The source code?
#[unstable(feature = "unwrap_infallible", reason = "newly added", issue = "61695")]
Your comment said:
> `Result::into_ok`, which was introduced in 2019, but is still unstable due to being "newly added".
Your comment makes it sound that the Rust team considers a four year old utility method as "newly added", and that's the reason why this method is marked as unstable. More likely, this "newly added" reason is something they add for any new unstable feature, and it is now out of date.
Considering that repository has 9,000 open issues, and 50,0000 total issues, you can imagine that this issue has simply not been prioritized. Rust being poor at prioritizing, handling issues, etc. is a totally separate discussion from "Rust thinks four year old code is new"
[0]: https://github.com/rust-lang/rust/commit/c784720f3a2d0b66142...
This is just a process error, IMHO. The process for stabilization in general just results in outliers like this and it's really frustrating for everyone involved. I know Rust is sort of unique here, just like it's unique in all sorts of other ways, but I can't help but think that there could have been some sort of provision for small methods like these.