Log Ruby, gem and bundler version info

[XhmikosR]

This was implemented on actions/setup-node#137 sometime ago, and I think it'd be very handy to have this info in the log, maybe in a new "Version Info" group.

Right now, I manually run ruby --version, gem --version and bundle --version.

[eregon]

The Ruby version is already logged as part of the download URL:
https://github.com/ruby/setup-ruby/runs/1487552093#step:3:8

And the Bundler version as part of the output of gem install:
https://github.com/ruby/setup-ruby/runs/1487552093#step:3:16

The builds use the RubyGems from the Ruby release, no gem update --system, so it is the well known RubyGems version from the Ruby release.

Running these commands also take time, so it's actually slowing down builds by a few seconds if unneeded (probably more severe on e.g. JRuby), and the information is mostly redundant.
So I think this is best left to user workflows if wanted.

[XhmikosR]

True, but right now the info is sort of hidden is what I mean.

I thought maybe you could construct this info from ruby-builder-versions.js and the found bundler version the action is installing, so that it's grouped together and not hidden.

No worries if it's too much trouble, I just find it nice to be able to see the versions easily.

[eregon]

For now I think it's easy enough to print these 3 versions manually in a workflow if desired.
Doing it by default would slow down CI by several seconds in some cases, so I think it's not a trade-off I want to make in this action.
Adding a new input to do that not by default does not seem worth it, it's very easy in a workflow to:

- run: |
    ruby --version
    gem --version
    bundle --version

The Ruby version and the Bundler version is already clearly shown in the log.
The gem version is just whatever RubyGems version shipped with that Ruby.
So in fact from a log we can already be sure of which versions are used for a run, even though that might require knowing which RubyGems version shipped with a given Ruby release.

So I'd like to close this. I might reconsider based on new input.