X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Frename%2FRnPat.lhs;h=01f621b792c4ea00a9e0e1be06e7d049a73f5829;hb=a8407757462804dfd51708d6cfdda0417a91bf8e;hp=bc174954787e022915dd776b2bb795f18bd47101;hpb=6f8ff0bbad3b9fa389c960ad1b5a267a1ae502f1;p=ghc-hetmet.git

diff --git a/compiler/rename/RnPat.lhs b/compiler/rename/RnPat.lhs
index bc17495..01f621b 100644
--- a/compiler/rename/RnPat.lhs
+++ b/compiler/rename/RnPat.lhs
@@ -40,13 +40,13 @@ import TcRnMonad
 import TcHsSyn		( hsOverLitName )
 import RnEnv
 import RnTypes
-import DynFlags		( DynFlag(..) )
+import DynFlags
 import PrelNames
 import Constants	( mAX_TUPLE_SIZE )
 import Name
 import NameSet
-import Module
 import RdrName
+import BasicTypes
 import ListSetOps	( removeDups, minusList )
 import Outputable
 import SrcLoc
@@ -135,15 +135,14 @@ data NameMaker
 
   | LetMk       -- Let bindings, incl top level
 		-- Do *not* check for unused bindings
-      (Maybe Module)   -- Just m  => top level of module m
-                       -- Nothing => not top level
+      TopLevelFlag
       MiniFixityEnv
 
-topRecNameMaker :: Module -> MiniFixityEnv -> NameMaker
-topRecNameMaker mod fix_env = LetMk (Just mod) fix_env
+topRecNameMaker :: MiniFixityEnv -> NameMaker
+topRecNameMaker fix_env = LetMk TopLevel fix_env
 
 localRecNameMaker :: MiniFixityEnv -> NameMaker
-localRecNameMaker fix_env = LetMk Nothing fix_env 
+localRecNameMaker fix_env = LetMk NotTopLevel fix_env 
 
 matchNameMaker :: HsMatchContext a -> NameMaker
 matchNameMaker ctxt = LamMk report_unused
@@ -162,15 +161,17 @@ newName (LamMk report_unused) rdr_name
 	   ; when report_unused $ warnUnusedMatches [name] fvs
 	   ; return (res, name `delFV` fvs) })
 
-newName (LetMk mb_top fix_env) rdr_name
+newName (LetMk is_top fix_env) rdr_name
   = CpsRn (\ thing_inside -> 
-        do { name <- case mb_top of
-                       Nothing  -> newLocalBndrRn rdr_name
-                       Just mod -> newTopSrcBinder mod rdr_name
-	   ; bindLocalNamesFV_WithFixities [name] fix_env $
+        do { name <- case is_top of
+                       NotTopLevel -> newLocalBndrRn rdr_name
+                       TopLevel    -> newTopSrcBinder rdr_name
+	   ; bindLocalName name $	-- Do *not* use bindLocalNameFV here
+					-- See Note [View pattern usage]
+             addLocalFixities fix_env [name] $
 	     thing_inside name })
 			  
-    -- Note: the bindLocalNamesFV_WithFixities is somewhat suspicious 
+    -- Note: the bindLocalName is somewhat suspicious
     --       because it binds a top-level name as a local name.
     --       however, this binding seems to work, and it only exists for
     --       the duration of the patterns and the continuation;
@@ -178,6 +179,14 @@ newName (LetMk mb_top fix_env) rdr_name
     --       before going on to the RHSes (see RnSource.lhs).
 \end{code}
 
+Note [View pattern usage]
+~~~~~~~~~~~~~~~~~~~~~~~~~
+Consider
+  let (r, (r -> x)) = x in ...
+Here the pattern binds 'r', and then uses it *only* in the view pattern.
+We want to "see" this use, and in let-bindings we collect all uses and
+report unused variables at the binding level. So we must use bindLocalName
+here, *not* bindLocalNameFV.  Trac #3943.
 
 %*********************************************************
 %*							*
@@ -233,7 +242,8 @@ rnPats ctxt pats thing_inside
 rnPat :: HsMatchContext Name -- for error messages
       -> LPat RdrName 
       -> (LPat Name -> RnM (a, FreeVars))
-      -> RnM (a, FreeVars)
+      -> RnM (a, FreeVars)     -- Variables bound by pattern do not 
+      	     	 	       -- appear in the result FreeVars 
 rnPat ctxt pat thing_inside 
   = rnPats ctxt [pat] (\[pat'] -> thing_inside pat')