags)
+  , finder_bypassHiFileCheck = MkDepend == (ghcMode flags)
+  , finder_ways = ways flags
+  , finder_enableSuggestions = gopt Opt_HelpfulErrors flags
+  , finder_hieDir = hieDir flags
+  , finder_hieSuf = hieSuf flags
+  , finder_hiDir = hiDir flags
+  , finder_hiSuf = hiSuf flags
+  , finder_objectDir = objectDir flags
+  , finder_objectSuf = objectSuf flags
+  , finder_stubDir = stubDir flags
+  }
diff --git a/compiler/GHC/Driver/Make.hs b/compiler/GHC/Driver/Make.hs
index 51fb469828..d40be12308 100644
--- a/compiler/GHC/Driver/Make.hs
+++ b/compiler/GHC/Driver/Make.hs
@@ -53,6 +53,7 @@ import GHC.Linker.Types
 
 import GHC.Runtime.Context
 
+import GHC.Driver.Config.Finder (initFinderOpts)
 import GHC.Driver.Config.Logger (initLogFlags)
 import GHC.Driver.Config.Parser (initParserOpts)
 import GHC.Driver.Config.Diagnostic
@@ -2311,9 +2312,10 @@ summariseFile hsc_env old_summaries src_fn mb_phase maybe_buf
         preimps@PreprocessedImports {..}
             <- getPreprocessedImports hsc_env src_fn mb_phase maybe_buf
 
+        let fopts = initFinderOpts (hsc_dflags hsc_env)
 
         -- Make a ModLocation for this file
-        location <- liftIO $ mkHomeModLocation (hsc_dflags hsc_env) pi_mod_name src_fn
+        location <- liftIO $ mkHomeModLocation fopts pi_mod_name src_fn
 
         -- Tell the Finder cache where it is, so that subsequent calls
         -- to findModule will find it, even if it's not on any search path
@@ -2428,6 +2430,7 @@ summariseModule hsc_env old_summary_map is_boot (L loc wanted_mod)
   | otherwise  = find_it
   where
     dflags    = hsc_dflags hsc_env
+    fopts        = initFinderOpts dflags
     home_unit = hsc_home_unit hsc_env
     fc        = hsc_FC hsc_env
     units     = hsc_units hsc_env
@@ -2439,7 +2442,7 @@ summariseModule hsc_env old_summary_map is_boot (L loc wanted_mod)
           old_summary location
 
     find_it = do
-        found <- findImportedModule fc units home_unit dflags wanted_mod Nothing
+        found <- findImportedModule fc fopts units home_unit wanted_mod Nothing
         case found of
              Found location mod
                 | isJust (ml_hs_file location) ->
diff --git a/compiler/GHC/Driver/MakeFile.hs b/compiler/GHC/Driver/MakeFile.hs
index 8207b37c7b..5719b7dc04 100644
--- a/compiler/GHC/Driver/MakeFile.hs
+++ b/compiler/GHC/Driver/MakeFile.hs
@@ -16,6 +16,7 @@ where
 import GHC.Prelude
 
 import qualified GHC
+import GHC.Driver.Config.Finder
 import GHC.Driver.Monad
 import GHC.Driver.Session
 import GHC.Driver.Ppr
@@ -291,9 +292,10 @@ findDependency hsc_env srcloc pkg imp is_boot include_pkg_deps = do
   let home_unit = hsc_home_unit hsc_env
   let units     = hsc_units hsc_env
   let dflags    = hsc_dflags hsc_env
+  let fopts     = initFinderOpts dflags
   -- Find the module; this will be fast because
   -- we've done it once during downsweep
-  r <- findImportedModule fc units home_unit dflags imp pkg
+  r <- findImportedModule fc fopts units home_unit imp pkg
   case r of
     Found loc _
         -- Home package: just depend on the .hi or hi-boot file
diff --git a/compiler/GHC/Driver/Pipeline/Monad.hs b/compiler/GHC/Driver/Pipeline/Monad.hs
index a760bb6022..f9067576ae 100644
--- a/compiler/GHC/Driver/Pipeline/Monad.hs
+++ b/compiler/GHC/Driver/Pipeline/Monad.hs
@@ -14,6 +14,7 @@ import GHC.Prelude
 import Control.Monad.IO.Class
 import qualified Data.Kind as K
 import GHC.Driver.Phases
+import GHC.Driver.Config.Finder
 import GHC.Utils.TmpFs
 import GHC.Driver.Session
 import GHC.Types.SourceFile
@@ -42,7 +43,7 @@ getLocation :: PipeEnv -> DynFlags -> HscSource -> ModuleName -> IO ModLocation
 getLocation pipe_env dflags src_flavour mod_name = do
     let PipeEnv{ src_basename=basename,
              src_suffix=suff } = pipe_env
-    location1 <- mkHomeModLocation2 dflags mod_name basename suff
+    location1 <- mkHomeModLocation2 fopts mod_name basename suff
 
     -- Boot-ify it if necessary
     let location2
@@ -69,6 +70,8 @@ getLocation pipe_env dflags src_flavour mod_name = do
                   = location3 { ml_obj_file = ofile }
                   | otherwise = location3
     return location4
+    where
+      fopts = initFinderOpts dflags
 
 data PipelineOutput
   = Temporary TempFileLifetime
diff --git a/compiler/GHC/Iface/Load.hs b/compiler/GHC/Iface/Load.hs
index f510e9bbda..157c26e49e 100644
--- a/compiler/GHC/Iface/Load.hs
+++ b/compiler/GHC/Iface/Load.hs
@@ -43,6 +43,7 @@ import {-# SOURCE #-} GHC.IfaceToCore
    ( tcIfaceDecls, tcIfaceRules, tcIfaceInst, tcIfaceFamInst
    , tcIfaceAnnotations, tcIfaceCompleteMatches )
 
+import GHC.Driver.Config.Finder
 import GHC.Driver.Env
 import GHC.Driver.Errors.Types
 import GHC.Driver.Session
@@ -318,9 +319,10 @@ loadSrcInterface_maybe doc mod want_boot maybe_pkg
   = do hsc_env <- getTopEnv
        let fc = hsc_FC hsc_env
        let dflags = hsc_dflags hsc_env
+       let fopts = initFinderOpts dflags
        let units = hsc_units hsc_env
        let home_unit = hsc_home_unit hsc_env
-       res <- liftIO $ findImportedModule fc units home_unit dflags mod maybe_pkg
+       res <- liftIO $ findImportedModule fc fopts units home_unit mod maybe_pkg
        case res of
            Found _ mod -> initIfaceTcRn $ loadInterface doc mod (ImportByUser want_boot)
            -- TODO: Make sure this error message is good
@@ -879,8 +881,9 @@ findAndReadIface logger name_cache fc hooks unit_state home_unit dflags doc_str
                        Just h  -> h
           return (Succeeded (iface, "<built in interface for GHC.Prim>"))
       else do
+          let fopts = initFinderOpts dflags
           -- Look for the file
-          mb_found <- liftIO (findExactModule fc dflags unit_state home_unit mod)
+          mb_found <- liftIO (findExactModule fc fopts unit_state home_unit mod)
           case mb_found of
               InstalledFound loc mod -> do
                   -- Found file, so read it
diff --git a/compiler/GHC/Iface/Recomp.hs b/compiler/GHC/Iface/Recomp.hs
index 72341ba147..2e2824a7cb 100644
--- a/compiler/GHC/Iface/Recomp.hs
+++ b/compiler/GHC/Iface/Recomp.hs
@@ -13,6 +13,7 @@ where
 import GHC.Prelude
 
 import GHC.Driver.Backend
+import GHC.Driver.Config.Finder
 import GHC.Driver.Env
 import GHC.Driver.Session
 import GHC.Driver.Ppr
@@ -454,7 +455,7 @@ checkDependencies hsc_env summary iface
  = do
     res <- liftIO $ traverse (\(mb_pkg, L _ mod) ->
               let reason = moduleNameString mod ++ " changed"
-              in classify reason <$> findImportedModule fc units home_unit dflags mod (mb_pkg))
+              in classify reason <$> findImportedModule fc fopts units home_unit mod (mb_pkg))
               (ms_imps summary ++ ms_srcimps summary)
     case sequence (res ++ [Right (fake_ghc_prim_import)| ms_ghc_prim_import summary]) of
       Left recomp -> return recomp
@@ -467,6 +468,7 @@ checkDependencies hsc_env summary iface
         return (res1 `mappend` res2)
  where
    dflags        = hsc_dflags hsc_env
+   fopts         = initFinderOpts dflags
    logger        = hsc_logger hsc_env
    fc            = hsc_FC hsc_env
    home_unit     = hsc_home_unit hsc_env
diff --git a/compiler/GHC/Linker/Loader.hs b/compiler/GHC/Linker/Loader.hs
index c9617f1c28..2c2e724d68 100644
--- a/compiler/GHC/Linker/Loader.hs
+++ b/compiler/GHC/Linker/Loader.hs
@@ -46,6 +46,7 @@ import GHC.Driver.Session
 import GHC.Driver.Ppr
 import GHC.Driver.Config
 import GHC.Driver.Config.Diagnostic
+import GHC.Driver.Config.Finder
 
 import GHC.Tc.Utils.Monad
 
@@ -754,7 +755,8 @@ getLinkDeps hsc_env hpt pls replace_osuf span mods
              let fc = hsc_FC hsc_env
              let home_unit = hsc_home_unit hsc_env
              let dflags = hsc_dflags hsc_env
-             mb_stuff <- findHomeModule fc home_unit dflags mod_name
+             let fopts = initFinderOpts dflags
+             mb_stuff <- findHomeModule fc fopts home_unit mod_name
              case mb_stuff of
                   Found loc mod -> found loc mod
                   _ -> no_obj mod_name
diff --git a/compiler/GHC/Runtime/Loader.hs b/compiler/GHC/Runtime/Loader.hs
index f64236350c..09f34b5e16 100644
--- a/compiler/GHC/Runtime/Loader.hs
+++ b/compiler/GHC/Runtime/Loader.hs
@@ -51,6 +51,7 @@ import GHC.Types.Name.Reader   ( RdrName, ImportSpec(..), ImpDeclSpec(..)
                                , greMangledName, mkRdrQual )
 
 import GHC.Unit.Finder         ( findPluginModule, FindResult(..) )
+import GHC.Driver.Config.Finder ( initFinderOpts )
 import GHC.Unit.Module   ( Module, ModuleName )
 import GHC.Unit.Module.ModIface
 
@@ -258,11 +259,12 @@ lookupRdrNameInModuleForPlugins :: HscEnv -> ModuleName -> RdrName
                                 -> IO (Maybe (Name, ModIface))
 lookupRdrNameInModuleForPlugins hsc_env mod_name rdr_name = do
     let dflags    = hsc_dflags hsc_env
+    let fopts     = initFinderOpts dflags
     let fc        = hsc_FC hsc_env
     let units     = hsc_units hsc_env
     let home_unit = hsc_home_unit hsc_env
     -- First find the unit the module resides in by searching exposed units and home modules
-    found_module <- findPluginModule fc units home_unit dflags mod_name
+    found_module <- findPluginModule fc fopts units home_unit mod_name
     case found_module of
         Found _ mod -> do
             -- Find the exports of the module
diff --git a/compiler/GHC/Tc/Gen/Splice.hs b/compiler/GHC/Tc/Gen/Splice.hs
index bcb77326e2..fcd1474afa 100644
--- a/compiler/GHC/Tc/Gen/Splice.hs
+++ b/compiler/GHC/Tc/Gen/Splice.hs
@@ -39,6 +39,7 @@ import GHC.Driver.Session
 import GHC.Driver.Env
 import GHC.Driver.Hooks
 import GHC.Driver.Config.Diagnostic
+import GHC.Driver.Config.Finder
 
 import GHC.Hs
 
@@ -1264,7 +1265,8 @@ instance TH.Quasi TcM where
       let fc        = hsc_FC hsc_env
       let home_unit = hsc_home_unit hsc_env
       let dflags    = hsc_dflags hsc_env
-      r <- liftIO $ findHomeModule fc home_unit dflags (mkModuleName plugin)
+      let fopts     = initFinderOpts dflags
+      r <- liftIO $ findHomeModule fc fopts home_unit (mkModuleName plugin)
       let err = hang
             (text "addCorePlugin: invalid plugin module "
                <+> text (show plugin)
diff --git a/compiler/GHC/Tc/Plugin.hs b/compiler/GHC/Tc/Plugin.hs
index fd5d21751e..0674f69903 100644
--- a/compiler/GHC/Tc/Plugin.hs
+++ b/compiler/GHC/Tc/Plugin.hs
@@ -77,6 +77,7 @@ import GHC.Types.TyThing
 import GHC.Core.TyCon
 import GHC.Core.DataCon
 import GHC.Core.Class
+import GHC.Driver.Config.Finder
 import GHC.Driver.Env
 import GHC.Utils.Outputable
 import GHC.Core.Type
@@ -102,7 +103,8 @@ findImportedModule mod_name mb_pkg = do
     let home_unit = hsc_home_unit hsc_env
     let units     = hsc_units hsc_env
     let dflags    = hsc_dflags hsc_env
-    tcPluginIO $ Finder.findImportedModule fc units home_unit dflags mod_name mb_pkg
+    let fopts     = initFinderOpts dflags
+    tcPluginIO $ Finder.findImportedModule fc fopts units home_unit mod_name mb_pkg
 
 lookupOrig :: Module -> OccName -> TcPluginM Name
 lookupOrig mod = unsafeTcPluginTcM . IfaceEnv.lookupOrig mod
diff --git a/compiler/GHC/Tc/Utils/Backpack.hs b/compiler/GHC/Tc/Utils/Backpack.hs
index ffaa882cf6..a2599c3a57 100644
--- a/compiler/GHC/Tc/Utils/Backpack.hs
+++ b/compiler/GHC/Tc/Utils/Backpack.hs
@@ -19,6 +19,8 @@ module GHC.Tc.Utils.Backpack (
 
 import GHC.Prelude
 
+
+import GHC.Driver.Config.Finder
 import GHC.Driver.Env
 import GHC.Driver.Ppr
 import GHC.Driver.Session
@@ -322,7 +324,7 @@ implicitRequirements' :: HscEnv
 implicitRequirements' hsc_env normal_imports
   = fmap concat $
     forM normal_imports $ \(mb_pkg, L _ imp) -> do
-        found <- findImportedModule fc units home_unit dflags imp mb_pkg
+        found <- findImportedModule fc fopts units home_unit imp mb_pkg
         case found of
             Found _ mod | not (isHomeModule home_unit mod) ->
                 return (uniqDSetToList (moduleFreeHoles mod))
@@ -332,6 +334,7 @@ implicitRequirements' hsc_env normal_imports
     home_unit = hsc_home_unit hsc_env
     units     = hsc_units hsc_env
     dflags    = hsc_dflags hsc_env
+    fopts     = initFinderOpts dflags
 
 -- | Like @implicitRequirements'@, but returns either the module name, if it is
 -- a free hole, or the instantiated unit the imported module is from, so that
@@ -347,10 +350,11 @@ implicitRequirementsShallow hsc_env normal_imports = go ([], []) normal_imports
   home_unit = hsc_home_unit hsc_env
   units     = hsc_units hsc_env
   dflags    = hsc_dflags hsc_env
+  fopts        = initFinderOpts dflags
 
   go acc [] = pure acc
   go (accL, accR) ((mb_pkg, L _ imp):imports) = do
-    found <- findImportedModule fc units home_unit dflags imp mb_pkg
+    found <- findImportedModule fc fopts units home_unit imp mb_pkg
     let acc' = case found of
           Found _ mod | not (isHomeModule home_unit mod) ->
               case moduleUnit mod of
diff --git a/compiler/GHC/Unit/Finder.hs b/compiler/GHC/Unit/Finder.hs
index a99c4b68c0..f0ecfb2ba7 100644
--- a/compiler/GHC/Unit/Finder.hs
+++ b/compiler/GHC/Unit/Finder.hs
@@ -10,6 +10,7 @@
 module GHC.Unit.Finder (
     FindResult(..),
     InstalledFindResult(..),
+    FinderOpts(..),
     FinderCache,
     initFinderCache,
     flushFinderCaches,
@@ -32,13 +33,10 @@ module GHC.Unit.Finder (
 
     -- Hash cache
     lookupFileCache
-
   ) where
 
 import GHC.Prelude
 
-import GHC.Driver.Session
-
 import GHC.Platform.Ways
 
 import GHC.Builtin.Names ( gHC_PRIM )
@@ -125,6 +123,38 @@ lookupFileCache (FinderCache _ ref) key = do
 -- -----------------------------------------------------------------------------
 -- The three external entry points
 
+-- | Locations and information the finder cares about.
+--
+-- Should be taken from 'DynFlags' via 'initFinderOpts'.
+data FinderOpts = FinderOpts
+  { finder_importPaths :: [FilePath]
+      -- ^ Where are we allowed to look for Modules and Source files
+  , finder_lookupHomeInterfaces :: Bool
+      -- ^ When looking up a home module:
+      --
+      --    * 'True':  search interface files (e.g. in '-c' mode)
+      --    * 'False': search source files (e.g. in '--make' mode)
+
+  , finder_bypassHiFileCheck :: Bool
+      -- ^ Don't check that an imported interface file actually exists
+      -- if it can only be at one location. The interface will be reported
+      -- as `InstalledFound` even if the file doesn't exist, so this is
+      -- only useful in specific cases (e.g. to generate dependencies
+      -- with `ghc -M`)
+  , finder_ways :: Ways
+  , finder_enableSuggestions :: Bool
+      -- ^ If we encounter unknown modules, should we suggest modules
+      -- that have a similar name.
+  , finder_hieDir :: Maybe FilePath
+  , finder_hieSuf :: String
+  , finder_hiDir :: Maybe FilePath
+  , finder_hiSuf :: String
+  , finder_objectDir :: Maybe FilePath
+  , finder_objectSuf :: String
+  , finder_stubDir :: Maybe FilePath
+  }
+
+
 -- | 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
@@ -133,35 +163,35 @@ lookupFileCache (FinderCache _ ref) key = do
 
 findImportedModule
   :: FinderCache
+  -> FinderOpts
   -> UnitState
   -> HomeUnit
-  -> DynFlags
   -> ModuleName
   -> Maybe FastString
   -> IO FindResult
-findImportedModule fc units home_unit dflags mod_name mb_pkg =
+findImportedModule fc fopts units home_unit mod_name mb_pkg =
   case mb_pkg of
         Nothing                        -> unqual_import
         Just pkg | pkg == fsLit "this" -> home_import -- "this" is special
                  | otherwise           -> pkg_import
   where
-    home_import   = findHomeModule fc home_unit dflags mod_name
+    home_import   = findHomeModule fc fopts home_unit mod_name
 
-    pkg_import    = findExposedPackageModule fc units dflags mod_name mb_pkg
+    pkg_import    = findExposedPackageModule fc fopts units  mod_name mb_pkg
 
     unqual_import = home_import
                     `orIfNotFound`
-                    findExposedPackageModule fc units dflags mod_name Nothing
+                    findExposedPackageModule fc fopts units mod_name Nothing
 
 -- | 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 -> UnitState -> HomeUnit -> DynFlags -> ModuleName -> IO FindResult
-findPluginModule fc units home_unit dflags mod_name =
-  findHomeModule fc home_unit dflags mod_name
+findPluginModule :: FinderCache -> FinderOpts -> UnitState -> HomeUnit -> ModuleName -> IO FindResult
+findPluginModule fc fopts units home_unit mod_name =
+  findHomeModule fc fopts home_unit mod_name
   `orIfNotFound`
-  findExposedPluginPackageModule fc units dflags 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
@@ -169,11 +199,11 @@ findPluginModule fc units home_unit dflags mod_name =
 -- reading the interface for a module mentioned by another interface,
 -- for example (a "system import").
 
-findExactModule :: FinderCache -> DynFlags -> UnitState -> HomeUnit -> InstalledModule -> IO InstalledFindResult
-findExactModule fc dflags unit_state home_unit mod = do
+findExactModule :: FinderCache -> FinderOpts -> UnitState -> HomeUnit -> InstalledModule -> IO InstalledFindResult
+findExactModule fc fopts unit_state home_unit mod = do
   if isHomeInstalledModule home_unit mod
-    then findInstalledHomeModule fc dflags home_unit (moduleName mod)
-    else findPackageModule fc unit_state dflags mod
+    then findInstalledHomeModule fc fopts home_unit (moduleName mod)
+    else findPackageModule fc unit_state fopts mod
 
 -- -----------------------------------------------------------------------------
 -- Helpers
@@ -213,21 +243,21 @@ homeSearchCache fc home_unit mod_name do_this = do
   let mod = mkHomeInstalledModule home_unit mod_name
   modLocationCache fc mod do_this
 
-findExposedPackageModule :: FinderCache -> UnitState -> DynFlags -> ModuleName -> Maybe FastString -> IO FindResult
-findExposedPackageModule fc units dflags mod_name mb_pkg =
-  findLookupResult fc dflags
+findExposedPackageModule :: FinderCache -> FinderOpts -> UnitState -> ModuleName -> Maybe FastString -> IO FindResult
+findExposedPackageModule fc fopts units mod_name mb_pkg =
+  findLookupResult fc fopts
     $ lookupModuleWithSuggestions units mod_name mb_pkg
 
-findExposedPluginPackageModule :: FinderCache -> UnitState -> DynFlags -> ModuleName -> IO FindResult
-findExposedPluginPackageModule fc units dflags mod_name =
-  findLookupResult fc dflags
+findExposedPluginPackageModule :: FinderCache -> FinderOpts -> UnitState -> ModuleName -> IO FindResult
+findExposedPluginPackageModule fc fopts units mod_name =
+  findLookupResult fc fopts
     $ lookupPluginModuleWithSuggestions units mod_name Nothing
 
-findLookupResult :: FinderCache -> DynFlags -> LookupResult -> IO FindResult
-findLookupResult fc dflags r = case r of
+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 dflags im (fst pkg_conf)
+       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
@@ -260,7 +290,7 @@ findLookupResult fc dflags r = case r of
                           , fr_suggestions = [] })
      LookupNotFound suggest -> do
        let suggest'
-             | gopt Opt_HelpfulErrors dflags = suggest
+             | finder_enableSuggestions fopts = suggest
              | otherwise = []
        return (NotFound{ fr_paths = [], fr_pkg = Nothing
                        , fr_pkgs_hidden = []
@@ -293,10 +323,10 @@ uncacheModule fc home_unit mod_name = do
 -- -----------------------------------------------------------------------------
 --      The internal workers
 
-findHomeModule :: FinderCache -> HomeUnit -> DynFlags -> ModuleName -> IO FindResult
-findHomeModule fc home_unit dflags mod_name = do
+findHomeModule :: FinderCache -> FinderOpts -> HomeUnit -> ModuleName -> IO FindResult
+findHomeModule fc fopts  home_unit mod_name = do
   let uid       = homeUnitAsUnit home_unit
-  r <- findInstalledHomeModule fc dflags home_unit mod_name
+  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
@@ -325,32 +355,32 @@ findHomeModule fc home_unit dflags mod_name = do
 --
 --  4. Some special-case code in GHCi (ToDo: Figure out why that needs to
 --  call this.)
-findInstalledHomeModule :: FinderCache -> DynFlags -> HomeUnit -> ModuleName -> IO InstalledFindResult
-findInstalledHomeModule fc dflags home_unit mod_name = do
+findInstalledHomeModule :: FinderCache -> FinderOpts -> HomeUnit -> ModuleName -> IO InstalledFindResult
+findInstalledHomeModule fc fopts home_unit mod_name = do
   homeSearchCache fc home_unit mod_name $
    let
-     home_path = importPaths dflags
-     hisuf = hiSuf dflags
+     home_path = finder_importPaths fopts
+     hisuf = finder_hiSuf fopts
      mod = mkHomeInstalledModule home_unit mod_name
 
      source_exts =
-      [ ("hs",   mkHomeModLocationSearched dflags mod_name "hs")
-      , ("lhs",  mkHomeModLocationSearched dflags mod_name "lhs")
-      , ("hsig",  mkHomeModLocationSearched dflags mod_name "hsig")
-      , ("lhsig",  mkHomeModLocationSearched dflags mod_name "lhsig")
+      [ ("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 dflags mod_name)
-               , (addBootSuffix hisuf,  mkHomeModHiOnlyLocation dflags mod_name)
+     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 | isOneShot (ghcMode dflags) = hi_exts
-          | otherwise                  = source_exts
+     exts | finder_lookupHomeInterfaces fopts = hi_exts
+          | otherwise                         = source_exts
    in
 
    -- special case for GHC.Prim; we won't find it in the filesystem.
@@ -362,12 +392,12 @@ findInstalledHomeModule fc dflags home_unit mod_name = do
 
 
 -- | Search for a module in external packages only.
-findPackageModule :: FinderCache -> UnitState -> DynFlags -> InstalledModule -> IO InstalledFindResult
-findPackageModule fc unit_state dflags mod = do
+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 dflags mod u
+     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
@@ -376,8 +406,8 @@ findPackageModule fc unit_state dflags mod = do
 -- 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 -> DynFlags -> InstalledModule -> UnitInfo -> IO InstalledFindResult
-findPackageModule_ fc dflags mod pkg_conf = do
+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 $
@@ -388,20 +418,20 @@ findPackageModule_ fc dflags mod pkg_conf = do
           else
 
     let
-       tag = waysBuildTag (ways dflags)
+       tag = waysBuildTag (finder_ways fopts)
 
              -- hi-suffix for packages depends on the build tag.
        package_hisuf | null tag  = "hi"
                      | otherwise = tag ++ "_hi"
 
-       mk_hi_loc = mkHiOnlyModLocation dflags package_hisuf
+       mk_hi_loc = mkHiOnlyModLocation fopts package_hisuf
 
        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] | MkDepend <- ghcMode dflags -> do
+      [one] | finder_bypassHiFileCheck fopts -> do
             -- there's only one place that this .hi file can be, so
             -- don't bother looking for it.
             let basename = moduleNameSlashes (moduleName mod)
@@ -443,10 +473,10 @@ searchPathExts paths mod exts = search to_search
         then do { loc <- mk_result; return (InstalledFound loc mod) }
         else search rest
 
-mkHomeModLocationSearched :: DynFlags -> ModuleName -> FileExt
+mkHomeModLocationSearched :: FinderOpts -> ModuleName -> FileExt
                           -> FilePath -> BaseName -> IO ModLocation
-mkHomeModLocationSearched dflags mod suff path basename =
-  mkHomeModLocation2 dflags mod (path </> basename) suff
+mkHomeModLocationSearched fopts mod suff path basename =
+  mkHomeModLocation2 fopts mod (path </> basename) suff
 
 -- -----------------------------------------------------------------------------
 -- Constructing a home module location
@@ -481,43 +511,43 @@ mkHomeModLocationSearched dflags mod suff path basename =
 -- ext
 --      The filename extension of the source file (usually "hs" or "lhs").
 
-mkHomeModLocation :: DynFlags -> ModuleName -> FilePath -> IO ModLocation
+mkHomeModLocation :: FinderOpts -> ModuleName -> FilePath -> IO ModLocation
 mkHomeModLocation dflags mod src_filename = do
    let (basename,extension) = splitExtension src_filename
    mkHomeModLocation2 dflags mod basename extension
 
-mkHomeModLocation2 :: DynFlags
+mkHomeModLocation2 :: FinderOpts
                    -> ModuleName
                    -> FilePath  -- Of source module, without suffix
                    -> String    -- Suffix
                    -> IO ModLocation
-mkHomeModLocation2 dflags mod src_basename ext = do
+mkHomeModLocation2 fopts mod src_basename ext = do
    let mod_basename = moduleNameSlashes mod
 
-       obj_fn = mkObjPath  dflags src_basename mod_basename
-       hi_fn  = mkHiPath   dflags src_basename mod_basename
-       hie_fn = mkHiePath  dflags src_basename mod_basename
+       obj_fn = mkObjPath  fopts src_basename mod_basename
+       hi_fn  = mkHiPath   fopts src_basename mod_basename
+       hie_fn = mkHiePath  fopts src_basename mod_basename
 
    return (ModLocation{ ml_hs_file   = Just (src_basename <.> ext),
                         ml_hi_file   = hi_fn,
                         ml_obj_file  = obj_fn,
                         ml_hie_file  = hie_fn })
 
-mkHomeModHiOnlyLocation :: DynFlags
+mkHomeModHiOnlyLocation :: FinderOpts
                         -> ModuleName
                         -> FilePath
                         -> BaseName
                         -> IO ModLocation
-mkHomeModHiOnlyLocation dflags mod path basename = do
-   loc <- mkHomeModLocation2 dflags mod (path </> basename) ""
+mkHomeModHiOnlyLocation fopts mod path basename = do
+   loc <- mkHomeModLocation2 fopts mod (path </> basename) ""
    return loc { ml_hs_file = Nothing }
 
-mkHiOnlyModLocation :: DynFlags -> Suffix -> FilePath -> String
+mkHiOnlyModLocation :: FinderOpts -> Suffix -> FilePath -> String
                     -> IO ModLocation
-mkHiOnlyModLocation dflags hisuf path basename
+mkHiOnlyModLocation fopts hisuf path basename
  = do let full_basename = path </> basename
-          obj_fn = mkObjPath  dflags full_basename basename
-          hie_fn = mkHiePath  dflags full_basename basename
+          obj_fn = mkObjPath fopts full_basename basename
+          hie_fn = mkHiePath fopts full_basename basename
       return ModLocation{    ml_hs_file   = Nothing,
                              ml_hi_file   = full_basename <.> hisuf,
                                 -- Remove the .hi-boot suffix from
@@ -531,14 +561,14 @@ mkHiOnlyModLocation dflags hisuf path basename
 -- | Constructs the filename of a .o file for a given source file.
 -- Does /not/ check whether the .o file exists
 mkObjPath
-  :: DynFlags
+  :: FinderOpts
   -> FilePath           -- the filename of the source file, minus the extension
   -> String             -- the module name with dots replaced by slashes
   -> FilePath
-mkObjPath dflags basename mod_basename = obj_basename <.> osuf
+mkObjPath fopts basename mod_basename = obj_basename <.> osuf
   where
-                odir = objectDir dflags
-                osuf = objectSuf dflags
+                odir = finder_objectDir fopts
+                osuf = finder_objectSuf fopts
 
                 obj_basename | Just dir <- odir = dir </> mod_basename
                              | otherwise        = basename
@@ -547,14 +577,14 @@ mkObjPath dflags basename mod_basename = obj_basename <.> osuf
 -- | Constructs the filename of a .hi file for a given source file.
 -- Does /not/ check whether the .hi file exists
 mkHiPath
-  :: DynFlags
+  :: FinderOpts
   -> FilePath           -- the filename of the source file, minus the extension
   -> String             -- the module name with dots replaced by slashes
   -> FilePath
-mkHiPath dflags basename mod_basename = hi_basename <.> hisuf
+mkHiPath fopts basename mod_basename = hi_basename <.> hisuf
  where
-                hidir = hiDir dflags
-                hisuf = hiSuf dflags
+                hidir = finder_hiDir fopts
+                hisuf = finder_hiSuf fopts
 
                 hi_basename | Just dir <- hidir = dir </> mod_basename
                             | otherwise         = basename
@@ -562,14 +592,14 @@ mkHiPath dflags basename mod_basename = hi_basename <.> hisuf
 -- | Constructs the filename of a .hie file for a given source file.
 -- Does /not/ check whether the .hie file exists
 mkHiePath
-  :: DynFlags
+  :: FinderOpts
   -> FilePath           -- the filename of the source file, minus the extension
   -> String             -- the module name with dots replaced by slashes
   -> FilePath
-mkHiePath dflags basename mod_basename = hie_basename <.> hiesuf
+mkHiePath fopts basename mod_basename = hie_basename <.> hiesuf
  where
-                hiedir = hieDir dflags
-                hiesuf = hieSuf dflags
+                hiedir = finder_hieDir fopts
+                hiesuf = finder_hieSuf fopts
 
                 hie_basename | Just dir <- hiedir = dir </> mod_basename
                              | otherwise          = basename
@@ -583,14 +613,14 @@ mkHiePath dflags basename mod_basename = hie_basename <.> hiesuf
 -- from other available information, and they're only rarely needed.
 
 mkStubPaths
-  :: DynFlags
+  :: FinderOpts
   -> ModuleName
   -> ModLocation
   -> FilePath
 
-mkStubPaths dflags mod location
+mkStubPaths fopts mod location
   = let
-        stubdir = stubDir dflags
+        stubdir = finder_stubDir fopts
 
         mod_basename = moduleNameSlashes mod
         src_basename = dropExtension $ expectJust "mkStubPaths"
diff --git a/compiler/ghc.cabal.in b/compiler/ghc.cabal.in
index 1176aa9c89..55e37b1d60 100644
--- a/compiler/ghc.cabal.in
+++ b/compiler/ghc.cabal.in
@@ -391,6 +391,7 @@ Library
         GHC.Driver.Config
         GHC.Driver.Config.CmmToAsm
         GHC.Driver.Config.Diagnostic
+        GHC.Driver.Config.Finder
         GHC.Driver.Config.Logger
         GHC.Driver.Config.Parser
         GHC.Driver.Env
diff --git a/ghc/GHCi/UI.hs b/ghc/GHCi/UI.hs
index f861c9b82a..d1e49dadd3 100644
--- a/ghc/GHCi/UI.hs
+++ b/ghc/GHCi/UI.hs
@@ -51,6 +51,7 @@ import GHC.Driver.Session as DynFlags
 import GHC.Driver.Ppr hiding (printForUser)
 import GHC.Utils.Error hiding (traceCmd)
 import GHC.Driver.Monad ( modifySession )
+import GHC.Driver.Config.Finder (initFinderOpts)
 import GHC.Driver.Config.Parser (initParserOpts)
 import GHC.Driver.Config.Diagnostic
 import qualified GHC
@@ -2035,8 +2036,9 @@ addModule files = do
       let home_unit = hsc_home_unit hsc_env
       let units     = hsc_units hsc_env
       let dflags    = hsc_dflags hsc_env
+      let fopts     = initFinderOpts dflags
       result <- liftIO $
-        Finder.findImportedModule fc units home_unit dflags m (Just (fsLit "this"))
+        Finder.findImportedModule fc fopts units home_unit m (Just (fsLit "this"))
       case result of
         Found _ _ -> return True
         _ -> (liftIO $ putStrLn $
diff --git a/ghc/Main.hs b/ghc/Main.hs
index ad975d1840..9c4c012247 100644
--- a/ghc/Main.hs
+++ b/ghc/Main.hs
@@ -29,6 +29,7 @@ import GHC.Driver.Pipeline  ( oneShot, compileFile )
 import GHC.Driver.MakeFile  ( doMkDependHS )
 import GHC.Driver.Backpack  ( doBackpack )
 import GHC.Driver.Plugins
+import GHC.Driver.Config.Finder (initFinderOpts)
 import GHC.Driver.Config.Logger (initLogFlags)
 import GHC.Driver.Config.Diagnostic
 
@@ -851,12 +852,13 @@ abiHash strs = do
   let home_unit = hsc_home_unit hsc_env
   let units     = hsc_units hsc_env
   let dflags    = hsc_dflags hsc_env
+  let fopts     = initFinderOpts dflags
 
   liftIO $ do
 
   let find_it str = do
          let modname = mkModuleName str
-         r <- findImportedModule fc units home_unit dflags modname Nothing
+         r <- findImportedModule fc fopts units home_unit modname Nothing
          case r of
            Found _ m -> return m
            _error    -> throwGhcException $ CmdLineError $ showSDoc dflags $
diff --git a/testsuite/tests/count-deps/CountDepsAst.stdout b/testsuite/tests/count-deps/CountDepsAst.stdout
index e9ee86cf09..184f20d7d0 100644
--- a/testsuite/tests/count-deps/CountDepsAst.stdout
+++ b/testsuite/tests/count-deps/CountDepsAst.stdout
@@ -1,4 +1,4 @@
-Found 273 Language.Haskell.Syntax module dependencies
+Found 274 Language.Haskell.Syntax module dependencies
 GHC.Builtin.Names
 GHC.Builtin.PrimOps
 GHC.Builtin.Types
@@ -84,6 +84,7 @@ GHC.Data.TrieMap
 GHC.Driver.Backend
 GHC.Driver.CmdLine
 GHC.Driver.Config.Diagnostic
+GHC.Driver.Config.Finder
 GHC.Driver.Config.Logger
 GHC.Driver.Env
 GHC.Driver.Env.Types
diff --git a/testsuite/tests/count-deps/CountDepsParser.stdout b/testsuite/tests/count-deps/CountDepsParser.stdout
index daaf8294a1..a2ef4064f5 100644
--- a/testsuite/tests/count-deps/CountDepsParser.stdout
+++ b/testsuite/tests/count-deps/CountDepsParser.stdout
@@ -1,4 +1,4 @@
-Found 279 GHC.Parser module dependencies
+Found 280 GHC.Parser module dependencies
 GHC.Builtin.Names
 GHC.Builtin.PrimOps
 GHC.Builtin.Types
@@ -85,6 +85,7 @@ GHC.Driver.Backend
 GHC.Driver.Backpack.Syntax
 GHC.Driver.CmdLine
 GHC.Driver.Config.Diagnostic
+GHC.Driver.Config.Finder
 GHC.Driver.Config.Logger
 GHC.Driver.Env
 GHC.Driver.Env.Types