[MacPorts] #16336: Allow multiple ports to satisfy a single dependency

[MacPorts]

#16336: Allow multiple ports to satisfy a single dependency
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  Reporter:  rhwood at macports.org  |       Owner:  macports-tickets at lists.macosforge.org
      Type:  enhancement          |      Status:  new                                  
  Priority:  Normal               |   Milestone:  MacPorts base enhancements           
 Component:  base                 |     Version:  1.6.0                                
Resolution:                       |    Keywords:                                       
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Comment (by raimue at macports.org):

 Replying to [comment:8 macsforever2000 at macports.org]:
 > Sometimes the dependency requires the entire port, not just a single
 file. For example, in the bacula port it requires a database be installed
 (when not using the client-only variant) but it really doesn't matter
 which precise version it is. To work around this, I had to create variants
 for each database version which is cumbersome. So instead of creating a
 variant for postgresql83, postgresql82, postgresql81 AND postgresl80, I
 decided to only use the latest version. However, it would be better to
 just have had a "postgresql8" variant which required any of them. The
 provides keyword would not work in this case.

 So all ports could specify `provides postgresql8` as well, but can they be
 installed at the same time?

 We would need some way to express if multiple ports providing the same
 thing can be installed. For example, python24 and python25 can be
 installed at the same time, mysql5 and mysql5-devel can not. These are
 different use cases, maybe we can solve this with only one solution or we
 need both methods.

 > However, it brings up an issue. If none of the ports are available,
 which one gets installed? The first one in the list?

 Sounds reasonable.

 > I fully agree that the provides keyword is also a great idea. But it
 seems limited in usefulness to devel type ports only.

 Just as a note, the OR method requires changing each dependent when adding
 new ports which would satisfy the dependency.

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Ticket URL: <http://trac.macports.org/ticket/16336#comment:9>
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