Re: [Qemu-devel] converting build system to Meson?

[Paolo Bonzini]

On 07/03/19 11:13, Peter Maydell wrote:
> Yes, that tends to be my view. Our current build system:
>  * has no dependencies that are problematic for older hosts
>    (contrast Meson, which needs Python 3.5, even if we take
>    the drastic step of shipping an entire build tool along
>    with QEMU; OSX python is 2.7 still)

Regarding OS X, don't we require Homebrew anyway?  (We will have to deal
with the Python 2 issue sometime in 2020, and I don't expect much
happening wrt Meson in QEMU before then).

>  * is not particularly hard to deal with for the common cases
>    ("add new source file" is straightforward)
>  * covers all our requirements as far as I'm aware
>    (whereas you've listed a couple of places where Meson
>    would need changes/extensions to support things we do already)

Indeed---I mentioned that rejection of these changes/extensions would be
a blocker.  I think those extensions are useful anyway, so I am
contributing them to Meson even if we don't end up using them.  My
experience so far with the Meson community makes me positive that _some_
kind of solution will be found even if it's not what I'm proposing.

> (This might change in the future, eg if Meson catches on to the
> extent that everybody is using it and competitors like CMake are
> more obviously eclipsed by it, in the way that git took over
> from svn and relegated mercurial and bzr to obscurity.)

It's very hard to displace established contenders in this area because
unlike, switching to git or svn, a switch involves a major rewrite
effort.  Nevertheless, big projects _are_ switching.

Meson has a very different design than Autotools or even CMake, despite
the apparent similarity with the latter.  The lack of an escape
mechanism sounds annoying, but it is much less of a problem than you'd
think.  In fact it has the interesting side effect, of discouraging
forks very much: new features are contributed upstream for everyone's
use and vetted by the Meson developers.

This makes Meson way more polished than CMake or Autotools, or
hand-crafted Makefile such as ours; so it takes more effort to switch,
but the result is good.  I have started following Meson about a year
ago, and a lot of missing features have been added since then, slowly
but surely, which is why I am only reaching out now to you and others.

Paolo