I think the point is that sometimes showing documentation that something exists isn't enough for everyone to "get it". Sometimes you need some kind of technology evangelist to show something really cool they did with a feature for the creative process to begin on a larger scale.

Out of curiousity, if this was just a macro and no one was using it, what would have been the harm in just leaving them in? Is this a part of the language that changes so much it made maintainance a pain?

Macros in Rust are global, insta-stable, and have no namespacing. This means any macro we put in std means you cannot define a macro in any Rust program with that same name. This is one of the reasons we've been working on a new macro system, to fix these kinds of issues.

"Just leave it in" isn't a good justification for a feature. We'd then require that every implementation of Rust ever, forever, implements this too. Being in std is a high bar.

Beyond that, there are a host of other reasons: https://github.com/rust-lang/rust/commit/454882dcb7fdb03867d...