You can pin versions with the rust-toolchain.toml file you need to be using Rustup afaik. Nightly is just the daily builds.
I assume any "nightly" version would work in this context, meaning it would not refer to a version from a year ago, as it would have already been made stable by that point, right?
"nightly" versions also allow to use unstable features, and unstable features may remain so for a very long time (potentially forever) without breaking, so an old nightly could maybe work
Right, not everything gets merged to stable. In that case: letting us know the specifics beyond "nightly" is advisable, IMO.
The readme does mention the specifics, immediately after mentioning nightly.
> BREAKPOINTS REQUIRE ENABLING THE EXPERIMENTAL core_intrinsics FEATURE
How do I know which versions of nightly support that feature, and that specific version of the feature though?
I like your username.
Just use a recent nightly and you should be fine. Rust project doesn't offically provide support even for old stable versions, so "using nightly" with no specifics generally means using any nightly build, around or newer than, the current stable release.
A lot of people pin a specific nightly since the feature they're depending on could change (or ostensibly it would be in stable), so they can keep working without continuously having to track nightly changes or deal with it breaking on a different system with a different nightly version.
That obviously only works for non-library uses of nightly.