Re: [gentoo-dev] RFC: USE=libav as replacement for broken || ( libav:= ffmpeg:= )

[Michał Górny]

Dnia 2015-01-21, o godz. 12:12:21
Alexis Ballier <aballier@g.o> napisał(a):

> On Wed, 21 Jan 2015 11:15:04 +0100
> Michał Górny <mgorny@g.o> wrote:
>
> > Dnia 2015-01-21, o godz. 11:05:01
> > Alexis Ballier <aballier@g.o> napisał(a):
> >
> > > > > > 2. Subslots work correctly. Rebuilds are forced when the
> > > > > > chosen library is upgraded. Moreover, USE flag change causes
> > > > > > a rebuild when user decides to change the ffmpeg provider.
> > > > >
> > > > > No offense, but this argument is complete crap. You should
> > > > > rather fix portage bugs than propose to introduce tree-wide
> > > > > changes to hide them... More precisely: || ( a:= b c:= d ) is
> > > > > perfectly defined (in the "what it means" sense, not in PMS
> > > > > sense). When the package is built, if 'a' is satisfied then a
> > > > > (and its subslot) is added to the subslot list of the package;
> > > > > ditto for c. You end up with a list of subslot deps, that you
> > > > > can store in vdb or whatever, and use that to decide when to
> > > > > rebuild the package.
> > > >
> > > > Following a specification is not a bug. I could argue here a lot
> > > > but... just implement it. And return to us when you do. We had an
> > > > item for this for EAPI 6, and it was removed because nobody
> > > > volunteered to implement it. In fact, nobody even were able to
> > > > fully specify what it should do... but if you want to discuss
> > > > that, please start a new thread, possibly at the -pms list.
> > >
> > > Above is a simple algorithm that works in all cases. What you're
> > > asking me to do is "go beg pms list to allow something they don't
> > > want because the subslot/:= spec was poorly written and thought
> > > of". I already gave you the solution, don't count on me for the
> > > administrative work :=) (NB: everytime I tried to improve/fix
> > > something in pms I failed miserably, so that I have no other choice
> > > but giving up on this, check bgo)
> >
> > No, it works in the one case you thought of. Two quick issues:
>
> Ok, so first thing: You are the one writing about putting || in
> "effective deps" (whatever that means), for me := deps that apply when
> the package is installed is just a list created when the package is
> built: no ||, no use conditional, and with subslots instantiated.

I'm just describing the current Portage behavior. By 'effective deps' I
mean 'what Portage puts in depgraph' when it sees || ( a:= b:= ).

>
> > 1. What does || ( a b:= c:= ) mean? i.e. only some having subslots.
>
> This makes sense only when in DEPEND+RDEPEND (because of the :=), so
> apply this (mostly copy/paste) for all such deps:
> for a in 'a' 'b' 'c':
> 	When the package is built, if 'a' is satisfied and has a :=
> 	dep then 'a' and its subslot is added to := deps list for the
> 	installed package
>
> As for the meaning, it uses all of a, b and c that are available at
> buildtime and at least one of them must be present.
> for 'b' and 'c', the := dep description/meaning from pms applies.
>
> > 2. What does || ( a:= b:= ) mean when a and b can be both installed?
>
> Ditto.

A fair bit inconsistent but I guess it is the safe solution. Of course,
it is ugly for making || () behave completely different from
the original meaning when := is used inside. You add subslot, you get
completely different behavior. You remove it, you get completely
different behavior...

> > Adding a very specific PMS rule for two packages doesn't sound like
> > a very good idea to me.
>
> I agree but I don't think it is that specific.
>
> > > Moreover, when I bumped ffmpeg subslot, portage did rebuild all
> > > those packages with || ( := := ) deps properly for me. So, you'll
> > > have to be a bit more specific on what goes wrong than 'broken ||
> > > ( libav:= ffmpeg:= )'...
> >
> > I already told you that before. Try switching from ffmpeg to libav,
> > and see what mess it causes. I'll summarize it for you:
> >
> > 1. if you have dynamic-deps enabled, portage will want to install both
> > ffmpeg (because of :=) and libav (because of ||). The effective
> > deps will look like:
> >
> >   || ( ffmpeg:0/51= libav ) ffmpeg:0/51=
>
> with a separate := deps list, you have 'ffmpeg:0/51=' in the list; you
> notice ffmpeg subslot has changed from '0/51' to '' (since it is not
> installed anymore) so trigger the package for rebuild and use the ||
> ( ffmpeg:= libav:= ) dep (which I assume works fine since that's what
> happens when you install the package). the bug here is that portage
> uses a crafted (r)depend string for reinstall, instead of the ones
> from the stock ebuild from either vdb or the portage tree.
>
> > 2. If you have dynamic-deps disabled, portage will happily switch impl
> > without rebuilding revdeps (breakage). Afterwards, it will allow
> > upgrading the other dep (libav) without rebuilds. The effective deps
> > will look like:
> >
> >   || ( ffmpeg:0/51= libav )
>
> this is also solved by having a separate := dep list in vdb

It is easy to write others how to do stuff without looking at the code,
isn't it?

-- 
Best regards,
Michał Górny