[MacPorts] #15712: Add versions to platforms

[Craig Treleaven]

> On Apr 12, 2018, at 5:09 PM, MacPorts <noreply at macports.org> wrote:
> 
> #15712: Add versions to platforms
> --------------------------+----------------------------
>  Reporter:  raimue       |      Owner:  larryv
>      Type:  enhancement  |     Status:  assigned
>  Priority:  Normal       |  Milestone:  MacPorts 2.6.0
> Component:  base         |    Version:
> Resolution:               |   Keywords:
>      Port:               |
> --------------------------+----------------------------
> 
> Comment (by raimue):
> 
> …

> Overall, we mostly care whether the current platform is supported or not.
> There is no need for complicated blacklists or whitelists. There is
> usually only a need to express a maximum or minimum version requirement
> for each platform.
> 
> …

> I do not understand why you also bring dependencies into this... They can
> declare whatever they want and yes, it might stop us from installing
> dependents. But this has no influence on the way we specify `platforms` in
> this port. We will check whether the current platform is supported each
> time we want to install ports, so we automatically do it for the
> dependency. If it does not support it, we stop at this point and all the
> dependents cannot be installed. To give an appropriate error message we
> have to evaluate this for each port separately anway, so I do not see when
> we would have to merge anything.

Are we intending to extend the port info command to report if a port is supported on the current platform or not?  Or at least report if the port is known to be NOT supported?  A given port is not supported if any of its dependencies are not supported.

For example, AFAICT, MythTV’s code has always been compatible with bascially any version of OS X.  However, it relies extensively on Qt and that generally defines the minimum platform that the system will run on.  

I don’t know how we handle this efficiently, though.  There are 200+ recursive deps for Myth!

Craig