[OE-core] DEPENDS tranlation with BBCLASSEXTEND

[Tom Rini]

On 03/28/2011 12:48 PM, Khem Raj wrote:
> On Mon, Mar 28, 2011 at 12:03 PM, Tom Rini <tom_rini at mentor.com> wrote:
>> 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.
>>
> 
> Yes no doubt on how it works and can be coded to likings of what we
> have but I think
> that having += and friends as well as _append and _prepend could be
> combined into one logic
> immediate appending/prepending operation may be confusing IMO while
> immediate assignments
> I think still are ok. We have more than one directives doing very
> similar yet semantically different operations
> It becomes hard for recipe writers. May be I am over simplifying

The problem is that we have different operators for different things.
Usually +=/=+ are what you want in a recipe for variables and append /
prepend are for classes that do tricky things.  The problem, as Richard
explains is that BBCLASSEXTEND makes things special and we need to deal
with that better.

-- 
Tom Rini
Mentor Graphics Corporation