[questioner8216]

That sounds really interesting, whether it is done in Rust, some Rust 2.0, or a successor or experimental language. I do not know whether it is possible, though. If one does not unwind, what should actually happen instead? How would for instance partial computations, and resources on the stack, be handled? Some partial or constrained unwinding? I have not given it a lot of thought, though. How do languages without exceptions handle it? How does C handle it? Error codes all the way? Maybe something with arenas or regions?

I do not have a good grasp on panics in Rust, but panics in Rust being able to either unwind or abort dependent on configuration, seems complex, and that design happened for historical reasons, from what I have read elsewhere.

[JoshTriplett]

Vague sketch: imagine if we had scoped panic hooks, unhooked via RAII. So, for use cases that today use unwinding for cleanup (e.g. "switch the terminal back out of curses mode"), you do that cleanup in a panic hook instead.

The hard use case to handle without unwinding is an HTTP server that wants to allow for panics in a request handler without panicking the entire process. Unwinding is a janky way to handle that, and creates issues in code that doesn't expect unwinding (e.g. half-modified states), and poisoning in particular seems likely to cascade and bring down other parts of the process anyway if some needed resource gets poisoned. But we need a reasonable alternative to propose for that use case, in order to seriously evaluate eliminating unwinding.

[questioner8216]

I am not sure that I understand what scoped panic hooks would or might look like. Are they maybe similar to something like try-catch-finally in Java? Would the language force the programmer to include them in certain cases somehow?

If a request handler for example has at some point in time 7 nested calls, in call no. 2 and call no. 6 have resources and partial computation that needs clean-up somehow and somewhere, and call no. 7 panics, I wonder what the code would look like in the different calls, and what would happen and when, and what the compiler would require, and what other relevant code would look like.