Kill the magic of Any

This turns `Any` into a standard wired-in type family defined in
`GHC.Types`, instead its current incarnation as a magical creature
provided by the `GHC.Prim`.  Also kill `AnyK`.

See #10886.

Test Plan: Validate

Reviewers: simonpj, goldfire, austin, hvr

Reviewed By: simonpj

Subscribers: goldfire, thomie

Differential Revision: https://phabricator.haskell.org/D2049

GHC Trac Issues: #10886

2 files changed, 23 insertions, 1 deletions

diff --git a/libraries/base/GHC/Exts.hs b/libraries/base/GHC/Exts.hs
index 21f7bfd8b9..9e58f5c40c 100755
--- a/libraries/base/GHC/Exts.hs
+++ b/libraries/base/GHC/Exts.hs
@@ -74,6 +74,9 @@ module GHC.Exts
         -- * The Constraint kind
         Constraint,
 
+        -- * The Any type
+        Any,
+
         -- * Overloaded lists
         IsList(..)
        ) where
diff --git a/libraries/ghc-prim/GHC/Types.hs b/libraries/ghc-prim/GHC/Types.hs
index 736ea3dbfa..827c3468ec 100644
--- a/libraries/ghc-prim/GHC/Types.hs
+++ b/libraries/ghc-prim/GHC/Types.hs
@@ -1,5 +1,6 @@
 {-# LANGUAGE MagicHash, NoImplicitPrelude, TypeFamilies, UnboxedTuples,
-             MultiParamTypeClasses, RoleAnnotations, CPP, TypeOperators #-}
+             MultiParamTypeClasses, RoleAnnotations, CPP, TypeOperators,
+             PolyKinds #-}
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  GHC.Types
@@ -29,6 +30,7 @@ module GHC.Types (
         isTrue#,
         SPEC(..),
         Nat, Symbol,
+        Any,
         type (~~), Coercible,
         TYPE, RuntimeRep(..), Type, type (*), type (★), Constraint,
           -- The historical type * should ideally be written as
@@ -81,6 +83,23 @@ data Symbol
 
 {- *********************************************************************
 *                                                                      *
+                  Any
+*                                                                      *
+********************************************************************* -}
+
+-- | The type constructor 'Any' is type to which you can unsafely coerce any
+-- lifted type, and back. More concretely, for a lifted type @t@ and
+-- value @x :: t@, -- @unsafeCoerce (unsafeCoerce x :: Any) :: t@ is equivalent
+-- to @x@.
+--
+type family Any :: k where { }
+-- See Note [Any types] in TysWiredIn. Also, for a bit of history on Any see
+-- #10886. Note that this must be a *closed* type family: we need to ensure
+-- that this can't reduce to a `data` type for the results discussed in
+-- Note [Any types].
+
+{- *********************************************************************
+*                                                                      *
                   Lists
 
    NB: lists are built-in syntax, and hence not explicitly exported