Tracking issue forrust-lang/rfcs#1216, which promotes! to a type.

About tracking issues

Tracking issues are used to record the overall progress of implementation. They are also used as hubs connecting to other relevant issues, e.g., bugs or open design questions. A tracking issue is howevernot meant for large scale discussion, questions, or bug reports about a feature. Instead, open a dedicated issue for the specific matter and add the relevant feature gate label.

Pending issues to resolve

• Regressions from fallback to()without fallback, never type introduces regressions #67225
• How to handle fallback of diverging expressionsTracking issue for fallback of diverging expressions to thenever_type (!) #65992

Interesting events and links

• Initial PRImplement the! type #35162
• Stabilization PRStabilize! in Rust 1.41.0 #65355
• Reverting stabilizationRevert stabilization of never type #67224 due to regressionsRegression in Error conversion from Infallible #66757

Latest Status

#35121 (comment):

The plan, asFCPed here, is to:

1. Change fallback to! in Rust 2024 (details of this elided as this work is done).
   • Tracking Issue for Rust 2024: Make! fall back to! #123748
2. Stabilize Rust 2024.
3. At a later date when 2024 edition adoption is widespread:
   • Make the breaking change to fall back to! always everywhere.
   • ChangeInfallible = !.
   • Stabilize! (!).

Rust 2024 is expected to be released in Q1 2025. We're not sure how long step 3 will take after that.

See the draft edition guide chapter for further background here:

https://doc.rust-lang.org/nightly/edition-guide/rust-2024/never-type-fallback.html

Switching the FCWs to lint in dependencies:

• Report never type lints in dependencies #141937