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

[Richard Purdie]

On Thu, 2014-01-23 at 08:43 -0800, Khem Raj wrote:
> On Thursday, January 23, 2014 09:31:47 AM Chris Larson wrote:
> > 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.
> 
> yes I think thats a good point. so lets consider this patch for inclusion
> now we know the reason, I can resubmit with proper subject and patch header

It might be worth trying to standardise this in OE-Core rather that pick
off the recipes one by one. Most new PACKAGECONFIGs are cut and paste
from others so the problem will spread until we fix them consistently.

Cheers,

Richard