Meta-issue: Relicense under dual MIT / Apache v2

[Manishearth]

Previously: #2885
The majority of the Rust ecosystem, and the Rust compiler itself, uses the dual MIT/Apache-2.0 license. This means that people can choose which of these two licenses to use a library under.

As Clippy starts uplifting lints to the compiler and generally being more accessible, I'd like to switch to this license for consistency. We currently use the copyleft MPL-2.0 license. This license is only file-level infectious, but still may hamper efforts to uplift lint code to the compiler. This initial choice of license was pretty random, and at the time the Rust ecosystem didn't have a consistent license.

For reasons why the Rust ecosystem uses this particular dual license, see the explainer text used when the community switched over

This requires each one of our contributors to sign off, and I'll be opening sub-issues for this.

[Manishearth]

See #3094, #3095, #3096, #3097, #3098, #3099, #3100 for the sub-issues. I split them up to avoid notification spam, folks can mute the issues if they wish.

[mati865]

It's been over two weeks, guess you could ping missing folks again or close those issues and create new one with those who didn't respond yet and new contributors.

[Manishearth]

Yeah, I plan to do something like that, but I'm travelling a bit. Feel free to do it if you'd like! Try to include new contributors too. (I was also considering sending out emails, though that might be very nag-y)

…

On Thu, Sep 13, 2018, 6:41 PM Mateusz Mikuła ***@***.***> wrote: It's been over two weeks, guess you could ping missing folks again or close those issues and create new one with those who didn't respond yet and new contributors. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#3093 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ABivSFU3Pw5jsVNI1RjIxuvpkFxNawEHks5ualmLgaJpZM4WOmpF> .

[Manishearth]

#3095 is full! six more to go 😄

I'm closing issues as they get filled out.

[Manishearth]

And #3100 is done

[mati865]

Pinging was helpful a bit but there are still contributors who didn't sign and mailing them seems to be the only way to bring their attention.

Maybe it's not worth to chase every contributor and just revert the commit if changes are small?
See this example, modified README.md section was already removed so revert would just bring back typo.
I'm not an licensing expert but there is just one way to fix typo so we could just fix it afterwards.

[Manishearth]

Typo fixes don't matter 😄, there's a bar for what's counted here.

However, redoing existing code does matter since there can still be licensing issues if you wrote a piece of code after looking at an existing piece of code that's licensed differently.