Implement correct handling of wide Unicode characters

CHANGELOG.md

@@ -1,5 +1,11 @@
 *Megaparsec follows [SemVer](https://semver.org/).*
 
+## Upcoming
+
+* Implemented correct handling of wide Unicode characters in error messages.
+  To that end, a new module `Text.Megaparsec.Unicode` was introduced. [Issue
+  370](https://github.com/mrkkrp/megaparsec/issues/370).
+
 ## Megaparsec 9.6.1
 
 * Exposed `Text.Megaparsec.State`, so that the new functions (`initialState`

Text/Megaparsec/Error.hs

@@ -64,6 +64,7 @@ import GHC.Generics
 import Text.Megaparsec.Pos
 import Text.Megaparsec.State
 import Text.Megaparsec.Stream
+import qualified Text.Megaparsec.Unicode as Unicode
 
 ----------------------------------------------------------------------------
 -- Parse error type
@@ -397,7 +398,7 @@ errorBundlePretty ParseErrorBundle {..} =
                   lineNumber = (show . unPos . sourceLine) epos
                   padding = replicate (length lineNumber + 1) ' '
                   rpshift = unPos (sourceColumn epos) - 1
-                  slineLen = length sline
+                  slineLen = Unicode.stringLength sline
                in padding
                     <> "|\n"
                     <> lineNumber

Text/Megaparsec/Stream.hs

@@ -52,6 +52,7 @@ import qualified Data.Text.Lazy as TL
 import Data.Word (Word8)
 import Text.Megaparsec.Pos
 import Text.Megaparsec.State
+import qualified Text.Megaparsec.Unicode as Unicode
 
 -- | Type class for inputs that can be consumed by the library.
 --
@@ -426,6 +427,7 @@ class (Stream s) => VisualStream s where
 
 instance VisualStream String where
   showTokens Proxy = stringPretty
+  tokensLength Proxy = Unicode.stringLength
 
 instance VisualStream B.ByteString where
   showTokens Proxy = stringPretty . fmap (chr . fromIntegral)
@@ -435,9 +437,11 @@ instance VisualStream BL.ByteString where
 
 instance VisualStream T.Text where
   showTokens Proxy = stringPretty
+  tokensLength Proxy = Unicode.stringLength
 
 instance VisualStream TL.Text where
   showTokens Proxy = stringPretty
+  tokensLength Proxy = Unicode.stringLength
 
 -- | Type class for inputs that can also be used for error reporting.
 --
@@ -510,37 +514,37 @@ class (Stream s) => TraversableStream s where
 instance TraversableStream String where
   -- NOTE Do not eta-reduce these (breaks inlining)
   reachOffset o pst =
-    reachOffset' splitAt foldl' id id ('\n', '\t') o pst
+    reachOffset' splitAt foldl' id id ('\n', '\t') charInc o pst
   reachOffsetNoLine o pst =
-    reachOffsetNoLine' splitAt foldl' ('\n', '\t') o pst
+    reachOffsetNoLine' splitAt foldl' ('\n', '\t') charInc o pst
 
 instance TraversableStream B.ByteString where
   -- NOTE Do not eta-reduce these (breaks inlining)
   reachOffset o pst =
-    reachOffset' B.splitAt B.foldl' B8.unpack (chr . fromIntegral) (10, 9) o pst
+    reachOffset' B.splitAt B.foldl' B8.unpack (chr . fromIntegral) (10, 9) byteInc o pst
   reachOffsetNoLine o pst =
-    reachOffsetNoLine' B.splitAt B.foldl' (10, 9) o pst
+    reachOffsetNoLine' B.splitAt B.foldl' (10, 9) byteInc o pst
 
 instance TraversableStream BL.ByteString where
   -- NOTE Do not eta-reduce these (breaks inlining)
   reachOffset o pst =
-    reachOffset' splitAtBL BL.foldl' BL8.unpack (chr . fromIntegral) (10, 9) o pst
+    reachOffset' splitAtBL BL.foldl' BL8.unpack (chr . fromIntegral) (10, 9) byteInc o pst
   reachOffsetNoLine o pst =
-    reachOffsetNoLine' splitAtBL BL.foldl' (10, 9) o pst
+    reachOffsetNoLine' splitAtBL BL.foldl' (10, 9) byteInc o pst
 
 instance TraversableStream T.Text where
   -- NOTE Do not eta-reduce (breaks inlining of reachOffset').
   reachOffset o pst =
-    reachOffset' T.splitAt T.foldl' T.unpack id ('\n', '\t') o pst
+    reachOffset' T.splitAt T.foldl' T.unpack id ('\n', '\t') charInc o pst
   reachOffsetNoLine o pst =
-    reachOffsetNoLine' T.splitAt T.foldl' ('\n', '\t') o pst
+    reachOffsetNoLine' T.splitAt T.foldl' ('\n', '\t') charInc o pst
 
 instance TraversableStream TL.Text where
   -- NOTE Do not eta-reduce (breaks inlining of reachOffset').
   reachOffset o pst =
-    reachOffset' splitAtTL TL.foldl' TL.unpack id ('\n', '\t') o pst
+    reachOffset' splitAtTL TL.foldl' TL.unpack id ('\n', '\t') charInc o pst
   reachOffsetNoLine o pst =
-    reachOffsetNoLine' splitAtTL TL.foldl' ('\n', '\t') o pst
+    reachOffsetNoLine' splitAtTL TL.foldl' ('\n', '\t') charInc o pst
 
 ----------------------------------------------------------------------------
 -- Helpers
@@ -564,6 +568,8 @@ reachOffset' ::
   (Token s -> Char) ->
   -- | Newline token and tab token
   (Token s, Token s) ->
+  -- | Increment in column position for a token
+  (Token s -> Pos) ->
   -- | Offset to reach
   Int ->
   -- | Initial 'PosState' to use
@@ -576,6 +582,7 @@ reachOffset'
   fromToks
   fromTok
   (newlineTok, tabTok)
+  columnIncrement
   o
   PosState {..} =
     ( Just $ case expandTab pstateTabWidth
@@ -624,7 +631,7 @@ reachOffset'
                     (g . (fromTok ch :))
               | otherwise ->
                   St
-                    (SourcePos n l (c <> pos1))
+                    (SourcePos n l (c <> columnIncrement ch))
                     (g . (fromTok ch :))
 {-# INLINE reachOffset' #-}
 
@@ -639,6 +646,8 @@ reachOffsetNoLine' ::
   -- | Newline token and tab token
   (Token s, Token s) ->
   -- | Offset to reach
+  -- | Increment in column position for a token
+  (Token s -> Pos) ->
   Int ->
   -- | Initial 'PosState' to use
   PosState s ->
@@ -648,6 +657,7 @@ reachOffsetNoLine'
   splitAt'
   foldl''
   (newlineTok, tabTok)
+  columnIncrement
   o
   PosState {..} =
     ( PosState
@@ -670,7 +680,7 @@ reachOffsetNoLine'
               | ch == tabTok ->
                   SourcePos n l (mkPos $ c' + w - ((c' - 1) `rem` w))
               | otherwise ->
-                  SourcePos n l (c <> pos1)
+                  SourcePos n l (c <> columnIncrement ch)
 {-# INLINE reachOffsetNoLine' #-}
 
 -- | Like 'BL.splitAt' but accepts the index as an 'Int'.
@@ -753,3 +763,13 @@ expandTab w' = go 0 0
     go !i 0 (x : xs) = x : go (i + 1) 0 xs
     go !i n xs = ' ' : go (i + 1) (n - 1) xs
     w = unPos w'
+
+-- | Return increment in column position that corresponds to the given
+-- 'Char'.
+charInc :: Char -> Pos
+charInc ch = if Unicode.isWideChar ch then pos1 <> pos1 else pos1
+
+-- | Return increment in column position that corresponds to the given
+-- 'Word8'.
+byteInc :: Word8 -> Pos
+byteInc _ = pos1

Text/Megaparsec/Unicode.hs

@@ -0,0 +1,180 @@
+{-# LANGUAGE Safe #-}
+
+-- |
+-- Module      :  Text.Megaparsec.Unicode
+-- Copyright   :  © 2024–present Megaparsec contributors
+-- License     :  FreeBSD
+--
+-- Maintainer  :  Mark Karpov <[email protected]>
+-- Stability   :  experimental
+-- Portability :  portable
+--
+-- Utility functions for working with Unicode.
+--
+-- @since 9.7.0
+module Text.Megaparsec.Unicode
+  ( stringLength,
+    charLength,
+    isWideChar,
+  )
+where
+
+import Data.Array (Array, bounds, listArray, (!))
+import Data.Char (ord)
+
+-- | Calculate length of a string taking into account the fact that certain
+-- 'Char's may span more than 1 column.
+--
+-- @since 9.7.0
+stringLength :: (Traversable t) => t Char -> Int
+stringLength = sum . fmap charLength
+
+-- | Return length of an individual 'Char'.
+--
+-- @since 9.7.0
+charLength :: Char -> Int
+charLength ch = if isWideChar ch then 2 else 1
+
+-- | Determine whether the given 'Char' is “wide”, that is, whether it spans
+-- 2 columns instead of one.
+--
+-- @since 9.7.0
+isWideChar :: Char -> Bool
+isWideChar c = go (bounds wideCharRanges)
+  where
+    go (lo, hi)
+      | hi < lo = False
+      | a <= n && n <= b = True
+      | n < a = go (lo, pred mid)
+      | otherwise = go (succ mid, hi)
+      where
+        mid = (lo + hi) `div` 2
+        (a, b) = wideCharRanges ! mid
+    n = ord c
+
+-- | Wide character ranges.
+wideCharRanges :: Array Int (Int, Int)
+wideCharRanges =
+  listArray
+    (0, 118)
+    [ (0x001100, 0x00115f),
+      (0x00231a, 0x00231b),
+      (0x002329, 0x00232a),
+      (0x0023e9, 0x0023ec),
+      (0x0023f0, 0x0023f0),
+      (0x0023f3, 0x0023f3),
+      (0x0025fd, 0x0025fe),
+      (0x002614, 0x002615),
+      (0x002648, 0x002653),
+      (0x00267f, 0x00267f),
+      (0x002693, 0x002693),
+      (0x0026a1, 0x0026a1),
+      (0x0026aa, 0x0026ab),
+      (0x0026bd, 0x0026be),
+      (0x0026c4, 0x0026c5),
+      (0x0026ce, 0x0026ce),
+      (0x0026d4, 0x0026d4),
+      (0x0026ea, 0x0026ea),
+      (0x0026f2, 0x0026f3),
+      (0x0026f5, 0x0026f5),
+      (0x0026fa, 0x0026fa),
+      (0x0026fd, 0x0026fd),
+      (0x002705, 0x002705),
+      (0x00270a, 0x00270b),
+      (0x002728, 0x002728),
+      (0x00274c, 0x00274c),
+      (0x00274e, 0x00274e),
+      (0x002753, 0x002755),
+      (0x002757, 0x002757),
+      (0x002795, 0x002797),
+      (0x0027b0, 0x0027b0),
+      (0x0027bf, 0x0027bf),
+      (0x002b1b, 0x002b1c),
+      (0x002b50, 0x002b50),
+      (0x002b55, 0x002b55),
+      (0x002e80, 0x002e99),
+      (0x002e9b, 0x002ef3),
+      (0x002f00, 0x002fd5),
+      (0x002ff0, 0x002ffb),
+      (0x003000, 0x00303e),
+      (0x003041, 0x003096),
+      (0x003099, 0x0030ff),
+      (0x003105, 0x00312f),
+      (0x003131, 0x00318e),
+      (0x003190, 0x0031ba),
+      (0x0031c0, 0x0031e3),
+      (0x0031f0, 0x00321e),
+      (0x003220, 0x003247),
+      (0x003250, 0x004db5),
+      (0x004e00, 0x009fef),
+      (0x00a000, 0x00a48c),
+      (0x00a490, 0x00a4c6),
+      (0x00a960, 0x00a97c),
+      (0x00ac00, 0x00d7a3),
+      (0x00f900, 0x00fa6d),
+      (0x00fa70, 0x00fad9),
+      (0x00fe10, 0x00fe19),
+      (0x00fe30, 0x00fe52),
+      (0x00fe54, 0x00fe66),
+      (0x00fe68, 0x00fe6b),
+      (0x00ff01, 0x00ff60),
+      (0x00ffe0, 0x00ffe6),
+      (0x016fe0, 0x016fe3),
+      (0x017000, 0x0187f7),
+      (0x018800, 0x018af2),
+      (0x01b000, 0x01b11e),
+      (0x01b150, 0x01b152),
+      (0x01b164, 0x01b167),
+      (0x01b170, 0x01b2fb),
+      (0x01f004, 0x01f004),
+      (0x01f0cf, 0x01f0cf),
+      (0x01f18e, 0x01f18e),
+      (0x01f191, 0x01f19a),
+      (0x01f200, 0x01f202),
+      (0x01f210, 0x01f23b),
+      (0x01f240, 0x01f248),
+      (0x01f250, 0x01f251),
+      (0x01f260, 0x01f265),
+      (0x01f300, 0x01f320),
+      (0x01f32d, 0x01f335),
+      (0x01f337, 0x01f37c),
+      (0x01f37e, 0x01f393),
+      (0x01f3a0, 0x01f3ca),
+      (0x01f3cf, 0x01f3d3),
+      (0x01f3e0, 0x01f3f0),
+      (0x01f3f4, 0x01f3f4),
+      (0x01f3f8, 0x01f43e),
+      (0x01f440, 0x01f440),
+      (0x01f442, 0x01f4fc),
+      (0x01f4ff, 0x01f53d),
+      (0x01f54b, 0x01f54e),
+      (0x01f550, 0x01f567),
+      (0x01f57a, 0x01f57a),
+      (0x01f595, 0x01f596),
+      (0x01f5a4, 0x01f5a4),
+      (0x01f5fb, 0x01f64f),
+      (0x01f680, 0x01f6c5),
+      (0x01f6cc, 0x01f6cc),
+      (0x01f6d0, 0x01f6d2),
+      (0x01f6d5, 0x01f6d5),
+      (0x01f6eb, 0x01f6ec),
+      (0x01f6f4, 0x01f6fa),
+      (0x01f7e0, 0x01f7eb),
+      (0x01f90d, 0x01f971),
+      (0x01f973, 0x01f976),
+      (0x01f97a, 0x01f9a2),
+      (0x01f9a5, 0x01f9aa),
+      (0x01f9ae, 0x01f9ca),
+      (0x01f9cd, 0x01f9ff),
+      (0x01fa70, 0x01fa73),
+      (0x01fa78, 0x01fa7a),
+      (0x01fa80, 0x01fa82),
+      (0x01fa90, 0x01fa95),
+      (0x020000, 0x02a6d6),
+      (0x02a700, 0x02b734),
+      (0x02b740, 0x02b81d),
+      (0x02b820, 0x02cea1),
+      (0x02ceb0, 0x02ebe0),
+      (0x02f800, 0x02fa1d)
+    ]
+{-# NOINLINE wideCharRanges #-}

megaparsec-tests/megaparsec-tests.cabal

@@ -58,6 +58,7 @@ test-suite tests
         Text.Megaparsec.ErrorSpec
         Text.Megaparsec.PosSpec
         Text.Megaparsec.StreamSpec
+        Text.Megaparsec.UnicodeSpec
         Text.MegaparsecSpec
 
     default-language:   Haskell2010