I read through the better part of a linked thread: https://forum.dlang.org/thread/ncbawciyybdksecurmsc@forum.dlang.org?page=1. And wow, as a C++ user, I'm not sure if I should feel blessed about how stable and backwards-compatible the language is, or that D users must be bonkers to put up with the breakages. Using C++ both professionally and for hobby projects, in the last 5 or so years I can remember encountering exactly 1 (gcc) compiler bug. There was a simple workaround + someone else had already reported it so with the next minor update the bug was fixed. And the code that triggered it was a nested CRTP spawn of hell so I didn't blame the compiler from borking on it in the first place, it would've been better for everyone had it never compiled :p

Upgrading a major C++ compiler version was never free in my experience, but even when working in a codebase with ~2M LOC the upgrade (e.g. 14 -> 17) was something that could be prepared in a set of feature branches by one person over the span of one, maybe two weeks. That's for fixing compile errors, I don't remember if we had issues with runtime errors due to an upgrade, but if we did it must've been minor because I remember the transition to 17 was pretty smooth. Note that 14 -> 17 requires changing the requested C++ version for the project, which is different from upgrading the actual compiler, i.e. you can do the latter without the former and your code should not require any changes.