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

16 files changed, 95 insertions, 107 deletions

diff --git a/testsuite/tests/parser/should_compile/DumpParsedAst.stderr b/testsuite/tests/parser/should_compile/DumpParsedAst.stderr
index ea9becb6c5..a1765035fb 100644
--- a/testsuite/tests/parser/should_compile/DumpParsedAst.stderr
+++ b/testsuite/tests/parser/should_compile/DumpParsedAst.stderr
@@ -80,77 +80,56 @@
                (HsParTy
                 (NoExt)
                 ({ DumpParsedAst.hs:8:11-16 }
-                 (HsAppsTy
+                 (HsOpTy
                   (NoExt)
-                  [({ DumpParsedAst.hs:8:11 }
-                    (HsAppPrefix
-                     (NoExt)
-                     ({ DumpParsedAst.hs:8:11 }
-                      (HsTyVar
-                       (NoExt)
-                       (NotPromoted)
-                       ({ DumpParsedAst.hs:8:11 }
-                        (Unqual
-                         {OccName: a}))))))
-                  ,({ DumpParsedAst.hs:8:13 }
-                    (HsAppInfix
-                     (NoExt)
-                     ({ DumpParsedAst.hs:8:13 }
-                      (Exact
-                       {Name: :}))))
-                  ,({ DumpParsedAst.hs:8:15-16 }
-                    (HsAppPrefix
-                     (NoExt)
-                     ({ DumpParsedAst.hs:8:15-16 }
-                      (HsTyVar
-                       (NoExt)
-                       (NotPromoted)
-                       ({ DumpParsedAst.hs:8:15-16 }
-                        (Unqual
-                         {OccName: as}))))))]))))]
-             (Prefix)
-             ({ DumpParsedAst.hs:8:21-36 }
-              (HsAppsTy
-               (NoExt)
-               [({ DumpParsedAst.hs:8:21-24 }
-                 (HsAppPrefix
-                  (NoExt)
-                  ({ DumpParsedAst.hs:8:21-24 }
+                  ({ DumpParsedAst.hs:8:11 }
                    (HsTyVar
                     (NoExt)
                     (NotPromoted)
-                    ({ DumpParsedAst.hs:8:21-24 }
+                    ({ DumpParsedAst.hs:8:11 }
                      (Unqual
-                      {OccName: Succ}))))))
-               ,({ DumpParsedAst.hs:8:26-36 }
-                 (HsAppPrefix
-                  (NoExt)
-                  ({ DumpParsedAst.hs:8:26-36 }
-                   (HsParTy
+                      {OccName: a}))))
+                  ({ DumpParsedAst.hs:8:13 }
+                   (Exact
+                    {Name: :}))
+                  ({ DumpParsedAst.hs:8:15-16 }
+                   (HsTyVar
                     (NoExt)
-                    ({ DumpParsedAst.hs:8:27-35 }
-                     (HsAppsTy
-                      (NoExt)
-                      [({ DumpParsedAst.hs:8:27-32 }
-                        (HsAppPrefix
-                         (NoExt)
-                         ({ DumpParsedAst.hs:8:27-32 }
-                          (HsTyVar
-                           (NoExt)
-                           (NotPromoted)
-                           ({ DumpParsedAst.hs:8:27-32 }
-                            (Unqual
-                             {OccName: Length}))))))
-                      ,({ DumpParsedAst.hs:8:34-35 }
-                        (HsAppPrefix
-                         (NoExt)
-                         ({ DumpParsedAst.hs:8:34-35 }
-                          (HsTyVar
-                           (NoExt)
-                           (NotPromoted)
-                           ({ DumpParsedAst.hs:8:34-35 }
-                            (Unqual
-                             {OccName: as}))))))]))))))])))))
+                    (NotPromoted)
+                    ({ DumpParsedAst.hs:8:15-16 }
+                     (Unqual
+                      {OccName: as}))))))))]
+             (Prefix)
+             ({ DumpParsedAst.hs:8:21-36 }
+              (HsAppTy
+               (NoExt)
+               ({ DumpParsedAst.hs:8:21-24 }
+                (HsTyVar
+                 (NoExt)
+                 (NotPromoted)
+                 ({ DumpParsedAst.hs:8:21-24 }
+                  (Unqual
+                   {OccName: Succ}))))
+               ({ DumpParsedAst.hs:8:26-36 }
+                (HsParTy
+                 (NoExt)
+                 ({ DumpParsedAst.hs:8:27-35 }
+                  (HsAppTy
+                   (NoExt)
+                   ({ DumpParsedAst.hs:8:27-32 }
+                    (HsTyVar
+                     (NoExt)
+                     (NotPromoted)
+                     ({ DumpParsedAst.hs:8:27-32 }
+                      (Unqual
+                       {OccName: Length}))))
+                   ({ DumpParsedAst.hs:8:34-35 }
+                    (HsTyVar
+                     (NoExt)
+                     (NotPromoted)
+                     ({ DumpParsedAst.hs:8:34-35 }
+                      (Unqual
+                       {OccName: as})))))))))))))
          ,({ DumpParsedAst.hs:9:3-24 }
            (HsIB
             (NoExt)
diff --git a/testsuite/tests/parser/should_compile/DumpRenamedAst.hs b/testsuite/tests/parser/should_compile/DumpRenamedAst.hs
index 493b736df5..bf3e372461 100644
--- a/testsuite/tests/parser/should_compile/DumpRenamedAst.hs
+++ b/testsuite/tests/parser/should_compile/DumpRenamedAst.hs
@@ -1,5 +1,5 @@
 {-# LANGUAGE DataKinds, GADTs, PolyKinds, RankNTypes, TypeOperators,
-             TypeFamilies #-}
+             TypeFamilies, StarIsType #-}
 
 module DumpRenamedAst where
 
diff --git a/testsuite/tests/parser/should_compile/DumpRenamedAst.stderr b/testsuite/tests/parser/should_compile/DumpRenamedAst.stderr
index 4ca996fde0..673b391d7f 100644
--- a/testsuite/tests/parser/should_compile/DumpRenamedAst.stderr
+++ b/testsuite/tests/parser/should_compile/DumpRenamedAst.stderr
@@ -69,10 +69,10 @@
          {Name: DumpRenamedAst.Peano})
         (HsQTvs
          (HsQTvsRn
-         []
-         {NameSet:
-          []})
-          [])
+          []
+          {NameSet:
+           []})
+         [])
         (Prefix)
         (HsDataDefn
          (NoExt)
@@ -124,8 +124,8 @@
            [({ DumpRenamedAst.hs:9:3-36 }
              (HsIB
               (HsIBRn
-              [{Name: a}
-              ,{Name: as}]
+               [{Name: a}
+               ,{Name: as}]
                (True))
               (FamEqn
                (NoExt)
@@ -182,7 +182,7 @@
            ,({ DumpRenamedAst.hs:10:3-24 }
              (HsIB
               (HsIBRn
-              []
+               []
                (True))
               (FamEqn
                (NoExt)
@@ -204,7 +204,7 @@
           {Name: DumpRenamedAst.Length})
          (HsQTvs
           (HsQTvsRn
-          [{Name: k}]
+           [{Name: k}]
            {NameSet:
             []})
           [({ DumpRenamedAst.hs:8:20-30 }
@@ -246,10 +246,10 @@
           {Name: DumpRenamedAst.Nat})
          (HsQTvs
           (HsQTvsRn
-          [{Name: k}]
-          {NameSet:
-           []})
-           [])
+           [{Name: k}]
+           {NameSet:
+            []})
+          [])
          (Prefix)
          ({ DumpRenamedAst.hs:12:17-30 }
           (KindSig
@@ -273,11 +273,9 @@
                  ({ DumpRenamedAst.hs:12:25 }
                   {Name: k})))
                ({ DumpRenamedAst.hs:12:30 }
-                (HsTyVar
+                (HsStarTy
                  (NoExt)
-                 (NotPromoted)
-                 ({ DumpRenamedAst.hs:12:30 }
-                  {Name: GHC.Types.*})))))))))
+                 (False)))))))))
          (Nothing))))]
      []
      [({ DumpRenamedAst.hs:(15,1)-(16,45) }
@@ -286,8 +284,8 @@
         (DataFamInstDecl
          (HsIB
           (HsIBRn
-          [{Name: k}
-          ,{Name: a}]
+           [{Name: k}
+           ,{Name: a}]
            (True))
           (FamEqn
            (NoExt)
@@ -312,11 +310,9 @@
                   ({ DumpRenamedAst.hs:15:28 }
                    {Name: k})))
                 ({ DumpRenamedAst.hs:15:33 }
-                 (HsTyVar
+                 (HsStarTy
                   (NoExt)
-                  (NotPromoted)
-                  ({ DumpRenamedAst.hs:15:33 }
-                   {Name: GHC.Types.*})))))))]
+                  (False)))))))]
            (Prefix)
            (HsDataDefn
             (NoExt)
@@ -341,17 +337,13 @@
                      ({ DumpRenamedAst.hs:15:40 }
                       {Name: k})))
                    ({ DumpRenamedAst.hs:15:45 }
-                    (HsTyVar
+                    (HsStarTy
                      (NoExt)
-                     (NotPromoted)
-                     ({ DumpRenamedAst.hs:15:45 }
-                      {Name: GHC.Types.*})))))))
+                     (False)))))))
                ({ DumpRenamedAst.hs:15:51 }
-                (HsTyVar
+                (HsStarTy
                  (NoExt)
-                 (NotPromoted)
-                 ({ DumpRenamedAst.hs:15:51 }
-                  {Name: GHC.Types.*}))))))
+                 (False))))))
             [({ DumpRenamedAst.hs:16:3-45 }
               (ConDeclGADT
                (NoExt)
@@ -360,11 +352,11 @@
                (False)
                (HsQTvs
                 (HsQTvsRn
-                [{Name: f}
-                ,{Name: g}]
-                {NameSet:
-                 []})
-                 [])
+                 [{Name: f}
+                 ,{Name: g}]
+                 {NameSet:
+                  []})
+                [])
                (Nothing)
                (PrefixCon
                 [({ DumpRenamedAst.hs:16:10-34 }
diff --git a/testsuite/tests/parser/should_compile/T10379.hs b/testsuite/tests/parser/should_compile/T10379.hs
index 1eb5f96382..eb231c4415 100644
--- a/testsuite/tests/parser/should_compile/T10379.hs
+++ b/testsuite/tests/parser/should_compile/T10379.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE KindSignatures, GADTs, DataKinds, TypeOperators #-}
+{-# LANGUAGE KindSignatures, GADTs, DataKinds #-}
 module Foo where
 
 data Foo1 :: [*] -> * where
diff --git a/testsuite/tests/parser/should_fail/T15209.stderr b/testsuite/tests/parser/should_fail/T15209.stderr
index f5418fab74..9d1e151cf2 100644
--- a/testsuite/tests/parser/should_fail/T15209.stderr
+++ b/testsuite/tests/parser/should_fail/T15209.stderr
@@ -1,2 +1,2 @@
 
-T15209.hs:6:8: error: Not in scope: type constructor or class ‘~#’
+T15209.hs:6:10: error: Not in scope: type constructor or class ‘~#’
diff --git a/testsuite/tests/parser/should_fail/all.T b/testsuite/tests/parser/should_fail/all.T
index 9fcc3ba97d..1e71e40420 100644
--- a/testsuite/tests/parser/should_fail/all.T
+++ b/testsuite/tests/parser/should_fail/all.T
@@ -120,3 +120,8 @@ test('NumericUnderscoresFail1',
      grep_errmsg(r'^NumericUnderscoresFail1.hs:'), compile_fail, [''])
 
 test('InfixAppPatErr', normal, compile_fail, [''])
+
+test('typeops_A', normal, compile_fail, [''])
+test('typeops_B', normal, compile_fail, [''])
+test('typeops_C', normal, compile_fail, [''])
+test('typeops_D', normal, compile_fail, [''])
diff --git a/testsuite/tests/parser/should_fail/readFail036.hs b/testsuite/tests/parser/should_fail/readFail036.hs
index 2bb23149dd..15afd980f8 100644
--- a/testsuite/tests/parser/should_fail/readFail036.hs
+++ b/testsuite/tests/parser/should_fail/readFail036.hs
@@ -1,5 +1,5 @@
-
 module Foo where
 
-data Foo (a :: *) = Foo a
+import Data.Kind (Type)
 
+data Foo (a :: Type) = Foo a
diff --git a/testsuite/tests/parser/should_fail/readFail036.stderr b/testsuite/tests/parser/should_fail/readFail036.stderr
index 0d22eb8363..a66afacacf 100644
--- a/testsuite/tests/parser/should_fail/readFail036.stderr
+++ b/testsuite/tests/parser/should_fail/readFail036.stderr
@@ -1,5 +1,5 @@
 
-readFail036.hs:4:16:
-    Illegal kind signature: ‘*’
+readFail036.hs:5:16: error:
+    Illegal kind signature: ‘Type’
       Perhaps you intended to use KindSignatures
     In the data type declaration for ‘Foo’
diff --git a/testsuite/tests/parser/should_fail/typeops_A.hs b/testsuite/tests/parser/should_fail/typeops_A.hs
new file mode 100644
index 0000000000..abd7f528c6
--- /dev/null
+++ b/testsuite/tests/parser/should_fail/typeops_A.hs
@@ -0,0 +1 @@
+type X = 1 +
diff --git a/testsuite/tests/parser/should_fail/typeops_A.stderr b/testsuite/tests/parser/should_fail/typeops_A.stderr
new file mode 100644
index 0000000000..69f7aac6be
--- /dev/null
+++ b/testsuite/tests/parser/should_fail/typeops_A.stderr
@@ -0,0 +1,2 @@
+
+typeops_A.hs:1:12: error: Operator applied to too few arguments: +
diff --git a/testsuite/tests/parser/should_fail/typeops_B.hs b/testsuite/tests/parser/should_fail/typeops_B.hs
new file mode 100644
index 0000000000..ac65f872de
--- /dev/null
+++ b/testsuite/tests/parser/should_fail/typeops_B.hs
@@ -0,0 +1 @@
+type X = + 1
diff --git a/testsuite/tests/parser/should_fail/typeops_B.stderr b/testsuite/tests/parser/should_fail/typeops_B.stderr
new file mode 100644
index 0000000000..030516a27f
--- /dev/null
+++ b/testsuite/tests/parser/should_fail/typeops_B.stderr
@@ -0,0 +1,2 @@
+
+typeops_B.hs:1:10: error: Operator applied to too few arguments: +
diff --git a/testsuite/tests/parser/should_fail/typeops_C.hs b/testsuite/tests/parser/should_fail/typeops_C.hs
new file mode 100644
index 0000000000..e55838934a
--- /dev/null
+++ b/testsuite/tests/parser/should_fail/typeops_C.hs
@@ -0,0 +1 @@
+type X = 1 + + 2
diff --git a/testsuite/tests/parser/should_fail/typeops_C.stderr b/testsuite/tests/parser/should_fail/typeops_C.stderr
new file mode 100644
index 0000000000..280323bb67
--- /dev/null
+++ b/testsuite/tests/parser/should_fail/typeops_C.stderr
@@ -0,0 +1,2 @@
+
+typeops_C.hs:1:12: error: Operator applied to too few arguments: +
diff --git a/testsuite/tests/parser/should_fail/typeops_D.hs b/testsuite/tests/parser/should_fail/typeops_D.hs
new file mode 100644
index 0000000000..655b2f15f0
--- /dev/null
+++ b/testsuite/tests/parser/should_fail/typeops_D.hs
@@ -0,0 +1 @@
+type X = +
diff --git a/testsuite/tests/parser/should_fail/typeops_D.stderr b/testsuite/tests/parser/should_fail/typeops_D.stderr
new file mode 100644
index 0000000000..0ce7e29559
--- /dev/null
+++ b/testsuite/tests/parser/should_fail/typeops_D.stderr
@@ -0,0 +1,2 @@
+
+typeops_D.hs:1:10: error: Operator applied to too few arguments: +