+  Mostly this change is only visible to authors of modules in `ghc-internal` or `base`.

+

+  Since the known-names are no longer fully wired in to the compiler, GHCi must

+  be able to find `base` for all the known-names like `print` and `IO` to be

+  available. Therefore `ghci -hide-all-packages`, which hides `base` from ghci,

+  no longer works. One must use `ghci -hide-all-packages -package base` to

+  bring in the known-names from base.

+

+import GHC.Iface.Load (KnownEntitySource(..), lookupKnownKeyName, lookupKnownKeysModule)

+              home_unit     = hsc_home_unit hsc_env

+        ; essentials_mod <- liftIO $ lookupKnownKeysModule hsc_env dflags

+                                    (moduleUnitId <$> essentials_mod)

+        lookupKnownKeysMap, lookupKnownKeysModule,

+            Just (kk_maps, _) -> return kk_maps ;

+       ; updateEps_ (\eps -> eps { eps_known_keys = Just ((kk_map, occ_map), mi_module iface) })

+-- | Lookup the module exporting the canonical known-entities definitions (GHC.Essentials)

+lookupKnownKeysModule :: HscEnv -> DynFlags {-^ Module dyn flags -} -> IO (Maybe Module)

+lookupKnownKeysModule hsc_env dflags = do

+  found_essentials <- findImportedModule hsc_env eSSENTIALS_NAME NoPkgQual

+  let rebindable_kn = gopt Opt_RebindableKnownNames dflags

+  let essentials_uid

+        | rebindable_kn                   = Nothing

+        | Found _ mod <- found_essentials = Just mod

+        | otherwise                       = Nothing

+  return essentials_uid

+

+  = do    let pluginModules = map lpModule (loadedPlugins (hsc_plugins hsc_env))

+          let home_unit     = hsc_home_unit hsc_env

+          let dflags        = ms_hspp_opts mod_summary

+          essentials_mod <- liftIO $ lookupKnownKeysModule hsc_env dflags

+                                    (moduleUnitId <$> essentials_mod)

+          docs  <- extractDocs dflags tc_result

+-- ^ Construct the implicit declaration "import Prelude" (or not)

+          -- We want instance declarations from all home-package

+          -- modules below this one, including boot modules, except

+          -- ourselves.  The 'except ourselves' is so that we don't

+          -- get the instances from this module's hs-boot file.  This

+          -- filtering also ensures that we don't see instances from

+          -- modules batch (@--make@) compiled before this one, but

+          -- which are not below this one.

+        ; (home_insts, home_fam_insts) <- liftIO $

+              hugInstancesBelow hsc_env unitId mnwib

+

+          -- We use 'unsafeInterleaveIO' to avoid redundant memory allocations

+          -- See Note [Lazily loading COMPLETE pragmas] from GHC.HsToCore.Monad

+          -- and see https://gitlab.haskell.org/ghc/ghc/-/merge_requests/14274#note_620545

+        ; completeSigsBelow <- liftIO $ unsafeInterleaveIO $

+              hugCompleteSigsBelow hsc_env unitId mnwib

+

+          -- Record boot-file info in the EPS, so that it's

+          -- visible to loadHiBootInterface in tcRnSrcDecls,

+          -- and any other incrementally-performed imports

+        ; when (isOneShot (ghcMode (hsc_dflags hsc_env))) $ do {

+            updateEps_ $ \eps  -> eps { eps_is_boot = imp_boot_mods imports }

+         }

+    Just ((kk_map, _), _) -> case lookupKnownKeysMap kk_map key of

+        ; hsc_env <- getTopEnv

+        ; essentials_mod <- liftIO $ lookupKnownKeysModule hsc_env dflags

+        ; case essentials_mod of

+            Nothing ->

+              -- If GHC.Essentials isn't available at all (e.g. -hide-all-packages),

+              -- don't add the built-in defaulting, bc e.g. Num is a known-entity.

+              return (user_defaults, extended_defaults)

+            _ | this_unit == ghcInternalUnit ->

+              -- see Remark [No built-in defaults in ghc-internal]

+              -- in Note [Builtin class defaults] in GHC.Tc.Utils.Env

+              return (user_defaults, extended_defaults)

+            _ -> do

+        eps_known_keys   :: Maybe (KnownKeyNameMaps, Module),

+                         -- ^ See Note [Overview of known entities].

+                         -- Caches the 'Module' where known entities are defined.

+-- The fifth argument is the unit-id of GHC.Essentials, unless -frebindable-known-names.

+mkDependencies :: HomeUnit -> Module -> ImportAvails -> [Module] -> Maybe UnitId -> Dependencies

+mkDependencies home_unit mod imports plugin_mods messentials_pkg =

+      direct_pkgs = add_essentials_pkg $

+        Set.map (\(lvl, uid) -> (IfaceImportLevel lvl, uid)) (imp_dep_direct_pkgs imports)

+

+      -- Add the GHC.Essentials package to direct deps unless -frebindable-known-names is on

+      -- (the modgraph has edges to GHC.Essentials similarly, see `getImportEdges` in GHC.Parser.Header)

+      add_essentials_pkg = case messentials_pkg of

+        Nothing             -> id

+        Just essentials_uid -> Set.insert (IfaceImportLevel NormalLevel, essentials_uid)

+TOP=../../..

+include $(TOP)/mk/boilerplate.mk

+include $(TOP)/mk/test.mk

+

+# Test that compiling X.hs without implicit Prelude does not recompile X the

+# second time or third time. In !15899, X.hs was recompiled because of an

+# incorrect "GHC.Essentials package changed"

+clean:

+	rm -f *.o *.hi

+

+T27013c: clean

+	'$(TEST_HC)' $(TEST_HC_OPTS) --make X.hs

+	'$(TEST_HC)' $(TEST_HC_OPTS) --make X.hs

+	'$(TEST_HC)' $(TEST_HC_OPTS) --make X.hs

+[1 of 1] Compiling X                ( X.hs, X.o )

+{-# LANGUAGE NoImplicitPrelude #-}

+module X where

+x = x

+test('T27013c', [extra_files(['X.hs'])],

+     makefile_test, [])