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

[Duncan]

Ciaran McCreesh posted on Tue, 25 Sep 2012 17:30:19 +0100 as excerpted:

> On Tue, 25 Sep 2012 18:20:06 +0200 Michał Górny <mgorny@g.o>
> wrote:
>> Who is we? I believe REQUIRED_USE is one of the features which will be
>> available thanks to staying compatible with USE flags instead of
>> reinventing the wheel.

Umm... if I read the preceding posts correctly, you missed his intent 
there.  He's not saying it'll be unavailable to be used in the 
implementation, he's saying we don't want to repeat the experience of the 
"bumpy ride" (see below) that required use is, for the user, in a new 
implementation.

> Yes, but the REQUIRED_USE wheel is square, and gives a *very* bumpy ride
> to users. It also isn't particularly easy for developers.

Umm... perhaps pentagonal, the physics of a square wheel... <shudder>.

But yes, as a user who has had to resolve REQUIRED_USE related problems a 
number of times recently, a *very* bumpy ride for the user, it often is!  
Definitely agreed there.

And also agreed with the implication, that we want to avoid a similarly 
bumpy-ride implementation here.

(Implimentation-wise, IMO the problem with REQUIRED_USE is often how the 
ebuild used the REQUIRED_USE, something I'm hopeful it'll improve over 
time as devs get a bit more used to how REQUIRED_USE works and design 
ebuild functionality around it, not triggering the double-uses where they 
can be avoided without seriously impairing the choices exposed by USE 
flags in the first place, and a better REQUIRED_USE implementation is 
certainly a challenge, but it's equally certainly an extremely bumpy ride 
for the user, as it is today.)

>> > 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?
>>
>> Then the package is rebuilt. Where's the problem?
>
> The problem is in implementing that correctly... It's certainly doable,
> but it's not entirely trivial, depending upon how you're doing
> resolution.
>
>> Handling of REQUIRED_USE is not perfectly user friendly but it works.
>
> Like a square wheel, yes.

Pentagonal (or at least rounded corners on the square... tho of course 
then there's patent issues!), but agreed.

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman