Re: deprecation of in-tree builds

[BALATON Zoltan]

On Tue, 31 Mar 2020, Daniel P. Berrangé wrote:
> On Tue, Mar 31, 2020 at 05:04:16PM +0200, BALATON Zoltan wrote:
> > OK, so then only supporting out-of-tree builds but adding convenience
> > function and Makefile to still allow people to run configure; make from
> > source dir would solve this without also needing people to change what they
> > always did so why is that solution not acceptable?
>
> There's several scenarios discussed. Currently we don't do anything to
> prevent src-dir builds, so there's no need to extra make magic described
> I proposed a patch to add a warning, but it still allows src-dir builds,
> so nothing functional has changed.
>
> We could forbid src-dir builds now and add the magic to redirct to a
> build-dir. That would work, but I don't think we should block src-dir
> builds in make, assuming we have a switch to meson arriving in the
> near-ish future.

So then why print a warning when it will change again when the build 
system is replaced? Isn't it enough to worry about it at that point? If it 
works now as before then no need to constantly bug people at every 
cofigure invocation. Simply put a warning in changelog that current build 
system is deprecated and will be replaced with something else like Meson 
in some future release and that should be enough to notify people about 
the coming change. You don't print warnings for every other deprecated 
features either.

> Once we switch to Meson there will inevitably be some disruption in
> build system ussage as it is a completely new tool. That makes it a
> good flag day for forbidding src-dir builds. Given that it is a flag
> day, I don't think there's any need to create makefile magic at that
> time.

Ideally a change in build system should make it more convenient to work 
with not more inconvenient otherwise it's questionable if we want to 
introduce it at all but we'll see then. But then why bug people with a 14 
line warning now if they'll have to change their ways again shortly? I 
thought you wanted to get rid of in-tree builds now to ease the 
maintenance of current make system and the convenience makefile would 
help that.

> IMHO we shouldn't be so afraid of change that we need to try to preserve
> every precise way of working we've had in the past. In the long term this
> frame of mind holds back the project and promotes a negative impression
> of QEMU as an old, outdated project resistant to any kind of change.

I did not say that. What I said was that you can change or replace the 
build system with whatever you want as long as I can still run make (or 
equivalently simple command) in source dir and it will build the project. 
I can live with build results moved to a subdir to ease your task of 
managing build system so you don't have to support two ways of building 
now. But if you say this will still work for now and don't mind continue 
to support it as before at least until a new build system is introduced 
I'm happy with that too. I'll raise same complaints against new build 
system then when it's about to be merged.

Regards,
BALATON Zoltan