Re: deprecation of in-tree builds

[BALATON Zoltan]

On Mon, 30 Mar 2020, Michal Suchánek wrote:
> On Mon, Mar 30, 2020 at 04:37:59PM +0200, Kevin Wolf wrote:
> > Am 30.03.2020 um 15:42 hat Daniel P. Berrangé geschrieben:
> > > On Mon, Mar 30, 2020 at 02:31:52PM +0100, Peter Maydell wrote:
> > > > On Mon, 30 Mar 2020 at 14:26, Markus Armbruster <address@hidden> wrote:
> > > > > Peter Maydell <address@hidden> writes:
> > > > >
> > > > > > AIUI from Paolo, the intention is to deprecate and eventually
> > > > > > stop supporting "in-tree" builds, so that the only option is
> > > > > > building in a separate build directory. I thought we should
> > > > > > probably mention that in the 5.0 changelog, so I wrote up some
> > > > > > text:
> > > > > >
> > > > > > https://wiki.qemu.org/ChangeLog/5.0#Build_Information
> > > > >
> > > > > Overdue.  Thanks for doing this!
> > > > >
> > > > > > Suggestions for changes/comments etc welcome.
> > > > >
> > > > > Looks fine to me.
> > > >
> > > > Consensus in the thread seemed to lean towards having
> > > > the 'configure/make' runes auto-create a build directory;
> > > > if we want to do that we should probably not say anything in
> > > > the release notes, because we'll cause people to change
> > > > unnecessarily. Or at least have them say "We recommend
> > > > out-of-tree builds. In future we might make the commands
> > > > that currently do an in-tree build automatically create
> > > > and use a build directory for you." rather than a blanket
> > > > "we're going to drop this and you should change what you
> > > > do now".
> > > >
> > > > Thoughts?
> > >
> > > When the time comes to switch to Meson, we'll be forcing a
> > > separate build directory & that will also potentially involve
> > > a change in build instructions for users.
> > >
> > > So if we expect Meson will arrive in QEMU soon (say before end
> > > of this year), then I'd try to keep changes related to make to
> > > the bare minimum, and have Meson switch as the "flag day" when
> > > developers are forced to adapt their build process.
> > >
> > > IOW, merely warn people that in-tree builds are deprecated and
> > > not tested by the project and enourage switching to out of tree
> > > builds. Dont try to magically create a separate build dir now.
> >
> > If manually dealing with separate build directories is inconvenient
> > today, it will still be inconvenient with Meson, so this would mean
> > introducing the automatic directly creation together with the other
> > changes to enable Meson. Which is fine by me, as long as it is really
> > done when the external directory becomes mandatory, so that people won't
> > have to switch back and forth between directories.
>
> From packaging point of view if something has auto* files the default is
> IIRC to do in-tree build with most package managers. You have to adjust
> manually for out-of-tree build. I am not sure what is state of Meson
> support in packaging scripts across distributions. Most likely it will
> not be picked automagically so you have to provide a custom build script
> anyway. Then it is the time to look up the canonical build instructions.
>
> In other words dealing with Meson is inconvenient either way. Building
> in-tree or out-of-tree becomes a non-issue whan you switch to exotic
> build system anyway.
>
> That's not to say that auto* tools are great. It's just the replacements
> have issues that are not well understood by average Joe Packager while
> the auto* tools have good old issues people know how to deal with.

Actually QEMU does not use auto* tools, it just has a configure script 
that mimics that. This may not be the best way to do it but this is 
convenient for people trying to compile it and works as expected so I 
think this behaviour should be preserved if possible just to not upset 
developers and packagers unnecessarily.

Regards,
BALATON Zoltan