restore the main loop

The ghc versions affected by the join point bug are long obsolete
and should not be being used by anyone.

This partially reverts #404.

CHANGES.md

@@ -8,6 +8,16 @@
 
 ### Bug Fixes
 
+### Other
+
+PR #404 (see last change in 0.17.1) has been reverted, because the affected
+compilers are (hopefully) no longer being used.
+
+All 9.0 releases of GHC, plus 9.2.1 and 9.2.2 have the join point bug.
+Note that 9.0.x is known to also have GC issues and is officially deprecated,
+and the only 9.2 release that should be used is 9.2.8. Additionally, GHC HQ
+doesn't support releases before 9.6.6.
+
 ## 0.18.0 (February 3, 2024)
 
 ### Breaking Changes

src/XMonad/Main.hs

@@ -26,7 +26,7 @@ import qualified Data.Map as M
 import qualified Data.Set as S
 import Control.Monad.Reader
 import Control.Monad.State
-import Control.Monad (filterM, guard, unless, void, when)
+import Control.Monad (filterM, guard, unless, void, when, forever)
 import Data.Maybe (fromMaybe, isJust)
 import Data.Monoid (getAll)
 
@@ -248,11 +248,10 @@ launch initxmc drs = do
             userCode $ startupHook initxmc
 
             rrData <- io $ xrrQueryExtension dpy
+            let rrUpdate = when (isJust rrData) . void . xrrUpdateConfiguration
 
             -- main loop, for all you HOF/recursion fans out there.
-            -- forever $ prehandle =<< io (nextEvent dpy e >> rrUpdate e >> getEvent e)
+            forever $ prehandle =<< io (nextEvent dpy e >> rrUpdate e >> getEvent e)
-            -- sadly, 9.2.{1,2,3} join points mishandle the above and trash the heap (see #389)
-            mainLoop dpy e rrData
 
     return ()
       where
@@ -263,8 +262,6 @@ launch initxmc drs = do
                       in local (\c -> c { mousePosition = mouse, currentEvent = Just e }) (handleWithHook e)
         evs = [ keyPress, keyRelease, enterNotify, leaveNotify
               , buttonPress, buttonRelease]
-        rrUpdate e r = when (isJust r) (void (xrrUpdateConfiguration e))
-        mainLoop d e r = io (nextEvent d e >> rrUpdate e r >> getEvent e) >>= prehandle >> mainLoop d e r
 
 
 -- | Runs handleEventHook from the configuration and runs the default handler