Can the license field better describe the licenses?

[voxik]

A while ago, I have submitted this PR trying to clarify the project license. Part of the PR was this line:

spec.license = "MIT AND (BSD-2-Clause OR GPL-2.0-or-later)"

And now it was pointed out to me that this is not according to the documentation and of course RubyGems complains:

WARNING:  license value 'MIT AND (BSD-2-Clause OR GPL-2.0-or-later)' is invalid.  Use a license identifier from
http://spdx.org/licenses or 'Nonstandard' for a nonstandard license.
Did you mean 'AGPL-1.0-or-later', 'AGPL-3.0-or-later', 'BSD-2-Clause-Patent', 'GPL-2.0-or-later', 'LGPL-2.0-or-later'?

The root issue is that I have not realized that the licenses field is an array of identifiers. The following could satisfy the RubyGems license validation:

spec.licenses = ["MIT", "BSD-2-Clause", "GPL-2.0-or-later"]

nevertheless, there is IMHO a lot of information lost. So I though I'll check here what is RubyGems view on this problem. I understand that trying to be more precise in this are would cost a lot of effort, therefore I'm fine if this was rejected. Or maybe the the documentation could be improved to better describe that this is only list of identifiers without capturing anything more complex. Not sure

[rubyFeedback]

That change was indeed a bit annoying. Rubygems warns me about just about all my projects now.

I can change my projects, but it is still tedious - every project that has e. g. "GPL-2.0" or something like
that is now "invalid". It would have been better to keep an internal list of aliases, really; that way we
could still use our own descriptions and internally it would match towards the "official" licence as-is.
And, conversely, voxik's example above could be valid, rather than require, in tedious micro-management,
to specify an Array of licences. The problem is not confined to more verbose handling, such as
the example shown via "MIT AND (BSD-2-Clause OR GPL-2.0-or-later)". I always have to look up the
"true" name now, and often it's just changing a few characters (e. g. for my GPL 2.0 projects I now
have to add "-only" to all of them). Not a great change really ...

Could you upstream devs perhaps consider the impact of those changes more in the future? The
real gains here are very, very marginal.

[clemens]

Shouldn't the goal be to simply comply with the SPDX License Expressions format? While this might break things initially, arguably it would be the sensible choice, since 1) it's an established standard, 2) Gemspecs already expect SPDX identifiers anyway (but don't support proper formats with choices and exceptions yet).

[voxik]

I am afraid that fully supporting SPDX could be project on its own. I believe that for example RPM does not interpret the License field and it is up to projects such as Fedora to define/validate its content. I guess that in retrospect, if upstream foreseen this kind of request, maybe they would never start to validate the license field 😉

BTW does spec.licenses support array of arrays? Can the nested arrays be interpreted as SPDX boolean logic? Just trying to brainstorm what could be the smallest reasonable change to improve the situation.