iface/MkIface.hs

    {-
    (c) The University of Glasgow 2006-2008
    (c) The GRASP/AQUA Project, Glasgow University, 1993-1998
    -}

    {-# LANGUAGE CPP, NondecreasingIndentation #-}

    -- | Module for constructing @ModIface@ values (interface files),
    -- writing them to disk and comparing two versions to see if
    -- recompilation is required.
    module MkIface (
            mkUsedNames,
            mkDependencies,
            mkIface,        -- Build a ModIface from a ModGuts,
                            -- including computing version information

            mkIfaceTc,

            writeIfaceFile, -- Write the interface file

            checkOldIface,  -- See if recompilation is required, by
                            -- comparing version information
            RecompileRequired(..), recompileRequired,

            tyThingToIfaceDecl -- Converting things to their Iface equivalents
     ) where

    {-
      -----------------------------------------------
              Recompilation checking
      -----------------------------------------------

    A complete description of how recompilation checking works can be
    found in the wiki commentary:

     http://ghc.haskell.org/trac/ghc/wiki/Commentary/Compiler/RecompilationAvoidance

    Please read the above page for a top-down description of how this all
    works.  Notes below cover specific issues related to the implementation.

    Basic idea:

      * In the mi_usages information in an interface, we record the
        fingerprint of each free variable of the module

      * In mkIface, we compute the fingerprint of each exported thing A.f.
        For each external thing that A.f refers to, we include the fingerprint
        of the external reference when computing the fingerprint of A.f.  So
        if anything that A.f depends on changes, then A.f's fingerprint will
        change.
        Also record any dependent files added with
          * addDependentFile
          * #include
          * -optP-include

      * In checkOldIface we compare the mi_usages for the module with
        the actual fingerprint for all each thing recorded in mi_usages
    -}

    #include "HsVersions.h"

    import IfaceSyn
    import LoadIface
    import FlagChecker

    import Id
    import IdInfo
    import Demand
    import Coercion( tidyCo )
    import Annotations
    import CoreSyn
    import CoreFVs
    import Class
    import Kind
    import TyCon
    import CoAxiom
    import ConLike
    import DataCon
    import PatSyn
    import Type
    import TcType
    import TysPrim ( alphaTyVars )
    import InstEnv
    import FamInstEnv
    import TcRnMonad
    import HsSyn
    import HscTypes
    import Finder
    import DynFlags
    import VarEnv
    import VarSet
    import Var
    import Name
    import Avail
    import RdrName
    import NameEnv
    import NameSet
    import Module
    import BinIface
    import ErrUtils
    import Digraph
    import SrcLoc
    import Outputable
    import BasicTypes       hiding ( SuccessFlag(..) )
    import UniqFM
    import Unique
    import Util             hiding ( eqListBy )
    import FastString
    import Maybes
    import ListSetOps
    import Binary
    import Fingerprint
    import Bag
    import Exception

    import Control.Monad
    import Data.Function
    import Data.List
    import Data.Map (Map)
    import qualified Data.Map as Map
    import Data.Ord
    import Data.IORef
    import System.Directory
    import System.FilePath

    {-
    ************************************************************************
    *                                                                      *
    \subsection{Completing an interface}
    *                                                                      *
    ************************************************************************
    -}

    mkIface :: HscEnv
            -> Maybe Fingerprint    -- The old fingerprint, if we have it
            -> ModDetails           -- The trimmed, tidied interface
            -> ModGuts              -- Usages, deprecations, etc
            -> IO (Messages,
                   Maybe (ModIface, -- The new one
                          Bool))    -- True <=> there was an old Iface, and the
                                    --          new one is identical, so no need
                                    --          to write it

    mkIface hsc_env maybe_old_fingerprint mod_details
             ModGuts{     mg_module       = this_mod,
                          mg_boot         = is_boot,
                          mg_used_names   = used_names,
                          mg_used_th      = used_th,
                          mg_deps         = deps,
                          mg_dir_imps     = dir_imp_mods,
                          mg_rdr_env      = rdr_env,
                          mg_fix_env      = fix_env,
                          mg_warns        = warns,
                          mg_hpc_info     = hpc_info,
                          mg_safe_haskell = safe_mode,
                          mg_trust_pkg    = self_trust,
                          mg_dependent_files = dependent_files
                        }
            = mkIface_ hsc_env maybe_old_fingerprint
                       this_mod is_boot used_names used_th deps rdr_env fix_env
                       warns hpc_info dir_imp_mods self_trust dependent_files
                       safe_mode mod_details

    -- | make an interface from the results of typechecking only.  Useful
    -- for non-optimising compilation, or where we aren't generating any
    -- object code at all ('HscNothing').
    mkIfaceTc :: HscEnv
              -> Maybe Fingerprint  -- The old fingerprint, if we have it
              -> SafeHaskellMode    -- The safe haskell mode
              -> ModDetails         -- gotten from mkBootModDetails, probably
              -> TcGblEnv           -- Usages, deprecations, etc
              -> IO (Messages, Maybe (ModIface, Bool))
    mkIfaceTc hsc_env maybe_old_fingerprint safe_mode mod_details
      tc_result@TcGblEnv{ tcg_mod = this_mod,
                          tcg_src = hsc_src,
                          tcg_imports = imports,
                          tcg_rdr_env = rdr_env,
                          tcg_fix_env = fix_env,
                          tcg_warns = warns,
                          tcg_hpc = other_hpc_info,
                          tcg_th_splice_used = tc_splice_used,
                          tcg_dependent_files = dependent_files
                        }
      = do
              let used_names = mkUsedNames tc_result
              deps <- mkDependencies tc_result
              let hpc_info = emptyHpcInfo other_hpc_info
              used_th <- readIORef tc_splice_used
              dep_files <- (readIORef dependent_files)
              mkIface_ hsc_env maybe_old_fingerprint
                       this_mod (hsc_src == HsBootFile) used_names
                       used_th deps rdr_env
                       fix_env warns hpc_info (imp_mods imports)
                       (imp_trust_own_pkg imports) dep_files safe_mode mod_details

    mkUsedNames :: TcGblEnv -> NameSet
    mkUsedNames TcGblEnv{ tcg_dus = dus } = allUses dus

    -- | Extract information from the rename and typecheck phases to produce
    -- a dependencies information for the module being compiled.
    mkDependencies :: TcGblEnv -> IO Dependencies
    mkDependencies
              TcGblEnv{ tcg_mod = mod,
                        tcg_imports = imports,
                        tcg_th_used = th_var
                      }
     = do
          -- Template Haskell used?
          th_used <- readIORef th_var
          let dep_mods = eltsUFM (delFromUFM (imp_dep_mods imports) (moduleName mod))
                    -- M.hi-boot can be in the imp_dep_mods, but we must remove
                    -- it before recording the modules on which this one depends!
                    -- (We want to retain M.hi-boot in imp_dep_mods so that
                    --  loadHiBootInterface can see if M's direct imports depend
                    --  on M.hi-boot, and hence that we should do the hi-boot consistency
                    --  check.)

              pkgs | th_used   = insertList thPackageKey (imp_dep_pkgs imports)
                   | otherwise = imp_dep_pkgs imports

              -- Set the packages required to be Safe according to Safe Haskell.
              -- See Note [RnNames . Tracking Trust Transitively]
              sorted_pkgs = sortBy stablePackageKeyCmp pkgs
              trust_pkgs  = imp_trust_pkgs imports
              dep_pkgs'   = map (\x -> (x, x `elem` trust_pkgs)) sorted_pkgs

          return Deps { dep_mods   = sortBy (stableModuleNameCmp `on` fst) dep_mods,
                        dep_pkgs   = dep_pkgs',
                        dep_orphs  = sortBy stableModuleCmp (imp_orphs  imports),
                        dep_finsts = sortBy stableModuleCmp (imp_finsts imports) }
                        -- sort to get into canonical order
                        -- NB. remember to use lexicographic ordering

    mkIface_ :: HscEnv -> Maybe Fingerprint -> Module -> IsBootInterface
             -> NameSet -> Bool -> Dependencies -> GlobalRdrEnv
             -> NameEnv FixItem -> Warnings -> HpcInfo
             -> ImportedMods -> Bool
             -> [FilePath]
             -> SafeHaskellMode
             -> ModDetails
             -> IO (Messages, Maybe (ModIface, Bool))
    mkIface_ hsc_env maybe_old_fingerprint
             this_mod is_boot used_names used_th deps rdr_env fix_env src_warns
             hpc_info dir_imp_mods pkg_trust_req dependent_files safe_mode
             ModDetails{  md_insts     = insts,
                          md_fam_insts = fam_insts,
                          md_rules     = rules,
                          md_anns      = anns,
                          md_vect_info = vect_info,
                          md_types     = type_env,
                          md_exports   = exports }
    -- NB:  notice that mkIface does not look at the bindings
    --      only at the TypeEnv.  The previous Tidy phase has
    --      put exactly the info into the TypeEnv that we want
    --      to expose in the interface

      = do
        usages  <- mkUsageInfo hsc_env this_mod dir_imp_mods used_names dependent_files

        let entities = typeEnvElts type_env
            decls  = [ tyThingToIfaceDecl entity
                     | entity <- entities,
                       let name = getName entity,
                       not (isImplicitTyThing entity),
                          -- No implicit Ids and class tycons in the interface file
                       not (isWiredInName name),
                          -- Nor wired-in things; the compiler knows about them anyhow
                       nameIsLocalOrFrom this_mod name  ]
                          -- Sigh: see Note [Root-main Id] in TcRnDriver

            fixities    = [(occ,fix) | FixItem occ fix <- nameEnvElts fix_env]
            warns       = src_warns
            iface_rules = map (coreRuleToIfaceRule this_mod) rules
            iface_insts = map instanceToIfaceInst insts
            iface_fam_insts = map famInstToIfaceFamInst fam_insts
            iface_vect_info = flattenVectInfo vect_info
            trust_info  = setSafeMode safe_mode
            annotations = map mkIfaceAnnotation anns
            sig_of = getSigOf dflags (moduleName this_mod)

            intermediate_iface = ModIface {
                  mi_module      = this_mod,
                  mi_sig_of      = sig_of,
                  mi_boot        = is_boot,
                  mi_deps        = deps,
                  mi_usages      = usages,
                  mi_exports     = mkIfaceExports exports,

                  -- Sort these lexicographically, so that
                  -- the result is stable across compilations
                  mi_insts       = sortBy cmp_inst     iface_insts,
                  mi_fam_insts   = sortBy cmp_fam_inst iface_fam_insts,
                  mi_rules       = sortBy cmp_rule     iface_rules,

                  mi_vect_info   = iface_vect_info,

                  mi_fixities    = fixities,
                  mi_warns       = warns,
                  mi_anns        = annotations,
                  mi_globals     = maybeGlobalRdrEnv rdr_env,

                  -- Left out deliberately: filled in by addFingerprints
                  mi_iface_hash  = fingerprint0,
                  mi_mod_hash    = fingerprint0,
                  mi_flag_hash   = fingerprint0,
                  mi_exp_hash    = fingerprint0,
                  mi_used_th     = used_th,
                  mi_orphan_hash = fingerprint0,
                  mi_orphan      = False, -- Always set by addFingerprints, but
                                          -- it's a strict field, so we can't omit it.
                  mi_finsts      = False, -- Ditto
                  mi_decls       = deliberatelyOmitted "decls",
                  mi_hash_fn     = deliberatelyOmitted "hash_fn",
                  mi_hpc         = isHpcUsed hpc_info,
                  mi_trust       = trust_info,
                  mi_trust_pkg   = pkg_trust_req,

                  -- And build the cached values
                  mi_warn_fn     = mkIfaceWarnCache warns,
                  mi_fix_fn      = mkIfaceFixCache fixities }

        (new_iface, no_change_at_all)
              <- {-# SCC "versioninfo" #-}
                       addFingerprints hsc_env maybe_old_fingerprint
                                       intermediate_iface decls

        -- Warn about orphans
        -- See Note [Orphans and auto-generated rules]
        let warn_orphs      = wopt Opt_WarnOrphans dflags
            warn_auto_orphs = wopt Opt_WarnAutoOrphans dflags
            orph_warnings   --- Laziness means no work done unless -fwarn-orphans
              | warn_orphs || warn_auto_orphs = rule_warns `unionBags` inst_warns
              | otherwise                     = emptyBag
            errs_and_warns = (orph_warnings, emptyBag)
            unqual = mkPrintUnqualified dflags rdr_env
            inst_warns = listToBag [ instOrphWarn dflags unqual d
                                   | (d,i) <- insts `zip` iface_insts
                                   , isOrphan (ifInstOrph i) ]
            rule_warns = listToBag [ ruleOrphWarn dflags unqual this_mod r
                                   | r <- iface_rules
                                   , isOrphan (ifRuleOrph r)
                                   , if ifRuleAuto r then warn_auto_orphs
                                                     else warn_orphs ]

        if errorsFound dflags errs_and_warns
          then return ( errs_and_warns, Nothing )
          else do
            -- Debug printing
            dumpIfSet_dyn dflags Opt_D_dump_hi "FINAL INTERFACE"
                          (pprModIface new_iface)

            -- bug #1617: on reload we weren't updating the PrintUnqualified
            -- correctly.  This stems from the fact that the interface had
            -- not changed, so addFingerprints returns the old ModIface
            -- with the old GlobalRdrEnv (mi_globals).
            let final_iface = new_iface{ mi_globals = maybeGlobalRdrEnv rdr_env }

            return (errs_and_warns, Just (final_iface, no_change_at_all))
      where
         cmp_rule     = comparing ifRuleName
         -- Compare these lexicographically by OccName, *not* by unique,
         -- because the latter is not stable across compilations:
         cmp_inst     = comparing (nameOccName . ifDFun)
         cmp_fam_inst = comparing (nameOccName . ifFamInstTcName)

         dflags = hsc_dflags hsc_env

         -- We only fill in mi_globals if the module was compiled to byte
         -- code.  Otherwise, the compiler may not have retained all the
         -- top-level bindings and they won't be in the TypeEnv (see
         -- Desugar.addExportFlagsAndRules).  The mi_globals field is used
         -- by GHCi to decide whether the module has its full top-level
         -- scope available. (#5534)
         maybeGlobalRdrEnv :: GlobalRdrEnv -> Maybe GlobalRdrEnv
         maybeGlobalRdrEnv rdr_env
             | targetRetainsAllBindings (hscTarget dflags) = Just rdr_env
             | otherwise                                   = Nothing

         deliberatelyOmitted :: String -> a
         deliberatelyOmitted x = panic ("Deliberately omitted: " ++ x)

         ifFamInstTcName = ifFamInstFam

         flattenVectInfo (VectInfo { vectInfoVar            = vVar
                                   , vectInfoTyCon          = vTyCon
                                   , vectInfoParallelVars     = vParallelVars
                                   , vectInfoParallelTyCons = vParallelTyCons
                                   }) =
           IfaceVectInfo
           { ifaceVectInfoVar            = [Var.varName v | (v, _  ) <- varEnvElts  vVar]
           , ifaceVectInfoTyCon          = [tyConName t   | (t, t_v) <- nameEnvElts vTyCon, t /= t_v]
           , ifaceVectInfoTyConReuse     = [tyConName t   | (t, t_v) <- nameEnvElts vTyCon, t == t_v]
           , ifaceVectInfoParallelVars   = [Var.varName v | v <- varSetElems vParallelVars]
           , ifaceVectInfoParallelTyCons = nameSetElems vParallelTyCons
           }

    -----------------------------
    writeIfaceFile :: DynFlags -> FilePath -> ModIface -> IO ()
    writeIfaceFile dflags hi_file_path new_iface
        = do createDirectoryIfMissing True (takeDirectory hi_file_path)
             writeBinIface dflags hi_file_path new_iface

    -- -----------------------------------------------------------------------------
    -- Look up parents and versions of Names

    -- This is like a global version of the mi_hash_fn field in each ModIface.
    -- Given a Name, it finds the ModIface, and then uses mi_hash_fn to get
    -- the parent and version info.

    mkHashFun
            :: HscEnv                       -- needed to look up versions
            -> ExternalPackageState         -- ditto
            -> (Name -> Fingerprint)
    mkHashFun hsc_env eps
      = \name ->
          let
            mod = ASSERT2( isExternalName name, ppr name ) nameModule name
            occ = nameOccName name
            iface = lookupIfaceByModule (hsc_dflags hsc_env) hpt pit mod `orElse`
                       pprPanic "lookupVers2" (ppr mod <+> ppr occ)
          in
            snd (mi_hash_fn iface occ `orElse`
                      pprPanic "lookupVers1" (ppr mod <+> ppr occ))
      where
          hpt = hsc_HPT hsc_env
          pit = eps_PIT eps

    -- ---------------------------------------------------------------------------
    -- Compute fingerprints for the interface

    addFingerprints
            :: HscEnv
            -> Maybe Fingerprint -- the old fingerprint, if any
            -> ModIface          -- The new interface (lacking decls)
            -> [IfaceDecl]       -- The new decls
            -> IO (ModIface,     -- Updated interface
                   Bool)         -- True <=> no changes at all;
                                 -- no need to write Iface

    addFingerprints hsc_env mb_old_fingerprint iface0 new_decls
     = do
       eps <- hscEPS hsc_env
       let
            -- The ABI of a declaration represents everything that is made
            -- visible about the declaration that a client can depend on.
            -- see IfaceDeclABI below.
           declABI :: IfaceDecl -> IfaceDeclABI
           declABI decl = (this_mod, decl, extras)
            where extras = declExtras fix_fn ann_fn non_orph_rules non_orph_insts
                                      non_orph_fis decl

           edges :: [(IfaceDeclABI, Unique, [Unique])]
           edges = [ (abi, getUnique (ifName decl), out)
                   | decl <- new_decls
                   , let abi = declABI decl
                   , let out = localOccs $ freeNamesDeclABI abi
                   ]

           name_module n = ASSERT2( isExternalName n, ppr n ) nameModule n
           localOccs = map (getUnique . getParent . getOccName)
                            . filter ((== this_mod) . name_module)
                            . nameSetElems
              where getParent occ = lookupOccEnv parent_map occ `orElse` occ

            -- maps OccNames to their parents in the current module.
            -- e.g. a reference to a constructor must be turned into a reference
            -- to the TyCon for the purposes of calculating dependencies.
           parent_map :: OccEnv OccName
           parent_map = foldr extend emptyOccEnv new_decls
              where extend d env =
                      extendOccEnvList env [ (b,n) | b <- ifaceDeclImplicitBndrs d ]
                      where n = ifName d

            -- strongly-connected groups of declarations, in dependency order
           groups = stronglyConnCompFromEdgedVertices edges

           global_hash_fn = mkHashFun hsc_env eps

            -- how to output Names when generating the data to fingerprint.
            -- Here we want to output the fingerprint for each top-level
            -- Name, whether it comes from the current module or another
            -- module.  In this way, the fingerprint for a declaration will
            -- change if the fingerprint for anything it refers to (transitively)
            -- changes.
           mk_put_name :: (OccEnv (OccName,Fingerprint))
                       -> BinHandle -> Name -> IO  ()
           mk_put_name local_env bh name
              | isWiredInName name  =  putNameLiterally bh name
               -- wired-in names don't have fingerprints
              | otherwise
              = ASSERT2( isExternalName name, ppr name )
                let hash | nameModule name /= this_mod =  global_hash_fn name
                         | otherwise = snd (lookupOccEnv local_env (getOccName name)
                               `orElse` pprPanic "urk! lookup local fingerprint"
                                           (ppr name)) -- (undefined,fingerprint0))
                    -- This panic indicates that we got the dependency
                    -- analysis wrong, because we needed a fingerprint for
                    -- an entity that wasn't in the environment.  To debug
                    -- it, turn the panic into a trace, uncomment the
                    -- pprTraces below, run the compile again, and inspect
                    -- the output and the generated .hi file with
                    -- --show-iface.
                in put_ bh hash

            -- take a strongly-connected group of declarations and compute
            -- its fingerprint.

           fingerprint_group :: (OccEnv (OccName,Fingerprint),
                                 [(Fingerprint,IfaceDecl)])
                             -> SCC IfaceDeclABI
                             -> IO (OccEnv (OccName,Fingerprint),
                                    [(Fingerprint,IfaceDecl)])

           fingerprint_group (local_env, decls_w_hashes) (AcyclicSCC abi)
              = do let hash_fn = mk_put_name local_env
                       decl = abiDecl abi
                   -- pprTrace "fingerprinting" (ppr (ifName decl) ) $ do
                   hash <- computeFingerprint hash_fn abi
                   env' <- extend_hash_env local_env (hash,decl)
                   return (env', (hash,decl) : decls_w_hashes)

           fingerprint_group (local_env, decls_w_hashes) (CyclicSCC abis)
              = do let decls = map abiDecl abis
                   local_env1 <- foldM extend_hash_env local_env
                                       (zip (repeat fingerprint0) decls)
                   let hash_fn = mk_put_name local_env1
                   -- pprTrace "fingerprinting" (ppr (map ifName decls) ) $ do
                   let stable_abis = sortBy cmp_abiNames abis
                    -- put the cycle in a canonical order
                   hash <- computeFingerprint hash_fn stable_abis
                   let pairs = zip (repeat hash) decls
                   local_env2 <- foldM extend_hash_env local_env pairs
                   return (local_env2, pairs ++ decls_w_hashes)

           -- we have fingerprinted the whole declaration, but we now need
           -- to assign fingerprints to all the OccNames that it binds, to
           -- use when referencing those OccNames in later declarations.
           --
           extend_hash_env :: OccEnv (OccName,Fingerprint)
                           -> (Fingerprint,IfaceDecl)
                           -> IO (OccEnv (OccName,Fingerprint))
           extend_hash_env env0 (hash,d) = do
              return (foldr (\(b,fp) env -> extendOccEnv env b (b,fp)) env0
                     (ifaceDeclFingerprints hash d))

       --
       (local_env, decls_w_hashes) <-
           foldM fingerprint_group (emptyOccEnv, []) groups

       -- when calculating fingerprints, we always need to use canonical
       -- ordering for lists of things.  In particular, the mi_deps has various
       -- lists of modules and suchlike, so put these all in canonical order:
       let sorted_deps = sortDependencies (mi_deps iface0)

       -- the export hash of a module depends on the orphan hashes of the
       -- orphan modules below us in the dependency tree.  This is the way
       -- that changes in orphans get propagated all the way up the
       -- dependency tree.  We only care about orphan modules in the current
       -- package, because changes to orphans outside this package will be
       -- tracked by the usage on the ABI hash of package modules that we import.
       let orph_mods = filter ((== this_pkg) . modulePackageKey)
                       $ dep_orphs sorted_deps
       dep_orphan_hashes <- getOrphanHashes hsc_env orph_mods

       orphan_hash <- computeFingerprint (mk_put_name local_env)
                          (map ifDFun orph_insts, orph_rules, orph_fis)

       -- the export list hash doesn't depend on the fingerprints of
       -- the Names it mentions, only the Names themselves, hence putNameLiterally.
       export_hash <- computeFingerprint putNameLiterally
                          (mi_exports iface0,
                           orphan_hash,
                           dep_orphan_hashes,
                           dep_pkgs (mi_deps iface0),
                            -- dep_pkgs: see "Package Version Changes" on
                            -- wiki/Commentary/Compiler/RecompilationAvoidance
                           mi_trust iface0)
                            -- Make sure change of Safe Haskell mode causes recomp.

       -- put the declarations in a canonical order, sorted by OccName
       let sorted_decls = Map.elems $ Map.fromList $
                              [(ifName d, e) | e@(_, d) <- decls_w_hashes]

       -- the flag hash depends on:
       --   - (some of) dflags
       -- it returns two hashes, one that shouldn't change
       -- the abi hash and one that should
       flag_hash <- fingerprintDynFlags dflags this_mod putNameLiterally

       -- the ABI hash depends on:
       --   - decls
       --   - export list
       --   - orphans
       --   - deprecations
       --   - vect info
       --   - flag abi hash
       mod_hash <- computeFingerprint putNameLiterally
                          (map fst sorted_decls,
                           export_hash,  -- includes orphan_hash
                           mi_warns iface0,
                           mi_vect_info iface0)

       -- The interface hash depends on:
       --   - the ABI hash, plus
       --   - the module level annotations,
       --   - usages
       --   - deps (home and external packages, dependent files)
       --   - hpc
       iface_hash <- computeFingerprint putNameLiterally
                          (mod_hash,
                           ann_fn (mkVarOcc "module"),  -- See mkIfaceAnnCache
                           mi_usages iface0,
                           sorted_deps,
                           mi_hpc iface0)

       let
        no_change_at_all = Just iface_hash == mb_old_fingerprint

        final_iface = iface0 {
                    mi_mod_hash    = mod_hash,
                    mi_iface_hash  = iface_hash,
                    mi_exp_hash    = export_hash,
                    mi_orphan_hash = orphan_hash,
                    mi_flag_hash   = flag_hash,
                    mi_orphan      = not (   all ifRuleAuto orph_rules
                                               -- See Note [Orphans and auto-generated rules]
                                          && null orph_insts
                                          && null orph_fis
                                          && isNoIfaceVectInfo (mi_vect_info iface0)),
                    mi_finsts      = not . null $ mi_fam_insts iface0,
                    mi_decls       = sorted_decls,
                    mi_hash_fn     = lookupOccEnv local_env }
       --
       return (final_iface, no_change_at_all)

      where
        this_mod = mi_module iface0
        dflags = hsc_dflags hsc_env
        this_pkg = thisPackage dflags
        (non_orph_insts, orph_insts) = mkOrphMap ifInstOrph    (mi_insts iface0)
        (non_orph_rules, orph_rules) = mkOrphMap ifRuleOrph    (mi_rules iface0)
        (non_orph_fis,   orph_fis)   = mkOrphMap ifFamInstOrph (mi_fam_insts iface0)
        fix_fn = mi_fix_fn iface0
        ann_fn = mkIfaceAnnCache (mi_anns iface0)

    getOrphanHashes :: HscEnv -> [Module] -> IO [Fingerprint]
    getOrphanHashes hsc_env mods = do
      eps <- hscEPS hsc_env
      let
        hpt        = hsc_HPT hsc_env
        pit        = eps_PIT eps
        dflags     = hsc_dflags hsc_env
        get_orph_hash mod =
              case lookupIfaceByModule dflags hpt pit mod of
                Nothing    -> pprPanic "moduleOrphanHash" (ppr mod)
                Just iface -> mi_orphan_hash iface
      --
      return (map get_orph_hash mods)

    sortDependencies :: Dependencies -> Dependencies
    sortDependencies d
     = Deps { dep_mods   = sortBy (compare `on` (moduleNameFS.fst)) (dep_mods d),
              dep_pkgs   = sortBy (stablePackageKeyCmp `on` fst) (dep_pkgs d),
              dep_orphs  = sortBy stableModuleCmp (dep_orphs d),
              dep_finsts = sortBy stableModuleCmp (dep_finsts d) }

    -- | Creates cached lookup for the 'mi_anns' field of ModIface
    -- Hackily, we use "module" as the OccName for any module-level annotations
    mkIfaceAnnCache :: [IfaceAnnotation] -> OccName -> [AnnPayload]
    mkIfaceAnnCache anns
      = \n -> lookupOccEnv env n `orElse` []
      where
        pair (IfaceAnnotation target value) =
          (case target of
              NamedTarget occn -> occn
              ModuleTarget _   -> mkVarOcc "module"
          , [value])
        -- flipping (++), so the first argument is always short
        env = mkOccEnv_C (flip (++)) (map pair anns)

    {-
    Note [Orphans and auto-generated rules]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    When we specialise an INLINEABLE function, or when we have
    -fspecialise-aggressively, we auto-generate RULES that are orphans.
    We don't want to warn about these, at least not by default, or we'd
    generate a lot of warnings.  Hence -fwarn-auto-orphans.

    Indeed, we don't even treat the module as an oprhan module if it has
    auto-generated *rule* orphans.  Orphan modules are read every time we
    compile, so they are pretty obtrusive and slow down every compilation,
    even non-optimised ones.  (Reason: for type class instances it's a
    type correctness issue.)  But specialisation rules are strictly for
    *optimisation* only so it's fine not to read the interface.

    What this means is that a SPEC rules from auto-specialisation in
    module M will be used in other modules only if M.hi has been read for
    some other reason, which is actually pretty likely.

    ************************************************************************
    *                                                                      *
              The ABI of an IfaceDecl
    *                                                                      *
    ************************************************************************

    Note [The ABI of an IfaceDecl]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    The ABI of a declaration consists of:

       (a) the full name of the identifier (inc. module and package,
           because these are used to construct the symbol name by which
           the identifier is known externally).

       (b) the declaration itself, as exposed to clients.  That is, the
           definition of an Id is included in the fingerprint only if
           it is made available as an unfolding in the interface.

       (c) the fixity of the identifier
       (d) for Ids: rules
       (e) for classes: instances, fixity & rules for methods
       (f) for datatypes: instances, fixity & rules for constrs

    Items (c)-(f) are not stored in the IfaceDecl, but instead appear
    elsewhere in the interface file.  But they are *fingerprinted* with
    the declaration itself. This is done by grouping (c)-(f) in IfaceDeclExtras,
    and fingerprinting that as part of the declaration.
    -}

    type IfaceDeclABI = (Module, IfaceDecl, IfaceDeclExtras)

    data IfaceDeclExtras
      = IfaceIdExtras IfaceIdExtras

      | IfaceDataExtras
           Fixity                   -- Fixity of the tycon itself
           [IfaceInstABI]           -- Local class and family instances of this tycon
                                    -- See Note [Orphans] in InstEnv
           [AnnPayload]             -- Annotations of the type itself
           [IfaceIdExtras]          -- For each constructor: fixity, RULES and annotations

      | IfaceClassExtras
           Fixity                   -- Fixity of the class itself
           [IfaceInstABI]           -- Local instances of this class *or*
                                    --   of its associated data types
                                    -- See Note [Orphans] in InstEnv
           [AnnPayload]             -- Annotations of the type itself
           [IfaceIdExtras]          -- For each class method: fixity, RULES and annotations

      | IfaceSynonymExtras Fixity [AnnPayload]

      | IfaceFamilyExtras   Fixity [IfaceInstABI] [AnnPayload]

      | IfaceOtherDeclExtras

    data IfaceIdExtras
      = IdExtras
           Fixity                   -- Fixity of the Id
           [IfaceRule]              -- Rules for the Id
           [AnnPayload]             -- Annotations for the Id

    -- When hashing a class or family instance, we hash only the
    -- DFunId or CoAxiom, because that depends on all the
    -- information about the instance.
    --
    type IfaceInstABI = IfExtName   -- Name of DFunId or CoAxiom that is evidence for the instance

    abiDecl :: IfaceDeclABI -> IfaceDecl
    abiDecl (_, decl, _) = decl

    cmp_abiNames :: IfaceDeclABI -> IfaceDeclABI -> Ordering
    cmp_abiNames abi1 abi2 = ifName (abiDecl abi1) `compare`
                             ifName (abiDecl abi2)

    freeNamesDeclABI :: IfaceDeclABI -> NameSet
    freeNamesDeclABI (_mod, decl, extras) =
      freeNamesIfDecl decl `unionNameSet` freeNamesDeclExtras extras

    freeNamesDeclExtras :: IfaceDeclExtras -> NameSet
    freeNamesDeclExtras (IfaceIdExtras id_extras)
      = freeNamesIdExtras id_extras
    freeNamesDeclExtras (IfaceDataExtras  _ insts _ subs)
      = unionNameSets (mkNameSet insts : map freeNamesIdExtras subs)
    freeNamesDeclExtras (IfaceClassExtras _ insts _ subs)
      = unionNameSets (mkNameSet insts : map freeNamesIdExtras subs)
    freeNamesDeclExtras (IfaceSynonymExtras _ _)
      = emptyNameSet
    freeNamesDeclExtras (IfaceFamilyExtras _ insts _)
      = mkNameSet insts
    freeNamesDeclExtras IfaceOtherDeclExtras
      = emptyNameSet

    freeNamesIdExtras :: IfaceIdExtras -> NameSet
    freeNamesIdExtras (IdExtras _ rules _) = unionNameSets (map freeNamesIfRule rules)

    instance Outputable IfaceDeclExtras where
      ppr IfaceOtherDeclExtras       = Outputable.empty
      ppr (IfaceIdExtras  extras)    = ppr_id_extras extras
      ppr (IfaceSynonymExtras fix anns) = vcat [ppr fix, ppr anns]
      ppr (IfaceFamilyExtras fix finsts anns) = vcat [ppr fix, ppr finsts, ppr anns]
      ppr (IfaceDataExtras fix insts anns stuff) = vcat [ppr fix, ppr_insts insts, ppr anns,
                                                    ppr_id_extras_s stuff]
      ppr (IfaceClassExtras fix insts anns stuff) = vcat [ppr fix, ppr_insts insts, ppr anns,
                                                     ppr_id_extras_s stuff]

    ppr_insts :: [IfaceInstABI] -> SDoc
    ppr_insts _ = ptext (sLit "<insts>")

    ppr_id_extras_s :: [IfaceIdExtras] -> SDoc
    ppr_id_extras_s stuff = vcat (map ppr_id_extras stuff)

    ppr_id_extras :: IfaceIdExtras -> SDoc
    ppr_id_extras (IdExtras fix rules anns) = ppr fix $$ vcat (map ppr rules) $$ vcat (map ppr anns)

    -- This instance is used only to compute fingerprints
    instance Binary IfaceDeclExtras where
      get _bh = panic "no get for IfaceDeclExtras"
      put_ bh (IfaceIdExtras extras) = do
       putByte bh 1; put_ bh extras
      put_ bh (IfaceDataExtras fix insts anns cons) = do
       putByte bh 2; put_ bh fix; put_ bh insts; put_ bh anns; put_ bh cons
      put_ bh (IfaceClassExtras fix insts anns methods) = do
       putByte bh 3; put_ bh fix; put_ bh insts; put_ bh anns; put_ bh methods
      put_ bh (IfaceSynonymExtras fix anns) = do
       putByte bh 4; put_ bh fix; put_ bh anns
      put_ bh (IfaceFamilyExtras fix finsts anns) = do
       putByte bh 5; put_ bh fix; put_ bh finsts; put_ bh anns
      put_ bh IfaceOtherDeclExtras = putByte bh 6

    instance Binary IfaceIdExtras where
      get _bh = panic "no get for IfaceIdExtras"
      put_ bh (IdExtras fix rules anns)= do { put_ bh fix; put_ bh rules; put_ bh anns }

    declExtras :: (OccName -> Fixity)
               -> (OccName -> [AnnPayload])
               -> OccEnv [IfaceRule]
               -> OccEnv [IfaceClsInst]
               -> OccEnv [IfaceFamInst]
               -> IfaceDecl
               -> IfaceDeclExtras

    declExtras fix_fn ann_fn rule_env inst_env fi_env decl
      = case decl of
          IfaceId{} -> IfaceIdExtras (id_extras n)
          IfaceData{ifCons=cons} ->
                         IfaceDataExtras (fix_fn n)
                            (map ifFamInstAxiom (lookupOccEnvL fi_env n) ++
                             map ifDFun         (lookupOccEnvL inst_env n))
                            (ann_fn n)
                            (map (id_extras . ifConOcc) (visibleIfConDecls cons))
          IfaceClass{ifSigs=sigs, ifATs=ats} ->
                         IfaceClassExtras (fix_fn n)
                            (map ifDFun $ (concatMap at_extras ats)
                                        ++ lookupOccEnvL inst_env n)
                               -- Include instances of the associated types
                               -- as well as instances of the class (Trac #5147)
                            (ann_fn n)
                            [id_extras op | IfaceClassOp op _ _ <- sigs]
          IfaceSynonym{} -> IfaceSynonymExtras (fix_fn n)
                                               (ann_fn n)
          IfaceFamily{} -> IfaceFamilyExtras (fix_fn n)
                            (map ifFamInstAxiom (lookupOccEnvL fi_env n))
                            (ann_fn n)
          _other -> IfaceOtherDeclExtras
      where
            n = ifName decl
            id_extras occ = IdExtras (fix_fn occ) (lookupOccEnvL rule_env occ) (ann_fn occ)
            at_extras (IfaceAT decl _) = lookupOccEnvL inst_env (ifName decl)

    lookupOccEnvL :: OccEnv [v] -> OccName -> [v]
    lookupOccEnvL env k = lookupOccEnv env k `orElse` []

    -- used when we want to fingerprint a structure without depending on the
    -- fingerprints of external Names that it refers to.
    putNameLiterally :: BinHandle -> Name -> IO ()
    putNameLiterally bh name = ASSERT( isExternalName name )
      do
        put_ bh $! nameModule name
        put_ bh $! nameOccName name

    {-
    -- for testing: use the md5sum command to generate fingerprints and
    -- compare the results against our built-in version.
      fp' <- oldMD5 dflags bh
      if fp /= fp' then pprPanic "computeFingerprint" (ppr fp <+> ppr fp')
                   else return fp

    oldMD5 dflags bh = do
      tmp <- newTempName dflags "bin"
      writeBinMem bh tmp
      tmp2 <- newTempName dflags "md5"
      let cmd = "md5sum " ++ tmp ++ " >" ++ tmp2
      r <- system cmd
      case r of
        ExitFailure _ -> throwGhcExceptionIO (PhaseFailed cmd r)
        ExitSuccess -> do
            hash_str <- readFile tmp2
            return $! readHexFingerprint hash_str
    -}

    instOrphWarn :: DynFlags -> PrintUnqualified -> ClsInst -> WarnMsg
    instOrphWarn dflags unqual inst
      = mkWarnMsg dflags (getSrcSpan inst) unqual $
        hang (ptext (sLit "Orphan instance:")) 2 (pprInstanceHdr inst)
        $$ text "To avoid this"
        $$ nest 4 (vcat possibilities)
      where
        possibilities =
          text "move the instance declaration to the module of the class or of the type, or" :
          text "wrap the type with a newtype and declare the instance on the new type." :
          []

    ruleOrphWarn :: DynFlags -> PrintUnqualified -> Module -> IfaceRule -> WarnMsg
    ruleOrphWarn dflags unqual mod rule
      = mkWarnMsg dflags silly_loc unqual $
        ptext (sLit "Orphan rule:") <+> ppr rule
      where
        silly_loc = srcLocSpan (mkSrcLoc (moduleNameFS (moduleName mod)) 1 1)
        -- We don't have a decent SrcSpan for a Rule, not even the CoreRule
        -- Could readily be fixed by adding a SrcSpan to CoreRule, if we wanted to

    ----------------------
    -- mkOrphMap partitions instance decls or rules into
    --      (a) an OccEnv for ones that are not orphans,
    --          mapping the local OccName to a list of its decls
    --      (b) a list of orphan decls
    mkOrphMap :: (decl -> IsOrphan) -- Extract orphan status from decl
              -> [decl]             -- Sorted into canonical order
              -> (OccEnv [decl],    -- Non-orphan decls associated with their key;
                                    --      each sublist in canonical order
                  [decl])           -- Orphan decls; in canonical order
    mkOrphMap get_key decls
      = foldl go (emptyOccEnv, []) decls
      where
        go (non_orphs, orphs) d
            | NotOrphan occ <- get_key d
            = (extendOccEnv_Acc (:) singleton non_orphs occ d, orphs)
            | otherwise = (non_orphs, d:orphs)

    {-
    ************************************************************************
    *                                                                      *
           Keeping track of what we've slurped, and fingerprints
    *                                                                      *
    ************************************************************************
    -}

    mkUsageInfo :: HscEnv -> Module -> ImportedMods -> NameSet -> [FilePath] -> IO [Usage]
    mkUsageInfo hsc_env this_mod dir_imp_mods used_names dependent_files
      = do
        eps <- hscEPS hsc_env
        hashes <- mapM getFileHash dependent_files
        let mod_usages = mk_mod_usage_info (eps_PIT eps) hsc_env this_mod
                                           dir_imp_mods used_names
        let usages = mod_usages ++ [ UsageFile { usg_file_path = f
                                               , usg_file_hash = hash }
                                   | (f, hash) <- zip dependent_files hashes ]
        usages `seqList` return usages
        -- seq the list of Usages returned: occasionally these
        -- don't get evaluated for a while and we can end up hanging on to
        -- the entire collection of Ifaces.

    mk_mod_usage_info :: PackageIfaceTable
                  -> HscEnv
                  -> Module
                  -> ImportedMods
                  -> NameSet
                  -> [Usage]
    mk_mod_usage_info pit hsc_env this_mod direct_imports used_names
      = mapMaybe mkUsage usage_mods
      where
        hpt = hsc_HPT hsc_env
        dflags = hsc_dflags hsc_env
        this_pkg = thisPackage dflags

        used_mods    = moduleEnvKeys ent_map
        dir_imp_mods = moduleEnvKeys direct_imports
        all_mods     = used_mods ++ filter (`notElem` used_mods) dir_imp_mods
        usage_mods   = sortBy stableModuleCmp all_mods
                            -- canonical order is imported, to avoid interface-file
                            -- wobblage.

        -- ent_map groups together all the things imported and used
        -- from a particular module
        ent_map :: ModuleEnv [OccName]
        ent_map  = foldNameSet add_mv emptyModuleEnv used_names
         where
          add_mv name mv_map
            | isWiredInName name = mv_map  -- ignore wired-in names
            | otherwise
            = case nameModule_maybe name of
                 Nothing  -> ASSERT2( isSystemName name, ppr name ) mv_map
                    -- See Note [Internal used_names]

                 Just mod -> -- This lambda function is really just a
                             -- specialised (++); originally came about to
                             -- avoid quadratic behaviour (trac #2680)
                             extendModuleEnvWith (\_ xs -> occ:xs) mv_map mod [occ]
                    where occ = nameOccName name

        -- We want to create a Usage for a home module if
        --  a) we used something from it; has something in used_names
        --  b) we imported it, even if we used nothing from it
        --     (need to recompile if its export list changes: export_fprint)
        mkUsage :: Module -> Maybe Usage
        mkUsage mod
          | isNothing maybe_iface           -- We can't depend on it if we didn't
                                            -- load its interface.
          || mod == this_mod                -- We don't care about usages of
                                            -- things in *this* module
          = Nothing

          | modulePackageKey mod /= this_pkg
          = Just UsagePackageModule{ usg_mod      = mod,
                                     usg_mod_hash = mod_hash,
                                     usg_safe     = imp_safe }
            -- for package modules, we record the module hash only

          | (null used_occs
              && isNothing export_hash
              && not is_direct_import
              && not finsts_mod)
          = Nothing                 -- Record no usage info
            -- for directly-imported modules, we always want to record a usage
            -- on the orphan hash.  This is what triggers a recompilation if
            -- an orphan is added or removed somewhere below us in the future.

          | otherwise
          = Just UsageHomeModule {
                          usg_mod_name = moduleName mod,
                          usg_mod_hash = mod_hash,
                          usg_exports  = export_hash,
                          usg_entities = Map.toList ent_hashs,
                          usg_safe     = imp_safe }
          where
            maybe_iface  = lookupIfaceByModule dflags hpt pit mod
                    -- In one-shot mode, the interfaces for home-package
                    -- modules accumulate in the PIT not HPT.  Sigh.

            Just iface   = maybe_iface
            finsts_mod   = mi_finsts    iface
            hash_env     = mi_hash_fn   iface
            mod_hash     = mi_mod_hash  iface
            export_hash | depend_on_exports = Just (mi_exp_hash iface)
                        | otherwise         = Nothing

            (is_direct_import, imp_safe)
                = case lookupModuleEnv direct_imports mod of
                    Just ((_,_,_,safe):_xs) -> (True, safe)
                    Just _                  -> pprPanic "mkUsage: empty direct import" Outputable.empty
                    Nothing                 -> (False, safeImplicitImpsReq dflags)
                    -- Nothing case is for implicit imports like 'System.IO' when 'putStrLn'
                    -- is used in the source code. We require them to be safe in Safe Haskell

            used_occs = lookupModuleEnv ent_map mod `orElse` []

            -- Making a Map here ensures that (a) we remove duplicates
            -- when we have usages on several subordinates of a single parent,
            -- and (b) that the usages emerge in a canonical order, which
            -- is why we use Map rather than OccEnv: Map works
            -- using Ord on the OccNames, which is a lexicographic ordering.
            ent_hashs :: Map OccName Fingerprint
            ent_hashs = Map.fromList (map lookup_occ used_occs)

            lookup_occ occ =
                case hash_env occ of
                    Nothing -> pprPanic "mkUsage" (ppr mod <+> ppr occ <+> ppr used_names)
                    Just r  -> r

            depend_on_exports = is_direct_import
            {- True
                  Even if we used 'import M ()', we have to register a
                  usage on the export list because we are sensitive to
                  changes in orphan instances/rules.
               False
                  In GHC 6.8.x we always returned true, and in
                  fact it recorded a dependency on *all* the
                  modules underneath in the dependency tree.  This
                  happens to make orphans work right, but is too
                  expensive: it'll read too many interface files.
                  The 'isNothing maybe_iface' check above saved us
                  from generating many of these usages (at least in
                  one-shot mode), but that's even more bogus!
            -}

    mkIfaceAnnotation :: Annotation -> IfaceAnnotation
    mkIfaceAnnotation (Annotation { ann_target = target, ann_value = payload })
      = IfaceAnnotation {
            ifAnnotatedTarget = fmap nameOccName target,
            ifAnnotatedValue = payload
        }

    mkIfaceExports :: [AvailInfo] -> [IfaceExport]  -- Sort to make canonical
    mkIfaceExports exports
      = sortBy stableAvailCmp (map sort_subs exports)
      where
        sort_subs :: AvailInfo -> AvailInfo
        sort_subs (Avail n) = Avail n
        sort_subs (AvailTC n []) = AvailTC n []
        sort_subs (AvailTC n (m:ms))
           | n==m      = AvailTC n (m:sortBy stableNameCmp ms)
           | otherwise = AvailTC n (sortBy stableNameCmp (m:ms))
           -- Maintain the AvailTC Invariant

    {-
    Note [Orignal module]
    ~~~~~~~~~~~~~~~~~~~~~
    Consider this:
            module X where { data family T }
            module Y( T(..) ) where { import X; data instance T Int = MkT Int }
    The exported Avail from Y will look like
            X.T{X.T, Y.MkT}
    That is, in Y,
      - only MkT is brought into scope by the data instance;
      - but the parent (used for grouping and naming in T(..) exports) is X.T
      - and in this case we export X.T too

    In the result of MkIfaceExports, the names are grouped by defining module,
    so we may need to split up a single Avail into multiple ones.

    Note [Internal used_names]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~
    Most of the used_names are External Names, but we can have Internal
    Names too: see Note [Binders in Template Haskell] in Convert, and
    Trac #5362 for an example.  Such Names are always
      - Such Names are always for locally-defined things, for which we
        don't gather usage info, so we can just ignore them in ent_map
      - They are always System Names, hence the assert, just as a double check.

    ************************************************************************
    *                                                                      *
            Load the old interface file for this module (unless
            we have it already), and check whether it is up to date
    *                                                                      *
    ************************************************************************
    -}

    data RecompileRequired
      = UpToDate
           -- ^ everything is up to date, recompilation is not required
      | MustCompile
           -- ^ The .hs file has been touched, or the .o/.hi file does not exist
      | RecompBecause String
           -- ^ The .o/.hi files are up to date, but something else has changed
           -- to force recompilation; the String says what (one-line summary)
       deriving Eq

    recompileRequired :: RecompileRequired -> Bool
    recompileRequired UpToDate = False
    recompileRequired _ = True

    -- | Top level function to check if the version of an old interface file
    -- is equivalent to the current source file the user asked us to compile.
    -- If the same, we can avoid recompilation. We return a tuple where the
    -- first element is a bool saying if we should recompile the object file
    -- and the second is maybe the interface file, where Nothng means to
    -- rebuild the interface file not use the exisitng one.
    checkOldIface
      :: HscEnv
      -> ModSummary
      -> SourceModified
      -> Maybe ModIface         -- Old interface from compilation manager, if any
      -> IO (RecompileRequired, Maybe ModIface)

    checkOldIface hsc_env mod_summary source_modified maybe_iface
      = do  let dflags = hsc_dflags hsc_env
            showPass dflags $
                "Checking old interface for " ++
                  (showPpr dflags $ ms_mod mod_summary)
            initIfaceCheck hsc_env $
                check_old_iface hsc_env mod_summary source_modified maybe_iface

    check_old_iface
      :: HscEnv
      -> ModSummary
      -> SourceModified
      -> Maybe ModIface
      -> IfG (RecompileRequired, Maybe ModIface)

    check_old_iface hsc_env mod_summary src_modified maybe_iface
      = let dflags = hsc_dflags hsc_env
            getIface =
                case maybe_iface of
                    Just _  -> do
                        traceIf (text "We already have the old interface for" <+>
                          ppr (ms_mod mod_summary))
                        return maybe_iface
                    Nothing -> loadIface

            loadIface = do
                 let iface_path = msHiFilePath mod_summary
                 read_result <- readIface (ms_mod mod_summary) iface_path
                 case read_result of
                     Failed err -> do
                         traceIf (text "FYI: cannot read old interface file:" $$ nest 4 err)
                         return Nothing
                     Succeeded iface -> do
                         traceIf (text "Read the interface file" <+> text iface_path)
                         return $ Just iface

            src_changed
                | gopt Opt_ForceRecomp (hsc_dflags hsc_env) = True
                | SourceModified <- src_modified = True
                | otherwise = False
        in do
            when src_changed $
                traceHiDiffs (nest 4 $ text "Source file changed or recompilation check turned off")

            case src_changed of
                -- If the source has changed and we're in interactive mode,
                -- avoid reading an interface; just return the one we might
                -- have been supplied with.
                True | not (isObjectTarget $ hscTarget dflags) ->
                    return (MustCompile, maybe_iface)

                -- Try and read the old interface for the current module
                -- from the .hi file left from the last time we compiled it
                True -> do
                    maybe_iface' <- getIface
                    return (MustCompile, maybe_iface')

                False -> do
                    maybe_iface' <- getIface
                    case maybe_iface' of
                        -- We can't retrieve the iface
                        Nothing    -> return (MustCompile, Nothing)

                        -- We have got the old iface; check its versions
                        -- even in the SourceUnmodifiedAndStable case we
                        -- should check versions because some packages
                        -- might have changed or gone away.
                        Just iface -> checkVersions hsc_env mod_summary iface

    -- | Check if a module is still the same 'version'.
    --
    -- This function is called in the recompilation checker after we have
    -- determined that the module M being checked hasn't had any changes
    -- to its source file since we last compiled M. So at this point in general
    -- two things may have changed that mean we should recompile M:
    --   * The interface export by a dependency of M has changed.
    --   * The compiler flags specified this time for M have changed
    --     in a manner that is significant for recompilaiton.
    -- We return not just if we should recompile the object file but also
    -- if we should rebuild the interface file.
    checkVersions :: HscEnv
                  -> ModSummary
                  -> ModIface       -- Old interface
                  -> IfG (RecompileRequired, Maybe ModIface)
    checkVersions hsc_env mod_summary iface
      = do { traceHiDiffs (text "Considering whether compilation is required for" <+>
                            ppr (mi_module iface) <> colon)

           ; recomp <- checkFlagHash hsc_env iface
           ; if recompileRequired recomp then return (recomp, Nothing) else do {
           ; if getSigOf (hsc_dflags hsc_env) (moduleName (mi_module iface))
                    /= mi_sig_of iface
                then return (RecompBecause "sig-of changed", Nothing) else do {
           ; recomp <- checkDependencies hsc_env mod_summary iface
           ; if recompileRequired recomp then return (recomp, Just iface) else do {

           -- Source code unchanged and no errors yet... carry on
           --
           -- First put the dependent-module info, read from the old
           -- interface, into the envt, so that when we look for
           -- interfaces we look for the right one (.hi or .hi-boot)
           --
           -- It's just temporary because either the usage check will succeed
           -- (in which case we are done with this module) or it'll fail (in which
           -- case we'll compile the module from scratch anyhow).
           --
           -- We do this regardless of compilation mode, although in --make mode
           -- all the dependent modules should be in the HPT already, so it's
           -- quite redundant
           ; updateEps_ $ \eps  -> eps { eps_is_boot = mod_deps }
           ; recomp <- checkList [checkModUsage this_pkg u | u <- mi_usages iface]
           ; return (recomp, Just iface)
        }}}}
      where
        this_pkg = thisPackage (hsc_dflags hsc_env)
        -- This is a bit of a hack really
        mod_deps :: ModuleNameEnv (ModuleName, IsBootInterface)
        mod_deps = mkModDeps (dep_mods (mi_deps iface))

    -- | Check the flags haven't changed
    checkFlagHash :: HscEnv -> ModIface -> IfG RecompileRequired
    checkFlagHash hsc_env iface = do
        let old_hash = mi_flag_hash iface
        new_hash <- liftIO $ fingerprintDynFlags (hsc_dflags hsc_env)
                                                 (mi_module iface)
                                                 putNameLiterally
        case old_hash == new_hash of
            True  -> up_to_date (ptext $ sLit "Module flags unchanged")
            False -> out_of_date_hash "flags changed"
                         (ptext $ sLit "  Module flags have changed")
                         old_hash new_hash

    -- If the direct imports of this module are resolved to targets that
    -- are not among the dependencies of the previous interface file,
    -- then we definitely need to recompile.  This catches cases like
    --   - an exposed package has been upgraded
    --   - we are compiling with different package flags
    --   - a home module that was shadowing a package module has been removed
    --   - a new home module has been added that shadows a package module
    -- See bug #1372.
    --
    -- Returns True if recompilation is required.
    checkDependencies :: HscEnv -> ModSummary -> ModIface -> IfG RecompileRequired
    checkDependencies hsc_env summary iface
     = checkList (map dep_missing (ms_imps summary ++ ms_srcimps summary))
      where
       prev_dep_mods = dep_mods (mi_deps iface)
       prev_dep_pkgs = dep_pkgs (mi_deps iface)

       this_pkg = thisPackage (hsc_dflags hsc_env)

       dep_missing (L _ (ImportDecl { ideclName = L _ mod, ideclPkgQual = pkg })) = do
         find_res <- liftIO $ findImportedModule hsc_env mod pkg
         let reason = moduleNameString mod ++ " changed"
         case find_res of
            Found _ mod
              | pkg == this_pkg
               -> if moduleName mod `notElem` map fst prev_dep_mods
                     then do traceHiDiffs $
                               text "imported module " <> quotes (ppr mod) <>
                               text " not among previous dependencies"
                             return (RecompBecause reason)
                     else
                             return UpToDate
              | otherwise
               -> if pkg `notElem` (map fst prev_dep_pkgs)
                     then do traceHiDiffs $
                               text "imported module " <> quotes (ppr mod) <>
                               text " is from package " <> quotes (ppr pkg) <>
                               text ", which is not among previous dependencies"
                             return (RecompBecause reason)
                     else
                             return UpToDate
               where pkg = modulePackageKey mod
            _otherwise  -> return (RecompBecause reason)

    needInterface :: Module -> (ModIface -> IfG RecompileRequired)
                  -> IfG RecompileRequired
    needInterface mod continue
      = do  -- Load the imported interface if possible
        let doc_str = sep [ptext (sLit "need version info for"), ppr mod]
        traceHiDiffs (text "Checking usages for module" <+> ppr mod)

        mb_iface <- loadInterface doc_str mod ImportBySystem
            -- Load the interface, but don't complain on failure;
            -- Instead, get an Either back which we can test

        case mb_iface of
          Failed _ -> do
            traceHiDiffs (sep [ptext (sLit "Couldn't load interface for module"),
                               ppr mod])
            return MustCompile
                      -- Couldn't find or parse a module mentioned in the
                      -- old interface file.  Don't complain: it might
                      -- just be that the current module doesn't need that
                      -- import and it's been deleted
          Succeeded iface -> continue iface

    -- | Given the usage information extracted from the old
    -- M.hi file for the module being compiled, figure out
    -- whether M needs to be recompiled.
    checkModUsage :: PackageKey -> Usage -> IfG RecompileRequired
    checkModUsage _this_pkg UsagePackageModule{
                                    usg_mod = mod,
                                    usg_mod_hash = old_mod_hash }
      = needInterface mod $ \iface -> do
        let reason = moduleNameString (moduleName mod) ++ " changed"
        checkModuleFingerprint reason old_mod_hash (mi_mod_hash iface)
            -- We only track the ABI hash of package modules, rather than
            -- individual entity usages, so if the ABI hash changes we must
            -- recompile.  This is safe but may entail more recompilation when
            -- a dependent package has changed.

    checkModUsage this_pkg UsageHomeModule{
                                    usg_mod_name = mod_name,
                                    usg_mod_hash = old_mod_hash,
                                    usg_exports = maybe_old_export_hash,
                                    usg_entities = old_decl_hash }
      = do
        let mod = mkModule this_pkg mod_name
        needInterface mod $ \iface -> do

        let
            new_mod_hash    = mi_mod_hash    iface
            new_decl_hash   = mi_hash_fn     iface
            new_export_hash = mi_exp_hash    iface

            reason = moduleNameString mod_name ++ " changed"

            -- CHECK MODULE
        recompile <- checkModuleFingerprint reason old_mod_hash new_mod_hash
        if not (recompileRequired recompile)
          then return UpToDate
          else do

            -- CHECK EXPORT LIST
            checkMaybeHash reason maybe_old_export_hash new_export_hash
                (ptext (sLit "  Export list changed")) $ do

            -- CHECK ITEMS ONE BY ONE
            recompile <- checkList [ checkEntityUsage reason new_decl_hash u
                                   | u <- old_decl_hash]
            if recompileRequired recompile
              then return recompile     -- This one failed, so just bail out now
              else up_to_date (ptext (sLit "  Great!  The bits I use are up to date"))

    checkModUsage _this_pkg UsageFile{ usg_file_path = file,
                                       usg_file_hash = old_hash } =
      liftIO $
        handleIO handle $ do
          new_hash <- getFileHash file
          if (old_hash /= new_hash)
             then return recomp
             else return UpToDate
     where
       recomp = RecompBecause (file ++ " changed")
       handle =
    #ifdef DEBUG
           \e -> pprTrace "UsageFile" (text (show e)) $ return recomp
    #else
           \_ -> return recomp -- if we can't find the file, just recompile, don't fail
    #endif

    ------------------------
    checkModuleFingerprint :: String -> Fingerprint -> Fingerprint
                           -> IfG RecompileRequired
    checkModuleFingerprint reason old_mod_hash new_mod_hash
      | new_mod_hash == old_mod_hash
      = up_to_date (ptext (sLit "Module fingerprint unchanged"))

      | otherwise
      = out_of_date_hash reason (ptext (sLit "  Module fingerprint has changed"))
                         old_mod_hash new_mod_hash

    ------------------------
    checkMaybeHash :: String -> Maybe Fingerprint -> Fingerprint -> SDoc
                   -> IfG RecompileRequired -> IfG RecompileRequired
    checkMaybeHash reason maybe_old_hash new_hash doc continue
      | Just hash <- maybe_old_hash, hash /= new_hash
      = out_of_date_hash reason doc hash new_hash
      | otherwise
      = continue

    ------------------------
    checkEntityUsage :: String
                     -> (OccName -> Maybe (OccName, Fingerprint))
                     -> (OccName, Fingerprint)
                     -> IfG RecompileRequired
    checkEntityUsage reason new_hash (name,old_hash)
      = case new_hash name of

            Nothing       ->        -- We used it before, but it ain't there now
                              out_of_date reason (sep [ptext (sLit "No longer exported:"), ppr name])

            Just (_, new_hash)      -- It's there, but is it up to date?
              | new_hash == old_hash -> do traceHiDiffs (text "  Up to date" <+> ppr name <+> parens (ppr new_hash))
                                           return UpToDate
              | otherwise            -> out_of_date_hash reason (ptext (sLit "  Out of date:") <+> ppr name)
                                                         old_hash new_hash

    up_to_date :: SDoc -> IfG RecompileRequired
    up_to_date  msg = traceHiDiffs msg >> return UpToDate

    out_of_date :: String -> SDoc -> IfG RecompileRequired
    out_of_date reason msg = traceHiDiffs msg >> return (RecompBecause reason)

    out_of_date_hash :: String -> SDoc -> Fingerprint -> Fingerprint -> IfG RecompileRequired
    out_of_date_hash reason msg old_hash new_hash
      = out_of_date reason (hsep [msg, ppr old_hash, ptext (sLit "->"), ppr new_hash])

    ----------------------
    checkList :: [IfG RecompileRequired] -> IfG RecompileRequired
    -- This helper is used in two places
    checkList []             = return UpToDate
    checkList (check:checks) = do recompile <- check
                                  if recompileRequired recompile
                                    then return recompile
                                    else checkList checks

    {-
    ************************************************************************
    *                                                                      *
                    Converting things to their Iface equivalents
    *                                                                      *
    ************************************************************************
    -}

    tyThingToIfaceDecl :: TyThing -> IfaceDecl
    tyThingToIfaceDecl (AnId id)      = idToIfaceDecl id
    tyThingToIfaceDecl (ATyCon tycon) = snd (tyConToIfaceDecl emptyTidyEnv tycon)
    tyThingToIfaceDecl (ACoAxiom ax)  = coAxiomToIfaceDecl ax
    tyThingToIfaceDecl (AConLike cl)  = case cl of
        RealDataCon dc -> dataConToIfaceDecl dc -- for ppr purposes only
        PatSynCon ps   -> patSynToIfaceDecl ps

    --------------------------
    idToIfaceDecl :: Id -> IfaceDecl
    -- The Id is already tidied, so that locally-bound names
    -- (lambdas, for-alls) already have non-clashing OccNames
    -- We can't tidy it here, locally, because it may have
    -- free variables in its type or IdInfo
    idToIfaceDecl id
      = IfaceId { ifName      = getOccName id,
                  ifType      = toIfaceType (idType id),
                  ifIdDetails = toIfaceIdDetails (idDetails id),
                  ifIdInfo    = toIfaceIdInfo (idInfo id) }

    --------------------------
    dataConToIfaceDecl :: DataCon -> IfaceDecl
    dataConToIfaceDecl dataCon
      = IfaceId { ifName      = getOccName dataCon,
                  ifType      = toIfaceType (dataConUserType dataCon),
                  ifIdDetails = IfVanillaId,
                  ifIdInfo    = NoInfo }

    --------------------------
    patSynToIfaceDecl :: PatSyn -> IfaceDecl
    patSynToIfaceDecl ps
      = IfacePatSyn { ifName          = getOccName . getName $ ps
                    , ifPatMatcher    = to_if_pr (patSynMatcher ps)
                    , ifPatBuilder    = fmap to_if_pr (patSynBuilder ps)
                    , ifPatIsInfix    = patSynIsInfix ps
                    , ifPatUnivTvs    = toIfaceTvBndrs univ_tvs'
                    , ifPatExTvs      = toIfaceTvBndrs ex_tvs'
                    , ifPatProvCtxt   = tidyToIfaceContext env2 prov_theta
                    , ifPatReqCtxt    = tidyToIfaceContext env2 req_theta
                    , ifPatArgs       = map (tidyToIfaceType env2) args
                    , ifPatTy         = tidyToIfaceType env2 rhs_ty
                    }
      where
        (univ_tvs, ex_tvs, prov_theta, req_theta, args, rhs_ty) = patSynSig ps
        (env1, univ_tvs') = tidyTyVarBndrs emptyTidyEnv univ_tvs
        (env2, ex_tvs')   = tidyTyVarBndrs env1 ex_tvs
        to_if_pr (id, needs_dummy) = (idName id, needs_dummy)

    --------------------------
    coAxiomToIfaceDecl :: CoAxiom br -> IfaceDecl
    -- We *do* tidy Axioms, because they are not (and cannot
    -- conveniently be) built in tidy form
    coAxiomToIfaceDecl ax@(CoAxiom { co_ax_tc = tycon, co_ax_branches = branches
                                   , co_ax_role = role })
     = IfaceAxiom { ifName       = name
                  , ifTyCon      = toIfaceTyCon tycon
                  , ifRole       = role
                  , ifAxBranches = brListMap (coAxBranchToIfaceBranch tycon
                                                (brListMap coAxBranchLHS branches))
                                             branches }
     where
       name = getOccName ax

    -- 2nd parameter is the list of branch LHSs, for conversion from incompatible branches
    -- to incompatible indices
    -- See Note [Storing compatibility] in CoAxiom
    coAxBranchToIfaceBranch :: TyCon -> [[Type]] -> CoAxBranch -> IfaceAxBranch
    coAxBranchToIfaceBranch tc lhs_s
                            branch@(CoAxBranch { cab_incomps = incomps })
      = (coAxBranchToIfaceBranch' tc branch) { ifaxbIncomps = iface_incomps }
      where
        iface_incomps = map (expectJust "iface_incomps"
                            . (flip findIndex lhs_s
                              . eqTypes)
                            . coAxBranchLHS) incomps

    -- use this one for standalone branches without incompatibles
    coAxBranchToIfaceBranch' :: TyCon -> CoAxBranch -> IfaceAxBranch
    coAxBranchToIfaceBranch' tc (CoAxBranch { cab_tvs = tvs, cab_lhs = lhs
                                            , cab_roles = roles, cab_rhs = rhs })
      = IfaceAxBranch { ifaxbTyVars = toIfaceTvBndrs tv_bndrs
                      , ifaxbLHS    = tidyToIfaceTcArgs env1 tc lhs
                      , ifaxbRoles  = roles
                      , ifaxbRHS    = tidyToIfaceType env1 rhs
                      , ifaxbIncomps = [] }
      where
        (env1, tv_bndrs) = tidyTyClTyVarBndrs emptyTidyEnv tvs
        -- Don't re-bind in-scope tyvars
        -- See Note [CoAxBranch type variables] in CoAxiom

    -----------------
    tyConToIfaceDecl :: TidyEnv -> TyCon -> (TidyEnv, IfaceDecl)
    -- We *do* tidy TyCons, because they are not (and cannot
    -- conveniently be) built in tidy form
    -- The returned TidyEnv is the one after tidying the tyConTyVars
    tyConToIfaceDecl env tycon
      | Just clas <- tyConClass_maybe tycon
      = classToIfaceDecl env clas

      | Just syn_rhs <- synTyConRhs_maybe tycon
      = ( tc_env1
        , IfaceSynonym { ifName    = getOccName tycon,
                         ifTyVars  = if_tc_tyvars,
                         ifRoles   = tyConRoles tycon,
                         ifSynRhs  = if_syn_type syn_rhs,
                         ifSynKind = tidyToIfaceType tc_env1 (synTyConResKind tycon)
                       })

      | Just fam_flav <- famTyConFlav_maybe tycon
      = ( tc_env1
        , IfaceFamily { ifName    = getOccName tycon,
                        ifTyVars  = if_tc_tyvars,
                        ifFamFlav = to_if_fam_flav fam_flav,
                        ifFamKind = tidyToIfaceType tc_env1 (synTyConResKind tycon)
                      })

      | isAlgTyCon tycon
      = ( tc_env1
        , IfaceData { ifName    = getOccName tycon,
                      ifCType   = tyConCType tycon,
                      ifTyVars  = if_tc_tyvars,
                      ifRoles   = tyConRoles tycon,
                      ifCtxt    = tidyToIfaceContext tc_env1 (tyConStupidTheta tycon),
                      ifCons    = ifaceConDecls (algTyConRhs tycon),
                      ifRec     = boolToRecFlag (isRecursiveTyCon tycon),
                      ifGadtSyntax = isGadtSyntaxTyCon tycon,
                      ifPromotable = isJust (promotableTyCon_maybe tycon),
                      ifParent  = parent })

      | otherwise  -- FunTyCon, PrimTyCon, promoted TyCon/DataCon
      -- For pretty printing purposes only.
      = ( env
        , IfaceData { ifName       = getOccName tycon,
                      ifCType      = Nothing,
                      ifTyVars     = funAndPrimTyVars,
                      ifRoles      = tyConRoles tycon,
                      ifCtxt       = [],
                      ifCons       = IfDataTyCon [],
                      ifRec        = boolToRecFlag False,
                      ifGadtSyntax = False,
                      ifPromotable = False,
                      ifParent     = IfNoParent })
      where
        (tc_env1, tc_tyvars) = tidyTyClTyVarBndrs env (tyConTyVars tycon)
        if_tc_tyvars = toIfaceTvBndrs tc_tyvars
        if_syn_type ty = tidyToIfaceType tc_env1 ty

        funAndPrimTyVars = toIfaceTvBndrs $ take (tyConArity tycon) alphaTyVars

        parent = case tyConFamInstSig_maybe tycon of
                   Just (tc, ty, ax) -> IfDataInstance (coAxiomName ax)
                                                       (toIfaceTyCon tc)
                                                       (tidyToIfaceTcArgs tc_env1 tc ty)
                   Nothing           -> IfNoParent

        to_if_fam_flav OpenSynFamilyTyCon        = IfaceOpenSynFamilyTyCon
        to_if_fam_flav (ClosedSynFamilyTyCon ax) = IfaceClosedSynFamilyTyCon axn ibr
          where defs = fromBranchList $ coAxiomBranches ax
                ibr  = map (coAxBranchToIfaceBranch' tycon) defs
                axn  = coAxiomName ax
        to_if_fam_flav AbstractClosedSynFamilyTyCon
          = IfaceAbstractClosedSynFamilyTyCon

        to_if_fam_flav (BuiltInSynFamTyCon {})
          = IfaceBuiltInSynFamTyCon

        ifaceConDecls (NewTyCon { data_con = con })     = IfNewTyCon  (ifaceConDecl con)
        ifaceConDecls (DataTyCon { data_cons = cons })  = IfDataTyCon (map ifaceConDecl cons)
        ifaceConDecls (DataFamilyTyCon {})              = IfDataFamTyCon
        ifaceConDecls (AbstractTyCon distinct)          = IfAbstractTyCon distinct
            -- The last case happens when a TyCon has been trimmed during tidying
            -- Furthermore, tyThingToIfaceDecl is also used
            -- in TcRnDriver for GHCi, when browsing a module, in which case the
            -- AbstractTyCon case is perfectly sensible.

        ifaceConDecl data_con
            = IfCon   { ifConOcc     = getOccName (dataConName data_con),
                        ifConInfix   = dataConIsInfix data_con,
                        ifConWrapper = isJust (dataConWrapId_maybe data_con),
                        ifConExTvs   = toIfaceTvBndrs ex_tvs',
                        ifConEqSpec  = map to_eq_spec eq_spec,
                        ifConCtxt    = tidyToIfaceContext con_env2 theta,
                        ifConArgTys  = map (tidyToIfaceType con_env2) arg_tys,
                        ifConFields  = map getOccName
                                           (dataConFieldLabels data_con),
                        ifConStricts = map (toIfaceBang con_env2) (dataConImplBangs data_con) }
            where
              (univ_tvs, ex_tvs, eq_spec, theta, arg_tys, _) = dataConFullSig data_con

              -- Tidy the univ_tvs of the data constructor to be identical
              -- to the tyConTyVars of the type constructor.  This means
              -- (a) we don't need to redundantly put them into the interface file
              -- (b) when pretty-printing an Iface data declaration in H98-style syntax,
              --     we know that the type variables will line up
              -- The latter (b) is important because we pretty-print type construtors
              -- by converting to IfaceSyn and pretty-printing that
              con_env1 = (fst tc_env1, mkVarEnv (zipEqual "ifaceConDecl" univ_tvs tc_tyvars))
                         -- A bit grimy, perhaps, but it's simple!

              (con_env2, ex_tvs') = tidyTyVarBndrs con_env1 ex_tvs
              to_eq_spec (tv,ty)  = (toIfaceTyVar (tidyTyVar con_env2 tv), tidyToIfaceType con_env2 ty)

    toIfaceBang :: TidyEnv -> HsImplBang -> IfaceBang
    toIfaceBang _    HsNoBang            = IfNoBang
    toIfaceBang _   (HsUnpack Nothing)   = IfUnpack
    toIfaceBang env (HsUnpack (Just co)) = IfUnpackCo (toIfaceCoercion (tidyCo env co))
    toIfaceBang _   HsStrict             = IfStrict
    toIfaceBang _   (HsSrcBang {})       = panic "toIfaceBang"

    classToIfaceDecl :: TidyEnv -> Class -> (TidyEnv, IfaceDecl)
    classToIfaceDecl env clas
      = ( env1
        , IfaceClass { ifCtxt   = tidyToIfaceContext env1 sc_theta,
                       ifName   = getOccName (classTyCon clas),
                       ifTyVars = toIfaceTvBndrs clas_tyvars',
                       ifRoles  = tyConRoles (classTyCon clas),
                       ifFDs    = map toIfaceFD clas_fds,
                       ifATs    = map toIfaceAT clas_ats,
                       ifSigs   = map toIfaceClassOp op_stuff,
                       ifMinDef = fmap getFS (classMinimalDef clas),
                       ifRec    = boolToRecFlag (isRecursiveTyCon tycon) })
      where
        (clas_tyvars, clas_fds, sc_theta, _, clas_ats, op_stuff)
          = classExtraBigSig clas
        tycon = classTyCon clas

        (env1, clas_tyvars') = tidyTyVarBndrs env clas_tyvars

        toIfaceAT :: ClassATItem -> IfaceAT
        toIfaceAT (ATI tc def)
          = IfaceAT if_decl (fmap (tidyToIfaceType env2) def)
          where
            (env2, if_decl) = tyConToIfaceDecl env1 tc

        toIfaceClassOp (sel_id, def_meth)
            = ASSERT(sel_tyvars == clas_tyvars)
              IfaceClassOp (getOccName sel_id) (toDmSpec def_meth)
                           (tidyToIfaceType env1 op_ty)
            where
                    -- Be careful when splitting the type, because of things
                    -- like         class Foo a where
                    --                op :: (?x :: String) => a -> a
                    -- and          class Baz a where
                    --                op :: (Ord a) => a -> a
              (sel_tyvars, rho_ty) = splitForAllTys (idType sel_id)
              op_ty                = funResultTy rho_ty

        toDmSpec NoDefMeth      = NoDM
        toDmSpec (GenDefMeth _) = GenericDM
        toDmSpec (DefMeth _)    = VanillaDM

        toIfaceFD (tvs1, tvs2) = (map (getFS . tidyTyVar env1) tvs1,
                                  map (getFS . tidyTyVar env1) tvs2)

    --------------------------
    tidyToIfaceType :: TidyEnv -> Type -> IfaceType
    tidyToIfaceType env ty = toIfaceType (tidyType env ty)

    tidyToIfaceTcArgs :: TidyEnv -> TyCon -> [Type] -> IfaceTcArgs
    tidyToIfaceTcArgs env tc tys = toIfaceTcArgs tc (tidyTypes env tys)

    tidyToIfaceContext :: TidyEnv -> ThetaType -> IfaceContext
    tidyToIfaceContext env theta = map (tidyToIfaceType env) theta

    tidyTyClTyVarBndrs :: TidyEnv -> [TyVar] -> (TidyEnv, [TyVar])
    tidyTyClTyVarBndrs env tvs = mapAccumL tidyTyClTyVarBndr env tvs

    tidyTyClTyVarBndr :: TidyEnv -> TyVar -> (TidyEnv, TyVar)
    -- If the type variable "binder" is in scope, don't re-bind it
    -- In a class decl, for example, the ATD binders mention
    -- (amd must mention) the class tyvars
    tidyTyClTyVarBndr env@(_, subst) tv
     | Just tv' <- lookupVarEnv subst tv = (env, tv')
     | otherwise                         = tidyTyVarBndr env tv

    tidyTyVar :: TidyEnv -> TyVar -> TyVar
    tidyTyVar (_, subst) tv = lookupVarEnv subst tv `orElse` tv
       -- TcType.tidyTyVarOcc messes around with FlatSkols

    getFS :: NamedThing a => a -> FastString
    getFS x = occNameFS (getOccName x)

    --------------------------
    instanceToIfaceInst :: ClsInst -> IfaceClsInst
    instanceToIfaceInst (ClsInst { is_dfun = dfun_id, is_flag = oflag
                                 , is_cls_nm = cls_name, is_cls = cls
                                 , is_tcs = mb_tcs
                                 , is_orphan = orph })
      = ASSERT( cls_name == className cls )
        IfaceClsInst { ifDFun    = dfun_name,
                    ifOFlag   = oflag,
                    ifInstCls = cls_name,
                    ifInstTys = map do_rough mb_tcs,
                    ifInstOrph = orph }
      where
        do_rough Nothing  = Nothing
        do_rough (Just n) = Just (toIfaceTyCon_name n)

        dfun_name = idName dfun_id

    --------------------------
    famInstToIfaceFamInst :: FamInst -> IfaceFamInst
    famInstToIfaceFamInst (FamInst { fi_axiom    = axiom,
                                     fi_fam      = fam,
                                     fi_tcs      = roughs })
      = IfaceFamInst { ifFamInstAxiom    = coAxiomName axiom
                     , ifFamInstFam      = fam
                     , ifFamInstTys      = map do_rough roughs
                     , ifFamInstOrph     = orph }
      where
        do_rough Nothing  = Nothing
        do_rough (Just n) = Just (toIfaceTyCon_name n)

        fam_decl = tyConName $ coAxiomTyCon axiom
        mod = ASSERT( isExternalName (coAxiomName axiom) )
              nameModule (coAxiomName axiom)
        is_local name = nameIsLocalOrFrom mod name

        lhs_names = filterNameSet is_local (orphNamesOfCoCon axiom)

        orph | is_local fam_decl
             = NotOrphan (nameOccName fam_decl)

             | not (isEmptyNameSet lhs_names)
             = NotOrphan (nameOccName (head (nameSetElems lhs_names)))

             | otherwise
             = IsOrphan

    --------------------------
    toIfaceLetBndr :: Id -> IfaceLetBndr
    toIfaceLetBndr id  = IfLetBndr (occNameFS (getOccName id))
                                   (toIfaceType (idType id))
                                   (toIfaceIdInfo (idInfo id))
      -- Put into the interface file any IdInfo that CoreTidy.tidyLetBndr
      -- has left on the Id.  See Note [IdInfo on nested let-bindings] in IfaceSyn

    --------------------------
    toIfaceIdDetails :: IdDetails -> IfaceIdDetails
    toIfaceIdDetails VanillaId                      = IfVanillaId
    toIfaceIdDetails (DFunId ns _)                  = IfDFunId ns
    toIfaceIdDetails (RecSelId { sel_naughty = n
                               , sel_tycon = tc })  = IfRecSelId (toIfaceTyCon tc) n
    toIfaceIdDetails other                          = pprTrace "toIfaceIdDetails" (ppr other)
                                                      IfVanillaId   -- Unexpected

    toIfaceIdInfo :: IdInfo -> IfaceIdInfo
    toIfaceIdInfo id_info
      = case catMaybes [arity_hsinfo, caf_hsinfo, strict_hsinfo,
                        inline_hsinfo,  unfold_hsinfo] of
           []    -> NoInfo
           infos -> HasInfo infos
                   -- NB: strictness and arity must appear in the list before unfolding
                   -- See TcIface.tcUnfolding
      where
        ------------  Arity  --------------
        arity_info = arityInfo id_info
        arity_hsinfo | arity_info == 0 = Nothing
                     | otherwise       = Just (HsArity arity_info)

        ------------ Caf Info --------------
        caf_info   = cafInfo id_info
        caf_hsinfo = case caf_info of
                       NoCafRefs -> Just HsNoCafRefs
                       _other    -> Nothing

        ------------  Strictness  --------------
            -- No point in explicitly exporting TopSig
        sig_info = strictnessInfo id_info
        strict_hsinfo | not (isNopSig sig_info) = Just (HsStrictness sig_info)
                      | otherwise               = Nothing

        ------------  Unfolding  --------------
        unfold_hsinfo = toIfUnfolding loop_breaker (unfoldingInfo id_info)
        loop_breaker  = isStrongLoopBreaker (occInfo id_info)

        ------------  Inline prag  --------------
        inline_prag = inlinePragInfo id_info
        inline_hsinfo | isDefaultInlinePragma inline_prag = Nothing
                      | otherwise = Just (HsInline inline_prag)

    --------------------------
    toIfUnfolding :: Bool -> Unfolding -> Maybe IfaceInfoItem
    toIfUnfolding lb (CoreUnfolding { uf_tmpl = rhs
                                    , uf_src = src
                                    , uf_guidance = guidance })
      = Just $ HsUnfold lb $
        case src of
            InlineStable
              -> case guidance of
                   UnfWhen {ug_arity = arity, ug_unsat_ok = unsat_ok, ug_boring_ok =  boring_ok }
                          -> IfInlineRule arity unsat_ok boring_ok if_rhs
                   _other -> IfCoreUnfold True if_rhs
            InlineCompulsory -> IfCompulsory if_rhs
            InlineRhs        -> IfCoreUnfold False if_rhs
            -- Yes, even if guidance is UnfNever, expose the unfolding
            -- If we didn't want to expose the unfolding, TidyPgm would
            -- have stuck in NoUnfolding.  For supercompilation we want
            -- to see that unfolding!
      where
        if_rhs = toIfaceExpr rhs

    toIfUnfolding lb (DFunUnfolding { df_bndrs = bndrs, df_args = args })
      = Just (HsUnfold lb (IfDFunUnfold (map toIfaceBndr bndrs) (map toIfaceExpr args)))
          -- No need to serialise the data constructor;
          -- we can recover it from the type of the dfun

    toIfUnfolding _ _
      = Nothing

    --------------------------
    coreRuleToIfaceRule :: Module -> CoreRule -> IfaceRule
    coreRuleToIfaceRule _ (BuiltinRule { ru_fn = fn})
      = pprTrace "toHsRule: builtin" (ppr fn) $
        bogusIfaceRule fn

    coreRuleToIfaceRule mod rule@(Rule { ru_name = name, ru_fn = fn,
                                         ru_act = act, ru_bndrs = bndrs,
                                         ru_args = args, ru_rhs = rhs,
                                         ru_auto = auto })
      = IfaceRule { ifRuleName  = name, ifActivation = act,
                    ifRuleBndrs = map toIfaceBndr bndrs,
                    ifRuleHead  = fn,
                    ifRuleArgs  = map do_arg args,
                    ifRuleRhs   = toIfaceExpr rhs,
                    ifRuleAuto  = auto,
                    ifRuleOrph  = orph }
      where
            -- For type args we must remove synonyms from the outermost
            -- level.  Reason: so that when we read it back in we'll
            -- construct the same ru_rough field as we have right now;
            -- see tcIfaceRule
        do_arg (Type ty)     = IfaceType (toIfaceType (deNoteType ty))
        do_arg (Coercion co) = IfaceCo   (toIfaceCoercion co)
        do_arg arg           = toIfaceExpr arg

            -- Compute orphanhood.  See Note [Orphans] in InstEnv
            -- A rule is an orphan only if none of the variables
            -- mentioned on its left-hand side are locally defined
        lhs_names = nameSetElems (ruleLhsOrphNames rule)

        orph = case filter (nameIsLocalOrFrom mod) lhs_names of
                            (n : _) -> NotOrphan (nameOccName n)
                            []      -> IsOrphan

    bogusIfaceRule :: Name -> IfaceRule
    bogusIfaceRule id_name
      = IfaceRule { ifRuleName = fsLit "bogus", ifActivation = NeverActive,
            ifRuleBndrs = [], ifRuleHead = id_name, ifRuleArgs = [],
            ifRuleRhs = IfaceExt id_name, ifRuleOrph = IsOrphan,
            ifRuleAuto = True }

    ---------------------
    toIfaceExpr :: CoreExpr -> IfaceExpr
    toIfaceExpr (Var v)         = toIfaceVar v
    toIfaceExpr (Lit l)         = IfaceLit l
    toIfaceExpr (Type ty)       = IfaceType (toIfaceType ty)
    toIfaceExpr (Coercion co)   = IfaceCo   (toIfaceCoercion co)
    toIfaceExpr (Lam x b)       = IfaceLam (toIfaceBndr x, toIfaceOneShot x) (toIfaceExpr b)
    toIfaceExpr (App f a)       = toIfaceApp f [a]
    toIfaceExpr (Case s x ty as)
      | null as                 = IfaceECase (toIfaceExpr s) (toIfaceType ty)
      | otherwise               = IfaceCase (toIfaceExpr s) (getFS x) (map toIfaceAlt as)
    toIfaceExpr (Let b e)       = IfaceLet (toIfaceBind b) (toIfaceExpr e)
    toIfaceExpr (Cast e co)     = IfaceCast (toIfaceExpr e) (toIfaceCoercion co)
    toIfaceExpr (Tick t e)
      | Just t' <- toIfaceTickish t = IfaceTick t' (toIfaceExpr e)
      | otherwise                   = toIfaceExpr e

    toIfaceOneShot :: Id -> IfaceOneShot
    toIfaceOneShot id | isId id
                      , OneShotLam <- oneShotInfo (idInfo id)
                      = IfaceOneShot
                      | otherwise
                      = IfaceNoOneShot

    ---------------------
    toIfaceTickish :: Tickish Id -> Maybe IfaceTickish
    toIfaceTickish (ProfNote cc tick push) = Just (IfaceSCC cc tick push)
    toIfaceTickish (HpcTick modl ix)       = Just (IfaceHpcTick modl ix)
    toIfaceTickish (SourceNote src names)  = Just (IfaceSource src names)
    toIfaceTickish (Breakpoint {})         = Nothing
       -- Ignore breakpoints, since they are relevant only to GHCi, and
       -- should not be serialised (Trac #8333)

    ---------------------
    toIfaceBind :: Bind Id -> IfaceBinding
    toIfaceBind (NonRec b r) = IfaceNonRec (toIfaceLetBndr b) (toIfaceExpr r)
    toIfaceBind (Rec prs)    = IfaceRec [(toIfaceLetBndr b, toIfaceExpr r) | (b,r) <- prs]

    ---------------------
    toIfaceAlt :: (AltCon, [Var], CoreExpr)
               -> (IfaceConAlt, [FastString], IfaceExpr)
    toIfaceAlt (c,bs,r) = (toIfaceCon c, map getFS bs, toIfaceExpr r)

    ---------------------
    toIfaceCon :: AltCon -> IfaceConAlt
    toIfaceCon (DataAlt dc) = IfaceDataAlt (getName dc)
    toIfaceCon (LitAlt l)   = IfaceLitAlt l
    toIfaceCon DEFAULT      = IfaceDefault

    ---------------------
    toIfaceApp :: Expr CoreBndr -> [Arg CoreBndr] -> IfaceExpr
    toIfaceApp (App f a) as = toIfaceApp f (a:as)
    toIfaceApp (Var v) as
      = case isDataConWorkId_maybe v of
            -- We convert the *worker* for tuples into IfaceTuples
            Just dc |  isTupleTyCon tc && saturated
                    -> IfaceTuple (tupleTyConSort tc) tup_args
              where
                val_args  = dropWhile isTypeArg as
                saturated = val_args `lengthIs` idArity v
                tup_args  = map toIfaceExpr val_args
                tc        = dataConTyCon dc

            _ -> mkIfaceApps (toIfaceVar v) as

    toIfaceApp e as = mkIfaceApps (toIfaceExpr e) as

    mkIfaceApps :: IfaceExpr -> [CoreExpr] -> IfaceExpr
    mkIfaceApps f as = foldl (\f a -> IfaceApp f (toIfaceExpr a)) f as

    ---------------------
    toIfaceVar :: Id -> IfaceExpr
    toIfaceVar v
        | Just fcall <- isFCallId_maybe v            = IfaceFCall fcall (toIfaceType (idType v))
           -- Foreign calls have special syntax
        | isExternalName name                        = IfaceExt name
        | otherwise                                  = IfaceLcl (getFS name)
      where name = idName v