Re: [OE-core] [PATCH] file: Remove unneccessary override of PACKAGECONFIG for native

["Peter Kjellerstedt" <peter.kjellerstedt@axis.com>]

> -----Original Message-----
> From: Andre McCurdy <armccurdy@gmail.com>
> Sent: den 14 maj 2020 00:49
> To: Richard Purdie <richard.purdie@linuxfoundation.org>
> Cc: Peter Kjellerstedt <peter.kjellerstedt@axis.com>; OE Core mailing
> list <openembedded-core@lists.openembedded.org>
> Subject: Re: [OE-core] [PATCH] file: Remove unneccessary override of
> PACKAGECONFIG for native
> 
> On Wed, May 13, 2020 at 2:31 PM Richard Purdie
> <richard.purdie@linuxfoundation.org> wrote:
> > On Wed, 2020-05-13 at 12:30 -0700, Andre McCurdy wrote:
> > > Yes. Unfortunately making recipes robust for users who want to change
> > > PACKAGECONFIG values doesn't seem to be a high priority for oe-core.
> > > Why else would default PACKAGECONFIG values be assigned with ??=
> > > instead of ?= other than as a trap for new users?
> >
> > I'm not sure I understand that, equally I'm tired so I'll assume I'm
> > just missing something.
> >
> > I will say that there is no intention to make OE-Core hard to use or
> > not robust, its only as good a the people contributing make it. In this
> > case I'm not sure I understand/see the problem.
> >
> > If we should be using ?= instead of ??= then I'm open to an explanation
> > why and patches to improve things.
> 
> If the default is assigned with ??= then trying to add to it with +=
> results in the default value being lost. If the default is assigned
> with ?= then adding to it with += works as expected.
> 
> To robustly enable a new PACKAGECONFIG option, users need to learn to
> use PACKAGECONFIG_append (and obviously learn about the leading space
> requirement there too) and not to try PACKAGECONFIG +=.
> 
> The reference manual does at least have an example which uses _append.
> However it doesn't mention that += isn't safe or that _append will
> affect native(sdk) and therefore _append_class-target is the safest
> approach.
> 
> > Unfortunately we do have quite some legacy and ??= vs ?= has been
> > troublesome in the many different contexts we have (recipe, class,
> > conf, inc and so on).

Actually, I have always wondered why the recipes in OE-Core typically 
use PACKAGECONFIG ??= "..." when no other variables (in the recipes) 
are defined that way. After all, if I want to override the default 
value in a bbappend as PACKAGECONFIG = "...", that works just as well 
if the variable is defined using = rather than ?= or ??=. And if I do 
it in local.conf, I would typically do it using PACKAGECONFIG_pn-foo 
and then it also doesn't matter whether = or ??= was used to define 
the default in the recipe. Add to that the complications with not 
being able to use += together with ??= in a sensible way, it even 
makes less sense.

For the record, in our own recipes we use PACKAGECONFIG = "..." in the 
recipes and that would be my recommendation for OE-Core as well.

//Peter