rtic/book/en/src/migration_v1_v2/nightly.md

RTIC now requires Rust Nightly

The new async features require that you use a nightly compiler, and that the feature type_alias_impl_trait is enabled for your applications.

To enable this feature, you must add the line #![feature(type_alias_impl_trait)] to the root file of your project, on the lines below or above where #![no_std] and #![no_main] are defined.