fix case #56: Text builder instance writes to wrong offset

Data/Double/Conversion/Internal/TextBuilder.hs

@@ -36,7 +36,7 @@ convert :: (RealFloat a, RealFloat b, b ~ ForeignFloating a) => String -> CInt
 {-# SPECIALIZE convert :: String -> CInt -> (forall s. CDouble -> MutableByteArray# s -> IO CInt) -> Double -> Builder #-}
 {-# SPECIALIZE convert :: String -> CInt -> (forall s. CFloat -> MutableByteArray# s -> IO CInt) -> Float -> Builder #-}
 {-# INLINABLE convert #-}
-convert func len act val = runST $ do 
+convert func len act val = runST $ do
 #if MIN_VERSION_text(2,0,0)
   mTempArr@(A.MutableByteArray tempMArr) <- A.new (fromIntegral len)
 #else
@@ -48,7 +48,7 @@ convert func len act val = runST $ do
       error $ "Data.Double.Conversion.Text." ++ func ++
               ": conversion failed."
 #if MIN_VERSION_text(2,0,0)
-  return $ writeN (fromIntegral size) $ \mArr _ -> A.copyI (fromIntegral size) mArr 0 tempArr 0
+  return $ writeN (fromIntegral size) $ \mArr offset -> A.copyI (fromIntegral size) mArr offset tempArr 0
 #else
-  return $ writeN (fromIntegral size) $ \mArr _ -> A.copyI mArr 0 tempArr 0 (fromIntegral size)
+  return $ writeN (fromIntegral size) $ \mArr offset -> A.copyI mArr offset tempArr 0 (fromIntegral size)
 #endif

tests/Properties.hs

@@ -1,8 +1,12 @@
 import Test.Framework (Test, defaultMain, testGroup)
 import Test.Framework.Providers.QuickCheck2 (testProperty)
 import qualified Data.ByteString.Char8 as B
+import qualified Data.ByteString.Builder as BB
 import qualified Data.Double.Conversion.Convertable as C
+import Data.Double.Conversion.Convertable
 import qualified Data.Text as T
+import qualified Data.Text.Lazy as TL
+import qualified Data.Text.Lazy.Builder as TLB
 import qualified Regressions
 
 shortest :: (Double -> String) -> Double -> Double -> Bool
@@ -12,10 +16,32 @@ shortest f a b = case read (f ab) of
                       | otherwise     -> ba == ab
   where ab = a / b
 
+-- | Compare concatenated sequence of numbers as Text and Builder
+catTextEqualsCatBuilder :: [Either Float Double] -> Bool
+catTextEqualsCatBuilder xs =
+  mconcat texts == (TL.toStrict . TLB.toLazyText . mconcat) builders
+  where
+    texts :: [T.Text]
+    texts = either (toExponential 3) (toExponential 3) <$> xs
+    builders :: [TLB.Builder]
+    builders = either (toExponential 3) (toExponential 3) <$> xs
+
+-- | Compare concatenated sequence of numbers as ByteString and Builder
+catByteStringEqualsCatBuilder :: [Either Float Double] -> Bool
+catByteStringEqualsCatBuilder xs =
+  mconcat byteStrings == (B.toStrict . BB.toLazyByteString . mconcat) builders
+  where
+    byteStrings :: [B.ByteString]
+    byteStrings = either (toExponential 3) (toExponential 3) <$> xs
+    builders :: [BB.Builder]
+    builders = either (toExponential 3) (toExponential 3) <$> xs
+
 tests :: Test
 tests = testGroup "Properties" [
     testProperty "b_shortest" $ shortest (B.unpack . C.toShortest)
   , testProperty "t_shortest" $ shortest (T.unpack . C.toShortest)
+  , testProperty "catTextEqualsCatBuilder" catTextEqualsCatBuilder
+  , testProperty "catByteStringEqualsCatBuilder" catByteStringEqualsCatBuilder
   ]
 
 main :: IO ()