Check that exported modules were actually imported; fixes #1384

compiler/deSugar/Desugar.lhs

@@ -166,7 +166,7 @@ deSugar hsc_env
 		mg_exports   	= exports,
 		mg_deps	     	= deps,
 		mg_usages    	= usages,
-		mg_dir_imps  	= [m | (m,_,_) <- moduleEnvElts dir_imp_mods],
+		mg_dir_imps  	= [m | (m, _) <- moduleEnvElts dir_imp_mods],
 	        mg_rdr_env   	= rdr_env,
 		mg_fix_env   	= fix_env,
 		mg_deprecs   	= deprecs,

compiler/iface/MkIface.lhs

@@ -705,7 +705,7 @@ bump_unless False v = bumpVersion v
 
 \begin{code}
 mkUsageInfo :: HscEnv 
-	    -> ModuleEnv (Module, Bool, SrcSpan)
+	    -> ModuleEnv (Module, [(ModuleName, Bool, SrcSpan)])
 	    -> [(ModuleName, IsBootInterface)]
 	    -> NameSet -> IO [Usage]
 mkUsageInfo hsc_env dir_imp_mods dep_mods used_names
@@ -717,6 +717,12 @@ mkUsageInfo hsc_env dir_imp_mods dep_mods used_names
 	 -- don't get evaluated for a while and we can end up hanging on to
 	 -- the entire collection of Ifaces.
 
+mk_usage_info :: PackageIfaceTable
+              -> HscEnv
+              -> ModuleEnv (Module, [(ModuleName, Bool, SrcSpan)])
+              -> [(ModuleName, IsBootInterface)]
+              -> NameSet
+              -> [Usage]
 mk_usage_info pit hsc_env dir_imp_mods dep_mods used_names
   = mapCatMaybes mkUsage dep_mods
 	-- ToDo: do we need to sort into canonical order?
@@ -739,8 +745,8 @@ mk_usage_info pit hsc_env dir_imp_mods dep_mods used_names
     		     add_item occs _ = occ:occs
     
     depend_on_exports mod = case lookupModuleEnv dir_imp_mods mod of
-    				Just (_,no_imp,_) -> not no_imp
-	    			Nothing		  -> True
+    				Just (_, xs) -> any (\(_, no_imp, _) -> not no_imp) xs
+	    			Nothing		 -> True
     
     -- We want to create a Usage for a home module if 
     --	a) we used something from; has something in used_names

compiler/rename/RnNames.lhs

@@ -229,7 +229,7 @@ rnImportDecl this_mod (L loc (ImportDecl loc_imp_mod_name want_boot
 			other 		     -> False
 
 	imports   = ImportAvails { 
-			imp_mods     = unitModuleEnv imp_mod (imp_mod, import_all, loc),
+			imp_mods     = unitModuleEnv imp_mod (imp_mod, [(qual_mod_name, import_all, loc)]),
 			imp_orphs    = orphans,
 			imp_finsts   = finsts,
 			imp_dep_mods = mkModDeps dependent_mods,
@@ -759,6 +759,10 @@ exports_from_avail (Just rdr_items) rdr_env imports this_mod
     kids_env :: NameEnv [Name]	-- Maps a parent to its in-scope children
     kids_env = mkChildEnv (globalRdrEnvElts rdr_env)
 
+    imported_modules = [ qual_name
+                       | (_, xs) <- moduleEnvElts $ imp_mods imports,
+                         (qual_name, _, _) <- xs ]
+
     exports_from_item :: ExportAccum -> LIE RdrName -> RnM ExportAccum
     exports_from_item acc@(ie_names, occs, exports) 
                       (L loc ie@(IEModuleContents mod))
@@ -770,10 +774,14 @@ exports_from_avail (Just rdr_items) rdr_env imports this_mod
 
 	| otherwise
 	= do { implicit_prelude <- doptM Opt_ImplicitPrelude
-	     ; let gres = filter (isModuleExported implicit_prelude mod) 
-				 (globalRdrEnvElts rdr_env)
+         ; let { exportValid = (mod `elem` imported_modules)
+                            || (moduleName this_mod == mod)
+               ; gres = filter (isModuleExported implicit_prelude mod)
+                               (globalRdrEnvElts rdr_env)
+               }
 
-	     ; warnIf (null gres) (nullModuleExport mod)
+         ; checkErr exportValid (moduleNotImported mod)
+	     ; warnIf (exportValid && null gres) (nullModuleExport mod)
 
 	     ; occs' <- check_occs ie occs (map gre_name gres)
                       -- This check_occs not only finds conflicts
@@ -1110,7 +1118,7 @@ reportUnusedNames export_decls gbl_env
 	-- qualified imports into account.  But it's an improvement.
     add_expall mod acc = addToFM_C plusAvailEnv acc mod emptyAvailEnv
 
-    add_inst_mod (mod,_,_) acc 
+    add_inst_mod (mod, _) acc 
       | mod_name `elemFM` acc = acc	-- We import something already
       | otherwise	      = addToFM acc mod_name emptyAvailEnv
       where
@@ -1120,7 +1128,7 @@ reportUnusedNames export_decls gbl_env
    
     imports = tcg_imports gbl_env
 
-    direct_import_mods :: [(Module, Bool, SrcSpan)]
+    direct_import_mods :: [(Module, [(ModuleName, Bool, SrcSpan)])]
 	-- See the type of the imp_mods for this triple
     direct_import_mods = moduleEnvElts (imp_mods imports)
 
@@ -1129,10 +1137,11 @@ reportUnusedNames export_decls gbl_env
     -- [Note: not 'minimal_imports', because that includes directly-imported
     --	      modules even if we use nothing from them; see notes above]
     --
-    -- BUG WARNING: does not deal correctly with multiple imports of the same module
-    --	 	    becuase direct_import_mods has only one entry per module
+    -- BUG WARNING: this code is generally buggy
     unused_imp_mods :: [(ModuleName, SrcSpan)]
-    unused_imp_mods = [(mod_name,loc) | (mod,no_imp,loc) <- direct_import_mods,
+    unused_imp_mods = [(mod_name,loc)
+                    | (mod, xs) <- direct_import_mods,
+                      (_, no_imp, loc) <- xs,
 		       let mod_name = moduleName mod,
     		       not (mod_name `elemFM` minimal_imports1),
     		       mod /= pRELUDE,
@@ -1354,6 +1363,11 @@ dupModuleExport mod
 	  quotes (ptext SLIT("Module") <+> ppr mod), 
           ptext SLIT("in export list")]
 
+moduleNotImported :: ModuleName -> SDoc
+moduleNotImported mod
+  = ptext SLIT("The export item `module") <+> ppr mod <>
+    ptext SLIT("' is not imported")
+
 nullModuleExport mod
   = ptext SLIT("The export item `module") <+> ppr mod <> ptext SLIT("' exports nothing")
 

compiler/typecheck/TcRnDriver.lhs

@@ -245,7 +245,7 @@ tcRnImports hsc_env this_mod import_decls
 
 		-- Check type-familily consistency
 	; traceRn (text "rn1: checking family instance consistency")
-	; let { dir_imp_mods = map (\ (mod, _, _) -> mod) 
+	; let { dir_imp_mods = map (\ (mod, _) -> mod) 
 			     . moduleEnvElts 
 			     . imp_mods 
 			     $ imports }

compiler/typecheck/TcRnTypes.lhs

@@ -491,8 +491,11 @@ It is used 	* when processing the export list
 \begin{code}
 data ImportAvails 
    = ImportAvails {
-	imp_mods :: ModuleEnv (Module, Bool, SrcSpan),
+	imp_mods :: ModuleEnv (Module, [(ModuleName, Bool, SrcSpan)]),
 		-- Domain is all directly-imported modules
+        -- The ModuleName is what the module was imported as, e.g. in
+        --     import Foo as Bar
+        -- it is Bar.
 		-- Bool means:
 		--   True => import was "import Foo ()"
 		--   False  => import was some other form
@@ -555,12 +558,13 @@ plusImportAvails
   (ImportAvails { imp_mods = mods2,
 		  imp_dep_mods = dmods2, imp_dep_pkgs = dpkgs2,
                   imp_orphs = orphs2, imp_finsts = finsts2 })
-  = ImportAvails { imp_mods     = mods1  `plusModuleEnv` mods2,	
+  = ImportAvails { imp_mods     = plusModuleEnv_C plus_mod mods1 mods2,	
 		   imp_dep_mods = plusUFM_C plus_mod_dep dmods1 dmods2,	
 		   imp_dep_pkgs = dpkgs1 `unionLists` dpkgs2,
 		   imp_orphs    = orphs1 `unionLists` orphs2,
 		   imp_finsts   = finsts1 `unionLists` finsts2 }
   where
+    plus_mod (m1, xs1) (_, xs2) = (m1, xs1 ++ xs2)
     plus_mod_dep (m1, boot1) (m2, boot2) 
 	= WARN( not (m1 == m2), (ppr m1 <+> ppr m2) $$ (ppr boot1 <+> ppr boot2) )
 		-- Check mod-names match