While writing some machinery for dealing with spans on built-in attributes last month, I was slightly bothered by a missing method on Iterator. I usually work on the compiler, not the library, but I decided to write a little proposal, which was then accepted, so today it was time to try and implement it. In fairness, that implementation itself was mostly trivial, and yet right now there's no way to stabilize it. What I actually want to share is the incredible compiler work going on as we speak that will unblock it.

I woke up last weekend, and someone assigned me to a PR to review. That's quite common. It fixed a crash with attributes, something I've worked a lot on. Some code crashed the compiler, but the code to reproduce it used a specific nightly feature called "contract attributes", and I didn't believe that that was the only way to reproduce the crash. So, I tried to see if any currently stable attribute would the same so the reproducer was more general. It turned out: I was wrong! But playing with it I found a complely new way to crash the compiler in a single line of code.

Deprecated is an attribute you can put on items to mark them as, well, deprecated. Any use of that item will give a warning, telling you that you're using something that's deprecated. The thing is, it doesn't always work...

The rust compiler is a giant project. Hundreds of contributors help maintain it. I consider myself quite lucky that this maintenance work has become my full time job. Most of that time though, isn't spent to work on new language features, though there is a bit of that. In fact, most maintenance is barely visible to users of the language. So what does maintaining the compiler look like?