From 72e37dedee9e8a109ebda4b13e49b7133b530591 Mon Sep 17 00:00:00 2001
From: "simonpj@microsoft.com" <unknown>
Date: Wed, 2 May 2007 11:47:38 +0000
Subject: [PATCH] Improve error reporting for type signatures

See Trac #1310
---
 compiler/rename/RnBinds.lhs      |   18 ++++++++++++++----
 compiler/rename/RnEnv.lhs        |   19 ++++++++++++++++++-
 compiler/typecheck/TcRnTypes.lhs |   12 ++++++++----
 3 files changed, 40 insertions(+), 9 deletions(-)

diff --git a/compiler/rename/RnBinds.lhs b/compiler/rename/RnBinds.lhs
index d7a5952..1c7bebb 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 50b0adb..54a768a 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
diff --git a/compiler/typecheck/TcRnTypes.lhs b/compiler/typecheck/TcRnTypes.lhs
index 9a08e9a..3c23921 100644
--- a/compiler/typecheck/TcRnTypes.lhs
+++ b/compiler/typecheck/TcRnTypes.lhs
@@ -306,11 +306,15 @@ data TcLclEnv		-- Changes as we move inside an expression
 		-- Maintained during renaming, of course, but also during
 		-- type checking, solely so that when renaming a Template-Haskell
 		-- splice we have the right environment for the renamer.
+		--
+		-- Used only for names bound within a value binding (bound by
+		-- lambda, case, where, let etc), but *not* for top-level names.
+		-- 
+		-- Does *not* include global name envt; may shadow it
+		-- Includes both ordinary variables and type variables;
+		-- they are kept distinct because tyvar have a different
+		-- occurrence contructor (Name.TvOcc)
 		-- 
-		--   Does *not* include global name envt; may shadow it
-		--   Includes both ordinary variables and type variables;
-		--   they are kept distinct because tyvar have a different
-		--   occurrence contructor (Name.TvOcc)
 		-- We still need the unsullied global name env so that
     		--   we can look up record field names
 
-- 
1.7.10.4