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Bug#771864: libdebian-installer - dependency resolver support excluding packages



Hi Cyril (and Bastian if TL;DR, then see note at the end)

On Sun, 31 Jan 2016 16:25:12 +0100, Cyril Brulebois <kibi@debian.org> wrote:
> Asbjørn Sloth Tønnesen <asbjorn@asbjorn.it> (2016-01-31):
> > On Thu, 4 Dec 2014 00:36:40 +0100, Cyril Brulebois <kibi@debian.org> wrote:
> > > Thanks for the patch, but clearly not for jessie.
> > 
> > How about stretch?
> 
> To be honest I'm not sure how wise it would be to have a less
> deterministic behaviour than the one we have right now.

It can only decreases the deterministic behaviour, when a list of packages
to be excluded is provided. Currently the only software with patches available
to allow this is cdebootstrap, and only as an extra argument, not by default.

Your point could be made against using this option by default,
 without the direct knowledge of the end-user, ie. in DI.

I'm not proposing that.

What I'm proposing is to make it possible for advanced users to install a
non-default system while still obeying the dependencies of all the packages.

In my patch for bug #805792, I have described how the logic works in the man
page, so users should know whats happening, if they use the --exclude option.

I would gladly add a few di_log() calls to this patch to make it more
obvious whats happening.

I highlu doubt that you will get an increased support burden due to this
feature.

I see three failure modes of this feature:
- Excluded packages installed anyway, due to lack of an alternative.
- Failure to resolve dependencies (due to incorrect dependencies)
- Failure to boot (due to missing dependencies on installed alternative)

The reason of the first one is explained in the man page, and could also be
added to the logfile, by added some di_log() calls.

The two last ones, I don't see as a problem, but rather a benefit as it improves
the packaging quality. I would also expect users who would use this feature to
be able to debug this on their own, if it works without a package excluded,
then it must be alternative dependency of said package causing trouble.


Bastian, could you please push your cdebootstrap git tree, it would make it
a bit easier to maintain unofficial packages. Your public tree is stuck at v0.7.0.


-- 
Best regards
Asbjørn Sloth Tønnesen

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