Tracking Issue for `derive_from` (RFC 3809)

This is a tracking issue for the RFC "3809" (https://github.com/rust-lang/rfcs/pull/3809).
The feature gate for the issue is #![feature(derive_from)].

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

• Implement the RFC (https://github.com/rust-lang/rust/pull/144922)
• 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 we include the other direction of the From impl before we stabilize this?

Implementation history

Start with RFC 3809 and the linked rustc-dev-guide stabilization and documentation instructions. Review the remaining checklist items for documentation, nightly syntax styling, Style Guide and rustfmt updates, and stabilization, then confirm the unresolved question about the reverse From implementation is addressed before the feature is complete.