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

[Michał Górny]

On Tue, 7 Jun 2016 17:31:49 -0400
Michael Orlitzky <mjo@g.o> wrote:

> On 06/07/2016 04:59 PM, Michał Górny wrote:
> >>
> >> 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.
> >
>
> I'm not arguing for anything here, I'm just toying around with an idea
> for fun. What we want is a way to declare USE flag constraints within an
> ebuild that,
>
>   1) Runs quickly
>   2) Prevents a package from being installed with conflicting flags
>   3) Preferably has a simple grammar and doesn't require bash
>   4) Outputs a sensible message to the user upon conflict
>
> The error message is the one clear point that pkg_pretend holds over
> REQUIRED_USE. If we can make portage do something sensible when it hits
> a REQUIRED_USE conflict, that would be ideal. But aren't (2) and (4) the
> most important points?
>
>
> >>
> >> 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.
> >
>
> It doesn't do this, does it? I think it waits until the end. It *could*
> run pkg_pretend earlier, too, but it doesn't.
>
>
> >
> >>> 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!
> >
>
> gtk2 is not the only solution: I could set B[gtk2] and A[gtk3] in
> package.use. (If gtk2 *were* the only solution, then why would you have
> the REQUIRED_USE in the first place? Just pass --with-gtk2.)
>
> In practice, I would set A[gtk3] in package.use, and then try to emerge
> it again. Portage would tell me that I needed to set B[gtk2] first, and
> I would do that and start over.
>
>
> >> 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.
> >
>
> Of course I haven't tried it =)
>
> One of two scenarios holds, though:
>
>  * if a trivial pkg_pretend() is slow, then one that checks for USE
>    flag conflicts isn't actually that much slower.
>
>  * if a trivial pkg_pretend() is fast, then only those packages that
>    have a non-trivial pkg_pretend() make it slower.
>
> REQUIRED_USE should be faster either way, but that's currently at the
> expense of the error messages and I'm not sure those *can* be fixed.

To summarize your point: bad solution is good because it's not much
worse than itself.

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