Fix Trac #2293: improve error reporting for duplicate declarations

diff --git a/compiler/basicTypes/RdrName.lhs b/compiler/basicTypes/RdrName.lhs
index acc17f1..5e18497 100644 (file)
--- a/compiler/basicTypes/RdrName.lhs
+++ b/compiler/basicTypes/RdrName.lhs
@@ -29,7 +29,7 @@ module RdrName (
        lookupGlobalRdrEnv, extendGlobalRdrEnv,
        pprGlobalRdrEnv, globalRdrEnvElts,
        lookupGRE_RdrName, lookupGRE_Name, getGRE_NameQualifier_maybes,
-        hideSomeUnquals,
+        hideSomeUnquals, findLocalDupsRdrEnv,
 
        -- GlobalRdrElt, Provenance, ImportSpec
        GlobalRdrElt(..), isLocalGRE, unQualOK, qualSpecOK, unQualSpecOK,
@@ -463,6 +463,27 @@ mkGlobalRdrEnv gres
                                 (nameOccName (gre_name gre)) 
                                 [gre]
 
+findLocalDupsRdrEnv :: GlobalRdrEnv -> [OccName] -> (GlobalRdrEnv, [[Name]])
+-- For each OccName, see if there are multiple LocalDef definitions
+-- for it.  If so, remove all but one (to suppress subsequent error messages)
+-- and return a list of the duplicate bindings
+findLocalDupsRdrEnv rdr_env occs 
+  = go rdr_env [] occs
+  where
+    go rdr_env dups [] = (rdr_env, dups)
+    go rdr_env dups (occ:occs)
+      = case filter isLocalGRE gres of
+         []       -> WARN( True, ppr occ <+> ppr rdr_env ) 
+                     go rdr_env dups occs      -- Weird!  No binding for occ
+         [_]      -> go rdr_env dups occs      -- The common case
+         dup_gres -> go (extendOccEnv rdr_env occ (head dup_gres : nonlocal_gres))
+                        (map gre_name dup_gres : dups)
+                        occs
+      where
+        gres = lookupOccEnv rdr_env occ `orElse` []
+       nonlocal_gres = filterOut isLocalGRE gres
+
+
 insertGRE :: GlobalRdrElt -> [GlobalRdrElt] -> [GlobalRdrElt]
 insertGRE new_g [] = [new_g]
 insertGRE new_g (old_g : old_gs)

diff --git a/compiler/rename/RnNames.lhs b/compiler/rename/RnNames.lhs
index fda5945..ae730c7 100644 (file)
--- a/compiler/rename/RnNames.lhs
+++ b/compiler/rename/RnNames.lhs
@@ -304,30 +304,28 @@ extendGlobalRdrEnvRn shadowP avails new_fixities
              (rdr_env2, lcl_env2) | shadowP   = (rdr_env1, lcl_env1)
                                   | otherwise = (rdr_env,  lcl_env)
 
-       ; (rdr_env', fix_env') <- foldlM extend (rdr_env2, fix_env) gres
+             rdr_env3 = foldl extendGlobalRdrEnv rdr_env2 gres
+             fix_env' = foldl extend_fix_env     fix_env  gres
+             (rdr_env', dups) = findLocalDupsRdrEnv rdr_env3 new_occs
+
+             gbl_env' = gbl_env { tcg_rdr_env = rdr_env', tcg_fix_env = fix_env' }
+             
+       ; mapM_ addDupDeclErr dups
        
-       ; let gbl_env' = gbl_env { tcg_rdr_env = rdr_env', tcg_fix_env = fix_env' }
        ; traceRn (text "extendGlobalRdrEnvRn" <+> (ppr new_fixities $$ ppr fix_env $$ ppr fix_env'))
        ; return (gbl_env', lcl_env2) }
   where
     gres = gresFromAvails LocalDef avails
 
-    extend envs@(cur_rdr_env, _cur_fix_env) gre
-       = let gres = lookupGlobalRdrEnv cur_rdr_env (nameOccName (gre_name gre)) 
-          in case filter isLocalGRE gres of -- Check for existing *local* defns 
-                  dup_gre:_ -> do { addDupDeclErr (gre_name dup_gre) (gre_name gre)
-                                 ; return envs }
-                  [] -> return (simple_extend envs gre)
-
-    simple_extend (rdr_env, fix_env) gre 
-      = (extendGlobalRdrEnv rdr_env gre, fix_env')
-      where
        --  If there is a fixity decl for the gre, add it to the fixity env
+    extend_fix_env fix_env gre 
+      | Just (L _ fi) <- lookupFsEnv new_fixities (occNameFS occ)
+      = extendNameEnv fix_env name (FixItem occ fi)
+      | otherwise
+      = fix_env
+      where
        name = gre_name gre
         occ  = nameOccName name
-        fix_env' = case lookupFsEnv new_fixities (occNameFS occ) of
-                     Nothing       -> fix_env
-                     Just (L _ fi) -> extendNameEnv fix_env name (FixItem occ fi)
 \end{code}
 
 @getLocalDeclBinders@ returns the names for an @HsDecl@.  It's
@@ -1398,16 +1396,16 @@ exportClashErr global_env name1 name2 ie1 ie2
                                    then (name1, ie1, name2, ie2)
                                    else (name2, ie2, name1, ie1)
 
-addDupDeclErr :: Name -> Name -> TcRn ()
-addDupDeclErr name_a name_b
-  = addErrAt (srcLocSpan loc2) $
-    vcat [ptext (sLit "Multiple declarations of") <+> quotes (ppr name1),
-         ptext (sLit "Declared at:") <+> vcat [ppr (nameSrcLoc name1), ppr loc2]]
-  where
-    loc2 = nameSrcLoc name2
-    (name1,name2) | nameSrcLoc name_a > nameSrcLoc name_b = (name_b,name_a)
-                 | otherwise                             = (name_a,name_b)
+addDupDeclErr :: [Name] -> TcRn ()
+addDupDeclErr []
+  = panic "addDupDeclErr: empty list"
+addDupDeclErr names@(name : _)
+  = addErrAt (getSrcSpan (last sorted_names)) $
        -- Report the error at the later location
+    vcat [ptext (sLit "Multiple declarations of") <+> quotes (ppr name),
+         ptext (sLit "Declared at:") <+> vcat (map (ppr . nameSrcLoc) sorted_names)]
+  where
+    sorted_names = sortWith nameSrcLoc names
 
 dupExportWarn :: OccName -> IE RdrName -> IE RdrName -> SDoc
 dupExportWarn occ_name ie1 ie2