In GHCi, filter instances by what is in scope, not just by what is in scope unqualified

[ghc-hetmet.git] / compiler / main / InteractiveEval.hs

diff --git a/compiler/main/InteractiveEval.hs b/compiler/main/InteractiveEval.hs
index 3de25ce..42b787a 100644 (file)
--- a/compiler/main/InteractiveEval.hs
+++ b/compiler/main/InteractiveEval.hs
@@ -711,8 +711,29 @@ moduleIsInterpreted s modl = withSession s $ \h ->
                 _not_a_home_module -> return False
 
 -- | Looks up an identifier in the current interactive context (for :info)
+-- Filter the instances by the ones whose tycons (or clases resp) 
+-- are in scope (qualified or otherwise).  Otherwise we list a whole lot too many!
+-- The exact choice of which ones to show, and which to hide, is a judgement call.
+--     (see Trac #1581)
 getInfo :: Session -> Name -> IO (Maybe (TyThing,Fixity,[Instance]))
-getInfo s name = withSession s $ \hsc_env -> tcRnGetInfo hsc_env name
+getInfo s name 
+  = withSession s $ \hsc_env -> 
+    do { mb_stuff <- tcRnGetInfo hsc_env name
+       ; case mb_stuff of
+           Nothing -> return Nothing
+           Just (thing, fixity, ispecs) -> do
+       { let rdr_env = ic_rn_gbl_env (hsc_IC hsc_env)
+       ; return (Just (thing, fixity, filter (plausible rdr_env) ispecs)) } }
+  where
+    plausible rdr_env ispec    -- Dfun involving only names that are in ic_rn_glb_env
+       = all ok $ nameSetToList $ tyClsNamesOfType $ idType $ instanceDFunId ispec
+       where   -- A name is ok if it's in the rdr_env, 
+               -- whether qualified or not
+         ok n | n == name         = True       -- The one we looked for in the first place!
+              | isBuiltInSyntax n = True
+              | isExternalName n  = any ((== n) . gre_name)
+                                        (lookupGRE_Name rdr_env n)
+              | otherwise         = True
 
 -- | Returns all names in scope in the current interactive context
 getNamesInScope :: Session -> IO [Name]