Re: deprecation of in-tree builds

[BALATON Zoltan]

On Tue, 31 Mar 2020, Eric Blake wrote:
> On 3/31/20 7:02 AM, Kevin Wolf wrote:
> > Am 31.03.2020 um 09:48 hat Paolo Bonzini geschrieben:
> > > On 30/03/20 16:37, Kevin Wolf wrote:
> > > > 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.
> > >
> > > Serious question: why is automatic directly creation more convenient for
> > > developers?  Even if "./configure" generates a "build" directory for
> > > you, you would still have to invoke the QEMU binary as
> > > "build/x86_64-softmmu/qemu-system-x86_64".  That is less convenient than
> > > doing "mkdir build" in the first place.
> >
> > Mainly because it allows me to start everything (most importantly: my
> > editor, git and make) from the same directory.
> >
> > I guess the automatic directory creation is the less important part
> > compared to a Makefile in the source tree that calls the Makefile in the
> > build directory, because creation the directory is a one-time thing, but
> > I call make all the time.
>
> If we make in-tree ./configure create a GNUmakefile shim that auto-forwards 
> to build/, it would also be possible to create symlinks to the various 
> targets that will live in build.  I recently switched my qemu playground to 
> use VPATH builds, but with symlinks such as qemu-img -> build/qemu-img, I can 
> still use my muscle memory of an in-tree build for normal development.
>
> > Creating it automatically is nice especially for those who build QEMU
> > for the first time and expect that the ./configure; make; make install
> > sequence they are used to just works.
> >
> > Prefixing build/ when using the binaries is a change, too, but I guess
> > tab completion means that it's not much worse than prefixing ./
>
> With symlinks, it is possible to give much more than 'make' the illusion of 
> working in-tree.  It then boils down to a question of how many symlinks are 
> worth creating.

Also creating symlinks, while nice, is probably added maintainance burden 
because it's something that only needs to be done in in-tree runs so it 
will likely get broken by those using only out of tree. I think getting 
results in a build dir is acceptable (most results are already in some 
subdir at least for system emulation) and just adding convenience Makefile 
is not much complexity while preserving symlinks for build results would 
be so that's probably not much maintenance improvement over current 
situarion.

Regards,
BALATON Zoltan