5 files changed, 66 insertions(+), 14 deletions(-)

M src/Data/Text/ParagraphLayout/Internal/Layout.hs
M src/Data/Text/ParagraphLayout/Internal/ProtoFragment.hs
M src/Data/Text/ParagraphLayout/Internal/Rich.hs
M src/Data/Text/ParagraphLayout/Internal/Run.hs
M test/Data/Text/ParagraphLayout/Internal/RunSpec.hs

@@ 246,12 246,22 @@ lastSpanBoxes xs = case reverse xs of
 -- output list will contain a run of zero characters. This can be used to
 -- correctly size an empty line.
 --
+-- If there is a hard line break in the input, the run containing it will have
+-- its `runHardBreak` set to `True`.
+--
 -- If there is no hard line break in the input, the first output list will
 -- contain the whole input, and the second output list will be empty.
 hardSplit :: NonEmpty (WithSpan d Run) -> ([WithSpan d Run], [WithSpan d Run])
-hardSplit runs = allowFstEmpty $ trimFst $ NonEmpty.last $ splits
+hardSplit runs = case reverse hSplits of
+    [] -> noSplit
+    (splitRuns : _) -> forcedSplit splitRuns
     where
-        trimFst (runs1, runs2) = (trim runs1, runs2)
+        noSplit =
+            (NonEmpty.toList (trim runs), [])
+        forcedSplit (runs1, runs2) =
+            (NonEmpty.toList $ markHard $ trim runs1, runs2)
+        markHard = mapLast markHard'
+        markHard' (WithSpan rs x) = WithSpan rs x { runHardBreak = True }
         trim
             = trimTextsStartPreserve isStartSpace
             . trimTextsEndPreserve isEndSpace


@@ 259,13 269,17 @@ hardSplit runs = allowFstEmpty $ trimFst $ NonEmpty.last $ splits
         -- TODO: Consider optimising.
         --       We do not need to look for any line breaks further than the
         --       shortest hard break.
-        splits = noSplit :| hSplits
-        noSplit = (runs, [])
         hSplits = nonEmptyFsts $
             -- from longest to shortest
             splitTextsBy (map fst . filter isHard . runLineBreaks) runs
         isHard (_, status) = status == BreakStatus.Hard
 
+-- | Apply a function to the last element of the non-empty list.
+mapLast :: (a -> a) -> NonEmpty a -> NonEmpty a
+mapLast f xs = case NonEmpty.uncons xs of
+    (x, Nothing) -> f x :| []
+    (x, Just rest) -> NonEmpty.cons x $ mapLast f rest
+
 -- | Treat a list of runs as a contiguous sequence,
 -- and find all possible ways to split them into two non-empty lists,
 -- using soft line break opportunities (typically after words) and then


@@ 312,10 326,11 @@ layoutRunsH runs = map layoutRunH runs
 layoutRunH :: WithSpan d Run -> ProtoFragmentWithSpan d
 layoutRunH (WithSpan rs run) = WithSpan rs pf
     where
-        pf = PF.protoFragmentH dir lvl glyphs
+        pf = PF.protoFragmentH dir lvl glyphs hard
         glyphs = shapeRun (WithSpan rs run)
         dir = runDirection run
         lvl = runLevel run
+        hard = runHardBreak run
 
 -- | Calculate layout for the given run independently of its position.
 shapeRun :: WithSpan d Run -> [(GlyphInfo, GlyphPos)]


@@ 356,7 371,7 @@ runBreaksFromSpan :: Run -> [(Int, a)] -> [(Int, a)]
 runBreaksFromSpan run spanBreaks =
     dropWhile (not . valid) $ subOffsetsDesc (runOffsetInSpan run) spanBreaks
     where
-        valid (off, _) = off < runLength
+        valid (off, _) = off <= runLength
         runLength = lengthWord8 $ getText run
 
 -- | Predicate for characters that can be potentially removed from the

@@ 1,5 1,5 @@
 module Data.Text.ParagraphLayout.Internal.ProtoFragment
-    ( ProtoFragment (direction, advance, glyphs)
+    ( ProtoFragment (direction, advance, glyphs, hardBreak)
     , protoFragmentH
     )
 where


@@ 20,13 20,15 @@ data ProtoFragment = ProtoFragment
     -- ^ Total advance of glyphs in this fragment,
     -- depending on the text direction.
     , glyphs :: [(GlyphInfo, GlyphPos)]
+    , hardBreak :: Bool
+    -- ^ Marks fragment that ends with a forced line break.
     }
 
 -- | Construct a `ProtoFragment`, automatically calculating the total advance
 -- for a horizontal text direction.
-protoFragmentH :: Direction -> BiDi.Level -> [(GlyphInfo, GlyphPos)] ->
+protoFragmentH :: Direction -> BiDi.Level -> [(GlyphInfo, GlyphPos)] -> Bool ->
     ProtoFragment
-protoFragmentH dir lvl gs = ProtoFragment dir lvl adv gs
+protoFragmentH dir lvl gs hard = ProtoFragment dir lvl adv gs hard
     where
         adv = sum $ map (x_advance . snd) gs
 

@@ 66,8 66,8 @@ resolveSpans p = do
     let lang = textLanguage textOpts
     -- TODO: Allow BiDi embedding/isolation for inner nodes.
     let pLevels = textLevels (textDirection rootTextOpts) pText
-    let lBreaks = paragraphBreaks breakLine pText lang
-    let cBreaks = paragraphBreaks breakCharacter pText lang
+    let lBreaks = paragraphBreaksDesc breakLine pText lang
+    let cBreaks = paragraphBreaksDesc breakCharacter pText lang
     -- TODO: Optimise. This has time complexity O(n*s), where n is number of
     --       characters and s is number of resolved spans.
     --       Maybe include byte offsets in the TextLevels data structure?


@@ 85,6 85,12 @@ resolveSpans p = do
         , RS.spanCharacterBreaks = subOffsetsDesc (sStart - pStart) cBreaks
         }
 
-paragraphBreaks :: (LocaleName -> Breaker a) -> Text -> String -> [(Int, a)]
-paragraphBreaks breakFunc txt lang =
-    breaksDesc (breakFunc (locale lang LBAuto)) txt
+paragraphBreaksDesc :: (LocaleName -> Breaker a) -> Text -> String -> [(Int, a)]
+paragraphBreaksDesc breakFunc txt lang =
+    -- Workaround: We are interested in the type of the end-of-text break
+    --             (if it is hard, that line needs to be always visible),
+    --             but `breaksDesc` does not provide it.
+    --
+    -- TODO: Consider optimising by creating a custom reimplementation
+    --       of `Data.Text.ICU.breaksRight`.
+    reverse $ breaksAsc (breakFunc (locale lang LBAuto)) txt

@@ 25,6 25,10 @@ data Run = Run
     , runLevel :: Level
     , runDirection :: Direction
     , runScript :: Maybe ScriptCode
+    , runHardBreak :: Bool
+    -- ^ Marks run that ends with a forced line break.
+    -- Those should prevent creation of invisible line boxes
+    -- according to <https://www.w3.org/TR/css-inline-3/#invisible-line-boxes>.
     }
     deriving (Eq, Show)
 


@@ 87,6 91,7 @@ spanToRuns s = snd $ mapAccumL run 0 $ protoRuns zipper levels
                 , runLevel = PR.level pr
                 , runDirection = levelDirectionH $ PR.level pr
                 , runScript = Just $ PR.script pr
+                , runHardBreak = False
                 }
             )
 

@@ 60,6 60,7 @@ spec = do
                     , runLevel = 0
                     , runDirection = DirLTR
                     , runScript = Just "Latn"
+                    , runHardBreak = False
                     }
                 ]
         it "handles Arabic hello" $ do


@@ 72,6 73,7 @@ spec = do
                     , runLevel = 1
                     , runDirection = DirRTL
                     , runScript = Just "Arab"
+                    , runHardBreak = False
                     }
                 ]
         it "handles Serbian with mixed script" $ do


@@ 85,6 87,7 @@ spec = do
                     , runLevel = 0
                     , runDirection = DirLTR
                     , runScript = Just "Latn"
+                    , runHardBreak = False
                     }
                 , Run
                     { runOffsetInSpan = 12


@@ 92,6 95,7 @@ spec = do
                     , runLevel = 0
                     , runDirection = DirLTR
                     , runScript = Just "Cyrl"
+                    , runHardBreak = False
                     }
                 ]
         it "handles mixed direction with base LTR" $ do


@@ 105,6 109,7 @@ spec = do
                     , runLevel = 0
                     , runDirection = DirLTR
                     , runScript = Just "Latn"
+                    , runHardBreak = False
                     }
                 , Run
                     { runOffsetInSpan = 7


@@ 112,6 117,7 @@ spec = do
                     , runLevel = 1
                     , runDirection = DirRTL
                     , runScript = Just "Arab"
+                    , runHardBreak = False
                     }
                 , Run
                     { runOffsetInSpan = 13


@@ 119,6 125,7 @@ spec = do
                     , runLevel = 0
                     , runDirection = DirLTR
                     , runScript = Just "Latn"
+                    , runHardBreak = False
                     }
                 ]
         it "handles mixed direction with base RTL" $ do


@@ 132,6 139,7 @@ spec = do
                     , runLevel = 2
                     , runDirection = DirLTR
                     , runScript = Just "Latn"
+                    , runHardBreak = False
                     }
                 , Run
                     { runOffsetInSpan = 7


@@ 139,6 147,7 @@ spec = do
                     , runLevel = 1
                     , runDirection = DirRTL
                     , runScript = Just "Arab"
+                    , runHardBreak = False
                     }
                 , Run
                     { runOffsetInSpan = 13


@@ 146,6 155,7 @@ spec = do
                     , runLevel = 2
                     , runDirection = DirLTR
                     , runScript = Just "Latn"
+                    , runHardBreak = False
                     }
                 ]
         it "handles Arabic text with English inside" $ do


@@ 159,6 169,7 @@ spec = do
                     , runLevel = 1
                     , runDirection = DirRTL
                     , runScript = Just "Arab"
+                    , runHardBreak = False
                     }
                 , Run
                     { runOffsetInSpan = 5


@@ 166,6 177,7 @@ spec = do
                     , runLevel = 2
                     , runDirection = DirLTR
                     , runScript = Just "Latn"
+                    , runHardBreak = False
                     }
                 , Run
                     { runOffsetInSpan = 14


@@ 173,6 185,7 @@ spec = do
                     , runLevel = 1
                     , runDirection = DirRTL
                     , runScript = Just "Arab"
+                    , runHardBreak = False
                     }
                 , Run
                     { runOffsetInSpan = 79


@@ 180,6 193,7 @@ spec = do
                     , runLevel = 2
                     , runDirection = DirLTR
                     , runScript = Just "Latn"
+                    , runHardBreak = False
                     }
                 , Run
                     { runOffsetInSpan = 82


@@ 187,6 201,7 @@ spec = do
                     , runLevel = 1
                     , runDirection = DirRTL
                     , runScript = Just "Zyyy"
+                    , runHardBreak = False
                     }
                 ]
         it "handles English text with Arabic inside" $ do


@@ 200,6 215,7 @@ spec = do
                     , runLevel = 0
                     , runDirection = DirLTR
                     , runScript = Just "Latn"
+                    , runHardBreak = False
                     }
                 , Run
                     { runOffsetInSpan = 13


@@ 207,6 223,7 @@ spec = do
                     , runLevel = 1
                     , runDirection = DirRTL
                     , runScript = Just "Arab"
+                    , runHardBreak = False
                     }
                 , Run
                     { runOffsetInSpan = 47


@@ 214,6 231,7 @@ spec = do
                     , runLevel = 0
                     , runDirection = DirLTR
                     , runScript = Just "Latn"
+                    , runHardBreak = False
                     }
                 ]
         -- Unrealistic example where text changes direction


@@ 229,6 247,7 @@ spec = do
                     , runLevel = 1
                     , runDirection = DirRTL
                     , runScript = Just "Latn"
+                    , runHardBreak = False
                     }
                 -- direction change
                 , Run


@@ 237,6 256,7 @@ spec = do
                     , runLevel = 2
                     , runDirection = DirLTR
                     , runScript = Just "Latn"
+                    , runHardBreak = False
                     }
                 -- direction change
                 , Run


@@ 245,6 265,7 @@ spec = do
                     , runLevel = 1
                     , runDirection = DirRTL
                     , runScript = Just "Latn"
+                    , runHardBreak = False
                     }
                 -- script change
                 , Run


@@ 253,6 274,7 @@ spec = do
                     , runLevel = 1
                     , runDirection = DirRTL
                     , runScript = Just "Cyrl"
+                    , runHardBreak = False
                     }
                 -- direction change
                 , Run


@@ 261,6 283,7 @@ spec = do
                     , runLevel = 2
                     , runDirection = DirLTR
                     , runScript = Just "Cyrl"
+                    , runHardBreak = False
                     }
                 -- direction change
                 , Run


@@ 269,5 292,6 @@ spec = do
                     , runLevel = 1
                     , runDirection = DirRTL
                     , runScript = Just "Cyrl"
+                    , runHardBreak = False
                     }
                 ]