Process.pipeProcess: stream stderr rather than capturing.

Signature of pipeProcess has changed: the return value is
now IO (ExitCode, ByteString) -- with only stdout. Stderr
is just inherited from the parent.

This means that stderr from filters will now be streamed
as the filters are run.

Closes #2729.

2 files changed, 15 insertions, 27 deletions

diff --git a/src/Text/Pandoc/PDF.hs b/src/Text/Pandoc/PDF.hs
index 7aaa257fa..d1d1c803c 100644
--- a/src/Text/Pandoc/PDF.hs
+++ b/src/Text/Pandoc/PDF.hs
@@ -37,7 +37,7 @@ import qualified Data.ByteString as BS
 import Data.Monoid ((<>))
 import System.Exit (ExitCode (..))
 import System.FilePath
-import System.IO (stderr, stdout)
+import System.IO (stdout)
 import System.IO.Temp (withTempFile)
 import System.Directory
 import Data.Digest.Pure.SHA (showDigest, sha1)
@@ -247,11 +247,10 @@ runTeXProgram verbose program args runNumber numRuns tmpDir source = do
       putStrLn $ "[makePDF] Contents of " ++ file' ++ ":"
       B.readFile file' >>= B.putStr
       putStr "\n"
-    (exit, out, err) <- pipeProcess (Just env'') program programArgs BL.empty
+    (exit, out) <- pipeProcess (Just env'') program programArgs BL.empty
     when verbose $ do
       putStrLn $ "[makePDF] Run #" ++ show runNumber
       B.hPutStr stdout out
-      B.hPutStr stderr err
       putStr "\n"
     if runNumber <= numRuns
        then runTeXProgram verbose program args (runNumber + 1) numRuns tmpDir source
@@ -264,7 +263,7 @@ runTeXProgram verbose program args runNumber numRuns tmpDir source = do
                    -- See https://github.com/jgm/pandoc/issues/1192.
                    then (Just . B.fromChunks . (:[])) `fmap` BS.readFile pdfFile
                    else return Nothing
-         return (exit, out <> err, pdf)
+         return (exit, out, pdf)
 
 html2pdf  :: Bool         -- ^ Verbose output
           -> [String]     -- ^ Args to wkhtmltopdf
@@ -286,12 +285,10 @@ html2pdf verbose args source = do
     putStrLn $ "[makePDF] Contents of " ++ file ++ ":"
     B.readFile file >>= B.putStr
     putStr "\n"
-  (exit, out, err) <- pipeProcess (Just env') "wkhtmltopdf"
-                              programArgs BL.empty
+  (exit, out) <- pipeProcess (Just env') "wkhtmltopdf" programArgs BL.empty
   removeFile file
   when verbose $ do
     B.hPutStr stdout out
-    B.hPutStr stderr err
     putStr "\n"
   pdfExists <- doesFileExist pdfFile
   mbPdf <- if pdfExists
@@ -303,9 +300,8 @@ html2pdf verbose args source = do
               removeFile pdfFile
               return res
             else return Nothing
-  let log' = out <> err
   return $ case (exit, mbPdf) of
-             (ExitFailure _, _)      -> Left log'
+             (ExitFailure _, _)      -> Left out
              (ExitSuccess, Nothing)  -> Left ""
              (ExitSuccess, Just pdf) -> Right pdf
 
@@ -341,10 +337,9 @@ context2pdf verbose tmpDir source = inDirectory tmpDir $ do
     putStrLn $ "[makePDF] Contents of " ++ file ++ ":"
     B.readFile file >>= B.putStr
     putStr "\n"
-  (exit, out, err) <- pipeProcess (Just env'') "context" programArgs BL.empty
+  (exit, out) <- pipeProcess (Just env'') "context" programArgs BL.empty
   when verbose $ do
     B.hPutStr stdout out
-    B.hPutStr stderr err
     putStr "\n"
   let pdfFile = replaceExtension file ".pdf"
   pdfExists <- doesFileExist pdfFile
@@ -354,10 +349,9 @@ context2pdf verbose tmpDir source = inDirectory tmpDir $ do
             -- See https://github.com/jgm/pandoc/issues/1192.
             then (Just . B.fromChunks . (:[])) `fmap` BS.readFile pdfFile
             else return Nothing
-  let log' = out <> err
   case (exit, mbPdf) of
        (ExitFailure _, _)      -> do
-          let logmsg = extractConTeXtMsg log'
+          let logmsg = extractConTeXtMsg out
           return $ Left logmsg
        (ExitSuccess, Nothing)  -> return $ Left ""
        (ExitSuccess, Just pdf) -> return $ Right pdf
diff --git a/src/Text/Pandoc/Process.hs b/src/Text/Pandoc/Process.hs
index bc71f1392..294a38a1b 100644
--- a/src/Text/Pandoc/Process.hs
+++ b/src/Text/Pandoc/Process.hs
@@ -42,9 +42,9 @@ Version of 'System.Process.readProcessWithExitCode' that uses lazy bytestrings
 instead of strings and allows setting environment variables.
 
 @readProcessWithExitCode@ creates an external process, reads its
-standard output and standard error strictly, waits until the process
-terminates, and then returns the 'ExitCode' of the process,
-the standard output, and the standard error.
+standard output strictly, waits until the process
+terminates, and then returns the 'ExitCode' of the process
+and the standard output.  stderr is inherited from the parent.
 
 If an asynchronous exception is thrown to the thread executing
 @readProcessWithExitCode@, the forked process will be terminated and
@@ -57,25 +57,21 @@ pipeProcess
     -> FilePath                 -- ^ Filename of the executable (see 'proc' for details)
     -> [String]                 -- ^ any arguments
     -> BL.ByteString            -- ^ standard input
-    -> IO (ExitCode,BL.ByteString,BL.ByteString) -- ^ exitcode, stdout, stderr
+    -> IO (ExitCode,BL.ByteString) -- ^ exitcode, stdout
 pipeProcess mbenv cmd args input =
     mask $ \restore -> do
-      (Just inh, Just outh, Just errh, pid) <- createProcess (proc cmd args)
+      (Just inh, Just outh, Nothing, pid) <- createProcess (proc cmd args)
                                                    { env     = mbenv,
                                                      std_in  = CreatePipe,
                                                      std_out = CreatePipe,
-                                                     std_err = CreatePipe }
+                                                     std_err = Inherit }
       flip onException
-        (do hClose inh; hClose outh; hClose errh;
+        (do hClose inh; hClose outh;
             terminateProcess pid; waitForProcess pid) $ restore $ do
         -- fork off a thread to start consuming stdout
         out <- BL.hGetContents outh
         waitOut <- forkWait $ evaluate $ BL.length out
 
-        -- fork off a thread to start consuming stderr
-        err <- BL.hGetContents errh
-        waitErr <- forkWait $ evaluate $ BL.length err
-
         -- now write and flush any input
         let writeInput = do
               unless (BL.null input) $ do
@@ -87,15 +83,13 @@ pipeProcess mbenv cmd args input =
 
         -- wait on the output
         waitOut
-        waitErr
 
         hClose outh
-        hClose errh
 
         -- wait on the process
         ex <- waitForProcess pid
 
-        return (ex, out, err)
+        return (ex, out)
 
 forkWait :: IO a -> IO (IO a)
 forkWait a = do