Revert "Data.List specialization to []"

This reverts commit bddecda1.

This implements the first step in the plan formulated in #20025 to
improve the communication and migration strategy for the proposed
changes to Data.List.

Requires changing the haddock submodule to update the test output.

compiler/GHC/Rename/Names.hs

@@ -594,8 +594,6 @@ calculateAvails home_unit iface mod_safe' want_boot imported_by =
 -- | Issue a warning if the user imports Data.List without either an import
 -- list or `qualified`. This is part of the migration plan for the
 -- `Data.List.singleton` proposal. See #17244.
---
--- Currently not used for anything.
 warnUnqualifiedImport :: ImportDecl GhcPs -> ModIface -> RnM ()
 warnUnqualifiedImport decl iface =
     when bad_import $ do
@@ -627,8 +625,7 @@ warnUnqualifiedImport decl iface =
       ]
 
     -- Modules for which we warn if we see unqualified imports
-    -- Currently empty.
-    qualifiedMods = mkModuleSet []
+    qualifiedMods = mkModuleSet [ dATA_LIST ]
 
 
 warnRedundantSourceImport :: ModuleName -> TcRnMessage

docs/users_guide/using-warnings.rst

@@ -275,8 +275,13 @@ of ``-W(no-)*``.
     :since: 8.10
 
     Warns on qualified imports of core library modules which are subject to
-    change in future GHC releases. Currently there are no modules
-    covered by this warning.
+    change in future GHC releases. Currently the following modules are covered
+    by this warning:
+
+     - ``Data.List`` due to the future addition of ``Data.List.singleton`` and
+       specialisation of exports to the ``[]`` type. See the
+       `mailing list <https://groups.google.com/forum/#!topic/haskell-core-libraries/q3zHLmzBa5E>`_
+       for details.
 
     This warning can be addressed by either adding an explicit import list or
     using a ``qualified`` import.

libraries/base/Data/Foldable.hs

@@ -2454,7 +2454,9 @@ elements in a single pass.
 -- The more general methods of the 'Foldable' class are now exported by the
 -- "Prelude" in place of the original List-specific methods (see the
 -- [FTP Proposal](https://wiki.haskell.org/Foldable_Traversable_In_Prelude)).
--- The List-specific variants are still available in "Data.List".
+-- The List-specific variants are for now still available in "GHC.OldList", but
+-- that module is intended only as a transitional aid, and may be removed in
+-- the future.
 --
 -- Surprises can arise from the @Foldable@ instance of the 2-tuple @(a,)@ which
 -- now behaves as a 1-element @Foldable@ container in its second slot.  In

libraries/base/Foreign/Marshal/Pool.hs

@@ -54,7 +54,7 @@ import GHC.IORef             ( IORef, newIORef, readIORef, writeIORef )
 import GHC.List              ( elem, length )
 import GHC.Num               ( Num(..) )
 
-import Data.List             ( delete )
+import Data.OldList          ( delete )
 import Foreign.Marshal.Alloc ( mallocBytes, reallocBytes, free )
 import Foreign.Marshal.Array ( pokeArray, pokeArray0 )
 import Foreign.Marshal.Error ( throwIf )

libraries/base/GHC/Event/Internal/Types.hs

@@ -33,7 +33,7 @@ module GHC.Event.Internal.Types
     , Timeout(..)
     ) where
 
-import Data.List (foldl', filter, intercalate, null)
+import Data.OldList (foldl', filter, intercalate, null)
 
 import Data.Bits ((.|.), (.&.))
 import Data.Semigroup.Internal (stimesMonoid)

libraries/base/GHC/Event/Manager.hs

@@ -67,7 +67,7 @@ import Data.Functor (void)
 import Data.IORef (IORef, atomicModifyIORef', mkWeakIORef, newIORef, readIORef,
                    writeIORef)
 import Data.Maybe (maybe)
-import Data.List (partition)
+import Data.OldList (partition)
 import GHC.Arr (Array, (!), listArray)
 import GHC.Base
 import GHC.Conc.Sync (yield)

libraries/base/GHC/Event/Windows.hsc

@@ -104,7 +104,7 @@ import GHC.Exception as E
 import GHC.IORef
 import GHC.Maybe
 import GHC.Word
-import Data.List (deleteBy)
+import GHC.OldList (deleteBy)
 import Foreign
 import qualified GHC.Event.Array    as A
 import GHC.Base

libraries/base/GHC/Exception.hs

@@ -37,7 +37,7 @@ module GHC.Exception
 import GHC.Base
 import GHC.Show
 import GHC.Stack.Types
-import Data.List (intercalate, reverse) -- TODO: remove import list?
+import GHC.OldList
 import GHC.Prim
 import GHC.IO.Unsafe
 import {-# SOURCE #-} GHC.Stack.CCS

libraries/base/GHC/Exts.hs

@@ -143,7 +143,7 @@ import GHC.Stack
 
 import qualified Data.Coerce
 import Data.String
-import Data.List (all, sortBy, span)
+import Data.OldList
 import Data.Data
 import Data.Ord
 import Data.Version ( Version(..), makeVersion )

libraries/base/GHC/IO/Encoding/CodePage.hs

@@ -27,7 +27,7 @@ import GHC.IO.Encoding.Types
 import GHC.IO.Buffer
 import Data.Bits
 import Data.Maybe
-import Data.List (lookup)
+import Data.OldList (lookup)
 
 import qualified GHC.IO.Encoding.CodePage.API as API
 import GHC.IO.Encoding.CodePage.Table

libraries/base/GHC/IO/Exception.hs

@@ -54,7 +54,7 @@ import GHC.Show
 import GHC.Read
 import GHC.Exception
 import GHC.IO.Handle.Types
-import Data.List ( intercalate )
+import GHC.OldList ( intercalate )
 import {-# SOURCE #-} GHC.Stack.CCS
 import Foreign.C.Types
 

libraries/base/GHC/OldList.hs

+{-# LANGUAGE NoImplicitPrelude #-}
+{-# LANGUAGE Safe #-}
+
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  GHC.OldList
+-- Copyright   :  (c) The University of Glasgow 2001
+-- License     :  BSD-style (see the file libraries/base/LICENSE)
+--
+-- Maintainer  :  libraries@haskell.org
+-- Stability   :  experimental
+-- Portability :  portable
+--
+-- This legacy module provides access to the list-specialised operations
+-- of "Data.List". This module may go away again in future GHC versions and
+-- is provided as transitional tool to access some of the list-specialised
+-- operations that had to be generalised due to the implementation of the
+-- <https://wiki.haskell.org/Foldable_Traversable_In_Prelude Foldable/Traversable-in-Prelude Proposal (FTP)>.
+--
+-- If the operations needed are available in "GHC.List", it's
+-- recommended to avoid importing this module and use "GHC.List"
+-- instead for now.
+--
+-- @since 4.8.0.0
+-----------------------------------------------------------------------------
+
+module GHC.OldList (module Data.OldList) where
+
+import Data.OldList

libraries/base/GHC/Windows.hs

@@ -76,7 +76,7 @@ module GHC.Windows (
 
 import Data.Bits (finiteBitSize, shiftL, shiftR, (.|.), (.&.))
 import Data.Char
-import Data.List (dropWhileEnd)
+import Data.OldList
 import Data.Maybe
 import Data.Word
 import Data.Int

libraries/base/base.cabal

@@ -254,6 +254,7 @@ Library
         GHC.MVar
         GHC.Natural
         GHC.Num
+        GHC.OldList
         GHC.OverloadedLabels
         GHC.Pack
         GHC.Profiling
@@ -324,6 +325,7 @@ Library
         Control.Monad.ST.Imp
         Control.Monad.ST.Lazy.Imp
         Data.Functor.Utils
+        Data.OldList
         Data.Semigroup.Internal
         Data.Typeable.Internal
         Foreign.ForeignPtr.Imp

libraries/base/changelog.md

@@ -79,9 +79,6 @@
   * `fromInteger :: Integer -> Float/Double` now consistently round to the
     nearest value, with ties to even.
 
-  * Functions in `Data.List` are specialized to list.
-    `Data.OldList` and `GHC.List` modules are removed.
-
   * Add `GHC.TypeError` module to contain functionality related to custom type
     errors. `TypeError` is re-exported from `GHC.TypeLits` for backwards
     compatibility.

libraries/base/tests/T9586.hs

@@ -4,6 +4,7 @@ module XPrelude (module X) where
 
 import Control.Monad    as X
 import Data.Foldable    as X
+import Data.List        as X
 import Data.Monoid      as X
 import Data.Traversable as X
 import Prelude          as X

libraries/base/tests/list001.hs

@@ -2,9 +2,6 @@
 {-# OPTIONS_GHC -Wno-compat-unqualified-imports #-}
 module Main where
 
-import Prelude (Int, String, print, putStr, error,
-                Eq (..), Ord (..), Num (..), Bool (..))
-
 import Data.List
 import Control.Exception
 

testsuite/tests/codeGen/should_run/T15038/common/Data/Trie/Naive.hs

@@ -19,7 +19,7 @@ import Data.Map (Map)
 import Data.Bifunctor (second)
 import Packed.Bytes (Bytes)
 import qualified Data.Char
-import qualified Data.List as L
+import qualified GHC.OldList as L
 import qualified Packed.Bytes.Parser as P
 import qualified Packed.Bytes as B
 import qualified Data.Semigroup as SG