[OE-core] [PATCH] base.bbclass: Add support to EXTRA_DISTRO_FEATURES

[Phil Blundell]

On Tue, 2013-07-30 at 09:46 -0500, Mark Hatle wrote:
> They want a method similar to the one posted by Otavio in order to tailor the 
> system.  End users never want to create a new distribution, they simply want to 
> start with one and tweak it.

They can already do that by overriding the distro's own DISTRO_FEATURES
in local.conf (modulo poky's alleged _append thing), and/or by copying
and hacking the distro.conf file itself.  And, of course, any distro
which intends itself to be explicitly end-user-tweakable like this is
welcome to include a mechanism like Otavio's one in their own layer.

> So with that said, my opinion is to enable this code, allowing end users to 
> tweak their distribution settings.  But make it a stated policy that 
> distribution layers should only "set" the value of DISTRO_FEATURES, and should 
> never modify/update this new EXTRA_DISTRO_FEATURES value.  (Of course, I doubt 
> there is a way to police that, other then state it's policy.)

Both end-users and distro maintainers already have enough trouble
understanding what the interactions are between the different variables
and who's meant to be setting which ones (see DISTRO_FEATURES_BACKFILL
for example which seems to be fairly frequently misunderstood).  Adding
extra complexity to what is already a fraught area seems like a bad
plan.

> This is the same type of reason that end users was a "don't install this 
> package" feature as well.  While anyone can write a new image recipe, nobody 
> wants to, especially when they only want one or two less packages in their image.

End users already have BAD_RECOMMENDATIONS for that, right?  And
courtesy Paul's recent changes I think this now even works for the
rpm-using fraternity.

p.