crash "Could not grab modal"

[joeyh]

Describe the bug

Paperwm crashes with "Could not grab modal" and I have to restart gnome shell in order to switch between windows.

Here's the top lines from journalctl --user after the crash:

Jan 24 13:25:43 darkstar alacritty[3796845]: ../../../../modules/im/ximcp/imDefLkup.c,419: The application disposed a key event with 133011 serial.
Jan 24 13:25:41 darkstar gnome-shell[1814058]: JS ERROR: Error: Could not grab modal
                                               ActionDispatcher@file:///home/joey/.local/share/gnome-shell/extensions/paperwm@paperwm.github.com/navigator.js:88:19
                                               getActionDispatcher@file:///home/joey/.local/share/gnome-shell/extensions/paperwm@paperwm.github.com/navigator.js:521:18
                                               preview_navigate@file:///home/joey/.local/share/gnome-shell/extensions/paperwm@paperwm.github.com/navigator.js:548:39
                                               asKeyHandler/<@file:///home/joey/.local/share/gnome-shell/extensions/paperwm@paperwm.github.com/keybindings.js:368:51
                                               @resource:///org/gnome/shell/ui/init.js:21:20
Jan 24 13:25:41 darkstar gnome-shell[1814058]: Failed to grab modal

To Reproduce

I don't have a reliable way to cause this crash, but I have seen it repeatedly when all I have open is some alacritty windows, probably fullscreen, and am switching back and forth between them using paperwm hotkeys.

System information:
Distribution: Debian GNU/Linux
GNOME Shell: 47.3
Display server: Xorg
PaperWM version: 47.1.0
Enabled extensions:

• netspeedsimplified@prateekmedia.extension
• executor@raujonas.github.io
• just-perfection-desktop@just-perfection
• paperwm@paperwm.github.com
• battery-usage-wattmeter@halfmexicanhalfamazing.gmail.com
• drive-menu@gnome-shell-extensions.gcampax.github.com

[icyflame]

@joeyh Thanks for this issue report. I have run into the same issue multiple times on Ubuntu 22.04 and Gnome 44 with this extension enabled.

I don't know much about Gnome Shell extensions, but looking through the code, this looks like it is caused by a function calling pushModal => failing to get a grab (?) over the keyboard => not restoring the state to the way that things were before pushModal and instead failing immediately.

My first attempt was to call only popModal, but this did not work. It left the minimap open on the screen, in addition to the crash that we see here. icyflame#1

My second attempt at a naive fix worked a bit better: icyflame#2

For this, I simply followed the stacktrace from the error that was seen in journalctl .../gnome-shell, and attempted to clean up the state properly by calling functions like popModal and destroy appropriately.

I have been using this for a week now (~8 hours a day), and I have not yet run into the same issue again. 🎉

I did not suggest a change to this repository directly because there is no reliable way to reproduce the bug, and thus no way that I can be confident this works or is even idiomatic in the Gnome Shell extensions world. I really like this extension, so I wanted to make a small change that would reduce the occurrence of this bug.

---

The main assumption made by this extension is that pushModal works and gets the appropriate grab; if not, there is a crash, with this extension holding partial control over the input methods. The code for gnome-shell does not make any guarantees that pushModal will work, so cleaning up the state after pushModal fails is perhaps what the extension's responsibility? https://github.com/GNOME/gnome-shell/blob/15a7b457dad3e745e450236a8cc336b134362fb1/js/ui/main.js#L682-L701

If anyone is more familiar with this, it would be great to get some input on whether my naive attempt at a fix above works for you (icyflame#2). And if we could collaborate on a way to reproduce the bug, and fix it in this extension for future versions too.

[icyflame]

@joeyh Hello again, I have been using the above "simple" fix for the past month and I did not run into a single could not grab modal crash 😌 🎉 I have opened a PR to the develop branch, with a clean change that does only graceful error handling: #1031 Please take a look! And if at all possible, and if you are still using PaperWM, please use this patched version of PaperWM and let us know if you run into any crashes! It would be great to get some eyes on my changes and experiences that validate whether this change actually helps others.