Rust compiler support works differently

Posted Dec 19, 2025 9:23 UTC (Fri) by farnz (subscriber, #17727)
In reply to: Rust compiler support works differently by rgmoore
Parent article: The state of the kernel Rust experiment

The thing is that "no new bugs" is not the only way to get "no incompatible changes"; a "fix regressions fast" policy also gets to the same point by fixing any changes that cause users problems.

And "fix regressions fast" so that users stay on the latest versions of your software has a serious advantage; by definition, it's easier to locate which change in the last week could have caused a bug than to locate which change in the last 15 years. Users don't stay put forever - someone who was using RHEL6 up until its end of support in 2024, waited (unsupported) for RHEL10, and is now on RHEL10 is going to want everything that (from their point of view) broke between RHEL6 and RHEL10 fixed. But that's a huge amount to deal with in one go - it's "regressions" in everything that's part of the base OS, and it's nearly 14 years worth of changes to look through and determine what's gone wrong.

Worse, because RHEL7, 8 and 9 were in the middle, it may be impossible to fix RHEL10 to suit someone who's just migrated from RHEL6, because there is no way to fix the "regression" between RHEL6 and RHEL10 without causing a regression between RHEL7 (or RHEL8, or RHEL9) and RHEL10. The only way this works is if you accept a time limit on support (as RHEL enforces), and understand that you will have to recertify/buy an update/find a new vendor who's still trading when the support window expires; but I'm not convinced that "big panic, maybe business-ending" every 14 years is better than "small panic every day", and while I've seen "big panic, maybe business-ending" from LTS distros such as Debian (Sarge to Etch broke stuff badly at my then job, and we couldn't have the regression undone since it was already relied upon by other users, but had to update our stuff), I'm also not convinced that frequent updates is actually "small panic every day" - it might well be "small panic every month, as upstream add your use case to their regression tests".