X.H.FloatConfigureReq: New module to customize ConfigureRequest handling

Implements a replacement event handler for 'ConfigureRequestEvent' to
work around misbehaving client applications such as Steam, URxvt and
others that try to restore their absolute window positions. Primarily
motivated by the Steam client being almost completely unusable in xmonad
lately.

(I've been running this code in my xmonad.hs for other purposes for
years.)

XMonad/Hooks/FloatConfigureReq.hs

@@ -0,0 +1,109 @@
+{-# LANGUAGE LambdaCase #-}
+-- |
+-- Module      :  XMonad.Hooks.FloatConfigureReq
+-- Description :  Customize handling of floating windows' move\/resize\/restack requests (ConfigureRequest).
+-- Copyright   :  (c) 2024 Tomáš Janoušek <tomi@nomi.cz>
+-- License     :  BSD3
+-- Maintainer  :  Tomáš Janoušek <tomi@nomi.cz>
+--
+-- xmonad normally honours those requests by doing exactly what the client
+-- application asked, and refreshing. There are some misbehaving clients,
+-- however, that:
+--
+-- * try to move their window to the last known absolute position regardless
+--   of the current xrandr/xinerama layout
+--
+-- * move their window to 0, 0 for no particular reason (e.g. rxvt-unicode)
+--
+-- * issue lots of no-op requests causing flickering (e.g. Steam)
+--
+-- This module provides a replacement handler for 'ConfigureRequestEvent' to
+-- work around such misbehaviours.
+--
+module XMonad.Hooks.FloatConfigureReq (
+    -- * Usage
+    -- $usage
+    MaybeMaybeManageHook,
+    floatConfReqHook,
+    ) where
+
+import qualified Data.Map.Strict as M
+import XMonad
+import XMonad.Hooks.ManageHelpers
+import XMonad.Prelude
+import qualified XMonad.StackSet as W
+
+-- $usage
+-- To use this, include the following in your @xmonad.hs@:
+--
+-- > import XMonad.Hooks.FloatConfigureReq
+-- > import XMonad.Hooks.ManageHelpers
+--
+-- > myFloatConfReqHook :: MaybeMaybeManageHook
+-- > myFloatConfReqHook = composeAll
+-- >     [ … ]
+--
+-- > myEventHook :: Event -> X All
+-- > myEventHook = mconcat
+-- >     [ …
+-- >     , floatConfReqHook myFloatConfReqHook
+-- >     , … ]
+--
+-- > main = xmonad $ …
+-- >               $ def{ handleEventHook = myEventHook
+-- >                    , … }
+--
+-- Then fill the @myFloatConfReqHook@ with whatever custom rules you need.
+--
+-- As an example, the following will prevent rxvt-unicode from moving its
+-- (floating) window to 0, 0 after a font change but still ensure its size
+-- increment hints are respected:
+--
+-- > className =? "URxvt" -?> pure <$> doFloat
+--
+-- Another example that avoids flickering and xmonad slowdowns caused by the
+-- Steam client (completely ignore all its requests, none of which are
+-- meaningful in the context of a tiling WM):
+--
+-- > map toLower `fmap` className =? "steam" -?> mempty
+
+-- | A variant of 'MaybeManageHook' that additionally may or may not make
+-- changes to the 'WindowSet'.
+type MaybeMaybeManageHook = Query (Maybe (Maybe (Endo WindowSet)))
+
+-- | Customizable handler for a 'ConfigureRequestEvent'. If the event's
+-- 'ev_window' is a managed floating window, the provided
+-- 'MaybeMaybeManageHook' is consulted and its result interpreted as follows:
+--
+--  * @Nothing@ - no match, fall back to the default handler
+--
+--  * @Just Nothing@ - match but ignore, no refresh, just send ConfigureNotify
+--
+--  * @Just (Just a)@ - match, modify 'WindowSet', refresh, send ConfigureNotify
+floatConfReqHook :: MaybeMaybeManageHook -> Event -> X All
+floatConfReqHook mh ConfigureRequestEvent{ev_window = w} =
+    runQuery (join <$> (isFloatQ -?> mh)) w >>= \case
+        Nothing -> mempty
+        Just e -> do
+            whenJust e (windows . appEndo)
+            sendConfEvent
+            pure (All False)
+  where
+    sendConfEvent = withDisplay $ \dpy ->
+        withWindowAttributes dpy w $ \wa -> do
+            io . allocaXEvent $ \ev -> do
+                -- We may have made no changes to the window size/position
+                -- and thus the X server didn't emit any ConfigureNotify,
+                -- so we need to send the ConfigureNotify ourselves to make
+                -- sure there is a reply to this ConfigureRequestEvent and the
+                -- window knows we (possibly) ignored its request.
+                setEventType ev configureNotify
+                setConfigureEvent ev w w
+                    (wa_x wa) (wa_y wa) (wa_width wa)
+                    (wa_height wa) (wa_border_width wa) none (wa_override_redirect wa)
+                sendEvent dpy w False 0 ev
+floatConfReqHook _ _ = mempty
+
+-- | A 'Query' to determine if a window is floating.
+isFloatQ :: Query Bool
+isFloatQ = ask >>= \w -> liftX . gets $ M.member w . W.floating . windowset

xmonad-contrib.cabal

@@ -192,6 +192,7 @@ library
                         XMonad.Hooks.EwmhDesktops
                         XMonad.Hooks.FadeInactive
                         XMonad.Hooks.FadeWindows
+                        XMonad.Hooks.FloatConfigureReq
                         XMonad.Hooks.FloatNext
                         XMonad.Hooks.Focus
                         XMonad.Hooks.InsertPosition