[Mesa-dev] last call for autotools

[Ilia Mirkin]

On Wed, Dec 19, 2018 at 1:30 PM Dylan Baker <dylan at pnwbakers.com> wrote:
>
> Quoting Nicolai Hähnle (2018-12-18 09:37:43)
> > On 17.12.18 23:46, Dylan Baker wrote:
> > > Quoting Marek Olšák (2018-12-17 12:25:29)
> > >> On Mon, Dec 17, 2018 at 1:18 PM Eric Anholt <eric at anholt.net> wrote:
> > >>
> > >>      Eero Tamminen <eero.t.tamminen at intel.com> writes:
> > >>
> > >>      > Hi,
> > >>      >
> > >>      > On 17.12.2018 8.08, Marek Olšák wrote:
> > >>      > [...]
> > >>      >> I think one of the serious usability issues is that
environment
> > >>      >> variables such as CFLAGS, CXXFLAGS, LDFLAGS, and
PKG_CONFIG_PATH are not
> > >>      >> saved by meson for future reconfigures.
> > >>      >
> > >>      > I don't know what Meson is supposed to do, but to me that
would be
> > >>      > a bug in a build tool.
> > >>      >
> > >>      > Re-configure is supposed to adapt SW to the changes in the
build
> > >>      > environment, and environment variables are part of that
(along with
> > >>      > command line options and SW installed to to the system).
Build
> > >>      > configure tool deciding to "remember" some of those things
instead
> > >>      > of checking the new situation, seems like a great opportunity
for
> > >>      > confusion.
> > >>
> > >>      A user-triggered reconfigure, sure.  Recapture env vars then.
But "git
> > >>      pull; ninja -C build" losing track of the configuration state
is broken.
> > >>      We don't have to specify all of your meson -Doption=state
configuration
> > >>      on every build, why should you need to specify your
PKG_CONFIG_PATH
> > >>      configure options on every build?
> > >>
> > >>
> > >> Thanks, Eric.
> > >>
> > >> Yes, meson behaves such that users have to set all environment
variables for
> > >> every "ninja" command that might reconfigure.
> > >>
> > >> I see 2 solutions:
> > >> 1) meson needs to remember the relevant env vars
> > >> 2) meson should FAIL to configure if any of the env vars are set (if
it wants
> > >> to ignore them)
> > >>
> > >> Marek
> > >
> > > Meson does remember the *_FLAGS variables. Those are translated on
configure
> > > into meson's internal ${lang}_args and ${lang}_link args. It does
look like
> > > those aren't remembered when --wipe is called though, I filed a bug
for that:
> > > https://github.com/mesonbuild/meson/issues/4650
> >
> > I ran into this same problem and noticed that Meson is already able to
> > *warn* about such changes.
> >
> > It should either ignore the changes, or better yet, fail.
> >
> > (Or even better: ignore environment variables entirely; IMO sourcing the
> > environment implicitly in a build system with an explicit configure is
> > just a broken design that was unfortunately inherited from plain make
> > without really considering the UI implications.)
>
> I agree with this, as do most of the upstream meson developers. So do the
> autotools developers, who recommend passing CFLAGS (and friends) as
arguments
> instead of as env variables:
>
> ./configure CFLAGS='-march=native -03' LDFLAGS='-O3' --enable-foo
>
> meson supports this using:
>
> meson -Dc_args='-march-native' -Dc_link_args='-O3' -Dfoo=true
>
> Meson basically inherited this from autotools, and in hindsight we
shouldn't
> have.
>
> I'm going to do 3 things I think:
> - Update our documentation to strongly recommend -Dc_args and not CLFAGS
> - Push for meson to warn about using environment variables and recommend
command
>   line options.
> - Push for meson to remove CFLAGS and friends support:
>   https://github.com/mesonbuild/meson/issues/4664

FWIW when I was talking about env vars, I was very much referring to

./configure CFLAGS=..., not the CFLAGS=... ./configure variant -- that's
fraught with peril.

An especially important one to be able to bake in is PKG_CONFIG_PATH.
Having support for just doing it rather than knowing what the mapping to
meson is would be rather preferable -- e.g.

meson CFLAGS=...
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