From 445d092a497add1f2f58be119255067be91932af Mon Sep 17 00:00:00 2001
From: Max Ulidtko <ulidtko@gmail.com>
Date: Sun, 27 Apr 2025 19:36:08 +0200
Subject: [PATCH 01/13] tests: chmod +x on test scripts

---
 tests/integration/run-single-test.sh | 0
 tests/integration/run-sort-tests.sh  | 0
 2 files changed, 0 insertions(+), 0 deletions(-)
 mode change 100644 => 100755 tests/integration/run-single-test.sh
 mode change 100644 => 100755 tests/integration/run-sort-tests.sh

diff --git a/tests/integration/run-single-test.sh b/tests/integration/run-single-test.sh
old mode 100644
new mode 100755
diff --git a/tests/integration/run-sort-tests.sh b/tests/integration/run-sort-tests.sh
old mode 100644
new mode 100755

From f68fc0f6434f477907034c37efbe1601c04166f1 Mon Sep 17 00:00:00 2001
From: Max Ulidtko <ulidtko@gmail.com>
Date: Sun, 27 Apr 2025 20:28:06 +0200
Subject: [PATCH 02/13] tests: fix missed -ignore-dot-ghci

---
 tests/integration/tests/3926-ghci-with-sublibraries/Main.hs | 2 +-
 tests/integration/tests/4270-files-order/Main.hs            | 2 +-
 tests/integration/tests/module-added-multiple-times/Main.hs | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs b/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs
index df43dd9891..ff3eb3c148 100644
--- a/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs
+++ b/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs
@@ -18,7 +18,7 @@ main
       replThread
 
 replThread :: IO ()
-replThread = repl [] $ do
+replThread = repl ["--ghci-options=-ignore-dot-ghci"] $ do
   -- The command must be issued before searching the output for the next prompt,
   -- otherwise, on Windows from msys2-20230526, `stack repl` encounters a EOF
   -- and terminates gracefully.
diff --git a/tests/integration/tests/4270-files-order/Main.hs b/tests/integration/tests/4270-files-order/Main.hs
index 4219d3ae7c..ee8479b2f0 100644
--- a/tests/integration/tests/4270-files-order/Main.hs
+++ b/tests/integration/tests/4270-files-order/Main.hs
@@ -4,7 +4,7 @@ import StackTest
 main :: IO ()
 main = do
   stack ["build"]
-  repl [] $ do
+  repl ["--ghci-options=-ignore-dot-ghci"] $ do
     -- The command must be issued before searching the output for the next
     -- prompt, otherwise, on Windows from msys2-20230526, `stack repl`
     -- encounters a EOF and terminates gracefully.
diff --git a/tests/integration/tests/module-added-multiple-times/Main.hs b/tests/integration/tests/module-added-multiple-times/Main.hs
index d2745cffa3..f9134e62d1 100644
--- a/tests/integration/tests/module-added-multiple-times/Main.hs
+++ b/tests/integration/tests/module-added-multiple-times/Main.hs
@@ -3,7 +3,7 @@ import Data.List
 import StackTest
 
 main :: IO ()
-main = repl [] $ do
+main = repl ["--ghci-options=-ignore-dot-ghci"] $ do
   -- The command must be issued before searching the output for the next prompt,
   -- otherwise, on Windows from msys2-20230526, `stack repl` encounters a EOF
   -- and terminates gracefully.

From 8e99af9dc937e647718f680e30ac07af3683b953 Mon Sep 17 00:00:00 2001
From: Max Ulidtko <ulidtko@gmail.com>
Date: Sun, 27 Apr 2025 20:43:43 +0200
Subject: [PATCH 03/13] tests(3926): fix test [on linux]

---
 tests/integration/lib/StackTest.hs            | 22 +++++++++++--------
 .../tests/3926-ghci-with-sublibraries/Main.hs | 18 +++++----------
 2 files changed, 18 insertions(+), 22 deletions(-)

diff --git a/tests/integration/lib/StackTest.hs b/tests/integration/lib/StackTest.hs
index b279bd0f08..ac571fd9e5 100644
--- a/tests/integration/lib/StackTest.hs
+++ b/tests/integration/lib/StackTest.hs
@@ -51,7 +51,9 @@ module StackTest
 
 import           Control.Monad ( forever, unless, void, when )
 import           Control.Monad.IO.Class ( liftIO )
-import           Control.Monad.Trans.Reader ( ReaderT, ask, runReaderT )
+import           Control.Monad.Trans.Reader ( ReaderT, ask, asks, runReaderT )
+import qualified Control.Monad.Trans.State as State
+import           Control.Monad.Trans ( lift )
 import           Control.Concurrent ( forkIO )
 import           Control.Exception
                    ( Exception (..), IOException, bracket_, catch, throw
@@ -157,14 +159,16 @@ data ReplConnection = ReplConnection
   }
 
 nextPrompt :: Repl ()
-nextPrompt = do
-  (ReplConnection _ replStdoutHandle) <- ask
-  c <- liftIO $ hGetChar replStdoutHandle
-  if c == '>'
-    then do
-      -- Skip next character
-      void $ liftIO $ hGetChar replStdoutHandle
-    else nextPrompt
+nextPrompt = State.evalStateT poll "" where
+  poll = do
+    c <- lift (asks replStdout) >>= liftIO . hGetChar
+    State.modify (++ [c]) -- FIXME crap perf
+    when (c == '\n') $ do
+      State.get >>= liftIO . putStr . ("ghci> " <>)
+      State.put ""
+    buf <- State.get
+    unless (buf == "ghci> ")
+      poll
 
 replCommand :: String -> Repl ()
 replCommand cmd = do
diff --git a/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs b/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs
index ff3eb3c148..b887697f87 100644
--- a/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs
+++ b/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs
@@ -1,4 +1,3 @@
-import Control.Concurrent
 import Control.Monad.IO.Class
 import Control.Monad
 import Data.List
@@ -14,7 +13,6 @@ main
       copy "src/Lib.v1" "src/Lib.hs"
       copy "src-internal/Internal.v1" "src-internal/Internal.hs"
       stack ["build"] -- need a build before ghci at the moment, see #4148
-      forkIO fileEditingThread
       replThread
 
 replThread :: IO ()
@@ -23,7 +21,9 @@ replThread = repl ["--ghci-options=-ignore-dot-ghci"] $ do
   -- otherwise, on Windows from msys2-20230526, `stack repl` encounters a EOF
   -- and terminates gracefully.
   replCommand ":main"
+  liftIO $ putStrLn "Awaiting prompt..."
   nextPrompt
+  liftIO $ putStrLn "Initial prompt received"
   line <- replGetLine
   let expected = "hello world"
   when (line /= expected) $
@@ -31,25 +31,17 @@ replThread = repl ["--ghci-options=-ignore-dot-ghci"] $ do
          "Main module didn't load correctly.\n"
       <> "Expected: " <> expected <> "\n"
       <> "Actual  : " <> line <> "\n"
-  liftIO $ threadDelay 1000000 -- wait for an edit of the internal library
+  liftIO $ copy "src-internal/Internal.v2" "src-internal/Internal.hs"
   reloadAndTest "testInt" "42" "Internal library didn't reload."
-  liftIO $ threadDelay 1000000 -- wait for an edit of the internal library
+  liftIO $ copy "src/Lib.v2" "src/Lib.hs"
   reloadAndTest "testStr" "\"OK\"" "Main library didn't reload."
 
-fileEditingThread :: IO ()
-fileEditingThread = do
-  threadDelay 1000000
-  -- edit the internal library and pure to ghci
-  copy "src-internal/Internal.v2" "src-internal/Internal.hs"
-  threadDelay 1000000
-  -- edit the internal library and end thread, returning to ghci
-  copy "src/Lib.v2" "src/Lib.hs"
-
 reloadAndTest :: String -> String -> String -> Repl ()
 reloadAndTest cmd exp err = do
   reload
   replCommand cmd
   line <- replGetLine
+  liftIO . putStrLn $ line
   unless (exp `isSuffixOf` line) $ error err
 
 reload :: Repl ()

From 007da91a0441bfea16435acaabeee08fd84265e7 Mon Sep 17 00:00:00 2001
From: Max Ulidtko <ulidtko@gmail.com>
Date: Fri, 16 May 2025 15:18:10 +0200
Subject: [PATCH 04/13] refactor: split off StackTest.Repl

---
 stack.cabal                                   |   1 +
 tests/integration/lib/StackTest.hs            |  96 +---------------
 tests/integration/lib/StackTest/Repl.hs       | 104 ++++++++++++++++++
 .../tests/3926-ghci-with-sublibraries/Main.hs |   1 +
 .../tests/4270-files-order/Main.hs            |   1 +
 .../tests/module-added-multiple-times/Main.hs |   3 +-
 6 files changed, 113 insertions(+), 93 deletions(-)
 create mode 100644 tests/integration/lib/StackTest/Repl.hs

diff --git a/stack.cabal b/stack.cabal
index d333e1291b..b7aab690b1 100644
--- a/stack.cabal
+++ b/stack.cabal
@@ -629,6 +629,7 @@ executable stack-integration-test
   main-is: IntegrationSpec.hs
   other-modules:
       StackTest
+      StackTest.Repl
       Paths_stack
   autogen-modules:
       Paths_stack
diff --git a/tests/integration/lib/StackTest.hs b/tests/integration/lib/StackTest.hs
index ac571fd9e5..e19838ed4c 100644
--- a/tests/integration/lib/StackTest.hs
+++ b/tests/integration/lib/StackTest.hs
@@ -13,14 +13,6 @@ module StackTest
   , stackCleanFull
   , stackIgnoreException
   , stackErr
-  , Repl
-  , ReplConnection (..)
-  , nextPrompt
-  , replCommand
-  , replGetChar
-  , replGetLine
-  , runRepl
-  , repl
   , stackStderr
   , stackCheckStderr
   , stackErrStderr
@@ -49,17 +41,11 @@ module StackTest
   , superslow
   ) where
 
-import           Control.Monad ( forever, unless, void, when )
-import           Control.Monad.IO.Class ( liftIO )
-import           Control.Monad.Trans.Reader ( ReaderT, ask, asks, runReaderT )
-import qualified Control.Monad.Trans.State as State
-import           Control.Monad.Trans ( lift )
-import           Control.Concurrent ( forkIO )
+import           Control.Monad ( unless, void, when )
 import           Control.Exception
-                   ( Exception (..), IOException, bracket_, catch, throw
+                   ( Exception (..), IOException, bracket_, catch
                    , throwIO
                    )
-import           Data.Maybe ( fromMaybe )
 import           GHC.Stack ( HasCallStack )
 import           System.Environment ( getEnv, lookupEnv )
 import           System.Directory
@@ -68,14 +54,12 @@ import           System.Directory
                    , setCurrentDirectory
                    )
 import           System.IO
-                   ( BufferMode (..), Handle, IOMode (..), hGetChar, hGetLine
-                   , hPutChar, hPutStr, hPutStrLn, hSetBuffering, stderr
-                   , withFile
+                   ( hPutStr, hPutStrLn, stderr
                    )
 import           System.IO.Error
-                   ( isDoesNotExistError, isEOFError )
+                   ( isDoesNotExistError )
 import           System.Process
-                   ( CreateProcess (..), StdStream (..), createProcess, proc
+                   ( CreateProcess (..), createProcess, proc
                    , readCreateProcessWithExitCode, readProcessWithExitCode
                    , shell, waitForProcess
                    )
@@ -151,76 +135,6 @@ stackErr args = do
   ec <- stack' args
   when (ec == ExitSuccess) $ error "stack was supposed to fail, but didn't"
 
-type Repl = ReaderT ReplConnection IO
-
-data ReplConnection = ReplConnection
-  { replStdin  :: Handle
-  , replStdout :: Handle
-  }
-
-nextPrompt :: Repl ()
-nextPrompt = State.evalStateT poll "" where
-  poll = do
-    c <- lift (asks replStdout) >>= liftIO . hGetChar
-    State.modify (++ [c]) -- FIXME crap perf
-    when (c == '\n') $ do
-      State.get >>= liftIO . putStr . ("ghci> " <>)
-      State.put ""
-    buf <- State.get
-    unless (buf == "ghci> ")
-      poll
-
-replCommand :: String -> Repl ()
-replCommand cmd = do
-  (ReplConnection replStdinHandle _) <- ask
-  liftIO $ hPutStrLn replStdinHandle cmd
-
-replGetLine :: Repl String
-replGetLine = ask >>= liftIO . hGetLine . replStdout
-
-replGetChar :: Repl Char
-replGetChar = ask >>= liftIO . hGetChar . replStdout
-
-runRepl ::
-     HasCallStack
-  => FilePath
-  -> [String]
-  -> ReaderT ReplConnection IO ()
-  -> IO ExitCode
-runRepl cmd args actions = do
-  logInfo $ "Running: " ++ cmd ++ " " ++ unwords (map showProcessArgDebug args)
-  (Just rStdin, Just rStdout, Just rStderr, ph) <-
-    createProcess (proc cmd args)
-      { std_in = CreatePipe
-      , std_out = CreatePipe
-      , std_err = CreatePipe
-      }
-  hSetBuffering rStdin NoBuffering
-  hSetBuffering rStdout NoBuffering
-  hSetBuffering rStderr NoBuffering
-  -- Log stack repl's standard error output
-  tempDir <- if isWindows
-                then fromMaybe "" <$> lookupEnv "TEMP"
-                else pure "/tmp"
-  let tempLogFile = tempDir ++ "/stderr"
-  _ <- forkIO $ withFile tempLogFile WriteMode $ \logFileHandle -> do
-    hSetBuffering logFileHandle NoBuffering
-    forever $
-      catch
-        (hGetChar rStderr >>= hPutChar logFileHandle)
-        (\e -> unless (isEOFError e) $ throw e)
-  runReaderT actions (ReplConnection rStdin rStdout)
-  waitForProcess ph
-
-repl :: HasCallStack => [String] -> Repl () -> IO ()
-repl args action = do
-  stackExe' <- stackExe
-  ec <- runRepl stackExe' ("repl":args) action
-  unless (ec == ExitSuccess) $ pure ()
-  -- TODO: Understand why the exit code is 1 despite running GHCi tests
-  -- successfully.
-  -- else error $ "Exited with exit code: " ++ show ec
-
 stackStderr :: HasCallStack => [String] -> IO (ExitCode, String)
 stackStderr args = do
   stackExe' <- stackExe
diff --git a/tests/integration/lib/StackTest/Repl.hs b/tests/integration/lib/StackTest/Repl.hs
new file mode 100644
index 0000000000..e0b5d7ca8b
--- /dev/null
+++ b/tests/integration/lib/StackTest/Repl.hs
@@ -0,0 +1,104 @@
+{- |
+Integration-test helpers & fixtures for testing `stack repl`
+-}
+module StackTest.Repl
+    ( Repl
+    , ReplConnection (..)
+    , nextPrompt
+    , repl
+    , replCommand
+    , replGetLine
+    ) where
+
+import Control.Concurrent (forkIO)
+import Control.Exception (throw, catch)
+import Control.Monad (forever, unless, when)
+import Control.Monad.IO.Class (liftIO)
+import Data.Maybe (fromMaybe)
+import GHC.Stack (HasCallStack)
+import System.Environment (lookupEnv)
+import System.Exit (ExitCode (..))
+import System.IO
+    ( BufferMode (NoBuffering), Handle, IOMode (WriteMode)
+    , hGetChar, hGetLine, hPutChar, hPutStrLn, hSetBuffering
+    , withFile
+    )
+import System.IO.Error (isEOFError)
+
+import Control.Monad.Trans (lift)
+import Control.Monad.Trans.Reader
+import Control.Monad.Trans.State qualified as State
+import System.Process
+    ( CreateProcess (std_err, std_in, std_out)
+    , StdStream (CreatePipe)
+    , createProcess, proc, waitForProcess
+    )
+
+import StackTest
+
+type Repl = ReaderT ReplConnection IO
+
+data ReplConnection = ReplConnection
+  { replStdin  :: Handle
+  , replStdout :: Handle
+  }
+
+nextPrompt :: Repl ()
+nextPrompt = State.evalStateT poll "" where
+  poll = do
+    c <- lift (asks replStdout) >>= liftIO . hGetChar
+    State.modify (++ [c]) -- FIXME crap perf
+    when (c == '\n') $ do
+      State.get >>= liftIO . putStr . ("ghci> " <>)
+      State.put ""
+    buf <- State.get
+    unless (buf == "ghci> ")
+      poll
+
+replCommand :: String -> Repl ()
+replCommand cmd = do
+  (ReplConnection replStdinHandle _) <- ask
+  liftIO $ hPutStrLn replStdinHandle cmd
+
+replGetLine :: Repl String
+replGetLine = ask >>= liftIO . hGetLine . replStdout
+
+runRepl
+  :: HasCallStack
+  => FilePath
+  -> [String]
+  -> ReaderT ReplConnection IO ()
+  -> IO ExitCode
+runRepl cmd args actions = do
+  logInfo $ "Running: " ++ cmd ++ " " ++ unwords (map showProcessArgDebug args)
+  (Just rStdin, Just rStdout, Just rStderr, ph) <-
+    createProcess (proc cmd args)
+      { std_in = CreatePipe
+      , std_out = CreatePipe
+      , std_err = CreatePipe
+      }
+  hSetBuffering rStdin NoBuffering
+  hSetBuffering rStdout NoBuffering
+  hSetBuffering rStderr NoBuffering
+  -- Log stack repl's standard error output
+  tempDir <- if isWindows
+                then fromMaybe "" <$> lookupEnv "TEMP"
+                else pure "/tmp"
+  let tempLogFile = tempDir ++ "/stderr"
+  _ <- forkIO $ withFile tempLogFile WriteMode $ \logFileHandle -> do
+    --hSetBuffering logFileHandle NoBuffering
+    forever $
+      catch
+        (hGetChar rStderr >>= hPutChar logFileHandle)
+        (\e -> unless (isEOFError e) $ throw e)
+  runReaderT actions (ReplConnection rStdin rStdout)
+  waitForProcess ph
+
+repl :: HasCallStack => [String] -> Repl () -> IO ()
+repl args action = do
+  stackExe' <- stackExe
+  ec <- runRepl stackExe' ("repl":args) action
+  unless (ec == ExitSuccess) $ pure ()
+  -- TODO: Understand why the exit code is 1 despite running GHCi tests
+  -- successfully.
+  -- else error $ "Exited with exit code: " ++ show ec
diff --git a/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs b/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs
index b887697f87..882c8f3bdb 100644
--- a/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs
+++ b/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs
@@ -2,6 +2,7 @@ import Control.Monad.IO.Class
 import Control.Monad
 import Data.List
 import StackTest
+import StackTest.Repl
 
 main :: IO ()
 main
diff --git a/tests/integration/tests/4270-files-order/Main.hs b/tests/integration/tests/4270-files-order/Main.hs
index ee8479b2f0..02d224faba 100644
--- a/tests/integration/tests/4270-files-order/Main.hs
+++ b/tests/integration/tests/4270-files-order/Main.hs
@@ -1,5 +1,6 @@
 import Control.Monad
 import StackTest
+import StackTest.Repl
 
 main :: IO ()
 main = do
diff --git a/tests/integration/tests/module-added-multiple-times/Main.hs b/tests/integration/tests/module-added-multiple-times/Main.hs
index f9134e62d1..eb762ee8bb 100644
--- a/tests/integration/tests/module-added-multiple-times/Main.hs
+++ b/tests/integration/tests/module-added-multiple-times/Main.hs
@@ -1,6 +1,5 @@
 import Control.Monad
-import Data.List
-import StackTest
+import StackTest.Repl
 
 main :: IO ()
 main = repl ["--ghci-options=-ignore-dot-ghci"] $ do

From a123a289113b324737030f3b5b24a39ab224ff8c Mon Sep 17 00:00:00 2001
From: Max Ulidtko <ulidtko@gmail.com>
Date: Fri, 16 May 2025 15:32:13 +0200
Subject: [PATCH 05/13] refactor: move -ignore-dot-ghci to repl fixture

---
 tests/integration/lib/StackTest/Repl.hs                     | 2 +-
 tests/integration/tests/3926-ghci-with-sublibraries/Main.hs | 2 +-
 tests/integration/tests/4270-files-order/Main.hs            | 2 +-
 tests/integration/tests/module-added-multiple-times/Main.hs | 2 +-
 4 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/tests/integration/lib/StackTest/Repl.hs b/tests/integration/lib/StackTest/Repl.hs
index e0b5d7ca8b..25c666904b 100644
--- a/tests/integration/lib/StackTest/Repl.hs
+++ b/tests/integration/lib/StackTest/Repl.hs
@@ -97,7 +97,7 @@ runRepl cmd args actions = do
 repl :: HasCallStack => [String] -> Repl () -> IO ()
 repl args action = do
   stackExe' <- stackExe
-  ec <- runRepl stackExe' ("repl":args) action
+  ec <- runRepl stackExe' ("repl" : "--ghci-options=-ignore-dot-ghci" : args) action
   unless (ec == ExitSuccess) $ pure ()
   -- TODO: Understand why the exit code is 1 despite running GHCi tests
   -- successfully.
diff --git a/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs b/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs
index 882c8f3bdb..c9f64ac4c7 100644
--- a/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs
+++ b/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs
@@ -17,7 +17,7 @@ main
       replThread
 
 replThread :: IO ()
-replThread = repl ["--ghci-options=-ignore-dot-ghci"] $ do
+replThread = repl [] $ do
   -- The command must be issued before searching the output for the next prompt,
   -- otherwise, on Windows from msys2-20230526, `stack repl` encounters a EOF
   -- and terminates gracefully.
diff --git a/tests/integration/tests/4270-files-order/Main.hs b/tests/integration/tests/4270-files-order/Main.hs
index 02d224faba..34e9669b86 100644
--- a/tests/integration/tests/4270-files-order/Main.hs
+++ b/tests/integration/tests/4270-files-order/Main.hs
@@ -5,7 +5,7 @@ import StackTest.Repl
 main :: IO ()
 main = do
   stack ["build"]
-  repl ["--ghci-options=-ignore-dot-ghci"] $ do
+  repl [] $ do
     -- The command must be issued before searching the output for the next
     -- prompt, otherwise, on Windows from msys2-20230526, `stack repl`
     -- encounters a EOF and terminates gracefully.
diff --git a/tests/integration/tests/module-added-multiple-times/Main.hs b/tests/integration/tests/module-added-multiple-times/Main.hs
index eb762ee8bb..41397416cc 100644
--- a/tests/integration/tests/module-added-multiple-times/Main.hs
+++ b/tests/integration/tests/module-added-multiple-times/Main.hs
@@ -2,7 +2,7 @@ import Control.Monad
 import StackTest.Repl
 
 main :: IO ()
-main = repl ["--ghci-options=-ignore-dot-ghci"] $ do
+main = repl [] $ do
   -- The command must be issued before searching the output for the next prompt,
   -- otherwise, on Windows from msys2-20230526, `stack repl` encounters a EOF
   -- and terminates gracefully.

From 609205c0d9f255706c06d3680e93931e04d308fe Mon Sep 17 00:00:00 2001
From: Max Ulidtko <ulidtko@gmail.com>
Date: Fri, 16 May 2025 19:28:57 +0200
Subject: [PATCH 06/13] fix: resolve a TODO about unexpected exit code 1

runRepl was missing the `hClose rStdin` call -- causing the ghci
subprocess to terminate abnormally with EPIPE on its stdin read.
---
 tests/integration/lib/StackTest/Repl.hs | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/tests/integration/lib/StackTest/Repl.hs b/tests/integration/lib/StackTest/Repl.hs
index 25c666904b..b9ea6073e7 100644
--- a/tests/integration/lib/StackTest/Repl.hs
+++ b/tests/integration/lib/StackTest/Repl.hs
@@ -19,8 +19,8 @@ import GHC.Stack (HasCallStack)
 import System.Environment (lookupEnv)
 import System.Exit (ExitCode (..))
 import System.IO
-    ( BufferMode (NoBuffering), Handle, IOMode (WriteMode)
-    , hGetChar, hGetLine, hPutChar, hPutStrLn, hSetBuffering
+    ( BufferMode (NoBuffering, LineBuffering), Handle, IOMode (WriteMode)
+    , hClose, hGetChar, hGetLine, hPutChar, hPutStrLn, hSetBuffering
     , withFile
     )
 import System.IO.Error (isEOFError)
@@ -67,7 +67,7 @@ runRepl
   :: HasCallStack
   => FilePath
   -> [String]
-  -> ReaderT ReplConnection IO ()
+  -> Repl ()
   -> IO ExitCode
 runRepl cmd args actions = do
   logInfo $ "Running: " ++ cmd ++ " " ++ unwords (map showProcessArgDebug args)
@@ -77,7 +77,7 @@ runRepl cmd args actions = do
       , std_out = CreatePipe
       , std_err = CreatePipe
       }
-  hSetBuffering rStdin NoBuffering
+  hSetBuffering rStdin LineBuffering
   hSetBuffering rStdout NoBuffering
   hSetBuffering rStderr NoBuffering
   -- Log stack repl's standard error output
@@ -91,14 +91,18 @@ runRepl cmd args actions = do
       catch
         (hGetChar rStderr >>= hPutChar logFileHandle)
         (\e -> unless (isEOFError e) $ throw e)
+
+  -- run the test script which is to talk to the GHCi subprocess.
   runReaderT actions (ReplConnection rStdin rStdout)
+
+  -- once done with the test, signal EOF on stdin for clean termination of ghci
+  hClose rStdin
+  -- read out the exit-code
   waitForProcess ph
 
 repl :: HasCallStack => [String] -> Repl () -> IO ()
 repl args action = do
   stackExe' <- stackExe
   ec <- runRepl stackExe' ("repl" : "--ghci-options=-ignore-dot-ghci" : args) action
-  unless (ec == ExitSuccess) $ pure ()
-  -- TODO: Understand why the exit code is 1 despite running GHCi tests
-  -- successfully.
-  -- else error $ "Exited with exit code: " ++ show ec
+  unless (ec == ExitSuccess) $
+    error $ "GHCi exited with " <> show ec

From 368a0e7c4ceaedbb1fb216c11af6e591b9cddcfb Mon Sep 17 00:00:00 2001
From: Max Ulidtko <ulidtko@gmail.com>
Date: Fri, 16 May 2025 20:22:28 +0200
Subject: [PATCH 07/13] tests: redirect stderr, instead of shuffling bytes
 one-by-one

---
 tests/integration/lib/StackTest/Repl.hs | 62 ++++++++++++-------------
 1 file changed, 31 insertions(+), 31 deletions(-)

diff --git a/tests/integration/lib/StackTest/Repl.hs b/tests/integration/lib/StackTest/Repl.hs
index b9ea6073e7..344d3ea89b 100644
--- a/tests/integration/lib/StackTest/Repl.hs
+++ b/tests/integration/lib/StackTest/Repl.hs
@@ -10,27 +10,24 @@ module StackTest.Repl
     , replGetLine
     ) where
 
-import Control.Concurrent (forkIO)
-import Control.Exception (throw, catch)
-import Control.Monad (forever, unless, when)
+import Control.Monad (unless, when)
 import Control.Monad.IO.Class (liftIO)
 import Data.Maybe (fromMaybe)
 import GHC.Stack (HasCallStack)
 import System.Environment (lookupEnv)
 import System.Exit (ExitCode (..))
 import System.IO
-    ( BufferMode (NoBuffering, LineBuffering), Handle, IOMode (WriteMode)
-    , hClose, hGetChar, hGetLine, hPutChar, hPutStrLn, hSetBuffering
-    , withFile
+    ( BufferMode (NoBuffering, LineBuffering), Handle
+    , hClose, hGetChar, hGetLine, hPutStrLn, hSetBuffering
+    , openTempFile
     )
-import System.IO.Error (isEOFError)
 
 import Control.Monad.Trans (lift)
 import Control.Monad.Trans.Reader
 import Control.Monad.Trans.State qualified as State
 import System.Process
     ( CreateProcess (std_err, std_in, std_out)
-    , StdStream (CreatePipe)
+    , StdStream (CreatePipe, UseHandle)
     , createProcess, proc, waitForProcess
     )
 
@@ -43,6 +40,16 @@ data ReplConnection = ReplConnection
   , replStdout :: Handle
   }
 
+replCommand :: String -> Repl ()
+replCommand cmd = do
+  (ReplConnection replStdinHandle _) <- ask
+  -- echo what we send to the test's stdout
+  liftIO . putStrLn $ "____> " <> cmd
+  liftIO $ hPutStrLn replStdinHandle cmd
+
+replGetLine :: Repl String
+replGetLine = ask >>= liftIO . hGetLine . replStdout
+
 nextPrompt :: Repl ()
 nextPrompt = State.evalStateT poll "" where
   poll = do
@@ -55,14 +62,6 @@ nextPrompt = State.evalStateT poll "" where
     unless (buf == "ghci> ")
       poll
 
-replCommand :: String -> Repl ()
-replCommand cmd = do
-  (ReplConnection replStdinHandle _) <- ask
-  liftIO $ hPutStrLn replStdinHandle cmd
-
-replGetLine :: Repl String
-replGetLine = ask >>= liftIO . hGetLine . replStdout
-
 runRepl
   :: HasCallStack
   => FilePath
@@ -70,27 +69,21 @@ runRepl
   -> Repl ()
   -> IO ExitCode
 runRepl cmd args actions = do
-  logInfo $ "Running: " ++ cmd ++ " " ++ unwords (map showProcessArgDebug args)
-  (Just rStdin, Just rStdout, Just rStderr, ph) <-
+  (stderrBufPath, stderrBufHandle) <- openTempStderrBufferFile
+  hSetBuffering stderrBufHandle NoBuffering
+
+  logInfo $ "Running: " ++ cmd ++ " " ++ unwords (map showProcessArgDebug args) ++ "\n\
+            \         with stderr in " ++ stderrBufPath
+
+  -- launch the GHCi subprocess, grab its FD handles and process handle
+  (Just rStdin, Just rStdout, Nothing, ph) <-
     createProcess (proc cmd args)
       { std_in = CreatePipe
       , std_out = CreatePipe
-      , std_err = CreatePipe
+      , std_err = UseHandle stderrBufHandle
       }
   hSetBuffering rStdin LineBuffering
   hSetBuffering rStdout NoBuffering
-  hSetBuffering rStderr NoBuffering
-  -- Log stack repl's standard error output
-  tempDir <- if isWindows
-                then fromMaybe "" <$> lookupEnv "TEMP"
-                else pure "/tmp"
-  let tempLogFile = tempDir ++ "/stderr"
-  _ <- forkIO $ withFile tempLogFile WriteMode $ \logFileHandle -> do
-    --hSetBuffering logFileHandle NoBuffering
-    forever $
-      catch
-        (hGetChar rStderr >>= hPutChar logFileHandle)
-        (\e -> unless (isEOFError e) $ throw e)
 
   -- run the test script which is to talk to the GHCi subprocess.
   runReaderT actions (ReplConnection rStdin rStdout)
@@ -100,6 +93,13 @@ runRepl cmd args actions = do
   -- read out the exit-code
   waitForProcess ph
 
+-- | Roll a bicycle, rather than just `import Path.IO (getTempDir, openTempFile)`,
+-- because it's a hassle to use anything beyond base & boot libs here.
+openTempStderrBufferFile :: IO (FilePath, Handle)
+openTempStderrBufferFile = getTempDir >>= (`openTempFile` "err.log") where
+  getTempDir | isWindows = fromMaybe "" <$> lookupEnv "TEMP"
+             | otherwise = pure "/tmp"
+
 repl :: HasCallStack => [String] -> Repl () -> IO ()
 repl args action = do
   stackExe' <- stackExe

From 38d03c229304a67f4ba9edef85368bfcebc0fd73 Mon Sep 17 00:00:00 2001
From: Max Ulidtko <ulidtko@gmail.com>
Date: Fri, 16 May 2025 20:52:15 +0200
Subject: [PATCH 08/13] feat: show repl stderr on exceptions in test

---
 tests/integration/lib/StackTest/Repl.hs       | 29 ++++++++--
 .../tests/3926-ghci-with-sublibraries/Main.hs | 55 ++++++++-----------
 2 files changed, 48 insertions(+), 36 deletions(-)

diff --git a/tests/integration/lib/StackTest/Repl.hs b/tests/integration/lib/StackTest/Repl.hs
index 344d3ea89b..cf58f88b84 100644
--- a/tests/integration/lib/StackTest/Repl.hs
+++ b/tests/integration/lib/StackTest/Repl.hs
@@ -10,16 +10,19 @@ module StackTest.Repl
     , replGetLine
     ) where
 
+import Control.Exception (SomeException, catch, displayException, finally)
 import Control.Monad (unless, when)
 import Control.Monad.IO.Class (liftIO)
 import Data.Maybe (fromMaybe)
 import GHC.Stack (HasCallStack)
+import System.Directory (removeFile)
 import System.Environment (lookupEnv)
-import System.Exit (ExitCode (..))
+import System.Exit (ExitCode (..), exitFailure)
 import System.IO
-    ( BufferMode (NoBuffering, LineBuffering), Handle
-    , hClose, hGetChar, hGetLine, hPutStrLn, hSetBuffering
+    ( BufferMode (NoBuffering, LineBuffering), Handle, IOMode (ReadMode)
+    , hClose, hGetChar, hGetContents', hGetLine, hPutStrLn, hSetBuffering
     , openTempFile
+    , withFile
     )
 
 import Control.Monad.Trans (lift)
@@ -87,6 +90,18 @@ runRepl cmd args actions = do
 
   -- run the test script which is to talk to the GHCi subprocess.
   runReaderT actions (ReplConnection rStdin rStdout)
+    -- the nested actions script may fail in arbitrary ways; handle that here,
+    -- attaching the subprocess stderr as relevant context
+    `catch` \(e :: SomeException) -> do
+      putStrLn "=============================="
+      putStrLn "EXCEPTION in test: "
+      putStrLn . quote $ displayException e
+      putStrLn "------[ stderr of repl ]------"
+      withFile stderrBufPath ReadMode $ \h -> hGetContents' h >>= putStr . quote
+      putStrLn "=============================="
+    `finally` do
+      hClose stderrBufHandle
+      removeFile stderrBufPath
 
   -- once done with the test, signal EOF on stdin for clean termination of ghci
   hClose rStdin
@@ -104,5 +119,9 @@ repl :: HasCallStack => [String] -> Repl () -> IO ()
 repl args action = do
   stackExe' <- stackExe
   ec <- runRepl stackExe' ("repl" : "--ghci-options=-ignore-dot-ghci" : args) action
-  unless (ec == ExitSuccess) $
-    error $ "GHCi exited with " <> show ec
+  unless (ec == ExitSuccess) $ do
+    putStrLn $ "repl exited with " <> show ec
+    exitFailure
+
+quote :: String -> String
+quote = unlines . map ("> " <>) . lines
diff --git a/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs b/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs
index c9f64ac4c7..a7768f6c5c 100644
--- a/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs
+++ b/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs
@@ -5,37 +5,30 @@ import StackTest
 import StackTest.Repl
 
 main :: IO ()
-main
-  | isWindows =
-      putStrLn "This test was disabled on Windows on 25 June 2023 (see \
-               \https://github.com/commercialhaskell/stack/issues/6170)."
-  | otherwise = do
-      stack ["clean"] -- to make sure we can load the code even after a clean
-      copy "src/Lib.v1" "src/Lib.hs"
-      copy "src-internal/Internal.v1" "src-internal/Internal.hs"
-      stack ["build"] -- need a build before ghci at the moment, see #4148
-      replThread
-
-replThread :: IO ()
-replThread = repl [] $ do
-  -- The command must be issued before searching the output for the next prompt,
-  -- otherwise, on Windows from msys2-20230526, `stack repl` encounters a EOF
-  -- and terminates gracefully.
-  replCommand ":main"
-  liftIO $ putStrLn "Awaiting prompt..."
-  nextPrompt
-  liftIO $ putStrLn "Initial prompt received"
-  line <- replGetLine
-  let expected = "hello world"
-  when (line /= expected) $
-    error $
-         "Main module didn't load correctly.\n"
-      <> "Expected: " <> expected <> "\n"
-      <> "Actual  : " <> line <> "\n"
-  liftIO $ copy "src-internal/Internal.v2" "src-internal/Internal.hs"
-  reloadAndTest "testInt" "42" "Internal library didn't reload."
-  liftIO $ copy "src/Lib.v2" "src/Lib.hs"
-  reloadAndTest "testStr" "\"OK\"" "Main library didn't reload."
+main = do
+  stack ["clean"] -- to make sure we can load the code even after a clean
+  copy "src/Lib.v1" "src/Lib.hs"
+  copy "src-internal/Internal.v1" "src-internal/Internal.hs"
+  stack ["build"] -- need a build before ghci at the moment, see #4148
+  repl [] $ do
+    -- The command must be issued before searching the output for the next prompt,
+    -- otherwise, on Windows from msys2-20230526, `stack repl` encounters a EOF
+    -- and terminates gracefully.
+    replCommand ":main"
+    liftIO $ putStrLn "Awaiting prompt..."
+    nextPrompt
+    liftIO $ putStrLn "Initial prompt received"
+    line <- replGetLine
+    let expected = "hello world"
+    when (line /= expected) $
+      error $
+          "Main module didn't load correctly.\n"
+        <> "Expected: " <> expected <> "\n"
+        <> "Actual  : " <> line <> "\n"
+    liftIO $ copy "src-internal/Internal.v2" "src-internal/Internal.hs"
+    reloadAndTest "testInt" "42" "Internal library didn't reload."
+    liftIO $ copy "src/Lib.v2" "src/Lib.hs"
+    reloadAndTest "testStr" "\"OK\"" "Main library didn't reload."
 
 reloadAndTest :: String -> String -> String -> Repl ()
 reloadAndTest cmd exp err = do

From 5b2927c351c788cf75f8eeffb5a7ec0b5ffba840 Mon Sep 17 00:00:00 2001
From: Max Ulidtko <ulidtko@gmail.com>
Date: Fri, 16 May 2025 20:59:27 +0200
Subject: [PATCH 09/13] =?UTF-8?q?refactor:=20rename=20StackTest.Repl.{repl?=
 =?UTF-8?q?=20=E2=86=92=20stackRepl}?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 tests/integration/lib/StackTest/Repl.hs                    | 7 ++++---
 tests/integration/tests/3315-multi-ghc-options/Main.hs     | 4 ++--
 .../integration/tests/3926-ghci-with-sublibraries/Main.hs  | 2 +-
 tests/integration/tests/4270-files-order/Main.hs           | 2 +-
 .../integration/tests/module-added-multiple-times/Main.hs  | 2 +-
 5 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/tests/integration/lib/StackTest/Repl.hs b/tests/integration/lib/StackTest/Repl.hs
index cf58f88b84..e75dd6afbb 100644
--- a/tests/integration/lib/StackTest/Repl.hs
+++ b/tests/integration/lib/StackTest/Repl.hs
@@ -5,9 +5,9 @@ module StackTest.Repl
     ( Repl
     , ReplConnection (..)
     , nextPrompt
-    , repl
     , replCommand
     , replGetLine
+    , stackRepl
     ) where
 
 import Control.Exception (SomeException, catch, displayException, finally)
@@ -115,8 +115,9 @@ openTempStderrBufferFile = getTempDir >>= (`openTempFile` "err.log") where
   getTempDir | isWindows = fromMaybe "" <$> lookupEnv "TEMP"
              | otherwise = pure "/tmp"
 
-repl :: HasCallStack => [String] -> Repl () -> IO ()
-repl args action = do
+-- | Testing helper to exercise `stack repl`.
+stackRepl :: HasCallStack => [String] -> Repl () -> IO ()
+stackRepl args action = do
   stackExe' <- stackExe
   ec <- runRepl stackExe' ("repl" : "--ghci-options=-ignore-dot-ghci" : args) action
   unless (ec == ExitSuccess) $ do
diff --git a/tests/integration/tests/3315-multi-ghc-options/Main.hs b/tests/integration/tests/3315-multi-ghc-options/Main.hs
index 1a0ea36fce..60d8c9eec4 100644
--- a/tests/integration/tests/3315-multi-ghc-options/Main.hs
+++ b/tests/integration/tests/3315-multi-ghc-options/Main.hs
@@ -1,6 +1,6 @@
-import StackTest
+import StackTest.Repl
 
 main :: IO ()
 main = do
   stack ["build", "--ghc-options=-ddump-simpl -ddump-asm -DBAR -DBAZ"]
-  repl ["--ghc-options=-ddump-simpl -ddump-asm"] (pure ())
+  stackRepl ["--ghc-options=-ddump-simpl -ddump-asm"] (pure ())
diff --git a/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs b/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs
index a7768f6c5c..1969d6ebaf 100644
--- a/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs
+++ b/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs
@@ -10,7 +10,7 @@ main = do
   copy "src/Lib.v1" "src/Lib.hs"
   copy "src-internal/Internal.v1" "src-internal/Internal.hs"
   stack ["build"] -- need a build before ghci at the moment, see #4148
-  repl [] $ do
+  stackRepl [] $ do
     -- The command must be issued before searching the output for the next prompt,
     -- otherwise, on Windows from msys2-20230526, `stack repl` encounters a EOF
     -- and terminates gracefully.
diff --git a/tests/integration/tests/4270-files-order/Main.hs b/tests/integration/tests/4270-files-order/Main.hs
index 34e9669b86..adcaa8ed01 100644
--- a/tests/integration/tests/4270-files-order/Main.hs
+++ b/tests/integration/tests/4270-files-order/Main.hs
@@ -5,7 +5,7 @@ import StackTest.Repl
 main :: IO ()
 main = do
   stack ["build"]
-  repl [] $ do
+  stackRepl [] $ do
     -- The command must be issued before searching the output for the next
     -- prompt, otherwise, on Windows from msys2-20230526, `stack repl`
     -- encounters a EOF and terminates gracefully.
diff --git a/tests/integration/tests/module-added-multiple-times/Main.hs b/tests/integration/tests/module-added-multiple-times/Main.hs
index 41397416cc..2163b70ff3 100644
--- a/tests/integration/tests/module-added-multiple-times/Main.hs
+++ b/tests/integration/tests/module-added-multiple-times/Main.hs
@@ -2,7 +2,7 @@ import Control.Monad
 import StackTest.Repl
 
 main :: IO ()
-main = repl [] $ do
+main = stackRepl [] $ do
   -- The command must be issued before searching the output for the next prompt,
   -- otherwise, on Windows from msys2-20230526, `stack repl` encounters a EOF
   -- and terminates gracefully.

From 27e3587adf170196fe9ca3ddf282b71564ee8911 Mon Sep 17 00:00:00 2001
From: Max Ulidtko <ulidtko@gmail.com>
Date: Fri, 16 May 2025 21:07:37 +0200
Subject: [PATCH 10/13] fix: avoid quadratic String traversals, resolving a
 fixme

---
 tests/integration/lib/StackTest/Repl.hs | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/tests/integration/lib/StackTest/Repl.hs b/tests/integration/lib/StackTest/Repl.hs
index e75dd6afbb..9df83204a8 100644
--- a/tests/integration/lib/StackTest/Repl.hs
+++ b/tests/integration/lib/StackTest/Repl.hs
@@ -13,7 +13,12 @@ module StackTest.Repl
 import Control.Exception (SomeException, catch, displayException, finally)
 import Control.Monad (unless, when)
 import Control.Monad.IO.Class (liftIO)
+import Control.Monad.Trans (lift)
+import Control.Monad.Trans.Reader
+import Control.Monad.Trans.State qualified as State
 import Data.Maybe (fromMaybe)
+import Data.Foldable (toList)
+import Data.Sequence as Seq (Seq(Empty), (|>), fromList)
 import GHC.Stack (HasCallStack)
 import System.Directory (removeFile)
 import System.Environment (lookupEnv)
@@ -24,10 +29,6 @@ import System.IO
     , openTempFile
     , withFile
     )
-
-import Control.Monad.Trans (lift)
-import Control.Monad.Trans.Reader
-import Control.Monad.Trans.State qualified as State
 import System.Process
     ( CreateProcess (std_err, std_in, std_out)
     , StdStream (CreatePipe, UseHandle)
@@ -54,15 +55,15 @@ replGetLine :: Repl String
 replGetLine = ask >>= liftIO . hGetLine . replStdout
 
 nextPrompt :: Repl ()
-nextPrompt = State.evalStateT poll "" where
+nextPrompt = State.evalStateT poll Seq.Empty where
   poll = do
     c <- lift (asks replStdout) >>= liftIO . hGetChar
-    State.modify (++ [c]) -- FIXME crap perf
+    State.modify (|> c)
     when (c == '\n') $ do
-      State.get >>= liftIO . putStr . ("ghci> " <>)
-      State.put ""
+      State.get >>= liftIO . putStr . ("ghci> " ++) . toList
+      State.put Seq.Empty
     buf <- State.get
-    unless (buf == "ghci> ")
+    unless (buf == Seq.fromList "ghci> ")
       poll
 
 runRepl

From 547f2746188865185990a4418bd41bd827eb4db9 Mon Sep 17 00:00:00 2001
From: Max Ulidtko <ulidtko@gmail.com>
Date: Sat, 17 May 2025 15:27:48 +0200
Subject: [PATCH 11/13] refactor(tests): reexport StackTest from StackTest.Repl

---
 tests/integration/lib/StackTest/Repl.hs                     | 2 ++
 tests/integration/tests/3926-ghci-with-sublibraries/Main.hs | 2 +-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/tests/integration/lib/StackTest/Repl.hs b/tests/integration/lib/StackTest/Repl.hs
index 9df83204a8..ef951da962 100644
--- a/tests/integration/lib/StackTest/Repl.hs
+++ b/tests/integration/lib/StackTest/Repl.hs
@@ -8,6 +8,8 @@ module StackTest.Repl
     , replCommand
     , replGetLine
     , stackRepl
+    -- * Reexport
+    , module StackTest
     ) where
 
 import Control.Exception (SomeException, catch, displayException, finally)
diff --git a/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs b/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs
index 1969d6ebaf..a0c94cb23d 100644
--- a/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs
+++ b/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs
@@ -1,7 +1,7 @@
 import Control.Monad.IO.Class
 import Control.Monad
 import Data.List
-import StackTest
+
 import StackTest.Repl
 
 main :: IO ()

From a0a5fd93f020d53f96ff8173cd83679c2ab90d41 Mon Sep 17 00:00:00 2001
From: Max Ulidtko <ulidtko@gmail.com>
Date: Sat, 17 May 2025 16:37:57 +0200
Subject: [PATCH 12/13] cleanup: undo tests workarounds for msys2-20230526

Resolves #6170
---
 tests/integration/tests/3926-ghci-with-sublibraries/Main.hs | 5 +----
 tests/integration/tests/4270-files-order/Main.hs            | 5 +----
 tests/integration/tests/module-added-multiple-times/Main.hs | 5 +----
 3 files changed, 3 insertions(+), 12 deletions(-)

diff --git a/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs b/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs
index a0c94cb23d..ba045b541a 100644
--- a/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs
+++ b/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs
@@ -11,13 +11,10 @@ main = do
   copy "src-internal/Internal.v1" "src-internal/Internal.hs"
   stack ["build"] -- need a build before ghci at the moment, see #4148
   stackRepl [] $ do
-    -- The command must be issued before searching the output for the next prompt,
-    -- otherwise, on Windows from msys2-20230526, `stack repl` encounters a EOF
-    -- and terminates gracefully.
-    replCommand ":main"
     liftIO $ putStrLn "Awaiting prompt..."
     nextPrompt
     liftIO $ putStrLn "Initial prompt received"
+    replCommand ":main"
     line <- replGetLine
     let expected = "hello world"
     when (line /= expected) $
diff --git a/tests/integration/tests/4270-files-order/Main.hs b/tests/integration/tests/4270-files-order/Main.hs
index adcaa8ed01..c4b1a56588 100644
--- a/tests/integration/tests/4270-files-order/Main.hs
+++ b/tests/integration/tests/4270-files-order/Main.hs
@@ -6,11 +6,8 @@ main :: IO ()
 main = do
   stack ["build"]
   stackRepl [] $ do
-    -- The command must be issued before searching the output for the next
-    -- prompt, otherwise, on Windows from msys2-20230526, `stack repl`
-    -- encounters a EOF and terminates gracefully.
-    replCommand "putStrLn greeting"
     nextPrompt
+    replCommand "putStrLn greeting"
     line <- replGetLine
     let expected = "Hello, world!"
     when (line /= expected) $
diff --git a/tests/integration/tests/module-added-multiple-times/Main.hs b/tests/integration/tests/module-added-multiple-times/Main.hs
index 2163b70ff3..73cfee36f5 100644
--- a/tests/integration/tests/module-added-multiple-times/Main.hs
+++ b/tests/integration/tests/module-added-multiple-times/Main.hs
@@ -3,11 +3,8 @@ import StackTest.Repl
 
 main :: IO ()
 main = stackRepl [] $ do
-  -- The command must be issued before searching the output for the next prompt,
-  -- otherwise, on Windows from msys2-20230526, `stack repl` encounters a EOF
-  -- and terminates gracefully.
-  replCommand ":main"
   nextPrompt
+  replCommand ":main"
   line <- replGetLine
   let expected = "Hello World!"
   when (line /= expected) $

From 3a939d5cfe31fdb222e4a83d4ac67c8d23d4a38f Mon Sep 17 00:00:00 2001
From: Max Ulidtko <ulidtko@gmail.com>
Date: Mon, 19 May 2025 09:03:52 +0200
Subject: [PATCH 13/13] cleanup: code review

---
 tests/integration/lib/StackTest/Repl.hs                   | 8 ++++++--
 .../integration/tests/3926-ghci-with-sublibraries/Main.hs | 2 --
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/tests/integration/lib/StackTest/Repl.hs b/tests/integration/lib/StackTest/Repl.hs
index ef951da962..f08bdfceb5 100644
--- a/tests/integration/lib/StackTest/Repl.hs
+++ b/tests/integration/lib/StackTest/Repl.hs
@@ -6,6 +6,7 @@ module StackTest.Repl
     , ReplConnection (..)
     , nextPrompt
     , replCommand
+    , replGetChar
     , replGetLine
     , stackRepl
     -- * Reexport
@@ -13,7 +14,7 @@ module StackTest.Repl
     ) where
 
 import Control.Exception (SomeException, catch, displayException, finally)
-import Control.Monad (unless, when)
+import Control.Monad ((>=>), unless, when)
 import Control.Monad.IO.Class (liftIO)
 import Control.Monad.Trans (lift)
 import Control.Monad.Trans.Reader
@@ -53,6 +54,9 @@ replCommand cmd = do
   liftIO . putStrLn $ "____> " <> cmd
   liftIO $ hPutStrLn replStdinHandle cmd
 
+replGetChar :: Repl Char
+replGetChar = asks replStdout >>= liftIO . hGetChar
+
 replGetLine :: Repl String
 replGetLine = ask >>= liftIO . hGetLine . replStdout
 
@@ -100,7 +104,7 @@ runRepl cmd args actions = do
       putStrLn "EXCEPTION in test: "
       putStrLn . quote $ displayException e
       putStrLn "------[ stderr of repl ]------"
-      withFile stderrBufPath ReadMode $ \h -> hGetContents' h >>= putStr . quote
+      withFile stderrBufPath ReadMode $ hGetContents' >=> putStr . quote
       putStrLn "=============================="
     `finally` do
       hClose stderrBufHandle
diff --git a/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs b/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs
index ba045b541a..2685fe87e4 100644
--- a/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs
+++ b/tests/integration/tests/3926-ghci-with-sublibraries/Main.hs
@@ -11,9 +11,7 @@ main = do
   copy "src-internal/Internal.v1" "src-internal/Internal.hs"
   stack ["build"] -- need a build before ghci at the moment, see #4148
   stackRepl [] $ do
-    liftIO $ putStrLn "Awaiting prompt..."
     nextPrompt
-    liftIO $ putStrLn "Initial prompt received"
     replCommand ":main"
     line <- replGetLine
     let expected = "hello world"