Tracking Issue for offset_of_slice

[RalfJung]

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

This is a tracking issue for allowing offset_of to determine the offset of unsized fields whose tail is a slice, and hence their alignment and their offset is statically known.

Steps

• Implement the RFC
• Adjust documentation (see instructions on rustc-dev-guide)
• Formatting for new syntax has been added to the Style Guide (nightly-style-procedure)
• Stabilization PR: Stabilize offset_of_slice #139673

Implementation history

• offset_of: allow (unstably) taking the offset of slice tail fields #126150