Flush stdout after prompt, before parsing response.

cabal-install/src/Distribution/Client/Init/Prompt.hs

@@ -25,6 +25,7 @@ import Prelude hiding (break, putStrLn, getLine, putStr)
 
 import Distribution.Client.Compat.Prelude hiding (break, empty, getLine, putStr, putStrLn)
 import Distribution.Client.Init.Types
+import qualified System.IO
 
 
 -- | Create a prompt with optional default value that returns a
@@ -149,6 +150,7 @@ promptDefault
     -> m t
 promptDefault parse pprint msg def = do
   putStr $ mkDefPrompt msg (pprint <$> def)
+  hFlush System.IO.stdout
   input <- getLine
   case def of
     DefaultPrompt d | null input  -> return d

cabal-install/src/Distribution/Client/Init/Types.hs

@@ -69,6 +69,7 @@ import Distribution.CabalSpecVersion
 import Distribution.Client.Utils as P
 import Distribution.Fields.Pretty
 import Language.Haskell.Extension ( Language(..), Extension )
+import qualified System.IO
 
 import qualified System.Directory as P
 import qualified System.Process as P
@@ -322,6 +323,7 @@ class Monad m => Interactive m where
     copyFile :: FilePath -> FilePath -> m ()
     renameDirectory :: FilePath -> FilePath -> m ()
     message :: Verbosity -> String -> m ()
+    hFlush :: System.IO.Handle -> m ()
 
     -- misc functions
     break :: m Bool
@@ -350,6 +352,7 @@ instance Interactive IO where
     copyFile = P.copyFile
     renameDirectory = P.renameDirectory
     message q = unless (q == silent) . putStrLn
+    hFlush = System.IO.hFlush
 
     break = return False
     throwPrompt = throwM
@@ -382,6 +385,7 @@ instance Interactive PurePrompt where
     copyFile !_ !_ = return ()
     renameDirectory !_ !_ = return ()
     message !_ !_ = return ()
+    hFlush _ = return ()
 
     break = return True
     throwPrompt (BreakException e) = PurePrompt $ \s -> Left $ BreakException