Read the next Ruby version from a file instead of hardcoding it in spec/truffleruby.mspec

Author: andrykonchin

doc/contributor/updating-ruby.md

@@ -160,7 +160,7 @@ Update all of these:
 
 For a new major version:
 * Update `TargetRubyVersion` in `.rubocop.yml`
-* Update the list of `:next` specs and change the "next version" in `spec/truffleruby.mspec`.
+* Update the list of `:next` specs.
 * Update the docs for next version specs in [workflow.md](workflow.md).
 * Update the versions in the `ruby/spec on CRuby` job of `.github/workflows/ci.yml`.
 

spec/truffleruby.mspec

@@ -154,8 +154,13 @@ if MSpecScript.child_process?
     ::VersionGuard.send :remove_const, :FULL_RUBY_VERSION
     ::VersionGuard::FULL_RUBY_VERSION = SpecVersion.new(version)
   elsif ARGV.include? ":next"
+    version = File.read(".ruby-version")
+
+    # get the next version, e.g. 3.1.2 -> 3.2.0
+    next_version = version.split(".").tap { |ary| ary[1] = ary[1].next; ary[2] = '0' }.join(".")
+
     ::VersionGuard.send :remove_const, :FULL_RUBY_VERSION
-    ::VersionGuard::FULL_RUBY_VERSION = SpecVersion.new("3.2.0")
+    ::VersionGuard::FULL_RUBY_VERSION = SpecVersion.new(next_version)
   end
 end