[MacPorts] #18794: Add conflicts option for Portfiles

[MacPorts]

#18794: Add conflicts option for Portfiles
------------------------------+---------------------------------------------
 Reporter:  blb@…             |       Owner:  macports-tickets@…                   
     Type:  enhancement       |      Status:  new                                  
 Priority:  Normal            |   Milestone:  MacPorts Future                      
Component:  base              |     Version:  1.7.0                                
 Keywords:                    |        Port:                                       
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 Attached is a patch (rooted in trunk/base) to add a conflicts option to
 Portfiles, to allow ports to indicate that they conflict with another port
 (or ports).

 The basic idea is like dependencies:
 {{{
 conflicts   port:portname
 }}}
 to both allow ease of use through familiarity and in case we want to add
 other options besides port: in the future.

 I'm not sure how best to handle what port should do when this occurs.
 With the current, patch, port simply exits with an error:
 {{{
 Error: Unable to execute port: Can't install dvdrtools because conflicting
 ports are installed: cdrtools
 }}}
 (I updated dvdrtools to have "conflicts port:cdrtools" for testing).  This
 only occurs if the conflicting port is active (for image mode) or simply
 installed (for direct).

 I also thought about maybe showing a message that "this port will fail to
 install/activate because conflicting port xyz is installed/active".

-- 
Ticket URL: <http://trac.macports.org/ticket/18794>
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