Would it be a good idea to allow consumers of autocfg to probe if their compiler is nightly or not? This could be used in instances where a crate uses a nightly api, but it is not essential to the functioning of the crate. For example, a nightly-only api might make a function faster, or enable more functionality. Allowing probing if the compiler is nightly could allow a crate to automatically enable a "nightly" feature, so nightly users don't have to manually enable the feature. Alternatively crates that require nightly (like the popular rocket not so long ago) could give custom error messages with links to explanations of why they need nightly.

The argument against such an api is that it could be too magic and it could be bad for crater i.e. did nightly break the code or was the code always broken with the nightly feature enabled.