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

3 files changed, 6 insertions, 6 deletions

diff --git a/testsuite/tests/pmcheck/complete_sigs/T14253.hs b/testsuite/tests/pmcheck/complete_sigs/T14253.hs
index 88cc4f88b3..bb56d437bf 100644
--- a/testsuite/tests/pmcheck/complete_sigs/T14253.hs
+++ b/testsuite/tests/pmcheck/complete_sigs/T14253.hs
@@ -2,7 +2,7 @@
 {-# LANGUAGE PatternSynonyms #-}
 {-# LANGUAGE TypeOperators #-}
 {-# LANGUAGE RankNTypes #-}
-{-# LANGUAGE TypeInType #-}
+{-# LANGUAGE PolyKinds #-}
 
 module T14253 where
 
diff --git a/testsuite/tests/pmcheck/should_compile/T14086.hs b/testsuite/tests/pmcheck/should_compile/T14086.hs
index de91229c24..5e69ce6a33 100644
--- a/testsuite/tests/pmcheck/should_compile/T14086.hs
+++ b/testsuite/tests/pmcheck/should_compile/T14086.hs
@@ -1,4 +1,4 @@
-{-# language TypeInType, EmptyCase #-}
+{-# language EmptyCase #-}
 module T14086 where
 import Data.Kind
 
diff --git a/testsuite/tests/pmcheck/should_compile/T3927b.hs b/testsuite/tests/pmcheck/should_compile/T3927b.hs
index 89b81534c7..d4cfa1e275 100644
--- a/testsuite/tests/pmcheck/should_compile/T3927b.hs
+++ b/testsuite/tests/pmcheck/should_compile/T3927b.hs
@@ -11,8 +11,8 @@
 
 module T3927b where
 
+import Data.Kind (Type, Constraint)
 import Data.Proxy
-import GHC.Exts
 
 data Message
 
@@ -30,16 +30,16 @@ type family Implements (t :: SocketType) :: [SocketOperation] where
     Implements Push = '[Write]
     Implements Pull = '[ 'Read]
 
-data SockOp :: SocketType -> SocketOperation -> * where
+data SockOp :: SocketType -> SocketOperation -> Type where
     SRead :: SockOp sock 'Read
     SWrite :: SockOp sock Write
 
-data Socket :: SocketType -> * where
+data Socket :: SocketType -> Type where
     Socket :: proxy sock
            -> (forall op . Restrict op (Implements sock) => SockOp sock op -> Operation op)
            -> Socket sock
 
-type family Operation (op :: SocketOperation) :: * where
+type family Operation (op :: SocketOperation) :: Type where
     Operation 'Read = IO Message
     Operation Write = Message -> IO ()