Fix crash when logical monitor is null

[maresb]

Note

AI Assistance Disclosure: This PR was created with assistance from Claude Opus 4.5 via Cursor. The crash analysis, diagnosis, and fix were AI-assisted based on actual crash logs from my system.

Summary

Fixes #11

The get_work_area_current_monitor(), get_work_area_all_monitors(), and get_work_area_for_monitor() methods can trigger a fatal assertion in Mutter's meta_window_get_work_area_for_logical_monitor() if the window's logical monitor is null or invalid.

This can occur during:

• Monitor hotplug (connecting/disconnecting displays)
• Display configuration changes
• Windows in transient states between monitors

The assertion failure causes GNOME Shell to abort, crashing the entire desktop session.

Changes

This PR wraps the work area calls in a helper function safeGetWorkArea() that catches any errors and returns null instead, preventing the crash.

Testing

I experienced this crash on my system (GNOME Shell 49.2, NixOS). Unfortunately I cannot easily test the fix without waiting for another crash to occur naturally, but the change is minimal and defensive—it simply wraps the existing calls in try/catch blocks.

Crash Log (for reference)

libmutter:ERROR:../src/core/window.c:6081:meta_window_get_work_area_for_logical_monitor: assertion failed: (logical_monitor)
#0   560760948308 i   file:///...extensions/focused-window-dbus@flexagoon.com/extension.js:51

[maresb]

I successfully tested this fix by unplugging my monitor while polling the focused window, causing a crash. Then I restarted my GNOME session with my fork of the extension activated, repeated the experiment of unplugging my monitor, and the crash did not occur.

[maresb]

Note

AI Assistance Disclosure: This comment was created with assistance from Claude Opus 4.5 via Cursor.

Update: try/catch approach doesn't work

After deploying the try/catch fix, GNOME Shell still crashed with the same assertion failure. The crash occurred at line 19 of the patched extension (inside the safeGetWorkArea function).

Root cause: Mutter's assertion failure calls abort() at the C level, which terminates the process immediately. JavaScript try/catch cannot intercept this.

I've pushed an updated fix that checks if the window has a valid monitor before calling the work area methods, rather than trying to catch the error afterward:

function hasValidMonitor(metaWindow) {
  const windowMonitor = metaWindow.get_monitor();
  if (windowMonitor < 0) {
    return false;
  }
  const numMonitors = global.display.get_n_monitors();
  if (windowMonitor >= numMonitors) {
    return false;
  }
  return true;
}

If the monitor is invalid, the area, area_all, and area_cust fields are set to null instead of calling the methods that would trigger the crash.

[flexagoon]

Thanks!