Source: Official Rust Blog announcement by The Rust Release Team, published November 12, 2026.
To unify `Infallible` with `!`, Rust 1.100 applies a rare breaking adjustment across Rust 2015, 2018, and 2021 editions: type inference fallback for unconstrained diverging expressions changes from the unit type `()` to `!`, matching behavior introduced in Rust 2024. The Rust team previously issued advance compatibility warnings and patched affected public crates to limit ecosystem disruption. Alongside type-system stabilization, the core library adds `core::mem::DropGuard`—an ergonomics helper pairing a value with an exit closure that can be canceled with `DropGuard::dismiss()` for transactional rollbacks—and `unsafe` `std::mem::conjure_zst()` to construct zero-sized types explicitly without abusing `MaybeUninit::uninit().assume_init()` on safety markers such as PyO3's `Python<'py>` GIL token.
Cargo receives three major workflow and security upgrades in the same release. Organizing `build-dir` around hashed build-step directories eliminates platform inconsistencies that previously forced extra or missed rebuilds across feature flags and git worktrees, clearing the path toward future cross-workspace cache deduplication and garbage collection. A new `cargo::unused_dependencies` warn-by-default lint flags dead crate entries when all package targets are compiled, while `global-min-publish-age` delays resolution of fresh crate uploads—showing held-back versions in `cargo update` output while letting maintainers allow single urgent patches on demand.
Limits: The Rust Release Team noted `cargo install` bypasses `min-publish-age`, registry entries lacking a `pubtime` timestamp cannot be delayed, `unused_dependencies` skips `dev-dependencies` and single-target builds, and custom `build-dir` workarounds targeting internal layouts (tracked under `cargo#17287`) may require updates.