X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcEnv.lhs;h=1f9d3050eff2fd7094b829ee8ace3e4949b43511;hb=4c6a3f787abcaed009a574196d82237d9ae64fc8;hp=aa27a43c88867f0e9d608da943e7d4acfdf8811c;hpb=30c122df62ec75f9ed7f392f24c2925675bf1d06;p=ghc-hetmet.git

diff --git a/compiler/typecheck/TcEnv.lhs b/compiler/typecheck/TcEnv.lhs
index aa27a43..1f9d305 100644
--- a/compiler/typecheck/TcEnv.lhs
+++ b/compiler/typecheck/TcEnv.lhs
@@ -134,10 +134,22 @@ tcLookupGlobal name
 
 tcLookupField :: Name -> TcM Id		-- Returns the selector Id
 tcLookupField name = do
-    thing <- tcLookupGlobal name
+    thing <- tcLookup name	-- Note [Record field lookup]
     case thing of
-	AnId id -> return id
-	other	-> wrongThingErr "field name" (AGlobal thing) name
+	AGlobal (AnId id) -> return id
+	thing -> wrongThingErr "field name" thing name
+
+{- Note [Record field lookup]
+   ~~~~~~~~~~~~~~~~~~~~~~~~~~
+You might think we should have tcLookupGlobal here, since record fields
+are always top level.  But consider
+	f = e { f = True }
+Then the renamer (which does not keep track of what is a record selector
+and what is not) will rename the definition thus
+	f_7 = e { f_7 = True }
+Now the type checker will find f_7 in the *local* type environment, not
+the global one. It's wrong, of course, but we want to report a tidy
+error, not in TcEnv.notFound.  -}
 
 tcLookupDataCon :: Name -> TcM DataCon
 tcLookupDataCon name = do