[snuxoll]

Actually, you're wrong about the MPL. The MPL is a file based copyleft license, the share-alike clause applies to any modifications made to a file already containing MPL'ed code. This is only an issue when you add new files to the project, and any MPL project should be vigilant about accepting patches to ensure new files added contain the MPL header.

[pash]

Yes, there's a good argument that the license would apply automatically to modifications to an existing file, but even in that case it is somewhat questionable. Is the modification substantial enough that it could be considered a new, stand-alone, derived work? If so, the pre-existing license may not apply. Was the modification submitted as a patch in a file format that does not incorporate all of the pre-existing code? If so, it may be a new, stand-alone work to which the pre-existing license does not apply. Etc., etc. Very little of this stuff has been well tested in court, so there's a lot of room for facially plausible legal challenges.

And it's fairly clear that new files are new works. So, really, in all cases, unless you're getting an explicit statement from contributors that they have placed their contributions under the relevant license, there will be a a lot of uncertainty about whether they really have been—particularly if the contributor (or his or her employer) later challenges your claim.

That's why Github and other platforms for projects on the pull-request model should really build explicit consent to licensing into the process.

[mintplant]

> And it's fairly clear that new files are new works. So, really, in all cases, unless you're getting an explicit statement from contributors that they have placed their contributions under the relevant license, there will be a a lot of uncertainty about whether they really have been

For a project using the MPLv2, new files added to the project would include the following header at the top:

> This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0. If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.

Wouldn't that cover this?

[PieterH]

You cannot modify a work so much that the original licence no longer applies, unless you in effect create a new work.

[pash]

Yes, absolutely a code file can be transformed enough that the original license no longer applies. Copyright law in the United States applies the same tests to code as to textual works and works in other media: is the transformation substantial enough to consider the transformation a new (derived) work, copyrightable in its own right? If so, its author holds its copyright completely independently of any copyrights or licenses attached to the work from which it is derived.

The case law on what constitutes a new, derived work is not at all well developed in the context of software. But looking at analogues from other media—and that's what the law does—it is easy to imagine that a very substantial refactor, touching basically every line, or a less substantial refactor with substantial additions, might qualify as a new, separately copyrightable work.

The claims of copyleft are almost entirely untested in court, and it's very likely that many of them will prove empty if they're ever challenged. Indeed, many of copyleft's claims, those which place obligations on users and contributors, are more TOS-style claims than claims that look like ordinary "reserved rights" under copyright law, and therefore presumably have a legal basis of enforcement in contract law, not in copyright law.

Explicit agreement by contributors to be bound by a license, however, covers most bases, whether the license is interpreted as a license per se, pursuant to copyright law, or whether it's ibstead interpreted as a contract under contract law (or both).

[PieterH]

If you claim that copyleft is almost 'untested in court' you are either wilfully ignorant or trolling.

[infinite8s]

Can you cite any cases where the case has gone to judgement?