X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcEnv.lhs;h=1f9d3050eff2fd7094b829ee8ace3e4949b43511;hb=a27c5f77da8b3b3f00f9902b69a504460f234e8c;hp=ad45c7ca4cafd399d43d71c7a121f9102dd65fb0;hpb=288213d7c2c65fa68ca466c1a1a3378e24fa1151;p=ghc-hetmet.git

diff --git a/compiler/typecheck/TcEnv.lhs b/compiler/typecheck/TcEnv.lhs
index ad45c7c..1f9d305 100644
--- a/compiler/typecheck/TcEnv.lhs
+++ b/compiler/typecheck/TcEnv.lhs
@@ -81,6 +81,7 @@ import HscTypes
 import SrcLoc
 import Outputable
 import Maybes
+import FastString
 \end{code}
 
 
@@ -133,10 +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