New withWarningsToStderr exported from Text.Pandoc.Class.

And use this in pandoc.hs so that messages actually get printed.

pandoc.hs

@@ -77,7 +77,7 @@ import System.Posix.Terminal (queryTerminal)
 import System.Posix.IO (stdOutput)
 #endif
 import Control.Monad.Trans
-import Text.Pandoc.Class (withMediaBag, PandocIO)
+import Text.Pandoc.Class (withMediaBag, PandocIO, withWarningsToStderr)
 
 type Transform = Pandoc -> Pandoc
 
@@ -1414,10 +1414,14 @@ convertWithOpts opts args = do
             srcs <- convertTabs . intercalate "\n" <$> readSources sources'
             doc <- handleIncludes' srcs
             case doc of
-              Right doc' -> runIOorExplode $ withMediaBag $ r readerOpts doc'
+              Right doc' -> runIOorExplode $ withMediaBag
+                                           $ withWarningsToStderr
+                                           $ r readerOpts doc'
               Left e -> error $ show e
           ByteStringReader r -> readFiles sources' >>=
-                                (\bs -> runIOorExplode $ withMediaBag $ r readerOpts bs)
+                                (\bs -> runIOorExplode $ withMediaBag
+                                                       $ withWarningsToStderr
+                                                       $ r readerOpts bs)
 
   -- We parse first if (1) fileScope is set, (2), it's a binary
   -- reader, or (3) we're reading JSON. This is easier to do of an AND
@@ -1489,7 +1493,9 @@ convertWithOpts opts args = do
 
   case writer of
     -- StringWriter f -> f writerOptions doc' >>= writerFn outputFile
-    ByteStringWriter f -> (runIOorExplode $ f writerOptions doc') >>= writeFnBinary outputFile
+    ByteStringWriter f -> (runIOorExplode $ withWarningsToStderr
+                                          $ f writerOptions doc')
+                                          >>= writeFnBinary outputFile
     StringWriter f
       | pdfOutput -> do
               -- make sure writer is latex or beamer or context or html5
@@ -1523,5 +1529,6 @@ convertWithOpts opts args = do
                   handleEntities = if htmlFormat && ascii
                                    then toEntities
                                    else id
-              output <- runIOorExplode $ f writerOptions doc'
+              output <- runIOorExplode $ withWarningsToStderr
+                                       $ f writerOptions doc'
               selfcontain (output ++ ['\n' | not standalone']) >>= writerFn outputFile . handleEntities

src/Text/Pandoc/Class.hs

@@ -51,6 +51,7 @@ module Text.Pandoc.Class ( PandocMonad(..)
                          , runIOorExplode
                          , runPure
                          , withMediaBag
+                         , withWarningsToStderr
                          ) where
 
 import Prelude hiding (readFile, fail)
@@ -64,7 +65,8 @@ import qualified Text.Pandoc.Shared as IO ( fetchItem
                                           , fetchItem'
                                           , getDefaultReferenceDocx
                                           , getDefaultReferenceODT
-                                          , readDataFile)
+                                          , readDataFile
+                                          , warn)
 import Text.Pandoc.Compat.Time (UTCTime)
 import Text.Pandoc.Parsing (ParserT, ParserState, SourcePos)
 import qualified Text.Pandoc.Compat.Time as IO (getCurrentTime)
@@ -119,6 +121,8 @@ class (Functor m, Applicative m, Monad m, MonadError PandocError m, MonadState C
 
 -- Functions defined for all PandocMonad instances
 
+-- TODO should we rename this to avoid conflict with the like-named
+-- function from Shared?  Perhaps "addWarning"?
 warn :: PandocMonad m => String -> m ()
 warn msg = modify $ \st -> st{stWarnings = msg : stWarnings st}
 
@@ -183,6 +187,12 @@ runIO ma = flip evalStateT def $ runExceptT $ unPandocIO ma
 withMediaBag :: PandocMonad m => m a ->  m (a, MediaBag)
 withMediaBag ma = ((,)) <$> ma <*> getMediaBag
 
+withWarningsToStderr :: PandocIO a -> PandocIO a
+withWarningsToStderr f = do
+  x <- f
+  getWarnings >>= mapM_ IO.warn
+  return x
+
 runIOorExplode :: PandocIO a -> IO a
 runIOorExplode ma = handleError <$> runIO ma