IHaskell.Eval.Evaluate: handle multiline input correctly

src/IHaskell/Eval/Evaluate.hs

@@ -692,13 +692,12 @@ evalCommand publish (Directive ShellCmd cmd) state = wrapExecution state $
             mExitCode <- getProcessExitCode process
             case mExitCode of
               Nothing -> do
-                -- Process still running
-                next <- readChars pipe "" maxSize
-                modifyMVar_ outputAccum (return . (++ next))
                 -- Write to frontend and repeat.
                 readMVar outputAccum >>= output
                 loop
               Just exitCode -> do
+                next <- readChars pipe "" maxSize
+                modifyMVar_ outputAccum (return . (++ next))
                 out <- readMVar outputAccum
                 case exitCode of
                   ExitSuccess -> return $ Display [plain out]

src/tests/IHaskell/Test/Eval.hs

@@ -157,6 +157,9 @@ testEval =
       "putStrLn \"Héllö, Üñiço∂e!\"" `becomes` ["Héllö, Üñiço∂e!"]
       "putStrLn \"Привет!\"" `becomes` ["Привет!"]
 
+    it "prints multiline output correctly" $ do
+      ":! printf \"hello\\nworld\"" `becomes` ["hello\nworld"]
+
     it "evaluates directives" $ do
 #if MIN_VERSION_ghc(8,2,0)
       -- It's `p` instead of `t` for some reason