[gentoo-dev] [RFC] New PROPERTIES=virtual value to identify meta-packages?

[gentoo-dev] [RFC] New PROPERTIES=virtual value to identify meta-packages?

[Zac Medico]

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Hi everyone,

I'd like you all to consider a PROPERTIES=virtual setting that
allows an ebuild to indicate that it installs no files and serves
only as a layer of dependency indirection. This will be another use
for the new PROPERTIES metadata variable that's already been
proposed to be added to the set of variables distributed via
${PORTDIR}/metadata/cache/ as part of the implementation of
PROPERTIES=live-sources [1].

The PROPERTIES=virtual attribute is useful as a means to indicate
that a package costs practically nothing to install. This knowledge
plays a vital role in distinguishing the most optimal state, when
deciding which packages should be chosen to satisfy the dependencies
of a virtual. Knowledge of this property is what allows bug #141118
[2] to be solved.

In the past it was possible to infer the property represented by
PROPERTIES=virtual from the fact that a package was in the virtual
category [3]. However, a java-virtuals category [4] has since been
added. Also, we have some other meta-packages like kde-*-meta or
whatnot that could legitimately advertise this attribute.

Does this seem like a desirable way to represent the "virtual"
attribute? Any suggestions?

Zac

[1]
http://archives.gentoo.org/gentoo-dev/msg_187585c5d49b69034183719ff473710d.xml
[2] http://bugs.gentoo.org/show_bug.cgi?id=141118
[3] http://packages.gentoo.org/category/virtual
[4] http://packages.gentoo.org/category/java-virtuals
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Re: [gentoo-dev] [RFC] New PROPERTIES=virtual value to identify meta-packages?

[Ciaran McCreesh]

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On Tue, 05 Aug 2008 22:15:11 -0700
Zac Medico <zmedico@gentoo.org> wrote:
> Does this seem like a desirable way to represent the "virtual"
> attribute? Any suggestions?

Again, I'm not so sure that this doesn't represent multiple separable
concepts. It seems to imply:

* that the install cost is effectively zero
* that the resolution cost is effectively zero
* that the package does not install any files
* that the package does not use any of the (normal?) ebuild phases, and
so does not require exclusive pkg_* execution or pkg_* system state
preservation.

-- 
Ciaran McCreesh

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Re: [gentoo-dev] [RFC] New PROPERTIES=virtual value to identify meta-packages?

[Zac Medico]

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Ciaran McCreesh wrote:
> On Tue, 05 Aug 2008 22:15:11 -0700
> Zac Medico <zmedico@gentoo.org> wrote:
>> Does this seem like a desirable way to represent the "virtual"
>> attribute? Any suggestions?
> 
> Again, I'm not so sure that this doesn't represent multiple separable
> concepts. It seems to imply:
> 
> * that the install cost is effectively zero
> * that the resolution cost is effectively zero
> * that the package does not install any files
> * that the package does not use any of the (normal?) ebuild phases, and
> so does not require exclusive pkg_* execution or pkg_* system state
> preservation.
> 

Can't we just treat them like other ebuilds except for the thing
about dependencies? Perhaps more fine-grained attributes could be
added for additional specificity.

Zac
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Re: [gentoo-dev] [RFC] New PROPERTIES=virtual value to identify meta-packages?

[Ciaran McCreesh]

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On Tue, 05 Aug 2008 22:57:28 -0700
Zac Medico <zmedico@gentoo.org> wrote:
> Can't we just treat them like other ebuilds except for the thing
> about dependencies? Perhaps more fine-grained attributes could be
> added for additional specificity.

Could do, yes, in which case the name should be something like
'zero-resolution-cost' rather than 'virtual'. But since giving more
information to the package manager is trivial, we might as well do
so.

-- 
Ciaran McCreesh

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[gentoo-dev] Re: [RFC] New PROPERTIES=virtual value to identify meta-packages?

[Steve Long]

Zac Medico wrote:

> Ciaran McCreesh wrote:
>> On Tue, 05 Aug 2008 22:15:11 -0700
>> Zac Medico <zmedico@gentoo.org> wrote:
>>> Does this seem like a desirable way to represent the "virtual"
>>> attribute? Any suggestions?
>> 
>> Again, I'm not so sure that this doesn't represent multiple separable
>> concepts. It seems to imply:
>> 
>> * that the install cost is effectively zero
>> * that the resolution cost is effectively zero
>> * that the package does not install any files
>> * that the package does not use any of the (normal?) ebuild phases, and
>> so does not require exclusive pkg_* execution or pkg_* system state
>> preservation.
>> 
> 
> Can't we just treat them like other ebuilds except for the thing
> about dependencies? Perhaps more fine-grained attributes could be
> added for additional specificity.
> 
Sounds good. Keep existing keyword working how it is, and add new ones
after.

I'd vote for free-{resolve,install} empty and threadable for the other
concepts.