export IsList from GHC.IsListwip/T21517

it is still re-exported from GHC.Exts

(cherry picked from commit 0092c67cffb707611b2684df24a1a77e40c01cb7)

10 files changed, 108 insertions, 86 deletions

diff --git a/compiler/GHC/Builtin/Names.hs b/compiler/GHC/Builtin/Names.hs
index 3a2dd41406..8dd355ced2 100644
--- a/compiler/GHC/Builtin/Names.hs
+++ b/compiler/GHC/Builtin/Names.hs
@@ -543,7 +543,7 @@ gHC_PRIM, gHC_PRIM_PANIC, gHC_PRIM_EXCEPTION,
     gHC_FLOAT, gHC_TOP_HANDLER, sYSTEM_IO, dYNAMIC,
     tYPEABLE, tYPEABLE_INTERNAL, gENERICS,
     rEAD_PREC, lEX, gHC_INT, gHC_WORD, mONAD, mONAD_FIX, mONAD_ZIP, mONAD_FAIL,
-    aRROW, gHC_DESUGAR, rANDOM, gHC_EXTS,
+    aRROW, gHC_DESUGAR, rANDOM, gHC_EXTS, gHC_IS_LIST,
     cONTROL_EXCEPTION_BASE, gHC_TYPEERROR, gHC_TYPELITS, gHC_TYPELITS_INTERNAL,
     gHC_TYPENATS, gHC_TYPENATS_INTERNAL,
     dATA_COERCE, dEBUG_TRACE, uNSAFE_COERCE :: Module
@@ -605,6 +605,7 @@ aRROW           = mkBaseModule (fsLit "Control.Arrow")
 gHC_DESUGAR = mkBaseModule (fsLit "GHC.Desugar")
 rANDOM          = mkBaseModule (fsLit "System.Random")
 gHC_EXTS        = mkBaseModule (fsLit "GHC.Exts")
+gHC_IS_LIST     = mkBaseModule (fsLit "GHC.IsList")
 cONTROL_EXCEPTION_BASE = mkBaseModule (fsLit "Control.Exception.Base")
 gHC_GENERICS    = mkBaseModule (fsLit "GHC.Generics")
 gHC_TYPEERROR   = mkBaseModule (fsLit "GHC.TypeError")
@@ -1470,10 +1471,10 @@ zipName           = varQual gHC_LIST (fsLit "zip")    zipIdKey
 
 -- Overloaded lists
 isListClassName, fromListName, fromListNName, toListName :: Name
-isListClassName = clsQual gHC_EXTS (fsLit "IsList")    isListClassKey
-fromListName    = varQual gHC_EXTS (fsLit "fromList")  fromListClassOpKey
-fromListNName   = varQual gHC_EXTS (fsLit "fromListN") fromListNClassOpKey
-toListName      = varQual gHC_EXTS (fsLit "toList")    toListClassOpKey
+isListClassName = clsQual gHC_IS_LIST (fsLit "IsList")    isListClassKey
+fromListName    = varQual gHC_IS_LIST (fsLit "fromList")  fromListClassOpKey
+fromListNName   = varQual gHC_IS_LIST (fsLit "fromListN") fromListNClassOpKey
+toListName      = varQual gHC_IS_LIST (fsLit "toList")    toListClassOpKey
 
 -- HasField class ops
 getFieldName, setFieldName :: Name
diff --git a/libraries/base/GHC/Exts.hs b/libraries/base/GHC/Exts.hs
index d4a59b440c..7a1166d241 100755
--- a/libraries/base/GHC/Exts.hs
+++ b/libraries/base/GHC/Exts.hs
@@ -142,18 +142,16 @@ import GHC.ArrayArray
 import GHC.Base hiding ( coerce )
 import GHC.Ptr
 import GHC.Stack
+import GHC.IsList (IsList(..)) -- for re-export
 
 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
 import Unsafe.Coerce ( unsafeCoerce# ) -- just for re-export
 
-import Control.Applicative (ZipList(..))
-
 -- XXX This should really be in Data.Tuple, where the definitions are
 maxTupleSize :: Int
 maxTupleSize = 64
@@ -218,73 +216,6 @@ data SpecConstrAnnotation = NoSpecConstr | ForceSpecConstr
                          )
 
 
-{- **********************************************************************
-*                                                                       *
-*              The IsList class                                         *
-*                                                                       *
-********************************************************************** -}
-
--- | The 'IsList' class and its methods are intended to be used in
---   conjunction with the OverloadedLists extension.
---
--- @since 4.7.0.0
-class IsList l where
-  -- | The 'Item' type function returns the type of items of the structure
-  --   @l@.
-  type Item l
-
-  -- | The 'fromList' function constructs the structure @l@ from the given
-  --   list of @Item l@
-  fromList  :: [Item l] -> l
-
-  -- | The 'fromListN' function takes the input list's length and potentially
-  --   uses it to construct the structure @l@ more efficiently compared to
-  --   'fromList'. If the given number does not equal to the input list's length
-  --   the behaviour of 'fromListN' is not specified.
-  --
-  --   prop> fromListN (length xs) xs == fromList xs
-  fromListN :: Int -> [Item l] -> l
-  fromListN _ = fromList
-
-  -- | The 'toList' function extracts a list of @Item l@ from the structure @l@.
-  --   It should satisfy fromList . toList = id.
-  toList :: l -> [Item l]
-
--- | @since 4.7.0.0
-instance IsList [a] where
-  type (Item [a]) = a
-  fromList = id
-  toList = id
-
--- | @since 4.15.0.0
-instance IsList (ZipList a) where
-  type Item (ZipList a) = a
-  fromList = ZipList
-  toList = getZipList
-
--- | @since 4.9.0.0
-instance IsList (NonEmpty a) where
-  type Item (NonEmpty a) = a
-
-  fromList (a:as) = a :| as
-  fromList [] = errorWithoutStackTrace "NonEmpty.fromList: empty list"
-
-  toList ~(a :| as) = a : as
-
--- | @since 4.8.0.0
-instance IsList Version where
-  type (Item Version) = Int
-  fromList = makeVersion
-  toList = versionBranch
-
--- | Be aware that 'fromList . toList = id' only for unfrozen 'CallStack's,
--- since 'toList' removes frozenness information.
---
--- @since 4.9.0.0
-instance IsList CallStack where
-  type (Item CallStack) = (String, SrcLoc)
-  fromList = fromCallSiteList
-  toList   = getCallStack
 
 -- | An implementation of the old @atomicModifyMutVar#@ primop in
 -- terms of the new 'atomicModifyMutVar2#' primop, for backwards
diff --git a/libraries/base/GHC/IsList.hs b/libraries/base/GHC/IsList.hs
new file mode 100644
index 0000000000..fb93952f23
--- /dev/null
+++ b/libraries/base/GHC/IsList.hs
@@ -0,0 +1,87 @@
+{-# LANGUAGE Trustworthy #-}
+{-# LANGUAGE NoImplicitPrelude #-}
+{-# LANGUAGE TypeFamilies #-}
+
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  GHC.IsList
+-- Copyright   :  (c) The University of Glasgow 2002
+-- License     :  see libraries/base/LICENSE
+--
+-- Maintainer  :  cvs-ghc@haskell.org
+-- Stability   :  internal
+-- Portability :  non-portable (GHC Extensions)
+--
+-- @since 4.17.0.0
+-----------------------------------------------------------------------------
+
+module GHC.IsList
+  ( IsList(..)
+  ) where
+
+import GHC.Base
+import GHC.Stack
+import Data.Version ( Version(..), makeVersion )
+import Control.Applicative (ZipList(..))
+
+-- | The 'IsList' class and its methods are intended to be used in
+--   conjunction with the OverloadedLists extension.
+--
+-- @since 4.7.0.0
+class IsList l where
+  -- | The 'Item' type function returns the type of items of the structure
+  --   @l@.
+  type Item l
+
+  -- | The 'fromList' function constructs the structure @l@ from the given
+  --   list of @Item l@
+  fromList  :: [Item l] -> l
+
+  -- | The 'fromListN' function takes the input list's length and potentially
+  --   uses it to construct the structure @l@ more efficiently compared to
+  --   'fromList'. If the given number does not equal to the input list's length
+  --   the behaviour of 'fromListN' is not specified.
+  --
+  --   prop> fromListN (length xs) xs == fromList xs
+  fromListN :: Int -> [Item l] -> l
+  fromListN _ = fromList
+
+  -- | The 'toList' function extracts a list of @Item l@ from the structure @l@.
+  --   It should satisfy fromList . toList = id.
+  toList :: l -> [Item l]
+
+-- | @since 4.7.0.0
+instance IsList [a] where
+  type (Item [a]) = a
+  fromList = id
+  toList = id
+
+-- | @since 4.15.0.0
+instance IsList (ZipList a) where
+  type Item (ZipList a) = a
+  fromList = ZipList
+  toList = getZipList
+
+-- | @since 4.9.0.0
+instance IsList (NonEmpty a) where
+  type Item (NonEmpty a) = a
+
+  fromList (a:as) = a :| as
+  fromList [] = errorWithoutStackTrace "NonEmpty.fromList: empty list"
+
+  toList ~(a :| as) = a : as
+
+-- | @since 4.8.0.0
+instance IsList Version where
+  type (Item Version) = Int
+  fromList = makeVersion
+  toList = versionBranch
+
+-- | Be aware that 'fromList . toList = id' only for unfrozen 'CallStack's,
+-- since 'toList' removes frozenness information.
+--
+-- @since 4.9.0.0
+instance IsList CallStack where
+  type (Item CallStack) = (String, SrcLoc)
+  fromList = fromCallSiteList
+  toList   = getCallStack
diff --git a/libraries/base/base.cabal b/libraries/base/base.cabal
index 50e9ca29b8..f1aab55614 100644
--- a/libraries/base/base.cabal
+++ b/libraries/base/base.cabal
@@ -249,6 +249,7 @@ Library
         GHC.Int
         GHC.Integer
         GHC.Integer.Logarithms
+        GHC.IsList
         GHC.Ix
         GHC.List
         GHC.Maybe
diff --git a/libraries/base/changelog.md b/libraries/base/changelog.md
index 73235a553b..379bf87bfb 100644
--- a/libraries/base/changelog.md
+++ b/libraries/base/changelog.md
@@ -50,6 +50,8 @@
 
   * Re-export `augment` and `build` function from `GHC.List`
 
+  * Re-export the `IsList` typeclass from the new `GHC.IsList` module.
+
 ## 4.16.1.0 *Feb 2022*
 
   * Shipped with GHC 9.2.2
diff --git a/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail01.stderr b/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail01.stderr
index e7daaeda0b..f3ccc3df17 100644
--- a/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail01.stderr
+++ b/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail01.stderr
@@ -14,10 +14,10 @@ overloadedlistsfail01.hs:5:8: error:
 
 overloadedlistsfail01.hs:5:14: error:
     • Ambiguous type variable ‘a0’ arising from an overloaded list
-      prevents the constraint ‘(GHC.Exts.IsList a0)’ from being solved.
+      prevents the constraint ‘(GHC.IsList.IsList a0)’ from being solved.
       Probable fix: use a type annotation to specify what ‘a0’ should be.
       Potentially matching instance:
-        instance GHC.Exts.IsList [a] -- Defined in ‘GHC.Exts’
+        instance GHC.IsList.IsList [a] -- Defined in ‘GHC.IsList’
         ...plus four instances involving out-of-scope types
         (use -fprint-potential-instances to see them all)
     • In the first argument of ‘print’, namely ‘[1]’
@@ -27,7 +27,7 @@ overloadedlistsfail01.hs:5:14: error:
 overloadedlistsfail01.hs:5:15: error:
     • Ambiguous type variable ‘a0’ arising from the literal ‘1’
       prevents the constraint ‘(Num
-                                  (GHC.Exts.Item a0))’ from being solved.
+                                  (GHC.IsList.Item a0))’ from being solved.
       Probable fix: use a type annotation to specify what ‘a0’ should be.
       Potentially matching instances:
         instance Num Integer -- Defined in ‘GHC.Num’
diff --git a/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail02.stderr b/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail02.stderr
index e0be7ab4e5..b1a7b24ba5 100644
--- a/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail02.stderr
+++ b/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail02.stderr
@@ -1,12 +1,12 @@
 
 overloadedlistsfail02.hs:6:8: error:
-    • No instance for (GHC.Exts.IsList Foo)
+    • No instance for (GHC.IsList.IsList Foo)
         arising from an overloaded list
     • In the expression: [7]
       In an equation for ‘test’: test = [7]
 
 overloadedlistsfail02.hs:6:9: error:
-    • No instance for (Num (GHC.Exts.Item Foo))
+    • No instance for (Num (GHC.IsList.Item Foo))
         arising from the literal ‘7’
     • In the expression: 7
       In the expression: [7]
diff --git a/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail03.stderr b/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail03.stderr
index 3ff4cb3678..1380dda229 100644
--- a/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail03.stderr
+++ b/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail03.stderr
@@ -1,7 +1,7 @@
 
 overloadedlistsfail03.hs:3:28: error:
     • Couldn't match type ‘[Char]’ with ‘Char’
-      Expected: GHC.Exts.Item [Char]
+      Expected: GHC.IsList.Item [Char]
         Actual: String
     • In the expression: "b"
       In the first argument of ‘length’, namely ‘(['a', "b"] :: [Char])’
diff --git a/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail05.stderr b/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail05.stderr
index 6f0045a462..1de0a59995 100644
--- a/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail05.stderr
+++ b/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail05.stderr
@@ -1,7 +1,7 @@
 
 overloadedlistsfail05.hs:3:24: error:
     • Couldn't match type ‘Char’ with ‘Int’
-      Expected: GHC.Exts.Item [Int]
+      Expected: GHC.IsList.Item [Int]
         Actual: Char
     • In the expression: 'a'
       In the first argument of ‘length’, namely
diff --git a/testsuite/tests/showIface/Orphans.stdout b/testsuite/tests/showIface/Orphans.stdout
index 08725b6715..fdb94e36e9 100644
--- a/testsuite/tests/showIface/Orphans.stdout
+++ b/testsuite/tests/showIface/Orphans.stdout
@@ -1,6 +1,6 @@
-instance [orphan] GHC.Exts.IsList [GHC.Types.Bool] = $fIsListBool
-instance GHC.Exts.IsList [X] = $fIsListX
-family instance GHC.Exts.Item [X] = D:R:ItemX
-family instance [orphan] GHC.Exts.Item [GHC.Types.Bool]
+instance [orphan] GHC.IsList.IsList [GHC.Types.Bool] = $fIsListBool
+instance GHC.IsList.IsList [X] = $fIsListX
+family instance GHC.IsList.Item [X] = D:R:ItemX
+family instance [orphan] GHC.IsList.Item [GHC.Types.Bool]
 "myrule1" [orphan] forall @a.
 "myrule2" GHC.Base.id @(X -> X) f = f