Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC
Commits:
ab20eb54 by Mike Pilgrem at 2025-12-01T22:46:55+00:00
Re CLC issue 292 Warn GHC.Internal.List.{init,last} are partial
Also corrects the warning for `tail` to refer to `Data.List.uncons` (like the existing warning for `head`).
In module `Settings.Warnings`, applies `-Wno-x-partial` to the `filepath`, and `parsec` packages (outside GHC's repository).
Also bumps submodules.
- - - - -
25 changed files:
- compiler/GHC/Core/Utils.hs
- compiler/GHC/Driver/Session/Units.hs
- compiler/GHC/Prelude/Basic.hs
- ghc/GHCi/UI.hs
- ghc/Main.hs
- hadrian/src/Settings/Warnings.hs
- libraries/base/changelog.md
- libraries/ghc-boot-th/GHC/Boot/TH/Ppr.hs
- libraries/ghc-internal/src/GHC/Internal/Float.hs
- libraries/ghc-internal/src/GHC/Internal/List.hs
- libraries/ghc-internal/src/GHC/Internal/System/IO.hs
- libraries/ghc-internal/src/GHC/Internal/TH/Syntax.hs
- libraries/template-haskell/vendored-filepath/System/FilePath/Posix.hs
- libraries/template-haskell/vendored-filepath/System/FilePath/Windows.hs
- testsuite/tests/driver/j-space/jspace.hs
- testsuite/tests/rts/KeepCafsBase.hs
- utils/check-exact/Main.hs
- utils/check-exact/Transform.hs
- utils/check-exact/Utils.hs
- utils/ghc-pkg/Main.hs
- utils/ghc-toolchain/src/GHC/Toolchain/Utils.hs
- utils/haddock/haddock-api/src/Haddock/Backends/Xhtml.hs
- utils/haddock/haddock-library/src/Documentation/Haddock/Parser.hs
- utils/hpc
- utils/hsc2hs
Changes:
=====================================
compiler/GHC/Core/Utils.hs
=====================================
@@ -115,7 +115,6 @@ import GHC.Utils.Misc
import Data.ByteString ( ByteString )
import Data.Function ( on )
import Data.List ( sort, sortBy, partition, zipWith4, mapAccumL )
-import qualified Data.List as Partial ( init, last )
import Data.Ord ( comparing )
import Control.Monad ( guard )
import qualified Data.Set as Set
@@ -1896,10 +1895,10 @@ app_ok fun_ok primop_ok fun args
PrimOpId op _
| primOpIsDiv op
- , Lit divisor <- Partial.last args
+ , Lit divisor <- last args
-- there can be 2 args (most div primops) or 3 args
-- (WordQuotRem2Op), hence the use of last/init
- -> not (isZeroLit divisor) && all (expr_ok fun_ok primop_ok) (Partial.init args)
+ -> not (isZeroLit divisor) && all (expr_ok fun_ok primop_ok) (init args)
-- Special case for dividing operations that fail
-- In general they are NOT ok-for-speculation
-- (which primop_ok will catch), but they ARE OK
=====================================
compiler/GHC/Driver/Session/Units.hs
=====================================
@@ -39,7 +39,7 @@ import System.FilePath
import Control.Monad
import Data.List ( partition, (\\) )
import qualified Data.Set as Set
-import Prelude
+import GHC.Prelude
import GHC.ResponseFile (expandResponse)
import Data.Bifunctor
import GHC.Data.Graph.Directed
=====================================
compiler/GHC/Prelude/Basic.hs
=====================================
@@ -2,8 +2,8 @@
{-# OPTIONS_HADDOCK not-home #-}
{-# OPTIONS_GHC -O2 #-} -- See Note [-O2 Prelude]
--- See Note [Proxies for head and tail]
-{-# OPTIONS_GHC -Wno-unrecognised-warning-flags -Wno-x-partial #-}
+-- See Note [Proxies for partial list functions]
+{-# OPTIONS_GHC -Wno-x-partial #-}
-- | Custom minimal GHC "Prelude"
--
@@ -24,7 +24,7 @@ module GHC.Prelude.Basic
, bit
, shiftL, shiftR
, setBit, clearBit
- , head, tail, unzip
+ , head, tail, init, last, unzip
, strictGenericLength
) where
@@ -59,7 +59,7 @@ NoImplicitPrelude. There are two motivations for this:
-}
import qualified Prelude
-import Prelude as X hiding ((<>), Applicative(..), Foldable(..), head, tail, unzip)
+import Prelude as X hiding ((<>), Applicative(..), Foldable(..), head, tail, init, last, unzip)
import Control.Applicative (Applicative(..))
import Data.Foldable as X (Foldable (elem, foldMap, foldl, foldl', foldr, length, null, product, sum))
import Data.Foldable1 as X hiding (head, last)
@@ -118,24 +118,35 @@ setBit = \ x i -> x Bits..|. bit i
clearBit :: (Num a, Bits.Bits a) => a -> Int -> a
clearBit = \ x i -> x Bits..&. Bits.complement (bit i)
-{- Note [Proxies for head and tail]
+{- Note [Proxies for partial list functions]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-Prelude.head and Prelude.tail have recently acquired {-# WARNING in "x-partial" #-},
+Prelude.head, Prelude.tail, Prelude.init and Prelude.last
+have recently acquired {-# WARNING in "x-partial" #-},
but the GHC codebase uses them fairly extensively and insists on building warning-free.
Thus, instead of adding {-# OPTIONS_GHC -Wno-x-partial #-} to every module which
employs them, we define warning-less proxies and export them from GHC.Prelude.
-}
--- See Note [Proxies for head and tail]
+-- See Note [Proxies for partial list functions]
head :: HasCallStack => [a] -> a
head = Prelude.head
{-# INLINE head #-}
--- See Note [Proxies for head and tail]
+-- See Note [Proxies for partial list functions]
tail :: HasCallStack => [a] -> [a]
tail = Prelude.tail
{-# INLINE tail #-}
+-- See Note [Proxies for partial list functions]
+init :: HasCallStack => [a] -> [a]
+init = Prelude.init
+{-# INLINE init #-}
+
+-- See Note [Proxies for partial list functions]
+last :: HasCallStack => [a] -> a
+last = Prelude.last
+{-# INLINE last #-}
+
{- |
The 'genericLength' function defined in base can't be specialised due to the
NOINLINE pragma.
=====================================
ghc/GHCi/UI.hs
=====================================
@@ -145,7 +145,7 @@ import Data.Time.LocalTime ( getZonedTime )
import Data.Time.Format ( formatTime, defaultTimeLocale )
import Data.Version ( showVersion )
import qualified Data.Semigroup as S
-import Prelude hiding ((<>))
+import GHC.Prelude
import GHC.Utils.Exception as Exception hiding (catch, mask, handle)
import Foreign hiding (void)
=====================================
ghc/Main.hs
=====================================
@@ -2,7 +2,7 @@
{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE NondecreasingIndentation #-}
{-# LANGUAGE TupleSections #-}
-{-# OPTIONS -fno-warn-incomplete-patterns -optc-DNON_POSIX_SOURCE #-}
+{-# OPTIONS_GHC -Wno-x-partial -Wno-incomplete-patterns -optc-DNON_POSIX_SOURCE #-}
-----------------------------------------------------------------------------
--
=====================================
hadrian/src/Settings/Warnings.hs
=====================================
@@ -72,7 +72,11 @@ ghcWarningsArgs = do
, package terminfo ? pure [ "-Wno-unused-imports", "-Wno-deriving-typeable" ]
, package stm ? pure [ "-Wno-deriving-typeable" ]
, package osString ? pure [ "-Wno-deriving-typeable", "-Wno-unused-imports" ]
- , package parsec ? pure [ "-Wno-deriving-typeable" ]
+ , package parsec ? pure [ "-Wno-deriving-typeable"
+ , "-Wno-x-partial"
+ ]
+
+ , package filepath ? pure [ "-Wno-x-partial" ]
, package cabal ? pure [ "-Wno-deriving-typeable", "-Wno-incomplete-record-selectors" ]
-- The -Wno-incomplete-record-selectors is due to
=====================================
libraries/base/changelog.md
=====================================
@@ -1,6 +1,9 @@
# Changelog for [`base` package](http://hackage.haskell.org/package/base)
## 4.23.0.0 *TBA*
+ * Add `{-# WARNING in "x-partial" #-}` to `Data.List.{init,last}`.
+ Use `{-# OPTIONS_GHC -Wno-x-partial #-}` to disable it.
+ ([CLC proposal #87](https://github.com/haskell/core-libraries-committee/issues/292))
* Remove deprecated, unstable heap representation details from `GHC.Exts` ([CLC proposal #212](https://github.com/haskell/core-libraries-committee/issues/212))
* Add `Data.List.NonEmpty.mapMaybe`. ([CLC proposal #337](https://github.com/haskell/core-libraries-committee/issues/337))
* Fix issues with toRational for types capable to represent infinite and not-a-number values ([CLC proposal #338](https://github.com/haskell/core-libraries-committee/issues/338))
=====================================
libraries/ghc-boot-th/GHC/Boot/TH/Ppr.hs
=====================================
@@ -1,5 +1,6 @@
{-# LANGUAGE Trustworthy #-}
{-# LANGUAGE LambdaCase #-}
+{-# OPTIONS_GHC -Wno-x-partial #-}
-- | contains a prettyprinter for the
-- Template Haskell datatypes
=====================================
libraries/ghc-internal/src/GHC/Internal/Float.hs
=====================================
@@ -13,6 +13,9 @@
{-# OPTIONS_HADDOCK not-home #-}
{-# OPTIONS_GHC -Wno-incomplete-uni-patterns #-}
+-- For init in formatRealFloatAlt
+{-# OPTIONS_GHC -Wno-x-partial #-}
+
-----------------------------------------------------------------------------
-- |
-- Module : GHC.Internal.Float
=====================================
libraries/ghc-internal/src/GHC/Internal/List.hs
=====================================
@@ -190,12 +190,18 @@ tail :: HasCallStack => [a] -> [a]
tail (_:xs) = xs
tail [] = errorEmptyList "tail"
-{-# WARNING in "x-partial" tail "This is a partial function, it throws an error on empty lists. Replace it with 'drop' 1, or use pattern matching or 'GHC.Internal.Data.List.uncons' instead. Consider refactoring to use \"Data.List.NonEmpty\"." #-}
+{-# WARNING in "x-partial" tail "This is a partial function, it throws an error on empty lists. Replace it with 'drop' 1, or use pattern matching or 'Data.List.uncons' instead. Consider refactoring to use \"Data.List.NonEmpty\"." #-}
-- | \(\mathcal{O}(n)\). Extract the last element of a list, which must be
-- finite and non-empty.
--
--- WARNING: This function is partial. Consider using 'unsnoc' instead.
+-- To disable the warning about partiality put
+-- @{-# OPTIONS_GHC -Wno-x-partial -Wno-unrecognised-warning-flags #-}@
+-- at the top of the file. To disable it throughout a package put the same
+-- options into @ghc-options@ section of Cabal file. To disable it in GHCi
+-- put @:set -Wno-x-partial -Wno-unrecognised-warning-flags@ into @~/.ghci@
+-- config file. See also the
+-- [migration guide](https://github.com/haskell/core-libraries-committee/blob/main/guides/warning...).
--
-- ==== __Examples__
--
@@ -218,10 +224,18 @@ last xs = foldl (\_ x -> x) lastError xs
lastError :: HasCallStack => a
lastError = errorEmptyList "last"
+{-# WARNING in "x-partial" last "This is a partial function, it throws an error on empty lists. Use 'Data.List.unsnoc' instead. Consider refactoring to use \"Data.List.NonEmpty\"." #-}
+
-- | \(\mathcal{O}(n)\). Return all the elements of a list except the last one.
-- The list must be non-empty.
--
--- WARNING: This function is partial. Consider using 'unsnoc' instead.
+-- To disable the warning about partiality put
+-- @{-# OPTIONS_GHC -Wno-x-partial -Wno-unrecognised-warning-flags #-}@
+-- at the top of the file. To disable it throughout a package put the same
+-- options into @ghc-options@ section of Cabal file. To disable it in GHCi
+-- put @:set -Wno-x-partial -Wno-unrecognised-warning-flags@ into @~/.ghci@
+-- config file. See also the
+-- [migration guide](https://github.com/haskell/core-libraries-committee/blob/main/guides/warning...).
--
-- ==== __Examples__
--
@@ -240,6 +254,8 @@ init (x:xs) = init' x xs
where init' _ [] = []
init' y (z:zs) = y : init' z zs
+{-# WARNING in "x-partial" init "This is a partial function, it throws an error on empty lists. Use 'Data.List.unsnoc' instead. Consider refactoring to use \"Data.List.NonEmpty\"." #-}
+
-- | \(\mathcal{O}(1)\). Test whether a list is empty.
--
-- >>> null []
=====================================
libraries/ghc-internal/src/GHC/Internal/System/IO.hs
=====================================
@@ -1,5 +1,6 @@
{-# LANGUAGE Trustworthy #-}
{-# LANGUAGE CPP, NoImplicitPrelude, CApiFFI #-}
+{-# OPTIONS_GHC -Wno-x-partial #-}
-----------------------------------------------------------------------------
-- |
=====================================
libraries/ghc-internal/src/GHC/Internal/TH/Syntax.hs
=====================================
@@ -1,4 +1,5 @@
{-# OPTIONS_HADDOCK not-home #-} -- we want users to import Language.Haskell.TH.Syntax instead
+{-# OPTIONS_GHC -Wno-x-partial #-}
{-# LANGUAGE CPP #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE DeriveGeneric #-}
=====================================
libraries/template-haskell/vendored-filepath/System/FilePath/Posix.hs
=====================================
@@ -1,6 +1,7 @@
-- Vendored from filepath v1.4.2.2
{-# LANGUAGE PatternGuards #-}
+{-# OPTIONS_GHC -Wno-x-partial #-}
-- This template expects CPP definitions for:
-- MODULE_NAME = Posix | Windows
=====================================
libraries/template-haskell/vendored-filepath/System/FilePath/Windows.hs
=====================================
@@ -1,6 +1,7 @@
-- Vendored from filepath v1.4.2.2
{-# LANGUAGE PatternGuards #-}
+{-# OPTIONS_GHC -Wno-x-partial #-}
-- This template expects CPP definitions for:
-- MODULE_NAME = Posix | Windows
=====================================
testsuite/tests/driver/j-space/jspace.hs
=====================================
@@ -7,7 +7,7 @@ import System.Environment
import GHC.Driver.Env.Types
import GHC.Profiling
import System.Mem
-import Data.List (isPrefixOf)
+import Data.List (isPrefixOf, unsnoc)
import Control.Monad
import System.Exit
import GHC.Platform
@@ -41,7 +41,9 @@ initGhcM xs = do
requestHeapCensus
performGC
[ys] <- filter (isPrefixOf (ghcUnitId <> ":GHC.Unit.Module.ModDetails.ModDetails")) . lines <$> readFile "jspace.hp"
- let (n :: Int) = read (last (words ys))
+ let (n :: Int) = case unsnoc (words ys) of
+ Nothing -> error "input is unexpectedly empty"
+ Just (_, lst) -> read lst
-- The output should be 50 * 8 * word_size (i.e. 3600, or 1600 on 32-bit architectures):
-- the test contains DEPTH + WIDTH + 2 = 50 modules J, H_0, .., H_DEPTH, W_1, .., W_WIDTH,
-- and each ModDetails contains 1 (info table) + 8 word-sized fields.
=====================================
testsuite/tests/rts/KeepCafsBase.hs
=====================================
@@ -1,3 +1,5 @@
+{-# OPTIONS_GHC -Wno-x-partial #-}
+
module KeepCafsBase (x) where
x :: Int
=====================================
utils/check-exact/Main.hs
=====================================
@@ -6,6 +6,7 @@
{-# OPTIONS_GHC -Wno-incomplete-uni-patterns #-}
{-# OPTIONS_GHC -Wno-incomplete-patterns #-}
{-# OPTIONS_GHC -Wno-orphans #-}
+{-# OPTIONS_GHC -Wno-x-partial #-}
import Data.Data
import Data.List (intercalate)
=====================================
utils/check-exact/Transform.hs
=====================================
@@ -96,6 +96,7 @@ import GHC.Data.FastString
import GHC.Types.SrcLoc
import Data.Data
+import Data.List (unsnoc)
import Data.List.NonEmpty (NonEmpty (..))
import qualified Data.List.NonEmpty as NE
import Data.Maybe
@@ -212,8 +213,9 @@ captureTypeSigSpacing (L l (SigD x (TypeSig (AnnSig (EpUniTok dca u) mp md) ns (
where
-- we want DPs for the distance from the end of the ns to the
-- AnnDColon, and to the start of the ty
- rd = case last ns of
- L (EpAnn anc' _ _) _ -> epaLocationRealSrcSpan anc'
+ rd = case unsnoc ns of
+ Nothing -> error "unexpected empty list in 'ns' variable"
+ Just (_, L (EpAnn anc' _ _) _) -> epaLocationRealSrcSpan anc'
dca' = case dca of
EpaSpan ss@(RealSrcSpan r _) -> (EpaDelta ss (ss2delta (ss2posEnd rd) r) [])
_ -> dca
@@ -294,7 +296,7 @@ setEntryDP (L (EpAnn (EpaSpan ss@(RealSrcSpan r _)) an cs) a) dp
where
cs'' = setPriorComments cs []
csd = L (EpaDelta ss dp NoComments) c:commentOrigDeltas cs'
- lc = last $ (L ca c:cs')
+ lc = NE.last (L ca c :| cs')
delta = case getLoc lc of
EpaSpan (RealSrcSpan rr _) -> ss2delta (ss2pos rr) r
EpaSpan _ -> (SameLine 0)
=====================================
utils/check-exact/Utils.hs
=====================================
@@ -37,7 +37,7 @@ import GHC.Base (NonEmpty(..))
import GHC.Parser.Lexer (allocateComments)
import Data.Data hiding ( Fixity )
-import Data.List (sortBy, partition)
+import Data.List (sortBy, partition, unsnoc)
import qualified Data.Map.Strict as Map
import Debug.Trace
@@ -734,8 +734,9 @@ ghead info [] = error $ "ghead "++info++" []"
ghead _info (h:_) = h
glast :: String -> [a] -> a
-glast info [] = error $ "glast " ++ info ++ " []"
-glast _info h = last h
+glast info xs = case unsnoc xs of
+ Nothing -> error $ "glast " ++ info ++ " []"
+ Just (_, lst) -> lst
gtail :: String -> [a] -> [a]
gtail info [] = error $ "gtail " ++ info ++ " []"
=====================================
utils/ghc-pkg/Main.hs
=====================================
@@ -8,7 +8,7 @@
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE TupleSections #-}
{-# LANGUAGE ScopedTypeVariables #-}
-{-# OPTIONS_GHC -fno-warn-orphans #-}
+{-# OPTIONS_GHC -Wno-orphans -Wno-x-partial #-}
-- Fine if this comes from make/Hadrian or the pre-built base.
#include