The Rust All Hands 2026 retrospective records settled reference and union validity, renewed momentum to stabilize Allocator, and a rustdoc JSON path for cargo-semver-checks

Sources: Inside Rust blog, HN discussion
Summary: The Inside Rust blog published a retrospective of the Rust All Hands 2026 on 2026-07-31. It records that the operational semantics of reference and union validity are settled and in an in-progress FCP, renewed momentum to stabilize the Allocator trait, and a path from rustdoc JSON to cargo-semver-checks. The post points to recorded sessions for the individual topics.
Why it matters: The operational semantics work that unblocks unsafe-code reasoning moved from open question to in-progress FCP, and the recorded sessions name which long-running features have a path forward rather than only a wish list.