Fix crash in `haddock-library` on unicode space

Our quickcheck tests for `haddock-library` stumbled across an edge case
input that was causing Haddock to crash: it was a unicode space
character.

The root cause of the crash is that we were implicitly assuming that
if a space character was not " \t\f\v\r", it would have to be "\n".
We fix this by instead defining horizontal space as: any space character
that is not '\n'.

Fixes #1142

2 files changed, 14 insertions, 8 deletions

diff --git a/haddock-library/src/Documentation/Haddock/Parser/Util.hs b/haddock-library/src/Documentation/Haddock/Parser/Util.hs
index 98570c22..eef744d8 100644
--- a/haddock-library/src/Documentation/Haddock/Parser/Util.hs
+++ b/haddock-library/src/Documentation/Haddock/Parser/Util.hs
@@ -31,16 +31,16 @@ import           Prelude hiding (takeWhile)
 import           Data.Char (isSpace)
 
 -- | Characters that count as horizontal space
-horizontalSpace :: [Char]
-horizontalSpace = " \t\f\v\r"
+horizontalSpace :: Char -> Bool
+horizontalSpace c = isSpace c && c /= '\n'
 
 -- | Skip and ignore leading horizontal space
 skipHorizontalSpace :: Parser ()
-skipHorizontalSpace = Parsec.skipMany (Parsec.oneOf horizontalSpace)
+skipHorizontalSpace = Parsec.skipMany (Parsec.satisfy horizontalSpace)
 
 -- | Take leading horizontal space
-takeHorizontalSpace :: Parser Text 
-takeHorizontalSpace = takeWhile (`elem` horizontalSpace)
+takeHorizontalSpace :: Parser Text
+takeHorizontalSpace = takeWhile horizontalSpace
 
 makeLabeled :: (String -> Maybe String -> a) -> Text -> a
 makeLabeled f input = case T.break isSpace $ removeEscapes $ T.strip input of
@@ -60,10 +60,10 @@ removeEscapes = T.unfoldr go
 
 -- | Consume characters from the input up to and including the given pattern.
 -- Return everything consumed except for the end pattern itself.
-takeUntil :: Text -> Parser Text 
+takeUntil :: Text -> Parser Text
 takeUntil end_ = T.dropEnd (T.length end_) <$> requireEnd (scan p (False, end)) >>= gotSome
   where
-    end = T.unpack end_ 
+    end = T.unpack end_
 
     p :: (Bool, String) -> Char -> Maybe (Bool, String)
     p acc c = case acc of
diff --git a/haddock-library/test/Documentation/Haddock/ParserSpec.hs b/haddock-library/test/Documentation/Haddock/ParserSpec.hs
index bc40a0a2..8b59b560 100644
--- a/haddock-library/test/Documentation/Haddock/ParserSpec.hs
+++ b/haddock-library/test/Documentation/Haddock/ParserSpec.hs
@@ -3,6 +3,7 @@
 
 module Documentation.Haddock.ParserSpec (main, spec) where
 
+import           Data.Char (isSpace)
 import           Data.String
 import qualified Documentation.Haddock.Parser as Parse
 import           Documentation.Haddock.Types
@@ -442,6 +443,10 @@ spec = do
       property $ \xs ->
         (length . show . parseParas) xs `shouldSatisfy` (> 0)
 
+    -- See <https://github.com/haskell/haddock/issues/1142>
+    it "doesn't crash on unicode whitespace" $ do
+      "\8197" `shouldParseTo` DocEmpty
+
     context "when parsing @since" $ do
       it "adds specified version to the result" $ do
         parseParas "@since 0.5.0" `shouldBe`
@@ -470,7 +475,8 @@ spec = do
 
 
     context "when parsing text paragraphs" $ do
-      let filterSpecial = filter (`notElem` (".(=#-[*`\v\f\n\t\r\\\"'_/@<> " :: String))
+      let isSpecial c = isSpace c || c `elem` (".(=#-[*`\\\"'_/@<>" :: String)
+          filterSpecial = filter (not . isSpecial)
 
       it "parses an empty paragraph" $ do
         "" `shouldParseTo` DocEmpty