Re: [RFC] calm, setup: per-version requires

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

On 09/11/2017 18:18, Achim Gratz wrote:
> Jon Turney writes:
>> On 05/11/2017 07:34, Achim Gratz wrote:
>> Yeah, I guess we could generate requires: line in each version section
>> now, and this might work with current setup.  I don't think this did
>> anything useful prior to [1] being fixed.
> 
> Yes, and even though I think the parser would accept them they weren't
> really expected anyway.
> 
>> The libsolv branch implements per-version '[dD]epends:' headers as per
>> [2] (which may also contain a version relation)
> 
> I'd really prefer we'd come up with a solution that does not have us
> repeat the common dependencies for each version present.

My current plan is to do the simplest thing:
- requires: remains the union of dependencies
- if the version has a depends: hint, use that for depends: (not 
something cygport is currently capable of generating)
- otherwise, generate depends: from the requires: hint for the version


It's probably useful to bear in mind how various versions of setup will 
behave if I was to turn on 'depends:' generation in calm.  From staring 
at the code (so subject to testing), I think it breaks down as follows:

prior to 2.880:  Will ignore 'depends:', so 'requires:' needs to remain 
the union of dependencies for the benefit of these versions of setup.

2.880 onwards: The curr: version will get the union of 'depends:' and 
'requires:', other versions will get 'requires:'.

The prereq checker checks that the dependencies are satisfied (including 
any version relation), but then installs the 'curr:' or 'test:' version 
(depending on chooser preference) imagining that will satisfy it.

libsolv-based: 'depends:' supersedes 'requires:', installs the right 
right thing (hopefully :))