[OE-core] RFC: FOO_subtract, the logical antidote to FOO_append.

[Chris Larson]

On Wed, May 16, 2012 at 8:07 AM, Mark Hatle <mark.hatle at windriver.com> wrote:
> On 5/15/12 11:35 PM, Saul Wold wrote:
>>
>> On 05/15/2012 11:46 PM, Manuel Bessler wrote:
>>>
>>> Just a few minutes ago I was wondering if such a feature did exist...
>>>
>>> I ran into a situation where I wanted to remove something from a
>>> .bbappend
>>> that is added to a variable using VARIABLE_append = "this and that"
>>>
>> My understanding is that a _subtract is fraught with danger, there all
>> sorts of ordering implications.
>>
>> For what you are trying to do in a .bbappend, can be done by using
>> oe_filter_out() from utils.bbclass, it has to be done in anonymous code.
>>
>> VARIABLE := "${@oe_filter_out('xxx', '${VARIABLE}', d)}"
>>
>> This might be what you want.
>
>
> There are two issues I believe Peter is having.. the first is trying to
> figure out how to filter stuff out of _append.  I'm sure sure the above will
> be able to do that.
>
> But the real problem we keep struggling with is .conf load order.. you try
> to set some nice value in local.conf, and some later configuration file adds
> to it, or simply overwrites it.  He'd like a way to strip out things like
> that.
>
> I suspect the real answer though is fix the various configuration settings
> to better allow them to be overridden, but I'm not sure exactly how.

One related thing that won't solve this, but is worth noting -- I
think ??= is a much more sane choice than ?= in almost all cases. We
should think about a janitorial task to switch to ??= after carefully
considering potential implications for each.
-- 
Christopher Larson