[OE-core] DEPENDS tranlation with BBCLASSEXTEND

[Khem Raj]

On Mon, Mar 28, 2011 at 1:06 PM, Tom Rini <tom_rini at mentor.com> wrote:
> 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.

well can you generalize like this for languages ? I am thinking of say
in C you cant
restrict usage to abstractions like this this only can be used in
header and this in C files

Even if we do then we should make
bitbake refuse do _append/_prepend operations in .bb files.

 The problem, as Richard
> explains is that BBCLASSEXTEND makes things special and we need to deal
> with that better.
>
> --
> Tom Rini
> Mentor Graphics Corporation
>