Merge pull request #657 from mjankowski/version-policy

Add doc around ruby version support/maintenance

docs/RUBY_VERSIONS.md

@@ -0,0 +1,51 @@
+# Ruby versions
+
+## Handling new releases
+
+When a new Ruby version comes out, you shouldn't have to make any immediate
+changes to Standard Ruby. The default configuration is the `base.yml`
+configuration and should continue to work correctly.
+
+Often, Rubocop will add new rules to encourage usage of new language features in
+new Ruby versions. When that happens:
+
+1. Add the rule to the `base.yml` file and disable it.
+1. Assess the new rule and see if it should be added to Standard Ruby. If not,
+   you're done. If so, enable it in `base.yml` and read on.
+1. Add a new config file for the penultimate minor version of Ruby. For example,
+   if the new version is `3.1` then the new config file would be for `3.0`.
+1. In the new config file, make sure it inherits from `base.yml` and disable the
+   new rule.
+1. In what was previously the latest config file, make sure it inherits from
+   your new config file.
+
+That should add new rules to Standard Ruby safely and gracefully.
+
+## Maintenance and support
+
+We will support the actively maintained ruby versions from the [ruby maintenance
+policy](https://www.ruby-lang.org/en/downloads/branches/) along with the most
+recently EOL version for an additional ~9 months, dropping support for EOL
+versions around the time that a new supported ruby version is released and
+added.
+
+With the current ruby release cadence (new version near end of year, EOL drop
+around April 1), this means we'll have a release of all the Standard gems around
+the new year which adds support for the new ruby version and drops support for
+what was an already-EOL but still-supported older ruby version.
+
+## Coordination across gems
+
+We will align versions/dependencies amongst the Standard gems:
+
+- [standard-custom](https://github.com/standardrb/standard-custom)
+- [standard-performance](https://github.com/standardrb/standard-performance)
+- [standard-rails](https://github.com/standardrb/standard-rails)
+- [standard-sorbet](https://github.com/standardrb/standard-sorbet)
+- [standard](https://github.com/standardrb/standard)
+
+This means keeping them consistent in regard to:
+
+- The minimum required ruby version configured in their `gemspec`
+- Using that version in their internal `.standard.yml` configurations
+- Including the full range of supported rubies in their CI ruby matrix