Tracing: give less misleading line information with parseWithString.

Previously positions would be reported past the end of the chunk.
We now reset the source position within the chunk and report
positions "in chunk."

src/Text/Pandoc/Class.hs

@@ -79,7 +79,7 @@ import qualified Text.Pandoc.Shared as IO ( readDataFile
 import qualified Text.Pandoc.UTF8 as UTF8
 import Text.Pandoc.Compat.Time (UTCTime)
 import Text.Pandoc.Logging
-import Text.Parsec (ParsecT, getPosition)
+import Text.Parsec (ParsecT, getPosition, sourceLine, sourceName)
 import qualified Text.Pandoc.Compat.Time as IO (getCurrentTime)
 import Text.Pandoc.MIME (MimeType, getMimeType, extensionFromMimeType)
 import Text.Pandoc.Definition
@@ -576,7 +576,12 @@ instance PandocMonad m => PandocMonad (ParsecT s st m) where
     when tracing $ do
       pos <- getPosition
       Debug.Trace.trace
-        ("[trace] Parsed " ++ msg ++ " at " ++ show pos) (return ())
+        ("[trace] Parsed " ++ msg ++ " at line " ++
+            show (sourceLine pos) ++
+            if sourceName pos == "chunk"
+               then " of chunk"
+               else "")
+        (return ())
   logOutput = lift . logOutput
 
 

src/Text/Pandoc/Parsing.hs

@@ -189,7 +189,7 @@ import qualified Text.Pandoc.Builder as B
 import Text.Pandoc.XML (fromEntities)
 import qualified Text.Pandoc.UTF8 as UTF8 (putStrLn)
 import Text.Parsec hiding (token)
-import Text.Parsec.Pos (newPos)
+import Text.Parsec.Pos (newPos, initialPos)
 import Data.Char ( toLower, toUpper, ord, chr, isAscii, isAlphaNum,
                    isHexDigit, isSpace, isPunctuation )
 import Data.List ( intercalate, transpose, isSuffixOf )
@@ -366,6 +366,7 @@ parseFromString :: Monad m
                 -> ParserT String st m a
 parseFromString parser str = do
   oldPos <- getPosition
+  setPosition $ initialPos "chunk"
   oldInput <- getInput
   setInput str
   result <- parser