Handle promoted data constructors in typeToLHsType correctly

Instead of using `nlHsTyVar`, which hardcodes `NotPromoted`, have
`typeToLHsType` pick between `Promoted` and `NotPromoted` by checking
if a type constructor is promoted using `isPromotedDataCon`.

Fixes #18020.

4 files changed, 28 insertions, 23 deletions

diff --git a/compiler/GHC/Hs/Utils.hs b/compiler/GHC/Hs/Utils.hs
index 99a5de9365..75d9219cbf 100644
--- a/compiler/GHC/Hs/Utils.hs
+++ b/compiler/GHC/Hs/Utils.hs
@@ -113,6 +113,7 @@ import GHC.Tc.Types.Evidence
 import GHC.Types.Name.Reader
 import GHC.Types.Var
 import GHC.Core.TyCo.Rep
+import GHC.Core.TyCon
 import GHC.Core.Type ( appTyArgFlags, splitAppTys, tyConArgFlags, tyConAppNeedsKindSig )
 import TysWiredIn ( unitTy )
 import GHC.Tc.Utils.TcType
@@ -686,7 +687,11 @@ typeToLHsType ty
       | otherwise = ty'
        where
         ty' :: LHsType GhcPs
-        ty' = go_app (nlHsTyVar (getRdrName tc)) args (tyConArgFlags tc args)
+        ty' = go_app (noLoc $ HsTyVar noExtField prom $ noLoc $ getRdrName tc)
+                     args (tyConArgFlags tc args)
+
+        prom :: PromotionFlag
+        prom = if isPromotedDataCon tc then IsPromoted else NotPromoted
     go ty@(AppTy {})        = go_app (go head) args (appTyArgFlags head args)
       where
         head :: Type
diff --git a/testsuite/tests/deriving/should_compile/T14578.stderr b/testsuite/tests/deriving/should_compile/T14578.stderr
index 25480b836c..58376989db 100644
--- a/testsuite/tests/deriving/should_compile/T14578.stderr
+++ b/testsuite/tests/deriving/should_compile/T14578.stderr
@@ -9,7 +9,7 @@ Derived class instances:
     GHC.Base.sconcat ::
       GHC.Base.NonEmpty (T14578.Wat f g a) -> T14578.Wat f g a
     GHC.Base.stimes ::
-      forall (b :: TYPE GHC.Types.LiftedRep).
+      forall (b :: TYPE 'GHC.Types.LiftedRep).
       GHC.Real.Integral b => b -> T14578.Wat f g a -> T14578.Wat f g a
     (GHC.Base.<>)
       = GHC.Prim.coerce
@@ -37,12 +37,12 @@ Derived class instances:
   instance GHC.Base.Functor f =>
            GHC.Base.Functor (T14578.App f) where
     GHC.Base.fmap ::
-      forall (a :: TYPE GHC.Types.LiftedRep)
-             (b :: TYPE GHC.Types.LiftedRep).
+      forall (a :: TYPE 'GHC.Types.LiftedRep)
+             (b :: TYPE 'GHC.Types.LiftedRep).
       (a -> b) -> T14578.App f a -> T14578.App f b
     (GHC.Base.<$) ::
-      forall (a :: TYPE GHC.Types.LiftedRep)
-             (b :: TYPE GHC.Types.LiftedRep).
+      forall (a :: TYPE 'GHC.Types.LiftedRep)
+             (b :: TYPE 'GHC.Types.LiftedRep).
       a -> T14578.App f b -> T14578.App f a
     GHC.Base.fmap
       = GHC.Prim.coerce
@@ -56,23 +56,23 @@ Derived class instances:
   instance GHC.Base.Applicative f =>
            GHC.Base.Applicative (T14578.App f) where
     GHC.Base.pure ::
-      forall (a :: TYPE GHC.Types.LiftedRep). a -> T14578.App f a
+      forall (a :: TYPE 'GHC.Types.LiftedRep). a -> T14578.App f a
     (GHC.Base.<*>) ::
-      forall (a :: TYPE GHC.Types.LiftedRep)
-             (b :: TYPE GHC.Types.LiftedRep).
+      forall (a :: TYPE 'GHC.Types.LiftedRep)
+             (b :: TYPE 'GHC.Types.LiftedRep).
       T14578.App f (a -> b) -> T14578.App f a -> T14578.App f b
     GHC.Base.liftA2 ::
-      forall (a :: TYPE GHC.Types.LiftedRep)
-             (b :: TYPE GHC.Types.LiftedRep)
-             (c :: TYPE GHC.Types.LiftedRep).
+      forall (a :: TYPE 'GHC.Types.LiftedRep)
+             (b :: TYPE 'GHC.Types.LiftedRep)
+             (c :: TYPE 'GHC.Types.LiftedRep).
       (a -> b -> c) -> T14578.App f a -> T14578.App f b -> T14578.App f c
     (GHC.Base.*>) ::
-      forall (a :: TYPE GHC.Types.LiftedRep)
-             (b :: TYPE GHC.Types.LiftedRep).
+      forall (a :: TYPE 'GHC.Types.LiftedRep)
+             (b :: TYPE 'GHC.Types.LiftedRep).
       T14578.App f a -> T14578.App f b -> T14578.App f b
     (GHC.Base.<*) ::
-      forall (a :: TYPE GHC.Types.LiftedRep)
-             (b :: TYPE GHC.Types.LiftedRep).
+      forall (a :: TYPE 'GHC.Types.LiftedRep)
+             (b :: TYPE 'GHC.Types.LiftedRep).
       T14578.App f a -> T14578.App f b -> T14578.App f a
     GHC.Base.pure
       = GHC.Prim.coerce
diff --git a/testsuite/tests/deriving/should_compile/T14579.stderr b/testsuite/tests/deriving/should_compile/T14579.stderr
index 18e64f7bb6..81212022ef 100644
--- a/testsuite/tests/deriving/should_compile/T14579.stderr
+++ b/testsuite/tests/deriving/should_compile/T14579.stderr
@@ -8,16 +8,16 @@ Derived class instances:
       T14579.Glurp a -> T14579.Glurp a -> GHC.Types.Bool
     (GHC.Classes.==)
       = GHC.Prim.coerce
-          @(T14579.Wat @a (Data.Proxy.Proxy @a)
-            -> T14579.Wat @a (Data.Proxy.Proxy @a) -> GHC.Types.Bool)
+          @(T14579.Wat @a ('Data.Proxy.Proxy @a)
+            -> T14579.Wat @a ('Data.Proxy.Proxy @a) -> GHC.Types.Bool)
           @(T14579.Glurp a -> T14579.Glurp a -> GHC.Types.Bool)
-          ((GHC.Classes.==) @(T14579.Wat @a (Data.Proxy.Proxy @a)))
+          ((GHC.Classes.==) @(T14579.Wat @a ('Data.Proxy.Proxy @a)))
     (GHC.Classes./=)
       = GHC.Prim.coerce
-          @(T14579.Wat @a (Data.Proxy.Proxy @a)
-            -> T14579.Wat @a (Data.Proxy.Proxy @a) -> GHC.Types.Bool)
+          @(T14579.Wat @a ('Data.Proxy.Proxy @a)
+            -> T14579.Wat @a ('Data.Proxy.Proxy @a) -> GHC.Types.Bool)
           @(T14579.Glurp a -> T14579.Glurp a -> GHC.Types.Bool)
-          ((GHC.Classes./=) @(T14579.Wat @a (Data.Proxy.Proxy @a)))
+          ((GHC.Classes./=) @(T14579.Wat @a ('Data.Proxy.Proxy @a)))
   
   instance forall a (x :: Data.Proxy.Proxy a).
            GHC.Classes.Eq a =>
diff --git a/testsuite/tests/deriving/should_fail/T15073.stderr b/testsuite/tests/deriving/should_fail/T15073.stderr
index d27ff4d216..5c1d99768f 100644
--- a/testsuite/tests/deriving/should_fail/T15073.stderr
+++ b/testsuite/tests/deriving/should_fail/T15073.stderr
@@ -3,7 +3,7 @@ T15073.hs:8:12: error:
     • Illegal unboxed tuple type as function argument: (# Foo a #)
       Perhaps you intended to use UnboxedTuples
     • In the type signature:
-        p :: Foo a -> Unit# @GHC.Types.LiftedRep (Foo a)
+        p :: Foo a -> Unit# @'GHC.Types.LiftedRep (Foo a)
       When typechecking the code for ‘p’
         in a derived instance for ‘P (Foo a)’:
         To see the code I am typechecking, use -ddump-deriv