Revert "Remove SpecConstrAnnotation (#13681)" (#19168)

This reverts commit 7bc3a65b467c4286377b9bded277d5a2f69160b3.

NoSpecConstr is used in the wild (see #19168)

1 files changed, 24 insertions, 2 deletions

diff --git a/libraries/base/GHC/Exts.hs b/libraries/base/GHC/Exts.hs
index 31788c24c0..d1ca1cfff8 100755
--- a/libraries/base/GHC/Exts.hs
+++ b/libraries/base/GHC/Exts.hs
@@ -5,8 +5,7 @@
 {-# LANGUAGE TypeFamilies #-}
 {-# LANGUAGE UnboxedTuples #-}
 {-# LANGUAGE Unsafe #-}
-
-{-# OPTIONS_HADDOCK not-home #-}
+{-# LANGUAGE DeriveDataTypeable #-}
 
 -----------------------------------------------------------------------------
 -- |
@@ -99,6 +98,9 @@ module GHC.Exts
         -- * Event logging
         traceEvent,
 
+        -- * SpecConstr annotations
+        SpecConstrAnnotation(..),
+
         -- * The call stack
         currentCallStack,
 
@@ -124,6 +126,7 @@ import GHC.Stack
 import qualified Data.Coerce
 import Data.String
 import Data.OldList
+import Data.Data
 import Data.Ord
 import Data.Version ( Version(..), makeVersion )
 import qualified Debug.Trace
@@ -173,6 +176,25 @@ traceEvent = Debug.Trace.traceEventIO
 
 {- **********************************************************************
 *                                                                       *
+*              SpecConstr annotation                                    *
+*                                                                       *
+********************************************************************** -}
+
+-- Annotating a type with NoSpecConstr will make SpecConstr
+-- not specialise for arguments of that type.
+
+-- This data type is defined here, rather than in the SpecConstr module
+-- itself, so that importing it doesn't force stupidly linking the
+-- entire ghc package at runtime
+
+data SpecConstrAnnotation = NoSpecConstr | ForceSpecConstr
+                deriving ( Data -- ^ @since 4.3.0.0
+                         , Eq   -- ^ @since 4.3.0.0
+                         )
+
+
+{- **********************************************************************
+*                                                                       *
 *              The IsList class                                         *
 *                                                                       *
 ********************************************************************** -}