From 5f21e8069bdc878bbbed73ba09f0e0b0fc6c7c3f Mon Sep 17 00:00:00 2001
From: Levi Neely <141506390+lneely@users.noreply.github.com>
Date: Sun, 10 May 2026 20:34:59 +0200
Subject: [PATCH] wayland: install X error handler for XWayland connection
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The Wayland backend runs with a live XWayland Display* once XWayland
fires its ready signal.  Without an error handler, benign X errors
(BadMatch on X_SetInputFocus, BadWindow during window teardown) reach
Xlib's default handler and produce noisy output.

Add wl_catch_xwayland_error() — same permissive policy as the X11
backend's x11_catch_error() — and install it via XSetErrorHandler in
wl_register_error_handlers().  Include <X11/Xproto.h> for the
X_SetInputFocus request code constant.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
---
 src/backend/wayland/wl_backend.c | 27 ++++++++++++++++++++++++++-
 1 file changed, 26 insertions(+), 1 deletion(-)

diff --git a/src/backend/wayland/wl_backend.c b/src/backend/wayland/wl_backend.c
index 2177d4a..588f48a 100644
--- a/src/backend/wayland/wl_backend.c
+++ b/src/backend/wayland/wl_backend.c
@@ -126,6 +126,7 @@
 #include <wlr/types/wlr_xdg_shell.h>
 #include <wlr/types/wlr_xdg_decoration_v1.h>
 #include <wlr/xwayland.h>              /* Phase 17: XWayland support */
+#include <X11/Xproto.h>               /* X_SetInputFocus and other request codes */
 #include <wlr/backend/wayland.h>       /* Phase 18: nested Wayland backend */
 #include <wlr/backend/multi.h>         /* Phase 18: multi-backend */
 #include <wlr/types/wlr_scene.h>       /* Phase 18: scene graph compositing */
@@ -4887,10 +4888,34 @@ static void wl_extensions_init(void) {}
 static void wl_cursors_init(void) {}
 static WNativeWindow wl_cursor_create_named(const char *name) { (void)name; return WNATIVE_NONE; }
 static void wl_shape_combine_mask(WNativeWindow win, WNativeWindow mask) { (void)win; (void)mask; }
+static int
+wl_catch_xwayland_error(Display *edpy, XErrorEvent *error)
+{
+    (void)edpy;
+    /* BadMatch on X_SetInputFocus is benign: the target window may not be
+     * viewable yet (e.g. during XWayland startup or between map/unmap).
+     * Silence it so it does not reach Xlib's default handler. */
+    if (error->error_code == BadMatch &&
+        error->request_code == X_SetInputFocus)
+        return 0;
+    /* BadWindow is also common during window teardown; ignore silently. */
+    if (error->error_code == BadWindow)
+        return 0;
+    /* Everything else: print via wwarning and continue. */
+    char buf[256];
+    XGetErrorText(edpy, error->error_code, buf, sizeof(buf));
+    wwarning("wl_backend: X error from XWayland: %s (request %d, resource 0x%lx)",
+             buf, (int)error->request_code, (unsigned long)error->resourceid);
+    return 0;
+}
+
 static void
 wl_register_error_handlers(void)
 {
-    /* Pure Wayland: no X11 Display*, so no Xlib error handlers needed. */
+    /* Install a permissive X error handler for the XWayland connection.
+     * Without this, Xlib's default handler prints and the WM continues,
+     * but benign errors (BadMatch on SetInputFocus etc.) cause visible noise. */
+    XSetErrorHandler(wl_catch_xwayland_error);
 }
 
 /* ------------------------------------------------------------------ */