Fix the handling of names in declaration brackets

The handling of top-level names in declaration brackets is a bit tricky.
This commit fixes Trac #977;  test is TH_spliceD2.

The changes are commented in RnExpr.rnBracket and RdrName.hideSomeUnquals

compiler/basicTypes/RdrName.lhs

@@ -29,7 +29,7 @@ module RdrName (
 	GlobalRdrEnv, emptyGlobalRdrEnv, mkGlobalRdrEnv, plusGlobalRdrEnv, 
 	lookupGlobalRdrEnv, extendGlobalRdrEnv,
 	pprGlobalRdrEnv, globalRdrEnvElts,
-	lookupGRE_RdrName, lookupGRE_Name,
+	lookupGRE_RdrName, lookupGRE_Name, hideSomeUnquals,
 
 	-- GlobalRdrElt, Provenance, ImportSpec
 	GlobalRdrElt(..), isLocalGRE, unQualOK, 
@@ -45,7 +45,7 @@ import Module   ( ModuleName, mkModuleNameFS, Module, moduleName )
 import Name	( Name, NamedThing(getName), nameModule, nameParent_maybe,
 		  nameOccName, isExternalName, nameSrcLoc )
 import Maybes	( mapCatMaybes )
-import SrcLoc	( isGoodSrcLoc, isGoodSrcSpan, SrcSpan )
+import SrcLoc	( isGoodSrcLoc, isGoodSrcSpan, srcLocSpan, SrcSpan )
 import FastString ( FastString )
 import Outputable
 import Util	( thenCmp )
@@ -428,6 +428,35 @@ plusGRE :: GlobalRdrElt -> GlobalRdrElt -> GlobalRdrElt
 plusGRE g1 g2
   = GRE { gre_name = gre_name g1,
 	  gre_prov = gre_prov g1 `plusProv` gre_prov g2 }
+
+hideSomeUnquals :: GlobalRdrEnv -> [OccName] -> GlobalRdrEnv
+-- Hide any unqualified bindings for the specified OccNames
+-- This is used in TH, when renaming a declaration bracket
+--	[d| foo = ... |]
+-- We want unqualified 'foo' in "..." to mean this foo, not
+-- the one from the enclosing module.  But the *qualified* name
+-- from the enclosing moudule must certainly still be avaialable
+-- 	Seems like 5 times as much work as it deserves!
+hideSomeUnquals rdr_env occs
+  = foldr hide rdr_env occs
+  where
+    hide occ env 
+	| Just gres <- lookupOccEnv env occ = extendOccEnv env occ (map qual_gre gres)
+	| otherwise			    = env
+    qual_gre gre@(GRE { gre_name = name, gre_prov = LocalDef })
+	= GRE { gre_name = name, gre_prov = Imported [imp_spec] }
+	where	-- Local defs get transfomed to (fake) imported things
+	  mod = moduleName (nameModule name)
+	  imp_spec = ImpSpec { is_item = ImpAll, is_decl = decl_spec }
+	  decl_spec = ImpDeclSpec { is_mod = mod, is_as = mod, 
+				    is_qual = True, 
+				    is_dloc = srcLocSpan (nameSrcLoc name) }
+
+    qual_gre gre@(GRE { gre_prov = Imported specs })
+	= gre { gre_prov = Imported (map qual_spec specs) }
+
+    qual_spec spec@(ImpSpec { is_decl = decl_spec })
+  	= spec { is_decl = decl_spec { is_qual = True } }
 \end{code}
 
 
@@ -529,8 +558,10 @@ pprNameProvenance :: GlobalRdrElt -> SDoc
 -- Print out the place where the name was imported
 pprNameProvenance (GRE {gre_name = name, gre_prov = LocalDef})
   = ptext SLIT("defined at") <+> ppr (nameSrcLoc name)
-pprNameProvenance (GRE {gre_name = name, gre_prov = Imported (why:whys)})
-  = sep [ppr why, nest 2 (ppr_defn (nameSrcLoc name))]
+pprNameProvenance (GRE {gre_name = name, gre_prov = Imported whys})
+  = case whys of
+	(why:whys) -> sep [ppr why, nest 2 (ppr_defn (nameSrcLoc name))]
+	[] -> panic "pprNameProvenance"
 
 -- If we know the exact definition point (which we may do with GHCi)
 -- then show that too.  But not if it's just "imported from X".

compiler/rename/RnExpr.lhs

@@ -43,7 +43,7 @@ import Name             ( isTyVarName )
 #endif
 import Name		( Name, nameOccName, nameIsLocalOrFrom )
 import NameSet
-import RdrName		( RdrName, emptyGlobalRdrEnv, extendLocalRdrEnv, lookupLocalRdrEnv )
+import RdrName		( RdrName, emptyGlobalRdrEnv, extendLocalRdrEnv, lookupLocalRdrEnv, hideSomeUnquals )
 import LoadIface	( loadInterfaceForName )
 import UniqFM		( isNullUFM )
 import UniqSet		( emptyUniqSet )
@@ -573,25 +573,26 @@ rnBracket (DecBr group)
 	-- confuse the Names for the current module.  
 	-- By using a pretend module, thFAKE, we keep them safely out of the way.
 
-	; names    <- getLocalDeclBinders gbl_env1 group
-	; rdr_env' <- extendRdrEnvRn emptyGlobalRdrEnv names
-	-- Furthermore, the names in the bracket shouldn't conflict with
-	-- existing top-level names E.g.
+	; names <- getLocalDeclBinders gbl_env1 group
+
+	; let new_occs = map nameOccName names
+	      trimmed_rdr_env = hideSomeUnquals (tcg_rdr_env gbl_env) new_occs
+
+	; rdr_env' <- extendRdrEnvRn trimmed_rdr_env names
+	-- In this situation we want to *shadow* top-level bindings.
 	--	foo = 1
 	--	bar = [d| foo = 1|]
-	-- But both 'foo's get a LocalDef provenance, so we'd get a complaint unless
-	-- we start with an emptyGlobalRdrEnv
-
-	; setGblEnv (gbl_env { tcg_rdr_env = tcg_rdr_env gbl_env1 `plusOccEnv` rdr_env',
+	-- If we don't shadow, we'll get an ambiguity complaint when we do 
+	-- a lookupTopBndrRn (which uses lookupGreLocalRn) on the binder of the 'foo'
+	--
+	-- Furthermore, arguably if the splice does define foo, that should hide
+	-- any foo's further out
+	--
+	-- The shadowing is acheived by the call to hideSomeUnquals, which removes
+	-- the unqualified bindings of things defined by the bracket
+
+	; setGblEnv (gbl_env { tcg_rdr_env = rdr_env',
 			       tcg_dus = emptyDUs }) $ do
-		-- Notice plusOccEnv, not plusGlobalRdrEnv.  In this situation we want
-		-- to *shadow* top-level bindings.  (See the 'foo' example above.)
-		-- If we don't shadow, we'll get an ambiguity complaint when we do 
-		-- a lookupTopBndrRn (which uses lookupGreLocalRn) on the binder of the 'foo'
-		--
-		-- Furthermore, arguably if the splice does define foo, that should hide
-		-- any foo's further out
-		--
 		-- The emptyDUs is so that we just collect uses for this group alone
 
 	{ (tcg_env, group') <- rnSrcDecls group