Pretty-printing of the * kind

Before this patch, GHC always printed the * kind unparenthesized.

This led to two issues:

1. Sometimes GHC printed invalid or incorrect code.
   For example, GHC would print:  type F @*   x = x
         when it meant to print:  type F @(*) x = x
   In the former case, instead of a kind application we were getting a
   type operator (@*).

2. Sometimes GHC printed kinds that were correct but hard to read.
   Should  Either * Int  be read as  Either (*) Int
                              or as  (*) Either Int  ?
   This depends on whether -XStarIsType is enabled, but it would be
   easier if we didn't have to check for the flag when reading the code.

We can solve both problems by assigning (*) a different precedence. Note
that Haskell98 kinds are not affected:

  ((* -> *) -> *) -> *  does NOT become  (((*) -> (*)) -> (*)) -> (*)

The parentheses are added when (*) is used in a function argument
position:

   F * * *   becomes  F (*) (*) (*)
   F A * B   becomes  F A (*) B
   Proxy *   becomes  Proxy (*)
   a * -> *  becomes  a (*) -> *

24 files changed, 123 insertions, 97 deletions

diff --git a/compiler/GHC/Hs/Types.hs b/compiler/GHC/Hs/Types.hs
index e92928c78f..324b1dd3d2 100644
--- a/compiler/GHC/Hs/Types.hs
+++ b/compiler/GHC/Hs/Types.hs
@@ -1676,7 +1676,7 @@ hsTypeNeedsParens p = go
     go (HsExplicitTupleTy{}) = False
     go (HsTyLit{})           = False
     go (HsWildCardTy{})      = False
-    go (HsStarTy{})          = False
+    go (HsStarTy{})          = p >= starPrec
     go (HsAppTy{})           = p >= appPrec
     go (HsAppKindTy{})       = p >= appPrec
     go (HsOpTy{})            = p >= opPrec
diff --git a/compiler/basicTypes/BasicTypes.hs b/compiler/basicTypes/BasicTypes.hs
index 7513e08f82..ce449b3562 100644
--- a/compiler/basicTypes/BasicTypes.hs
+++ b/compiler/basicTypes/BasicTypes.hs
@@ -51,7 +51,8 @@ module BasicTypes(
 
         Boxity(..), isBoxed,
 
-        PprPrec(..), topPrec, sigPrec, opPrec, funPrec, appPrec, maybeParen,
+        PprPrec(..), topPrec, sigPrec, opPrec, funPrec, starPrec, appPrec,
+        maybeParen,
 
         TupleSort(..), tupleSortBoxity, boxityTupleSort,
         tupleParens,
@@ -729,14 +730,16 @@ pprSafeOverlap False = empty
 newtype PprPrec = PprPrec Int deriving (Eq, Ord, Show)
 -- See Note [Precedence in types]
 
-topPrec, sigPrec, funPrec, opPrec, appPrec :: PprPrec
+topPrec, sigPrec, funPrec, opPrec, starPrec, appPrec :: PprPrec
 topPrec = PprPrec 0 -- No parens
 sigPrec = PprPrec 1 -- Explicit type signatures
 funPrec = PprPrec 2 -- Function args; no parens for constructor apps
                     -- See [Type operator precedence] for why both
                     -- funPrec and opPrec exist.
 opPrec  = PprPrec 2 -- Infix operator
-appPrec = PprPrec 3 -- Constructor args; no parens for atomic
+starPrec = PprPrec 3 -- Star syntax for the type of types, i.e. the * in (* -> *)
+                     -- See Note [Star kind precedence]
+appPrec  = PprPrec 4 -- Constructor args; no parens for atomic
 
 maybeParen :: PprPrec -> PprPrec -> SDoc -> SDoc
 maybeParen ctxt_prec inner_prec pretty
@@ -775,6 +778,33 @@ By treating opPrec = funPrec we end up with more parens
 
 But the two are different constructors of PprPrec so we could make
 (->) bind more or less tightly if we wanted.
+
+Note [Star kind precedence]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+We parenthesize the (*) kind to avoid two issues:
+
+1. Printing invalid or incorrect code.
+   For example, instead of  type F @(*) x = x
+         GHC used to print  type F @*   x = x
+   However, (@*) is a type operator, not a kind application.
+
+2. Printing kinds that are correct but hard to read.
+   Should  Either * Int  be read as  Either (*) Int
+                              or as  (*) Either Int  ?
+   This depends on whether -XStarIsType is enabled, but it would be
+   easier if we didn't have to check for the flag when reading the code.
+
+At the same time, we cannot parenthesize (*) blindly.
+Consider this Haskell98 kind:          ((* -> *) -> *) -> *
+With parentheses, it is less readable: (((*) -> (*)) -> (*)) -> (*)
+
+The solution is to assign a special precedence to (*), 'starPrec', which is
+higher than 'funPrec' but lower than 'appPrec':
+
+   F * * *   becomes  F (*) (*) (*)
+   F A * B   becomes  F A (*) B
+   Proxy *   becomes  Proxy (*)
+   a * -> *  becomes  a (*) -> *
 -}
 
 {-
diff --git a/compiler/iface/IfaceType.hs b/compiler/iface/IfaceType.hs
index db3157f39b..d649be701b 100644
--- a/compiler/iface/IfaceType.hs
+++ b/compiler/iface/IfaceType.hs
@@ -1315,7 +1315,7 @@ pprTyTcApp' ctxt_prec tc tys dflags style
   | tc `ifaceTyConHasKey` tYPETyConKey
   , IA_Arg (IfaceTyConApp rep IA_Nil) Required IA_Nil <- tys
   , rep `ifaceTyConHasKey` liftedRepDataConKey
-  = kindType
+  = ppr_kind_type ctxt_prec
 
   | otherwise
   = getPprDebug $ \dbg ->
@@ -1332,6 +1332,14 @@ pprTyTcApp' ctxt_prec tc tys dflags style
     info = ifaceTyConInfo tc
     tys_wo_kinds = appArgsIfaceTypesArgFlags $ stripInvisArgs dflags tys
 
+ppr_kind_type :: PprPrec -> SDoc
+ppr_kind_type ctxt_prec =
+  sdocWithDynFlags $ \dflags ->
+    if useStarIsType dflags
+    then maybeParen ctxt_prec starPrec $
+         unicodeSyntax (char '★') (char '*')
+    else text "Type"
+
 -- | Pretty-print a type-level equality.
 -- Returns (Just doc) if the argument is a /saturated/ application
 -- of   eqTyCon          (~)
@@ -1440,7 +1448,7 @@ ppr_iface_tc_app pp _ tc [ty]
 
 ppr_iface_tc_app pp ctxt_prec tc tys
   | tc `ifaceTyConHasKey` liftedTypeKindTyConKey
-  = kindType
+  = ppr_kind_type ctxt_prec
 
   | not (isSymOcc (nameOccName (ifaceTyConName tc)))
   = pprIfacePrefixApp ctxt_prec (ppr tc) (map (pp appPrec) tys)
diff --git a/compiler/main/DynFlags.hs-boot b/compiler/main/DynFlags.hs-boot
index bed4ae2fd1..6f9bdc5138 100644
--- a/compiler/main/DynFlags.hs-boot
+++ b/compiler/main/DynFlags.hs-boot
@@ -13,7 +13,6 @@ pprCols                  :: DynFlags -> Int
 unsafeGlobalDynFlags     :: DynFlags
 useUnicode               :: DynFlags -> Bool
 useUnicodeSyntax         :: DynFlags -> Bool
-useStarIsType            :: DynFlags -> Bool
 shouldUseColor           :: DynFlags -> Bool
 shouldUseHexWordLiterals :: DynFlags -> Bool
 hasPprDebug              :: DynFlags -> Bool
diff --git a/compiler/utils/Outputable.hs b/compiler/utils/Outputable.hs
index bbc365b774..0dda99020f 100644
--- a/compiler/utils/Outputable.hs
+++ b/compiler/utils/Outputable.hs
@@ -28,7 +28,7 @@ module Outputable (
         semi, comma, colon, dcolon, space, equals, dot, vbar,
         arrow, larrow, darrow, arrowt, larrowt, arrowtt, larrowtt,
         lparen, rparen, lbrack, rbrack, lbrace, rbrace, underscore,
-        blankLine, forAllLit, kindType, bullet,
+        blankLine, forAllLit, bullet,
         (<>), (<+>), hcat, hsep,
         ($$), ($+$), vcat,
         sep, cat,
@@ -91,7 +91,7 @@ import GhcPrelude
 
 import {-# SOURCE #-}   DynFlags( DynFlags, hasPprDebug, hasNoDebugOutput,
                                   targetPlatform, pprUserLength, pprCols,
-                                  useUnicode, useUnicodeSyntax, useStarIsType,
+                                  useUnicode, useUnicodeSyntax,
                                   shouldUseColor, unsafeGlobalDynFlags,
                                   shouldUseHexWordLiterals )
 import {-# SOURCE #-}   Module( UnitId, Module, ModuleName, moduleName )
@@ -649,12 +649,6 @@ rbrace     = docToSDoc $ Pretty.rbrace
 forAllLit :: SDoc
 forAllLit = unicodeSyntax (char '∀') (text "forall")
 
-kindType :: SDoc
-kindType = sdocWithDynFlags $ \dflags ->
-    if useStarIsType dflags
-    then unicodeSyntax (char '★') (char '*')
-    else text "Type"
-
 bullet :: SDoc
 bullet = unicode (char '•') (char '*')
 
diff --git a/testsuite/tests/generics/T10604/T10604_deriving.stderr b/testsuite/tests/generics/T10604/T10604_deriving.stderr
index f8a4acc371..99c5ee8088 100644
--- a/testsuite/tests/generics/T10604/T10604_deriving.stderr
+++ b/testsuite/tests/generics/T10604/T10604_deriving.stderr
@@ -18,7 +18,7 @@ Derived class instances:
           (GHC.Generics.R1 (GHC.Generics.M1 (GHC.Generics.M1 (GHC.Generics.K1 g1))))
             -> T10604_deriving.Starify2 g1
   
-  instance GHC.Generics.Generic1 @* T10604_deriving.Starify where
+  instance GHC.Generics.Generic1 @(*) T10604_deriving.Starify where
     GHC.Generics.from1 x
       = GHC.Generics.M1
           (case x of
@@ -140,7 +140,7 @@ Derived class instances:
           (GHC.Generics.M1 (GHC.Generics.M1 g1))
             -> T10604_deriving.Wrap (GHC.Generics.unRec1 g1) }
   
-  instance GHC.Base.Functor (T10604_deriving.Proxy @*) where
+  instance GHC.Base.Functor (T10604_deriving.Proxy @(*)) where
     GHC.Base.fmap _ = GHC.Prim.coerce
   
   instance forall k (a :: k).
@@ -183,7 +183,7 @@ Derived type family instances:
                                                            "main"
                                                            'GHC.Types.False)
                                                         ((GHC.Generics.:+:)
-                                                           @*
+                                                           @(*)
                                                            (GHC.Generics.C1
                                                               @{*}
                                                               ('GHC.Generics.MetaCons
@@ -215,46 +215,41 @@ Derived type family instances:
                                                                     'GHC.Generics.DecidedLazy)
                                                                  (GHC.Generics.Rec0
                                                                     @{*} GHC.Types.Int))))
-  type GHC.Generics.Rep1 @* T10604_deriving.Starify = GHC.Generics.D1
-                                                        @{*}
-                                                        ('GHC.Generics.MetaData
-                                                           "Starify"
-                                                           "T10604_deriving"
-                                                           "main"
-                                                           'GHC.Types.False)
-                                                        ((GHC.Generics.:+:)
-                                                           @*
-                                                           (GHC.Generics.C1
-                                                              @{*}
-                                                              ('GHC.Generics.MetaCons
-                                                                 "Starify1"
-                                                                 'GHC.Generics.PrefixI
-                                                                 'GHC.Types.False)
-                                                              (GHC.Generics.S1
-                                                                 @{*}
-                                                                 ('GHC.Generics.MetaSel
-                                                                    ('GHC.Maybe.Nothing
-                                                                       @GHC.Types.Symbol)
-                                                                    'GHC.Generics.NoSourceUnpackedness
-                                                                    'GHC.Generics.NoSourceStrictness
-                                                                    'GHC.Generics.DecidedLazy)
-                                                                 GHC.Generics.Par1))
-                                                           (GHC.Generics.C1
-                                                              @{*}
-                                                              ('GHC.Generics.MetaCons
-                                                                 "Starify2"
-                                                                 'GHC.Generics.PrefixI
-                                                                 'GHC.Types.False)
-                                                              (GHC.Generics.S1
-                                                                 @{*}
-                                                                 ('GHC.Generics.MetaSel
-                                                                    ('GHC.Maybe.Nothing
-                                                                       @GHC.Types.Symbol)
-                                                                    'GHC.Generics.NoSourceUnpackedness
-                                                                    'GHC.Generics.NoSourceStrictness
-                                                                    'GHC.Generics.DecidedLazy)
-                                                                 (GHC.Generics.Rec0
-                                                                    @{*} GHC.Types.Int))))
+  type GHC.Generics.Rep1
+         @(*) T10604_deriving.Starify = GHC.Generics.D1
+                                          @{*}
+                                          ('GHC.Generics.MetaData
+                                             "Starify" "T10604_deriving" "main" 'GHC.Types.False)
+                                          ((GHC.Generics.:+:)
+                                             @(*)
+                                             (GHC.Generics.C1
+                                                @{*}
+                                                ('GHC.Generics.MetaCons
+                                                   "Starify1"
+                                                   'GHC.Generics.PrefixI
+                                                   'GHC.Types.False)
+                                                (GHC.Generics.S1
+                                                   @{*}
+                                                   ('GHC.Generics.MetaSel
+                                                      ('GHC.Maybe.Nothing @GHC.Types.Symbol)
+                                                      'GHC.Generics.NoSourceUnpackedness
+                                                      'GHC.Generics.NoSourceStrictness
+                                                      'GHC.Generics.DecidedLazy)
+                                                   GHC.Generics.Par1))
+                                             (GHC.Generics.C1
+                                                @{*}
+                                                ('GHC.Generics.MetaCons
+                                                   "Starify2"
+                                                   'GHC.Generics.PrefixI
+                                                   'GHC.Types.False)
+                                                (GHC.Generics.S1
+                                                   @{*}
+                                                   ('GHC.Generics.MetaSel
+                                                      ('GHC.Maybe.Nothing @GHC.Types.Symbol)
+                                                      'GHC.Generics.NoSourceUnpackedness
+                                                      'GHC.Generics.NoSourceStrictness
+                                                      'GHC.Generics.DecidedLazy)
+                                                   (GHC.Generics.Rec0 @{*} GHC.Types.Int))))
   type GHC.Generics.Rep
          (T10604_deriving.SumOfProducts @{k} a) = GHC.Generics.D1
                                                     @{*}
@@ -264,7 +259,7 @@ Derived type family instances:
                                                        "main"
                                                        'GHC.Types.False)
                                                     ((GHC.Generics.:+:)
-                                                       @*
+                                                       @(*)
                                                        (GHC.Generics.C1
                                                           @{*}
                                                           ('GHC.Generics.MetaCons
@@ -272,7 +267,7 @@ Derived type family instances:
                                                              'GHC.Generics.PrefixI
                                                              'GHC.Types.False)
                                                           ((GHC.Generics.:*:)
-                                                             @*
+                                                             @(*)
                                                              (GHC.Generics.S1
                                                                 @{*}
                                                                 ('GHC.Generics.MetaSel
@@ -302,7 +297,7 @@ Derived type family instances:
                                                              'GHC.Generics.PrefixI
                                                              'GHC.Types.False)
                                                           ((GHC.Generics.:*:)
-                                                             @*
+                                                             @(*)
                                                              (GHC.Generics.S1
                                                                 @{*}
                                                                 ('GHC.Generics.MetaSel
@@ -412,7 +407,7 @@ Derived type family instances:
                                                 (GHC.Generics.Rec0
                                                    @{*}
                                                    (T10604_deriving.Proxy
-                                                      @* (T10604_deriving.Proxy @(k -> *) a)))))
+                                                      @(*) (T10604_deriving.Proxy @(k -> *) a)))))
   type GHC.Generics.Rep1
          @(k -> *) (T10604_deriving.Wrap2 @k) = GHC.Generics.D1
                                                   @{k -> *}
@@ -435,9 +430,9 @@ Derived type family instances:
                                                            'GHC.Generics.NoSourceStrictness
                                                            'GHC.Generics.DecidedLazy)
                                                         ((GHC.Generics.:.:)
-                                                           @*
+                                                           @(*)
                                                            @(k -> *)
-                                                           (T10604_deriving.Proxy @*)
+                                                           (T10604_deriving.Proxy @(*))
                                                            (GHC.Generics.Rec1
                                                               @(k -> *)
                                                               (T10604_deriving.Proxy @(k -> *))))))
@@ -491,7 +486,7 @@ Derived type family instances:
                                              @{*}
                                              ('GHC.Generics.MetaCons
                                                 "Proxy" 'GHC.Generics.PrefixI 'GHC.Types.False)
-                                             (GHC.Generics.U1 @*))
+                                             (GHC.Generics.U1 @(*)))
   type GHC.Generics.Rep1
          @k (T10604_deriving.Proxy @k) = GHC.Generics.D1
                                            @{k}
@@ -509,7 +504,7 @@ Derived type family instances:
                                                          "T10604_deriving"
                                                          "main"
                                                          'GHC.Types.False)
-                                                      (GHC.Generics.V1 @*)
+                                                      (GHC.Generics.V1 @(*))
   type GHC.Generics.Rep1
          @GHC.Types.Bool T10604_deriving.Empty = GHC.Generics.D1
                                                    @{GHC.Types.Bool}
@@ -523,7 +518,7 @@ Derived type family instances:
 
 
 ==================== Filling in method body ====================
-GHC.Base.Functor [T10604_deriving.Proxy @*]
-  GHC.Base.<$ = GHC.Base.$dm<$ @(T10604_deriving.Proxy @*)
+GHC.Base.Functor [T10604_deriving.Proxy @(*)]
+  GHC.Base.<$ = GHC.Base.$dm<$ @(T10604_deriving.Proxy @(*))
 
 
diff --git a/testsuite/tests/indexed-types/should_compile/T11361a.stderr b/testsuite/tests/indexed-types/should_compile/T11361a.stderr
index a3e3a22a31..a7d5ad16af 100644
--- a/testsuite/tests/indexed-types/should_compile/T11361a.stderr
+++ b/testsuite/tests/indexed-types/should_compile/T11361a.stderr
@@ -1,7 +1,7 @@
 
 T11361a.hs:7:3: error:
     • Illegal argument ‘*’ in:
-        ‘type F @* x = x’
+        ‘type F @(*) x = x’
         The arguments to ‘F’ must all be distinct type variables
     • In the default type instance declaration for ‘F’
       In the class declaration for ‘C’
diff --git a/testsuite/tests/indexed-types/should_fail/T12041.stderr b/testsuite/tests/indexed-types/should_fail/T12041.stderr
index 4c008661d1..e15f23471a 100644
--- a/testsuite/tests/indexed-types/should_fail/T12041.stderr
+++ b/testsuite/tests/indexed-types/should_fail/T12041.stderr
@@ -2,6 +2,6 @@
 T12041.hs:12:3: error:
     • Type indexes must match class instance head
       Expected: Ob @i (I @{i} @{i})
-        Actual: Ob @* (I @{*} @{*})
+        Actual: Ob @(*) (I @{*} @{*})
     • In the type instance declaration for ‘Ob’
       In the instance declaration for ‘Category I’
diff --git a/testsuite/tests/indexed-types/should_fail/T13877.stderr b/testsuite/tests/indexed-types/should_fail/T13877.stderr
index 674b258c24..fdbc89ab1e 100644
--- a/testsuite/tests/indexed-types/should_fail/T13877.stderr
+++ b/testsuite/tests/indexed-types/should_fail/T13877.stderr
@@ -1,7 +1,7 @@
 
 T13877.hs:65:41: error:
     • Expecting one more argument to ‘p’
-      Expected kind ‘(-?>) [a] * (':->)’, but ‘p’ has kind ‘[a] ~> *’
+      Expected kind ‘(-?>) [a] (*) (':->)’, but ‘p’ has kind ‘[a] ~> *’
     • In the type ‘p’
       In the expression: listElimPoly @(:->) @a @p @l
       In an equation for ‘listElimTyFun’:
diff --git a/testsuite/tests/indexed-types/should_fail/T13971.stderr b/testsuite/tests/indexed-types/should_fail/T13971.stderr
index eec7ad11e6..fe4ab4ca3c 100644
--- a/testsuite/tests/indexed-types/should_fail/T13971.stderr
+++ b/testsuite/tests/indexed-types/should_fail/T13971.stderr
@@ -1,7 +1,7 @@
 
 T13971.hs:7:3: error:
     • Illegal argument ‘*’ in:
-        ‘type T @{k} @* a = Int’
+        ‘type T @{k} @(*) a = Int’
         The arguments to ‘T’ must all be distinct type variables
     • In the default type instance declaration for ‘T’
       In the class declaration for ‘C’
diff --git a/testsuite/tests/indexed-types/should_fail/T14246.stderr b/testsuite/tests/indexed-types/should_fail/T14246.stderr
index 4bb45d6399..fcc2605527 100644
--- a/testsuite/tests/indexed-types/should_fail/T14246.stderr
+++ b/testsuite/tests/indexed-types/should_fail/T14246.stderr
@@ -6,14 +6,14 @@ T14246.hs:18:5: error:
 
 T14246.hs:22:27: error:
     • Expected kind ‘Vect (KLN f) L’,
-        but ‘Cons (Label (t :: v)) l’ has kind ‘Vect ('S (KLN (f t))) *’
+        but ‘Cons (Label (t :: v)) l’ has kind ‘Vect ('S (KLN (f t))) (*)’
     • In the second argument of ‘Reveal’, namely
         ‘(Cons (Label (t :: v)) l)’
       In the type family declaration for ‘Reveal’
 
 T14246.hs:22:67: error:
     • Expected kind ‘Vect (KLN (f t)) L’,
-        but ‘l’ has kind ‘Vect (KLN (f t)) *’
+        but ‘l’ has kind ‘Vect (KLN (f t)) (*)’
     • In the second argument of ‘Reveal’, namely ‘l’
       In the type ‘Reveal (f t) l’
       In the type family declaration for ‘Reveal’
diff --git a/testsuite/tests/indexed-types/should_fail/T16356_Fail1.stderr b/testsuite/tests/indexed-types/should_fail/T16356_Fail1.stderr
index b354d1db00..74935362b6 100644
--- a/testsuite/tests/indexed-types/should_fail/T16356_Fail1.stderr
+++ b/testsuite/tests/indexed-types/should_fail/T16356_Fail1.stderr
@@ -1,7 +1,7 @@
 
 T16356_Fail1.hs:10:3: error:
     • Illegal argument ‘*’ in:
-        ‘type T @* a = Maybe a’
+        ‘type T @(*) a = Maybe a’
         The arguments to ‘T’ must all be distinct type variables
     • In the default type instance declaration for ‘T’
       In the class declaration for ‘C’
diff --git a/testsuite/tests/indexed-types/should_fail/T9160.stderr b/testsuite/tests/indexed-types/should_fail/T9160.stderr
index e918013f67..8508bee1a9 100644
--- a/testsuite/tests/indexed-types/should_fail/T9160.stderr
+++ b/testsuite/tests/indexed-types/should_fail/T9160.stderr
@@ -1,7 +1,7 @@
 
 T9160.hs:19:3: error:
     • Type indexes must match class instance head
-      Expected: F @*
+      Expected: F @(*)
         Actual: F @(* -> *)
     • In the type instance declaration for ‘F’
       In the instance declaration for ‘C (a :: *)’
diff --git a/testsuite/tests/indexed-types/should_fail/T9171.stderr b/testsuite/tests/indexed-types/should_fail/T9171.stderr
index 6567570d46..320a6add8d 100644
--- a/testsuite/tests/indexed-types/should_fail/T9171.stderr
+++ b/testsuite/tests/indexed-types/should_fail/T9171.stderr
@@ -1,9 +1,9 @@
 
 T9171.hs:10:20: error:
     • Couldn't match expected type ‘GetParam
-                                      @* @k2 @* Base (GetParam @* @* @k2 Base Int)’
+                                      @(*) @k2 @(*) Base (GetParam @(*) @(*) @k2 Base Int)’
                   with actual type ‘GetParam
-                                      @* @k20 @* Base (GetParam @* @* @k20 Base Int)’
+                                      @(*) @k20 @(*) Base (GetParam @(*) @(*) @k20 Base Int)’
       NB: ‘GetParam’ is a non-injective type family
       The type variable ‘k20’ is ambiguous
     • In the ambiguity check for an expression type signature
diff --git a/testsuite/tests/partial-sigs/should_compile/T15039b.stderr b/testsuite/tests/partial-sigs/should_compile/T15039b.stderr
index 8f9c2c8a45..949995ddda 100644
--- a/testsuite/tests/partial-sigs/should_compile/T15039b.stderr
+++ b/testsuite/tests/partial-sigs/should_compile/T15039b.stderr
@@ -37,21 +37,21 @@ T15039b.hs:25:14: warning: [-Wpartial-type-signatures (in -Wdefault)]
         ex3 :: Dict ((a :: *) ~~ (b :: k)) -> () (bound at T15039b.hs:25:1)
 
 T15039b.hs:33:14: warning: [-Wpartial-type-signatures (in -Wdefault)]
-    • Found type wildcard ‘_’ standing for ‘Dict (Coercible @* a b)’
+    • Found type wildcard ‘_’ standing for ‘Dict (Coercible @(*) a b)’
       Where: ‘a’, ‘b’ are rigid type variables bound by
                the type signature for:
-                 ex6 :: forall a b. Dict (Coercible @* a b) -> ()
+                 ex6 :: forall a b. Dict (Coercible @(*) a b) -> ()
                at T15039b.hs:32:1-53
     • In a pattern type signature: _
       In the pattern: Dict :: _
       In an equation for ‘ex6’: ex6 (Dict :: _) = ()
     • Relevant bindings include
-        ex6 :: Dict (Coercible @* a b) -> () (bound at T15039b.hs:33:1)
+        ex6 :: Dict (Coercible @(*) a b) -> () (bound at T15039b.hs:33:1)
 
 T15039b.hs:35:8: warning: [-Wpartial-type-signatures (in -Wdefault)]
-    • Found type wildcard ‘_’ standing for ‘Coercible @* a b’
+    • Found type wildcard ‘_’ standing for ‘Coercible @(*) a b’
       Where: ‘a’, ‘b’ are rigid type variables bound by
-               the inferred type of ex7 :: Coercible @* a b => Coercion @{*} a b
+               the inferred type of ex7 :: Coercible @(*) a b => Coercion @{*} a b
                at T15039b.hs:36:1-14
     • In the type signature:
         ex7 :: _ => Coercion (a :: Type) (b :: Type)
diff --git a/testsuite/tests/partial-sigs/should_compile/T15039d.stderr b/testsuite/tests/partial-sigs/should_compile/T15039d.stderr
index 8548356001..6e26d5a1cb 100644
--- a/testsuite/tests/partial-sigs/should_compile/T15039d.stderr
+++ b/testsuite/tests/partial-sigs/should_compile/T15039d.stderr
@@ -38,21 +38,21 @@ T15039d.hs:25:14: warning: [-Wpartial-type-signatures (in -Wdefault)]
         ex3 :: Dict ((a :: *) ~~ (b :: k)) -> () (bound at T15039d.hs:25:1)
 
 T15039d.hs:33:14: warning: [-Wpartial-type-signatures (in -Wdefault)]
-    • Found type wildcard ‘_’ standing for ‘Dict (Coercible @* a b)’
+    • Found type wildcard ‘_’ standing for ‘Dict (Coercible @(*) a b)’
       Where: ‘a’, ‘b’ are rigid type variables bound by
                the type signature for:
-                 ex6 :: forall a b. Dict (Coercible @* a b) -> ()
+                 ex6 :: forall a b. Dict (Coercible @(*) a b) -> ()
                at T15039d.hs:32:1-53
     • In a pattern type signature: _
       In the pattern: Dict :: _
       In an equation for ‘ex6’: ex6 (Dict :: _) = ()
     • Relevant bindings include
-        ex6 :: Dict (Coercible @* a b) -> () (bound at T15039d.hs:33:1)
+        ex6 :: Dict (Coercible @(*) a b) -> () (bound at T15039d.hs:33:1)
 
 T15039d.hs:35:8: warning: [-Wpartial-type-signatures (in -Wdefault)]
-    • Found type wildcard ‘_’ standing for ‘Coercible @* a b’
+    • Found type wildcard ‘_’ standing for ‘Coercible @(*) a b’
       Where: ‘a’, ‘b’ are rigid type variables bound by
-               the inferred type of ex7 :: Coercible @* a b => Coercion @{*} a b
+               the inferred type of ex7 :: Coercible @(*) a b => Coercion @{*} a b
                at T15039d.hs:36:1-14
     • In the type signature:
         ex7 :: _ => Coercion (a :: Type) (b :: Type)
diff --git a/testsuite/tests/polykinds/T10503.stderr b/testsuite/tests/polykinds/T10503.stderr
index a47a872253..0895bdba26 100644
--- a/testsuite/tests/polykinds/T10503.stderr
+++ b/testsuite/tests/polykinds/T10503.stderr
@@ -13,5 +13,5 @@ T10503.hs:8:6: error:
       To defer the ambiguity check to use sites, enable AllowAmbiguousTypes
       In the type signature:
         h :: forall k r.
-             (Proxy ('KProxy :: KProxy k) ~ Proxy ('KProxy :: KProxy *) => r)
+             (Proxy ('KProxy :: KProxy k) ~ Proxy ('KProxy :: KProxy (*)) => r)
              -> r
diff --git a/testsuite/tests/polykinds/T11399.stderr b/testsuite/tests/polykinds/T11399.stderr
index cd78c24792..e5c9e0e37c 100644
--- a/testsuite/tests/polykinds/T11399.stderr
+++ b/testsuite/tests/polykinds/T11399.stderr
@@ -4,6 +4,6 @@ T11399.hs:10:32: error:
       When matching kinds
         a :: * -> *
         TYPE :: GHC.Types.RuntimeRep -> *
-      Expected kind ‘* -> *’, but ‘UhOh a’ has kind ‘a * -> *’
+      Expected kind ‘* -> *’, but ‘UhOh a’ has kind ‘a (*) -> *’
     • In the first argument of ‘Functor’, namely ‘(UhOh a)’
       In the instance declaration for ‘Functor (UhOh a)’
diff --git a/testsuite/tests/polykinds/T14450.stderr b/testsuite/tests/polykinds/T14450.stderr
index 927ae6a720..c631bade87 100644
--- a/testsuite/tests/polykinds/T14450.stderr
+++ b/testsuite/tests/polykinds/T14450.stderr
@@ -2,6 +2,6 @@
 T14450.hs:33:3: error:
     • Type indexes must match class instance head
       Expected: Dom @k @k (IddSym0 @k)
-        Actual: Dom @* @* (IddSym0 @*)
+        Actual: Dom @(*) @(*) (IddSym0 @(*))
     • In the type instance declaration for ‘Dom’
       In the instance declaration for ‘Varpi (IddSym0 :: k ~> k)’
diff --git a/testsuite/tests/polykinds/T14520.stderr b/testsuite/tests/polykinds/T14520.stderr
index cc7619d39b..b8a1ed1bf0 100644
--- a/testsuite/tests/polykinds/T14520.stderr
+++ b/testsuite/tests/polykinds/T14520.stderr
@@ -1,6 +1,6 @@
 
 T14520.hs:15:24: error:
     • Expected kind ‘bat w w’,
-        but ‘Id’ has kind ‘XXX @a0 @* (XXX @a0 @(a0 ~>> *) kat0 b0) b0’
+        but ‘Id’ has kind ‘XXX @a0 @(*) (XXX @a0 @(a0 ~>> *) kat0 b0) b0’
     • In the first argument of ‘Sing’, namely ‘(Id :: bat w w)’
       In the type signature: sId :: Sing w -> Sing (Id :: bat w w)
diff --git a/testsuite/tests/polykinds/T8566.stderr b/testsuite/tests/polykinds/T8566.stderr
index 23dddf66c7..44fae4202e 100644
--- a/testsuite/tests/polykinds/T8566.stderr
+++ b/testsuite/tests/polykinds/T8566.stderr
@@ -6,7 +6,7 @@ T8566.hs:34:9: error:
         bound by the instance declaration at T8566.hs:32:10-67
       or from: 'AA t (a : as) ~ 'AA t1 as1
         bound by a pattern with constructor:
-                   A :: forall v (t :: v) (as :: [U *]) (r :: [*]). I ('AA t as) r,
+                   A :: forall v (t :: v) (as :: [U (*)]) (r :: [*]). I ('AA t as) r,
                  in an equation for ‘c’
         at T8566.hs:34:5
       The type variable ‘fs0’ is ambiguous
diff --git a/testsuite/tests/saks/should_fail/saks007_fail.stderr b/testsuite/tests/saks/should_fail/saks007_fail.stderr
index ab15984030..431b5dede9 100644
--- a/testsuite/tests/saks/should_fail/saks007_fail.stderr
+++ b/testsuite/tests/saks/should_fail/saks007_fail.stderr
@@ -1,8 +1,8 @@
 
 saks007_fail.hs:15:10: error:
     • Couldn't match kind ‘'True’ with ‘'False’
-      Expected kind: G *
-        Actual kind: F *
+      Expected kind: G (*)
+        Actual kind: F (*)
     • In the type ‘X Integer String’
       In the definition of data constructor ‘MkX’
       In the data declaration for ‘X’
diff --git a/testsuite/tests/typecheck/should_fail/T15801.stderr b/testsuite/tests/typecheck/should_fail/T15801.stderr
index 887c0f2a35..e74972332c 100644
--- a/testsuite/tests/typecheck/should_fail/T15801.stderr
+++ b/testsuite/tests/typecheck/should_fail/T15801.stderr
@@ -3,4 +3,4 @@ T15801.hs:52:10: error:
     • Couldn't match representation of type ‘UnOp op_a -> UnOp b’
                                with that of ‘op_a --> b’
         arising from the superclasses of an instance declaration
-    • In the instance declaration for ‘OpRíki (Op *)’
+    • In the instance declaration for ‘OpRíki (Op (*))’
diff --git a/testsuite/tests/typecheck/should_fail/T16821.stderr b/testsuite/tests/typecheck/should_fail/T16821.stderr
index f5d77720c7..a93ba8c33f 100644
--- a/testsuite/tests/typecheck/should_fail/T16821.stderr
+++ b/testsuite/tests/typecheck/should_fail/T16821.stderr
@@ -1,5 +1,5 @@
 
 T16821.hs:12:1: error:
     • Kind signature on newtype declaration has non-TYPE
-      return kind ‘Id *’
+      return kind ‘Id (*)’
     • In the newtype declaration for ‘T’