shadowNames: Accept an OccName, not a GreName

previously, the `shadowNames` function would take `[GreName]`. This has
confused me for two reasons:

* Why `GreName` and not `Name`? Does the difference between a normal
  name and a field name matter? The code of `shadowNames` shows that it
  does not, but really its better if the type signatures says so.

* Why `Name` and not `OccName`? The point of `shadowNames` is to shadow
  _unqualified names_, at least in the two use cases I am aware of
  (names defined on the GHCI prompt or in TH splices).

  The code of `shadowNames` used to have cases that peek at the module
  of the given name and do something if that module appears in the
  `GlobalRdrElt`, but I think these cases are dead code, I don’t see
  how they could occur in the above use cases. Also, I replaced them
  with `errors` and GHC would still validate. Hence removing this code
  (yay!)

This change also allows `shadowNames` to accept an `OccSet` instead,
which allows for a faster implemenation; I’ll try that separately. This
in stead might help with !6703.

1 files changed, 2 insertions, 1 deletions

diff --git a/compiler/GHC/Runtime/Context.hs b/compiler/GHC/Runtime/Context.hs
index 6b4a4d0624..aaf99ee9a7 100644
--- a/compiler/GHC/Runtime/Context.hs
+++ b/compiler/GHC/Runtime/Context.hs
@@ -367,7 +367,8 @@ icExtendGblRdrEnv env tythings
        | otherwise
        = foldl' extendGlobalRdrEnv env1 (concatMap localGREsFromAvail avail)
        where
-          env1  = shadowNames env (concatMap availGreNames avail)
+          new_gres = concatMap availGreNames avail
+          env1  = shadowNames env (map occName new_gres)
           avail = tyThingAvailInfo thing
 
     -- Ugh! The new_tythings may include record selectors, since they