Use stderr for Cabal's diagnostic messages instead of stdout

Send all diagnostic messages (including debug, info, notice) to stderr
instead of stdout.  Likewise, redirect GHC's stdout to stderr as GHC
sends progress output to stdout due to GHC Trac #3636.

Cabal/Distribution/Simple/Program/GHC.hs

@@ -281,7 +281,8 @@ ghcInvocation :: ConfiguredProgram -> Compiler -> Platform -> GhcOptions
               -> ProgramInvocation
 ghcInvocation prog comp platform opts =
     (programInvocation prog (renderGhcOptions comp platform opts)) {
-        progInvokePathEnv = fromNubListR (ghcOptExtraPath opts)
+        progInvokePathEnv = fromNubListR (ghcOptExtraPath opts),
+        progInvokeOutAsErr = True
     }
 
 renderGhcOptions :: Compiler -> Platform -> GhcOptions -> [String]

Cabal/Distribution/Simple/Program/Run.hs

@@ -37,6 +37,7 @@ import Distribution.Compat.Environment
 
 import qualified Data.Map as Map
 import System.FilePath
+import System.IO ( stderr )
 import System.Exit
          ( ExitCode(..), exitWith )
 
@@ -56,7 +57,8 @@ data ProgramInvocation = ProgramInvocation {
        progInvokeCwd   :: Maybe FilePath,
        progInvokeInput :: Maybe String,
        progInvokeInputEncoding  :: IOEncoding,
-       progInvokeOutputEncoding :: IOEncoding
+       progInvokeOutputEncoding :: IOEncoding,
+       progInvokeOutAsErr :: Bool
      }
 
 data IOEncoding = IOEncodingText   -- locale mode text
@@ -76,7 +78,8 @@ emptyProgramInvocation =
     progInvokeCwd   = Nothing,
     progInvokeInput = Nothing,
     progInvokeInputEncoding  = IOEncodingText,
-    progInvokeOutputEncoding = IOEncodingText
+    progInvokeOutputEncoding = IOEncodingText,
+    progInvokeOutAsErr = False
   }
 
 simpleProgramInvocation :: FilePath -> [String] -> ProgramInvocation
@@ -116,16 +119,20 @@ runProgramInvocation verbosity
     progInvokeEnv   = envOverrides,
     progInvokePathEnv = extraPath,
     progInvokeCwd   = mcwd,
-    progInvokeInput = Nothing
+    progInvokeInput = Nothing,
+    progInvokeOutAsErr = outAsErr
   } = do
     pathOverride <- getExtraPathEnv envOverrides extraPath
     menv <- getEffectiveEnvironment (envOverrides ++ pathOverride)
     exitCode <- rawSystemIOWithEnv verbosity
                                    path args
                                    mcwd menv
-                                   Nothing Nothing Nothing
+                                   Nothing childStdout Nothing
     when (exitCode /= ExitSuccess) $
       exitWith exitCode
+  where
+    childStdout | outAsErr  = Just stderr
+                | otherwise = Nothing
 
 runProgramInvocation verbosity
   ProgramInvocation {

Cabal/Distribution/Simple/Utils.hs

@@ -222,8 +222,8 @@ import System.FilePath
     , splitExtension, splitExtensions, splitDirectories
     , searchPathSeparator )
 import System.IO
-    ( Handle, hSetBinaryMode, hGetContents, stderr, stdout, hPutStr, hFlush
-    , hClose, hSetBuffering, BufferMode(..) )
+    ( Handle, hSetBinaryMode, hGetContents, stderr, stdout, hPutStr, hPutStrLn
+    , hFlush, hClose, hSetBuffering, BufferMode(..) )
 import System.IO.Error
 import System.IO.Unsafe
     ( unsafeInterleaveIO )
@@ -466,7 +466,8 @@ notice :: Verbosity -> String -> IO ()
 notice verbosity msg = withFrozenCallStack $ do
   when (verbosity >= normal) $ do
     ts <- getPOSIXTime
-    hPutStr stdout . withMetadata ts NormalMark FlagTrace verbosity
+    hFlush stdout
+    hPutStr stderr . withMetadata ts NormalMark FlagTrace verbosity
                    . wrapTextVerbosity verbosity
                    $ msg
 
@@ -477,7 +478,8 @@ noticeNoWrap :: Verbosity -> String -> IO ()
 noticeNoWrap verbosity msg = withFrozenCallStack $ do
   when (verbosity >= normal) $ do
     ts <- getPOSIXTime
-    hPutStr stdout . withMetadata ts NormalMark FlagTrace verbosity $ msg
+    hFlush stdout
+    hPutStr stderr . withMetadata ts NormalMark FlagTrace verbosity $ msg
 
 -- | Pretty-print a 'Disp.Doc' status message at 'normal' verbosity
 -- level.  Use this if you need fancy formatting.
@@ -486,7 +488,8 @@ noticeDoc :: Verbosity -> Disp.Doc -> IO ()
 noticeDoc verbosity msg = withFrozenCallStack $ do
   when (verbosity >= normal) $ do
     ts <- getPOSIXTime
-    hPutStr stdout . withMetadata ts NormalMark FlagTrace verbosity
+    hFlush stdout
+    hPutStr stderr . withMetadata ts NormalMark FlagTrace verbosity
                    . Disp.renderStyle defaultStyle $ msg
 
 -- | Display a "setup status message".  Prefer using setupMessage'
@@ -504,15 +507,17 @@ info :: Verbosity -> String -> IO ()
 info verbosity msg = withFrozenCallStack $
   when (verbosity >= verbose) $ do
     ts <- getPOSIXTime
-    hPutStr stdout . withMetadata ts NeverMark FlagTrace verbosity
+    hFlush stdout
+    hPutStr stderr . withMetadata ts NeverMark FlagTrace verbosity
                    . wrapTextVerbosity verbosity
                    $ msg
 
 infoNoWrap :: Verbosity -> String -> IO ()
 infoNoWrap verbosity msg = withFrozenCallStack $
   when (verbosity >= verbose) $ do
     ts <- getPOSIXTime
-    hPutStr stdout . withMetadata ts NeverMark FlagTrace verbosity
+    hFlush stdout
+    hPutStr stderr . withMetadata ts NeverMark FlagTrace verbosity
                    $ msg
 
 -- | Detailed internal debugging information
@@ -523,31 +528,34 @@ debug :: Verbosity -> String -> IO ()
 debug verbosity msg = withFrozenCallStack $
   when (verbosity >= deafening) $ do
     ts <- getPOSIXTime
-    hPutStr stdout . withMetadata ts NeverMark FlagTrace verbosity
+    hFlush stdout
+    hPutStr stderr . withMetadata ts NeverMark FlagTrace verbosity
                    . wrapTextVerbosity verbosity
                    $ msg
     -- ensure that we don't lose output if we segfault/infinite loop
-    hFlush stdout
+    hFlush stderr
 
 -- | A variant of 'debug' that doesn't perform the automatic line
 -- wrapping. Produces better output in some cases.
 debugNoWrap :: Verbosity -> String -> IO ()
 debugNoWrap verbosity msg = withFrozenCallStack $
   when (verbosity >= deafening) $ do
     ts <- getPOSIXTime
-    hPutStr stdout . withMetadata ts NeverMark FlagTrace verbosity
+    hFlush stdout
+    hPutStr stderr . withMetadata ts NeverMark FlagTrace verbosity
                    $ msg
     -- ensure that we don't lose output if we segfault/infinite loop
-    hFlush stdout
+    hFlush stderr
 
 -- | Perform an IO action, catching any IO exceptions and printing an error
 --   if one occurs.
 chattyTry :: String  -- ^ a description of the action we were attempting
           -> IO ()   -- ^ the action itself
           -> IO ()
 chattyTry desc action =
-  catchIO action $ \exception ->
-    putStrLn $ "Error while " ++ desc ++ ": " ++ show exception
+  catchIO action $ \exception -> do
+    hFlush stdout
+    hPutStrLn stderr $ "Error while " ++ desc ++ ": " ++ show exception
 
 -- | Run an IO computation, returning @e@ if it raises a "file
 -- does not exist" error.
@@ -754,7 +762,7 @@ rawSystemExitWithEnv verbosity path args env = withFrozenCallStack $ do
         debug verbosity $ path ++ " returned " ++ show exitcode
         exitWith exitcode
 
--- Closes the passed in handles before returning.
+-- Closes the passed in handles before returning (excluding standard handles).
 rawSystemIOWithEnv :: Verbosity
                    -> FilePath
                    -> [String]

Cabal/Distribution/Utils/LogProgress.hs

@@ -54,7 +54,7 @@ runLogProgress verbosity (LogProgress m) =
       }
     step_fn :: LogMsg -> NoCallStackIO a -> NoCallStackIO a
     step_fn doc go = do
-        putStrLn (render doc)
+        notice verbosity (render doc)
         go
     fail_fn :: Doc -> NoCallStackIO a
     fail_fn doc = do

cabal-install/Distribution/Client/GenBounds.hs

@@ -39,7 +39,7 @@ import Distribution.Simple.Compiler
 import Distribution.Simple.Program
          ( ProgramDb )
 import Distribution.Simple.Utils
-         ( tryFindPackageDesc )
+         ( notice, tryFindPackageDesc, warn )
 import Distribution.System
          ( Platform )
 import Distribution.Text
@@ -116,13 +116,13 @@ genBounds verbosity packageDBs repoCtxt comp platform progdb mSandboxPkgInfo
     let epd = finalizePD [] defaultComponentRequestedSpec
                     (const True) platform cinfo [] gpd
     case epd of
-      Left _ -> putStrLn "finalizePD failed"
+      Left _ -> warn verbosity "finalizePD failed"
       Right (pd,_) -> do
         let needBounds = filter (not . hasUpperBound . depVersion) $
                          buildDepends pd
 
         if (null needBounds)
-          then putStrLn
+          then notice verbosity
                "Congratulations, all your dependencies have upper bounds!"
           else go needBounds
   where
@@ -131,7 +131,7 @@ genBounds verbosity packageDBs repoCtxt comp platform progdb mSandboxPkgInfo
                   verbosity packageDBs repoCtxt comp platform progdb
                   mSandboxPkgInfo globalFlags freezeFlags
 
-       putStrLn boundsNeededMsg
+       notice verbosity boundsNeededMsg
 
        let isNeeded pkg = unPackageName (packageName pkg)
                           `elem` map depName needBounds

cabal-install/Distribution/Client/Install.hs

@@ -56,7 +56,7 @@ import System.Directory
 import System.FilePath
          ( (</>), (<.>), equalFilePath, takeDirectory )
 import System.IO
-         ( openFile, IOMode(AppendMode), hClose )
+         ( openFile, IOMode(AppendMode), hPutStr, hClose, stderr )
 import System.IO.Error
          ( isDoesNotExistError, ioeGetFileName )
 
@@ -1206,11 +1206,11 @@ executeInstallPlan verbosity jobCtl keepGoing useLogFile plan0 installPkg =
               Nothing                 -> return ()
               Just (mkLogFileName, _) -> do
                 let logName = mkLogFileName pkgid uid
-                putStr $ "Build log ( " ++ logName ++ " ):\n"
+                hPutStr stderr $ "Build log ( " ++ logName ++ " ):\n"
                 printFile logName
 
     printFile :: FilePath -> IO ()
-    printFile path = readFile path >>= putStr
+    printFile path = readFile path >>= hPutStr stderr
 
 -- | Call an installer for an 'SourcePackage' but override the configure
 -- flags with the ones given by the 'ReadyPackage'. In particular the