[libvirt PATCH 037/351] meson: add readline build option

[Andrea Bolognani]

On Wed, 2020-08-05 at 11:23 +0200, Erik Skultety wrote:
> On Wed, Aug 05, 2020 at 10:59:08AM +0200, Andrea Bolognani wrote:
> > Erik reports that there are issues with building RPMs on CentOS. He
> > opened https://gitlab.com/libvirt/libvirt-ci/-/merge_requests/42, but
> > it seems to me that the topic should be discussed here instead, so
> > I'm quoting his message and replying inline.
> > 
> > > After libvirt switched to the meson build system, rpmbuild on
> > > CentOS is no longer viable as meson >= 0.54.0 is required while
> > > only 0.49.2 (at the time of this patch) is available from the
> > > package manager. Even if --nodeps is passed, the "%meson" RPM macro
> > > won't expand and the build will fail.
> > 
> > The question is, was dropping RPM build support for CentOS an
> > intentional change? I'm not sure it was, because otherwise the spec
> > file could have been cleaned up a bit at the same time. If it was
> > not, then we need to make use of the `%meson` macro conditional.
> > 
> > As an aside, I haven't actually checked, but I think that even though
> > CentOS 8 ships a version of Meson that's too old for us it should at
> > least have the `%meson` macro. Maybe that won't work with a Meson
> > installed from PyPi, though...
> 
> One thing I haven't tried is to install the old meson and use --nodeps with
> rpmbuild, still, rather than having 2 version of meson installed on CentOS for
> the rpmbuild, we should fallback to something else if %meson isn't defined.

Oh, I see now the %meson macro is shipped as part of meson itself. We
definitely don't want to install two versions of meson, and if we end
up agreeing that keeping RPM builds working on CentOS is important we
will have to work around the need for the macro on CentOS 7 anyway,
so we should be able to use that same workaround on CentOS 8 too.

> > > It doesn't end there though, even if meson 0.54.0 were available,
> > > the rpm build would still fail because of readline-devel not
> > > providing the pkg config file on CentOS-8 which we rely on.
> > 
> > Looking at the lastest pipeline, all CentOS versions have "readline:
> > NO" in their build summary, but the build still succeeded, so I'm not
> > sure why the RPM build would fail? readline is an optional
> > dependency, and we're not passing `-Dreadline=enabled`.
> > 
> > Additionally, the complex logic necessary to detect readline
> > correctly, even in the absence of its pkg-config file, is still
> > present in `meson.build`, so I'm not sure why it's not doing what
> > it's supposed to do...
> 
> Well, I just reported what happened to me yesterday when I was doing some mdev
> review on CentOS 8 and wanted to do an RPM install of the latest libvirt, meson
> couldn't be re-built from the latest spec on CentOS 8, but taking the binary
> package directly from Fedora 32 worked like a charm and then I hit the readline
> issue for some reason, it's true I've had a bunch of packages (including
> readline) installed manually in order to overcome the meson issues.
> I'll re-try in a completely clean environment to see whether the missing
> readline pkg config was only related to my environment or it actually fails the
> build.

I don't understand exactly what issue you ran into based on your
description, but even just looking at the pipeline shows that
something is not quite right, since readline was detected correctly
on CentOS before the switch and now it isn't. I'm hoping Pavel can
shed some light there :)

-- 
Andrea Bolognani / Red Hat / Virtualization