[pacman-dev] [PATCH 2/5] meson.build: Fix detection of symbols

[Emil Velikov]

On Mon, 19 Apr 2021 at 15:05, Allan McRae <allan at archlinux.org> wrote:
>
> On 19/4/21 9:34 pm, Emil Velikov wrote:
> > On Mon, 19 Apr 2021 at 08:10, Allan McRae <allan at archlinux.org> wrote:
> >>
> >> On 17/4/21 1:45 pm, Mark Weiman wrote:
> >>> This patch changes the behavior of meson to define configuration options
> >>> *only* when the symbol checked is present. Currently, it defines all of
> >>> them in config.h whether the symbol exists or not and the code that
> >>> looks for it doesn't check the macro's value, but whether it's defined.
> >>>
> >>
> >> Remember back when we used autotools and all this just worked!  :D
> >>
> >> Patch looks good to me.
> >>
> > Food for thought:
> >
> > Usually the more robust approach is to always set the respective
> > defines to 0/1 and evaluate them directly (aka #if HAVE_).
> > In addition one could set -Werror=undef in the build to catch any issues.
> >
> > This will produce clear traces with potential issues, while #if
> > defined will silently fallback to the "other" path.
> > If people are OK with the above, I will follow-up with some patches.
> >
> > Note: above suggestion is not meant to dismiss the original patch.
> >
>
>
> I still live in the good old autotools days where there were lots of
> #undef in config.h...
>
> It appears some of that still happens.  This is my build/config.h:
>
> #undef HAVE_STRUCT_STATFS_F_FLAGS
> #define HAVE_STRUCT_STATVFS_F_FLAG
>
> But it is not consistent.
>
Speaking of consistency - here is a quick grep from an old-ish checkout:

$ git grep HAVE_LIBGPGME
...
lib/libalpm/be_sync.c:#ifndef HAVE_LIBGPGME // not defined, ok
...
lib/libalpm/sync.c:#ifdef HAVE_LIBGPGME // is defined, ok
meson.build:conf.set('HAVE_LIBGPGME', gpgme.found()) // hmm we always
define it, right?

Looking at the above one would say - we need CI to catch it. But we do
- see the arch-no-gpg config, still has gpgme installed :-\
Since the headers are in the standard location, they end up used. Even
if the final binary is missing the DT_NEEDED on gpgme.
Mind you that link thing is likely meson just adding a linker flag
(don't recall which one) to drop unneeded libraries from the DT_NEEDED
list.

Disclaimer: above is an educated guess, didn't stare at the build logs (yet).

Hmm HAVE_LIBSSL, ENABLE_NLS seems similar.

>
> I'm not sure whether the better solution is to add more #undef, or to go
> to the #if 0/1 style.
>
IMHO the above example/braindump illustrates why I'm in favour of 0/1
style. In addition, we had far too many bugs in Mesa and X (Xorg or
otherwise) so we gradually switched to 0/1.

-Emil