[fedora-java] Weak dependencies

[Jiri Vanek]

On 04/01/2014 02:14 PM, Mikolaj Izdebski wrote:
> On 04/01/2014 01:46 PM, Jiri Vanek wrote:
>> On 04/01/2014 01:28 PM, Mikolaj Izdebski wrote:
>>> Fedora 21 will likely introduce so called "weak" or "soft" dependencies,
>>> also known as recommends and suggests.  For proposed change see [1].
>>> What do you think about Java packages adopting usage of weak
>>> dependencies?
>>>
>>> An example: Dependencies declared as optional in POM files could be
>>> translated by dependency generators to Recommends instead of Requires.
>>>
>>> Any thoughts on this?
>>>
>>> [1] https://fedoraproject.org/wiki/Changes/RPM-4.12
>>>
>>
>> There is always issue that end users will hardly know why, should he
>> install something and mostly there is no nice dialogue "This feature
>> works only when you download also .....(and put it on classapth)" Not
>> mentioning that upstreams do not care about "to enable this feature yum
>> install someRpm"
>>
>> Well I have (me-touching) example in mind. IcedTea-Web have "weak"
>> dependence on tagsoup. Well it works without it, but then some JNLP
>> files are not parsed. User get jsut "invalid xml" exception in this
>> case. So he will have no clue, that he should install tagsoup,
>>
>> Will there be any mechanism for this? I doubt:(
>>
>> TBH - I can come only with one good usage - to use soft dependence
>> *only* for dependence which are not in fedora. Once it is packed, lets
>> it be installed all.
>
> I don't think what you described here is the behaviour of Recommends.
>
> If package A recommends B then by installing A you also install B,
> unless something conflicts with it or obsoletes it.  After installing A
> you can erase B without breaking dependencies.
>
> Example.  Lets assume we have package maven with:
>    Requires:   java-headless
>    Recommends: java-devel
>    Suggests:   maven-doc
>
> When you do "yum install maven", YUM should print something like:
>
> Installing: maven
> Installing for dependencies: java-1.8.0-openjdk-headless
> Installing recommended dependencies: java-1.8.0-openjdk-devel
> You may also consider installing: maven-doc
>
> Maven obviously cannot run without java-headless, so hard requirement is
> used here.
>
> Maven is usually used to compile Java sources, hence Recommends on
> java-devel.  But Maven itself works perfectly fine without java-devel,
> so users can erase java-devel after installing maven, if they want to.
> java-devel is a dependency that most users would expect, so it is
> "recommends".
>
> maven-doc is just added as suggestion and it will not be pulled by yum
> with default settings.  It's added there just to point users to other
> useful resources.
>

Oh I see. Well then it gave much more sense o try to handle optional dependecs of maven this way.

J.