> make a breaking change to the gem versioning system to force all library, framework and gem authors to use versions properly.

I really like the RubyGems rational versioning policy ( http://docs.rubygems.org/read/chapter/7 ) and wish everyone followed that.

I think it might be harder for gems like Rails that are actually metagems. But I do agree that it's surprising for a move from 2.3.5 to 2.3.6 to break backwards compatibility. Have we forgotten Ruby's ideal of the principle of least surprise?

Perhaps a good compromise between what Rails is currently doing and what it should be doing is to add a fourth version number. When the fourth version number changes, you can rest assured that the change is backwards compatible. (However, there is always the danger that some plugin/engine/gem author monkey-patched a part of Rails which could make their code break during a "backwards-compatible" upgrade to Rails.)