A &(dyn Error + 'static) should be fine for that; you don't need any allocated/variable sized data in a memory allocation failure.

Anything other than panic/abort on allocation failure is outside the scope of the vast majority of programs, including anything using the standard library in Rust. I wouldn't worry about Box<dyn Error>.

You're already writing Rust in a very different style if you're writing the type of code that gracefully handles allocation failure. It's to Rust's immense credit that this type of coding is actually fairly well-supported (unlike in Go), but you're already a bit off the beaten path for stuff like error handling.

Not sure what your problem is?

If you need to handle an allocation error in the error path, then the error reporting path must abort, which means that the allocation error must be bubbled up.

There is no real solution to an allocation error inside the error path. Even if you preallocate an arena for errors, the error might be large enough that it won't fit inside the arena.

Hence the best thing you can do from that point onwards is to have an error enum with an AllocError variant that doesn't allocate. Said error won't contain any information beyond line numbers of the allocation error since you just don't have the space for it.

In the end you will basically end up with panic free code, but the error still bubbles up like regular unwinding.

So yeah you can do it, and I will do it in the future, but I personally think that the people who think this is some huge deal breaker don't understand the problem in the first place.

The comparison here is to Go, which doesn't have any way to handle memory allocation failure AFAIK.

In Rust you can do that (mostly on nightly although not only), and yes there are alternatives for this case, but it's rare anyway.