MiMa CLI tool

[jeremyrsmith]

I really wanted to have a command-line utility: mima old.jar new.jar to get a report of bincompat issues.

I asked on discord, and found that such a thing didn't currently, exist, and frowned about it for a few minutes.

Then I realized it would be only a couple of (important) lines of code to write such a utility. So I open-sourced it here (it is literally a single Scala file) https://github.com/jeremyrsmith/mima-cli

My question is – why not have an official CLI tool? I don't mind writing one, but uniformity is definitely a big deal in CLIs, so it would probably be best for there to be an official one. @SethTisue pointed out that the previously-existing CLI tool was removed here: #208 – but it seems like maybe that was motivated by issues with the implementation rather than the notion of a CLI? If the notion of a CLI in the MiMa repository is problematic, maybe it could be a separate repo (as I've done) but still official?

[SethTisue]

A big part of the reason we axed the old CLI is that it was a pain to publish (and update the Lightbend site). We also weren't interested in maintaining it if it wasn't being used much.

But that was years ago. In the meantime, one thing that's changed is that Coursier came into existence and has become a standard for installing command-line tools for Scala. That beats having to download a tarball. Perhaps command-line MiMa would become more popular again if it were available this way.

We can also see if @dwijnand has an opinion here, but as I see it there should be two requirements for bringing your work in-repo and making it official:

• it shouldn't make publishing any more difficult (such as by adding manual steps to the publishing process)
• it should be available to users through Coursier

if you (or anyone) is willing to meet those requirements, I can't think of any other reason we shouldn't accept it.

[kubukoz]

Having seen @SethTisue's response, I made #823 to kickstart the effort.

When such a PR is merged, we can add MiMa to the apps channel in Coursier, so that running it will be as simple as:

cs launch mima -- old new

as a user, I think that'd be great UX ;)