[OE-core] [PATCH] boost: Convert ??= weaker assingment to weak ?= assignment

[Chris Larson]

On Wed, Jan 22, 2014 at 6:16 PM, Khem Raj <raj.khem at gmail.com> wrote:

> On Friday, December 06, 2013 05:42:26 PM Khem Raj wrote:
> > ??= does not react at all with
> > BOOST_LIBS += "${@base_contains('PACKAGECONFIG', 'python', 'python', '',
> > d)}"
> >
> > even though we have
> >
> > PACKAGECONFIG ??= "" it does not honor it and always add python to
> > BOOST_LIBS but the dependency is not added so it fails to build
> > complaining for missing python headers which is a understood outcome
> >
> > When converted to ?= it works as expected and only add --with-python
> > in bjam when python is specified in PACKAGECONFIG otherwise not.
> >
> > Is it a bitbake bug ? in anycase ?= should be enough of loose rope
> > to let user/distro configure the packageconfig policy
> >
>
> OK so the problem is that I have meta-ros in my layer-mix and in that layer
> it defines PACKAGECONFIG ?= "python" IMO it should have appended instead of
> redefining. Thats why I was seeing what I was seeing.


It's worth noting that recipes, in general, should use ?= rather than ??=,
but config files, in general, should use ??=. Otherwise it becomes
impossible for the config metadata to define an overriding default -- the
last ??= wins, after all, and that would always be the recipe. IMO default
values in the recipe are there to give sane behavior when there's no
configuration coming in from elsewhere, not to override configuration
defaults.
-- 
Christopher Larson
clarson at kergoth dot com
Founder - BitBake, OpenEmbedded, OpenZaurus
Maintainer - Tslib
Senior Software Engineer, Mentor Graphics
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