Fedora, GNOME, Linux

Story of GNOME Shell Extensions

A long time ago (exactly 10 years ago) it was decided that the the shell for GNOME would be written in JavaScript. GNOME 3 was still looking for its new face, a lot of UI experimentation was taking place, and JavaScript looked like the best candidate for it. Moreover it was a popular language on the web, so barriers to entry for new contributors would be significantly lowered.

When you have the shell written in JavaScript you can very easily patch it and alter its look and behaviour. And that’s what people started doing. Upstream was not very keen to officially support extensions due to their nature: they’re just hot patching the GNOME Shell code. They have virtually unlimited possibilities in changing look and behaviour, but also in introducing instability.

But tweaking the shell became really popular. Why wouldn’t it? You can tweak your desktop by simply clicking buttons in your browser. No recompilations, no restarts. So extensions.gnome.org was introduced.

The number of available extensions grew to hundreds and instability some of them occasionally introduced seemed like a fair price for the unlimited tweakability. In the end when the Shell crashed it was just a blink. Xorg held up the session with opened clients, the Shell/Mutter was restarted and the show could go on.

In 2016 GNOME switches to Wayland by default. No Xorg and also nothing to hold up the session with opened clients when the Shell crashes. There is only Mutter as a Wayland compositor, but unfortunately it runs in the same process as GNOME Shell (a decision also made 10 years ago when it also looked like a good idea). If the Shell goes down, so does Mutter. Suddenly harmless blinks became desktop crashes with losing all unsaved data in opened applications.

I read user feedback and problems users are having with Fedora Workstation (and Linux desktop in general) a lot on the Internet. And desktop crashes caused by GS extensions are by far the most frequent problem I’ve seen recently. I read stories like “I upgraded my Fedora to 28 and suddenly my desktop crashes 5 times a day. I can’t take it any more and I’m out of ideas” on daily basis. If someone doesn’t step in and say: “Hey, do you have any GS extensions installed? If so, disable them and see if it keeps crashing. The extensions are not harmless, any error in them or incompatibility between them and the current version of GS can take the whole desktop down”, users usually leave with the experience of unstable Linux desktop. It hurts our reputation really badly.

Are there any ways to fix or at least improve the situation? Certainly:

  1. Extensions used to be disabled when the Shell crashed hard (couldn’t be restarted). Since on Wayland it’s the result of every crash, we should do that after every GS crash. And when the user goes back to GNOME Tweak Tool to enable the extensions again, she/he should be told that it was mostly likely one of the 3rd party extensions that made the desktop crash, and she/he should be careful when enabling them.
  2. Decoupling GNOME Shell and Mutter or/and other steps that would bring back the same behaviour like on Xorg: GS crash would not take everything down. This would require major changes in the architecture and a lot of work and GNOME Shell and Mutter developer community has already a lot on their plates.
  3. Discontinuing the unlimited extensions, introducing a limited API they can use instead of hot patching the GS code itself. This would be a very unpopular step because it’d mean that many of the existing extensions would be impossible to implement again. But it may become inevitable in the future.
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