Improve error reporting for type signatures

See Trac #1310

2 files changed, 32 insertions, 5 deletions

diff --git a/compiler/rename/RnBinds.lhs b/compiler/rename/RnBinds.lhs
index d7a5952ee2..1c7bebbd7d 100644
--- a/compiler/rename/RnBinds.lhs
+++ b/compiler/rename/RnBinds.lhs
@@ -33,12 +33,12 @@ import RnEnv		( bindLocatedLocalsRn, lookupLocatedBndrRn,
 			  warnUnusedLocalBinds, mapFvRn, extendTyVarEnvFVRn,
 			)
 import DynFlags	( DynFlag(..) )
-import Name		( Name, nameOccName, nameSrcLoc )
+import Name
 import NameEnv
 import NameSet
 import PrelNames	( isUnboundName )
 import RdrName		( RdrName, rdrNameOcc )
-import SrcLoc		( mkSrcSpan, Located(..), unLoc )
+import SrcLoc		( Located(..), unLoc )
 import ListSetOps	( findDupsEq )
 import BasicTypes	( RecFlag(..) )
 import Digraph		( SCC(..), stronglyConnComp )
@@ -629,10 +629,20 @@ dupSigDeclErr sigs@(L loc sig : _)
     ppr_sig (L loc sig) = ppr loc <> colon <+> ppr sig
 
 unknownSigErr (L loc sig)
-  = addErrAt loc $
-	sep [ptext SLIT("Misplaced") <+> what_it_is <> colon, ppr sig]
+  = do	{ mod <- getModule
+	; addErrAt loc $
+		vcat [sep [ptext SLIT("Misplaced") <+> what_it_is <> colon, ppr sig],
+		      extra_stuff mod sig] }
   where
     what_it_is = hsSigDoc sig
+    extra_stuff mod  (TypeSig (L _ n) _)
+	| nameIsLocalOrFrom mod n
+	= ptext SLIT("The type signature must be given where")
+		<+> quotes (ppr n) <+> ptext SLIT("is declared")
+	| otherwise
+	= ptext SLIT("You cannot give a type signature for an imported value")
+
+    extra_stuff mod other = empty
 
 methodBindErr mbind
  =  hang (ptext SLIT("Pattern bindings (except simple variables) not allowed in instance declarations"))
diff --git a/compiler/rename/RnEnv.lhs b/compiler/rename/RnEnv.lhs
index 50b0adb83c..54a768af26 100644
--- a/compiler/rename/RnEnv.lhs
+++ b/compiler/rename/RnEnv.lhs
@@ -195,8 +195,25 @@ lookupTopBndrRn rdr_name
 -- The Haskell98 report does not stipulate this, but it will!
 -- So we must treat the 'f' in the signature in the same way
 -- as the binding occurrence of 'f', using lookupBndrRn
+--
+-- However, consider this case:
+--	import M( f )
+--	f :: Int -> Int
+--	g x = x
+-- We don't want to say 'f' is out of scope; instead, we want to
+-- return the imported 'f', so that later on the reanamer will
+-- correctly report "misplaced type sig".
 lookupLocatedSigOccRn :: Located RdrName -> RnM (Located Name)
-lookupLocatedSigOccRn = lookupLocatedBndrRn
+lookupLocatedSigOccRn = wrapLocM $ \ rdr_name -> do
+	{ local_env <- getLocalRdrEnv
+	; case lookupLocalRdrEnv local_env rdr_name of {
+		Just n  -> return n ;
+		Nothing -> do
+	{ mb_gre <- lookupGreLocalRn rdr_name
+	; case mb_gre of 
+		Just gre -> return (gre_name gre) 
+		Nothing  -> lookupGlobalOccRn rdr_name
+	}}}
 
 -- lookupInstDeclBndr is used for the binders in an 
 -- instance declaration.   Here we use the class name to