Use stderr for Cabal's diagnostic messages instead of stdout

Cabal/Distribution/Simple/Program/GHC.hs

@@ -566,7 +566,8 @@ 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

@@ -40,6 +40,7 @@ import Distribution.Verbosity
 
 import System.Exit     (ExitCode (..), exitWith)
 import System.FilePath
+import System.IO       (stderr)
 
 import qualified Data.ByteString.Lazy as LBS
 import qualified Data.Map             as Map
@@ -60,7 +61,8 @@ data ProgramInvocation = ProgramInvocation {
        progInvokeCwd   :: Maybe FilePath,
        progInvokeInput :: Maybe IOData,
        progInvokeInputEncoding  :: IOEncoding, -- ^ TODO: remove this, make user decide when constructing 'progInvokeInput'.
-       progInvokeOutputEncoding :: IOEncoding
+       progInvokeOutputEncoding :: IOEncoding,
+       progInvokeOutAsErr :: Bool
      }
 
 data IOEncoding = IOEncodingText   -- locale mode text
@@ -81,7 +83,8 @@ emptyProgramInvocation =
     progInvokeCwd   = Nothing,
     progInvokeInput = Nothing,
     progInvokeInputEncoding  = IOEncodingText,
-    progInvokeOutputEncoding = IOEncodingText
+    progInvokeOutputEncoding = IOEncodingText,
+    progInvokeOutAsErr = False
   }
 
 simpleProgramInvocation :: FilePath -> [String] -> ProgramInvocation
@@ -121,16 +124,20 @@ 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 as FilePath
     , getSearchPath, joinPath, takeDirectory, splitExtension
     , 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 )
@@ -453,7 +453,8 @@ 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
 
@@ -464,7 +465,8 @@ 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.
@@ -473,7 +475,8 @@ 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'
@@ -491,15 +494,17 @@ 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
@@ -510,31 +515,34 @@ 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.
@@ -741,7 +749,7 @@ 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

@@ -17,6 +17,7 @@ import Distribution.Utils.Progress
 import Distribution.Verbosity
 import Distribution.Simple.Utils
 import Text.PrettyPrint
+import System.IO (hPutStrLn, stderr)
 
 type CtxMsg = Doc
 type LogMsg = Doc
@@ -54,7 +55,7 @@ runLogProgress verbosity (LogProgress m) =
       }
     step_fn :: LogMsg -> NoCallStackIO a -> NoCallStackIO a
     step_fn doc go = do
-        putStrLn (render doc)
+        hPutStrLn stderr (render doc)
         go
     fail_fn :: Doc -> NoCallStackIO a
     fail_fn doc = do

cabal-install/Distribution/Client/GenBounds.hs

@@ -43,7 +43,7 @@ import Distribution.Simple.Compiler
 import Distribution.Simple.Program
          ( ProgramDb )
 import Distribution.Simple.Utils
-         ( tryFindPackageDesc )
+         ( notice, tryFindPackageDesc, warn )
 import Distribution.System
          ( Platform )
 import Distribution.Deprecated.Text
@@ -120,13 +120,13 @@ genBounds verbosity packageDBs repoCtxt comp platform progdb mSandboxPkgInfo
     let epd = finalizePD mempty 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) $
                          enabledBuildDepends pd defaultComponentRequestedSpec
 
         if (null needBounds)
-          then putStrLn
+          then notice verbosity
                "Congratulations, all your dependencies have upper bounds!"
           else go needBounds
   where
@@ -135,7 +135,7 @@ 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 )
 
@@ -1230,11 +1230,11 @@ 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