2 files changed, 78 insertions(+), 16 deletions(-)

M balkon.cabal
M test/Data/Text/ParagraphLayout/RichSpec.hs

@@ 116,6 116,7 @@ library balkon-internal
         Data.Text.ParagraphLayout.Internal.Paginable,
         Data.Text.ParagraphLayout.Internal.ParagraphAlignment,
         Data.Text.ParagraphLayout.Internal.ParagraphConstruction,
+        Data.Text.ParagraphLayout.Internal.ParagraphLine,
         Data.Text.ParagraphLayout.Internal.ParagraphOptions,
         Data.Text.ParagraphLayout.Internal.Plain,
         Data.Text.ParagraphLayout.Internal.Plain.Paragraph,


@@ 139,7 140,6 @@ library balkon-internal
         Data.Text.ParagraphLayout.Internal.Layout,
         Data.Text.ParagraphLayout.Internal.LineNumbers,
         Data.Text.ParagraphLayout.Internal.ParagraphExtents,
-        Data.Text.ParagraphLayout.Internal.ParagraphLine,
         Data.Text.ParagraphLayout.Internal.ProtoFragment,
         Data.Text.ParagraphLayout.Internal.ProtoLine,
         Data.Text.ParagraphLayout.Internal.ProtoRun,

@@ 9,6 9,7 @@ import System.FilePath ((</>))
 import Data.Text.ParagraphLayout
 import Data.Text.ParagraphLayout.FontLoader
 import Data.Text.ParagraphLayout.Internal.Paginable (paginateAll)
+import Data.Text.ParagraphLayout.Internal.ParagraphLine (forceLeftAlign)
 import Data.Text.ParagraphLayout.Internal.Rich.ParagraphLayout (shapedRuns)
 import Data.Text.ParagraphLayout.PrettyShow
 import Data.Text.ParagraphLayout.PrettyShow.Golden


@@ 28,6 29,20 @@ glyphRuns = map (map (codepoint . fst) . fragmentGlyphs) . paragraphFragments
 largeWidth :: Int32
 largeWidth = 1000000000
 
+-- | Expect two paragraph layouts to contain the same fragments,
+-- except possibly shifted left or right.
+shouldBeWrappedLike :: (Show d, Eq d) =>
+    ParagraphLayout d -> ParagraphLayout d -> Expectation
+shouldBeWrappedLike a b =
+    forceLeftAlign a `shouldBe` forceLeftAlign b
+
+-- | Expect two paragraph layouts to not contain the same fragments,
+-- even if ignoring a possible shift to the left or to the right.
+shouldNotBeWrappedLike :: (Show d, Eq d) =>
+    ParagraphLayout d -> ParagraphLayout d -> Expectation
+shouldNotBeWrappedLike a b =
+    forceLeftAlign a `shouldNotBe` forceLeftAlign b
+
 spec :: Spec
 spec = do
 


@@ 40,32 55,79 @@ spec = do
             font <- runIO $ loadFont latinFont 0 testingOptions
             fontSmall <- runIO $ loadFont latinFont 0 testingOptionsSmall
 
-            it "wraps lorem ipsum at 20em, left aligned" $ do
+            let commonWrapWidth = 20000
+            let expectedSafeWidth = 19791
+
+            describe "lorem ipsum at 20em, left aligned" $ do
                 let opts = defaultParagraphOptions
                         { paragraphAlignment = AlignLeft
-                        , paragraphMaxWidth = 20000
                         }
-                let input = loremIpsumParagraph font opts
-                let result = layoutRich input
-                result `shouldBeGolden` "loremIpsum20em"
+                let input w = loremIpsumParagraph font $
+                        opts { paragraphMaxWidth = w }
+                let result20em = layoutRich $ input commonWrapWidth
+                let resultSafe = layoutRich $ input expectedSafeWidth
+                let resultUnsafe = layoutRich $ input (expectedSafeWidth - 1)
+
+                it "wraps correctly" $
+                    result20em `shouldBeGolden` "loremIpsum20em"
 
-            it "wraps lorem ipsum at 20em, right aligned" $ do
+                it "gives correct safe width" $
+                    paragraphSafeWidth result20em `shouldBe` expectedSafeWidth
+
+                it "wraps the same at safe width" $
+                    resultSafe `shouldBeWrappedLike` result20em
+
+                it "does not wrap the same at smaller width" $
+                    resultUnsafe `shouldNotBeWrappedLike` result20em
+
+            describe "lorem ipsum at 20em, right aligned" $ do
                 let opts = defaultParagraphOptions
                         { paragraphAlignment = AlignRight
-                        , paragraphMaxWidth = 20000
                         }
-                let input = loremIpsumParagraph font opts
-                let result = layoutRich input
-                result `shouldBeGolden` "loremIpsum20emRight"
+                let input w = loremIpsumParagraph font $
+                        opts { paragraphMaxWidth = w }
+                let result20em = layoutRich $ input commonWrapWidth
+                let resultSafe = layoutRich $ input expectedSafeWidth
+                let resultUnsafe = layoutRich $ input (expectedSafeWidth - 1)
 
-            it "wraps lorem ipsum at 20em, centred" $ do
+                it "wraps correctly" $
+                    result20em `shouldBeGolden` "loremIpsum20emRight"
+
+                it "gives correct safe width" $
+                    paragraphSafeWidth result20em `shouldBe` expectedSafeWidth
+
+                it "wraps the same at safe width" $
+                    resultSafe `shouldBeWrappedLike` result20em
+
+                it "does not wrap the same at smaller width" $
+                    resultUnsafe `shouldNotBeWrappedLike` result20em
+
+            describe "lorem ipsum at 20em, centred" $ do
                 let opts = defaultParagraphOptions
                         { paragraphAlignment = AlignCentreH
-                        , paragraphMaxWidth = 20000
                         }
-                let input = loremIpsumParagraph font opts
-                let result = layoutRich input
-                result `shouldBeGolden` "loremIpsum20emCentre"
+                let input w = loremIpsumParagraph font $
+                        opts { paragraphMaxWidth = w }
+                let result20em = layoutRich $ input commonWrapWidth
+                let resultSafe = layoutRich $ input expectedSafeWidth
+                let resultUnsafe = layoutRich $ input (expectedSafeWidth - 1)
+                let resultUnsafe2 = layoutRich $ input (expectedSafeWidth - 2)
+
+                it "wraps correctly" $
+                    result20em `shouldBeGolden` "loremIpsum20emCentre"
+
+                it "gives correct safe width" $
+                    paragraphSafeWidth result20em `shouldBe` expectedSafeWidth
+
+                it "wraps the same at safe width" $
+                    resultSafe `shouldBeWrappedLike` result20em
+
+                it "does not wrap the same at smaller width" $
+                    resultUnsafe `shouldNotBeWrappedLike` result20em
+
+                -- Cover for false negatives when halving odd numbers.
+                it "does not wrap the same at 2 units smaller width" $
+                    resultUnsafe2 `shouldNotBeWrappedLike` result20em
 
             it "handles mixed line height" $ do
                 let opts = defaultParagraphOptions