[OE-core] DEPENDS tranlation with BBCLASSEXTEND

[Tom Rini]

On 03/27/2011 04:03 PM, Chris Larson wrote:
> On Sun, Mar 27, 2011 at 1:08 PM, Khem Raj <raj.khem at gmail.com> wrote:
>> I observed that if I have
>> DEPENDS = "a b" in recipe.bb which has BBCLASSEXTEND = "native"
>> then dependecies for recipe-native shows a-native b-native so far so
>> good
>>
>> Now if I want to add a dependency which only is needed for native recipe
>> I do
>>
>> DEPENDS_virtclass-native += "c-native"
>>
>> what this does is it will ignore a-native and b-native dependencies and
>> only adds "c-native" to depends of native recipe
>>
>> DEPENDS_virtclass-native_append = " c-native"
>>
>> This does what I wanted i.e. have deps on a-native b-native c-native
>>
>> I think behavior of += or _append should be similar. Is my understanding
>> correct ?
> 
> They've never been the same.  += is immediate, _append is delayed.  If
> a class, say, native.bbclass, defines the variable with ?=, and you
> used += before the inherit, then it will have a value, and the ?=
> won't assign.  I assume native.bbclass does it this way today so you
> can override the automatic behavior by defining the variable yourself,
> but I'll let Richard speak to that decision.

As Richard said, this is a good summary.  And a shorter still summary
(as Chris reminds me everytime I forget) is that since BBCLASSEXTENDS
makes use of an override already (virtclass-native/cross/etc) you must
keep that in mind when further modifying it as you get not what you
expected but what you asked for.

-- 
Tom Rini
Mentor Graphics Corporation