Rust 1.99.1 repairs FFI returns and two linking regressions

Rust 1.99.1 fixes three regressions: missing wcslen symbols on targets including UEFI, incorrectly extended boolean return values across x86_64 foreign-function boundaries, and a macOS linker failing to locate LLVM when invoked without rustup. The FFI fix restores the expected zero-or-one representation for callers. This is a targeted stable patch, not a new language-feature release.

Rust · Oct 15, 2026

Why it matters

Compiler and linker regressions can break otherwise unchanged projects during toolchain upgrades.

More context

Upgrade the stable toolchain with rustup update stable and rerun affected integration builds. These release notes do not list a fix for the separate lifetime issue covered yesterday.

Keep in mind

The fixes address specific targets and invocation paths; check which ones affect your build.

Original read