[PATCH wayland] RFC: Require WAYLAND_DISPLAY to be set instead of using wayland-0 as the default

[Pekka Paalanen]

On Mon, 25 May 2015 01:12:15 -0700
Dima Ryazanov <dima at gmail.com> wrote:

> Although defaulting to wayland-0 seems convenient, it has an undesirable
> side effect: clients may unintentionally connect to the wrong compositor.
> Generally, it's safer to fail instead. Here's a real example:
> 
> In Fedora 22, Gtk+ prefers Wayland over X11, though the default session is still
> a normal X11 Gnome session. When you launch a Gtk+ app, it will try Wayland,
> fail, then try X11, and succesfully start up. That works fine.
> 
> Now suppose you launch Weston while running the Gnome session. Suddenly, all
> of the Gtk+ apps launched from Gnome will show up inside Weston instead.
> That's unexpected. There's also no good way to prevent that from happening
> (other than perhaps setting WAYLAND_DISPLAY to an invalid value when launching
> an app).
> 
> Not using wayland-0 as the default will solve that problem: an app launched
> from the X11 Gnome session will use the X11 backend regardless of whether
> there's a wayland compositor running at the same time.
> 
> Everything else should work as before. The compositor already sets
> the WAYLAND_DISPLAY when starting the session, so the lack of the default value
> should not make a difference to the user.

Hi,

I have a vague recollection this has been proposed before, but I can't
remember if there was any interest or discussion, nor what was the
original intent behind defaulting to "wayland-0".

Personally I'd be fine with this change, but I can't imagine what would
break if we did this.

Need more opinions.


Thanks,
pq