Re: [gentoo-dev] [RFC] Global USE=gui

[Michał Górny]

On Tue, 7 Jun 2016 16:31:52 -0400
Michael Orlitzky <mjo@g.o> wrote:

> On 06/07/2016 02:57 PM, Michał Górny wrote:
> >
> > The point is that:
> >
> > 1. REQUIRED_USE is semi-machine-understandable while pkg_pretend() is
> > some random function crap.
>
> Why do users care about that? Why do I even care about that? The whole
> ebuild is random function crap. The only benefit is consistent output,
> but it's consistently awful.
>
>
> > Portage can be improved to take some sensible action on it.
>
> I'll believe this when I see it =P

You won't because the Gentoo way is to create a shitload of hacks
instead of fixing the root issue.

> > 2. REQUIRED_USE can be handled early during dependency resolution.
> > pkg_pretend() is like I want 5 minutes for Portage to calculate
> > the dependencies, then 2 minutes to run pkg_pretend()s, then it tells
> > me I am supposed to change one thing and start over.
>
> So 7 minutes for an understandable English description of the error and
> how to fix it, versus 5 minutes for line noise? There's a great story in
> The Psychology of Computer Programming that ends like this:

Not 5 minutes. Depending on the context, Portage can complain about
REQUIRED_USE in a few seconds because it has no further point
in evaluating the depgraph.

Versus wasting a lot of time on a huge depgraph that will be never used
because although it seems to be correct, it isn't and pkg_pretend() is
used to tell 'you did all the work for nothing'. Back to EAPI 0, eh?

> > 3. REQUIRED_USE can take USE dependencies into account. pkg_pretend()
> > can't.
>
> What do you mean here?

I mean that if A depends on B[gtk2], and you have ^^ ( gtk2 gtk3 ),
Portage will clearly know gtk2 is the only solution. Your pkg_pretend()
will tell user to enable gtk3, then Portage will hit unsolvable deps.
Congratulations, your helpful output just resulted in even worse
output!

> > 4. pkg_pretend() is slow, and should be used scarcely. Adding
> > an additional slow step for each package on the list, before starting to
> > build packages is not really helpful.
> >
>
> See #2, but "each package" is an overestimate. Only the ones with a
> non-trivial pkg_pretend() phase would take any time.

Have you tried it, or is it wild guess? What I'm saying is that
*pkg_pretend implementation in Portage is TERRIBLY SLOW*. Even
a complete no-op takes a lot of time because Portage needs to do a lot
of setup to run it, and can't do multiple packages in parallel.

-- 
Best regards,
Michał Górny
<http://dev.gentoo.org/~mgorny/>