Conflicting Packages Policy (was: python26 note)

[Kevin Fenzi]

On Tue, 5 Oct 2010 19:46:53 -0500
BJ Dierkes <wdierkes at 5dollarwhitebox.org> wrote:

> NOTE: This is likely a topic to revisit/finalize in the next EPEL SIG
> Meeting (every Monday at 19:30 UTC).
> 
> Hello all,
> 
> I would like to start an official discussion regarding the current
> policy on conflicting packages.  Currently, the EPEL documentation
> [1] is a bit sparse and does not reflect certain situations (such as
> the discussion on mod_python26/mod_wsgi26).  Per the FPG [1], Fedora
> packagers should avoid an explicit 'Conflicts: xxxxx' as much as
> possible.  However, due to some new developments in EPEL 5 (namely
> python26), some situations may require explicitly conflicting
> packages.  
> 
> As an example, during my package review for mod_python26 [3] the
> subject was brought up due to my use of 'Conflicts: mod_python' in
> the spec for mod_python26.  The packages conflict because mod_python
> and mod_python26 both provide the 'python_module', and the same
> Apache directives when enabled.  Therefore, the two can not be loaded
> at the same time.  The issue would be the same for mod_wsgi and
> mod_wsgi26 (built against/for python26).  In this specific situation,
> the possible solutions to work around this are:
> 
>  * Change policy to account for situations like those related to
> python26 and allow explicit 'Conflicts: xxxxx'
>  * Silently disable mod_python26 if python_module is already loaded
> via IfModule [4]
> 
> 
> Though the second option (IfModule) is a cleaner approach, it hides
> the fact that mod_python26 just won't load if mod_python is
> installed/enabled and assumes the user will know to look
> at /etc/httpd/conf.d/mod_python26.conf for comments on why that might
> be.  On the other hand, conflicting with mod_python doesn't inform
> the user why it conflicts... it just conflicts.  In my opinion it
> would be slightly more obvious why mod_python26 would Conflict:
> mod_python, but I don't know what is collectively in the best
> interest of EPEL maintainers.
> 
> In Fedora, an explicit 'Conflicts: xxxxx' is unwanted behavior and
> would be troubling/confusing for a lot of users.  However, being that
> EPEL is a different audience and different use case... I would like
> to open discussion regarding current policy and determine,
> officially, how these situations should be handled.

So, some more questions I have: 

* Would this conflicts case be restricted to just these python26-mod*
  packages? Or is this more general? I can see the case for packages
  that use a parallel installable stack and can't load at the same
  time, but I worry that we should make sure this isn't used more
  broadly. 

* Perhaps it would be worth making sure we document and require adding
  a 'README-conflicts' to any package that has these conflicts with a
  more verbose description of why and with what they conflict? Or some
  other way to get info to users as to why they conflict?

I guess I would be ok with the conflict in this corner case, but would
want to make sure we discuss/approve any further expansion of it
anywhere. 

kevin
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