rustc --print unstable-features

[lnicola]

It would be nice to have a --print unstable-features or -F help, because an IDE would then be able to offer auto-completions for tailored for the user's toolchain.

The best alternative today seems to be scraping the source code of https://doc.rust-lang.org/unstable-book/the-unstable-book.html.

[est31]

Code to collect all feature names in the compiler/std library would also be helpful for #77226 . I think for this param, the user should also specify whether there is a no_std/no_core context or whether std is included, because the list would be different each time.