Determine before installation whether a port can be installed

[Artur Szostak]

"... A better implementation would let the port indicate that a port builds on macOS 10.X or older, or macOS 10.Y or newer. ..."

This sounds like there is a need to allow encoding of version ranges. In which case I would suggest to solve this problem generically, to allow encoding version ranges in port dependencies also. Similar to what is possible with RPMs or Debian packages. If the logic is implemented for dependencies then one could surely easily have things like the following encoded in the Portfile:

  macosx >= 10.9
  macosx < 10.10

Kind regards.

Artur