SafeHaskell: Force all imports to be safe in Safe mode

compiler/iface/MkIface.lhs

@@ -907,9 +907,11 @@ mk_usage_info pit hsc_env this_mod direct_imports used_names
 
         (is_direct_import, imp_safe)
             = case lookupModuleEnv direct_imports mod of
-                Just ((_,_,_,safe):xs) -> (True, safe)
-                Just _                 -> pprPanic "mkUsage: empty direct import" empty
-                Nothing                -> (False, False)
+                Just ((_,_,_,safe):_xs) -> (True, safe)
+                Just _                  -> pprPanic "mkUsage: empty direct import" empty
+                Nothing                 -> (False, safeImportsRequired 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 SafeHaskell
     
         used_occs = lookupModuleEnv ent_map mod `orElse` []
 

compiler/main/DynFlags.hs

@@ -31,8 +31,10 @@ module DynFlags (
         fFlags, fLangFlags, xFlags,
         DPHBackend(..), dphPackageMaybe,
         wayNames,
+
+        -- ** SafeHaskell
         SafeHaskellMode(..),
-        safeHaskellOn,
+        safeHaskellOn, safeImportsRequired,
 
         Settings(..),
         ghcUsagePath, ghciUsagePath, topDir, tmpDir, rawSettings,
@@ -985,6 +987,11 @@ setSafeHaskell s = upd f
                          safeHaskell = combineSafeFlags sf s
                      }
 
+-- | Are all imports required to be safe for this SafeHaskell mode?
+safeImportsRequired :: DynFlags -> Bool
+safeImportsRequired dflags = m == Sf_SafeLanguage || m == Sf_Safe
+                            where m = safeHaskell dflags
+
 -- | Combine two SafeHaskell modes correctly. Used for dealing with multiple flags.
 -- This makes SafeHaskell very much a monoid but for now I prefer this as I don't
 -- want to export this functionality from the module but do want to export the

compiler/rename/RnNames.lhs

@@ -219,8 +219,10 @@ rnImportDecl this_mod implicit_prelude
                         Just (is_hiding, ls) -> not is_hiding && null ls
                         _                    -> False
 
+        mod_safe' = mod_safe || safeImportsRequired dflags
+
         imports   = ImportAvails {
-                        imp_mods     = unitModuleEnv imp_mod [(qual_mod_name, import_all, loc, mod_safe)],
+                        imp_mods     = unitModuleEnv imp_mod [(qual_mod_name, import_all, loc, mod_safe')],
                         imp_orphs    = orphans,
                         imp_finsts   = finsts,
                         imp_dep_mods = mkModDeps dependent_mods,
@@ -234,7 +236,7 @@ rnImportDecl this_mod implicit_prelude
           _           -> return ()
      )
 
-    let new_imp_decl = L loc (ImportDecl loc_imp_mod_name mb_pkg want_boot mod_safe
+    let new_imp_decl = L loc (ImportDecl loc_imp_mod_name mb_pkg want_boot mod_safe'
                                          qual_only as_mod new_imp_details)
 
     return (new_imp_decl, gbl_env, imports, mi_hpc iface)