Tracking issue for Effective Target Features

This is a tracking issue for the (proposed) lang experiment "Effective Target Features".
It is meant to be an experiment to evaluate whether a model for integrating target features with the propose effect system underlying const traits is feasible.

See https://hackmd.io/M5ZAoRqSTb27oLBuEpByIA for an initial proposal, and https://hackmd.io/xydafCtMQ1aqUbm6wqmEmA?view#Extending-to-target-features for more context on the syntax.

The feature gate for the issue is #![feature(effective_target_features)].

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 however not 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.
Discussion comments will get marked as off-topic or deleted.
Repeated discussions on the tracking issue may lead to the tracking issue getting locked.

Steps

• Discuss in design meeting
  • https://github.com/rust-lang/lang-team/issues/317
• Approve as a lang experiment
  • We accepted this experiment in the 2025-07-09 lang triage call.
• Implement in nightly
• Write and accept an RFC
• Adjust documentation (see instructions on rustc-dev-guide)
• Style updates for any new syntax (nightly-style-procedure)
  • Style team decision on new formatting
  • Formatting for new syntax has been added to the Style Guide
  • (non-blocking) Formatting has been implemented in rustfmt
• Stabilization PR (see instructions on rustc-dev-guide)

Unresolved Questions

Should https://github.com/rust-lang/rfcs/pull/3820 be implemented before/as part of this feature?

Is the syntax proposed in the document the best option we have?

Implementation history

Start by reading the linked proposal and the context on extending to target features, then review the tracking checklist for the experiment gated by #![feature(effective_target_features)]. The work is complete only after nightly implementation, an accepted RFC, documentation and syntax-style updates, and a stabilization PR; the unresolved syntax and RFC questions still need decisions.