alt Hacker News> It may just be a matter of perspective -- if you don't count rust pre 1.0, then yeah it "never" involved backtrace.
Yes. I'm only counting what has been part of the stable API since Rust 1.0.
I agree that following the stabilization path and future direction of a feature can be difficult.
> Because if the only purpose was error chains, it could have been in core on the day of rust 1.0, as it is today. I think what actually happened is `fn backtrace(&self) -> Option<Backtrace>` was removed shortly before 1.0, but there were some misgivings about that and some on the core team wanted to bring that back eventually. And that was the main reason that it could not move to core, because that would make it a breaking change to bring `fn backtrace` back. At least that's what I remember from PRs I followed at the time. (There may have been other reasons besides this though?)
The only purpose is not chaining. Backtraces were definitely a desirable part of it! But we wanted to move `Error` to `core` and having backtraces be tightly coupled to `Error` would not allow that. As far as I remember, that was always the tension. To my memory, it wasn't until Jane wrote down the "generic member access" direction[1] for the `Error` trait that this tension was finally broken.