trac #1789 (warnings for missing import lists)

compiler/main/DynFlags.hs

@@ -164,6 +164,7 @@ data DynFlag
    | Opt_WarnIncompletePatterns
    | Opt_WarnIncompletePatternsRecUpd
    | Opt_WarnMissingFields
+   | Opt_WarnMissingImportList
    | Opt_WarnMissingMethods
    | Opt_WarnMissingSigs
    | Opt_WarnNameShadowing
@@ -1493,6 +1494,7 @@ fFlags = [
   ( "warn-incomplete-patterns",         Opt_WarnIncompletePatterns, const Supported ),
   ( "warn-incomplete-record-updates",   Opt_WarnIncompletePatternsRecUpd, const Supported ),
   ( "warn-missing-fields",              Opt_WarnMissingFields, const Supported ),
+  ( "warn-missing-import-lists",        Opt_WarnMissingImportList, const Supported ),
   ( "warn-missing-methods",             Opt_WarnMissingMethods, const Supported ),
   ( "warn-missing-signatures",          Opt_WarnMissingSigs, const Supported ),
   ( "warn-name-shadowing",              Opt_WarnNameShadowing, const Supported ),

compiler/rename/RnNames.lhs

@@ -70,8 +70,8 @@ rnImports imports
             when (notNull prel_imports) $ addWarn (implicitPreludeWarn)
           )
 
-         stuff1 <- mapM (rnImportDecl this_mod) (prel_imports ++ ordinary)
-         stuff2 <- mapM (rnImportDecl this_mod) source
+         stuff1 <- mapM (rnImportDecl this_mod implicit_prelude) (prel_imports ++ ordinary)
+         stuff2 <- mapM (rnImportDecl this_mod implicit_prelude) source
          let (decls, rdr_env, imp_avails,hpc_usage) = combine (stuff1 ++ stuff2)
          return (decls, rdr_env, imp_avails,hpc_usage) 
 
@@ -86,11 +86,11 @@ rnImports imports
                    imp_avails1 `plusImportAvails` imp_avails2,
 		   hpc_usage1 || hpc_usage2)
 
-rnImportDecl  :: Module
+rnImportDecl  :: Module -> Bool
 	      -> LImportDecl RdrName
 	      -> RnM (LImportDecl Name, GlobalRdrEnv, ImportAvails,AnyHpcUsage)
 
-rnImportDecl this_mod (L loc (ImportDecl loc_imp_mod_name mb_pkg want_boot
+rnImportDecl this_mod implicit_prelude (L loc (ImportDecl loc_imp_mod_name mb_pkg want_boot
                                          qual_only as_mod imp_details))
   = setSrcSpan loc $ do
 
@@ -104,6 +104,11 @@ rnImportDecl this_mod (L loc (ImportDecl loc_imp_mod_name mb_pkg want_boot
 	imp_mod_name = unLoc loc_imp_mod_name
 	doc = ppr imp_mod_name <+> ptext (sLit "is directly imported")
 
+    case imp_details of
+        (Just _) -> return ()
+        Nothing -> when (not (implicit_prelude && imp_mod_name == pRELUDE_NAME)) $
+            ifOptM Opt_WarnMissingImportList (addWarn (missingImportListWarn imp_mod_name))
+
     iface <- loadSrcInterface doc imp_mod_name want_boot mb_pkg
 
 	-- Compiler sanity check: if the import didn't say
@@ -1447,6 +1452,10 @@ nullModuleExport :: ModuleName -> SDoc
 nullModuleExport mod
   = ptext (sLit "The export item `module") <+> ppr mod <> ptext (sLit "' exports nothing")
 
+missingImportListWarn :: ModuleName -> SDoc
+missingImportListWarn mod
+  = ptext (sLit "The module") <+> quotes (ppr mod) <+> ptext (sLit "is missing an import list")
+
 moduleWarn :: ModuleName -> WarningTxt -> SDoc
 moduleWarn mod (WarningTxt txt)
   = sep [ ptext (sLit "Module") <+> quotes (ppr mod) <> ptext (sLit ":"), 

docs/users_guide/flags.xml

@@ -1128,6 +1128,13 @@
 	    <entry><option>-fno-warn-missing-fields</option></entry>
 	  </row>
 
+	  <row>
+	    <entry><option>-fwarn-missing-import-lists</option></entry>
+	    <entry>warn when explicit imports lack an import list</entry>
+	    <entry>dynamic</entry>
+	    <entry><option>-fnowarn-missing-import-lists</option></entry>
+	  </row>
+
 	  <row>
 	    <entry><option>-fwarn-missing-methods</option></entry>
 	    <entry>warn when class methods are undefined</entry>