[commit: ghc] master: delete shadowed entries from tcg_rdr_env (#5564) (0d6529f)

[Simon Marlow]

Repository : ssh://darcs.haskell.org//srv/darcs/ghc

On branch  : master

http://hackage.haskell.org/trac/ghc/changeset/0d6529f669104b6f22049d456a9600d949a09018

>---------------------------------------------------------------

commit 0d6529f669104b6f22049d456a9600d949a09018
Author: Simon Marlow <marlowsd at gmail.com>
Date:   Wed Oct 19 11:46:20 2011 +0100

    delete shadowed entries from tcg_rdr_env (#5564)
    
    This just tidies up the out-of-scope error messages in GHCi by not
    suggesting some names twice.

>---------------------------------------------------------------

 compiler/typecheck/TcRnDriver.lhs |   13 +++++++++++--
 1 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/compiler/typecheck/TcRnDriver.lhs b/compiler/typecheck/TcRnDriver.lhs
index aa4c7d7..b021917 100644
--- a/compiler/typecheck/TcRnDriver.lhs
+++ b/compiler/typecheck/TcRnDriver.lhs
@@ -1106,7 +1106,14 @@ setInteractiveContext hsc_env icxt thing_inside
         -- Perhaps it would be better to just extend the global TyVar
         -- list from the free tyvars in the Ids here?  Anyway, at least
         -- this hack is localised.
-
+        --
+        -- Note [delete shadowed tcg_rdr_env entries]
+        -- We also *delete* entries from tcg_rdr_env that we have
+        -- shadowed in the local env (see above).  This isn't strictly
+        -- necessary, but in an out-of-scope error when GHC suggests
+        -- names it can be confusing to see multiple identical
+        -- entries. (#5564)
+        --
         (tmp_ids, types_n_classes) = partitionWith sel_id (ic_tythings icxt)
           where sel_id (AnId id) = Left id
                 sel_id other     = Right other
@@ -1123,7 +1130,9 @@ setInteractiveContext hsc_env icxt thing_inside
                      , c <- tyConDataCons t ]
     in
     updGblEnv (\env -> env {
-          tcg_rdr_env      = ic_rn_gbl_env icxt
+          tcg_rdr_env      = delListFromOccEnv (ic_rn_gbl_env icxt)
+                                               (map getOccName visible_tmp_ids)
+                                 -- Note [delete shadowed tcg_rdr_env entries]
         , tcg_type_env     = type_env
         , tcg_inst_env     = extendInstEnvList
                               (extendInstEnvList (tcg_inst_env env) ic_insts)