fix: Explicitly flush stdout on plugin

Because of #20791, the plugins tests often fail.  This is a temporary
fix to stop the tests from failing due to unflushed outputs on windows
and the explicit flush should be removed when #20791 is fixed.

3 files changed, 14 insertions, 8 deletions

diff --git a/testsuite/tests/plugins/all.T b/testsuite/tests/plugins/all.T
index 468f509b91..ef0096f064 100644
--- a/testsuite/tests/plugins/all.T
+++ b/testsuite/tests/plugins/all.T
@@ -294,26 +294,22 @@ test('T20803b',
 
 test('test-echo-in-turn',
      [extra_files(['echo-plugin/']),
-      pre_cmd('$MAKE -s --no-print-directory -C echo-plugin package.test-echo-in-turn TOP={top}'),
-      when(opsys('linux') and not ghc_dynamic(), expect_broken(20706))],
+      pre_cmd('$MAKE -s --no-print-directory -C echo-plugin package.test-echo-in-turn TOP={top}')],
      makefile_test, [])
 
 test('test-echo-in-line',
      [extra_files(['echo-plugin/']),
-      pre_cmd('$MAKE -s --no-print-directory -C echo-plugin package.test-echo-in-line TOP={top}'),
-      when(opsys('linux') and not ghc_dynamic(), expect_broken(20706))],
+      pre_cmd('$MAKE -s --no-print-directory -C echo-plugin package.test-echo-in-line TOP={top}')],
      makefile_test, [])
 
 test('test-echo-in-turn-many-args',
      [extra_files(['echo-plugin/']),
-      pre_cmd('$MAKE -s --no-print-directory -C echo-plugin package.test-echo-in-turn-many-args TOP={top}'),
-      when(opsys('linux') and not ghc_dynamic(), expect_broken(20706))],
+      pre_cmd('$MAKE -s --no-print-directory -C echo-plugin package.test-echo-in-turn-many-args TOP={top}')],
      makefile_test, [])
 
 test('test-echo-in-line-many-args',
      [extra_files(['echo-plugin/']),
-      pre_cmd('$MAKE -s --no-print-directory -C echo-plugin package.test-echo-in-line-many-args TOP={top}'),
-      when(opsys('linux') and not ghc_dynamic(), expect_broken(20706))],
+      pre_cmd('$MAKE -s --no-print-directory -C echo-plugin package.test-echo-in-line-many-args TOP={top}')],
      makefile_test, [])
 
 test('plugins-external',
diff --git a/testsuite/tests/plugins/echo-plugin/Echo.hs b/testsuite/tests/plugins/echo-plugin/Echo.hs
index 9c2a71a088..5a8ea1adfd 100644
--- a/testsuite/tests/plugins/echo-plugin/Echo.hs
+++ b/testsuite/tests/plugins/echo-plugin/Echo.hs
@@ -5,6 +5,7 @@ import GHC.Tc.Plugin
 import GHC.Tc.Utils.Monad
 import qualified GHC.Tc.Utils.Monad as Utils
 import GHC.Types.Unique.FM ( emptyUFM )
+import System.IO
 
 plugin :: Plugin
 plugin = mkPureOptTcPlugin optCallCount
@@ -27,6 +28,10 @@ optCallCount opts = Just $
             n <- unsafeTcPluginTcM $ readMutVar c
             let msg = if null opts then "" else mconcat opts
             tcPluginIO . putStrLn $ "Echo TcPlugin " ++ msg ++ "#" ++ show n
+
+            -- TODO: Remove #20791
+            tcPluginIO $ hFlush stdout
+
             unsafeTcPluginTcM $ writeMutVar c (n + 1)
             return $ TcPluginOk [] []
 
diff --git a/testsuite/tests/plugins/hooks-plugin/Hooks/Plugin.hs b/testsuite/tests/plugins/hooks-plugin/Hooks/Plugin.hs
index adfa6e28cf..bf717b26c0 100644
--- a/testsuite/tests/plugins/hooks-plugin/Hooks/Plugin.hs
+++ b/testsuite/tests/plugins/hooks-plugin/Hooks/Plugin.hs
@@ -10,6 +10,7 @@ import GHC.Hs.Lit
 import GHC.Driver.Hooks
 import GHC.Tc.Utils.Monad
 import GHC.Parser.Annotation
+import System.IO
 
 plugin :: Plugin
 plugin = defaultPlugin { driverPlugin = hooksP }
@@ -28,6 +29,10 @@ hooksP opts hsc_env = do
 fakeRunMeta :: [CommandLineOption] -> MetaHook TcM
 fakeRunMeta opts (MetaE r) _ = do
   liftIO . putStrLn $ "Options = " ++ show opts
+
+  -- TODO: Remove #20791
+  liftIO $ hFlush stdout
+
   pure $ r zero
 
   where zero :: LHsExpr GhcPs