Misc cleanup

- Remove Note [Existentials in shift_con_pat].
  The function shift_con_pat has been removed 15 years ago in 23f40f0e9be6d4.
- Remove kcLookupTcTyCon - it's the same as tcLookupTcTyCon
- Remove ASSERT in tyConAppArgN. It's already done by getNth,
  and it's the only reason getNth exists.
- Remove unused function nextRole

6 files changed, 9 insertions, 58 deletions

diff --git a/compiler/GHC/HsToCore/Match/Constructor.hs b/compiler/GHC/HsToCore/Match/Constructor.hs
index ab662a2f0e..3785fde948 100644
--- a/compiler/GHC/HsToCore/Match/Constructor.hs
+++ b/compiler/GHC/HsToCore/Match/Constructor.hs
@@ -261,36 +261,4 @@ positional patterns (T a b) and (a `T` b) all match the arguments
 in order.  Also T {} is special because it's equivalent to (T _ _).
 Hence the (null rpats) checks here and there.
 
-
-Note [Existentials in shift_con_pat]
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-Consider
-        data T = forall a. Ord a => T a (a->Int)
-
-        f (T x f) True  = ...expr1...
-        f (T y g) False = ...expr2..
-
-When we put in the tyvars etc we get
-
-        f (T a (d::Ord a) (x::a) (f::a->Int)) True =  ...expr1...
-        f (T b (e::Ord b) (y::a) (g::a->Int)) True =  ...expr2...
-
-After desugaring etc we'll get a single case:
-
-        f = \t::T b::Bool ->
-            case t of
-               T a (d::Ord a) (x::a) (f::a->Int)) ->
-            case b of
-                True  -> ...expr1...
-                False -> ...expr2...
-
-*** We have to substitute [a/b, d/e] in expr2! **
-Hence
-                False -> ....((/\b\(e:Ord b).expr2) a d)....
-
-Originally I tried to use
-        (\b -> let e = d in expr2) a
-to do this substitution.  While this is "correct" in a way, it fails
-Lint, because e::Ord b but d::Ord a.
-
 -}
diff --git a/compiler/typecheck/TcEnv.hs b/compiler/typecheck/TcEnv.hs
index c525ce15e9..71ca0044ad 100644
--- a/compiler/typecheck/TcEnv.hs
+++ b/compiler/typecheck/TcEnv.hs
@@ -456,6 +456,9 @@ tcLookupLocalIds ns
                 Just (ATcId { tct_id = id }) ->  id
                 _ -> pprPanic "tcLookupLocalIds" (ppr name)
 
+-- inferInitialKind has made a suitably-shaped kind for the type or class
+-- Look it up in the local environment. This is used only for tycons
+-- that we're currently type-checking, so we're sure to find a TcTyCon.
 tcLookupTcTyCon :: HasDebugCallStack => Name -> TcM TcTyCon
 tcLookupTcTyCon name = do
     thing <- tcLookup name
diff --git a/compiler/typecheck/TcHsType.hs b/compiler/typecheck/TcHsType.hs
index 01e3bc19fc..b18b56fb56 100644
--- a/compiler/typecheck/TcHsType.hs
+++ b/compiler/typecheck/TcHsType.hs
@@ -32,7 +32,7 @@ module TcHsType (
         ContextKind(..),
 
                 -- Type checking type and class decls
-        kcLookupTcTyCon, bindTyClTyVars,
+        bindTyClTyVars,
         etaExpandAlgTyCon, tcbVisibilities,
 
           -- tyvars
@@ -2753,7 +2753,7 @@ bindTyClTyVars :: Name
 -- in the "kind checking" and "type checking" pass,
 -- but not in the initial-kind run.
 bindTyClTyVars tycon_name thing_inside
-  = do { tycon <- kcLookupTcTyCon tycon_name
+  = do { tycon <- tcLookupTcTyCon tycon_name
        ; let scoped_prs = tcTyConScopedTyVars tycon
              res_kind   = tyConResKind tycon
              binders    = tyConBinders tycon
@@ -2761,16 +2761,6 @@ bindTyClTyVars tycon_name thing_inside
        ; tcExtendNameTyVarEnv scoped_prs $
          thing_inside binders res_kind }
 
--- inferInitialKind has made a suitably-shaped kind for the type or class
--- Look it up in the local environment. This is used only for tycons
--- that we're currently type-checking, so we're sure to find a TcTyCon.
-kcLookupTcTyCon :: Name -> TcM TcTyCon
-kcLookupTcTyCon nm
-  = do { tc_ty_thing <- tcLookup nm
-       ; return $ case tc_ty_thing of
-           ATcTyCon tc -> tc
-           _           -> pprPanic "kcLookupTcTyCon" (ppr tc_ty_thing) }
-
 
 {- *********************************************************************
 *                                                                      *
diff --git a/compiler/typecheck/TcTyClsDecls.hs b/compiler/typecheck/TcTyClsDecls.hs
index e712f79e1d..2c4c09722c 100644
--- a/compiler/typecheck/TcTyClsDecls.hs
+++ b/compiler/typecheck/TcTyClsDecls.hs
@@ -1503,7 +1503,7 @@ kcLTyClDecl :: LTyClDecl GhcRn -> TcM ()
   -- Called only for declarations without a signature (no CUSKs or SAKs here)
 kcLTyClDecl (L loc decl)
   = setSrcSpan loc $
-    do { tycon <- kcLookupTcTyCon tc_name
+    do { tycon <- tcLookupTcTyCon tc_name
        ; traceTc "kcTyClDecl {" (ppr tc_name)
        ; addVDQNote tycon $   -- See Note [Inferring visible dependent quantification]
          addErrCtxt (tcMkDeclCtxt decl) $
diff --git a/compiler/typecheck/TcType.hs b/compiler/typecheck/TcType.hs
index 65e77ab9da..205951ddc8 100644
--- a/compiler/typecheck/TcType.hs
+++ b/compiler/typecheck/TcType.hs
@@ -68,7 +68,7 @@ module TcType (
   tcTyConAppTyCon, tcTyConAppTyCon_maybe, tcTyConAppArgs,
   tcSplitAppTy_maybe, tcSplitAppTy, tcSplitAppTys, tcRepSplitAppTy_maybe,
   tcRepGetNumAppTys,
-  tcGetCastedTyVar_maybe, tcGetTyVar_maybe, tcGetTyVar, nextRole,
+  tcGetCastedTyVar_maybe, tcGetTyVar_maybe, tcGetTyVar,
   tcSplitSigmaTy, tcSplitNestedSigmaTys, tcDeepSplitSigmaTy_maybe,
 
   ---------------------------------
diff --git a/compiler/types/Type.hs b/compiler/types/Type.hs
index 71a0622787..2f87ca7a2f 100644
--- a/compiler/types/Type.hs
+++ b/compiler/types/Type.hs
@@ -34,7 +34,7 @@ module Type (
         mkTyConApp, mkTyConTy,
         tyConAppTyCon_maybe, tyConAppTyConPicky_maybe,
         tyConAppArgs_maybe, tyConAppTyCon, tyConAppArgs,
-        splitTyConApp_maybe, splitTyConApp, tyConAppArgN, nextRole,
+        splitTyConApp_maybe, splitTyConApp, tyConAppArgN,
         tcSplitTyConApp_maybe,
         splitListTyConApp_maybe,
         repSplitTyConApp_maybe,
@@ -1267,7 +1267,7 @@ tyConAppArgN :: Int -> Type -> Type
 -- Executing Nth
 tyConAppArgN n ty
   = case tyConAppArgs_maybe ty of
-      Just tys -> ASSERT2( tys `lengthExceeds` n, ppr n <+> ppr tys ) tys `getNth` n
+      Just tys -> tys `getNth` n
       Nothing  -> pprPanic "tyConAppArgN" (ppr n <+> ppr ty)
 
 -- | Attempts to tease a type apart into a type constructor and the application
@@ -1322,16 +1322,6 @@ splitListTyConApp_maybe ty = case splitTyConApp_maybe ty of
   Just (tc,[e]) | tc == listTyCon -> Just e
   _other                          -> Nothing
 
-nextRole :: Type -> Role
-nextRole ty
-  | Just (tc, tys) <- splitTyConApp_maybe ty
-  , let num_tys = length tys
-  , num_tys < tyConArity tc
-  = tyConRoles tc `getNth` num_tys
-
-  | otherwise
-  = Nominal
-
 newTyConInstRhs :: TyCon -> [Type] -> Type
 -- ^ Unwrap one 'layer' of newtype on a type constructor and its
 -- arguments, using an eta-reduced version of the @newtype@ if possible.