feat: add .compare(a, b), .rcompare(a, b)

[keithamus]

I've exposed the compare function which give access to the raw sorting algo, useful when sorting on more than one dimension.

[mislav]

This CI failure in Ruby 1.8 looks like it might be unrelated to the changes in this branch. But just to be sure, care to look into why it might be failing?

[mislav]

Since we're exposing a low-level function, I don't think it makes sense to expose an alternate rcompare() function that simply returns a negated result of compare(). If the user needs to write low-level comparison code, then they can negate the result of compare() themselves, and they don't strictly need rcompare(). Does that make sense?

If we got rid of rcompare, we wouldn't have the need for the internal rb_version_compare_1 function either.

[keithamus]

Agreed. I simply added it for completeness.

[keithamus]

Looks like the build is failing because of the version of Gem - which is used in the tests to ensure we sort the same version set that Gem would. The last passing build installed Gem 2.4.5 ($ gem --version == 2.4.5) while the very next build started using Gem 2.0.17 ($ gem --version == 2.0.17) I'm guessing somewhere between those two versions, Gem was able to parse version strings like 2.0-rc2

[mislav]

@keithamus Thanks for investigating! It's really a bummer that rubygems got downgraded from 2.4 to 2.0 between builds 😕

[keithamus]

@mislav build now passing 🎉! Had to add before_install step to upgrade gem, bundler.

[mislav]

Thanks for figuring this out!

However, gem update --system; gem install bundler are kind of slow to perform on every CI build, for every ruby version, even if they are not necessary (they are just needed for 1.8.7). Could we either just do this on 1.8.7, and avoid doing it for other versions, or could we simply skip the offending test at runtime if RUBY_VERSION == '1.8.7'?

[keithamus]

Okay noted. I'll probably go with something like the latter option.

[keithamus]

So rather than skip the test entirely, I just removed the offending version that cannot be parsed with older rubygems versions. So the test still runs and works - it just isn't as comprehensive for old versions.

[keithamus]

Yay it actually passes now @mislav!