Embrace -XTypeInType, add -XStarIsType

Summary:
Implement the "Embrace Type :: Type" GHC proposal,
.../ghc-proposals/blob/master/proposals/0020-no-type-in-type.rst

GHC 8.0 included a major change to GHC's type system: the Type :: Type
axiom. Though casual users were protected from this by hiding its
features behind the -XTypeInType extension, all programs written in GHC
8+ have the axiom behind the scenes. In order to preserve backward
compatibility, various legacy features were left unchanged. For example,
with -XDataKinds but not -XTypeInType, GADTs could not be used in types.
Now these restrictions are lifted and -XTypeInType becomes a redundant
flag that will be eventually deprecated.

* Incorporate the features currently in -XTypeInType into the
  -XPolyKinds and -XDataKinds extensions.
* Introduce a new extension -XStarIsType to control how to parse * in
  code and whether to print it in error messages.

Test Plan: Validate

Reviewers: goldfire, hvr, bgamari, alanz, simonpj

Reviewed By: goldfire, simonpj

Subscribers: rwbarton, thomie, mpickering, carter

GHC Trac Issues: #15195

Differential Revision: https://phabricator.haskell.org/D4748

10 files changed, 16 insertions, 14 deletions

diff --git a/testsuite/tests/ghci/scripts/T10321.hs b/testsuite/tests/ghci/scripts/T10321.hs
index 44d264a801..443ebe41a4 100644
--- a/testsuite/tests/ghci/scripts/T10321.hs
+++ b/testsuite/tests/ghci/scripts/T10321.hs
@@ -5,9 +5,10 @@
 
 module T10321 where
 
+import Data.Kind (Type)
 import GHC.TypeLits
 
-data Vec :: Nat -> * -> * where
+data Vec :: Nat -> Type -> Type where
   Nil  :: Vec 0 a
   (:>) :: a -> Vec n a -> Vec (n + 1) a
 
diff --git a/testsuite/tests/ghci/scripts/T11252.script b/testsuite/tests/ghci/scripts/T11252.script
index 485cd8fa0d..3cec1d348d 100644
--- a/testsuite/tests/ghci/scripts/T11252.script
+++ b/testsuite/tests/ghci/scripts/T11252.script
@@ -1,3 +1,3 @@
-:set -XTypeInType
+:set -XPolyKinds
 data Proxy1 k (a :: k) = Proxy1
 :kind Proxy1
diff --git a/testsuite/tests/ghci/scripts/T11376.script b/testsuite/tests/ghci/scripts/T11376.script
index d359b66542..0cda4f02ba 100644
--- a/testsuite/tests/ghci/scripts/T11376.script
+++ b/testsuite/tests/ghci/scripts/T11376.script
@@ -3,7 +3,7 @@ let { bar :: Show a => a -> b -> a; bar = error "urk" }
 :type bar @Int
 :set -fprint-explicit-foralls
 :type bar @Int
-:set -fprint-explicit-kinds -XTypeApplications -XTypeInType
+:set -fprint-explicit-kinds -XTypeApplications -XPolyKinds
 data Prox a = Prox
 let { prox :: Prox a; prox = Prox }
 :t prox
diff --git a/testsuite/tests/ghci/scripts/T12550.script b/testsuite/tests/ghci/scripts/T12550.script
index dad2a47e65..7c07e8f1dd 100644
--- a/testsuite/tests/ghci/scripts/T12550.script
+++ b/testsuite/tests/ghci/scripts/T12550.script
@@ -1,4 +1,4 @@
-:set -fprint-explicit-foralls -XKindSignatures -XExplicitNamespaces
+:set -fprint-explicit-foralls -XKindSignatures -XExplicitNamespaces -XUnicodeSyntax
 import Data.Kind (type Type)
 
 
diff --git a/testsuite/tests/ghci/scripts/T13407.script b/testsuite/tests/ghci/scripts/T13407.script
index f77fd42afe..3956a3a210 100644
--- a/testsuite/tests/ghci/scripts/T13407.script
+++ b/testsuite/tests/ghci/scripts/T13407.script
@@ -1,4 +1,4 @@
-:set -XTypeInType -XRankNTypes
+:set -XPolyKinds -XRankNTypes
 import Data.Kind
-data Foo :: (* -> *) -> (forall k. k -> *)
+data Foo :: (Type -> Type) -> (forall k. k -> Type)
 :info Foo
diff --git a/testsuite/tests/ghci/scripts/T13963.script b/testsuite/tests/ghci/scripts/T13963.script
index fdd4d78338..c5e830aad1 100644
--- a/testsuite/tests/ghci/scripts/T13963.script
+++ b/testsuite/tests/ghci/scripts/T13963.script
@@ -1,4 +1,4 @@
-:set -XTypeInType -XRankNTypes
+:set -XPolyKinds -XDataKinds -XRankNTypes
 import GHC.Exts (TYPE, RuntimeRep(LiftedRep))
 type Pair (a :: TYPE rep) (b :: TYPE rep') rep'' = forall (r :: TYPE rep''). (a -> b -> r)
 :kind Pair
diff --git a/testsuite/tests/ghci/scripts/T13988.hs b/testsuite/tests/ghci/scripts/T13988.hs
index 54969cad4d..d26135e26d 100644
--- a/testsuite/tests/ghci/scripts/T13988.hs
+++ b/testsuite/tests/ghci/scripts/T13988.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE TypeInType, GADTs #-}
+{-# LANGUAGE PolyKinds, GADTs #-}
 
 module T13988 where
 
diff --git a/testsuite/tests/ghci/scripts/T7873.script b/testsuite/tests/ghci/scripts/T7873.script
index 404c1f5bda..1a358a478e 100644
--- a/testsuite/tests/ghci/scripts/T7873.script
+++ b/testsuite/tests/ghci/scripts/T7873.script
@@ -1,4 +1,4 @@
-:set -XPolyKinds -XRankNTypes -XGADTs -XTypeInType
+:set -XPolyKinds -XRankNTypes -XGADTs
 data D1 = MkD1 (forall p (a :: k). p a -> Int)
 data D2 = MkD2 (forall p a. p a -> Int)
 data D3 = MkD3 (forall k p (a :: k). p a -> Int)
diff --git a/testsuite/tests/ghci/scripts/T7939.hs b/testsuite/tests/ghci/scripts/T7939.hs
index fbdf883b51..04a1f1a623 100644
--- a/testsuite/tests/ghci/scripts/T7939.hs
+++ b/testsuite/tests/ghci/scripts/T7939.hs
@@ -1,6 +1,6 @@
 {-# LANGUAGE TypeFamilies, PolyKinds, DataKinds, TypeOperators #-}
-
 module T7939 where
+import Data.Kind (Type)
 
 class Foo a where
    type Bar a b
@@ -22,6 +22,6 @@ type family K a where
   K '[] = Nothing
   K (h ': t) = Just h
 
-type family L (a :: k) (b :: *) :: k where
+type family L (a :: k) (b :: Type) :: k where
   L Int Int = Bool
   L Maybe Bool = IO
diff --git a/testsuite/tests/ghci/scripts/T8357.hs b/testsuite/tests/ghci/scripts/T8357.hs
index 82a34afdc6..322ec11e19 100644
--- a/testsuite/tests/ghci/scripts/T8357.hs
+++ b/testsuite/tests/ghci/scripts/T8357.hs
@@ -5,11 +5,12 @@
 {-# LANGUAGE TypeOperators #-}
 module T8357 where
 
+import Data.Kind (Type)
 import GHC.TypeLits 
 
 data (:::) (sy :: Symbol) ty 
 data Key (sy :: Symbol) 
-data Rec (rs :: [*])
+data Rec (rs :: [Type])
 
 (*=) :: Key sy -> ty -> Rec '[sy ::: ty]
 (*=) = undefined
@@ -17,7 +18,7 @@ data Rec (rs :: [*])
 (.*.) :: (Union xs ys ~ rs) => Rec xs -> Rec ys -> Rec rs
 (.*.) = undefined
 
-type family Union (xs :: [*]) (ys :: [*]) :: [*]  where
+type family Union (xs :: [Type]) (ys :: [Type]) :: [Type]  where
     Union ((sy ::: t) ': xs) ys = (sy ::: t) ': Union xs ys
     Union '[] ys = ys
 
@@ -30,4 +31,4 @@ fBar = undefined
 
 foo = fFoo *= "foo"
 bar = fBar *= "bar"
-both = foo .*. bar
\ No newline at end of file
+both = foo .*. bar