Re: [gentoo-dev] [pre-GLEP] Optional runtime dependencies via runtime-switchable USE flags

[Ian Stakenvicius]

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On 25/09/12 12:00 PM, Ciaran McCreesh wrote:
> On Tue, 25 Sep 2012 12:43:00 -0300 Alexis Ballier
> <aballier@g.o> wrote:
>> Could you please elaborate on what kind of problems may arise ?
>> The proposal seems pretty simple and sane to me: PM only has to
>> switch the useflags that are IUSE_RUNTIME in his installed
>> packages db after installing the deps and without triggering a
>> rebuild of said package.
>
> a) How do we provide a good user interface for it? It took an awful
> lot of experimenting to get the exheres-0 suggestions user
> interface to be good, and it requires quite a bit more information
> from the package side than this proposal is providing. We want to
> avoid a REQUIRED_USE here...

Standard USE flag interface.  This doesn't need anything special.  Why
will a user care if the flag doesn't trigger a package rebuild?

>
> b) How is consistency checking to be done? Related, what happens
> when a runtime switch introduces a dependency that then requires a
> non-runtime rebuild of the original package?

flag needs to be dropped from IUSE_RUNTIME, so the rebuild would occur.


> c) How do we deal with flag? ( cat/dep[foo] ) or flag? (
> >=cat/dep-2.1 ) cases where cat/dep[-foo] or =cat/dep-2.0 is
> installed and flag is off? From experience, quite a few places
> where you'd want to use suggestions will break if their suggested
> package is installed but doesn't meet version or use requirements.

Use flag deps are dealt with identically to the way they are now.  the
only difference , again, is that the package doesn't get re-emerged.
The VDB would still update imo as if the package did get re-emerged
(ie:  USE and RDEPEND would update), to handle the use flag change
info in metadata but from what I can tell nothing else would need to
be touched.



>
> However, addressing these probably isn't enough, since this is
> just the things we had to think about for SDEPEND-style
> suggestions... There are likely to be things I've not thought of
> specific to this method that won't crop up until someone tries to
> deliver a decent implementation. This isn't a trivial feature.
>

..it really is.  It piggy backs entirely on the current USE
implementation, and only skips triggering rebuilds because the
files-on-disk for a package don't need to change.


Now, I do realize that the potential for abuse here is large, and it
will be up to dev's to ensure that these use flags (or groups of use
flag conditions) added to IUSE_RUNTIME will not result in any
files-changed-on-disk.  However that to me doesn't seem to be a good
enough reason to exclude it from a future EAPI.

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