From fa9f19cc68a3bb52bd0ac3a21225a486f4cd2beb Mon Sep 17 00:00:00 2001
From: simonpj <unknown>
Date: Thu, 28 Jan 1999 14:22:17 +0000
Subject: [PATCH] [project @ 1999-01-28 14:22:15 by simonpj] Fix erroneous
 name-clash report when a module ends up importing itself
 (eg TcEnv)

---
 ghc/compiler/rename/RnEnv.lhs    |   20 ++++++++++++--------
 ghc/compiler/rename/RnIfaces.lhs |   31 +++++++++++++++++++++++++++----
 ghc/compiler/rename/RnNames.lhs  |    1 +
 3 files changed, 40 insertions(+), 12 deletions(-)

diff --git a/ghc/compiler/rename/RnEnv.lhs b/ghc/compiler/rename/RnEnv.lhs
index ca8d876..ebe6af2 100644
--- a/ghc/compiler/rename/RnEnv.lhs
+++ b/ghc/compiler/rename/RnEnv.lhs
@@ -462,8 +462,8 @@ combine_globals :: [Name] 	-- Old
 combine_globals ns_old ns_new	-- ns_new is often short
   = foldr add ns_old ns_new
   where
-    add n ns | all (no_conflict n) ns_old = map choose ns	-- Eliminate duplicates
-	     | otherwise	          = n:ns
+    add n ns | any (is_duplicate n) ns_old = map choose ns	-- Eliminate duplicates
+	     | otherwise	           = n:ns
 	     where
 	       choose n' | n==n' && better_provenance n n' = n
 			 | otherwise			   = n'
@@ -479,12 +479,16 @@ better_provenance n1 n2
 	(NonLocalDef (UserImport _ _ _   ) _, NonLocalDef ImplicitImport _) -> True
 	other								    -> False
 
-no_conflict :: Name -> Name -> Bool
-no_conflict n1 n2 | isLocallyDefined n1 && isLocallyDefined n2 = False
-		  | otherwise 		                       = n1 == n2
-	-- We complain of a conflict if one RdrName maps to two different Names,
-	-- OR if one RdrName maps to the same *locally-defined* Name.  The latter
-	-- case is to catch two separate, local definitions of the same thing.
+is_duplicate :: Name -> Name -> Bool
+is_duplicate n1 n2 | isLocallyDefined n1 && isLocallyDefined n2 = False
+		   | otherwise 		                        = n1 == n2
+	-- We treat two bindings of a locally-defined name as a duplicate,
+	-- because they might be two separate, local defns and we want to report
+	-- and error for that, *not* eliminate a duplicate.
+
+	-- On the other hand, if you import the same name from two different
+	-- import statements, we *do* want to eliminate the duplicate, not report
+	-- an error.
 	--
 	-- If a module imports itself then there might be a local defn and an imported
 	-- defn of the same name; in this case the names will compare as equal, but
diff --git a/ghc/compiler/rename/RnIfaces.lhs b/ghc/compiler/rename/RnIfaces.lhs
index 0407764..5010eed 100644
--- a/ghc/compiler/rename/RnIfaces.lhs
+++ b/ghc/compiler/rename/RnIfaces.lhs
@@ -203,16 +203,21 @@ loadInterface doc_str load_mod
 
 	-- LOAD IT INTO Ifaces
 	-- First set the module
-    setModuleRn load_mod 	$
 
 	-- NB: *first* we do loadDecl, so that the provenance of all the locally-defined
 	---    names is done correctly (notably, whether this is an .hi file or .hi-boot file).
 	--     If we do loadExport first the wrong info gets into the cache (unless we
 	-- 	explicitly tag each export which seems a bit of a bore)
+
+    getModuleRn 		`thenRn` \ this_mod ->
+    setModuleRn load_mod  $	-- First set the module name of the module being loaded,
+				-- so that unqualified occurrences in the interface file
+				-- get the right qualifer
     foldlRn loadDecl (iDecls ifaces) rd_decls		`thenRn` \ new_decls ->
     foldlRn loadFixDecl (iFixes ifaces) rd_decls	`thenRn` \ new_fixities ->
-    mapRn   loadExport exports				`thenRn` \ avails_s ->
     foldlRn loadInstDecl insts rd_insts			`thenRn` \ new_insts ->
+
+    mapRn (loadExport this_mod) exports			`thenRn` \ avails_s ->
     let
 	 mod_details = (new_hif, mod_vers, concat avails_s)
 
@@ -229,8 +234,26 @@ loadInterface doc_str load_mod
     returnRn new_ifaces
     }}
 
-loadExport :: ExportItem -> RnMG [AvailInfo]
-loadExport (mod, entities)
+loadExport :: Module -> ExportItem -> RnMG [AvailInfo]
+loadExport this_mod (mod, entities)
+  | mod == this_mod = returnRn []
+	-- If the module exports anything defined in this module, just ignore it.
+	-- Reason: otherwise it looks as if there are two local definition sites
+	-- for the thing, and an error gets reported.  Easiest thing is just to
+	-- filter them out up front. This situation only arises if a module
+	-- imports itself, or another module that imported it.  (Necessarily,
+	-- this invoves a loop.)  Consequence: if you say
+	--	module A where
+	--	   import B( AType )
+	--	   type AType = ...
+	--
+	--	module B( AType ) where
+	--	   import {-# SOURCE #-} A( AType )
+	--
+	-- then you'll get a 'B does not export AType' message.  A bit bogus
+	-- but it's a bogus thing to do!
+
+  | otherwise
   = mapRn load_entity entities
   where
     new_name occ = newImportedGlobalName mod occ
diff --git a/ghc/compiler/rename/RnNames.lhs b/ghc/compiler/rename/RnNames.lhs
index a0dbf46..926fd59 100644
--- a/ghc/compiler/rename/RnNames.lhs
+++ b/ghc/compiler/rename/RnNames.lhs
@@ -73,6 +73,7 @@ getGlobalNames (HsModule this_mod _ exports imports decls mod_loc)
 	   rec_unqual_fn = unQualInScope rec_rn_env
 	in
 	setOmitQualFn rec_unqual_fn		$
+	setModuleRn this_mod			$
 
 		-- PROCESS LOCAL DECLS
 		-- Do these *first* so that the correct provenance gets
-- 
1.7.10.4