GHCi: Don't remove shadowed bindings from typechecker scope.

The shadowed out bindings are accessible via qualified names like
Ghci1.foo.  Since they are accessable in the renamer the typechecker
should be able to see them too.  As a consequence they show up in :show
bindings.

This fixes T11547

Test Plan:
Fixed current tests to accomodate to new stuff in :show bindings
Added a test that verifies that the typechecker doesn't crash

Reviewers: austin, bgamari, simonpj

Reviewed By: simonpj

Subscribers: simonpj, thomie

Differential Revision: https://phabricator.haskell.org/D2447

GHC Trac Issues: #11547

compiler/main/HscTypes.hs

@@ -1522,7 +1522,7 @@ extendInteractiveContext ictxt new_tythings new_cls_insts new_fam_insts defaults
   = ictxt { ic_mod_index  = ic_mod_index ictxt + 1
                             -- Always bump this; even instances should create
                             -- a new mod_index (Trac #9426)
-          , ic_tythings   = new_tythings ++ old_tythings
+          , ic_tythings   = new_tythings ++ ic_tythings ictxt
           , ic_rn_gbl_env = ic_rn_gbl_env ictxt `icExtendGblRdrEnv` new_tythings
           , ic_instances  = ( new_cls_insts ++ old_cls_insts
                             , new_fam_insts ++ old_fam_insts )
@@ -1530,8 +1530,6 @@ extendInteractiveContext ictxt new_tythings new_cls_insts new_fam_insts defaults
           , ic_fix_env    = fix_env  -- See Note [Fixity declarations in GHCi]
           }
   where
-    new_ids = [id | AnId id <- new_tythings]
-    old_tythings = filterOut (shadowed_by new_ids) (ic_tythings ictxt)
 
     -- Discard old instances that have been fully overrridden
     -- See Note [Override identical instances in GHCi]
@@ -1544,17 +1542,10 @@ extendInteractiveContextWithIds :: InteractiveContext -> [Id] -> InteractiveCont
 extendInteractiveContextWithIds ictxt new_ids
   | null new_ids = ictxt
   | otherwise    = ictxt { ic_mod_index  = ic_mod_index ictxt + 1
-                         , ic_tythings   = new_tythings ++ old_tythings
+                         , ic_tythings   = new_tythings ++ ic_tythings ictxt
                          , ic_rn_gbl_env = ic_rn_gbl_env ictxt `icExtendGblRdrEnv` new_tythings }
   where
     new_tythings = map AnId new_ids
-    old_tythings = filterOut (shadowed_by new_ids) (ic_tythings ictxt)
-
-shadowed_by :: [Id] -> TyThing -> Bool
-shadowed_by ids = shadowed
-  where
-    shadowed id = getOccName id `elemOccSet` new_occs
-    new_occs = mkOccSet (map getOccName ids)
 
 setInteractivePackage :: HscEnv -> HscEnv
 -- Set the 'thisPackage' DynFlag to 'interactive'

testsuite/tests/ghci.debugger/scripts/break011.stdout

@@ -23,6 +23,13 @@ _exception = SomeException
                   "foo"
                   "CallStack (from HasCallStack):
   error, called at Test7.hs:2:18 in main:Main")
+Ghci1._exception :: SomeException = SomeException
+                                      (ErrorCallWithLocation
+                                         "foo"
+                                         "CallStack (from HasCallStack):
+  error, called at Test7.hs:<line>:<column> in <package-id>:Main")
+Ghci2._result :: a = _
+Ghci3._result :: IO a = _
 _result :: a = _
 _exception :: SomeException = SomeException
                                 (ErrorCallWithLocation

testsuite/tests/ghci.debugger/scripts/hist001.stdout

@@ -12,6 +12,7 @@ Logged breakpoint at Test3.hs:2:22-31
 _result :: [a]
 f :: t -> a
 xs :: [t]
+Ghci1._result :: [a] = _
 xs :: [t] = []
 f :: t -> a = _
 _result :: [a] = _
@@ -19,7 +20,10 @@ Logged breakpoint at Test3.hs:2:18-20
 _result :: a
 f :: Integer -> a
 x :: Integer
+Ghci1._result :: [a] = _
 xs :: [t] = []
+Ghci2.f :: t -> a = _
+Ghci2._result :: [a] = _
 x :: Integer = 2
 f :: Integer -> a = _
 _result :: a = _

testsuite/tests/ghci/scripts/T11547.script

+foo = foo
+:t Ghci1.foo
+foo = foo
+:t Ghci2.foo
+:t Ghci1.foo
+data Foo = Foo | Bar
+data Foo = Bar
+:t Foo
+:t Ghci3.Bar

testsuite/tests/ghci/scripts/T11547.stdout

+Ghci1.foo :: t
+Ghci2.foo :: t
+Ghci1.foo :: t
+Foo :: Ghci3.Foo
+Ghci3.Bar :: Ghci3.Foo

testsuite/tests/ghci/scripts/T2976.stdout

 test :: Integer = 0
 test = 0
 test :: Integer = 0
+Ghci1.test :: Integer = 0
 test :: [Char] = _
 test = "test"
+Ghci1.test :: Integer = 0
 test :: [Char] = "test"

testsuite/tests/ghci/scripts/all.T

@@ -258,6 +258,7 @@ test('T11376', normal, ghci_script, ['T11376.script'])
 test('T12007', normal, ghci_script, ['T12007.script'])
 test('T11975', normal, ghci_script, ['T11975.script'])
 test('T10963', normal, ghci_script, ['T10963.script'])
+test('T11547', normal, ghci_script, ['T11547.script'])
 test('T12520', normal, ghci_script, ['T12520.script'])
 test('T12091',
      [expect_broken(12091), extra_run_opts('-fobject-code')],