Add support for version range, using semvers version range syntax

[normanr]

actions/setup-ruby allows ruby-version to be a "Version range or exact version of a Ruby version to use, using semvers version range syntax", e.g: ">= 2.7" is supported. Please could you support this in ruby/setup-ruby too.

[eregon]

What's a concrete use case?

>= 2.7 just means latest Ruby, including new major releases.
For that case, you can simply use ruby-version: ruby.

https://github.com/actions/setup-ruby doesn't support ruby-version: ">= 2.7" as far as I know, only 2.7 or 2.7.x.
This action supports 2, 2.7 and 2.7.2, and not 2.7.x (doesn't seem useful).
All details in https://github.com/ruby/setup-ruby#supported-version-syntax

[eregon]

ruby-version: ">= 2.7" appears to work for https://github.com/actions/setup-ruby (https://github.com/eregon/setup-ruby-test/runs/1402242516?check_suite_focus=true), although I'm not sure if it was intended.
Probably because toolcache supports such version constraints: https://github.com/actions/toolkit/tree/main/packages/tool-cache#find

Still, there seems to be very limited usefulness to specify a Ruby version that way.

[normanr]

I didn't realize that "ruby" was a valid option. Upon re-reading the supported syntax, this is now "obviously" (not to me at first reading) covered by the "engine only" item. (Is there a reason why this isn't the default if .ruby-version and .tool-versions don't exist?)

A slightly more realistic example might be something like Jekyll requires Ruby version 2.5.0 or higher, so ">=2.5" would be a valid option for that if you wanted to allow using non-latest stable (for caching reasons).

[normanr]

I tried ruby-version: ruby, and it installed ruby-3.0.0-preview1. I found it surprising and not "the latest stable release". Is that expected?

[eregon]

For Jekyll and literally any application, it's much safer to pin down at least to a minor version (e.g., 2.5).
There is no compatibility guarantee between Ruby minor versions, and in fact Jekyll e.g. was broken/emitted many warnings when Ruby 2.7 came out, and this is pretty much expected.
So I'm against a default of latest version, that would just be unstable.
Also, having a .ruby-version is useful to communicate which Ruby version is compatible with a project for other developers.

I tried ruby-version: ruby, and it installed ruby-3.0.0-preview1. I found it surprising and not "the latest stable release". Is that expected?

That's not intended, will try to fix.

[eregon]

I fixed ruby-version: ruby (which now resolves to 2.7.2) in https://github.com/ruby/setup-ruby/releases/tag/v1.51.2

So ruby-version: ruby should work fine now for "latest stable CRuby release".