D. Wheeler 5/25/2017
Technically “GPL-2.0” in SPDX means “only this version”, but in practice many practitioners & tools are sloppy about this. Part of the problem is that tools can easily determine that “GPL version 2.0 is in this package” but in many cases they cannot easily determine automatically a distinction between “2.0 or greater” versus “2.0 and no other”. In addition, in many cases it doesn’t matter, so the increased effort would be a waste of time. What the tools really need to indicate is a way in SPDX to indicate “2.0 at least is here, and I don’t know if ‘or later’ is okay”. Since SPDX doesn’t have a mechanism to report this, “GPL-2.0” is sometimes being used to report of “I know 2.0 is here, and I don’t know if ‘or later’ is okay” - even though it’s technically not compliant with the SDPX spec.
It’d be helpful to have a simple way to indicate “I really mean this specific version” (my “!” suffix) vs. “this version at least is okay, and I’m not sure about later versions” (which is how “GPL-2.0” is currently interpreted; maybe another suffix like “?” or “*” would help to mark this case).
Selected responses/ideas/solution proposals
NOTE: Please feel free to add/clarify below
K. Stewart 5/25/2017
We've started having some discussions with FSF about what they'd prefer, and their preference seems to be GPL-2.0-only, so we probably want to go that way rather than introducing the "!" idea.
D. Wheeler 5/25/2017
K. Stewart: We've started having some discussions with FSF about what they'd prefer, and their preference seems to be GPL-2.0-only, so we probably want to go that way rather than introducing the "!" idea.
Okay. Although that's less flexible, that's much easier to transition (you don't have to change any parsing code), so I see the advantages of this.
If this is done: 1. It needs to cover all the licenses where this is likely. At *least* GPL and LGPL; I think MPL is probably in this case too. 2. The original license terms need to *stay* in SPDX, with modified clarifying text. Something like this:
GPL-2.0: The GNU General Public License (GPL), version 2.0 is acceptable, and without any clear statement if later versions are acceptable. Where practical, try to use more specific license expressions such as "GPL-2.0+", "GPL-2.0-only", or "(GPL-2.0-only OR GPL-3.0-only)". Historically this indicator meant "GPL version 2.0 only", but in practice tools often can't determine if later ones are acceptable (or not) & used this term in such cases. This specification acknowledges this practice and provides more specific alternatives when that information is available.
D. Wheeler 5/26/2017
We need at least *3* cases. Here they are, with potential names/expressions:
- GPL-2.0-only. I *know* that *only* the GPL version 2.0 is acceptable. I had originally proposed a "!" suffix.
- GPL-2.0+. I *know* that GPL version 2.0, or later, is acceptable.
- GPL-2.0. I *know* that at least GPL version 2.0 is acceptable (e.g., I found its license text). However, I'm not entirely certain whether or not later versions are acceptable, so I make *no* assertion either way. This appears to be what "GPL-2.0" has become, in some cases, in spite of the spec. Which is why we need a way to mark certainty vs. uncertainty. If you prefer, you could label this "GPL-2.0-at-least", or add a "?" suffix to mean "I don't know if later/other versions are acceptable".
The problem is that while tools can detect the presence of a license, it's often difficult for them to determine if an "or later" clause is valid in some cases. In many cases SPDX is capturing tool output, so we need for there to be a valid expression for tools to output. My understanding is that some tools that find GPL version 2.0 will currently report "GPL-2.0"... even if a later version is also acceptable... and as a result, "GPL-2.0" is not being interpreted as originally intended.
What's more, without a third case, it'll just happen again. Tools can't easily determine if "or later" applies, and in many cases you do *NOT* need more information than this. It can take a lot of effort ($) to determine if it's really "GPL-2.0-only" or "GPL-2.0+", and if the spec only supports those two options, then that's a problem.. because people are *not* going to spend effort unnecessarily.
If "GPL-2.0" is deprecated, then tools will start reporting "GPL-2.0-only" when they're not sure if later versions apply, because in many cases they can't easily determine it. Then we'll be back to the original problem, where "GPL-2.0-only" may mean "I found GPL 2.0 but maybe later versions will be okay". Ugh. Since many tools can only determine "at least this version", there needs to be a standard way to report it.
T. King 5/26/2017
Digging at this “acceptable” idea a bit more, I'm guessing it's something like “adapters may share adapted works under”. But the SPDX isn't just about copyleft (e.g. it includes CC-BY-ND-*). I think it makes more sense to focus on licenses (just the text, e.g. GPL-2.0) and license grants. For example, here are some SPDX License Expressions translated into grants:
- GPL-2.0: You can redistribute it and/or modify it under the terms of the GNU General Public License version 2 as published by the Free Software Foundation.
- GPL-2.0+: You can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.
- CC-BY-SA-4.0: This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
You can distribute an adaptation under a later version of the CC BY-SA because that's part of the CC-BY-SA-4.0 .
- CC-BY-SA-4.0+: This work is licensed under a Creative Commons Attribution 4.0 International License; either version 4.0 of the License, or (at your option) any later version.
The CC-BY-SA-4.0 tries to grant you that right anyway, but regardless of how you read the CC-BY-SA-4.0, I'm granting you that right directly.
> CC-BY-SA-3.0+ would be a synonym for CC-BY-SA-3.0 , but I don't > see a problem with that. It would probably be useful to call that > out in the wording that forbids the -only suffix for CC-BY-SA-3.0…
If the SPDX doesn't want to get into the business of determining when licenses grant + semantics, then we probably don't want an -only suffix and we certainly don't want a GPL-2.0-only short identifier.
But if you want to be in the business of warning users about the lack of built-in or-later wording in the GPL, CC-BY-ND-4.0, etc. and the presence of built-in or-later in the CC-BY-SA-4.0, etc., I don't see how you'd avoid making claims about whether the license had built-in or-later wording.
D. Seaward 5/26/2017
Perhaps "GPL-2.0"could be deprecated and instead whoever is tagging must use one of:
...where "only" means only, "+" means "or later" and "?" means unclear. Legacy data still tagged "GPL-2.0" would be treated as "GPL-2.0?" until updated. (This assumes the SPDX team want people tagging things as unclear!)