[commit: ghc] master: Fix looking up of Exact RdrNames, fixes Trac #6005 (2a11904)

[Simon Peyton Jones]

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

On branch  : master

http://hackage.haskell.org/trac/ghc/changeset/2a1190431218f838797be3c09084e22dc131c58a

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

commit 2a1190431218f838797be3c09084e22dc131c58a
Author: Simon Peyton Jones <simonpj at microsoft.com>
Date:   Wed Apr 25 12:55:41 2012 +0100

    Fix looking up of Exact RdrNames, fixes Trac #6005
    
    See Note [Splicing Exact names] in RnEnv.

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

 compiler/rename/RnEnv.lhs |   43 ++++++++++++++++++++++++++++++++++---------
 1 files changed, 34 insertions(+), 9 deletions(-)

diff --git a/compiler/rename/RnEnv.lhs b/compiler/rename/RnEnv.lhs
index 364ce46..85d77a6 100644
--- a/compiler/rename/RnEnv.lhs
+++ b/compiler/rename/RnEnv.lhs
@@ -238,7 +238,14 @@ lookupExactOcc name
   = return name
   | otherwise           
   = do { env <- getGlobalRdrEnv
-       ; let gres = lookupGRE_Name env name
+       ; let -- See Note [Splicing Exact names] 
+             main_occ =  nameOccName name
+             demoted_occs = case demoteOccName main_occ of
+                              Just occ -> [occ]
+                              Nothing  -> []
+             gres = [ gre | occ <- main_occ : demoted_occs
+                          , gre <- lookupGlobalRdrEnv env occ
+	                  , gre_name gre == name ]
        ; case gres of
            []    -> -- See Note [Splicing Exact names]
                     do { lcl_env <- getLocalRdrEnv
@@ -471,6 +478,19 @@ otherwise the type checker will get confused.  To do this we need to
 keep track of all the Names in scope, and the LocalRdrEnv does just that;
 we consult it with RdrName.inLocalRdrEnvScope.
 
+There is another wrinkle.  With TH and -XDataKinds, consider
+   $( [d| data Nat = Zero 
+          data T = MkT (Proxy 'Zero)  |] )
+After splicing, but before renaming we get this:
+   data Nat_77{tc} = Zero_78{d}
+   data T_79{tc} = MkT_80{d} (Proxy 'Zero_78{tc})  |] )
+THe occurrence of 'Zero in the data type for T has the right unique,
+but it has a TcClsName name-space in its OccName.  (This is set by
+the ctxt_ns argument of Convert.thRdrName.)  When we check that is 
+in scope in the GlobalRdrEnv, we need to look up the DataName namespace
+too.  (An alternative would be to make the GlobalRdrEnv also have
+a Name -> GRE mapping.)
+
 Note [Usage for sub-bndrs]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~
 If you have this
@@ -531,18 +551,23 @@ lookupTypeOccRn rdr_name
   = do { mb_name <- lookupOccRn_maybe rdr_name 
        ; case mb_name of {
              Just name -> return name ;
-             Nothing   -> 
-
-    do { -- Maybe it's the name of a *data* constructor
-         data_kinds <- xoptM Opt_DataKinds
-       ; mb_demoted_name <- case demoteRdrName rdr_name of
-                              Just demoted_rdr -> lookupOccRn_maybe demoted_rdr
-                              Nothing          -> return Nothing
+             Nothing   -> lookup_demoted rdr_name } }
+
+lookup_demoted :: RdrName -> RnM Name
+lookup_demoted rdr_name
+  | Just demoted_rdr <- demoteRdrName rdr_name
+    -- Maybe it's the name of a *data* constructor
+  = do { data_kinds <- xoptM Opt_DataKinds
+       ; mb_demoted_name <- lookupOccRn_maybe demoted_rdr
        ; case mb_demoted_name of
            Nothing -> unboundName WL_Any rdr_name
            Just demoted_name 
              | data_kinds -> return demoted_name
-             | otherwise  -> unboundNameX WL_Any rdr_name suggest_dk }}}
+             | otherwise  -> unboundNameX WL_Any rdr_name suggest_dk }
+ 
+  | otherwise
+  = unboundName WL_Any rdr_name 
+
   where 
     suggest_dk = ptext (sLit "A data constructor of that name is in scope; did you mean -XDataKinds?")
 \end{code}