Re-license Tidy under a weak-copyleft license like MPL 2.0?

[sts10]

I've recently learned more about weak copyleft licenses like the Mozilla Public License 2.0. I like the concept, and MPL 2 specifically! I wonder if I should re-license Tidy under such a license, in the next big release of Tidy.

I'm thinking MPL 2.0 (I found the Wikipedia article to be a helpful resource).

Logistics of re-licensing

I think I can legally do this. I'm not a lawyer, but Kyle Mitchell is, and last year he wrote:

There’s no inherent legal issue with making new work on a permissively licensed project available under a new and different license, be it a GPL, a noncommercial license like Prosperity, or some other choice.

What about older versions of Tidy?

My understanding is that all previous versions of Tidy will remain available under MIT, the current license (which is fine, whatever), while versions starting with v0.3.0 will be under MPL 2.0. Again, from Mitchell:

The “work” in an existing, permissive-licensed project remains available under the original permissive terms. But the owner of copyright in new work on the project can choose to license it differently. The result is a project that combines work made available under different license terms. To use and share the new versions without infringing copyright, users and distributors need permission for all the work it contains. So they have to comply with both licenses.

Theoretically, users could carefully excise old, permissive-licensed work from the new versions, then comply only with the permissive license terms for that work. But that’s a big hassle. In practice, they’ll almost always prefer to just turn back the clock to before the change, and use an old version.

What about previous contributions, when Tidy was under MIT, from people who aren't me

Tidy has 2 contributors who aren't me. I'm a bit confused if/how that complicates things. Mitchell writes:

If you’ve taken contributions from others under terms that require notice, those terms for their work continue to require notices, and you aren’t exempt from those requirements. In practice, that means you need to include their copyright lines and license terms, in addition to your own, in LICENSE. It’s completely normal to see license terms concatenated there.

I'm not sure exactly what a concatenated license would look like in Tidy's case. I wonder if I can avoid that if I successfully get consent from all previous (non-trivial) contributors to agree to re-license their contributions under MPL 3.0?

I welcome any thoughts/discussion!

[wezm]

Tidy has 2 contributors who aren't me. I'm a bit confused if/how that complicates things.

Contributors contributed code under the terms of the project license so you need to honour the terms of that license if that code is continued to be used. For MIT it says:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

So I think what the concatenated licence would look like is the new licence plus copyright attribution for the contributions.

I wonder if I can avoid that if I successfully get consent from all previous (non-trivial) contributors to agree to re-license their contributions under MPL 3.0?

Yes if you get all contributors to agree to a relicense then you can republish the whole work under that new license.

[sts10]

Recently, it seems that an Apple employee requested that the developers of popular text editor nano re-license the editor under a permissive license rather than GPL3. So far, the developers seem to be unmoved by the request. Interesting to see a very recent example of a copyleft license keeping software free and open.

[sts10]

Thinking about this some more, and with some help from @copiesofcopies, let's imagine how a company might use Tidy. Let's say the company sells a password manager. If they were to use Tidy, it'd likely be to create or edit the passphrase word list (a text file) that they bundle with the password manager. They would need not bundle Tidy itself with their product, nor even offer Tidy over the web. Really, their customers would never use/touch Tidy.

Since, in this imagined case, they never distribute Tidy, it's my understanding the the copyleft clauses of MPL, GPL, and even AGPL would not be "triggered." Thus, the company would be free to keep any changes they make to Tidy -- exactly the kinds of modifications that a copyleft license intends to force it to make public -- completely private. In this way, even strong copyleft licenses like GPL and AGPL don't seem to be strong enough for programs like Tidy. So switching Tidy to one of these licenses probably isn't that significant.