Add binary compatibility guide

[gkossakowski]

Provide a guide that covers:

• history of binary compatibility in Scala so we can show that our policy evolves in the right direction
• define binary compatibility (there different concerns like serialization, linkage errors, etc.)
• present tradeoffs we face when it comes to binary compatibility
• describe current policy in 2.10.x series
• mention tools we use (mima) which is related to hackers guide

[gkossakowski]

I created this ticket to let you guys know what I'm working right now.

Originally, I planned to work on something like hacker's guide but @xeno-by beat me on it and did a lot better job than I would do anyway.

[heathermiller]

Awesome, this is very welcome Greg!

My only question is: who's your intended audience? Is this for people who would like to contribute something but don't know what they can contribute, to which branch, under the binary compatibility policy?

Feel free to work in the contribute folder. Just drop in an *.md file with the following YAML front matter:

---
layout: page
title: Your Title Here
---

We can review it and comment on it as you go, or later in batch, however you wish :)

[vjovanov]

@gkossakowski do you have anything written that we could shape up? Also, can this also come after the main release?

[gkossakowski]

@vjovanov: I tried to find my early draft but I have no idea where I saved it. It's been so long that I forgot where I saved that markdown file. Sorry :-/

When it comes to timing I think it's ok to add it later on. This kind of document will have to be refined over time anyway. I can promise I'll look into it again after May 7th assuming my recovery will be going ok. Before that date I can't really help as I barely keep up with everything I'm supposed to do right now. If somebody wants to work on this before that date I can provide at least outline of topics that we should cover. Binary compatibility is a hairy subject.

[vjovanov]

That is cool. We do not have to finish this right now; There is no reason to tie the release of this guide with the release of the new website. Also, here no one is competent to write it well, I will check with Martin still.

For now marking as future, and unassigned.

[heathermiller]

Sorry, I understood that he'd be able to look at it post May 7th? So Greg, I will keep it assigned to you. And we can revisit this later :)

[heathermiller]

(PS, we discussed this in the meeting yesterday, and the understanding there was also that Greg was still out for a a bit, but that he was the most competent one to write this for now. We said we'd consider finding someone else, but no one was suggested yesterday)

[SethTisue]

http://docs.scala-lang.org/overviews/core/binary-compatibility-of-scala-releases.html

[lrytz]

We should still have a binary compatibility guide for authors, explaining what kind of changes are binary compatible. The page above only explains the policy of the Scala library. Should I open a separate issue for that?

[SethTisue]

@lrytz sure

[SethTisue]

but in https://github.com/scala/scala.github.com/issues, I think