In fact, in even conflicts with the next release's ABI version: ``` $ ruby -ve 'p RbConfig::CONFIG["ruby_version"]' ruby 3.1.0dev (2021-10-11T10:13:16Z master 0c3ac87345) [x86_64-linux] "3.1.0" ``` This mismatch can very easily result in segfaults, memory corruption, etc when using dev versions of CRuby, or when using a dev version and then later the release. CRuby. Possible solutions: * Include the git commit sha in the ABI. Pros: always correct and simple. Cons: changing more then necessary. * Track the ABI explicitly, and bump it whenever the ABI changes. Pros: changes only when needed. Cons: easy to forget bumping it, and if checked in CI already too late. From https://bugs.ruby-lang.org/issues/18239#note-14: FWIW TruffleRuby actually tracks the ABI of dev versions through [this file](https://github.com/oracle/truffleruby/blob/master/lib/cext/ABI_version.txt) which means it is possible to sensibly cache compiled gems even for dev versions [details](https://github.com/oracle/truffleruby/issues/2284). Also it [stores](https://github.com/oracle/truffleruby/commit/d497bae73fdc60585b66cd183768a16563b2886b) the ABI version in .so/.bundle files and checks them when loading, so it can be sure the ABI used to compile and runtime ABI match (if not, an exception is raised). ruby/setup-ruby has no choice for CRuby dev but [to use the commit](https://github.com/ruby/setup-ruby/blob/a6f22865941e122a37e097fbded3dd0b54c39207/bundler.js#L188) as the ABI version. This issue is made worse by Ruby switchers like RVM & chruby setting GEM_HOME (so the ABI is effectively ignored by RubyGems in those cases, and those directories need to be cleaned manually). When GEM_HOME is not set, it would be enough to rebuild CRuby dev and remove the directory before installing (which includes both CRuby & gems), but Ruby installers don't do that yet. Bundler always includes the ABI version when setting the bundler path (`bundle config --local path`), but if the ABI version is incorrect like for CRuby dev it's of no use.