Use SPDX license identifiers

[ryandesign (Ryan Carsten Schmidt)]

MacPorts has its own guidelines for how to specify port license names. We should probably move toward using the same license identifiers popularized by SPDX: ​https://spdx.org/licenses/

The license names we use have to be understood by our port_binary_distributable.tcl script. There may need to be a transitional period during which the script is updated to recognize both our old license names and new SPDX license identifiers. Later, once all ports have been updated to use SPDX, we can remove our old license names.

[iefdev (Eric F)]

Yes, that'd be great. +1

Maybe some of the repos be used to make it easier to keep it updated? (ie keep track of deprecated and new licenses, etc.)

​https://github.com/spdx/

[dbevans (David B. Evans)]

I agree. The SPDX scheme seems to be more comprehensive than ours and gaining popularity elsewhere. Perl now has added a standardized (but optional) metadata element

"x_spdx_expression" : "Artistic-1.0-Perl OR GPL-1.0-or-later"

in addition to the existing

    "license" : [
       "perl_5"
    ]

We might add something similar to our Portfile syntax.

[ryandesign (Ryan Carsten Schmidt)]

Our portfile syntax already accommodates Boolean combinations of licenses.

We might consider introducing a new option licenses and defining it to use SPDX identifiers, leaving the old license option using the current MacPorts custom license identifiers during the transitional period. This might make it easier to identify whether a port is using new or old license names, and would make it easier to write new lint rules to point out which ports still need their license info updated. And it finally fixes the long-standing obvious misnaming of the license option. port_binary_distributable.tcl could be updated to look for licenses first and fall back on license.

We would want to make sure that SPDX identifiers cover 100% of our current license use cases, and if they do not, then we should think about what to do about that. For example, what would be the SPDX equivalent of our license identifiers "Permissive", "Restrictive", "Restrictive/Distributable", "Commercial", "NoMirror"?