Meson build

[Pavel Hrdina]

On Tue, Sep 01, 2020 at 11:38:59AM -0600, Jim Fehlig wrote:
> On 9/1/20 7:55 AM, Daniel P. Berrangé wrote:
> > On Tue, Sep 01, 2020 at 03:50:36PM +0200, Ján Tomko wrote:
> > > On a Tuesday in 2020, Pavel Hrdina wrote:
> > > > On Tue, Sep 01, 2020 at 03:13:39PM +0200, Ján Tomko wrote:
> > > > > On a Tuesday in 2020, Pavel Hrdina wrote:
> > > > > > On Sun, Aug 30, 2020 at 02:34:56AM +0200, Toolybird wrote:
> > > > > > > Hi,
> > > > > > > 
> > > > > > > Just a heads up on my experiences with the new build system.
> > > > > > > 
> > > > > > > Arch Linux
> > > > > > > meson-0.55.1
> > > > > > > 
> > > > > > > Overall, it looks good, so well done!
> > > > > > > 
> > > > > > > Just a couple of minor things I noted:
> > > > > > > 
> > > > > > > 1. Arch uses a meson wrapper script (arch-meson) that sets:
> > > > > > > 
> > > > > > >    --buildtype plain
> > > > > > > 
> > > > > > > This seems to trigger a bug in meson that results in copious bogus compiler warnings:
> > > > > > > 
> > > > > > > cc1: warning: ‘-Wformat-y2k’ ignored without ‘-Wformat’ [-Wformat-y2k]
> > > > > > > cc1: warning: ‘-Wformat-extra-args’ ignored without ‘-Wformat’ [-Wformat-extra-args]
> > > > > > > cc1: warning: ‘-Wformat-zero-length’ ignored without ‘-Wformat’ [-Wformat-zero-length]
> > > > > > > cc1: warning: ‘-Wformat-contains-nul’ ignored without ‘-Wformat’ [-Wformat-contains-nul]
> > > > > > > cc1: warning: ‘-Wformat-security’ ignored without ‘-Wformat’ [-Wformat-security]
> > > > > > > 
> > > > > > > which of course breaks -Werror builds.
> > > > > > > 
> > > > > > > I can easily work around it by setting `-D git_werror=disabled' or even better still:
> > > > > > > 
> > > > > > > CFLAGS+=" -Wall" arch-meson...
> > > > > > 
> > > > > > This should be easily fixable by adding -Wformat in our list of flags
> > > > > > that we pass to compiler. We were incorrectly relying on meson to add
> > > > > > -Wformat automatically and since we add the other -Wformat* flags
> > > > > > manually we should add -Wformat as well. I'll post a patch to fix this.
> > > > > > 
> > > > > 
> > > > > What would that fix?
> > > > > 
> > > > > It would neither be a plain build, nor a full -Werror build (since we're
> > > > > missing -Wall).
> > > > 
> > > > It would fix building libvirt from git in case user uses
> > > > buildtype=plain.
> > > > 
> > > 
> > > For a build from git, we expect people to build with all the warnings
> > > and -Werror.
> > > 
> > > Per your comment in the below issue:
> > > https://github.com/mesonbuild/meson/issues/7399#issuecomment-684856012
> > > meson does not add the warnings there on purpose.
> > > 
> > > The combination of disabling the most important warnings and enabling
> > > just the extras doesn't make much sense. Especially if we still pretend
> > > it's a -Werror build.
> > 
> > Yeah, I'd recommend distros to NOT use  buildtype=plain.
> 
> AFAICT, rpm builds that use the %meson macro will also have buildtype=plain.
> From /usr/lib/rpm/macros.d/macros.meson of the meson-0.54 package
> 
> %meson \
>     %set_build_flags
>     %{shrink:%{__meson} \
>         --buildtype=plain \
>         --prefix=%{_prefix} \
>     ...
> 
> > Having the full set of warnings including -Werror enabled is a good thing
> > in general, even for distros. There have certainly been cases where
> > distros backported a patch incorrectly and warning flags would have
> > identified it, especially combined with -Werror.
> 
> Nod. Should we adjust the upstream spec file to enable the full set of
> warnings? And if so what would be the best way to do that? Add
> --buildtype=debug to the meson options? E.g.
> 
> %meson \
>            --buildtype=debug \
>            -Drunstatedir=%{_rundir} \
>            %{?arg_qemu} \
>            ...

There is no need to do anything for spec file, see the patch I posted to
libvir-list [1].

Pavel

[1] <https://www.redhat.com/archives/libvir-list/2020-September/msg00045.html>
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