[Buildroot] [PATCH 2/4] prepare build infrastructure to pick up installed meson tool

[Yann E. MORIN]

Norbert, Thomas, All,

On 2019-10-16 21:01 +0200, Thomas Petazzoni spake thusly:
> On Wed, 16 Oct 2019 18:28:02 +0200
> Norbert Lange <nolange79 at gmail.com> wrote:
> > Well I do effectively use it, meson and its dependencies multiply my build-time,
> > builds systemd and my libfuse3 package fine.

So this had me wonder: why do you report that it works for you (and I am
ready to believe you), although we do have a patch that you are not
using?

Put in other words, I was wondering that, maybe, your report was an
indication that our patch was in fact no longer needed, in which case we
could drop it and would reconsider your proposal.

So I had to dig a bit on what this patch was doing (it is a relatively
simple patch), and why it was needed.

It turns out that the prupose of that patch is to ensure that a
host-meson-package that also uses a library installed by one of our
other host packages, keeps an RPATH to find that library (instead of not
finding it, or of finding the system-provided one).

This is nicely laid out in the git log for our patch:

    commit 5c939246a802c0ad9704dac1505105037542a1d3
    Author: Eric Le Bihan <eric.le.bihan.dev at free.fr>
    Date:   Sat Oct 27 19:59:22 2018 +0200

        meson: re-add patch for skipping RPATH fixing

        The patch to skip RPATH fixing performed by Meson was removed in commit
        a03f46ca6e9f43028003aedc92f1a1204ae7480f, as the script
        support/scripts/check-host-rpath was not complaining anymore.

        But without it, the problem still occurs for host packages [1].

        So, restore this patch to fix build of host packages with Meson.

        [1] http://lists.busybox.net/pipermail/buildroot/2018-October/232956.html

        Signed-off-by: Eric Le Bihan <eric.le.bihan.dev at free.fr>
        Signed-off-by: Thomas Petazzoni <thomas.petazzoni at bootlin.com>

So yes, ther are situations where using a system-provided meson _may_
work, but the generic case is that our patch is still required to ensure
that the situatiuon dexribed above still works.

Note that the only package in that situation in upstream Buildroot, is
libglib2, so if you don't have that, then you do not have the problem
this patch is solving.

So, with those explanations, I hope it is now clearer why we can't rely
on the system-provided meson.

Anyway, your proposal was interesting, if at least because it really
made us reconsider the usefulness of our patch.

> > > Another (more useful ?) thing to look at: is it possible to use the
> > > system-provided Python for Meson and Ninja, when python3 is provided by
> > > the system ? I think Meson and Ninja by themselves are not long at all
> > > to build, and it would be a much more useful direction for this patch
> > > series.  
> > Define "useful". The patches work correctly for me (tm), and I dont
> > use more than 1000 included packages that are useless for me (tm).
> > Even if meson is not ready (again: it is for me), then improving
> > buildroot ahead of it causes no harm?

The case "works for me" is not a valid reason, because as demonstrated
above, there are cases where it won't work.

Regards,
Yann E. MORIN.

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