Wayland and Weston 1.6 alpha snapshot (1.5.91)

[Jason Ekstrand]

On Aug 26, 2014 4:32 AM, "Pekka Paalanen" <ppaalanen at gmail.com> wrote:
>
> On Tue, 26 Aug 2014 10:36:58 +0100
> Daniel Stone <daniel at fooishbar.org> wrote:
>
> > Hi,
> >
> > On 23 August 2014 15:38, Pekka Paalanen <ppaalanen at gmail.com> wrote:
> >
> > > On Fri, 22 Aug 2014 10:51:19 -0700
> > > Jason Ekstrand <jason at jlekstrand.net> wrote:
> > > > On Fri, Aug 22, 2014 at 9:08 AM, Pekka Paalanen <ppaalanen at gmail.com
>
> > > wrote:
> > > > > Just before this alpha release, we bumped the xdg-shell
experimental
> > > > > version[1]. This means that the world breaks, as the experimental
> > > > > version must be matched exactly. Jasper will be bumping Mutter
and Gtk
> > > > > to match. We expect to have another bump before 1.6.0 is out, but
after
> > > > > that I think it will be solid.
> > > > >
> > > > > Then, in 1.7.0 we plan to move the xdg-shell.xml file into
Wayland, to
> > > > > be installed as a stable protocol for everyone to use, and
projects can
> > > > > throw away their private copies of xdg-shell.xml. That would be
the
> > > > > point where xdg-shell starts to guarantee backwards
compatibility. The
> > > > > 1.7.0 release should be the last flag day for xdg-shell.
> > > >
> > > > One small note here.  Even if we don't make any changes to xdg_shell
> > > > between 1.6 and 1.7, the universe will break again at 1.7.  This is
> > > because
> > > > we'll pull the experimental_version request which changes the order
of
> > > > things.  Do we have a plan for how to keep this from going too
badly?
> > >
> > > Well, yeah, that is what I meant by a flag day, the world breaks,
> > > but that should be the final one.
> > >
> > > Or do you think we should leave the experimental_version request
> > > in, and just document it is no longer used, and make all code work
> > > with it but ignore it? That would seem a bit strange to me.
> > >
> >
> > How about the following as a happy compromise:
> >   - bump the extension version from 1 to 2
> >   - require set_experimental_version for clients binding v1
> >   - assume an implicit experimental_version of 4 for clients binding v2,
> > accepting but not requiring set_experimental_version == 4
> >
> > That avoids breaking existing clients regardless of which version they
> > bind, but also means people hitting the new stable API don't have to
bother
> > with it. It would be nice if v1 was the stable API, and v0 was
> > unstable/development, but alas the scanner won't let us do that ...
>
> That still means leaving the use_unstable_version request in the
> protocol. This is the only time we could ever remove it.
>
> I think I would like more of the following, because for the 1.6 alpha,
> we already broke the world:
>
> - During the 1.6 alpha phase, as changes land to xdg-shell, we bump the
>   unstable version, breaking the world each time. This is a 2 week
>   period already running.
> - Just before 1.6-RC1 is about to be released, we remove the
>   set_unstable_version request. This acts as the final break-the-world.
> - 1.6.0 will be released with a stable xdg-shell protocol, but still in
>   Weston repository.
> - During the 1.7 development cycle, maybe towards the end, we move
>   xdg-shell.xml from Weston to Wayland, unchanged.
> - 1.7.0 will release with stable xdg-shell in Wayland.
>
> The good thing about this is that we do not leave the
> set_unstable_version haunting us, everything that worked against 1.6.0
> will continue to work against 1.7.0 and later, unless we find a serious
> flaw in xdg-shell that warrants a final break-the-world before 1.7.0 is
> out.

The problem is that we can't really break the world once we remove
set_unstable_version, or can we...?  In theory, if we really needed to, we
could make break-the-world changes and bump the interface version and then
kill any client that attaches to anything other than the "stable" version.
It'd be ugly, but it would work.

> It also means, that during the 1.7 development cycle, we must do our
> best to keep xdg-shell stable. New features may land, but they need to
> bump the interface versions properly, and be completely backwards
> compatible.

I'm not sure how confident I am in our ability to keep xdg_shell stable in
1.7.  Not that Jasper's doing a bad job or anything and xdg_shell has been
pretty stable for a while.  I'm just not sure if my confidence level is
quite high enough for that.  I'll give the xdg_shell spec another read with
Jasper's changes and think about it.

--Jason
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