Bodigrim pushed to branch wip/warning-for-last-and-init at Glasgow Haskell Compiler / GHC Commits: 3da64044 by Mike Pilgrem at 2025-07-10T23:41:02+01:00 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-unrecognised-warning-flags` `-Wno-x-partial` to the `Cabal`, `filepath`, `hsc2hs`, `hpc`, `parsec`, `text` and `time` packages (outside GHC's repository). - - - - - 16 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 - 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/Windows.hs - testsuite/tests/driver/j-space/jspace.hs - testsuite/tests/rts/KeepCafsBase.hs - utils/check-exact/Utils.hs - utils/haddock/haddock-api/src/Haddock/Backends/Xhtml.hs - utils/haddock/haddock-library/src/Documentation/Haddock/Parser.hs Changes: ===================================== compiler/GHC/Core/Utils.hs ===================================== @@ -112,8 +112,7 @@ 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.List ( sort, sortBy, partition, zipWith4, mapAccumL, unsnoc ) import Data.Ord ( comparing ) import Control.Monad ( guard ) import qualified Data.Set as Set @@ -1871,10 +1870,10 @@ app_ok fun_ok primop_ok fun args PrimOpId op _ | primOpIsDiv op - , Lit divisor <- Partial.last args + , Just (initArgs, Lit divisor) <- unsnoc 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) initArgs -- 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 ===================================== @@ -183,7 +183,7 @@ checkUnitCycles dflags graph = processSCCs (HUG.hugSCCs graph) processSCCs [] = return () processSCCs (AcyclicSCC _: other_sccs) = processSCCs other_sccs - processSCCs (CyclicSCC uids: _) = throwGhcException $ CmdLineError $ showSDoc dflags (cycle_err uids) + processSCCs (NECyclicSCC uids: _) = throwGhcException $ CmdLineError $ showSDoc dflags (cycle_err uids) cycle_err uids = @@ -195,8 +195,8 @@ checkUnitCycles dflags graph = processSCCs (HUG.hugSCCs graph) (map (\uid -> text "-" <+> ppr uid <+> text "depends on") start) ++ [text "-" <+> ppr final] where - start = init uids - final = last uids + start = NE.init uids + final = NE.last uids -- | Check that we don't have multiple units with the same UnitId. checkDuplicateUnits :: DynFlags -> [(FilePath, DynFlags)] -> Ghc () ===================================== 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 ===================================== @@ -133,7 +133,7 @@ import Data.Char import Data.Function import qualified Data.Foldable as Foldable import Data.IORef ( IORef, modifyIORef, newIORef, readIORef, writeIORef ) -import Data.List ( find, intercalate, intersperse, +import Data.List ( find, intercalate, intersperse, unsnoc, isPrefixOf, isSuffixOf, nub, partition, sort, sortBy, (\\) ) import qualified Data.List.NonEmpty as NE import qualified Data.Set as S @@ -2399,9 +2399,9 @@ setContextAfterLoad keep_ctxt (Just graph) = do [] -> let graph' = flattenSCCs $ filterToposortToModules $ GHC.topSortModuleGraph True (GHC.mkModuleGraph loaded_graph) Nothing - in case graph' of - [] -> setContextKeepingPackageModules keep_ctxt [] - xs -> load_this (last xs) + in case unsnoc graph' of + Nothing -> setContextKeepingPackageModules keep_ctxt [] + Just (_, lst) -> load_this lst (m:_) -> load_this m where ===================================== ghc/Main.hs ===================================== @@ -88,7 +88,7 @@ import System.Exit import Control.Monad import Control.Monad.Trans.Class import Control.Monad.Trans.Except (throwE, runExceptT) -import Data.List ( isPrefixOf, partition, intercalate ) +import Data.List ( isPrefixOf, partition, intercalate, unsnoc ) import Prelude import qualified Data.List.NonEmpty as NE @@ -115,8 +115,7 @@ main = do argv0 <- getArgs let (minusB_args, argv1) = partition ("-B" `isPrefixOf`) argv0 - mbMinusB | null minusB_args = Nothing - | otherwise = Just (drop 2 (last minusB_args)) + mbMinusB = drop 2 . snd <$> unsnoc minusB_args let argv2 = map (mkGeneralLocated "on the commandline") argv1 ===================================== libraries/ghc-boot-th/GHC/Boot/TH/Ppr.hs ===================================== @@ -13,7 +13,7 @@ import GHC.Boot.TH.PprLib import GHC.Boot.TH.Syntax import Data.Word ( Word8 ) import Data.Char ( toLower, chr ) -import Data.List ( intersperse ) +import Data.List ( intersperse, unsnoc ) import GHC.Show ( showMultiLineString ) import GHC.Lexeme( isVarSymChar ) import Data.Ratio ( numerator, denominator ) @@ -214,9 +214,10 @@ pprExp i (MDoE m ss_) = parensIf (i > noPrec) $ pprStms [s] = ppr s pprStms ss = braces (semiSep ss) -pprExp _ (CompE []) = text "<<Empty CompExp>>" -- This will probably break with fixity declarations - would need a ';' -pprExp _ (CompE ss) = +pprExp _ (CompE ss) = case unsnoc ss of + Nothing -> text "<<Empty CompExp>>" + Just (ss', s) -> if null ss' -- If there are no statements in a list comprehension besides the last -- one, we simply treat it like a normal list. @@ -225,8 +226,6 @@ pprExp _ (CompE ss) = <+> bar <+> commaSep ss' <> text "]" - where s = last ss - ss' = init ss pprExp _ (ArithSeqE d) = ppr d pprExp _ (ListE es) = brackets (commaSep es) pprExp i (SigE e t) = parensIf (i > noPrec) $ pprExp sigPrec e ===================================== 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 ===================================== @@ -825,11 +825,12 @@ output_flags = std_flags where -- XXX bits copied from System.FilePath, since that's not available here - combine a b - | null b = a - | null a = b - | pathSeparator [last a] = a ++ b - | otherwise = a ++ [pathSeparatorChar] ++ b + combine a [] = a + combine a b = case unsnoc a of + Nothing -> b + Just (_, lastA) + | pathSeparator [lastA] -> a ++ b + | otherwise -> a ++ [pathSeparatorChar] ++ b tempCounter :: IORef Int tempCounter = unsafePerformIO $ newIORef 0 ===================================== libraries/ghc-internal/src/GHC/Internal/TH/Syntax.hs ===================================== @@ -39,6 +39,7 @@ import Control.Exception.Base (FixIOException (..)) import Control.Concurrent.MVar (newEmptyMVar, readMVar, putMVar) import System.IO ( hPutStrLn, stderr ) import Data.Char ( isAlpha, isAlphaNum, isUpper ) +import Data.List ( unsnoc ) import Data.List.NonEmpty ( NonEmpty(..) ) import Data.Word import qualified Data.Kind as Kind (Type) @@ -54,6 +55,7 @@ import GHC.Internal.Base hiding (NonEmpty(..),Type, Module, sequence) import GHC.Internal.Data.Data hiding (Fixity(..)) import GHC.Internal.Data.NonEmpty (NonEmpty(..)) import GHC.Internal.Data.Traversable +import GHC.Internal.List (unsnoc) import GHC.Internal.Word import GHC.Internal.Generics (Generic) import GHC.Internal.IORef @@ -73,7 +75,7 @@ import GHC.Internal.Control.Monad.Fix import GHC.Internal.Control.Exception import GHC.Internal.Num import GHC.Internal.IO.Unsafe -import GHC.Internal.List (dropWhile, break, replicate, reverse, last) +import GHC.Internal.List (dropWhile, break, replicate, reverse) import GHC.Internal.MVar import GHC.Internal.IO.Exception import GHC.Internal.Unicode @@ -1296,7 +1298,7 @@ mkName str -- (i.e. non-empty, starts with capital, all alpha) is_rev_mod_name rev_mod_str | (compt, rest) <- break (== '.') rev_mod_str - , not (null compt), isUpper (last compt), all is_mod_char compt + , Just (_, lastCompt) <- unsnoc compt, isUpper lastCompt, all is_mod_char compt = case rest of [] -> True (_dot : rest') -> is_rev_mod_name rest' ===================================== libraries/template-haskell/vendored-filepath/System/FilePath/Windows.hs ===================================== @@ -104,7 +104,7 @@ module System.FilePath.Windows import Data.Char(toLower, toUpper, isAsciiLower, isAsciiUpper) import Data.Maybe(isJust) -import Data.List(stripPrefix, isSuffixOf) +import Data.List(stripPrefix, isSuffixOf, uncons, unsnoc) import System.Environment(getEnv) @@ -203,14 +203,20 @@ isExtSeparator = (== extSeparator) splitSearchPath :: String -> [FilePath] splitSearchPath = f where - f xs = case break isSearchPathSeparator xs of - (pre, [] ) -> g pre - (pre, _:post) -> g pre ++ f post - - g "" = ["." | isPosix] - g ('\"':x@(_:_)) | isWindows && last x == '\"' = [init x] - g x = [x] - + f xs = let (pre, post) = break isSearchPathSeparator xs + in case uncons post of + Nothing -> g pre + Just (_, t) -> g pre ++ f t + + g x = case uncons x of + Nothing -> ["." | isPosix] + Just (h, t) + | h == '"' + , Just{} <- uncons t -- >= 2 + , isWindows + , Just (i, l) <- unsnoc t + , l == '"' -> [i] + | otherwise -> [x] -- | Get a list of 'FilePath's in the $PATH variable. getSearchPath :: IO [FilePath] @@ -233,12 +239,17 @@ getSearchPath = fmap splitSearchPath (getEnv "PATH") -- > splitExtension "file/path.txt.bob.fred" == ("file/path.txt.bob",".fred") -- > splitExtension "file/path.txt/" == ("file/path.txt/","") splitExtension :: FilePath -> (String, String) -splitExtension x = case nameDot of - "" -> (x,"") - _ -> (dir ++ init nameDot, extSeparator : ext) - where - (dir,file) = splitFileName_ x - (nameDot,ext) = breakEnd isExtSeparator file +splitExtension x = case unsnoc nameDot of + -- Imagine x = "no-dots", then nameDot = "" + Nothing -> (x, mempty) + Just (initNameDot, _) + -- Imagine x = "\\shared.with.dots\no-dots" + | isWindows && null (dropDrive nameDot) -> (x, mempty) + -- Imagine x = "dir.with.dots/no-dots" + | any isPathSeparator ext -> (x, mempty) + | otherwise -> (initNameDot, extSeparator : ext) + where + (nameDot, ext) = breakEnd isExtSeparator x -- | Get the extension of a file, returns @\"\"@ for no extension, @.ext@ otherwise. -- @@ -594,9 +605,13 @@ replaceBaseName pth nam = combineAlways a (nam <.> ext) -- > hasTrailingPathSeparator "test" == False -- > hasTrailingPathSeparator "test/" == True hasTrailingPathSeparator :: FilePath -> Bool -hasTrailingPathSeparator "" = False -hasTrailingPathSeparator x = isPathSeparator (last x) +hasTrailingPathSeparator = isJust . getTrailingPathSeparator +getTrailingPathSeparator :: FilePath -> Maybe Char +getTrailingPathSeparator x = case unsnoc x of + Just (_, lastX) + | isPathSeparator lastX -> Just lastX + _ -> Nothing hasLeadingPathSeparator :: FilePath -> Bool hasLeadingPathSeparator "" = False @@ -619,12 +634,12 @@ addTrailingPathSeparator x = if hasTrailingPathSeparator x then x else x ++ [pat -- > Windows: dropTrailingPathSeparator "\\" == "\\" -- > Posix: not (hasTrailingPathSeparator (dropTrailingPathSeparator x)) || isDrive x dropTrailingPathSeparator :: FilePath -> FilePath -dropTrailingPathSeparator x = - if hasTrailingPathSeparator x && not (isDrive x) - then let x' = dropWhileEnd isPathSeparator x - in if null x' then [last x] else x' - else x - +dropTrailingPathSeparator x = case getTrailingPathSeparator x of + Just lastX + | not (isDrive x) + -> let x' = dropWhileEnd isPathSeparator x + in if null x' then [lastX] else x' + _ -> x -- | Get the directory name, move up one level. -- @@ -863,28 +878,37 @@ makeRelative root path -- > Posix: normalise "bob/fred/." == "bob/fred/" -- > Posix: normalise "//home" == "/home" normalise :: FilePath -> FilePath -normalise path = result ++ [pathSeparator | addPathSeparator] - where - (drv,pth) = splitDrive path - result = joinDrive' (normaliseDrive drv) (f pth) +normalise filepath = + result <> + (if addPathSeparator + then [pathSeparator] + else mempty) + where + (drv,pth) = splitDrive filepath + + result = joinDrive' (normaliseDrive drv) (f pth) - joinDrive' "" "" = "." - joinDrive' d p = joinDrive d p + joinDrive' d p + = if null d && null p + then "." + else joinDrive d p - addPathSeparator = isDirPath pth - && not (hasTrailingPathSeparator result) - && not (isRelativeDrive drv) + addPathSeparator = isDirPath pth + && not (hasTrailingPathSeparator result) + && not (isRelativeDrive drv) - isDirPath xs = hasTrailingPathSeparator xs - || not (null xs) && last xs == '.' && hasTrailingPathSeparator (init xs) + isDirPath xs = hasTrailingPathSeparator xs || case unsnoc xs of + Nothing -> False + Just (initXs, lastXs) -> lastXs == '.' && hasTrailingPathSeparator initXs - f = joinPath . dropDots . propSep . splitDirectories + f = joinPath . dropDots . propSep . splitDirectories - propSep (x:xs) | all isPathSeparator x = [pathSeparator] : xs - | otherwise = x : xs - propSep [] = [] + propSep (x:xs) + | all isPathSeparator x = [pathSeparator] : xs + | otherwise = x : xs + propSep [] = [] - dropDots = filter ("." /=) + dropDots = filter ("." /=) normaliseDrive :: FilePath -> FilePath normaliseDrive "" = "" ===================================== 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/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/haddock/haddock-api/src/Haddock/Backends/Xhtml.hs ===================================== @@ -755,7 +755,7 @@ ppHtmlIndex divAlphabet << unordList ( map (\str -> anchor ! [href (subIndexHtmlFile str)] << str) $ - [ [c] | c <- initialChars, any ((== c) . toUpper . head . fst) index + [ [c] | c <- initialChars, any (maybe False ((== c) . toUpper . fst) . List.uncons . fst) index ] ++ [merged_name] ) @@ -772,7 +772,7 @@ ppHtmlIndex writeUtf8File (joinPath [odir, subIndexHtmlFile [c]]) (renderToString debug html) where html = indexPage True (Just c) index_part - index_part = [(n, stuff) | (n, stuff) <- this_ix, toUpper (head n) == c] + index_part = [(n, stuff) | (n@(headN : _), stuff) <- this_ix, toUpper headN == c] index :: [(String, Map GHC.Name [(Module, Bool)])] index = sortBy cmp (Map.toAscList full_index) ===================================== utils/haddock/haddock-library/src/Documentation/Haddock/Parser.hs ===================================== @@ -30,7 +30,7 @@ import Control.Arrow (first) import Control.Monad import Data.Char (chr, isAlpha, isSpace, isUpper) import Data.Functor (($>)) -import Data.List (elemIndex, intercalate, intersperse, unfoldr) +import Data.List (elemIndex, intercalate, intersperse, unfoldr, unsnoc) import Data.Maybe (fromMaybe, mapMaybe) import Data.Monoid import qualified Data.Set as Set @@ -870,10 +870,10 @@ codeblock = DocCodeBlock . parseParagraph . dropSpaces <$> ("@" *> skipHorizontalSpace *> "\n" *> block' <* "@") where - dropSpaces xs = - case splitByNl xs of - [] -> xs - ys -> case T.uncons (last ys) of + dropSpaces xs = let ys = splitByNl xs in + case unsnoc ys of + Nothing -> xs + Just (_, lastYs) -> case T.uncons lastYs of Just (' ', _) -> case mapM dropSpace ys of Nothing -> xs Just zs -> T.intercalate "\n" zs View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/3da640443d33216ac5f6a235baf0d419... -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/3da640443d33216ac5f6a235baf0d419... 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