The fact that it wasn't raised till more than 6 months after we committed the pg_am changes
This means that nobody was testing compatibility of "postgresql's master branch with existing third-party clients".
Testing against well-known clients makes sense to catch bugs early.
I've added "build postgresql from master branch" test to the pgjdbc's regression suite a week ago, so I hope it would highlight issues early (even before the official postgresql beta is released).
However, pgjdbc tests are executed only for pgjdbc commits, so if there's no pgjdbc changes, then there is no logic to trigger "try newer postgres with current pgjdbc".
Ideally, postgresql's regression suite should validate well-known clients as well.
I've no idea how long would it take to add something to postgresql's buildfarm, so I just went ahead and created Travis test configuration at https://github.com/vlsi/postgres
Do you think those Travis changes can be merged to the upstream?