[gentoo-user] Re: Portage is proposing an ncurses update and I don't understand what it means

[walt]

On Wed, 2 Sep 2015 15:34:43 +0200
Alan McKinnon <alan.mckinnon@×××××.com> wrote:

> On 02/09/2015 15:04, Neil Bothwick wrote:
> > On Wed, 2 Sep 2015 05:24:33 -0700, walt wrote:
> >
> >> If the devs can't explain slots to their
> >> users then they don't understand it themselves.  (Hm.  That phrase
> >> sounds familiar.  Where did I get that?)
> >
> > I think it is an Einstein quote that says something like "if you
> > can't explain it in simple terms, you don't understand it". He was
> > probably having a pop at Niels Bohr and quantum theory at the time.
> >
> > Bohr said something like "if thinking about quantum theory doesn't
> > give you a headache, you don't understand it".
> >
> >
>
> And Feynmann said something along the lines of "Anyone who claims to
> understand quantum mechanics, doesn't".
>
> Back to subslots and not replying to Neil directly: They aren't that
> hard to grasp, they look like this:
>
> cat/pkg/pkg-1.2:3/4
>
> The SLOT is 3 and the subslot is 4. As usual, different versions of
> the same package in different SLOTs can co-exist. Subslots are a
> different matter, and it's an unfortunate choice of name, as they are
> *not* a subset of a SLOT. Look at ncurses:
>
> [I] sys-libs/ncurses
>      Available versions:
>      (0)    5.9-r3 (~)5.9-r4 5.9-r5(0/5) (~)6.0-r1(0/6)
>      (5)    5.9-r99(5/5) (~)5.9-r101(5/5) (~)6.0(5/6)
>
> There's 2 SLOTs (0 and 5), and both have versions of subslot 5 and 6.
> Subslots are most useful for things like api/abi versions where
> upstream breaks these but don't increment the major version, this is
> why we had endless issues in the past where emerge world broke stuff
> horribly and it only got fixed much later when we could run
> revdep-rebuild. Nowadays we have better tools, if the subslot changes
> for a consumed library, then all consuming packages need to be
> rebuilt.
>
> Describing and defining subslots is not hard, neither are the
> operators. The problem with subslots is the usual one - you have to
> deal with real life, and in real life upstreams sometimes do peculiar
> things to their code that doesn't exactly match the effect of a
> subslot operation.
>
> Or put another way: subslot docs describe the effect you should end up
> with, it's not always the same thing as what you *do* end up with.
> Finding that out means testing every possible circumstances and seeing
> the results, but there's an infinite variety of those.

I just updated my virtualbox ~amd64 guest and all went well when I ran
emerge ncurses:5/5, so I'm encouraged but not fearless about doing the
same on my real machine.  I'm going to be quickpkged to the max before
I try it.

BTW, emerge world on the vbox guest did not offer to touch ncurses in
any way.  I had to do it manually as I just said.  

Leveraging Neil's quote:  thinking about slots (and their misnamed
subslots) gives me a 4-dimensional headache.

Anyway, thanks for the helpful explanation.