Support ruby-build ruby-X.Y.Z DIR

[eregon]

• By searching a X.Y.Z definition if no ruby-X.Y.Z definition is not found.

So this enables for example:

$ ruby-build ruby-3.3.5 PREFIX

And with #2447 it enables:

$ ruby-build -d ruby-3.3.4 ~/.rubies
...
==> Installed ruby-3.3.4 to /home/eregon/.rubies/ruby-3.3.4

It would remove the need for https://github.com/ruby/ruby-builder/blob/135bc7c215df24a672d0735189aafc510923d380/.github/workflows/build.yml#L67-L74 and likely other places working around the "asymmetry" that CRuby definitions don't have a prefix.

[mislav]

I think some feature in this direction would be great; thank you.

But first of all: without #2447 I don't think this feature makes sense on its own, so I would even suggest lumping it together in a single PR rather that treating them as distinct features. WDYT?

Second, if ruby-build 3.3.4 ... and ruby-build ruby-3.3.4 ... are basically equivalent invocations since they resolve to the same version of CRuby, should they be guaranteed to be completely interchangeable? I'm asking because it seems that if you add the -d option to this invocation, you will end up with different installation prefixes based on your argument input. That seems slightly wrong to me because I think it could be seen as counter-intuitive.

[eregon]

But first of all: without #2447 I don't think this feature makes sense on its own, so I would even suggest lumping it together in a single PR rather that treating them as distinct features. WDYT?

It's how I had it locally but I figured it's easier to review independently, and this change has value on its own (first example and last paragraph of the description).
I can move it to #2447, or we can just merge both PRs, as you prefer, let me know.

I'm asking because it seems that if you add the -d option to this invocation, you will end up with different installation prefixes based on your argument input.

Indeed it will install to either $PREFIX/3.3.4 or $PREFIX/ruby-3.3.4.
What I would like to achieve is to install to $PREFIX/ruby-3.3.4 with the -d option.
I can see both sides:

• It installs to $PREFIX/$(first argument passed to ruby-build) (current behavior on the PR)
• ruby-X.Y.Z is resolved to X.Y.Z earlier, but then this could be a compatibility issue if someone has a custom definition matching ^ruby-[0-9] as then it wouldn't be picked anymore. So that's why I didn't go that way.

[mislav]

Thanks!

Added some tests and documentation updates. Feel free to merge when all looks good to you 🙏

[eregon]

Amazing, thank you!