On 2016-08-25 at 23:06, Paul Wise wrote:

> On Thu, Aug 25, 2016 at 9:29 PM, The Wanderer wrote:

>> If there exists a dependency solution which will achieve the
>> result requested on the command line (here, installing the lower
>> version of the depended-on package), that solution should be chosen
>> over any which do not achieve that result; if that solution
>> involves removing or downgrading packages, it should be presented
>> for confirmation before proceeding.
> 
> I don't think that apt should step outside the configured priorities 
> without instruction from the user. Since apt doesn't currently 
> interact with the user (but aptitude does), it can only print an 
> error. That error could be improved with info about alternative 
> solutions to try that are outside the configured priorities, using
> the -t suite and somepkg/suite syntax.

To clarify or expand on my previous request somewhat:

What I read you as saying is essentially that in the case of multiple
repositories with differing configured priorities, you think that a
dependency solution which does not adhere to those priorities should not
be considered to exist, for purposes of my statement above.

I might be persuaded to agree with that, but at least at a first
impression, I don't think I do. I think that what the user has requested
on the command line should be considered the top priority, so that it is
always possible (with sufficiently clear and explicit syntax) to
temporarily override the "global" priority settings - rather than having
to manually edit those settings, do this install run, then revert the edit.

The fact that such a departure from the configured "global" priorities
is being made should indeed be made very clear in an install-time
prompt, but I am not immediately convinced that it would be better to
fail with an informative error rather than to present such a prompt.

At the very least, any such error should include a statement of the fact
that a solution which would violate the configured priorities does
exist, and explain which priorities need to be adjusted (and/or at least
which package versions, from which repositories having which current
priorities, would satisfy it) in order for that solution to not be ruled
out in this way.

> That said, in this case the solution is within the configured 
> priorities so apt could do better.

Agreed.

-- 
   The Wanderer

The reasonable man adapts himself to the world; the unreasonable one
persists in trying to adapt the world to himself. Therefore all
progress depends on the unreasonable man.         -- George Bernard Shaw

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