Tracking Issue for #[export] (RFC 3435)

This is a tracking issue for #[export] (rust-lang/rfcs#3435).

Feature gate: #![feature(export_stable)].

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 / History

• Lang team experiment: Niko as liaison
• Implementation of #[export]
  • https://github.com/rust-lang/rust/pull/134767
  • ...
• Evaluate experiment
• Update RFC based on experiment and research
• Implement 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

XXX --- list all the "unresolved questions" found in the RFC to ensure they are
not forgotten

Start by reading RFC 3435 and the existing experiment PR 134767, then use the tracking checklist to identify the remaining work for #[export]. Done requires implementation, RFC and research updates, documentation and style updates, and a stabilization PR; unresolved RFC questions must also be recorded.