deSugar/DsUsage.hs

    {-# LANGUAGE CPP #-}

    module DsUsage (
        -- * Dependency/fingerprinting code (used by MkIface)
        mkUsageInfo, mkUsedNames, mkDependencies
        ) where

    #include "HsVersions.h"

    import DynFlags
    import HscTypes
    import TcRnTypes
    import Name
    import NameSet
    import Module
    import Outputable
    import Util
    import UniqSet
    import UniqFM
    import Fingerprint
    import Maybes

    import Data.List
    import Data.IORef
    import Data.Map (Map)
    import qualified Data.Map as Map
    import qualified Data.Set as Set

    {- Note [Module self-dependency]
       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    RnNames.calculateAvails asserts the invariant that a module must not occur in
    its own dep_orphs or dep_finsts. However, if we aren't careful this can occur
    in the presence of hs-boot files: Consider that we have two modules, A and B,
    both with hs-boot files,

        A.hs contains a SOURCE import of B B.hs-boot contains a SOURCE import of A
        A.hs-boot declares an orphan instance A.hs defines the orphan instance

    In this case, B's dep_orphs will contain A due to its SOURCE import of A.
    Consequently, A will contain itself in its imp_orphs due to its import of B.
    This fact would end up being recorded in A's interface file. This would then
    break the invariant asserted by calculateAvails that a module does not itself in
    its dep_orphs. This was the cause of Trac #14128.

    -}

    -- | 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 = modDepsElts (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.)

              dep_orphs = filter (/= mod) (imp_orphs imports)
                    -- We must also remove self-references from imp_orphs. See
                    -- Note [Module self-dependency]

              pkgs | th_used   = Set.insert (toInstalledUnitId thUnitId) (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 = sort (Set.toList pkgs)
              trust_pkgs  = imp_trust_pkgs imports
              dep_pkgs'   = map (\x -> (x, x `Set.member` trust_pkgs)) sorted_pkgs

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

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

    mkUsageInfo :: HscEnv -> Module -> ImportedMods -> NameSet -> [FilePath] -> [(Module, Fingerprint)] -> IO [Usage]
    mkUsageInfo hsc_env this_mod dir_imp_mods used_names dependent_files merged
      = 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
            usages = mod_usages ++ [ UsageFile { usg_file_path = f
                                               , usg_file_hash = hash }
                                   | (f, hash) <- zip dependent_files hashes ]
                                ++ [ UsageMergedRequirement
                                        { usg_mod = mod,
                                          usg_mod_hash = hash
                                        }
                                   | (mod, hash) <- merged ]
        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  = nonDetFoldUniqSet add_mv emptyModuleEnv used_names
         -- nonDetFoldUFM is OK here. If you follow the logic, we sort by OccName
         -- in ent_hashs
         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 ->
                    -- See Note [Identity versus semantic module]
                    let mod' = if isHoleModule mod
                                then mkModule this_pkg (moduleName mod)
                                else mod
                    -- This lambda function is really just a
                    -- specialised (++); originally came about to
                    -- avoid quadratic behaviour (trac #2680)
                    in 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

          | moduleUnitId 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

            by_is_safe (ImportedByUser imv) = imv_is_safe imv
            by_is_safe _ = False
            (is_direct_import, imp_safe)
                = case lookupModuleEnv direct_imports mod of
                    -- ezyang: I'm not sure if any is the correct
                    -- metric here. If safety was guaranteed to be uniform
                    -- across all imports, why did the old code only look
                    -- at the first import?
                    Just bys -> (True, any by_is_safe bys)
                    Nothing  -> (False, safeImplicitImpsReq dflags)
                    -- Nothing case is for references to entities which were
                    -- not directly imported (NB: the "implicit" Prelude import
                    -- counts as directly imported!  An entity is not directly
                    -- imported if, e.g., we got a reference to it from a
                    -- reexport of another module.)

            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!
            -}