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Re: deprecation of in-tree builds

From: BALATON Zoltan
Subject: Re: deprecation of in-tree builds
Date: Tue, 31 Mar 2020 17:20:57 +0200 (CEST)
User-agent: Alpine 2.22 (BSF 395 2020-01-19)

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.


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