[project @ 2001-12-07 17:33:26 by simonpj]

----------------------------
	More jiggling in the renamer
	----------------------------

I was a little hasty before.  (Thanks Sigbjorn for finding
this.)  This commit tidies up the handling of AvailEnvs.
Principally:

  * filterImports now deals completely with hiding
    (before it handed off part of the job to mkGlobalRdrEnv)

  * The AvailEnv in an ExportAvails does not have class ops and
    data constructors in its domain.  This makes plusExportAvails
    more efficient, but the main thing is that it collects things
    up right.  (Previously, if we had
	import M( C )
	import M( op )
    then we got an AvailEnv which had C |-> AvailTC C [C]
    (no 'op').

  * In Rename, we do need a "filled-out" version of the overall
    AvailEnv, full_avail_env, which we construct on the spot in 'rename'.

1 files changed, 30 insertions, 20 deletions

diff --git a/ghc/compiler/rename/RnEnv.lhs b/ghc/compiler/rename/RnEnv.lhs
index affbcc9e91..25307f2a7f 100644
--- a/ghc/compiler/rename/RnEnv.lhs
+++ b/ghc/compiler/rename/RnEnv.lhs
@@ -56,6 +56,7 @@ import Util		( sortLt )
 import BasicTypes	( mapIPName )
 import List		( nub )
 import UniqFM		( lookupWithDefaultUFM )
+import Maybe		( mapMaybe )
 import CmdLineOpts
 import FastString	( FastString )
 \end{code}
@@ -258,8 +259,10 @@ lookupInstDeclBndr cls_name rdr_name
   | otherwise	
   = getGlobalAvails	`thenRn` \ avail_env ->
     case lookupNameEnv avail_env cls_name of
-	  -- class not in scope; don't fail as later checks will catch this,
-	  -- but just return (bogus) name. Icky.
+	  -- The class itself isn't in scope, so cls_name is unboundName
+	  -- e.g.   import Prelude hiding( Ord )
+	  --	    instance Ord T where ...
+	  -- The program is wrong, but that should not cause a crash.
 	Nothing -> returnRn (mkUnboundName rdr_name)
 	Just (AvailTC _ ns) -> case [n | n <- ns, nameOccName n == occ] of
 				(n:ns)-> ASSERT( null ns ) returnRn n
@@ -681,13 +684,11 @@ mkGlobalRdrEnv :: ModuleName		-- Imported module (after doing the "as M" name ch
 	       -> Bool			-- True <=> want unqualified import
 	       -> (Name -> Provenance)
 	       -> Avails		-- Whats imported
-	       -> Avails		-- What's to be hidden
-					-- I.e. import (imports - hides)
 	       -> Deprecations
 	       -> GlobalRdrEnv
 
-mkGlobalRdrEnv this_mod unqual_imp mk_provenance avails hides deprecs
-  = gbl_env3
+mkGlobalRdrEnv this_mod unqual_imp mk_provenance avails deprecs
+  = gbl_env2
   where
  	-- Make the name environment.  We're talking about a 
 	-- single module here, so there must be no name clashes.
@@ -698,12 +699,9 @@ mkGlobalRdrEnv this_mod unqual_imp mk_provenance avails hides deprecs
 	-- (Qualified names are always imported)
     gbl_env1 = foldl add_avail emptyRdrEnv avails
 
-	-- Delete (qualified names of) things that are hidden
-    gbl_env2 = foldl del_avail gbl_env1 hides
-
 	-- Add unqualified names
-    gbl_env3 | unqual_imp = foldl add_unqual gbl_env2 (rdrEnvToList gbl_env2)
-	     | otherwise  = gbl_env2
+    gbl_env2 | unqual_imp = foldl add_unqual gbl_env1 (rdrEnvToList gbl_env1)
+	     | otherwise  = gbl_env1
 
     add_unqual env (qual_name, elts)
 	= foldl add_one env elts
@@ -715,13 +713,6 @@ mkGlobalRdrEnv this_mod unqual_imp mk_provenance avails hides deprecs
 	-- the module (multiple bindings for the same name) we may get
 	-- duplicates.  So the simple thing is to do the fold.
 
-    del_avail env avail 
-	= foldl delOneFromGlobalRdrEnv env rdr_names
-	where
-	  rdr_names = map (mkRdrQual this_mod . nameOccName)
-			  (availNames avail)
-
-
     add_avail :: GlobalRdrEnv -> AvailInfo -> GlobalRdrEnv
     add_avail env avail = foldl add_name env (availNames avail)
 
@@ -740,7 +731,7 @@ mkIfaceGlobalRdrEnv m_avails
   = foldl add emptyRdrEnv m_avails
   where
     add env (mod,avails) = plusGlobalRdrEnv env (mkGlobalRdrEnv mod True 
-								(\n -> LocalDef) avails [] NoDeprecs)
+								(\n -> LocalDef) avails NoDeprecs)
 		-- The NoDeprecs is a bit of a hack I suppose
 \end{code}
 
@@ -793,8 +784,12 @@ in error messages.
 
 \begin{code}
 unQualInScope :: GlobalRdrEnv -> Name -> Bool
--- True if 'f' is in scope, and has only one binding
+-- True if 'f' is in scope, and has only one binding,
+-- and the thing it is bound to is the name we are looking for
 -- (i.e. false if A.f and B.f are both in scope as unqualified 'f')
+--
+-- This fn is only efficient if the shared 
+-- partial application is used a lot.
 unQualInScope env
   = (`elemNameSet` unqual_names)
   where
@@ -919,6 +914,21 @@ sortAvail (AvailTC n ns) | n `elem` ns = AvailTC n (n : sortLt lt (filter (/= n)
 			   n1 `lt` n2 = nameOccName n1 < nameOccName n2
 \end{code}
 
+\begin{code}
+pruneAvails :: (Name -> Bool)	-- Keep if this is True
+	    -> [AvailInfo]
+	    -> [AvailInfo]
+pruneAvails keep avails
+  = mapMaybe del avails
+  where
+    del :: AvailInfo -> Maybe AvailInfo	-- Nothing => nothing left!
+    del (Avail n) | keep n    = Just (Avail n)
+    	          | otherwise = Nothing
+    del (AvailTC n ns) | null ns'  = Nothing
+		       | otherwise = Just (AvailTC n ns')
+		       where
+		         ns' = filter keep ns
+\end{code}
 
 %************************************************************************
 %*									*