From 6e011c818a62f3d3ae7554f67f24fc8f3abf031b Mon Sep 17 00:00:00 2001
From: Jaro <jaro@argonaut-constellation.org>
Date: Mon, 19 Jun 2023 20:56:24 +0200
Subject: [PATCH] Allow generating an empty run.

---
 src/Data/Text/ParagraphLayout/Internal/Run.hs   | 17 ++++++++++++++++-
 .../Text/ParagraphLayout/Internal/RunSpec.hs    | 13 +++++++++++--
 2 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/src/Data/Text/ParagraphLayout/Internal/Run.hs b/src/Data/Text/ParagraphLayout/Internal/Run.hs
index 5f118bd..62bb083 100644
--- a/src/Data/Text/ParagraphLayout/Internal/Run.hs
+++ b/src/Data/Text/ParagraphLayout/Internal/Run.hs
@@ -78,7 +78,22 @@ considerNext z = case next z of
 data Merged a = Incompatible | Merged a
 
 spanToRuns :: ResolvedSpan d -> [Run]
-spanToRuns s = snd $ mapAccumL run 0 $ protoRuns zipper levels
+spanToRuns s
+    | Text.null (spanText s) = [emptyRun]
+    | otherwise = spanToRuns' s
+    where
+        emptyRun = Run
+            { runOffsetInSpan = 0
+            , runText = Text.empty
+            , runLevel = defaultLevel
+            , runDirection = levelDirectionH defaultLevel
+            , runScript = Nothing
+            , runHardBreak = False
+            }
+        defaultLevel = baseLevel $ spanBiDiLevels s
+
+spanToRuns' :: ResolvedSpan d -> [Run]
+spanToRuns' s = snd $ mapAccumL run 0 $ protoRuns zipper levels
     where
         wholeText = spanText s
         zipper = start wholeText
diff --git a/test/Data/Text/ParagraphLayout/Internal/RunSpec.hs b/test/Data/Text/ParagraphLayout/Internal/RunSpec.hs
index 4da8e80..8c7019c 100644
--- a/test/Data/Text/ParagraphLayout/Internal/RunSpec.hs
+++ b/test/Data/Text/ParagraphLayout/Internal/RunSpec.hs
@@ -1,6 +1,6 @@
 module Data.Text.ParagraphLayout.Internal.RunSpec (spec) where
 
-import Data.Text (Text, pack)
+import Data.Text (Text, empty, pack)
 import Data.Text.Glyphize (Direction (..), emptyFont)
 
 import Test.Hspec
@@ -49,7 +49,16 @@ spec = do
         it "handles span with no text" $ do
             let inputSpan = sampleSpan englishEmpty allLTR
             let runs = spanToRuns inputSpan
-            runs `shouldBe` []
+            runs `shouldBe`
+                [ Run
+                    { runOffsetInSpan = 0
+                    , runText = empty
+                    , runLevel = 0
+                    , runDirection = DirLTR
+                    , runScript = Nothing
+                    , runHardBreak = False
+                    }
+                ]
         it "handles Czech hello" $ do
             let inputSpan = sampleSpan czechHello allLTR
             let runs = spanToRuns inputSpan
-- 
2.30.2