Re: Question about 'provides' and emacs packaging

[Jon Turney <jon.turney@dronecode.org.uk>]

On 06/10/2021 17:23, Jon Turney wrote:
> On 06/10/2021 13:01, Ken Brown via Cygwin-apps wrote:
>>
>> This seems to work, with one caveat.  Suppose package P requires 
>> feature f, and packages Q, R, S,... provide f.  If the user selects P 
>> and one or more of Q, R, S,..., setup is happy.  But if the user 
>> simply selects P, then setup/libsolv will choose among Q, R, S,... the 
>> one whose name is alphabetically first.  In the emacs case, this would 
>> be emacs-lucid, which is a stupid default.  The default ought to be 
>> emacs-nox.  So I can make it work if I call that package emacs-basic 
>> instead of emacs-nox.
> 
> Yeah, I think what's wanted here is for the solver to output a problem 
> with the choices, rather than picking one.  I'm not sure how to get it 
> to do that.
> 
> (Ofc, then we need some UI for picking problem solutions, rather than 
> just always using the default)

Thinking about this some more, that's probably not how it wants to work, 
since just installing emacs-common would then require user interaction 
to solve the problem, rather than just installing emacs-nox as well...

> (and I'm not sure how we'd encode "emacs-basic" should be the default 
> provider of "emacs-bin" as the input into the solver; presumably there'd 
> by some scheme with weights attached to provide names to set the order 
> rather than alphabetic)

So all that's left is to fix that.

This is discussed somewhat in [1], and it seems that having emacs-common 
suggest: or weak-dep: on emacs-nox would cause that to be the preferred 
provide:r by the solver (in the absence of other provide:ing packages 
being selected or installed)

So I guess we'd need to add something like that to setup.ini and feed 
that data into the solver as well.

[1] https://github.com/openSUSE/libsolv/issues/66